Nitrogen Management BMPs Parker Valley Demonstration

Item Type text; Article

Authors Watson, J.; Winans, S.; Sheedy, M.

Publisher College of Agriculture, University of Arizona (Tucson, AZ)

Journal Cotton: A College of Agriculture Report

Download date 25/09/2021 03:53:57

Link to Item http://hdl.handle.net/10150/210297 NITROGEN MANAGEMENT BMPs PARKER VALLEY DEMONSTRATION

J. Watson, S. Winans, M. Sheedy

Abstract

A nitrogen management demonstration was conducted in the Parker Valley in 1994. Grower nitrogen application practices were compared with nitrogen application recommendations based upon pre plant soil samples plus petiole nitrates and plant mapping data. The only significant difference in amounts applied occurred in May, with grower applied rates exceeding recommended rates. Grower rationale for the application was logical, however, it being dependent upon the uncertainty of irrigation timing in June.

Introduction

A nitrogen management study was initiated in the Parker Valley in the spring of 1994. The intent of the study was to demonstate the implementation of some Best Management Practices (BMPs) for nitrogen application to cotton. Since the implementation of nitrogen BMPs is required in the state of Arizona, and the US EPA is encouraging the adoption of similar regulations on federal lands, it is important for growers to become familiar with the application of such practices in their crop management decision making. The continued protection of the Colorado River and of nearby groundwater from non -point source contamination is important to the maintainence of economic development of the region.It is particularly important for local water users to insure that the perception of their protection of the area's water resources is a positive one. A simple, straight -forward method for growers to accomplish this, while maintaining optimum yields is through the use of BMPs that account for plant condition. The mapping of plant growth parameters, in combination with petiole nitrate monitoring, split applications of planned amounts of nitrogen and early season soil analysis.

Materials and Methods

A 37 acre field was used for the demonstration. The north half of the field was assigned to the cooperator for managment (Grower); the south half of the field was managed for nitrogen using a combination of yield -goal based, plant feedback and soil sampling practices (UA). These practices included the following. 1) Pre -plant soil analysis for nitrate -N concentrations 2) Establishment of a realistic yield goal and total nitrogen requirement 3) Weekly monitoring of petiole nitrate concentrations 4) Weekly plant mapping 5) Split nitrogen applications, with the first at approximately 600 HUAP, and the remainder based upon petiole nitrate concentrations and plant mapping information

The soil was a sandy loam to clay loam, in texture.It was considered a productive field by the grower. Small subplots (approximately 80 inches wide by 80 inches long) were established, to which potassium bromide was applied before the first post -planting irrigation. The purpose of the bromide was to indicate the depth of movement

336 of applied water after the first irrigation and at the end of the growing season. Bromide is a useful tracer of the water front, since it moves with water, rather than being attracted to soil particles. Upland cotton (DPL 5409) was planted on April7, 1994at the rate of 10# /ac, and irrigated up on April8, 1994.Tables 1 and 2 provide information related to nitrogen and water application.

Results and Discussion

In any such project, "glitches" inevitably occur. The first such error occurred at the beginning of the season. The laboratory soil analyses were not available until after the cooperator was ready to apply his pre -plant fertilizer. Since there was no basis for any other recommendation than past grower experience, the south side of the field (the BMP side) received the same amount of fertilizer as did the north side (see table 1), although the soil tests eventually indicated that no preplant fertilizer N was needed. The second error occurred during a water -run nitrogen application in July. The recommendation for the south side of the field called for20pounds of N per acre on July3.Due to irrigator error, approximately57pounds were actually applied.In spite of such "glitches ", however, the plant mapping data and petiole analyses provided reliable data for crop management decisions.

Petiole nitrate data is provided in Figure 1. Height to node ratios are provided in Figure2.The use of both pieces of information is important when making decisions regarding nitrogen inputs.It was agreed that the total applied nitrogen should be approximately180# N /ac for an expected3bales /acre yield. The first observable difference in nitrogen management decisions occurred on May5. The cooperator felt that 100# N /ac was needed to provide a healthy crop and good production. The UA recommendation was to more evenly split the nitrogen applications, rather than apply over half of it this early in the season, and thus recommended50#N /ac, at this time. The petiole nitrates from early May through early June indicated adequate to slightly excessive nitrogen levels. However, the Height to Node ratios indicated that the plants on both sites were well within the recommended ranges. In early June, a decision was required regarding the application of additional nitrogen. Anhydrous ammonia was applied with the irrigation to supply another42#N /ac. The petioles at this time indicated that the nitrate levels may be slightly excessive, but the Height to Node ratios were well within recommended ranges, and this was the only time that nitrogen could be applied and become available to the plant prior to an irrigation expected near the end of June or early July. In late June (about1500HUAP), the Height to Node ratios of the north side of the field were bordering on the excessive side. The Height to Node ratios of the south side of the field were well within the recommended range. A decision was made to PIX the field. About this same time, the petiole nitrates were decreasing. At the next irrigation on July3,it was decided to add another7# N/ac on the north side of the field, and about20#N /ac on the south side of the field, to maintain the nutritional status of the crop. (Due to irrigator error, the .anhydrous tank wasn't shut off in time, and57# N/ac was applied to the south side of the field rather than the recommended 20#).The additional amount of20#was recommended for the south side of the field because the petiole nitrates had dropped into the warning range. On July30,another7#N /ac was applied to both the north and south sides of the field as CAN-17,due to grower preference, based on his experience with the field site.

Since the purpose of the project was demonstration rather than research, a replicated study was not established. Therefore, yields were not statistically comparable, although they were virtually equal.

One of the considerations of this study was whether, and to what extent the original soil nitrogen available prior to planting remained available after irrigation.To evaluate this, a comparison was made between the soil nitrate nitrogen concentrations immediately after planting just prior to irrigating up (collected4/8/94),and within two weeks after planting (collected4/20/94).The concentration of soil nitrate nitrogen collected from the soil surface to a depth of12inches, from the bed, was53ppm on4/8/94.The average nitrate nitrogen concentration in the same depth collected on4/20/94was48ppm. Thus, only a minimal decrease in soil nitrate nitrogen occurred, and certainly not to the extent envisioned. The impact of the nitrification of the ammonium polyphosphat applied on this date to the maintenance of the nitrate concentrations cannot be determined from this sampling scheme.However, the concentration of chloride in the same soil samples remained constant, indicating little leaching of soluble chemicals such as nitrate and chloride from the bed. In contrast, as expected, the soil nitrate nitrogen concentration in the first

337 foot below the furrow decreased from an average of approximately 33 ppm on 4/8 to 8 ppm on 4/20, indicating that most of the nitrogen available at this depth had moved deeper into the profile. The enormous variability is quite spectacular.

In an attempt to answer the question "How deep would nitrate likely move in the profile due to this irrigation ? ", a soluble tracer (bromide) was applied to the soil surface prior to the application of irrigation water on 4/8. The result of the soil samples indicated that virtually none of the applied bromide could be recovered in the top six feet of the root zone on 4/20. The implication, of course, is that most of the nitrogen available in the root zone below the furrow would be lost as well, thus arguing strongly for side -dressing as an effective method of early season nitrogen applications.

The authors would like to acknowledge the cooperation and assistance of Mr. Phil Thompson, manager of Mayfair Farms, Ms. Deb Esquerra, Agricultural Technician, La Paz County extension, and Mr. Conner Byestewa, Environmental Office, Colorado River Indian Tribes.

338 Table 1. Dates and rates of nitrogen applications.

NORTH SIDE SOUTH SIDE OF FIELD OF FIELD DATE AMOUNT FORM AMOUNT FORM lbs actual N lbs actual N

04/07/94 20 10 -34 -0 20 10 -34 -0

05/05/94 100 UAN -32 50 UAN -32

06/10/94 42 ANHYDROUS 42 ANHYDROUS AMMONIA AMMONIA

07/03/94 7 CAN -17 57** ANHYDROUS AMMONIA

07/30/94 7 CAN -17 7 CAN -17

Total Applied 176 176 N`

N in soil 32 30 at planting

Total 208 206 Available N

* The total applied N does not include N applied from natural concentrations in the irrigation water, as this is usually less than 2 pounds per acre foot of applied water. ** The amount recommended was about 20 pounds per acre, based upon petiole nitrate concentrations and plant data.

Table 2. Irrigation dates and amounts.

IRRIGATION DATES IRRIGATION AMOUNTS Heat Units After Planting AC- INCHES /AC (approximate)

04/08/94 6 0

05/26/94 6 750

06/10/94 6 1150

07/03/94 6 1750

07/30/94 6 2550

08/14/94 6 2950

TOTAL APPLIED WATER 36

339 NITRATE - N (ppm) LOCATION NITRATE - N (ppm) (Date = 4/8) (Furrow sample) (Date = 4/20)

25.5 NORTH SIDE 1.9 EAST END

45.8 NORTH SIDE 34.4 MIDDLE

21.2 NORTH SIDE 12.2 WEST END

60.4 SOUTH SIDE <1 EAST END

6.3 SOUTH SIDE <1 MIDDLE

30.7 SOUTH SIDE <1 WEST END

(Bed sample)

53.3 47.6 Petiole Nitrates; Medium Season Upland Cotton 30000

La Paz; Grower (north) La Paz; UA (south) 25000 -

20000 - ná ë 8

c 15000 - o U

Z ó 10000 - p am

5000 -

o i i i i i i

5/6 5126 6115 7/5 7/25 6114 9/3 9/23

Datte

Figure 1. Petiole nitrate concentrations.

341 Figure 2. Height to Node Ratios.

342