The effect of phosphorus application on the growth, nitrogen fixation and yield of three varieties of soyabean (Glycine max [L] Merrill)

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Pot and field experiments were conducted at the Plantation section of the Department of Crop Science, University of Science and Technology, Kumasi to investigate the effects of P on the growth, N2-fixation, nodulation and yield of three varieties of soybean (G1ine max [L] Merrill). The varieties of soybean used were Anidado, TGX 183 5-12E and GMX 92-6-7m. The experimental design was a split plot with four and three replications for the field and pot experiments, respectively. Three varieties of soybean were assigned to the main plots whilst four fertilizer rates (0, 25, 50 and 75 kg P ha-1) constituted the subplots. The study showed that P fertilization increased shoot dry weight, plant height, LAI, nodulation, N2- fixation, grain yield and components of yield. Grain yield was highly and positively correlated with nodulation, N2-fixation and yield components. Shoot dry weight in both experiments was significantly influenced by P fertilization with the field experiment recording the highest shoot dry matter accumulation. In both experiments, Anidaso recorded the highest biomass yield of 6.3g and 4.4g per plant in the field and pot experiments, respectively. Total N in shoot and nodule formation were higher in the pot than in the field experiment. The average values of total N fixed were 1.5% and 2.1% for the field and pot experiments respectively. The TGX 1835-1 2E variety was the best fixer, recording 2.3% and 1.8% in the pot and field experiments respectively. The highest total N fixed in shoots and grain yields coincided with application of 75kg P ha-1. The increase in grain yield was mainly due to an increased number of pods/plant and one hundred seed weight. Grain yield increased from 925 kg ha-1 at zero fertilization to 1249 kg ha at the highest phosphorus rate of 75kg P ha-1 representing an increase of 35%. Yield estimates for the varieties ranged from 1009 to 1355 kg ha for GMX 92-6-7m and Anidaso. The highest number of pods per plant (51.8) was obtained at the highest P rate of 75kg P ha-1. Phosphorus fertilization significantly (P< 0.05) influenced the number of pod per plant with Anidaso recording the highest value of 51.5. Significant differences (P< 0.05) existed among the three varieties in the number of seeds/pod. TGX 183 5- 12E record the highest number of seeds/pod (2.4), followed by Anidaso (2.2) and then GMX 92-6-7m (1.8). One hundred seed weight increased significantly (P< 0.05) with P application. Significant fertilizer x variety interaction was recorded in the number of branches/plant and mean seed weight in the field experiment. Significant fertilizer x variety interaction was also recorded in the plant height in the pot experiment. The results revealed that P fertilization influenced growth, nodulation, N2- fixation and grain yield of soybean. It is envisaged that results obtained in this study will help to stimulate further research.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of the Degree of Master of Science in Agronomy, 1999