Effects of band applications of polyolefin-coated fertilizers on the nitrate and oxalate content in spinach [Spinacia oleracea]
1999
Ombodi, A. (Tohoku Univ., Sendai (Japan)) | Miyoshi, S. | Saigusa, M.
Spinach plants can contain large amounts of nitrate and oxalate, representing a health hazard. With a continuous supply of ammonium-nitrogen in a solution culture, the nitrate and oxalate content of spinach plants can be decreased, while vitamin C concentration can be increased simultaneously. Long-term ammonium nutrition in soil culture can be cerried out with band applications of polyolefin-coated urea-N or ammonium-N fertilizers. In this pot experiment, the effects of band applications of four different polyolefin-coated fertilizers (POCFs) (polyolefin-coated urea (POCU), polyolefin-coated urea with dicyandiamid in the coating (POCU-Dd), polyolefin-coated diammonium-phosphate (POC-DAP), polyolefin-coated ammonium-sulfate (POC-AS)) on spinach were compared to those of split applications of ammonium sulfate (AS). Compared to AS, yields were reduced by 29, 52, 21 and 16% for POCU, POCU-Dd, POD-DAP and POC-AS, respectively. However, the nitrate content in plants of POCF treatments was less than 10% of that for AS treatments. POCFs, with the exception of POCU, significantly decreased the oxalate content of spinach plants, due to decreased cation uptake as a consequence of long tern ammonium nutrition. Vitamin C concentration was significantly lower in the AS treatment than in the POCF treatments. Long-term ammonium nutrition, carried out with band applications of ammonium-N or urea-N form POCF, resulted in an improved nutritional quality of spinach, as compared to the AS treatment. Considering both yield and quality, band applications of POC-DAP and POC-AS are feasible fertilization methods for producing high quality spinach
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