Lowland Rice Response to Thermophosphate Fertilization

Use of adequate rates of phosphorus (P) in crop production on high‐P‐fixing acid soils is essential because of high crop response to P fertilization and the high cost of P fertilizers. Information on lowland rice response to thermophosphate fertilization grown on Inceptisols is limited, and data are also lacking for soil‐test‐based P fertilization recommendations for this crop. The objective of this study was to evaluate response of lowland rice to added thermophosphate and to calibrate P soil testing for making P fertilizer recommendations. A field experiment was conducted for two consecutive years in central Brazil on a Haplaquept Inceptisol. The broadcast P rates used were 0, 131, 262, 393, 524, and 655 kg P ha−1, applied as thermophosphate Yoorin. Rice yield and yield components were significantly increased with the application of P fertilizer. Average maximum grain yield was obtained with the application of 509 kg P ha−1. Uptake of macro‐ and micronutrients had significant quadratic responses with increasing P rates. Application of thermophosphate significantly decreased soil acidity and created favorable macro‐ and micronutrient environment for lowland rice growth. Across 2 years, soil‐test levels of Mehlich 1–extractable P were categorized, based on relative grain yield, as very low (0–17 mg P kg−1 soil), low (17–32 mg P kg−1 soil), medium (32–45 mg P kg−1 soil), or high (>45 mg P kg−1 soil). Similarly, soil‐test levels of Bray 1–extractable P across 2 years were very low (0–17 mg P kg−1 soil), low (17–28 mg P kg−1 soil), medium (28–35 mg P kg−1 soil), or high (>35 mg P kg−1 soil). Soil P availability indices for Mehlich 1 extractant were slightly higher at higher P rates. However, both the extracting solutions had highly significant association with grain yield.