Fertilizer Nitrogen Use Efficiency by Winter Wheat in the Willamette Valley

AN ABSTRACT OF THE THESIS OF

Roger Keith Kjelgren for the degree of Master of Science in Soil Science presented on May 30, 1984

Title: Fertilizer Nitrogen Use Efficiency by Winter Wheat in

the Willamette AT91e)p A

Abstract approved: Redacted for Privacy

I. Neil W. Christensen

Efficiency of nitrogen fertilizer uptake by soft white winter wheat (Triticum aestivum L.) was measured over two cropping seasons across a range of soils and cropping histories in the Willamette

Valley. Fate and potential losses of applied nitrogen were also assessed over a seventeen month period.

15 In both cropping seasons, N labeled nitrogen was used to obtain a direct assessment of fertilizer nitrogen use efficiency (NUE), and to follow the distribution of fertilizer N in plant and soil.

Nitrogen rate experiments were used to obtain an indirect assessment of NUE by regressing total N uptake on fertilizer N applied.

Plant uptake of applied N ranged from 42 to 67%, with sites having poor soils or high root disease potential giving the lowest

15 efficiencies. Direct assessment of uptake efficiency with N was more precise than indirect assessment, but was not necessarily more accurate. Recovery of fertilizer N in the grain ranged from 54% to

73% of the total fertilizer N taken up. Recovery in the grain was less the first year because of widespread leaf disease. Optimum economic N fertilization rates could be predicted (r2 = 0.92) based on uptake of soil N and NUE. Availability of soil N was the most important parameter in determining optimum economic rate of N fertilization.

Accountability of fertilizer N in plant and soil after the first crop ranged from 65% to 108% of that applied. Fertilizer N left in the soil was almost exclusively found in an organically combined form, primarily in the top 15 cm of soil. The contribution of residual fertilizer N to the following year's crop was minimal, but only half of the residual N was accounted for following the second crop. It appeared that 10 to 31% of the applied fertilizer N was lost between the end of the first cropping season and before the winter of the second cropping season.

NUE by winter wheat in the Willamette Valley appears to be higher than NUE by dryland wheat grown in the Midwest. Sufficiently accurate assessment of NUE can be determined by indirect methods. This determination, combined with a method for determining soil N uptake, can contribute to improved N fertilizer recommendations for wheat in the Willamette Valley. FERTILIZER NITROGEN USE EFFICIENCY BY WINTER WHEAT IN THE WILLAMETTE VALLEY

Roger Keith Kjelgren

A THESIS

submitted to

Oregon State University

in partial fulfillment of the requirements for the degree of

Master of Science

Completed May 30, 1984

Commencement June 1985 APPROVED:

Redacted for Privacy

dI Professorf Soil Science in charge of major Redacted for Privacy

ad of Department of Soil Science

Redacted for Privacy

Dean of G ate School dr

Date thesis is presented May 30, 1984

Typed by Roger Kjelgren for Roger Keith Kjelgren ACKNOWLEDGEMENTS

I would like to acknowledge the financial support the STEEP project (Solutions To Environmental and Economic Problems) and Oregon Ag. Experiment Station provided for this research. The STEEP project is administered by the Science and Education Adm, Cooperative Research,USDA. I would like to thank University of California Kearney Agricultural Center for the use of so much of their equipment during the long, arduous process of completing this thesis while working at a full time job. At the same location I would very much like to thank Dr. David Goldhamer for allowing the me the time that was otherwise very hard to come by to finish this thesis. I would like to thank Dr. Peter Bottomly for giving timely input into the why's and howto's of this project, Dr. Moyle Harward for offering this project to me,Dr. Tom Jackson for providing the field sites for the experiments, and to Dr. Greg Gustafson for providing an economist's viewpoint on the data. I could not have reached this point without the dedicated interest and guidance of Dr. Neil Christensen, who, despite an onslaught of pregnancies, managed to persevere and provide tremendous support in finishing this thesis. I would like to thank Bill Inskeep, Priscilla Sheets, Dave Laird, and Alan and Lorrie Flint for their treasured friendship throughout my graduate work. For providing undying confidence, emotional and financial support, and keen interest in my work through all the years, I thank my parents. Finally, for waiting patiently up so many nights and weekends, and for giving me the boosts in confidence when I needed them the most, I thank my wife, Ronda. TABLE OF CONTENTS

Page

INTRODUCTION 1

LITERATUREREVIEW 5 Nitrogen Pools 5 Fluxes Between Soil N Pools 5 Inputs 5 Transformations within the soil 6 Losses of nitrogen 8 Fate of Fertilizer Nitrogen 9 Plant recovery 9 Losses 10 Fertilizer N remaining in the soil 12 Nitrogen Uptake by Wheat 14 Nitrogen Use Efficiency 15 Use of 15N 16

MATERIALS AND METHODS 18 Site Descriptions 18 1981 18 1982 21 Nitrogen Rate Study 22 Nitrogen Recovery Study 23 Sample Analysis 26 Data Analysis 27

RESULTS AND DISCUSSION 29 Nitrogen Rate Study 29 Grain yield response 29 Fertilizer nitrogen uptake efficiency 34 Partitioning of fertilizer nitrogen 39 Economically optimum rates of nitrogen fertilization 39 Nitrogen Recovery Study 48 Growth stage sampling 48 Nitrogen balance sheet 50 Soluble nitrogen 53

DISCUSSION 56

CONCULSIONS 60

BIBLIOGRAPHY 61

APPENDICES 66 LIST OF FIGURES

Figures Page

1 Diagram of porous cup used for sampling soluble nitrogen 25

2 Grain yield response to nitrogen fertilization, 1981. 30

3 Grain yield response to nitrogen fertilization, 1982. 31

4 Total and fertilizer N uptake as influenced by rate of applied nitrogen fertilizer, 1981. 35

5 Total and fertilizer N uptake as influenced by rate of applied nitrogen fertilizer, 1982. 36

6 Fertilizer N uptake by grain and grain plus straw as influenced by rate of applied fertilizer, 1981. 40

7 Fertilizer N uptake by grain and grain plus straw as influenced by rate of applied fertilizer, 1982. 41

8 Unfertilized grain yield as a function of soil N uptake by grain plus straw. 46

9 Total dry matter, %N, and fertilizer N uptake as a function of time after application of spring top dressed N. 49

10 Soluble N concentration in soil water extracted with porous cups placed at 30 cm depth in 1982. 54 LIST OF TABLES Table Page

1 Locations, soil test data, previouscrop, and winter wheat varieties used for rate experiments in 1981 and 1982. 19

2 Grain yield response toN and KC1 in 1981. 32

3 Grain yield response to N and Cl in 1982. 33

4 N fertilizer use efficiency estimates and uptake of soil N as influenced by rate of applied N in 1981 and 1982. 37

5 Optimum economic N rates as influenced by grain and fertilizer N prices. 43

6 Economic N fertilizer rates as related to soil N availability and fertilizer Nuse efficiency. 44

7 Residual NO3 -N and total soil N to a depth of 12" after cropping to wheat in 1981. 47

8 Recovery of spring topdressed N fertilizer over two cropping seasons. 51

9 Percentage of soluble nitrogen derived from labeled nitrogen fertilizer applied on April 13, 1981. 55 LIST OF APPENDIX TABLES

Table Page

1 Individual plot grain yields as influenced by N and K rates at five locations, 1981. 66

2 Individual plot grain yields as influenced by N and Cl rates at four locations, 1982. 67

3 Individual plot data for 1 atom % 15N subplots inN rate study,1981. 68-69

4 Individual plot data for 1 atom % 15N subplots in N rate study, 1982. 70-71

5 Total dry matter, % N, and % fertilizer N from 15N labeled subplots, 1981. 72

6 Total, fertilizer, and soil nitrogen yields from 15N labeled subplots. 73

7 Total dry matter, % N, and % fertilizer N from 15N labeled subplots. 74

8 Total, fertilizer, and soil nitrogen yields from 15N labeled subplots. 75

9 Total dry matter, % N, and nitrogen yield from maximum uptake sampling, 1981. 76

10 Total dry matter, % N, and nitrogen yield from maximum uptake sampling, 1981. 77

11 Total dry matter, % N, and nitrogen yield from maximum uptake sampling, 1982. 78

12 Equations for 1981 grain yield and N yield regressed on rate of applied N fertilizer. 79

13 Equations for 1982 grain yield and N yield regressed on rate of applied N fertilizer. 80

14 Dry matter, % total N, total N yield, % fertilizer N, and fertilizer N yield for growth stage subsampling from N recovery plots at Hyslop, Hamlin, and Bronson farms. 81

15 Plant analysis data from nitrogen recovery study using N fertilizer enriched to 5 atom % I5N, 1982. 82

16 Soil analysis data from nitrogen recovery study using N fertilizer enriched to 5 atom % 15N, 1982. FERTILIZER NITROGEN USE EFFICIENCY BY WINTER WHEAT IN THE WILLAMETTE

VALLEY

INTRODUCTION

Recent studies (Harward et al.,1981) have monitered water

quality and erosion from two watersheds in the Willamette Valley;one

each in south Polk county (Elkins Road) and northPolk county.

Nitrate - nitrogen (NO3-N) concentrations in discharge waters at the

watershed outlets averaged 8.3 mg /iover three winters (1978-81) at

Elkins Road, and 24.8 mg/1 at the north Polk county location. At

Elkins Road the volume of dischargewas monitored for two winters. Estimated losses were 63 and 40 kg N/ha in 1978 and 1979,

respectively. Since both watersheds contained substantial wheat

acreage, concern was raised about the degree to which nitrogen ferti-

lizer practices contribute to these losses. If one assumes that all

the nitrogen lost at Elkins Road came from residual fertilizer nitro-

gen, this would account for approximately one half to one-third of the

average annual application of nitrogen fertilizer. Since the nitro-

gen found in surface runoff waters is mostly in organically combined

form (Simmons, 1980), the source of NO3 -N at the outlets of these

watersheds would be NO3 -N leaching fromthe rooting zone and then

moving into surface drainage waters (Simmons, 1980).

Several local research efforts have focused on the level of NO3-N leaching from wheat fields (Istok, 1983; Owre, 1980). In the summer of 1979 tile lines were installed ona subwatershed planted to wheat at the Elkins Road site. Discharge and water quality were monitored 2

for two winters while thissubwatershed was continuously cropped to

winter wheat.Total nitrogen loss from the watershed during the first

winter was 76 kg N/ha, while only 18 kg N/hawas lost the second year.

Although total precipitation was nearly thesame for both years, there

was a marked difference between the twoyears in the volume of water

discharged from tile lines. In 1979-80 it was 2.5 times greater than

discharge in 1980-81, which probablyaccounts for some of the in-

creased NO3-N loss in 1979-80. Installation of the tile lines reduced

surface runoff and erosion whileincreasing water flow through the

soil (Istok, 1983). In addition, several years of poor wheatcrops

and normal fertilization practicesprior to the 1981 crop may have

left substantial amounts of residual fertilizerN in the soil.

A second study of effluent froma tile drained wheat field was

carried out for two winters (1977-79) at Jacksonresearch farm near

Lebanon, Oregon (Owre, 1980). This was part of a larger, ongoing tile

drainage experiment. Wheat was planted on three 1170 m2 tiled plots

and the NO3- N levels in the effluent monitored. Both years the NO3-N

levels averaged approximately 20 mg/l. Discharge was determined the

second year only, and the average annual loss for all three plots combined was 14 kg N/ha. The calculated losses for Jackson Farm and

the second year after tilingat Elkins Road may representa more accurate picture of how much N is being lost from wheat fields in the

Willamette Valley.

The amount of N leached froman agricultural field is a function of two parameters; the amount of water moving below the rootingzone, and the concentration of NO3-N in that water. Installing the tile lines in 1979 at Elkins Road subwatershed increased the flow of 3

drainage water and hence increased the amount of N lost.Increased

flow from tile lines probably occurs inmost tile drained fields the

first year after installation, but isnot likely to be representative

of established tiled land. The second parameter, the N concentration

of water moving below the rootzone, is controlled by two factors.

The first is the amount of NO3 -N left in the soil after the wheat crop

has been harvested.The second is the amount of organic N mineralized

and subsequentlynitrified between the time the wheat is harvested in

late summer and the time when subsurface drainageceases the following

spring. Since mineralization and nitrification rates are strongly in-

fluenced by soil temperature and soilwater content (Stanford and

Smith, 1978; Cassman and Munns, 1980), it would be expected that under

Willamette Valley conditions, mineralization andnitrification rates

would be highest in early fall when the soil is stillwarm and the

moisture content is increasing from fall rains. Once subsurface flow

has started, it would be expected thatmuch of the residual and

mineralized NO3_N would be moved below the root zone by mass flow and

that NO3 concentrations in drainage waters would decrease in time.

This expectation is consistant with measured changes inNO3_N

concentration at Jackson farm and Elkins Road during 1977-81.

Given that water movement through Willamette Valley soils is

common during winter months, the potential for losing fertilizer N

through NO3-N leaching depends in large part upon the size of soil and plant pools of fertilizer N and the fluxes between these pools during critical periods. Important considerations include;(a)the quantity of fertilizer N removed in the harvested crop, (b) the quantity of organically combined fertilizer N remaining in the soil at harvest, 4

in the soil at harvest, (d) therate of mineralization of organically

combined fertilizer N,(e) the rate of nitrification, and (f) the rate

of denitrification.

Leaching losses of fertilizer N can be accurately assessed using

a combination of lysimetry and 15N labeling of fertilizer N (Owens,

1960). Limited resources precluded theuse of lysimetry in this

study, however. The approach taken was to use 15N labeled fertilizer

to quantify the major pools of fertilizer N in orderto estimate

maximum fertilizer N losses by difference (ie. N applied- crop uptake

of fertilizer N- residual fertilizer N in soil = fertilizer N losses

from NO3-N leaching + denitrification + gaseous N loss from plants).

Specific objectives of this studywere:

(1) To measure the efficiency with which spring topdressed NH4-N fertilizer is recovered by winter wheatcrops.

(2) To measure the influence of cropping history and rate of N fertilization on the quantity of soil N takenup by the crop.

(3) To measure partitioning of fertilizer N between wheat grain and straw.

(4) To measure the rate of wheat growth and fertilizerN uptake following a spring application of N.

(5) To measure the quantity and distribution with depth of residual fertilizer remaining in the soil after six months (following first crop) and again after 18 months (following second crop).

(6) To measure soluble fertilizer N and total soluble N in soil solution during the winter.

(7) To estimate maximum losses (leaching + denitrification +gaseous losses from plants) of fertilizer N applied to winter wheat across a range of soils and cropping conditions in the Willamette Valley.

(8) To evaluate N fertilizer rates using an economic approach andto relate economic N rates to estimates of available soil N and fertilizer use efficiency. 5

LITERATURE REVIEW

NITROGEN POOLS

To adequately describe fertilizer nitrogenuse efficiency (NUE)

of wheat, it is necessary to characterize the nature of the soil N

pools. Soil N can be separated into two categories.The first is

inorganic N consisting of ammonium (NH4-N), nitrate (NO3-N),and

nitrite (NO2-N) Inorganic N makes up between 0.5-5% of the surface

soil N by weight, and higher rainfall climates generally have lower

levels of inorganic N than drier climates.Nitrate tends to be the

dominant inorganic N species, followed by ammonium, with nitrite

present in small quantities. Organically combined N (OM-N) is the

largest N pool in most soils and contains from 90-99% of the total soil N (Parr, 1960). Approximately 75% of the OM-N is associated with

low molecular weight compounds such as amino acids, amides, and hexose amines, the balance is found in large, often ringed, stableorganic compounds (Russell,1973).

FLUXES BETWEEN SOIL N POOLS

Inputs

The source of inputs into the soil N pools, and annual amounts, are in order of decreasing magnitude:

1) Fertilizer N. 2) Nitrogen fixation. 3) Nitrogen dissolved in precipitation. 4) Ammonia absorption from the air by plants.

In most natural systems N fixation is the major input of N, and can be divided into two categories.The first is non-symbiotic N fixation carried out by free living bacteria such as Azotobacter sp. and cer- 6

tain species of blue-greenalgae. Their ability to fix atmospheric N2

in the soil is controlled by theoxygen content of the soil atmos-

phere, available carbon andenergy sources, and the presence of other,

more easily available N sources. Low oxygen levels and a lack of

alternative N sources favors fixation (Grayand Williams, 1971).

Because the levels of oxygen and nitrogenare dependent on dynamic

factors such as water and temperature,the amount of atmospheric N2

these organisms can fix is variable.

The second group of N fixers is composedof certain heterotrophic

microorganisms which live in a symbiotic relationshipswith higher

plants. Agriculturally speaking the most important of theseare

Rhizobium sp., which live in association with leguminous plants. Be-

cause the plant is able to provide the bacteriumwith photosynthate, and an environment of ocntrolledoxygen content, Rhizobium sp. are able to fix much more atmospheric N2than autotrophic N fixers.

Nitrogen inputs from ions dissolved in rainfall and ammonia absorption from the air are of secondaryimportance in terms of amounts contributed to the soil in comparison to fertilizer and fixation.

Transformations within the soil

Soil N is involved in three transformationsprocesses contained within the soil system. They are:

1) Mineralization 2) Immobilization 3) Nitrification

The first, mineralization, is the conversion oforganic matter nitrogen (OM -N) to inorganic form by microbial decomposition. When total soil N exists in excess of that needed forgrowth, microbial decomposition of typically low molecular weight compounds forenergy and 7

carbon releases previouslyorganically combined N as a byproduct.

Mineralization is favored by a low carbon to nitrogen ratio in the

soil, and is associated with the <0.02mm particle size fraction of

the soil (Legg et. al., 1971; Cameron and Posner, 1979). Soil water

content and temperature have a significant effecton mineralization.

Stanford et.al. (1973) observed that in the range of 15-30 ° C,

mineralization doubled with a 10 degree increase in soil temperature.

Cassman and Munns (1980), found that mineralization was greatest when

soil water was at field capacity.

The opposite of mineralization is immobilizationof inorganic

soil N by incorporation into organic compounds. This can occur by

chemical means, or biologically by microbesor plant roots. Microbial

immobilizationis favored by a high C/N ratio. Under these condi-

tions carbon exists as anenergy source in excess of the N needed for

the microbes to utilize it, hence available N is incorporated in order

to further growth. Immobilization increases with increasing soil OM

content (Tomar and Soper, 1981), and is associated with the <0.02 mm

soil particle size fraction (Cameron and Posner, 1979; Chichester,

1978).Kissel and Smith (1978), found that a clay soil immobilized

more fertilizer N than a sandy soil.

The third transformation of N is the microbial oxidation of

reduced N (ammonium) to NO2-N and finally to NO3 -N. This two step

process is more unique than either immobilization or mineralization in

that there are two species of autotrophic bacteria which are primarily

responsible. Under agricultural conditions, oxidation to NO2-N is carried out Nitrosomonas sp., with Nitrobacter sp. oxidizing this product to NO3-N in the subsequentstep. This latter step is much 8

faster than the former, andas a result most inorganic soil N is found

as NO3-N. This is fortunate as NO2 -N is toxic to many organisms in

any substantial quantities (Russell, 1973).The energy released by

this oxidation is then utilized by the two bacterial species. Since

nitrification as an oxidative process, NH4will accumulate as the dominant inorganic N form in soils with limited oxygen (Russell,

1973). Russell (1973) also cites research showing that nitrification

progresses slowly when soil temperature falls below 4-5 °C, when the

soil pH does not fall within therange of 5-8, and when soil water

potential falls below -1 bar or exceeds field capacity.

Losses of Nitrogen

The avenues of nitrogen loss from the plant-soil system are:

1) leaching of NO3-N 2) gaseous loss 3) removal of plant material

Since NO3-Nas the predominant inorganic N species in the soil carries a negative charge, it is repulsed by the negatively charged soil colloids. Thus NO3 -N is foundprimarily in solution and is subject to movement by mass flow with water. Leaching occurs when mass flow of water carries NO3 -N downward andout of the root zone. The amount of

NO3-N leached is determined by the downward water flux and the NO3-N concentration of the water. In arid climates NO3-N may only be moved farther down in the root zone from infrequent rains, and accumulate at certain depths. Under non-cultivated soil conditions NO3-N leaching losses are minimal because NO3-N pools are in equilibrium with other soil N pools. Cultivated soils in comparison often have additions of fertilizer N, and rapid increases in oxidation of OM. This keeps the soil N pool in a non-equilibrium state where high levels of NO3-N, 9

and potential leaching, can occur (Bolton et. al., 1970).

Nitrogen losses by plant removal ina non-agricultural environ-

ment are generally low because the cycling of N between plant and soil

is in equilibrium. Losses do occur due to animals and erosion, but

these are balanced by fixation and rainborne inputs.

Primary among the means ofgaseous N loss is denitrification.

This is the reduction of NO3-N to N2 and N20 by anaerobic microbial

respiration, which occurs when theoxygen concentration in the soil is

sufficiently low to preclude aerobic respiration (Russell, 1973).

Soluble organic compounds serve as an energy source, NO3-N is the

electron acceptor in place ofoxygen,thus oxygen inhibits denitrifi-

cation.

The other means ofgaseous N loss is ammonia volatilization from

the soil, which occurs when the soil's abilityto retain NH4 -N is

diminished. In a review of the literature, Allison (1966)cites

studies where ammonia volatilization in dry,sandy, and particularly

calcareous soils, has been documented.High levels of calcium car-

bonate are associated with high pH's, at which ammonium formsNH3 and

H20. Ammonia has also been foundto be lost from the growing plant

(Allison, 1966), and has been measured by several researchers (Daigger

et. al., 1976; Hooker et. al., 1980).

FATE OF FERTILIZER NITROGEN

Plant recovery

Nitrogen fertilizer is added to crop plants to increase produc-

tion, as soil N pools rarely provide sufficient N to achieve optimum crop growth. Under field conditions, however, 100% recovery of the applied fertilizer N by the crop isnever realized. Gaseous losses, 10

immobilization, and leaching can render from 25 to 40%or more of the

applied fertilizer N unavailableto the crop (Broadbent, 1977). Of

great importance is the quantity of N recovered in the plantpart of

economic interest. Since recovery of N by the crop isan active

biological process, factors that inhibitcrop growth will also inhibit

fertilizer N recovery. For small grains, factors such as disease,

temperature stress (Terman et. al., 1968), and moisturestress (Ramig,

1960) will restrictrecovery. Additions of fertilizer N may also

stimulate the uptake of soil N,a phenomenon which has been observed

in the field (Westerman andKurtz, 1973).

Losses

Applied fertilizerN whichis not taken up by the crop either remains in the soil in organically combinedor inorganic forms, or it is lost through themeans previously described.The first, ammonia volatilization, occurs before the N iseven available to the plant.

Nitrogen applied asurea is rapidly hydrolyzed to ammonium carbonate and under some conditions can be lostas ammonia (Fenn and Kissel,

1973). Ammonia losscan reduce the ammount of fertilizer N recovered by the crop (Christensen and Meints, 1982; Matzelet. al., 1971).

Fenn and Kissel (1974, 1976) found that hightemperatures promoted high initial volatilization losses while a high cation exchangecapa- city tended to reduce such losses. Rolston (1977) points out that these losses can be reduced by placing the fertilizer 10cm below the soil surface.

Once ammonium fertilizer N is in the soil it is rapidly nitrified to NO3-N if soil temperature, pH, and water content are favorable. 11

As NO3_N, fertilizer N is subject to loss throughdenitrification and leaching. Many studies have tried to quantifydenitrification with

the balance sheet method (Hauckand Bremner, 1976). This meant quan-

titatively accounting for all fertilizerN found in the plant, soil,

or lost through leaching. Knowing how much fertilizer Nwas applied,

that not accounted for was assumed lost throughdenitrification.

Direct methods of measuringdenitrification have been developed

through the use of 15N. Using these methods it has been determined

that unsaturated soil conditionsdo not preclude denitrification.

Field studies have shown that denitrification can occur within soil

aggregrates, despite unsaturated inter-aggregratepores, if the respi-

ratory demand for oxygen within theaggregrate exceeds the supply

(Dowdell and Smith, 1974).

The second avenue of NO3-N loss is leaching. In irrigated agri-

culture, leaching losses of fertilizerN can be controlled by not

applying water inexcess of the evapotranspiration needs of thecrop

(McNeal and Pratt, 1977). In dryland agriculture, N fertilization in

excess of the crop's ability to take itup can result in downward

NO3 -N movement if there is sufficient rainfall. Larson e t. a l.,

(1971) found the greatest depth ofNO3 -Nmovement under bromegrass

occurred at the highest, 300 kg N/ha, rate. Fertilizer N may accumu-

late in the lower depths of theroot zone (Sommerfeldt and Smith,

1973), and can either be leached entirely out of the root zone during wet years, or serve as a source of N for thecrop. Soil texture and structure influence leaching by determining how fast the water will flow downward under saturated conditions. Boswell and Andersen (1964) noted faster NO3-N movement in a loamy soil compared to a sandy clay 12

loam soil. Where soil texture or structure restricts water movement,

NO3-N can be lost by denitrification in saturated zones caused by a

perched water table (Pratt, 1979; Gambrell et. al., 1975). While deep

leaching may be reduced under such conditions (Gambrell et. al.,

1975), lateral movement of water along the restrictive layermay

remove NO3-N from the crop root zone.

Gaseous N, including fertilizer N, loss from the above ground plant has been documented. Daigger et. al. (1976) found significant N

losses from Nebraska wheat after heading, and noted that emissions of nitrous oxides or ammonia could be responsible. Martin and Ross

(1968) found negligible emissions of N2and NO2 from a grassland, but did find significant amounts of ammonia released to the air. In

Nebraska, Hooker et.al., (1980) measured substantial ammonia losses from wheat grown in air tight growth chambers, while NO and NO2 losses were insignificant. The onset of ammonia loss from the wheat coin- cided with the growth stage at which Daigger et. al. (1976) found the

N content of field grown wheat to be decreasing.However, the measured loss of ammonia in the growth chambers would only account for a small fraction of the quantity of N reported lost by Daigger et. al

(1976). They submitted the explanation that the evapotranspiation rate was much higher in the field than the growth chamber, and the greater vapor flux from the plants in the field would encourage greater ammonia volatilization.

Fertilizer remaining in the soil

Fertilizer N remaining in the soil can either be in inorganic or, predominantly, in organically combined form.Olson (1980,1982) has found approximately 90% ofthe residual fertilizer N immobilized in 13

soil OM. Chichester and Smith (1978), used lysimeters to comparea

limed soil rotated in pasture with the same soil which had been con-

tinously cropped and unlimed. They found more N immobilized in the

soil rotated to pasture. Fredrickson (1983) followed labeled fertili-

zer N applied to no-till and conventionally tilled treatments in

eastern Washington and found less fertilizer N immobilized under the no-till system. This was attributed to the lower OM content under the no-till soil due to the crop residue being kept on the soil surface, and also to possible immobilization of topdressed labeled N in the surface stubble, although this was not measured. Tomar and Soper

(1981) studied N retention in 11 Canadian soils differing in OMcon-

tents but with similar C/N ratios. They found that the soils with the highest OM levels immobilized the most fertilizer N.

Once the fertilizer N is immobilized in the soil OM, it either remains organically combined or is remineralized. Smith et. al.

(1978) found that a greater percentage of the residual fertilizer N immobilized in the readily mineralizable (low molecular weight) OM fraction was mineralized than indigenous soil N in the same fraction.

Smith et. al. (1978) showed that for five soils, 21-57% of the organically combined residual fertilizer N was potentially mineralizable, while just 6-11% of the indigenous soil N was potentially mineralizable. In terms of contribution to subsequent crops, the mineralization of residual fertilizer N appears to be small (Broadbent and

Nakashima, 1967). particularly when inorganic residual fertilizer N levels were high (Broadbent, 1980). Even though up to half of the residual fertilizer N is potentially mineralizable, the absolute amount actually mineralized is small compared to amounts of indigenous 14

soil N mineralized and fresh additions of fertilizer N.

NITROGEN UPTAKE BY WHEAT

The amount of N taken up by wheat is dictatedby the N needs of

the plant. As previously mentioned, factors which inhibit wheat

growth also inhibit the demand for N. Kolderup (1975) observed that

spring wheat grown in a growth chamber held at 24 C had N concentra-

tions twice as high as thesame varieties grown at 12 C. Ramig

(1960) found that applying 15cm of water to dryland winter wheat in

Nebraska increased the recovery of fertilizer N from 38to 75%.

Terman et. al. (1968) found that increasing the water supply to winter

wheat in Nebraska allowed the plant to increase theamount of fertili-

zer N taken up, even at higher rates of fertilization. Under optimum

environmental conditions it isnecessary to establish the N sink

essential for maximum yield. Research has shown that approximately

80% of the total N found in the wheat plantat harvest is taken up by

anthesis (Austin et. al., 1977; McNeal et. al.,1966; Spratt and

Gasser, 1970). This vegetative nitrogen sink in turn becomes a source

of N as it is translocated to the grain during kernel development.

Recoveries of fertilizer N applied to wheat vary greatly. Olson

et. al., (1979) measured recoveries of 44 and 57% of fall and spring applied N,respectively. Olson (1982) recovered 55% of the 80 kg N/ha applied to winter wheat in Kansas, 75% of that recovered being found in the grain. Christensen and Meints (1982) recovered an average of

30% of the fertilizer N applied at rates ranging from 34 to 101 kg

N/ha, 85% of that recovered was in the grain. Christensen and Killorn

(1981) recovered an average of 52% of the 100 kg N/ha applied at different times to irrigated spring wheat in Montana. 15

Timing of N fertilizer application can affect Nrecovery by

wheat. Applications split between seeding and tillering have in-

creased wheat yields (Wahhad and Hussein, 1957). If the grain N

concentration remains the same for split as non-split application, the

increased grain yield would translate into greater N recovery for the

split application. Applications of fertilizer N after heading often

result in a higher N content in the grain but a lower grain yield

(Andersen,1977a). Such late applied N is preferentially taken up in

the grain over remobilization of N from the vegetative sinks.This

takes energy that otherwise would be going to grain development

(Andersen, 1977a, 1977b). Christensen and Killorn (1981) found higher

N concentration in the grain in those treatments where at least half

of the applied N was split between seeding, flowering, and heading.

Fertilizer N uptake in the straw was lower when the applicationwas

split compared to applying it all at seeding.

NITROGEN USE EFFICIENCY

Nitrogen use efficiency (NUE) by wheat can be defined in three

ways (Tucker and Hauck, 1978):

1) The quantity of fertilizer N taken up in above ground parts perunit of fertilizer N applied. 2) Theincreasein grain yield per unit of fertilizer N applied. 3) Theeconomicreturn in dollars per dollar spent for fertili- zerN.

Definition #1 is efficiency evaluated from a technical standpoint: how

much of the applied fertilizerN is removed from the soil by the

crop. It does not address how efficiently the N is used in the plant.

It can be measured two ways; either directly by use of 15N labeled

fertilizer N or indirectly by subtracting the plant N yield of an 16

unfertilized plot from the N yield ofa fertilized plot and dividing

by the quantity of fertilizerapplied.

Definition #2 evaluates NUE interms of how effective the plant

utilizes N to produce grain. If N is available in excess of that

needed to produce grain, it is stilltaken up and stored in the plant.

Thus uptake efficiency may not reflect production efficiencyin cases

where additional N takenup goes into vegetative production or storage

and not grain production.Production efficiency can be empirically

determined from a curvilinear yieldresponse curve to N by setting the

derivative of the equation equal tozero and finding the N rate at

that point. All N rates beyond that point havea negative production

efficiency.

Definition #3 is the economic efficiency ofN use.This is the

point on the yield response curve to N after whichany added units of

N fertilizerdo not pay for themselves with increasedgrain yield.

It is determined from the same equation described in def. #2 bytaking

the derivative of theresponse equation and setting it equal to the

ratio of the price of grain to the price of N fertilizer.

THE USE OF 15N

Since the heavy isotope of N (15N) is usedto label fertilizer N in this experiment, it is important to discuss the assumptions under- lying it's use. The primary assumption is that whenever 15N isap- plied to soil,the soil biological systems being investigated do not significantly discriminate against 15N in reactions and transformaions involving nitrogen (Hauck, 1973; Hauck and Bremner, 1976).In reactions involving N,14Nis preferentially used because of it's lighter 17

molecular weight. This enriches the atom % 15N in the reactants and

depletes the atom % 15N in the products. Eventually all the reac-

tants are consumed and the reactant 15N abundance is reconstituted.

In scientific measurements of biological processes wherea N transfor-

mation may be stopped before completion in order to analyze it's

constituents, recovery of 15N in the reactants and productsmay be an

artifact of isotopic discrimination and not truly reflect N behavior.

Hauck (1973) and Hauck and Bremner (1976) point out, however, that

since this isotopic discrimination effect is in the parts per thousand

range, and that most agricultural work involves sufficiently labeled N

that produces changes in 15N abundance in the parts per hundred range,

it can be considered negligible for most work. Isotopic discrimina-

tion can be very important when variations in natural abundance of I5N between different biological processes or systems are being studied, however. Isotopic discrimination has been successfully used in

Kreitler and Jones' (1975) study of nitrate groundwater pollution from soil and feed lots,where the percent variation of 15N natural abundance derived from either cattle feed lots or the soil was quite large. In general it is a very difficult method to apply. Broadbent et. al. (1980) in their study of spatial variability in 15N natural abundance in soil concluded that lateral and vertical variation are so great that natural abundance tracer studies are precluded under most circumstances. 18

MATERIALS AND METHODS

SITE DESCRIPTIONS

In 1981 four locations were selected for five experiments. One location contained two experiments. In 1982 three new locations and one from the previous year were selected. Sites differed in cropping history and pre-fertilization NO3 -N levels in the soil(Table 1).

Huddleston (1982) made a study of the inherent suitability of Willa- mette Valley soils to cropping. Soils were rated on a 100 point scale as to their native productivity, and the productivity when optimal management practices, such as liming, fertilization, drainage, and irrigation are implemented. Column 5 in table 1 gives native productivity ratings, as well as other characteristics, for the soils used in this investigation.

1981 Experiments

-KEYT farm. This farm, located in north Polk county, has been historically well managed, with a typical rotation consisting of crimson clover-wheat, or crimson clover-wheat-wheat. This site had a high OM content (3.9-4.5%),total soil N of 0.17%, and pH of 6.1

(Table 1). There were two adjacent experiments at this location.

Experiments were conducted on a Willamette soil which has one of the highest productivity ratings of western Oregon soils. The first experiment (K W/W) was on land that had been cropped to wheat the three previous years and had a moderate risk of take-all root rot caused by Gaeummanomyces graminis, var tritici (OSU Extension Bulletin

FS250). The second experiment (K W/C) was placed on land that had been in clover the yea before.Decomposition of nitrogen rich resi Table 1. Locations,soiltest data, previous crop, and winterwheatvarieties used for rateexperiment in 1981 and 1982.

SOIL TEST DATA Wheat Exp. Soil Taxonomic Prod. Prev. Soil NO) -N Total variety site Location series Name Rating crop -pre-Cert. OM N pH planted

depth ug/g In cm KEPT R 5W, T 6S WILLAMETTE FINE-SILTY, 75 WHEAT 0-30 4.3 4.5 0.16 0.1 STEPHENS FARM SECTION 29 SILT LOAM MIXED MESIC, 30-60 2.4 0-3% PACHIC ULTIC, ARIC1XEROLL

KEYT same as above CRIMSON 0-30 10.1 3.9 0.17 u.i STEPHENs FARM CLOVER 30-60 2.4

,--4 HYSLOP R 4W, T IIS WOODBURN FINE-SILTY, 65 FALLOW 0-30 2.1 2.4 0.12 5.6 STEPHENS 00 RESEARCH SECTION 5 SILT LOAM MIXED MESIC, 30-60 2.1 CN FARM 0-3Z AQUULTIC e--4 ARCIXEROLL

HAMLIN R 4W, TIIS CHEHALIS FINE-SILTY, 75 TABLE 0-30 6.8 2.9 0.12 6.0 STEPHENS FARM SECTION 36 SILTY CLAY MIXED MESIC, BEETS 30-60 2.5 LOAM CUMULIC ULTIC HAPLOXEROLL

BRONSON R 4W, T 15S DAYTON FINE-MONT- 10 RYE- 0-30 0.8 3.7 0.17 5.5 YAmMILL H FARM SECTION 10 SILT LOAM MORILLONITIC, CRASS 30-60 --- MESITYPIC ALBAQUALF

I-4 WILSON R 3W, T 6S CHEHALIS FINE-SILTY 75 WHEAT 0-30 25.0 3.1 0.15 5.3 STEPHENs FARM SECTION 34 SILTY CLAY MIXED MESIC, LOAM CUMULIC ULTIC ANGIXEROLL

JONES R 5W, T 55 WILLAMETTE FINE-SILTY, 75 WHEAT 0-30 --- 2.9 0.15 5.3 STEPHENS op FARM SECTION 23 SILT LOAM MIXED MESIC O. 0-3% PACHIC ULTIC ARCIXEROLL

KEYI same as above WHEAT 0-30 15.5 3.7 0.17 6.o STEPHENh FARM

EV ERS R 30,I 4S AMITY FINE-SILTY, 55 WHEAT 0-30 25.3 4.3 0.20 5.7 YAMHILL

1--1 FARM SECTION 19 SILT LOAM MIXED MESIC, ARCIAQUIC ARGIXEROLL 20

dues accounts for the higher NO3 -N levels measured on the site cropped

to clover in 1981.

-HYSLOP research farm. This is the field laboratory for Oregon

State University's Crop Science Department and is located seven miles

north of Corvallis. The experiment was on Woodburn soil that has a

high native productivity (Table 1). The soil, however, has been

planted to numerous experiments over the years with little regard to

soil tilth. Consequently, the soil OM, total N, and pH are lower than

what could be found on a Woodburn soil that had been managed more

carefully. The experimental site was located on a strip of land that

had lain fallow the previous year.

-HAMLIN farm. This farm, located in west Linn county, typically

has a crop rotation of sweet corn, a row crop, and wheat. The Cheha-

lis soil on which the experiment was located has a high native produc-

tivity (Table 1). Significant quantities of residual fertilizer N

were expected at this site because of the rate of N applied to the

previous crop of table beets.

-BRONSON farm. This site was situated on a Dayton soil in south-

west Linn county. The Dayton soil series is one of the poorest arable

soils in the Valley, as evidenced by it's low native productivity

rating (Table 1).This is because of a very high water table during

winter months. This field had been in ryegrass for two previous

years. Because of the physical and chemical limitations imposed by the

high water table, ryegrass is one of the few crops that can grow on

this soil. Wheat can be grown on the Dayton soil with careful management. The soil is ridged during tillage, and the wheat sown on the ridges is sufficiently elevated above the standing water that the 21

crowns ofthe plants are ableto survive the winter. Prior to

seeding, two Mg lime/ha was spread on the soil surface but not incor-

porated. This raised the pH of the surface soil from 4.9to 5.5

(Table 1).

1982 Experiments

-WILSON farm. This site was located ten miles north of Salem in

Marion county and had a history of frequent sewage sludge applica-

tions. Soil was a Chehalis, the same series studied at Hamlin farm in

1981. The high levels of pre-fertilization NO3 -Nare probably due to previous applications of sewage sludge.

-JONES farm. This site was located in south Yamhill county and

the experiment was on a Willamette soil.Although the soil series was the same as that studied at the Keyt farm in 1981 and 1982, soil tests for total N, organic matter, and pH were lower that at the Keyt location because of differences in previous soil management (Table 1).

It had been cropped to wheat two successive years and had a moderate risk of take-all root rot.

-KEYT farm.This is the same location as described for the two

1981 experiments. The 1982 experiment was laid out on the same land as K W/W, thus making it the fifth year in a row cropped to wheat.

Less severe take-all root rot was expected at this site in 1981-82 because of the possibility that biological suppression of take-all

(take-all decline) had become established.

-EVERS farm.This site is located in East Yamhill county on an

Amity soil.Amity soil is one of the catena of soils consisting of

Willamette, Woodburn, Amity and Dayton. Amity soil is not as wet as the Dayton, but does experience periodic high water tables during the 22

winter. This particular field had a history of beinga disposal site

for turkey manure. Manure had been applied approximately every other

year. In addition, the site had been continuously cropped to wheat

for the past 20 years, and had yielded reasonably wellover that time.

NITROGEN RATE STUDY

At every experimental site except Hyslop, wheatwas seeded by the

farmer. In 1982 wheat was seeded in early February at Wilson's, but all other sites were fall seeded. The experimental treatments (Appen-

dix Tables 1 and 2) were arranged in a randomized complete block design with four replicates. Subplots (1.5 m x 1.5 m) within N rate

treatments were fertilized with 15N labeled fertilizer at equivalent rates.

Subsequent handling of the experimentwas as follows:

-Application dates: In both years, unlabeled fertilizer treatments were applied in mid March. 15N labeled fertilizerwas applied at the same time as theunlabeled fertilizer in 1982, but was applied two weeks after the application of unlabeled fertilizer in 1981.

-Application method: Unlabeled fertilizer was uniformly spread by hand at the appropriate rates to all areas except the subplots slated to receive I5N. The labeled nitrogen was applied as a 500 ml solution of

15 N enriched ammonium sulfate which was sprinkled uniformly over the subplot area. Labeled ammonium sulfate was enriched to 1 atom % I5N

(diluted down from 73 atom % 15N).

-Sampling: At approximately soft dough stage, 0.82 m2 (1 yd2)areas were harvested from unlabeled part of plots containing the labeled subplots. This was done to determine if maximum dry matter production and nitrogen uptake had been reached at this stage. Based on 23

earlier work by Ambler (1976), a decrease in both dry matter and N

uptake after soft dough stage was anticipated.

-Harvest: The wheat reached maturity in late July of both years.

Just prior to combine harvest, the subplots were harvested with a

sickle on 22 July 1981 and 26 July 1982.Plot yield was determined

from the combined subplot and surrounding large plot yield. Sub-

samples were taken from the subplots for total nitrogen and 15N nitrogen determination.

NITROGEN RECOVERY STUDY

In 1981 separate experiments were conducted at three sites (Hys- lop, Hamlin, and Bronson farms) to follow the fate of the applied fertilizer nitrogen over two cropping seasons. Experiments consisted of single large plots (14 to 19 m2, depending on space available) at each site, situated either in or adjacent to the N rate experiment.

The handling of these experiments was as follows:

-Application: Six liters of an ammonium sulfate solution labeled at 5 atom % I5N (diluted from 73 atom %) was uniformly sprinkled on the plots at a rate of 146 kg N/ha. Each plot was divided into six subsections, and the fertilizer was applied by subsection to ensure even application.

-Plant sampling: Starting two weeks after application of the fertilizer, growth stage was recorded and plants were sampled every 10 days up until two weeks beforeharvest. Six 30 cm sections of row were taken from each plot at each sampling. A 0.25 meter buffer strip was left along the edge of each plot from which no samples were taken.

The plant samples were taken toward the edges of the harvestable area to ensure a reasonable area was left for yield determination. 24

-Harvest: Plots were harvested at the same time in late Julyas were

the plots from the N rate experiment. All plant matter in the plot,

excluding the buffer strip, was harvestedand root crowns were re

moved from three 1 m2areas of the plot. In 1982, root crowns were

removed from the entire harvested area.

-Soil sampling: At each site six soilcores were taken to a depth of

120 cm in 30 cm increments between the wheat rows. The top 30 cm

were divided into two 15 cm sections. Soil samples were taken in

1981 with a Giddings hydraulic probe while samples were taken with a

bucket auger in 1982.

-Plot re-establishment: Just after harvest benchmarkswere placed on

the edges of each field and the plots were triangulated for later

location. Plots were then re-staked after the fields had been fall

plowed. The Hyslop and Bronson plots were replanted to winter wheat.

At Hamlin farm the field was fall plowed and left fallow until being

planted to field beans in April. A 0.5 m bdffer strip within the perimeter of the 1981 harvested area was drawn at Hyslop and Bronson sites to ensure no contamination from non- labeled soil during tillage. The center of the plot enclosed by the buffer strip was harvested. Because of late fertilizer application and gopher damage, the entire plot at Hyslop was harvested at watery kernel stage. Due to incomplete communication with the grower, a plant sample at Hamlins was not taken prior to bean harvest.

-Porous cups and water wells: To identify how much fertilizer nitrogen was in soluble form, hence potentially available to be leached during the winter, three porous cups and a four foot water well were installed in the center of each plot. Porous cups with an air entry value to pump

--,'

plastic tubing

V quart jar

1 I soil surface

12" depth

PVC pipe

1 bar porous ceramic cup

Fig. 1 Diagram of porous ceramic cup used for sampling soluble nitrogen 26

of 1 bar were used (see Fig.1 for diagram), and non collapsible

rubber tubing connected to a 6 volt portable pump was used to withdraw a water sample. Porous cups were not installed until mid January of

1982, hence several major rain storms were missed in December. Soil

solution samples were collected approximately every 15 days from

January to April. Because samples could not be processed immediately,

they were acidified with two drops of concentrated sulfuric acid to stop biological activity.

SAMPLE ANALYSIS

Plant samples of sufficient size to yield 2.5 mg of NH4-N after distillation were digested using the micro-kjeldahl method on a block digester. Following digestion, NH4_N was recovered using an all glass steam distillation unit, following the method outlined by Bremner

(1965c). Distilled water was used as the ammonia trap, which was then titrated with 0.2 N sulfuric acid to a pH 3.8 end point. Samples were distilled in order of increasing I5N enrichment to avoid possible cross contamination. Samples were then dried down to approximately 10 mis on a warming plate and subsequently transferred to scintillation vials. These were taken to dryness in a forced air oven, then stored until analysis for atom % I5N. Automated mass spectrometer analysis of 15N content was carried out by Isotopic Services, Inc. of Los

Alamos, New Mexico.

In 1981 soil samples were taken from each subplot to a depth of

30 cm. They were air dried, ground, and three grams of soil sub- sampled from each sample for total nitrogen determination. The macro-kjeldahl procedure modified to recover NO3-N (Bremner,1965a) was used. Distilled water used as the ammonia trap and the samples 27

titrated to a pH 3.8 end point of ter distillation. Samples used for

15 N determination were run in duplicate, with the second sample being

used for the 15N analysis to avoid possible cross contamination. The

titration and sample preparation for 15N analysis was thesame as

previously described for plant analysis. Separate 20 gram subsamples

were taken from all soil samples and extracted with 2 N KC1. The KC1

solution was recovered by filtration, and NO3-N and NH4 -N concentra-

tions determined on a Scientific Instruments CFA 200 autoanalyzer.

The volume of water removed from the porous cups and water wells

at each sampling was determined, and then the volumewas evaporated

down to 20 mls on a warm plate in a ventilation hood. Samples were

transferred to a digestion tube for Kjeldahl digestion. Distillation

of the sample and preparation of the distillate for 15N analysis was

carried out as described for the plant samples.

DATA ANALYSIS

Fertilizer nitrogen yield was calculatedas outlined by Hauck and

Bremner (1976) for both the N rate and nitrogen recovery experiments using the following equation: Y=N x (A-C/B-C), where,

Y=fertilizer nitrogen yield, kg/ha. N=total nitrogen in material being investigated, kg/ha. A=atom percent 15N in material being investigated. B=atom percent I5N in labeled fertilizer applied. C=atompercentI5N in either plant or soil to which no labeled fertilizer has been added (natural abundance).

The expression within the parenthesis, (A-C/B-C), is the percentage of

N in the material under investigation (ie. plant matter, soil, or water) which was derived from labeled fertilizer.

A two way analysis of variance was conducted on all measured and calculated parameters in the N rate experiment. Data are presented in 30

0 0 0 0 4

Y.7.4+0.019(N)-1.0x10-4(N2) 1.3.2+0.033(N)-7.5x10-5(N2) r20.20 r2.0.69 4 Keyt W/C Keyt W/%V"

0 0 0 0

ON=

Y5.4+0.052(N)-2.8x10-4(N2) P.5.240.25(N) r2.0.45 r4.0.90

HYslop

O 50 100 150 2

N Fertilizer Rate, kg/ha

Y.2.6+0.021(5)-5.5x10 5(N2) 1'40.65

0 0 0

N Fertiffzer Rate, kg/ha

Figure 2. Grain yield response to N fertilization, 1981. = Treatments with addition of 78 kg K/ha as KC1. 0= Treatments without additions of KC1. 31

1111111 liVIII ... .

9 Y.4.0+0.030(N)-1.1x10 -4 (N 2 ) '' Y=1.5+0.034(N)-7.4x10-5(N2) .. 1.40.51 r2.0.80

T- 8 - - - a - 5- S + 0

o o "' Wilson. Jones I till!II101lii fill - if-3.841).040(N)-1.2x10-4(0) Y- 3.4+0.0 0(N)- 6.5x10 -5(N2) , r2m0.76 r4-o.55 )- .... .

0 - 3 -- o _ Evers 1 Keyt-

1 ...!..e. I _i_ i L_ t i I ji...... t_i 1 I 1 a 1 too

N Fertilizer Rate, kg/ha N Fertilizer Rate, kg/ha

Figure 3. Grain yield response. to N fertilization, 1982. 0= Treatments with-15N labeled subplot. = Treatments without 15N labeled subplots. Table 2. Grain yieldresponse to N and KCL in1981.

1981 ExperimentalLocations Nutrient+Rate Keyt W/C Keyt W/W Hyslop Hamlin Bronson kg/ha Mg/ha

N 0 7.34 3.14 5.45 5.18 2.29 34 - 6.33* 90 8.56* 5.75* 7.90* 7.68* 3.74* 147 7.73* 6.06* 7.15* 8.93* 4.26* 202 7.28 6.84 LSD(P 0.05) 4.29* 0.91 0.84 1.87 0.55 0.49

K( CL ) 0 7.73 4.92 3.74 78 7.72 5.98 3.54 LSD(P<0.05) NS 0.59 NS + N applied as (NH4) 2SO4, K appliedasKCL. *N rates with 15N labeledsubplots. Table3: Grain yield responseto N andCL in1982. 1982 ExperimentalLocations Nutrient+Rate Wilson Jones Evers Keyt kg/ha Mg/ha

N 0 3.80 1.62 3.69 3.40 45 5.21* 67 3.38* 5.96* 4.94* 90 5.67* 134 5.73 4.97* 6.87* 6.25* 179 5.74 - - 202 5.44 6.95 LSD(P 0.05) 6.71 0.91 0.84 1.87 0.55

CL 0 5.70 6.54 45 5.69 56 5.37 134 6.52 LSD(P.<0.05) NS NS +N appliedas (NH4)2 SO4, Cl appliedas NH4-Cl. * N rates with I5N labeledsubplots. 34

two week dry period in February, it had a growth habit similarto

spring wheat. Since its growth and development period was shorter

than fall seeded winter wheat,the yield potential for this site was

limited in 1982.

The overall yields were higher in 1981as compared to 1982. This

was likely due to the abundant rainfall and mild temperatures during

the spring of 1981. These conditions, however, were also conducive to

leaf disease,particularly Septoria. The incidence of Septoria pro-

bably contributed to declining grain yield with high N rates at Keyt

W/C, Hyslop, and the flat response curve at Bronson. Late spring

during 1982, on the other hand,was hot and dry for several weeks

which reduced leaf disease incidence,but possibly affected pollina-

tion and increased stress on plants infected with take-all.

Fertilizer nitrogen uptake efficiency

Data comparing the different methods of evaluating nitrogenup-

take efficiency by the above ground portion of wheat plants arepre-

sented in Figures 4 and 5 and Table 3. In Figures 4 and 5, Line Y1

represents the total N yield at the mid-June sampling, line Y2 the

total nitrogen yield at harvest, and line Y3 the fertilizer N yield

at harvest. The intercepts for lines Yl and Y2 are estimates of N

yield from unfertilized check plots and represent the amount of indigenous soil N taken up. The anticipated reduction in total N yield

from mid-June to harvest was generally not discernible from the data collected during either year. Ambler (1976) compared N yields between winter wheat varieties at several locations and measured decreases in

total N yield between soft dough and harvest at Eastern Oregon sites but not in the Willamette Valley. The apparent curvilinear response 35

z. 1 1 1 I D _ Keyt W/C 0 I- Keyt W/W

7. / 17) 200-

150 me.

0 50- 1-J=100+0.66(N) r2=0.80H ,r , 12=110+0.55(N) ri. ,1.63(N1 r2=0.98 U.i3(N). r2=0.98

I I I I I PI I I /0 rHyslop / - Hamm 250- 2 200- / 200? 150- 150- 8 0 10'-/ 1008 C a 71=77+0.75(N), r2 =0.72 50- 0Y=155+0.96N, r2 =0.76 77=95+0.60(N). r 2 .0.73 1 Y 2 =120+0.62N. r2 .0.74 . Y)= 52(8). r20.96

0.67N, r 2 =0.98 . 0 - Bronson N Fertilizer Rate, kg/ha 200-

150-

100

50-

7,=61+0.44(N1. 1-2=0.41" '`. .1.42(N). 2=0.99

1 1 1 0 100 150

N Fertilizer Rate, kg/ha

Figure 4. Total and fertilizer N uptake as influenced by rate of applied N fertilizer, 1981. Y1 = Maximum uptake sampling, Y2 = Total N, Y3 = Fertilizer N. 36

VAISCIA eY2 Jones .

150 .... Y.19+0.66(8)-3. x10 -3(12), 3 r2 -0.85 Y,.28+0.56(N),1 r =0.94 Y 2 =77+1.06(8), r2=0.88.- Y-.. 0.44(8). r2 =0.95 3 Yy. 0.52(N), r2 -0.94

Y 2 D. -. -

... .

8 y 1 3- Y3 .. ... -0 0 0 .Y O 3 .... 8 0

F i 1 i i i f I f I I I Evers Keyt . O. e Y132+0.89(8)-4.Zx10--(N 2), r 2-0.58 Y=64+0.71(N), r4=0.79 2 2 Y 0.63(N), r 0.97 15C)- -- 3 =

. -- 0 0

-10 11- Y1 8 aO , ---. g 21 'I+ --- ..-- ...- .-- .0. ..-- ' o 5,- ,,. ..., II'-- ii-' 0 r2=0.6Q .0 IU Y1 =37+0.84(1)- 3.5x10 (N2) Y 2 =75+0.68(N), r2=0.84 Y 3 = 0.630), r 2 =0.99

a 1 1 . I I 1 II 0 40 80 40 0

N Fertilizer Rate, kg/ha N Fertilizer Rate, kg/ha

Figure 5. Total and fertilizer N uptake as influenced by rate of applied N fertilizer, 1982. Y1 = Maximum uptake sampling, Y2 = Total N, Y3 = Fertilizer N. Table 4. N fertilizer use efficiency estimates and uptake of soil N as influenced by rate of applied N in 1981 and 1982.

1981 Locations

Keyt W/C Keyt W/W Hyslop Hamlin Bronson 410pp PffSoil N Aline eft', Soil N 12,,F. Pff Soil N p,pgc. Pff Soil N LIX41. Pff Soil N Nrate '7N diff uptake '7N diff uptake '7N diff uptake '7N diff uptake R ' 7N diff uptake kg/ha ----%---- kg/ha ----%---- kg/ha ----%---- kg/ha ----%---- kg/ha ----%---- kg/ha

- 0 - - 132.4 - 54.7 - 120.9 105.2 - - 58.4 34 ------37.1 10.5 96.2 - - - 90 65.5 53.9 121.8 47.148.4 55.8 59.5 60.8 122.1 36.930.4 99.5 44.755.0 67.6 146 62.4 55.1 121.7 55.166.2 70.9 69.8 61.5 108.8 58.159.8 107.8 40.445.6 63.6 202 ------43.145.6 63.6 LSD NS NS 7.6 11.8 NS NS 20.5 NS NS 6.3 mean 64.0 54.5 125.3 51.157.3 60.5 64.6 61.2 117.3 44.033.6 102.2 42.748.2 63.3 U(%) 14.0 31.6 15.521.3 16.3 30.4 27.681.1 11.417.5

1982 Locations Wilson Jones Evers Keyt pyskePff.Soil N pff, Soil N Nvppeff Soil N HAse eff. Soil N Nrate '7N diff uptake '7N diff uptake '7N diff uptake 17N diff uptake

kg/ha ----%---- kg/ha ----%---- kg/ha ----%---- kg/ha ----%---- kg/ha

0 81.1 26.9 72.3 67.1 44 39.478.9 98.4 ------67 - - - 45.462.7 38.5 58.7 79.3 86.2 56.9 58.4 68.1 90 55.6105.4125.8 ------134 - - - 43.356.6 44.6 64.5 68.7 77.9 64.3 71.5 76.8 LSD 30.1 17.2 16.5 9.2 NS NS NS NS mean 47.592.1 101.8 44.359.6 36.7 61.6 74.0 78.8 60.6 64.9 70.7 CV(%) 28.927.3 33.027.3 10.9 35.5 20.5 42.3 38

for Y1 in 1982 is probably an artifact due to insufficient sample size, given the variability within treatments. The exception was

Hyslop, for which the slope of line Y1 was 0.98 while slopes of lines

Y2 and Y3 were 0.62 and 0.67, respectively. However,this high estimate of total N recovery at mid-June rests largely on the strength of the N yields at the highest N rate, and thus may also be an artifact.

In comparing lines Y2 and Y3 within a location, there are two points to consider. The first is the degree of fit of the regression line to the data. This information is given by the coefficient of determination (r2) for each regression line. Use of 15N labeled fertilizer gave more precise estimates of nitrogen use efficiency

(NUE) than did the "by difference" method. This increase in precision with 15N is evidenced by the fact that r2 values for Y3 lines ranged from 0.94 to 0.99 while r2 values for Y2 ranged from 0.73 to 0.94.A comparison of the within site coefficients of variation (CV) (Table 4) for the two NUE methods leads to a similar conclusion.

Estimates of the percentage of the applied N which was recovered by the above ground portion of the plant are given by the slopes of lines in Figures 3 and 4. Comparing the slopes of lines Y2 and Y3 indicates whether I5N labeling and by-difference approaches gave the same or diffrent estimates of nitrogen fertilizer recovery. Examina- tion of the slopes of the Y2 and Y3 regression lines shows that for all locations except the Wilson site,the NUE estimates were within

0.12 (12%) of one another. At the Wilson site, the much higher NUE estimated by the slope of Y2 (1.02) as compared to Y3 (0.52) indicates that the availability of indigenous soil N was markedly increased by the application of fertilizer N. This increased uptake of indigenous 39

soil N with N fertilization (priming effect)was probably related to the history of previous applications ofsewage sludge.With the exception of the Wilson site, slope comparisons indicate thatthe 15N and by difference methods gave reasonably comparable estimates of NUE and that either technique can be used in the Willamette Valley. Where the priming effect is likely to be significant or where very precise estimates of NUE are required,use ofthe 15N technique may be preferable. Partitioning of fertilizer nitrogen Figures 6 and 7 show the partitioning of fertilizer N between grain and straw at harvest.Y2 represents fertilizer N taken up in grain and straw, and Y1 is the fertilizer N taken up in the grain. Within a year, the partioning of fertilizer nitrogenbetween grain and straw was fairly constant, ranging from 0.54 to 0.63 in 1981 and from 0.68 to 0.73 in 1982.The partitioning ratio (b grain/b straw) in 1981 (0.58) was significantly different (p<0.001) fromthe partioning ratio in 1982 (0.71), however.This indicates that the wheat grown on the experimental sites in 1981 was less efficient in translocating nitrogen to the grain from the vegetative parts.This difference in N translocation was probably due to environmental and disease conditions experienced in 1981. Economically optimum nitrogen fertilization rates Table 5 shows the optimum N fertilization rates for eight of the nine sites given three different prices for wheat and nitrogen fertilizer.Optimum N rates for the 1981 Hamlin location could not be calculated because the grain yield response to N was linear over the rates of N applied.The optimumfertilizer N level is calculated by 40

yfl.in(N), r;=1).4N ii.U.32(N). ,;=.1.98 80- Y,-0.63(xl. 1', =4.51(?:), r--n.9R

! _ horain -0.57 fife -0.41 °total total 60- 0 o"- 40. o

Keyt W/C Keyt W/W - 0 f

4 SN Fertilizer Rate, kg/ha 80. 1 =0 21(%) r2 .0.94 r2.0.99

6 0-

4 0 - 0 Y 0 0 2 0 - Bronson - 0 8a lo fo N Fertilizer Rate, kg/ha

Figure 6. Fertilizer N uptake by grain (Y1) and grain plus straw (Y2) as influenced by rate of applied fertilizer N, 1981. 41

. 4

...

8 V0.39(N) r4-0.94 ... Y10.10(4), r20.94 ''' Y21 ..0.5307). r 2 .4.94 Y20.44(N), r 2 O.95 b ...... Trout.A7, °total "." 1.!ZIAin 0.6R I wfoTal 6 11 ... 0 .. 3 ..

4 .. w . Yi

0 S 0 . 0 2

MI I Is o n -6 15 Jones-

.. .

Y10.45(0), r2 -0.99 Y2 Y1.0.44(0). r2.0.97 -- - 8( 92.0.63(N), r2 -0.99 41 Y2.0.63(0). r2.0.97 41

!)Rrain - () '' _basal..0.70 n6Err '0. 71 °total 6 Fir Y1 .. Y1 . 0 .... 0 .

4 ... .

:: .. .., .

2 .., Evers Keyt-

I .4 1 1 i 1 . 0 . , 1 1 1 1 a 80 0 40 1-20 N Fertilizer Rate, kg/ha N Fertilizer Rate, kg/ha

Figure 7. Fertilizer N uptake by grain (Y1) and grain plus straw (Y2) as influenced by rate of applied fertilizer N, 1982. 42

taking the first derivative of the grain yield response to N (Figures

2 and 3) and setting it equal to the ratio of the price of N to the

price received for grain.Going down the column at each site, it is

apparent that the optimum N rate changes little within the range of

nitrogen and grain prices used in this example. However,there were

large differences in optimum levels of N fertilization between sites.

This indicates that if a farmer chooses to fertilize at a maximum

economic N rate, it would probably be more profitable to adjust appli-

cation rates to site factors such as cropping history and soil, than

to attempt to fine-tune N rate to the price of N or grain.A farmer

would probably not want to fertilize right to the optimum N level

however, since there is some risk involved in raising a dryland wheat

crop. Also, a grower may find that the money used to purchase those

last units of N gives a greater return in some other investment.

Given that optimum economic rates of N fertilization are more

sensitive to site related factors than to the prices of N fertiliza-

tion and grain, a multiple linear regression model was developed to

predict maximum economic N rate. The values of the dependent variable

(optimum economic N rate) and independant variables (available soil N

and NUE) are given in Table 6 for each Location. Regression equations

derived from these data are given in the lower half of Table 6. The

coefficient of determination (r2) for equation #4 indicates that 85%

of the between site variation in estimated optimum N rate can be explained by the amount of indigenous sol N taken up by the crop.

When N recovery from 15N labeled fertilizer (I5NUE) is added (equation

#1), the model explains 92% of the between site variation in optimum N rate. Inclusion of nitrogen fertilizer use efficiencies estimated by Table 5. Optimum economic N rates+asinfluenced by grain and fertilizer N prices.

Locations

1981 1982 Price Keyt Keyt N Grain W/W W/C Hys Bron Wils Jns* Evrs Keyt $/kg $/Mg kg N/ha 0.44 147 198 80 89 162 117 214 154 208 0.44 156 199 81 89 163 118 215 155 209 0.44 165 200 82 89 165 119 216 155 210 0.55 147 193 77 87 155 114 209 151 202 0.55 156 195 78 88 157 115 210 152 204 0.55 165 196 79 88 159 116 211 152 205 0.66 147 188 73 86 148 111 204 148 196 0.66 156 190 74 86 151 112 205 149 198 0.66 165 192 75 87 153 113 207 150 200

Grain Yield at optimum economic Nrate bu/A 100 123 118 63 87 82 104 101 Mg/ha 6.71 8.27 7.90 4.27 5.85 5.52 7.02 6.76 + Defined as N rate where dY/dN=Pn/Py. N prices of 0.44, 0.55, 0.66 $/kg equal0.20, 0.25, and 0.30 $/lb, respectively. Grain prices of 147, 156, and 165 $/Mg equal 4.00, 4.25, 4.50 $/bu, respectively. * Rates extrapolated beyond optimumN rate applied (202 kg/ha). Table 6. Economic N fertilizer rates as related to soil N availability and fertilizer N use efficiency.

N fert Optimum+ 15N fert. use Unfert. Prvs economic N use Eff by grain Location Year crop fert. rate Soil N Eff. diff yield kg/ha Mg/ha

Wilson 1982 wheat 115 77 53 106 3.35 Evers 1982 wheat 152 75 63 68 3.75 Keyt 1982 wheat 204 64 63 71 3.36 Keyt 1981 wheat 195 51 53 55 3.19 Jones 1982 wheat 210 28 43 56 1.53 Bronson 1981 ryegr. 157 61 43 44 2.36 Hyslop 1981 fallow 88 120 67 62 5.45 Keyt 1981 clover 78 130 63 55 7.39

Regressionequations for predicting optimumeconomicN fertilizerrates: 1) Y=166-1.85(soil N)+2.22(15NUE), r2=0.92 =all sites 2) Y=279-1.39(soil N)-0.38(NUE by diff.),r2=0.86 =all sites 3) Y=187-1.43(soil N)+1.29(NUE by diff.), r2=0.96 =excl.Wilson site 4) Y=255-1.40(soil N), r2=0.85 =all sites

# Optimum economic N rate at point where dY/dN=Py/Pn. + Calculated based on $0.55/kg N ($0.25/lb N) and $156/Mg grain ($4.25/bu grain). 45

difference (NUE by difference) gave an even better predictive model

(equation #3) provided the data from the Wilson sitewas excluded from

the regression. The unreasonably high value for N fertilizer recovery

estimated by difference (106%) resulted in a predictive equation

(equation #2) with a lower coefficient of determination (0.86). In

addition, the negative (-) algebraic sign on the regression coeffi-

cient for NUE by difference in equation #2 is not sensible since it

predicts that a grower can economically apply less N when fertilizer N

recovery is high than when it is low.

Regression models represented by equations 1,3, and 4 in Table 5 all look promising for predicting optimum economic N rates. They are

intuitively sensible and consistent with field observations that wheat crops have lower N fertilizer requirements when grown on soils having high levels of available soil N. Before one could apply these models, however,it would be necessary to measure or estimate values for the dependent variables (available soil N and NUE). Since soil tests currentlyused in Western Oregon do not measure available soil N, it might be worthwhile to develop or modify a soil test for available soil N (residual inorganic N plus readily mineralizable organic N) and then attempt to calibrate the test by comparing soil test values with uptake of soil N by field grown plants.Since the N requirement of unfertilized winter wheat comes entirely from available soil N,one might also by able to estimate available soil N based upon unfertilized grain yield. Data in table 6 for unfertilized grain yield is shown plotted versus available soil N in Figure 8. If growers had information about the yield of wheat which could be obtained without N fertilizer, it might allow them to make reasonable predictions of 46

0 40 80 120

Soil N, kg/ha

Fig. 8 Unfertilized grain yield as a function of soil N uptake by grain plus straw. Table7. ResidualNO3-N and total soil N toa depth of 12" after cropping to wheatin 1981.

KeytW/W KeytW/C Hyslop Hamlin Bronson NO Total NO Total NO 3 3 3 Total NO Total NO Total N Rate -N Soil N -N 3 3 SoilN -N Soil N -N Soil N -N Soil. N kg/ha ug/g % ug/g % ug/g % ug/g % ug/g

0 2.600.181 1.420.193 1.48 0.130 2.42 0.121 2.25 0.169 34 0.81 0.127 90 3.940.184 0.690.191 1.18 0.135 0.87 0.128 3.31 0.162 146 3.360.173 0.990.195 2.03 0.138 0.69 0.126 3.42 0.158 202 7.49 0.160 LSD 0.50 NS 0.27 NS 0.42 NS 0.45 NS 2.32 0.007 (w.00.05) 48

available soil N for each specific crop rotation-soil combination.

The efficiency of N fertilizer use by plants had a much less

striking effect on optimum economic N rates. From the data in Table 6

it appears that NUE values of 45 to 55 would be reasonable estimates

for soils with poor drainage or where take-all diseaseis a problem.

NUE values of 60 to 70 might be appropriate for deep, well drained

soils where take-all root rot does not limit yield.

Table 7 shows the levels of total soil N and NO3 -N left in the

soil after cropping in 1981. Nitrogen fertilization had no effect on

total soil N except at Bronson farm, and then it was not significantly

different at all rates. There were differences between rates in the amount of NO3-N left in the soil to 12".However, NO3 -N levels were

low in all cases. Even at 3 ug/g there would only be approximately 12

lbs of N in an acre foot of soil. It appears then that the wheat

plant and soil microorganisms reduced levels of soil NO3-N at these sites in 1981 to negligible amounts relative to the N fertilizer applied.

NITROGEN RECOVERY STUDY

Growth stage subsampling

The results from the periodic sampling of the N balance plots are shown in Figure 9. The top curve shows the gain in total dry matter through the growing season. All sites show the same pattern of dry matter accumulation over time, although at the Bronson site the overall dry matter accumulation was lower than at the other two sites. The second curve shows changes in percent N in the total plant over time. For all sites the N content decreased as dry matter in- Hyslop Hamlin Bronson

2000 2000 2000

1500 1500

1500

1000 1000 41Sterag ',ay., 71irain ,tems 1,,U,. 1000

500 z 500 Seisms feekes Stage 500 C;rain Stems Leav feltvs Stage 10 10.1 10.5.4.10.5111.11 11.2,11.3 0 9 10 10.5.1 10.5.4 11.1 11.1511.1 Feekes Stage 0 4

Fert. 8 8 10 10.1 10.5.4 10.5.4 11.1 11.1 11.3 3.0 1-7F;1 W °'"19°39 I I I 4 0 O O 3.0 .0.522!0.154 15 Total N 2.0 fort. N 3.0 Total n-0.489.9.044 2.0-

'ft's118 3 1.0 0 z "'-'111116 2.0 1.0 z SQ 0 aR 1.0 0 4 1 4 0 16 N rate applied es E 0 4 I 4 16 I rate applied- S rate applied 12 sr ..../ sr 12 12 0 8 C) 5' 8 z 8 Stems 4 Leaves 0Crain Shaw Leaves 4 9 tams Leave,. 4 Ot:Ya g St tnt9 ...ay., 0-rain Sten. Leave. LL 0 U- 2b 40 60 00 00 80 20 40 60 80 20 40 60 80 Time after N Fertilizer Applied, days Time after N Fertilizer Applied, days Time after N Fertilizer Applied, days

Figure 9. Total dry matter, % N, and fertilizer N uptakeas a function of time after spring topdressed N. 50

creased. The seasonal average ratio of fertilizer Nto total N is

also shown in this graph with all sites showing similar ratios. This

ratio through the sampling period varied fromthe ratio at harvest at

all three sites, but there was no pattern discernable through the

sampling period. Consequently itwas assumed that fertilizer N was

taken up in the same ratio to soil N throughout the growingseason at

these sites in 1981. The last curve shows fertilizer N uptake through

the sampling period. There is a great deal of variation in this data,

particularly for the samplings at 54 and 64 days after fertilization.

This variability was likely due to the difficulty in weighing out a

representative plant sample for kjeldahl digestion,as the filling

kernels were too small to separate from straw and leaves but of enough

mass to affect the N content if they were not sampled in proportion to

the vegetative matter. It appears from the data that uptake of ferti-

lizer N is completed approximately 40 days afterapplication, or

around the watery kernel stage. Other research (McNeal, 1966), has

also indicated that total N uptake is completed by watery kernel

stage and that N in wheat leaves and stems is remobilized for trans-

location to the grain.

Nitrogen balance sheet

The results of the N balance study are shown in table 8.Of the

residual fertilizer N in the soil after cropping in 1981, over 70% was

found in the top 15 cm at the Hyslop and Hamlin sites, and 80% within

the top 30 cm at Bronsons. There was approximately twice as much fertilizer N left in the soil at Bronsons compared to the other sites.

This was probably due to fertilization in excess of the crop's ability

to take up the fertilizer N. Total fertilizer N recovery by the crop, Table 8. Recovery of spring topdressed Nfertilizer over two croppingseasons.

1 1 1980 -81 1 1 1981 -82 Fert. N Residual Fert. N Residual Fert. N uptake fert. N uptake fert. N rate by cro in soil by crop in soil Location kg/ha fraction kg/ha fraction kg/ha fraction kg/ha fraction kg/ha

Hyslop Grain 51.7 Root Crown 6.1 Total top 1.0 Root Crown 0.2 straw 49.5 0-15 cm 39.9 0.-30 cm 19.8 15-30 cm 2.5 30-60 cm 3.0 30-60 cm 2.1 60-90 cm 2.3 60-90 cm 2.3 90-120 cm 2.0 90-120 cm 3.5 146 101.2 56.4 1.0 27.3

Hamlin Grain 32.1 Root Crown 2.2 N/A Roots N/A Straw 24.9 0-15 cm 29.2 0-15 cm 13.3 15-30 cm 0.0 15-30 cm 5.1 30-60 cm 3.4 30-60 cm 1.6 60-90 cm 0.0 60-90 cm 1.6 90-120 cm 2.7 90-120 cm 0.8 146 57.0 37.5 22.4 Bronson Grain 29.8 Root Crown 6.2 Grain 2.2 Root Crown 0.1 Straw 26.4 0-15 cm 49.4 Straw 0.4 0-30 cm 38.2 15-30 cm 30.2 30-60 cm 7.4 30-60 cm 6.6 60-90 cm 2.0 60-90 cm 3.3 90-120 cm 1.7 90-120 cm 2.6 146 56.2 98.3 2.6 49.4 52 root crowns and soil was 108% and 106% of the fertilizer N applied after the first crop at the Hyslop and Bronson sites, respectively.

Recovery in excess of 100% is due to cumulative sampling error.Total recovery of fertilizer N at Hamlin farm in 1981 was only 65%. The plot at this site became infested with wild oats early in the growing season. It was weeded as soon as the infestation became apparent, but the vigorous growth typical of the weed probably resulted in substantial N uptake by the wild oats. One can presume that if the fertilizer N removed by the wild oats were added to the balance sheet, recovery of applied fertilizer N in this plot would have been closer to 100%.

The last two columns in Table 8 show how much of the residual fertilizer N left in the soil after the first crop was accounted for after the second crop. Column 4 shows the residual fertilizer N contribution to the second crop at Hyslop and Bronson sites. It is evident that little of the residual fertilizer N was taken up,indi- cating that for these sites residual fertilizer N in the organically combined form is of little value to the subsequent crop. Similar findings were reported by Broadbent (1980) and Fredrickson et al.

(1982). Approximately one half of the residual fertilizer N left in the soil after the 1981 season was accounted for in the soil after the

1982 season at all three sites. Since negligible amounts were taken up by the 1982 crop at Hyslop and Bronson farms, 19, 10 and 31%of the

146 kg N/ha applied at the Hyslop, Hamlin, and Bronson sites, respectively, would be considered unaccounted for.Residual N fertilizer unaccounted for at the end of the second cropping season was probably lost through leaching or denitrification of NO3-N 53

Soluble nitrogen

Figure 10 shows rainfall during the late winter and spring sam-

pling period, and the levels of total solubleN at 30 cm as determined

from the porous cup samples. The porous cups at the Hamlin site were

destroyed in early February when the plotarea was plowed under by the

grower after two samples were taken. For the other two sites the data

show that soluble N levels change little during the late winter but

increase rapidly in mid March or early April. Some of the early increase at the Hyslop site may be mineralization, but it appears that fertilization, as indicated by the arrows, brought a very sharp increase. Table 9 shows how much of this soluble Nwas actually residual fertilizer N. The highest value was slightly more than 6% at the

Hamlin site, but values averaged only 1.48% and 2.27%for the Hyslop and Bronson sites, respectively, for the sampling period. There was no apparent increasing or decreasing trend in the percentage of soluble fertilizer N during the sampling period. The amount of fertilizer N that was potentially leachable during the sampling period appears then to be quite small. -0

-12

6.0 -24

-36 5.0

4.0 Hyslop Hamlin Bronson 3.0

2.0

1.0

JAN 18 FEB 1 FEB 15 MAR 1 MAR 15 APR 1 APR 15 DATE

Figure 10. Soluble N concentration in soil water extracted withporous cups placed at 30 cm depth in 1982. Arrows indicate date of spring topdressed N. Table 9. Percentage of soluble nitrogenderived from 15N labeledfertilizer applied on April 13, 1981.

Location

Hyslop Bronson Hamlin P. Cup Well P. Cup Well P. Cup Sampling @ @ @ @ @ Date (1982) 30 cm 120 cm 30 cm 120 cm 30 cm

Jan. 18 2.74 1.06 3.13 7.13 Feb. 1 0.91 1.26 6.30 Feb. 3 2.94 1.90 1.46 1.20 Feb. 12 1.58 6.03 2.82 Feb. 15 2.08 0.91 6.32 Mar. 12 2.59 1.97 Mar. 15 1.50 1.66 1.85 Apr. 1 1.52 0.98 Apr. 12 0.09 0.67 Apr. 16 0.17 1.59 0.74 2.84 Apr. 19 0.21 1.76 0.75 1.31 Seasonal Mean 1.48 1.44 2.27 2.00 56

DISCUSSION

Using 15N is the most precise means of estimating NUE, but in comparison to estimation of NUE by the difference method, the accuracy of the two methods is not markedly different unless there is a substantial priming effect. This means that if one is interested in studying the fate of N molecules applied as fertilizer ,then 15N labeling techniques should be used. If one is interested in the overall effect of N fertilization on a crop, however, then theby difference approach may be more appropriate.

Of note is that a much greater proportion of the N taken up by the plant remained in the straw under Willamette Valley conditions as compared to midwest wheat growing regions. From 74 to 80% of the N recovered in the plant was found in the grain for winter wheat grown in Kansas (Olson, 1982) and for spring and winter wheats grownin

Montana (Christensen and Killorn, 1981; Christensen and Meints, 1982), respectively. In this study 70% of the plant N was found in the grain in 1982, while only 58% was found in the grain in 1981; probably because on severe leaf disease. Consequently, while total uptake may be high, other factors may reduce the efficiency with which the fertilizer N is translocated to the grain. The other side of this is that a substantial quantity of N is being returned tothe soil in the straw. This N may provide a pool of N that can be, in the processof straw decomposition, mineralized and used by subsequent crops.

Given a curvilinear yield response to N and the priceof wheat and N fertilizer, the economically optimum rate of N fertilization can be calculated. The evidence indicates that differences in theoptimum 57

rate of N fertilization overa range of wheat and fertilizer prices

would not be great enough to warrant adjusting applicationrates to

flucuations in these prices. However,the differences between loca-

tions or fields due to cropping history and NUEare large enough to

justify fine tuning fertilizerrecommendations to these parameters.

The predictive ability of these parameters is shown in theequations

in table 6. Quantifying the contribution ofsoil N to the N needs of

wheat is no easy task, but probably the bestway is to raise a crop of

wheat without any addition of fertilizer N, with the subsequent

amount of N recovered in the plant an index of available soil N.To

make such a predictive equation widely applicable,this method would

have to be carried out on different soil types and fields with dif-

ferent cropping histories, around theWillamette Valley. How much NUE

varies with changes in cropping history, soil type, and disease inci-

dence would also have to be determined.

The amount of inorganic fertilizer N remaining in the soil after

a crop of vigorous wheat appears to be small. Only at the Bronson

site were appreciable levels of inorganic N noted. Under management

conditions where stubble is plowed down,one can expect to see the

inorganic N immobilized during microbial decomposition of the straw.

What fertilizer N remains in the soil is predominantly incorporated

into soil organic matter in the top 15 cm. This agrees with the

findings of Olson (1979, 1982) and Olson et. al., (1979).

The accountability of fertilizer N in plant and soil after the

1981 cropping season was near 100% at the Hyslop and Bronson sites, but was confounded at the Hamlin site because of N uptake by wild oats. Loss of fertilizer N,then, occurred between the 1981 and 1982 58

cropping seasons. Since gaseous N losses from plants were not ap-

parent from the data and the recovery of fertilizer N in plant and

soil was high after the first cropping season, the possibility of

ammonia loss from the growing wheat crop in the Willamette Valley

would have to be discounted. Consequently the 10 to 31% of the ferti-

lizer N not accounted for would have to be attributed to either

leaching or denitrification. It is apparent from Fig. 10 and table 9

that at least for the period of mid January to April, potential

leaching losses of residual fertilizer N are not great. The trends in

NO3_N leaching losses found by Istok (1983) and Owre (1980) show low

levels during this same period relative to higher NO3 -N levelsprior

to this period. It is possible that the fertilizer N not accounted for in the N balance study was lost during the fall when soil tempera-

tures are still warm, and the increase in soil moisture from fall rains stimulates a flush of mineralization and subsequent nitrification. The resulting nitrate could possibly be lost through leaching as the soil becomes saturated and subsurface saturated flow isini- tiated. Owre (1980) found up to 16 kg N/ha/year lost through tile drainage, and Istok found 18 kg N/ha lost in tile lines the second year after tiling. The amounts of fertilizerN not accounted for at

Hamlin and Hyslop are of the same order of magnitude as these observed losses. The amount of fertilizer N not accounted for at the Bronson site would seem to be higher than one would expect from these two studies.

The other possible avenue of fertilizer N loss is denitrification. Given the frequent saturated conditions that the soil at the

Bronson site experiences during winter months, this possibility is 59

quite strong, especially in light of the clay layer at 70 cm which

would restrict leaching. The production of NO3 -N in the fallresul-

ting from a flush of mineralization may provide a pool of denitrifi-

able nitrogen. The losses noted at the Hyslop and Hamlin sites fall

within the magnitude of losses ascribed to denitrification, approxi-

mately 5-15% ofthe fertilizer applied,by several researchers

(Rolston et. al., 1982; Allison, 1966).

The minimal contribution of residual fertilizer N to the sub-

sequent crop is probably due to it coming exclusively from mineraliza-

tion of organically combined N. Although a greater proportion of

organically combined residual fertilizer N is found in the readily

mineralizable fraction after the growing season (Smith, et. al.,

1978), most of this was probably mineralized during the initial fall

rains,and lost from the soil either by leaching or denitrification.

Even if most of the organically combined residual fertilizer N is in a

readily mineralizable form, Smith et. al. (1978), showed that the pool

of indigenous mineralizable soil N is so large that the absolute

amount of soil N mineralized is much greater than the amount of la-

beled organic N. One could then expect that the residual value of

fertilizer N is small in the Willamette Valley, as inorganic fertilizer N and readily mineralizable organcially combined residual fertilizer N is either leached out or denitrified from the rooting zone during the rainy winter season. 60

CONCLUSIONS

With respect to the initial objectives of this study, itwas

determined that total N uptake efficiencyof Willamette Valley winter

wheat ranged from 42 to 67% of the spring applied fertilizer N

applied (obj. #1). Cropping histories which included recent additions

of nitrogen rich organic residues substantially increased available

soil N, but only at one site where sewage applicationswere common did

fertilizer N increase uptake of soil N (obj. #2). Data for parti-

tioning of fertilizerN between grain and straw indicated a higher

retention of N in the straw as compared to results from the midwest,

and also a higher rentention in the straw when leaf diseaseincidence

was high (obj. #3). Wheat ceased taking up fertilizer N within ap-

proximately 40 days after application (obj. #4). From 28% to 66% of

the applied fertilizer N remained in the soil after the first year's

harvest, while 20% to 30% was accounted for in the soil after the

second year's harvest (obj. #5).

Levels of soluble N at 30 cm depth from mid January to Aprilwere

generally below 3 ug/g, of which only a negligible portion was ferti-

lizer N (obj. #6). Gaseous N loss from wheat plant during the growing season was not evident, while possible leaching and denitrification may account for the 10% to 31% of fertilizer N lost between the two growing seasons (obj. #7). Economic rates of N fertilization were determined, and it was found that they weremore strongly influenced by levels of soil N as determined by cropping history than by the price of wheat or nitrogen fertilizer. Soil N together with NUE estimates (obj. #1) showed promise in fine tuning recommended fertilizer rates. 61

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Andersen, A. J. 1977(b). Effects of fertilizers on barley protein quantity and quality. Cereal Res. Comm. 5:159-167

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Austin, R. B.,M. A. Ford, J. A. Edrich, and R. D. Blackwell. 1977. The nitrogen economy of winter wheat. J. Agri. Sci. Camb. 88:159-167.

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Broadbent, F.E. and T. Nakashima. 1967. Reversion of fertilizer nitrogen in soils. Soil Sci. Soc. Am. Proc. 31:648-652. Broad- bent, F. E. 1980. Residual effects of labeled N in field trials. Agron. J. 72:325-329.

Broadbent, F. E., R. S. Rauskolb, K. A. Lewis, and G. Y. Chang. 1980. Spatial variability of nitrogen- 15 and total nitrogen in some virgin and cultivated soils. Soil Sci.Soc. Am. J. 44:524-527.

Cameron, R. S. and A. M. Posner. 1979. Mineralisable organic nitrogen in soil fractionated according to particle size.J. Soil Sci. 30:565-577. 62

Cassman, K.G. and D.N. Munns. 1980. Nitrogen mineralized as affected by soil moisture, temperature, and depth. Soil Sci. Soc. Am. J. 44:1233-1237.

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Appendix table 1. Individual plot grain yields as influenced by N and K rates at five locations, 1981

Nutrient+ Keyt Keyt N K Rep W/W W/C Hys Ham Bron

kg/ha Mg/ha

0 0 1 3.0 7.0 6.7 5.9 1.5 0 0 2 3.2 7.5 3.9 5.3 2.4 0 0 3 2.8 7.2 6.8 4.7 2.7 0 0 4 2.4 6.0 4.4 4.8 2.9 0 70 1 3.4 6.5 2.3 0 70 2 2.9 7.4 2.2 0 70 3 2.5 8.2 2.6 0 70 4 4.9 8.9 1.7 34 0 1 6.8 34 0 2 6.3 34 0 3 5.6 34 0 4 6.6 90 0 1 4.8 8.4 7.9 8.3 4.8 ?8 8 3 g:9 3:6 90 0 4 5.0 8.3 7.1 7.7 4.0 90 78 1 6.5 9.8 3.9 90 78 2 5.8 9.1 2.5 90 78 3 7.2 8.9 3.6 90 78 4 6.6 7.0 3.1 146 0 1 7.1 9.0 8.5 9.4 4.6 146 0 2 4.0 8.1 6.6 8.9 4.2 146 0 3 5.0 9.0 6.2 9.1 3.9 146 0 4 5.1 7.0 7.3 8.3 4.4 146 78 1 7.4 8.0 4.7 146 78 2 5.7 6.1 4.4 146 78 3 7.8 7.9 4.3 146 78 4 6.4 6.7 3.6 202 0 1 5.9 7.6 4.3 202 0 2 7.2 6.1 4.4 202 0 3 6.4 8.8 3.4 202 0 4 6.7 6.7 4.4 202 78 1 6.5 8.1 4.3 202 78 2 6.8 5.6 4.6 202 78 3 7.0 7.9 4.4 202 78 4 8.2 7.4 4.5 SEM 0.57 0.62 0.76 0.24 0.33 (error df) (21) (21) (6) (9) (21)

+ K applied as KCL,N applied as (NH4)2504 Appendix table 2. Individual plot grain yields as influenced by N and CLrates at four locations, 1982.

Wilson Jones Evers Keyt NrateClrateRepYield NrateClrate RepYield NrateClrate RepYield NrateClrate RepYield

---kg/ha--- Mg/ha ---kg/ha--- Mg/ha ---kg/ha--- Mg/ha ---kg/ha--- Mg/ha

0 0 1 3.83 0 0 1 1.88 0 0 1 4.61 0 0 1 3.79 0 0 2 0 3.73 0 2 1.97 0 0 2 2.52 0 0 2 3.65 0 0 3 4 . 2 2 0 0 3 1 . 1 3 0 0 3 3.44 0 0 3 - 0 0 4 3.42 0 0 4 1.49 0 0 4 4.19 0 0 4 2.17 45 0 1 5.29 67 90 1 4.91 67 90 1 6.73 67 90 1 6.02 45 0 2 5.41 67 90 2 3.46 67 90 2 6.27 67 90 2 6.44 45 0 3 5.48 67 90 3 3.06 67 90 3 5.32 67 90 3 3.35 45 0 4 5.18 67 90 4 2.53 67 90 4 5.63 67 90 4 3.93 45 56 1 4.36 67 90 1 3.72 67 0 1 6.60 134 134 1 7.10 45 56 2 5.17 67 90 2 4.26 67 0 2 5.84 134 134 2 7.27 45 56 3 5.53 67 90 3 3.41 67 0 3 4.98 134 134 3 5.47 45 56 4 5.22 67 90 4 1.71 67 0 4 6.34 134 134 4 6.24 90 0 1 6.98 134 134 1 3.51 134 90 1 6.57 134 0 1 6.40 90 0 2 6.75 134 134 2 4-51 134 90 2 7.16 134 0 2 7.21 90 0 3 5.50 134 134 3 3.80 134 90 3 7.18 134 0 3 7.27 90 0 4 4.95 134 134 4 2.53 134 90 4 7.19 134 0 4 5.29 90 56 1 4.41 134 90 1 5.87 134 90 1 7.57 134 45 1 3.93 90 56 2 6.15 134 90 2 5.51 134 90 2 7.60 134 45 2 6.70 90 56 3 5.82 134 90 3 4.02 134 90 3 6.26 134 45 3 6.72 90 56 4 4.80 134 90 4 4.84 134 90 4 5.52 134 45 4 5.41 134 0 1 5.08 134 308 1 5.37 134 134 1 7.22 202 45 1 7.80 134 0 2 5.78 134 308 2 5.34 134 134 2 7.10 202 45 2 7.62 134 0 3 6.24 134 308 3 4.02 134 134 3 6.55 202 45 3 5.84 134 0 4 5.73 134 308 4 4.75 134 134 4 7.20 202 45 4 5.56 134 56 1 4.96 202 45 1 6.24 134 403 1 7.05 134 56 2 6.27 202 45 2 4.93 134 403 2 5.72 134 56 3 6.05 202 45 3 5.50 134 403 3 7.35 134 56 4 5.74 202 45 4 5.11 134 403 4 6.75 179 0 1 4.60 202 45 1 5.92 202 90 1 7.10 179 0 2 6.21 202 45 2 5.40 202 90 2 7.02 179 0 3 6.43 202 45 3 5.46 202 90 3 6.80 179 0 4 5.72 202 45 4 _ 4.98 202 _._90 4 6.89 ---- SEM 0.38 0.40 0.45 0.68 (errordt) (21) (21) (21) (15) Appendix table 3. Individual plot data for 1 atom % subplots in N rate study, 1981.

Soil N Fraction of MUS Straw Crain fertilizer N NO3 NH4 Total Nitrogen in Rate Rep DM ZN DM %N DM %17 -N -N Straw Grain kg/ha 8/m g/m g/m --mg/kg--

Keyt W/W 0 1 580 0.60 640 0.36 300 1.18 3.31 4.43 .183 0 0 0 2 550 0.58 680 0.33 320 1.13 2.36 4.43 .164 0 0 0 3 610 0.58 550 0.39 280 1.19 2.36 4.48 .176 0 0 0 4 840 0.58 540 0.34 240 1.19 2.36 4.48 .202 0 0 90 1 1290 0.66 840 0.54 400 1.30 4.25 5.34 .183 .358 .395 90 21230 0.58 830 0.55 390 1.42 4.02 3.98 .190 .492 .523 90 3 1160 0.46 790 0.40 450 1.30 3.54 4.43 .188 .413 .393 90 41160 0.64 850 0.57 430 1.30 0.95 4.43 .176 .425 .443 146 1 1650 0.66 904 0.63 650 1.64 3.07 3.98 .171 .462 .472 146 2 1450 0.58 980 0.61 630 1.55 3.54 4.88 .172 .558 .532 146 31510 0.64 980 0.51 640 1.27 3.31 3.98 .174 .546 .523 146 41860 0.76 980 0.64 530 1.70 3.54 4.43 .174 .580 .595 Keyt WIC 0 1 1460 0.64 1100 0.37 700 1.25 1.42 5.79 .194 0 0 0 2 1560 0.76 1560 0.37 750 1.19 1.89 4.43 .186 0 0 0 3 1480 0.79 1240 0.39 720 1.24 1.18 4.88 .197 0 0 0 4 1680 0.73 1000 0.38 600 1.31 1.18 5.34 .194 0 0 90 1 1350 0.76 1110 0.64 710 1.58 0.93 7.28 .198 .342 .323 90 2 1920 0.73 1340 0.58 790 1.47 0.89 3.54 .204 .350 .343 90 3 1710 0.90 1060 0.58 700 1.40 0.70 3.54 .190 .350 .308 90 4 1970 0.84 1200 0.62 710 1.58 0.23 4.01 .172 .333 .284 146 1 2150 0.89 1190 0.62 720 1.52 1.16 4.01 .191 .400 .377 146 22310 0.96 1260 0.73 810 1.64 1.16 4.01 .195 .467 .439 146 3 2020 0.84 1210 0.66 720 1.59 0.70 4.48 .195 .441 .432 146 4 1990 0.96 1360 0.82 780 1.76 0.93 4.48 .198 .451 .418 Hyslop 0 1 2180 0.84 1290 0.32 670 1.25 1.18 3.98 .110 0 0 0 2 1700 0.95 850 0.44 390 1.48 1.89 5.79 .135 0 0 0 3 2160 0.99 1200 0.45 680 1.61 1.66 5.34 .146 0 0 0 41300 0.71 1000 0.37 440 1.43 1.18 4.43 .131 0 0 90 1 2150 1.01 1170 0.62 670 1.39 1.42 3.53 .128 .339 .331 90 2 2080 1.16 1200 0.78 640 1.69 1.18 3.53 .135 .263 .255 90 3 2160 1.10 1050 0.73 630 1.70 1.18 4.43 .142 .349 .362 90 4 1850 1.03 1090 0.54 580 1.59 0.95 3.98 .134 .265 .273 146 1 2100 1.46 1070 0.93 582 1.74 2.26 4.28 .136 .470 .500 146 2 2310 1.42 1210 0.98 630 1.94 2.03 4.73 .140 .475 .508 146 3 1960 1.55 1040 0.78 600 1.87 2.49 5.17 .146 .467 .497 146 4 1870 1.55 1210 0.68 750 1.68 1.33 4.73 .133 .457 .482 Appendix table 3, continued. Individual plot data for1 atom X subplots in N rate study, 1981.

Soil N Fraction of NHS Straw Grain fertilizer N NO3 NH4 Total Nitrogen in Rate Rep DM 2N DM X1,1 DM ZN -N -N Straw Grain kg/ha g/m g /m' --mg/kg-- Hamlin 0 1 1340 0.64 1010 0.35 590 1.36 1.89 5.34 .112 0 0 0 2 1200 0.78 960 0.35 530 1.47 3.31 5.34 .118 0 0 0 3 1260 0.64 930 0.35 470 1.47 2.13 4.43 .115 0 0 0 41240 0.58 1020 0.33 480 1.22 2.36 5.34 .140 0 0 34 1 1550 0.70 1120 0.35 640 L.30 0.64 4.73 .114 .106 .121 34 2 1650 0.70 920 0.31 570 1.41 1.10 4.73 .117 .116 .102 34 3 1670 0.64 860 0.28 550 1.41 0.87 3.83 .131 .087 .079 34 4 1390 0.54 1100 0.35 540 1.18 0.64 4.73 .145 .163 .160 90 1 1810 0.88 1130 0.54 730 1.46 0.87 4.73 .108 .214 .204 90 2 1250 0.76 870 0.34 610 1.35 0.87 3.83 .123 .273 .260 90 3 1890 1.00 1040 0.36 750 1.41 1.10 4.73 .142 .212 .199 90 4 1440 0.58 860 0.36 630 1.22 0.64 5.62 .139 .361 .366 146 1 1540 1.17 1430 0.64 780 1.54 0.93 4.01 .110 .393 .386 146 2 1690 1.11 1330 0.62 810 1.59 0.70 4.01 .115 .404 .431 146 3 1740 1.17 1130 0.61 66031.53 0.46 5.88 .139 .488 .498 146 4 1860 1.10 1150 0.57 760 1.47 0.70 5.41 .138 .455 .485 Bronson 0 1 930 0.67 600 0.48 150 1.37 2.13 6.24 .169 0 0 0 2 740 0.56 650 0.49 240 1.31 1.66 8.50 .169 0 0 0 3 890 0.73 550 0.42 270 1.25 2.36 9.30 .172 0 0 0 4 550 0.67 710 0.41 290 1.20 2.84 7.15 .167 0 0 90 1 1270 0.84 780 0.60 400 1.47 3.02 6.81 .168 .416 .411 90 2 1300 0.79 720 0.73 320 1.52 1.39 6.34 .155 .396 .337 90 3 1300 0.95 830 0.60 420 1.47 3.02 5.88 .160 .375 .341 90 41160 0.73 830 0.604 380 1.58 5.81 6.81 .163 .348 .363 146 1 1320 0.90 740 0.62 380 1.70 3.95 6.34 .158 .562 .571 146 2 1260 1.01 820 0.77 440 1.70 3.25 6.34 .157 .529 .504 146 3 1020 1.07 720 0.73 440 1.58 5.35 5.41 .154 .461 .424 146 4 1360 1.29 790 0.74 400 1.52 1.11 6.81 .161 .394 .415 202 1 1160 1.12 740 0.86 370 1.81 6.75 6.34 .156 .566 .616 202 2 1080 1.18 820 0.73 500 1.69 3.72 6.34 .170 .564 .582 202 3 1370 1.23 900 0.92 440 1.93 9.60 4.01 .153 .579 .587 202 4 1400 1.23 890 0.89 440 1.82 9.90 6.81 .160 .554 .572 70

Appendix Table 4. Individual plot datafor1 atom % subplots in N rate study, 1982.

Fraction of NUS Straw Grain fertilizer N Nitrogen in Rate Rep DM PI DM 1/41.1 DM %N Straw Grain g/m2 g/m2 kg/ha g/m Wilson 0 1 580 0.22 437 1.66 0 0 0 2 580 0.23 434 1.58 0 0 0 3 640 0.21 483 1.57 0 0 0 4 520 0.21 389 1.46 0 0 44 1 840 0.27 529 1.64 .145 44 .116 2 860 0.26 541 1.72 .207 .182 44 3 870 0.34 548 1.79 .194 .134 44 4 820 0.24 518 1.75 .167 .134 90 1 1480 0.36 698 2.19 .306 .280 90 2 1430 0.30 675 2.06 .358 .336 90 3 1170 0.34 550 2.06 .261 .228 90 4 1050 0.41 495 2.41 .274 .260 Jones 0 1 439 0.45 200 0.28 173 1.49 0 0 0 2 344 0.53 200 0.27 179 1.46 0 0 0 3 362 0.47 130 0.29 104 1.46 0 0 0 4 417 0.48 180 0.31 137 1.47 0 0 67 1 1020 0.58 470 0.37 491 1.43 .645 .533 67 2 890 0.50 580 0.36 346 1.44 .524 .417 67 3 810 0.67 520 0.39 306 1.54 .449 .368 67 4 650 0.56 440 0.31 253 1.43 .317 .292 134 1 867 0.62 580 0.67 351 2.01 .669 .585 134 2 1070 0.49 750 0.44 451 1.78 .624 .555 134 3 872 0.46 630 0.49 380 1.73 .483 .461 134 4 817 0.60 590 0.48 335 1.88 .579 .604 71

Appendix Table 4, continued. Individual plot data for 1 atom % subplots in N rate study,1982.

Fraction of MUS Straw Grain fertilizer N Nitrogen in Rate Rep DM ZN DM ZN DM XN Straw Grain kg/ha g/m2 g/m1 g/m Evers 0 1 1330 0.29 430 0.22 483 1.37 0 0 0 2 630 0.44 710 0.26 270 1.39 0 0 0 3 720 0.53 730 0.26 374 1.40 0 0 0 4 1290 0.33 830 0.26 456 1.42 0 0 67 1 1490 0.51 1150 0.36 673 1.72 .317 .258 67 2 1710 0.49 1030 0.33 627 1.57 .316 .283 67 3 1320 0.69 890 0.24 532 1.47 .375 .320 67 4 1200 0.49 1070 0.29 563 1.45 .345 .391 134 1 1440 0.49 1020 0.35 657 1.63 .605 .502 134 2 1830 0.53 1170 0.35 716 1.73 .619 .492 134 3 1490 0.41 1180 0.45 718 1.69 .574 .510 134 4 1610 0.73 1140 0.35 719 1.88 .549 .516 Keyt 0 1 760 0.49 570 0.30 385 1.54 0 0 0 2 1050 0.40 520 0.30 375 1.49 0 0 0 3 430 0.53 560 0.29 404 1.40 0 0 0 4 490 0.55 400 0.36 218 1.53 0 0

67 1 1240 0.44 790 0.38 602 1.58 .463 .341 67 2 1600 0.56 920 0.36 644 1.57 .410 .319 67 3 1580 0.57 530 0.52 335 1.75 .406 .377 67 4 940 0.64 630 0.32 393 1.51 .382 .327 134 1 1240 0.61 910 0.35 710 1.73 .621 .465 134 2 1420 0.78 980 0.52 730 1.87 .585 .522 134 3 940 0.46 750 0.40 550 1.84 .582 .525 134 4 1140 0.69 390 0.64 624 1.96 .620 .500 Appendix Table 5. 1981 total dry matter, % N, and% fertilizer N from 15N labeled sublplots.

TotalDryMatter NConcentration I5N*

Site N rate Grain Straw TDM Grain Straw Grain Straw kg/ha Mg/ha 7.. ---atom%--- Keyt W/W 0 2.85 6.02 8.88 1.17 0.35 0 0 90 4.17 8.28 12.40 1.33 0.52 0.438 147 0.422 6.12 9.61 15.70 1.54 0.60 0.530 SEM(6 df) 0.27 0.536 0.36 0.49 0.08 0.38 0.029 0.024 Keyt W/C 0 6.92 12.20 19.10 1.25 0.38 0 90 0 7.28 11.80 19.10 1.51 0.60 0.314 147 0.344 7.58 12.60 20.20 1.63 0.71 0.416 0.440 SEM(6 df) 0.29 1.00 1.20 0.047 0.039 0.015 0.012 Hyslop 0 5.45 10.80 16.20 1.44 0.40 0 0 90 6.30 11.30 17.60 1.59 0.67 0.305 0.304 147 6.40 11.30 17.70 1.81 0.84 0.497 0.467 SEM(6 df) 0.79 1.08 1.84 0.051 0.058 0.021 0.019 Hamlin 0 5.18 9.80 15.00 1.38 0.34 0 0 33 5.75 10.00 15.80 1.32 0.32 0.116 90 0.118 6.80 9.75 16.60 1.36 0.40 0.257 0.265 147 7.52 12.70 20.20 1.53 0.61 0.450 SEM(9 df) 0.435 0.38 0.72 0.95 0.039 0.032 0.031 0.028 Bronson 0 2.38 6.28 8.66 1.28 0.45 0 0 90 3.80 7.90 11.70 1.51 0.64 0.363 0.384 147 4.15 7.68 11.80 1.62 0.72 0.478 0.386 202 4.38 8.38 12.80 1.81 0.85 0.589 0.566 SEM(9 df) 0.31 0.40 0.59 0.063 0.051 0.024 0.025

* 3 degrees of freedom for percent fertilizernitrogen. Appendix Table6. 1981totalTotal,fertilzer, and soil nitrogen yields from 15N labeled subplots.

Total N Yield Fertilizer NYield* 15N

Site N rate Grain Straw TDM Grain Straw TDM Grain Straw TOM

kg/ha Keyt W/W 0 33.4 21.3 54.7 0 0 0 33.4 21.3 54.7 90 55.4 42.8 98.2 24.3 18.1 42.4 31.1 24.7 558 147 93.9 57.4 151.3 49.6 30.8 80.4 44.3 26.5 70.8 SEM(6 df) 5.0 3.2 5.8 2.2 2.0 3.7 4.0 2.0 4.8 Keyt W/C 0 86.1 46.2 132.3 0 0 0 86.1 46.2 132.3 90 110.0 71.2 181.0 34.5 24.4 59.0 75.1 46.7 121.8 147 123.0 89.3 213.0 51.6 39.5 91.1 71.9 49.8 121.7 SEM(6 df) 6.7 7.8 14.0 3.6 3.6 7.1 4.3 5.3 9.1 Hyslop 0 78.5 42.4 121.0 0 0 0 77.7 42.4 120.1 90 100.0 75.4 176.0 30.6 22.9 53.5 69.6 52.5 122.1 147 115.0 95.4 211.0 57.3 44.6 101.9 58.1 50.7 108.8 SEM(6 df) 11.9 8.6 18.6 3.6 3.8 6.6 11.6 6.3 17.1 Hamlin 0 71.4 33.8 105.0 0 0 0 71.4 33.8 105.2 33 76.2 32.6 109.0 8.7 4.0 12.6 67.6 28.6 96.2 90 92.9 39.8 133.0 23.1 10.1 33.2 69.8 29.7 99.5 147 115.0 77.1 192.0 51.6 33.1 84.8 63.8 SEM(9 df) 43.9 107.7 6.7 5.7 10.3 1.8 1.4 2.2 6.5 4.9 10.0

Bronson 0 30.1 28.2 58.4 0 0 0 30.1 28.2 58.4 90 57.3 50.6 108.0 20.8 19.4 40.2 36.5 31.2 67.7 147 67.4 55.0 122.0 32.3 26.6 58.9 35.1 28.4 63.5 202 79.1 71.4 150.0 46.5 40.4 86.9 32.6 31.0 63.6 SEM(9 df) 4.4 5.0 6.6 3.1 3.2 5.4 2.0 2.8 2.8 * 3 degrees of freedom for fertilzer nitrogen yield. Appendix Table 7. 1982 total dry matter, % N, and % fertilizerN from 15N labeled sublplots.

Total Dry Matter N Concentration I5N*

Site N rate Grain Straw TDM Grain Straw Grain Straw

kg/ha Mg/ha 7. ---atom%---

Wilson 0 4.36 5.80 10.20 1.57 0.22 0 0 45 5.34 8.48 13.80 1.72 0.28 0.141 0.178 90 0.04 12.80 18.90 2.18 0.35 0.276 0.300 SEM(6df) 0.40 0.82 1.21 0.09 0.03 0.015 0.016

Jones 0 1.48 1.78 3.26 1.47 0.29 0 0 67 3.49 5.02 8.52 1.46 0.36 0.402 0.483 134 0.79 6.38 12.20 1.85 0.52 0.551 0.589 SEM(6df) 0.43 0.31 0.61 0.06 0.04 0.039 0.045

Evers 0 3.96 6.75 10.70 1.40 0.25 0 0 67 5.99 10.30 16.30 1.55 0.30 0.313 0.338 134 0.02 11.30 18.30 1.73 0.38 0.505 0.587 SEM(6df) 0.53 0.94 1.17 0.08 0.04 0.018 0.016

Keyt 0 3.46 5.12 8.58 1.49 0.31 0 0 67 4.94 7.18 12.10 1.60 0.40 0.341 0.415 134 0.52 8.82 15.30 1.85 0.48 0.503 0.602 SEM(9df) 0.58 0.70 1.27 0.07 0.07 0.012 0.012 * 3 degrees of freedom for percent fertilizer nitrogen. Appendix table 8. 1982 total Total, fertilzer, and soilnitrogen yields from 15N labeled subplots.

Total N Yield Fertilizer N Yield* 15N

Site N rate Grain Straw TDM Grain Straw TDM Grain Straw TOM

kg/ha

Wilson 0 68.4 12.6 81.0 0 0 0 68.4 12.6 81.0 45 92.1 23.6 116.0 13.1 4.2 17.3 79.1 19.3 98.4 90 131.0 44.8 176.0 36.6 13.4 50.0 94.5 31.3 125.8 SEM(6df) 8.6 3.2 11.2 3.3 1.1 4.3 4.4 1.8 5.8 Jones 0 21.8 5.1 26.9 0 0 0 21.8 5.1 26.9 67 50.8 18.0 68.9 21.5 8.9 30.4 29.3 9.2 38.5 134 69.9 32.8 103 38.5 19.5 58.0 31.3 13.3 44.6 SEM(6df) 5.4 2.2 5.3 4.0 1.6 4.8 2.4 1.0 3.1 Evers 0 55.2 17.7 72.3 0 0 0 55.2 17.1 72.3 67 93.5 31.9 125.0 28.7 10.6 39.3 64.8 21.3 86.1 134 122.0 42.4 164.0 61.6 24.8 86.4 60.3 17.6 77.9 SEM(6df) 11.2 6.1 15.3 2.2 1.8 3.4 7.9 3.6 10.2 Keyt 0 51.3 15.8 67.1 0 0 0 51.3 15.8 67.1 67 78.5 27.7 106.0 26.5 11.6 38.1 52.0 16.1 68.1 134 120.0 42.4 163.0 60.5 25.6 86.1 59.9 16.8 76.8 SEM(6df) 9.0 6.5 14.5 3.0 3.2 5.9 5.5 2.2 7.0 * 3 degrees of freedom for fertilizer nitrogenyield. Appendix table 9. TDM, % N, and nitrogen yield from maximum uptake sampling, 1981

Total Dry Matter % Nitrogen Nitrogen Yield Rate N K K W/W K W/C K W/W K W/C K W/W K W/C

---Mg/ha------kg/ha---

078 6.4 15.4 0.58 0.73 38 113 9078 12.1 17.4 0.58 0.81 71 140 134 0 16.9 19.4 0.87 1.06 146 205 13478 16.2 21.1 0.66 0.91 108 193 134 0(late)13.5 19.3 0.97 1.06 131 205 20278 17.8 20.3 1.01 1.20 181 244

SEM(16 df) 0.98 1.1 0.04 0.06 10 13 Appendix table 10. TDM, % N,and nitrogen yield from maximum uptakesampling, 1981.

Total Dry Matter %Nitrogen Nitrogen Yield Rate N Hys Ham Bron Hys Ham Bron Hys Ham Bron

Mg/ha % kg/ha----

0 18.4 12.2 7.8 0.87 0.66 0.66 16 83 51 34 15.6 0.64 102 90 20.6 16.012.6 1.07 0.80 0.83 222 132 104 147 20.6 17.112.4 1.49 1.14 1.19 307 194 133 202 12.5 1.19 150

SEM 1.6 1.3 3.6 0.06 0.06 0.07 18 19 16 (df) 6 9 9 6 9 9 6 9 9 Appendix table 11. TDM, % N, and nitrogen yield from maximumuptake sampling, 1982.

Total Dry Matter % Nitrogen Nitrogen Yield Rate N Cl Jns Evrs Keyt Jns Evrs Keyt Jns Evrs Keyt

Mg/ha kg/ha

0 0 3.9 9.9 6.8 0.48 0.40 0.49 18.8 36.6 32.3 67 90 8.4 14.3 13.4 0.58 0.54 0.55 48.6 77.4 73.5 67 90 7.7 13.5 10.8 0.50 0.50 0.60 38.0 68.4 63.6 134 120,80,120* 9.1 15.9 11.9 0.54 0.54 0.64 48.8 86.5 77.3 134 0 8.3 18.9 14.7 0.51 0.64 0.78 42.5119.0113.0 134 0,80,40* 9.9 15.2 14.3 0.72 0.71 0.84 76.2108.0119.0 202 80,80,40* 12.6 16.9 15.3 0.79 0.92 0.92 99.9156.0141.0 SEM 1.0 3.3 1.2 0.07 0.07 0.07 8.6 21.3 13.5 * Jones, Evers, and Keyt, respectively. Appendix table 12. Regression equations for 1981 grain yield (Mg/ha) and N yield (kg/ha) on rate of applied N fertilizer (kg/ha).

VARIABLE KEYT W/W KEYT W/C HYSLOP HAMLIN BRONSON

Grain Yield (excluding 15N subplots)

Intercept+se 3.19+0.34 7.39+0.34 5.45+0.65 5.32+0.20 2.36+0.25 +bl+se: 3.26E-2+0.78 1.92E-2+0.78 5.24E-2+2.35 2.53E-2+0.22 2.08E-2+0 -b2+se: 7.46e-5+0.38 1.01e-4+0.38 2.79e-4+1.6I 5.50e-5+0 r" 0.6867 0.1998 0.4501 0.9010 0.6460

Maximum UptakeSampling: N yield

intercept+se:24.8+16.0 101+11 155+17 77.4+10.7 55.4+9.3 bl+se: 68.1E-2+11.9 65.5E-2+8.8 96.0E-2+17.1 74.6E-2+12.3 49.5E-2+7

r2. 0.7017 07984 0.7581 0.7251 0.7808

15N Labeled subplot Grain Nitrogen Yield

intercept+se:29.5+0.5 86.3+0.4 78.2+0.7 68.4+0.4 32.1+0.3 bl+se: 37.6E-2+4.8 28.7E-2+4.4 25.2E-2+7.2 30.6E-2+5.1 24.1E-2+2

r" 0.8726 0.7755 0.5475 0.7218 0.8910

15 N Labeled subplot Total Dry Matter Nitrogen Yield

intercept+se:50.7+5.7 132+9 121+11 94.7+8.4 61.1+4.9 bl+se: 64.6E-2+5.8 55.1E-2+9.4 61.6E-2+11.4 59.6E-2+9.7 44.5E-2+3

r2. 0.9253 0.7740 0.7418 0.7300 0.9120

15N Labeled subplot Grain Fertilizer Nitrogen Yield

bl+se: 32.1E-2+1.3 36.2E-2+1.4 37.9E-2+1.4 32.5E-2+1.4 22.8E-2+C

r2.. 0.9815 0.9828 0.9852 0.9745 0.9870

15N Labeled subplot TotalDry Matter Fertilizer Nitrogen Yield

bl+se: 53.0E-2+2.1 63.4E-2+2.8 67.1E-2+2.7 51.8E-2+2.6 42.5E-2+1

r2. 0.9813 0.9795 0.9820 0.9623 0.9879 Appendix table 13. Regression equations for 1981 grain yield (Mg/ha) and N yield (kg/ha) on rate of applied N fertilizer (kg/ha).

VARIABLE Wilson Jones Evers Keyt

Grain Yield (including 15N subplots)

Intercept+se 3.95+0.28 1.53+0.33 3.75+0.29 3.36+0.53 +61+se: 2.95E-2+0.69 3.45E-2+0.69 3.96E-2+0.58 2.99E-2+1.07 - b2 +se: 1.13e-4+0.47 7.37e-5+0.06 1.19e-4+0.28 6.48e-5+5.28

0.5073 0.7467 0.7937 0.6252

Maximum Uptake Sampling: N yield intercept+se: 19.8+3.4 36.6+8.6 32.3+10.0 +61+se: 6.64E-2+1.31 8.40E-2+3.27 8.93E-2+3.79 -62+se: 3.28e-3+0.94 3.50e-3+2.33 4.16e-3+2.71 r2. 0.8481 0.6788 0.5805

15N Labeled subplot Grain Nitrogen Yield intercept+se: 65.9+5.4 23.5+4.4 56.9+6.3 48.8+7.6 bl+se: 70.0E-2+9.4 35.8E-2+5.1 49.6E-2+7.2 51.4E-2+8.7 r2. 0.8467 0.8331 0.8245 0.7756

15N Labeled subplot Total Dry Matter Nitrogen Yield

intercept+se: 76.8+7.3 28.3+5.0 74.7+8.1 62.4+10.19 bl +ae: 105.8E-2+12.6 56.4E-2+5.8 68.4E-2+19.4 71.2E-2+11.7 r2. 0.8752 0.9057 0.8417 0.7884

15N Labeled subplot Grain Fertilizer Nitrogen Yield

l+se: 38.5E-2+3.0 29.4E-2+2.3 45.3E-2+1.3 44.0E-2+1.9

r2.. 0.939 0.938 0.991 0.980

15N Labeled subplot Total Dry Matter Fertilizer Nitrogen Yield

bl+se: 52.5E-2+3.9 43.7E-2+3.0 63.3E-2+1.7 62.8E-2+3.2

r" 0.924 0.950 0.992 0.972 Appendix table 14.Dry matter, % total N, total N yield, X fertilizer N, and fertilizer N yield for growth stage subsampling from nitrogen recovery plots at Hyslop, Hamlin, and Bronson farms.

tem plus Leaves

Dry Matter % Total N Total N Yield X Fertilizer N* Fertilizer N Yield Feekes Scale Growth Stage Sampling date Hys Ham Bron Hys Ham Bron Hys Ham Bron Hys Ham Bron Hys Ham Bron Hys Ham Bron

g /m2 % g /m2 % g/m1

Apr. 27 432 522 397 3.20 2.68 2.16 13.82 13.99 8.58 0.541 0.498 0.409 7.48 6.97 3.51 8 8 6

May 7 744 869 656 2.73 2.09 2.18 20.31 18.16 14.30 0.536 0.481 0.524 10.89 8.73 7.49 10 10 9

May 16 1076 991 844 2.14 1.52 1.54 23.03 15.06 13.00 0.540 0.567 0.487 12.44 8.55 6.33 10.1 10.1 10

May 27 1432 1319 1122 1.84 1.41 1.44 26.35 18.60 16.16 0.527 0.545 0.588 13.89 10.14 9.50 10.5.4 10.5.4 10.5.1

June 6 L461 1753 1159 L.50 1.04 1.20 21.92 18.23 13.91 0.515 0.506 0.577 11.29 9.22 8.03 10.5.4 10.5.4 10.5.4 June 16 1693 1809 1497 1.19 0.93 1.13 20.15 16.82 16.92 0.427 0.463 0.598 8.60 7.79 10.12 11.1 11.1 11.1

June 26 1941 1966 1672 1.06 0.70 0.92 20.57 13.76 15.38 0.544 0.451 0.541 11.19 6.21 8.31 11.2 11.2 11.2

July 6 1956 1994 1481 0.93 0.60 0.70 18.19 11.96 10.37 0.486 0.482 0.472 8.84 5.76 4.89 11.3 11.3 11.3

Grain

11.2 June 26 393 434 334 1.84 1.70 1.77 10.52 7.38 5.91 0.564 0.436 0.541 5.93 3.22 3.20 11.2 11.2 8.18 0.528 0.464 0.484 6.01 4.91 3.96 11.3 11.3 11.3 July 6 537 663 447 2.12 1.58 1.83 11.38 10.58 mean (excluding harvest) 0.521 0.489 0.522 +sd 0.039 0.041 0.059 * fertilizer N applied at 14.6 g /mL on Apr. 13. Appendix table 15. 1982 Plant analysis datafrom nitrogenrecoverystudy using N fertilzerenrichedto 5 atom %.

Dry Matter Yield TotalN conc. Total N Yield Atom% I5N N Fertilizer Fertilizer N Plant Part Hyslop Bronson HyslopBronson Hyslop Bronson HyslopBronson Hyslop Bronson Hyslop Bronson

g/m % g/mL g/m Total top 683 0.93 6.35 0.4359 0.0154 0.098 Grain 445 2.00 8.90 0.4759 0.0242 0.215 Straw 339 0.53 1.80 0.4624 0.0212 0.038 Root crown 119 108 0.66 0.73 0.79 0.79 0.45900.4302 0.0205 0.0139 0.016 0.011

Applied N fertilizer (1981) 4.852 4.827 Natural abundance, plant 0.367 0.368 Natural abumdance, soil 0.367 0.368 Table 16. 1982 Soil analysis data from nitrogen recovery study using N fertilizer enriched to 5 atom % 15N.

Sampling 1981 Total Atom N Fertilizer Fertilizer Location Depth BD OM N % 15N Fraction

cm g/m3 7. g/m

Hyslop 0- 30 1.44 2.40 0.102 0.3873 0.0045 1.983 30- 60 1.33 0.62 0.040 0.3755 0.0019 0.303 60- 90 1.37 0.26 0.023 0.3777 0.0024 0.227 60-120 1.40 0.26 0.020 0.3778 0.0024 0.202

Hamlin 0- 30 1.35 3.40 0.140 0.3921 0.0047 1.332 15- 30 1.35 2.40 0.115 0.3809 0.0022 0.512 30- 60 1.20 1.60 0.090 0.3732 0.0005 0.162 60- 90 1.26 1.20 0.082 0.3732 0.0005 0.155 90-120 1.31 1.10 0.068 0.3722 0.0003 0.080

Bronson 0- 30 1.27 3.75 0.152 0.3976 0.0066 3.822 30- 60 1.40 1.50 0.080 0.3779 0.0022 0.739 60- 90 1.52 0.36 0.026 0.3756 0.0017 0.202 90-120 1.45 0.36 0.026 0.3759 0.0018 0.172 * Sampled on Sept. 10, 1982. # Atom % 15N in applied fertilizer: Hyslop=4.852, Hamlin=4.817, Bronson=4.827 Natural abundance soil: Hyslop=0.367, Hamlin=0.368, Bronson=0.368, atom % 15N.