Effects of liming and phosphorus application on the growth and nodulation of soybeans (glycine max (l.) merr.) cv "hill" in acid soils
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A study on the effects of lime and phosphorus application on the growth and nodulation of soybeans (Glycine max (L.) merr.) cv "Hill" was conducted in a factorial experiment under greenhouse conditions using two strongly acid soils (a umbric andosol from Gituamba and a humic nitisol from Kisii) The soils were limed with calcium carbonate (CaC03) based on the levels of exchangeable Al present in the soil. The phosphorus levels were 0, 50, 100 and 150 kg P/ha, applied as triple superphosphate (TSP). Half the seeds were inoculated with Rhizobium strain, NUM 508 before planting and half were not. The plants were harvested 51 days after planting and the variables measured were nodule number and nodule dry weight, total dry matter yield and uptake of N, P, K, Ca and Mg. Inoculating the seeds significantly increased nodulation. The nodule numbers and nodule dry weights increased significantly with initial liming. The application of 100 Kg P/ha significantly increased nodulation. There was no interaction between lime and phosphorus with respect to nodulation. Initial liming (3 meq CaC03/100g) increased the shoot dry matter yield significantly (P=O.OS) in Gituamba soil. Further increases in lime application did not affect the yield significantly. In Kisii soil the application of 3 and 6 meq CaC03/100g increased the shoot dry matter yield significantly (P=O.OS). Application of 9 meq CaC03/100g decreased the yield but not significantly. The highest shoot dry matter yield occurred at the highest level of phosphorus (150 kg P/ha). There was a positive interaction between lime and phosphorus with respect to dry matter yield in Kisii soil. The application of P increased the dry matter yield significantly at lime levels 3 and 6 meq CaC03/100g. At the highest level of lime application (9 meq CaC03/100g) the yields decreased though not significantly. The application of phosphorus significantly increased the uptake of N, P, K, Ca and Mg. The growth response to liming and phosphorus application was attributed to the reduction of exchangeable. Significant increases of dry matter yield with increasing levels of P application suggest that further investigations with regard to optimum P level would be advisable.