Agronomic Evaluation of Phosphorus Sources Applied to Upland and Lowland Rice

Rice is a staple food for more than 50 percent world’s population. It is mainly grown under two ecosystems, known as upland and lowland. Soils on which these two types of rice are grown are mostly deficient in phosphorus (P). Two field experiments were conducted (one with upland rice and another with lowland rice) with the objective to determine responses of upland and lowland rice to two sources of P fertilizers. The P sources were mono-ammonium phosphate and polymer coated mono-ammonium phosphate. The P rates used in the two experiments were 25, 50, 100, and 200 kg P ₂O ₅ ha ⁻¹ plus one control treatment. Plant height and grain yield of upland rice significantly increased with the addition of P fertilization. Similarly, plant height, straw yield, grain yield, panicle density, 1000-grain weight, P concentration, and uptake of lowland rice were significantly increased with the application of P fertilization. The response of these plant parameters to P fertilization was quadratic in nature. Rate of P for maximum growth, yield, and yield components varied for both upland and lowland rice. Maximum grain yield of upland rice was obtained with the addition of 108 kg phosphorus pentoxide (P ₂O ₅) ha ⁻¹ by mono-ammonium phosphate and 105 kg P ₂O ₅ ha ⁻¹ by polymer-coated mono-ammonium phosphate. Similarly, maximum grain yield of lowland rice was obtained with the addition of 143 kg P ₂O ₅ by mono-ammonium phosphate and 151 kg P ₂O ₅ by polymer-coated mono-ammonium phosphate. There were no significant differences between both the P sources for the growth, yield, and yield components of upland and lowland rice. Phosphorus-use efficiency defined in several ways decreased with increasing P rate in lowland rice.