Effects of nitrogen and phosphorous fertilization on growth and yield of snowpeas (pisum sativum l. Var. Oregon sugar pod ii)
Njoroge, P K
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Two field experiments were carried out concurrently at the Faculty of Agriculture, Field station farm, University of Nairobi in March -July 2000 (season I) and June -September 2000 (season II) to determine the effect of application of different levels of either nitrogen (N) or phosphorous (P) fertilizer on growth and yield of snowpea (PiS1tll1 sativum L. var. Oregon sugar pod II). The experiments were laid out in a complete randomized block design with three replicates. Four levels of N (0, 50, 100 and 150 kg N ha') were split applied in equal halves as CAN (26% N) at 29and 58 days after sowing (DAS). In the parallel experiment, four levels of P (0,57, 114 and 171 kg P20S ha") were applied as TSP (46% P20S) at planting. Plant heights were measured at 31,38,45,58,71,84 and 97 DAS. Leaf area index and above ground dry mass were determined at 29, 43, 63, 77 and 94 DAS. Harvesting of pods was done at 68, 72, 75, 79, 82, 86, 89,93,96 and 100DAS. Nitrogen application did not affect plant height, leaf area index, total above ground dry matter accumulation, number of pods and pod dry mass plant -I in both seasons indicating that the snowpeas growth and yield did not substantially benefit from N fertilizer application. It is possible that either snowpeas were able to fix enough N to meet their requirements or these N requirements were met from the soil supply. Pod yields in this study were not affected by N probably through its lack of effect on growth and development. It is therefore recommended that less N be applied for growth and yield of snowpeas. In the parallel experiment on P fertilization, significant (P ~ 0.05) increases in plant height, leaf area index, and total above ground dry matter accumulation in both seasons were observed. Number of pods planfl showed a quadratic trend with increasing P at 68, 89 and 93 DAS in season 1. Linear and quadratic increases in number of pods plant -I were observed at 96 xiii DAS and on total number of pods plant -I. At 100 DAS, only linear increase was observed. Pod dry mass plant" showed a quadratic increase at 68, 89, 93 and 96 DAS. At 100 DAS, linear increase in pod dry mass plant-I was observed. Linear and quadratic increases were observed in total pod dry mass plant-I. P application did not affect both the number of pods and pod dry mass planrl in season IIbecause of the low amount of rainfall.. Application of 57 kg P 205 ha-I resulted in dry pod yields of up to 9.75 tons ha -I which is higher than the national dry mass averages of 5 to 6 tons ha -I. It is therefore recommended that judicious levels of P be applied for growth of snowpeas.