NITROGEN-FERTILIZER EFFECTS ON GROWTH, GRAIN-YIELD, AND YIELD COMPONENTS OF MALTING BARLEY

Optimal strategies for using nitrogen fertilizer with malting barley (Hordeum vulgare L.) must aim to maximize yield while maintaining low N content in grain to preserve malting quality. Eleven field experiments were conducted during 1989-91 with the objective of determining the impact of N fertilizer applied at different growth stages on crop growth, grain yield, and yield components of malting barley. Treatments included single applications of N fertilizer at sowing, at Zadoks growth stages Z-22 (midtillering) or Z-30 (end of tillering) and differing levels of N applied at each of these times. High rates of N applied early in the growing season stimulated tillering but many of these tillers did not produce spikes. An effect of N on spike number was evident only in comparisons of fertilized and unfertilized treatments through a positive correlation between number of spikes at maturity and the number of tillers at Z-30. Nitrogen fertilizer applied at Z-30 resulted in 30% to 100% increases in number of kernels/spike over unfertilized plots though number of kernels/spike was negatively correlated with number of spikes/m(2), indicating compensation effects. Nitrogen applications at Z-30 were also most effective for increasing number of kernels/m(2) while kernel weight responded only slightly to N. Mean kernel weight for all site-years revealed that none of the three years presented limiting conditions for grain filling. Cumulative probability curves for yields and yield components indicated that N fertilizer applied at Z-30 gave the best results in most situations but only when sufficient N was available at sowing to ensure crop establishment and initial tiller development. In contrast, the Z-30 treatment had the least impact on yield and yield components when no fertilizer was applied at sowing. Number of kernels/spike and number of kernels/m(2) were the only two yield components with a clear association with grain yields. The research indicates that N fertilizer strategies for malting barley should ensure relatively small amounts of available N at sowing for crop establishment and initial tiller development. Additional N would then be applied at the end of tillering, the amount required depending on the crop and soil management systems used.