Characteristics of P supply from polyolefin-coated P fertilizers in soil

Improvement of the availability of phosphorus (P) fertilizers in soil has been one of the major topics in the field of soil science and plant nutrition. We evaluated the P supplying characteristics of the polyolefin-coated (POC)-P fertilizers, POC double superphosphate (POC-DSP), POC multi-phosphate (POC-MP) and POC high-analysis compound fertilizer (POC-HACF) to improve the P recovery rate by crops in comparison with those of uncoated DSP, MP and fused magnesium phosphate (Fused P) in two soils (A horizon soils of Alic Pachic Melanudand and Oxyaquic Udorthent) with different P fixing capacity. The P supply from these fertilizers was examined using anion exchange resin and barley seedlings. P recovery from POC-DSP and POC-MP was maximal after 2 to 5 weeks while P recovery from uncoated DSP and MP markedly decreased with time. P recovery from POC-DSP and POC-MP was 3-5 times that from uncoated DSP and MP. P recovery from Fused P was very low because of its low solubility rather than fixation by soil. The P recovery markedly decreased with increasing depth of fertilizer placement, especially in Alic Pachic Melanudand. These findings suggest that close contact between crop root and POC-phosphorus fertilizers (POC-Ps) is important to improve P recovery. Findings obtained by using barley seedlings were in agreement with those obtained by using the resin.