Optimum combination of phosphorus, potassium and density for double-rice systems

【Objectives】 In order to determine effects of phosphorus (P) and potassium (K) fertilizer application and transplanting density (D) on double-rice systems, field experiments were conducted to study yield, yield components and phosphorus and potassium use efficiency of double-rice in Jiangxi province.【Methods】 Two split-plot experimental designs were conducted with different phosphorus and potassium application amounts and transplanting density to study grain yield and phosphorus and potassium use efficiency. There were four P rates (P2O5 0, 60, 90 and 120 kg/hm2 designated P0, P60, P90 and P120) and four transplanting densities (21×104, 27×104, 33×104, 39×104 hole/hm2 designated D21, D27, D33 and D39) for phosphorus experiment. In potassium experiment, there were four K rates (K2O 0, 90, 120, 150 kg/hm2 designated K0, K90, K120 and K150) and four transplanting densities similar to phosphorus experiment. The grain yield and its components were measured, and P and K uptake and use efficiency were analyzed at rice maturity.【Results】 In the P and plant density experiment for the same P level, the early rice yield and P uptake kept increased with the increasing of plant density until that the P application rate exceeded 60 kg/hm2. The P recovery efficiency (REP), P agronomic efficiency (AEP) and P partial factor productivity (PFPP) were decreased in similar trends like yield. The highest yield and REP were in combination of P2O5 60 kg/hm2 and 39×104 hole/hm2, in which the yield was 5303.9 kg/hm2 and REP 24.4%, and the AEP 29.4 kg/kg. The highest yield and REP were obtained in combination of P2O5 60 kg/hm2 and 33×104 hole/hm2 for late rice, in which the yield was 7246.9 kg/hm2, REP was 42.4% and AEP 36.2 kg/kg. In potassium experiment, transplanting density and K fertilizer application increase K uptake for early rice, the highest grain yield and K recovery efficiency (REK) were in combination of K2O 120 kg/hm2 and density of 39×104 hole/hm2, in which the yield was 6376.3 kg/hm2, REK was 67.2% and K agronomic efficiency (AEK) 15.6 kg/kg for early rice, the three highest indexes in late rice were obtained in combination of K2O 90 kg/hm2 and density of 33×104 hole/hm2, in which the yield was 7025.6 kg/hm2, REK was 74.0% and AEK 21.7 kg/kg.【Conclusions】 Rational combination of phosphorus and potassium fertilizer and transplanting density can indeed significantly increase the effective panicle number of per unit area and total nutrient uptake, which is the main reason for yield increases and fertilizer use efficiency. High P and K fertilizer applications alone do not contribute to yield increases. The results suggested the optimum combination is P2O5 60 kg/hm2, K2O 120 kg/hm2 plus density of 39×104 hole/hm2 for early rice, and P2O5 60 kg/hm2, K2O 90 kg/hm2 plus density of 33×104 hole/hm2 for late rice under double-rice systems in the studied region.