Moisture and nitrate conservation and reponses to following after medic ley in the Wimmera

Abstract

The effect of three times of initial cultivation (August, October, February-March) on grain yield, grain protein content, moisture conservation, and nitrate accumulation was studied over a period of seven years at three sites in the Wimmera on land that had been under medic ley. Fallowing in winter (August) or spring (October) markedly increased grain yields but not grain-protein content when compared with the non-fallow control (initial cultivation in February-March). Variation in yield response to both winter and spring fallowing appeared to be associated mainly with variation in moisture conservation in the 30-60 cm layer. With winter fallowing, the nitrate that accumulated was associated with yield increases, but with spring fallowing the nitrate appeared to he associated with yield depression. However, the role of nitrate accumulation in determining yield responses to fallowing was only of minor importance. Suppression of weeds in the crop was not a factor in producing the large yield responses to fallowing since crops on both fallowed and non-fallowed areas were generally weedfree. Results obtained in the current experiments indicate that the aspects of climate suggested by work in South Australia as being the ones that determine yield responses to fallowing are not the ones which are important in the Wimmera. In this environment the most promising predictors of yield responses to fallowing appear to be April to August rainfall before commencement of the winter fallow and September rainfall before commencement of the spring fallow.