Phosphorus soil test calibration for lowland rice on an inceptisol

Efficient use of an adequate level of P in crop production on high-P-fixing acid soils is essential, due to high crop response to P Fertilization and the high cost of P fertilizers. Soil-test-based P fertilization recommendations are not available for lowland rice (Oryza sativa L.) grown on Inceptisols. The objective of this study was to calibrate P soil testing for the response of lowland rice (cv. Javae) to added P. Two field experiments were conducted in two years at two locations in central Brazil on Haplaquept Inceptisols. In the first year, the broadcast P levels used in both experiments were 0, 87, 175, 262, 350, and 437 kg P ha(-1), applied as triple superphosphate. In the second year, each residual broadcast P level from the previous year received band application of 0, 22, 44, and 66 kg P ha(-1). Soil test levels of Mehlich-1 extractable P were categorized, based on relative grain yield from the first year, as very low (0-2.6 mg P kg(-1) soil), low (2.6-8.8), medium (8.8-13.0), or high (>13.0). The amount of broadcast P needed to build up soil P test concentrations at very low, low, medium, and high soil test categories was 80, 220, 292, and >444 kg P ha(-1), respectively. The rice crop produced 0 to 70%, 70 to 95%, 95 to 100%, and 100% of relative yield at the very low, low medium, and high P levels, respectively. The amount of banded Fertilizer P required to obtain maximum yield at both locations was 66 kg P ha(-1) for the very low and low soil P levels, 44 kg P ha(-1) for the medium soil P level, and 22 kg P ha(-1) for the high soil P level.