Vol. 8, Issue 6 (2019)

Author(s):
R Thamaraiselvi and K Arulmozhiselvan

Abstract:
Phosphorus (P) is a major nutrient required for plants particularly for the root growth, nucleoprotein synthesis and energy transfer. It does not exist as soluble forms abundantly in soil. Different forms applied P supplied through fertilizers are not fully absorbed by the plant, because substantial amount of P is precipitated in soil immediately after application and irrigation. The precipitated P exists in fixed forms and may dissolve and become available in the next season to some extent, which is known as residual effect. Precipitation of P occurs mainly due to interaction of soluble P with metal ions that are present in soil and also in irrigation water. In this study P precipitation of different P forms with different saline irrigation water was estimated. Precipitation of P recorded was high in saline water and per cent P precipitated decreased with P fertilizers in the order: Single Super Phosphate (6.49 mg P L^-1), Diammonium Phosphate (5.65 mg P L^-1), Monoammonium Phosphate (2.47 mg P L^-1), All-19 (2.44 mg P L^-1) and Potassium dihydrogen Phosphate (2.26 mg P L^-1)_. Precipitation of P was moderate in medium saline water and low in non-saline water. By scaling up to a practical range it was calculated that with the irrigation at 5 cm depth of water, surface application of 40 kg P ha^-1 (91.6 kg P₂O₅ ha^-1) would cause fertilizer P to become insoluble to the tune of 34.4 kg P ha^-1 (78.7 kg P₂O₅ ha^-1) if SSP is applied, 27.0 kg ha^-1 (61.8 kg P₂O₅ ha^-1) if DAP is applied, 19.7 kg ha^-1 (45.1 kg P₂O₅ ha^-1) if MAP is applied and 16.1 kg ha^-1 (36.8 kg P₂O₅ ha^-1) if All-19 is applied.