The effect of surface treatments on soil water storage and yield of wheat

Abstract

Soil water changes under six pre-seeding surface treatments and the following wheat crop were recorded at three- to four-weekly intervals in two consecutive seasons (1966-67 and 1967-68) on a hard setting red-brown earth in South Australia. The treatments were 'fallow' (initial cultivation in spring, nine months before sowing), 'grassland' (initial cultivation in autumn, two months before sowing), 'chemical fallow' (sprayed with herbicides in spring), and three fallows separately modified with gypsum, straw and hexadecanol. In both experiments grassland lost water rapidly in spring and this lower water content was never completely restored. The fallow + straw gave the biggest recharge of soil water following rain and the highest water storage efficiency during the fallow period. In 1966-67, recharge of soil water followed rain in summer at a time of high evaporation rates. The effectiveness of the treatments in increasing soil water storage was related to their ability to reduce evaporation. In 1967-68, soil water recharge occurred in autumn when evaporation rates were low. The effectiveness of the treatments was then related to their ability to curb surface sealing by raindrop impact. Nitrate-N contents in the top 60 cm of soil at seeding were higher in 1967 than 1968, probably due to efficient mineralization in 1967 after summer rain, and leaching by heavy rain and denitrification before seeding in 1968. Crops on the fallow + straw treatment used most water and produced the highest wheat yields with the highest water-use efficiency in both years.