Consequences of rainfall during summer-autumn fallow on available soil water and subsequent drainage in annual-based cropping systems.

Book Title: NA
Year Published: 2006
Month Published: NA
Author: Dolling, P. J. ; Fillery, I. R. P. ; Ward, P. R. ; Asseng, S. ; Robertson, M. J.
Book Group Author: NA

This paper investigates factors controlling soil water content changes during the non-growing summer-autumn season or fallow (December-May) in annual farming systems in southern Western Australia. This was achieved by examining variation in available soil water storage to a depth of 1.0-1.5 m at 3 sites within 13 seasons. Reasons for the variation were examined using the Agricultural Production Systems Simulator (APSIM). This paper also investigated whether water accumulation during the summer-autumn period (fallow) contributed to drainage during the following growing season (May-November). This was achieved by determining the relationship between soil water content at the end of the fallow period (1 May) and the amount of drainage below 2.5 m by using APSIM coupled to historical weather records at 3 locations. At the end of the fallow, 24 mm (or 25%) of rain falling during the fallow was retained in the soil. Evaporation was the main loss of soil water during fallow periods (mean of 60 mm). Other losses included transpiration from plant cover (mean of 12 mm) and drainage below the root zone and runoff (combined mean of 13 mm). Evaporation and transpiration losses of soil water were concentrated in the surface 0.3 m. The use of APSIM to determine changes in the soil water content during the fallow indicated the importance of plants to soil water losses, the potential for higher evaporation than previously reported, and the possibility of an extended period (4-6 weeks) of drainage in sandy soils after large rainfall events (>50 mm). Soil water accumulation during the fallow period had a significant effect on simulated drainage under wheat in the following growing season. By the end of fallow there was limited ability of the soil to store water before drainage occurred due to rainfall during the fallow and the small soil water deficit under annual farming systems (1-67 mm). A 1-mm increase in soil wetness at the end of the fallow resulted in a 0.7-1-mm increase in simulated drainage during the growing season.

Pages: 281 - 296
Volume: 57
Number: 3
Journal: Australian Journal of Agricultural Research
Journal ISO: NA
Organization: NA
Publisher: NA
ISSN: 0004-9409

autumn, change, cropping systems, drainage, evaporation,fallow, growth stages, losses from soil, rain, runoff, sandy soils,seasonal variation, simulation, soil water, soil water balance, soilwater content, storage, subsurface drainage, summer, transpiration,water deficit, wheat, Australia, Western Australia, Triticum, Triticumaestivum, Australasia, Oceania, Developed Countries, Commonwealth ofNations, OECD Countries, Triticum, Poaceae, Cyperales, monocotyledons,angiosperms, Spermatophyta, plants, Australia, Field Crops (FF005) (NewMarch 2000), Plant Water Relations (FF062), Plant Production (FF100),Plant Cropping Systems (FF150), Soil Physics (JJ300), Soil WaterManagement (Irrigation and Drainage) (JJ800) (Revised June 2002)[formerly Soil Water Management], Erosion; Soil and Water Conservation(PP400), Meteorology and Climate (PP500)

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