Optimal Phosphorus Management Strategies for Wheat–Rice Cropping on a Loamy Sand

Knowledge about optimal P rates for wheat ( Triticum aestivum L.)–rice ( Oryza sativa L.) cropping is insufficient because of nutrient availability differences between aerobic and anaerobic soil. We assessed P management strategies in a wheat–rice rotation on a Typic Ustochrept at Ludhiana, India. Seven P fertilizer treatments applied to wheat and rice, respectively, (P0‐0, P0‐26, P13‐13, P26‐0, P26‐13, P39‐0, and P26‐26; treatment abbreviations used include P applied to wheat followed by P applied to rice, both in kg ha −1 ) were compared from 1990 to 1997. Grain yield and seasonal P accumulation by wheat were highest for higher P rates and remained stable in treatments with P applied to wheat. Phosphorus application to rice increased P accumulation by rice, but did not consistently increase rice yields because flooding decreased soil P sorption and increased P diffusion resulting in higher P supply to rice relative to wheat. Indigenous soil P supply measured in wheat was 5.8 to 8.0 kg P ha −1 , as compared with 14.9 to 18.1 kg P ha −1 in rice. Phosphorus adsorbed by ion‐exchange resin capsules placed in situ was five times greater under rice than under wheat. Applying only 26 kg P ha −1 to wheat and no P to rice was not economical and led to a negative P balance and a decline in soil P. Applying 32 kg P ha −1 to wheat and 15 kg P ha −1 to rice was optimal for achieving short‐term economic and long‐term agronomic goals when both grain and straw were removed from the field. These findings require further validation at other sites, at higher rice yield levels, and for different straw management.