INFLUENCE OF PHOSPHOROUS FERTILIZER AND LIME ON SEED QUALITY OF SOYBEAN (Glycine max (L.) Merrill) IN WESTERN KENYA

Abstract

Soybean (Glycine max (L.) Merrill) is a versatile crop useful in the economy as human diet, animal feed and for industrial purposes. However, production has been dwindling due to poor seed quality among other constraints. Therefore, a field experiment was conducted from June-November 2015 at University of Eldoret farm in Uasin Gishu County and Agricultural Training Centre (ATC) farm in Busia County. The aim of the study was to study the influence of phosphorous fertilizer and lime in improving the seed yield, quality and storability of soybean cultivars. A factorial experiment was laid out in RCBD with three replicates involving: two varieties of soybean; SB 19 (proteinous) and SB 133 (oily), three P fertilizer rates at 0, 30 and 60 kg P ha-1 and two levels of lime at 0 and 2 ton ha-1. All the agronomic practices were carried out as recommended, the seeds were harvested and sundried to 13 % moisture content. The parameters measured before storage were seed yield, 1000 seed weight (g), initial electrical conductivity, percent germination, seed oil and protein content. The seed were subjected to storage treatment under controlled temperature at 10 ˚C and ambient condition for a period of 6 months, after which seed vigour and viability were determined. All the data collected was subjected to analysis of variance and significant differences (p < 0.05) separated using Tukey’s HSD in R® statistical package version 3.3.1. Seed yield was significantly influenced by phosphorous fertilizer, where yield increase was highest at 30 kg P ha-1 of 39 % in SB 133 in Busia and 37 % in SB 19 in Eldoret. Lime increased seed yield for SB 19 by 27 % and 4 % in Busia and Eldoret respectively. Seed oil content was influenced by phosphorous fertilizer and lime in Busia where high value of 21.92 % recorded at 60 kg P ha-1. Seed protein increased with phosphorous fertilizer to 40.40 % in SB 19 and 39.64 % in SB 133 in Eldoret. Lime application was effective in both sites and increased seed protein content. Seed electrical conductivity responded to phosphorous fertilizer where high value of 107.93 and 120.75 μ S cm-1 g-1 was recorded at 60 kg P ha-1 implying seed vigour loss. Seed germination was not influenced by phosphorous fertilizer and lime. Seed storability as measured by vigour and viability was influenced by cultivar, storage duration and condition. Oily seeds (SB 133) deteriorated rapidly compared to proteinous as storage duration increases and more rapidly in ambient condition. Deductions from this study indicates that high phosphorous level is detrimental to seed yield and physiological quality. It recommends that the application rate of phosphorous fertilizer should not exceed 30 kg P ha-1 in ferralsols soil of Western Kenya. Finally, the study suggests further research on different phosphorous fertilizer rates at different agro-ecological zones to ascertain optimum P application rates that guarantees optimal seed yield and quality.