Effect of phosphorus and of irrigation on alfalfa seed yield

Abstract

A field trial was carried out in the Summer 1991, at the Estação Experimental Agronômica of the UFRGS, Eldorado do Sul, RS, Brazil, to identify the effects of three soil water availability levels as determined by the ratio ETr/ETm (0.85 to 0.80; 0.76 to 0.68; 0.67 to 0.46) and of two rates of phosphorus (130 and 520 kg/ha P₂O₅) on seed yield components of alfalfa (Medicago sativa L.) cv. Crioula. Seed yield components were not significantly affected by phosphate (P>0.05). The lower soil water availability level benefited most the number of pods per inflorescence and seed size; this improved condition, coupled with the tendency for an increased number of seeds per inflorescence, determined higher seed yield of plants under the lower soil water availability level. Seed yield varied from 120 up to 178 kg/ha, on average. Lack of pollination, among other non-determined factors, might account for the low alfalfa seed yield response, by limiting the percentage of flowers originating a pod and particularly, on number of seeds per pod.