Foliar application of phosphite reduces grain weight of soybean facing postflowering phosphorus deficiency

Background and aim We aimed to contribute with the foundation to adopt foliar P fertilization on soybean. Methods Treatments were a combination of contrasting postflowering root P supply versus foliar application of phosphate (Pi) or phosphite (Phi). Results Pi improved grain yield of P‐limited plants, while Phi was detrimental because of negative effects on grain weight. Conclusions Thus, cautions should be taken with foliar application of Phi during the generative phase of soybean under low‐P stress, as Phi impairs grain filling process.