Time of sowing and wheat production in southern NSW

Abstract

Wheat (CV. Heron) sown on clover-improved soils at Wagga Wagga, New South Wales, over the period 1961 to 1965 showed a general reduction in yield and an increase in grain protein percentage with delay in sowing. Grain yield decreased by 3.7 per cent for each week's delay in sowing after the end of April and the rate of grain protein increase ranged from 0.09 to 0.56 per cent for each week's delay, depending on seasonal conditions. This grain protein increase was accompanied by a reduced kernel size which resulted in a decrease in grain protein yield of 12.5 lb an acre for each week's delay in sowing. The reduced grain yield with later sowings was associated with less efficient use of soil moisture the post-flowering period. Although the cumulative evapotranspiration of early sown crops was about two inches greater than that for late sown crops in mid-spring, all sowings reduced the soil moisture potential to -15 bars to a depth of four to five feet at maturity. However, the late sown crops matured more rapidly with a reduction in all yield components. Changes in soil mineral nitrogen concentration during the growing season indicated that there Was adequate nitrogen available for all sowings. In two years mineralization of soil organic nitrogen occurred under the crops and contributed significantly to the crops requirement. In a third year mineral nitrogen losses from the soil could not be accounted for by plant uptake.