Fallow soil evaporation and water storage as affected by stubble in sub-humid (Argentina) and semi-arid (Australia) environments

J.P. MONZON; V.O. SADRAS; F.H. ANDRADE

FIELD CROPS RESEARCH

ELSEVIER SCIENCE BV

Año: 2006 vol. 98 p. 83 - 90

0378-4290

The effect of stubble mulch on soil water storage during fallow is highly variable. In environments with low rainfall and coarse-textured soil, contribution of stubble to gains in water storage is often smaller than in wetter environments with heavier soil. While this pattern is recognised, the effect of rainfall, evaporative demand and soil remains confounded. This paper investigates the effect of stubble on soil evaporation and soil water storage during fallow in contrasting environments atBalcarce (Argentina) and Walpeup (Australia). Field and modelling experiments were combined to quantify stubble effects on soilevaporation and water storage for loam (Balcarce) and sandy loam soils (Walpeup). Simulations with the CropSyst model and long-termweather records included reference evapotranspiration from 185 to 240 mm, and rainfall from 108 to 471 mm for the winter fallow period atBalcarce, and reference evapotranspiration from 595 to 686 mm, and rainfall from 46 to 305 mm for the summer fallow period at Walpeup.The effect of size of rainfall events, quantified with power laws, was emphasised.Amount of rainfall during fallow accounted for most of the variation in soil evaporation, irrespective of reference evapotranspiration andsoil type. For bare soil, evaporation was lower than expected in years with higher frequency of large rainfall events, but no relationshipbetween soil evaporation and size of rainfall event was found for soil with stubble. The response of soil evaporation and soil water storage torainfall comprised three phases. In the first phase, all the rainfall was evaporated irrespective of soil cover; hence, there were no benefits ofstubble in terms of water storage. In the second phase, stubble reduced soil evaporation with respect to bare soil, with a subsequent gain in soilwater. In the third phase, the benefit of stubble declines up to the point in which rainfall is high enough to meet evaporative and storagedemands irrespectively of soil cover. It is proposed that gains in stored soil water due to stubble could be estimated as a function of rainfallusing a non-linear model with locally adjusted parameters