Grain number and its relationship with dry matter, N and P in the spikes at heading in response to N x P fertilization in barley

The aim of this work was to study the effects of nitrogen (N) and phosphorus (P) deficiencies and their interaction on spike N, P and biomass around flowering in barley (Hordeum vulgare spp. distichum L.) and its relationship with grain number and grain yield. Two experiments were carried out with microcrops grown in 2001 containers using malting barley (cv. Quilmes Palomar). Treatments were a factorial combination of two levels of N and two or three levels of P fertilization. Dry matter partitioning to spikes was not or only slightly affected by nutrient deficiencies. Then, the effects on spike biomass were similar to those on total aboveground dry matter. Although partitioning of N to the spike in N fertilized treatments was lower than in N stressed ones, spike N content was higher in the N fertilized. Number of grains was positively associated with spike N and P content as well as spike dry matter at heading in both experiments. Number of grains per unit of spike dry matter at heading in N fertilized microcrops tended to be higher than in N stressed ones, though this effect was not associated with N fertilization effects on N concentration in spikes. Combining these results with others from the literature from wheat crops, we found a strong relationship between number of grains and spike N content at flowering, but this relationship does not seem to be better than that with spike biomass, judged by the regression coefficients. This indicates that the early application of N may induce a higher number of grains than that predicted by increased spike dry weight at flowering, but this additional effect is not universally related to differences in spike N concentration. (C) 2004 Elsevier B.V. All rights reserved.