Effects of Nitrogen and Foliar Sulphur Interaction on Grain Yield and Yield Components in Barley

In this study, conducted from 1979 to 1986 in southern Spain, the objective was to analyze the effects of a possible interaction between soil-applied N and foliar S applied to barley (Hordeum vulgare L.) during tillering on grain yield and to identify the mechanism involved. From 1979 to 1982, we used rates of 20, 40, 60 and 80 kg a.i. N ha^?1, together with 12.5 or 25 kg foliar a.i. S ha^?1 during tillering. The results demonstrated that foliar S at both dosages acted as a partial (but not total) substitute for N, when the latter was applied at levels of 40 to 60 kg ha^?1. These effects of S did not appear to result only from a nutritive mechanism, but rather from a hormonal mechanism through the increase in ethylene biosynthesis. Therefore, during 1983 to 1986, we used 40, 60 and 80 kg a. i. N ha^?1, together with 12.5 a. i. S ha^?1 and 0.55 kg a.i. ethrel (2-chloroethyl-phosphonic acid) ha^?1. The results showed that the effects of S and ethrel on yield were practically the same. Assayed with 40 and 60 kg N ha^?1, S and ethrel acted as partial (but not total) substitutes for N, exceeding the yield of the control without S or ethrel, and equalling the yield obtained with 20 kg more of N ha^?1. The S or ethrel applied with 80 kg N ha^?1 presented an additive effect with the N. The increases in yield using S or ethrel were in all cases due to the increased final number of spikes m^?2, which was principally a consequence of the higher number of tillers formed but also a result of increased survival of tillers to form a viable spike. In addition, the positive effects of S on yield were greater the smaller the N dosage and the lower the annual yield. Finally, we present a possible mechanism of hormonal action, to explain how foliar S applied during tillering affects grain yield in barley.