Stubble retention and tillage in a semi-arid environment .1. Soil water accumulation during fallow

A study was carried out over 4 years at two sites in semi-arid, north-west Victoria, Australia, to examine the effect of soil surface management during fallow on water and nitrogen accumulation and their effect on the growth and yield of the subsequent wheat crop. The fallow treatments comprised four combinations of stubble management and tillage in Is-month-long fallows of a fallow-wheat rotation together with a pea-wheat rotation which included an annual short (6 month) tilled summer fallow. The two sites are representative of the major soil types of the region; a chromic vertisol at Dooen and a calcic xerosol at Walpeup. This paper reports observations and analyses of soil water accumulation during the fallow phase. At Dooen, tillage without stubble increased soil water storage, at sowing, on average by 76 mm (range 24-122 mm) above the summer fallow. Stubble retention added a further 52 mm (range 36-65 mm). Zero tillage was beneficial in one year, and was enhanced by the presence of stubble. In contrast, at Walpeup, tillage without stubble provided an average of 37 mm more water at sowing than the summer fallow. Stubble retention without tillage increased water storage by 27 mm in only one year. At both sites the additional water stored due to stubble retention was located deep in the profile to 2.0 m. In general, zero tillage, primarily with stubble retention, offered large and consistent increases in soil water storage on heavy-textured clay soils in a 420-mm rainfall zone. On the lighter, sandy loam soil under the lower rainfall regime (343 mm), the advantage in soil water storage, through both stubble retention and zero tillage, was less frequent.