Paspalum guenoarum seed production; harvesting time and nitrogen fertilization

Abstract

An experiment was carried out during two consecutive years at Itapetininga, State of São Paulo, Brazil, in order to study the effects of N rates and harvest times on the seed yield of Paspalum guenoarum Arech. var. guenoarum.Three N rates (0, 75 and 150 kg N.ha^-1) and ten harvest times were the treatments. Those treatments were completely randomized with three replications, in a split-plot design. Nitrogen rates were the plots and the harvest time were the subplots (12 m² each). The first harvest was set at 14 days after the initial flowering date (IF) which was defined as the presence of 5 to 10 inflorescence.m^-2 (at least one raceme free of the flag Ieaf). Other harvest were performed wokly. Total seed yield (TS), pure seed yield (PS), pure viable seed yield (PVS), purity (P) and germination (G) were evaluated. In the first year the interaction harvest time x N rates was significant (P < 0.05) for the PS and PVS. The highest values for PS and PVS were observed at 56 days after IF (7^th harvest) at an N rate. Nitrogen had a significant effect (P < 0.01) only at the 9th harvest, when the seed yield was very low. In the second year the interaction harvest time x N rate was significant for TS (P < 0.05) and the other variables (P < 0.01). Nitrogen fertilization increased TS and PS at the 6^th (P < 0.01) and 7^th (P < 0.05) harvest, respectively 49 and 56 days after IF. The highest values for PVS were observed in the 5^th (P < 0.05), 6^th and 7^{th (}P < 0.01) harvest. The highest pure seed yield, when no N fertilizer was used, was obtained in the 5^th harvest (42 days after IF) and in the 6^th harvest (49 days after IF) when 75 or 150 kg N.ha^-1 was applied.