THE TRANSFORMATION PROCESSES OF STRUVITE SLOW RELEASE FERTILLZER IN VEGETABLE BY ISOTOPIC TRACING

Discharge of nitrogen and phosphorus greatly exceed the limitation in China. The precipitation of struvite, for its efficient recycling and environmentally friendly, is superior method for ammonium and phosphate removal. In this study, struvite as slow-releasing fertilizer were investigated. The results showed that the best pH for struvite release was at neutral soil, the release periods of struvite was more than two weeks, and the concentrations of ammonium and phosphate in soil were 4-6 mg/L and 2-6 mg/L at 10 day, respectively. The release rate of struvite has nothing to do with salinity, which was related to soil humidity. When struvite with N15 was used as slow-releasing fertilizer, it can be uptake by vegetable, especially by root, and the release period can meet vegetable growth cycle. The precipitation of struvite as slow-release fertilizer can provide opportunities for reusing ammonium and phosphate and keeping the cost of recycling and reusing of ammonium/phosphate down.