EVALUATION OF WINTER-WHEAT MANAGEMENT-PRACTICES UNDER SEMIARID CONDITIONS

A study was conducted to evaluate European cereal management techniques in winter wheat under semi-arid growing conditions. Combinations of rates and split applications of ammonium nitrate fertilizer with a plant growth regulator and/or a late season fungicide application were investigated using no-till "stubbled-in" production practices in two winter wheat cultivars, Norwin and Norstar at two locations over 3 yr. Nitrogen fertilizer gave the maximum yield when it was applied in mid-April. Split applications of nitrogen did not improve grain yields or grain protein concentration. A height reduction was observed with the use of plant growth regulators in both cultivars but no benefits were incurred due to the lack of lodging. The late season fungicide application had some effect on increasing kernel weight in both cultivars but rarely translated into a higher yield. Nitrogen and growing conditions had the largest effects on yield and the dilemma faced by producers is to correctly match nitrogen rates with environmental conditions given that the nitrogen has to be applied early in the spring. Available spring soil moisture and soil residual nitrogen provided little help in determining the rate of nitrogen giving the maximum economic yield because assumptions on growing season precipitation have to be made. It is suggested that nitrogen management be based on a risk analysis which would involve determining the probability of different levels of growing season precipitation for various climatic zones and soil types and the corresponding yield levels expected. Rates of nitrogen fertilizer would then be adjusted according to soil residual nitrogen levels and the risk the producer is willing to assume. This will require more extensive research and development of crop production models.