The Effect of Phosphorus Fertilizer Rate and Application Time on Rice Growth and Yield

Three studies have been conducted since 2001 to examine rice growth, nutrition, and yield response to phosphorus (P) application rate and time. The three sites represent high-pH silt loam soils (>7.5) with a range of Mehlich 3-extractable P (8 to 41 mg P/ kg). The objective of this research was to measure rice biomass and tissue-P concentration during the growing season and rice grain yield response as affected by Pfertilizer application time and rate. In 2002, P fertilizer was applied at rates of 0, 25, 50, and 100 lb P2O5/acre before rice emergence, preflood, midseason, and at the late boot stage in a study conducted in a Cross County, AR, rice field and at the Pine Tree Branch Experiment Station (PTBS). Significant yield responses were only observed in the 2001 study (Slaton et al., 2002b). However, tissue-P concentrations have tended to increase as P-fertilizer application during vegetative growth was delayed from the time of seeding until the 5-leaf stage at two of three sites. This provides solid evidence that P application time is critical for efficient plant uptake of applied P fertilizer on P-deficient soils. Until soil chemical properties are accurately correlated with tissue-P concentrations, growers should continue to apply P based on current soil-test recommendations at the time that best suits their crop management system.