Influence of mulching on the pattern of growth and water use by spring wheat and moisture storage on a fine textured soil

Abstract

Eight tonnes ha−1 of stubble were used to mulch spring wheat (Triticum aestivum) on a fine textured soil with the aim of controlling both transpiration and soil evaporation during the wet pre-anthesis phase to increase moisture supply during grain filling in the eastern wheatbelt of Western Australia. Mulching reduced leaf area per plant by reducing the culm number; consequently the green area index was reduced. Reduced culm number was associated with low soil temperature which at 50 mm depth averaged 7°C lower under the mulched crop relative to the control crop in mid-season. The smaller canopies of the mulched crop used 15 mm less water than those of the control before anthesis; this difference in water-use was due equally to reduced transpiration and soil evaporation. However, the mulched crop was unable to increase ET during grain filling, a response associated with the persistence of low soil temperature for most of the growth period. Hence, total ET for the season was significantly lower (18 mm) under the mulched crop than the control crop. At harvest, mulching did not have significant effects on total above-ground dry matter and grain yields, but it increased water use efficiency for grain yield by 18%, grain weight by almost 17% and available moisture in both uncropped and cropped plots by an average of 43 mm. To determine whether there was any residual effects of soil treatment on moisture storage during the summer fallow period, soil moisture was monitored both in cropped plots and uncropped plots, that were either mulched or unmulched during the growing season, from harvest in October 1988 until next planting in June 1989. Available moisture at next planting was correlated with moisture storage at harvest despite the differences in run-off, soil evaporation and fallowing efficiency (increase in moisture storage as a percentage of rainfall) between treatments during fallowing. Therefore, the mulched treatments had more moisture available (30 mm), mostly as a result of less water use during cropping in the previous growing season, than the unmulched treatment. The study shows that mulching may be used to restrain both transpiration and soil evaporation early in the season to increase availability of soil moisture during grain filling. Secondly, mulching during the previous growing season had little effect on soil moisture during the summer fallow period, however, the moisture saved by mulching during cropping was conserved for the following season. These results indicate the importance of evaluating mulching of winter crops in terms of crop yield in the subsequent growing season as well as in the current season in which the soil was treated.