19th World Congress of Soil Science Symposium 2.1.1 Optimizing water use with soil physics Soil Solutions for a Changing World, Brisbane, Australia 1 – 6 August 2010 Table of Contents Page Table of Contents ii 1 A variation of the Field Capacity (FC) definition and a FC 1 database for Brazilian soils 2 An evaluation of plant available water during reclamation of 5 saline soils: Laboratory and field approaches 3 Analytical Solution for Drainage from a Uniformly Wetted Deep 9 Soil Profile 4 Application of GPR ground wave for mapping of spatiotemporal 13 variations in the surface moisture content at a natural field site 5 Assessment of Soil-Amendment Mixtures for Subsurface Drip 17 Irrigation Systems 6 Calculation of Canopy Resistance with a Recursive 20 Evapotranspiration Model 7 Contribution of stony phase in hydric properties of soils 24 8 Deep drainage in a Vertosol under irrigated cotton 27 9 Determination of irrigation depths using a numerical model and 31 quantitative weather forecast 10 Development of preferential flow below a soil moisture 35 threshold 11 Differences in topsoil properties of a sandy loam soil under 38 different tillage treatments 12 Drip irrigation as a sustainable practice under saline shallow 42 ground water condtions 13 Effect of land use on the soil physical properties and water 46 budget in a small water shed in NE Thailand 14 Effect of leaching on hydrophobicity and infiltration into a 50 texture contrast soil 15 Electrical conductivity and nitrate concentrations in an Andisol 54 field using time domain reflectometry 16 Estimating hysteretic soil-water retention curves in hydrophobic 58 soil by a mini tensiometer-TDR coil probe 17 Estimating unsaturated hydraulic conductivity from air 62 permeability 18 Estimation of crop losses associated with soil water repellency in 66 horticultural crops ii Table of Contents (Cont.) Page 19 Evaluating the scale dependency of measured hydraulic 69 conductivity using double-ring infiltrometers and numerical simulation 20 Evaluation of conservation tillage by means of physical soil 73 quality indicators 21 Field-scale bromide transport as a function of rainfall amount, 77 intensity and application time delay 22 Green, blue and grey waters: Minimising the footprint using soil 81 physics 23 Hydrological and erosional responses in woody plant 85 encroachment areas of semi-arid south–eastern Australia 24 Hydro-pedotransfer functions for predicting the effective annual 89 capillary rise 25 Impact of conservation agriculture on runoff, soil loss and crop 93 yield on a Vertisol in the northern Ethiopian highlands 26 Impacts of sodic soil amelioration on deep drainage 97 27 In situ soil water repellency is affected by soil water potential 101 rather than by water content as revealed by periodic field observations on a hill slope in a Japanese humid-temperate forest 28 Increases in available water content of soils by applying 105 bagasse-charcoals 29 Late season sugarcane performance as affected by soil water 109 regime at the yield formation stage on commercial farms in northern Ivory Coast 30 Modeling of coupled water and heat fluxes in both unfrozen and 113 frozen soils 31 Multi-TDR probe designed for measuring soil moisture 117 distribution near the soil surface 32 Numerical Analysis of Coupled Liquid Water, Water Vapor, and 121 Heat Transport in a Sandy Loam Soil 33 Numerical evaluation of inverse modelling methods for 1D and 125 3D water infiltration experiments in homogeneous soils 34 Optimizing Water Use with High-Transpiration-Efficiency 129 Plants 35 Plant available water capacity of dryland cropping soils in the 133 south-eastern Australia iii Table of Contents (Cont.) Page 36 Raised beds in South West Victoria: Pore structure dynamics 137 deliver increased plant available water in sub-optimal rainfall years 37 Rapid estimation of soil water retention functions 141 38 Seasonal variability of soil structure and soil hydraulic 145 properties 39 Short-term effects of conservation tillage on soil (Vertisol) and 149 crop (teff, Eragrostis tef) attributes in the northern Ethiopian highlands 40 Siberian Wildrye Grass Yield and Water Use Response to Single 153 Irrigation Time in Semiarid Agropastoral Ecotone of North China 41 Influence of Soil Profile Characteristics on the Efficiency of 157 Water Management Practice in Northeast Florida 42 Soil resistance to penetration under the dynamic and predictive 161 perspective of restriction to crop yield 43 Subsoil manuring with different organic manures increased 165 canola yield in a dry spring 44 The effect of drip emitter rate on bromide movement in a drip 169 irrigated vineyard 45 The effect of tillage and nitrogen application on soil water 173 retention, hydraulic conductivity and bulk density at Loskop, KwaZulu-Natal, South Africa 46 The matric flux potential as a measure of plant-available water 177 in soils restricted by hydraulic properties alone 47 The relationship between field soil water content variability and 179 soil moisture deficit prediction from meteorological data 48 Toward improving estimates of field soil water capacity from 182 laboratory-measured soil properties 49 Use of simulation modeling and pedotransfer functions to 186 evaluate different irrigation scheduling scenarios in a heterogeneous field 50 Visualising and quantifying rhizosphere processes: root-soil 190 contact and water uptake 51 Water exchange between the fine earth and pebbles in 194 remoulded soil samples iv Table of Contents (Cont.) Page 52 Water retention estimation and plant availability for subtropical 197 Brazilian soils 53 What are the chances of successfully replacing buffel grass with 201 native plant communities in central Queensland’s coal mine rehabilitation sites? v A variation of the Field Capacity (FC) definition and a FC database for Brazilian soils Theophilo B. Ottoni Filho A and Marta V. Ottoni B ADepartamento de Recursos Hídricos e Meio Ambiente, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil, Email [email protected] BCompanhia de Pesquisa de Recursos Minerais - CPRM, Rio de Janeiro, RJ, Brazil, Email [email protected] . Abstract Field capacity (FC) is a widely applied parameter in Soil Science. It is related to frequent sequential infiltration and drainage in soils. This paper proposes a variation of the FC definition, based on 48-h drainage time, aiming not only at minimizing the inadequacies of its concept and determination, but also at maintaining its original, practical meaning. Data of 22 Brazilian soils showed that FC determined from standardized field procedures can primarily depend on basic soil data, especially volumetric water content data, such as θ(6 kPa) or θ(33 kPa). Key Words Drainage, pedotransfer function, Brazilian soils Introduction Field capacity (FC) is a soil parameter that is widely used in soil and water engineering. The original definition of FC by Veihmeyer and Hendrickson (1949) was slightly modified in the Glossary of Soil Science Terms (SSSA 1984) as: “FC is the amount of water remaining in soil two or three days after having been wetted and after free drainage is negligible”. Despite the broad application of FC, its concept bears substantial uncertainty (Cassel and Nielsen 1986; Hillel 1998, chap. 16; Nachabe et al ., 2003). Indeed, what a negligible free drainage rate is must be better stated. In addition, evapotranspiration is not specifically mentioned, profile wetting and initial soil moisture before water application are not precisely described, which may be relevant, particularly when hysteresis in soil water redistribution after infiltration (Hillel 1998, chap. 6) is significant. The presence of impeding or highly permeable layers and phreatic levels, as well as the influence of lateral flow in sloping landscapes, are also overlooked, especially if it is considered that the ‘free drainage’ in the above definition implies absence of these conditions. Indeed, all of these factors must be clarified before FC can be considered a reproducible, consistent, and intrinsic soil water variable. The best standardized procedure to evaluate FC is by flooding a square or rectangular plot on a bare field (Cassel and Nielsen 1986); after irrigation, it is covered with a plastic sheet to avoid evaporation. The distribution of moisture in the upper part of the soil profile, which was fully moistened at the end of infiltration (quasi-saturated), measured 2 or 3 days after water application, defines the FC profile. This FC profile usually depends on the texture and structure of the individual soil layers (Salter and Williams 1965). Based on this dependence and on the operational difficulties of a field test, FC is commonly evaluated in a laboratory setting as the moisture of undisturbed soil samples at a specific matric potential. Cassel and Nielsen (1986) reported that a wide range of matric potentials (from -2.5 kPa to -50 kPa) has been used for this purpose, although suctions of 5 kPa, 6 kPa, 10 kPa, and 33 kPa are more common choices; however, there is no satisfactory general criterion for selection of the suction values for the determination of FC (Hillel 1998, chap. 16). Taking into account the dynamic nature of drainage, some authors (Nachabe et al ., 2003) argue that the definition of FC must be based on an arbitrary choice for the “negligible” downward flux, instead of the drainage time of 2 or 3 days, or the suction at FC. Meyer and Gee (1999) considered that such selected small fluxes could be between 0.01 mm/d and 1.0 mm/d depending on the type of application. When FC is evaluated by the flux-based method, the drainage times may vary by an enormous range, even for an individual soil, from tens of hours to tens of days, depending on the flow rate chosen, as clearly demonstrated in Hillel (1998, chap. 16). Overall, despite being a widely applied soil parameter, the understanding of FC is neither unique nor exact. In this paper, a variation of the definition of FC is proposed and empirically tested by the development and analysis of a FC database.