Effect of Phosphorus Levels on Soil Properties and Plant Tissues of Two Nerica Varieties

Phosphorus levels in the soil are easily fixed and rendered unavailable to plants even if they are found to be high and therefore, its influence on uptake of other nutrients such as nitrogen, and potassium cannot be overemphasized. In that view, an experiment was set out at KALRO-Mwea to investigate on the effect of phosphorus levels on soil properties and plant tissue nutrient contents of Nerica rice variety. The experiment was laid out in a Randomized Complete Block Design in split-split plot arrangement and replicated thrice. Two rice varieties (Nerica 11 and Nerica 4) formed the main plots and 4 phosphorus levels (0 kg P/ha, 25 kg P/ha, 50 kg P/ha and 75 kg P/ha) formed the sub plots. Highest net pH decreases of 0.20 and 0.22 units were recorded at 75 Kg haˉ¹ P2O5 in season 1 and season 2 respectively, while the lowest net decreases of 0.12 and 0.16 were elicited at 50 Kg haˉ¹ P2O5 treatment in season 1 and season 2 respectively. A net decrease was observed in all the CEC levels where phosphorus was applied in all the seasons in which the highest net decrease of 1.09 and 1.03 during season 1 and 2 respectively was elicited on the control treatment, while the lowest net decrease of 0.61 and 0.59 was elicited by the 50 Kg haˉ¹ P2O5 rate in season 1 and 2 respectively. There was an inverse relationship exhibited between the phosphorus level of applications and the soil phosphorus net decrease across the two seasons. The net decrease was highest at 0 Kg haˉ¹ P2O5 and increased significantly with increasing phosphorus rate. That content of soil nitrogen were low with a marginal increase recorded with application of phosphorus across the seasons. The highest net increase of 0.05% was observed at the 75 Kg haˉ¹ P2O5 rate and control in season 1 while the application rate of 50 Kg haˉ¹ P2O5 had the lowest net increase of 0.02% in season 2. Highest mean plant-tissue phosphorus of 62.05 ppm was recorded in Nerica 4 under 75 kg P/ha treatment. Highest plant tissue nitrogen of 0.686% and 0.713% for Nerica 4 and 11 respectively were elicited at 75 kg haˉ¹ P2O5 in season 1, whereas in season 2 the highest plant tissue nitrogen of 0.721% and 0.691% at 75 kg haˉ¹ P2O5 for Nerica 11 and 4 respectively was recorded. Application of phosphorous led to the highest plant-tissue phosphorus in both seasons indicating the importance of proper P fertilizer application where from this study 50-75 kg haˉ¹ P2O5 rate is recommended in rice growing.