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Characterisation of the Least Limiting Water Range of a Texture-Contrast Soil

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Characterisation of the Least Limiting Water Range of a Texture-Contrast Soil q, È 'c)ç.\ CHARACTERISATION OF THE LEAST LIMITING WATER RANGE OF A TEXTURE- CONTRAST SOIL Thesis submitted for the degree of Master of Agricultural Science ln The UniversitY of Adelaide Faculty of Agricultural and Natural Resource Sciences by STANLEY RABASHI SEMETSA Department of Soil and Water January 2000 \Maite Agricuttural Research Institute Glen Osmond, South Australia Thisworkisdedicatedtomylateson,KITOSEANSEMETSA TABLE OF CONTENTS PAGE CHAPTER iv ABSTRACT..... viii STATEMENT... tx ACKNO\ryLEDGEMENTS. x LIST OF' F'IGURES... xlr LIST OF' TABLES... I CHAPTER1 : INTRODUCTION 1 3 I.2 Research Questions and Objectives 4 1.3 Structure of the Thesis CHAPTER2: LITERATURE REVIEIV' """"6 6 2.I Introduction .....'......" """"""""' temporal variability """"' 6 z.z Definition of soil structure incorporating spatial & 9 2.3 Soil structural quality indices for plant growth""' """" 9 2.3-l Aggregate Characteristics """"".' """"' t2 2.3.2 Bulk density and relative bulk density"""""""' 13 2.3.3 Macroporosity and pore continuity """""" 2.3.4 Plant available water capacity Relevance to Plant Growthl6 2.3.5 Least Limiting water Range (LLWR) and its z.3.sJUpper limit (Wet end)""""" """""'17 18 2.3.5.2lower limit .....'.'. """"" 18 2.3.5.3 Prediction of the LLWR"""' """""' (WRC) 20 2.3.5.4Estimation of the Water Retention Curve (SÃO 24 2.3.5.5 Estimation of the Soil Resistance Curve " the LLWR""""" 25 2.3.5.6 Pedotransfer functions and their use to characterise 26 2.4 Duplex soils and pedotransfer functions 2.4.1 Definition """"')6 soils 2.4.2 Origin, distribution and agricultural use of duplex """"' """"""""27 28 2.5 SummarY """""""" I CH^PTER3:ESTIMATIONoTLLWRFROMSOILPHYSICAL 30 PROPERTIES .......... """"' 30 3.1 Introduction...........' "" 31 3.2 Materials and methods """""""' """""""' 31 3.2.1 Location """""' 3.2.2 SamPling """""32 ..33 3.2.2.1Sample identification .. " ' .33 3.2.3 Physical and chemical properties 33 3.2.3.LParticle size distribution"""""" """ 3.2.3.2Organic carbon content....' """""""34 3.2.3.3Carbonate content-...' ""'34 34 3.2.3.4 pH and EC .. 3.2.3.5Water Retention Cvrve(WRQ """"'36 38 3.2.3.6Soi1Resistance Curve (SRC)"""' "" 79 3.2.4 Statistical Methods..........." 4t 3.2.4.|Modelsaccountingforlandscapepositionandsoildepth: 42 3.2.4.2 Models accounting for soil properties: 43 3.2.4.3 Models fromthe literatwe: 44 3.3 Results and Discussion.....""" 44 3.3.1 Soil Properties........."' 46 3.3.2 Models accounting for landscape position and soil depth...""' 46 3.3.2.1Multiple regression analysis fot WRC 48 3.3.z.2Multiple regression analysis for SRC 50 3.3.3TheinfluenceofsoilpropertiesontheWRCandsRc...'...... 50 3.3.3.1 Influence of soil properties WRCs """""""""" 52 3.3.3.2lnfluence of soil properties SRCs 52 3.3.4 Models proposed in the literature' 3.3.4.1Models for WRCs """""52 53 3.3.4.2Models for SRCs-.. """"' 53 3.3.5 Least Limiting Water Range """""""' 5t 55 3.4.1 Prediction of WRC.... 56 3.4.2 Prediction of SRC..... """"' 3.4.3 Prediction of LLWR """""'56 il LLWR""' 58 CHAPTER 4 SOIL WATER CONTENT VARIATION AND 58 4.1 Introduction......'....... 60 4.2 Materials and methods ..""""""' 60 4.2.1 Meteorological data.. " 60 4.2.2 Measurement of soil water content 60 4.2.3 Pout.....-..... 61 4.2.4 Statistical analYsis 6r 4.3 Results and Discussion..""""' 6l 4.3.1 DePth eflects 62 4.3.2 Surface soil (0 - 30 cm) effects""" 63 4.3.3 Treatment effects.....' 66 4.3.4 LLWRandPoø.... 66 4.4 Conclusions ............... AND YIELD CHAPTER 5: INFLUENCE OF LLWR ON CROP GROWTII R8SPONS8.............. """"" 68 68 5.1 Introduction -....."...'.." """""""' """"""""' 68 ,I 5.2 Materials and Methods""""""' id 68 5.2.1 Treatment Design """"""" il 69 5.2.2 Crop Management """"""' 5.2.3 Agronomic parameters """'70 70 5.2.3.1Establishment counts and dry matter yield 70 5.2.3.3Protein...-. ""'70 5.2.3.4 Pout.......... ""'71 5.3 Results and Discussion......""' """""""""'71 5.3.1 Agronomic measurements ".'"""" """71 growing season 5.3.2 Crop responses to soil water content during the """"""76 77 80 CHAPTER 6: SUMMARY & GENERAL DISCUSSION .80 6.1 Conclusions .82 for future research 6.2Implications 84 CHAPTER 7: APPENDICE S 93 CHAPTER 8: REFERENCES....... ut k ABSTRACT This thesis addresses three main questions: LLWR, of a texture-contrast 1. To what extent does the Least Limiting Water Range, been conducted on relatively soil change with depth? Most previous studies have with depth in the root uniform soils, where clay content does not vary signiflrcantly water holding zone; the occuffence of clay at depth may provide increased capacity for use by plants later in the growing season' the LLIUR during a 2. To what extent does the volumetric water content fall outside between typical mediterranean growing seasoî, Poot? An inverse relationship in moderated climates' but LLWR and Poulhas previously been shown to exist is strongly seasonal. little is known about this relationship where rainfall performance in a 3. What impact do the LLWR and Pou¡ have on field plant .'I when Itf plant performance is generally thought to improve ìt mediterranean climate? I conducted using LLll/R is large and pou¡ is small, but little work has been in mediterranean cropping patterns designed to maximise water use effîciency climates functions were required: the To calculat e the LLWRof the soils used in the study, two volumetric soil water content water retention curves, wRC, (A: ( fl, where d is the curves, sftc (sà : f(Ø, where and y is the matric potential) and the soil resistance of these were i) taken Sft is the soil resistance to a cone penetrometer). Examples relevant soil and from published pedotransfer functions and ii) developed from including landscape position' landscape properties collected from undisturbed cores' ¡ density (and of course cþ content, carbonate content, organic carbon content, bulk lv r soil matric potential)' The volumetric water content and soil resistance as functions of lines: for the published pedotransfer functions included models along the following + dlog 0+e log p' WRC,tog 0=loga+b tog Wand forthesRÇ log SR:logc e are constants' The functions where p is the soil dry bulk density and a, b, c' d and models of the following types: developed from soil and landscape properties included log SRi¡*r: C * + P¡+ D¡ for the WRC,\q*r= C + P¡+Di+ Vk+ pband forthe SRÇ water content and soil + 0* * pt, where hijn and SRy*r are respectively the volumetric P, the jth depth in the soil resistance corresponding to the ilh position in the landscape' Minor variations to profile, D,Íhekth matric potential, Y andthe fh bulk density, p. into account the presence the models for the l¿7RCsand SRCs were necessary to take with differing trends' or absence of carbonates in the soil, which seemed to correlate soil cores were To obtain the data necessary for the wRC and sRÇ undisturbed 'I tlt ,iT cm) at 5 different locations down ! from 6 different depths (between 0 and 80 i collected at Roseworthy Agricultural a topographic transect of a sodic hypercalcic chromosol ranged from 10 to 37o/o' College, South Australia. Across the landscape, clay contents soil, calcium carbonate organic carbon contents ranged from 0.1 to 10.3 g C kg-t densities ranged from 1'3 contents ranged from 0 fo 441.29 CaCO3 kg-l soil, and bulk ranging between to I.l g cfrr3. The soil cores were equilibrated at 8 matric potentials content and cone-penetration resistance --0.001 and -1.5 MPa, and volumetric water were measured. of LLzLshowed that no aeration problems were experienced at the wet Í Calculation I of available water at the end, but that high soil strength severely limited the amount ; rather small (all < dry end. Because of high soil strength, all values of LLI{R were r v plant available water in this 0.12 cnr3 cm3; many < 0.07 om' crn3¡ indicating minimal this was attributed soil. There was a minor trend of increasing LLWRwith depth, and depth, both of which to an increase in clay content and adecrease in bulk density with of the coincident coincided with an increase in the concentration of CaCO3. Because established occufïence of these soil properties, no simple relationship could be between the LLlltR and inherent soil properties' a typical mediterranean To address the second question (viz. Pou¡ vs. LLÍVR during the growing growing season), the volumetric water content was measured throughout patterns (and thus season as a function of depth for crops having different rooting shallow-rooting, diflererrt patterns of water extraction). Cereal grains, which were ('inter-cropped') with were growïr either alone ('mono-cropped') or else inter-seeded depths throughout the lucerne, which is deep-rootrng; Pou¡was determined at various .I and [,t to be greater for smaller values of LLÍIR' if profile. values of Poo¡wefe expected I particularly later in this was borne out by the data in a strong curvilinear relationship, Pou¡ > 0'70 were not the growing season when the soil began to dry out. Values of effect onPout' uncommon in the top 30 cn¡ and both wheat and oats had the same Poo, on crop performance), To address the third question (viz. impact of LLIIR and grain mass' and dry matter yields at tillering and anthesis were measured, and final grain protein were measured. Dry matter and grain yields were found to be inter-cropped significantly greater in the mono-cropped cereal treatments than in the water content treatments, and this was due to the higher aveÍage seasonal volumetric related to the in the mono-cfopped treatments. obviously this was strongly I ! vl with magdtude of P6¡11in the top 30 cm in as much as laxger values of Psú coincided reduced dry matter and grain yields.
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