Effect of phosphorus and nitrogen fertilization on sunflower (Helianthus annus L.) nitrogen uptake and yield

Abstract

Little is known about the effect of combined phosphorus and nitrogen (P-N) fertilization on the N requirement of sunflower (Helianthus annus L.). This study was carried out to evaluate the effects of varying levels of P and N, as well as the interaction P x N, on the N uptake, yield and N apparent utilization efficiency under field conditions. Split-plot design experiments were conducted in the mid-western Pampas in Argentina. Four levels of N (0, 46, 92 and 138 kg N ha-1) and three levels of P (0, 12 and 40 kg P ha-1) were applied to two Typic Hapludolls over two growing seasons (1997-98 and 1998-99). N uptake and soil N-NO3 contents were determined at the V7, R5 and R9 growth stages. The sunflower yield ranged from 2.5 to 5.0 Mg ha-1. The total N requirement was around 45 kg N Mg-1 grain, and this result suggests that it is not necessary to use different N requirements (parameter b) for fertilized crops when a yield response is expected. To achieve a 100 % yield maximum a N supply (soil plus fertilizer) of 181 kg N ha-1 at P40 was needed. However, at P0, the highest yield was about 80 % of the maximum yield with a N supply (soil plus fertilizer) of 164 kg N ha-1. P application increased the apparent use efficiency of the supplied N.