Two sets of trials were conducted for three seasons, beginning the 1994/95 cropping season, to establish the place of sunflower in the sequencing of crops by smallholder farmers and determine its soil N and P requirements in those sequences. Productivity of the cropping sequences was also measured and economic implications of the N and P rates evaluated on all crops. In the first trial varying rates of P2O5 (30, 60, 90 and 120 kg ha-1) with zero as control, were assessed in crop sequences that were structured such that sunflower would follow two crops of maize (MZ-MZ-SF). In the second trial, three nitrogen rates (30, 60 and 90 kg ha-1 N) were applied to sunflower every year, with non application as the control. The sequences were structured such that beginning with the second season, every cropping season would have the following sequences: sunflower after maize; sunflower after groundnut; maize after groundnut; maize after sunflower; groundnut after maize and groundnut after sunflower.|Farm fields selected in Natural Regions (NR) II and IV were classified as deficient in N (<20 ppm N) and P (<15 ppm P2O5). In the first two seasons sunflower did not respond to applied P. But good responses (P0.01) were observed in the third season, indicating the positive effects of P build-up in the soil. At NR IV locations, maize following another crop of maize performed better than that which followed sunflower at the various P rates, and a similar trend was observed in season three at the NR II location. In sunflower, significant increases in seed yield peaked at the 30 kg P2O5 ha-1 rate. Maize was more responsive to P application, with responses up to 90 kg P2O5 ha-1 recorded in some years. To cut down on costs, where both crops are included in a system it may be worthwhile to apply the P to the maize and let a subsequent sunflower crop use the residual P; especially on fields where a grower deliberately targets P build-up or its management. With better rainfall distribution, soil pH and soil available P also increased. This demonstrates the great influence exerted by interactions between P application and seasonal rainfall amount and its distribution on performance of crops.|Nitrogen management on sunflower rotated with maize or groundnut showed a peak N requirement for the crop at 60 kg ha-1 across locations. There were also notable differences in performance between the sequences. Sunflower or maize planted after groundnuts, on average, produced the highest kernel or grain yields irrespective of the N rate, showing the positive influence of a legume in the system. Where no N was applied, monetary returns from growing sunflower or maize after groundnut were much higher than when those same crops were rotated with each other, when N was not applied.|

English

9906|AGRIS 9902|R98-99ANALY

Jose Juan Caballero

CIMMYT Publications Collection