Copmarison of the effects of application of deep placement of slow release N (lime nitrogen and coated urea), P and K fertilizers on yield and quality of soybean (Glycine max (L.) Merr.) seed

Nitrogen, phosphorus and potassium are three major nutrients, whose availability often become limiting factor to plant growth and crop yield. We have published in our previous reports that a new fertilization method with deep placement of slow release N fertilizers, such as coated urea and lime nitrogen (calcium cyanamide) supplied at 20cm depth from soil surface promoted soybean growth and seed yield. In the present experiment the effects of deep placement below plants of 100kgN ha(-1) of N fertilizers, coated urea (CU) and lime nitrogen (LN) in addition to 100kgP2O5 ha(-1) of fused phosphorus (P) and 100kgK2O ha(-1) of potassium silicate (K) fertilizers, on growth and seed yield of soybean (Glycine max [L] Merr.) plants were examined by comparing with those from control plots in rotated paddy field of Nagaoka. The fertilizers were applied for both the nodulated soybean (cv. Enrei) and the non-nodulated isogenic line (En1282). Different fertilizer combinations were used which include CU, CU+P, CU+K, CU+P+K, LN, LN+P, LN+K and LN+P+K. The deep placement of the fertilizers, especially LN+P+K, markedly increased the growth of Enrei plants compared to other treatments. The seed yield and visual quality of harvested seeds also showed that LN+P+K enhanced the yield as well as quality of seeds compared to the other treatments. Thus, it is suggested that N fertilization management, like deep placement of slow release N fertilizers in addition to P and K fertilizer, is important for maximum yield and enhancement of seed quality of soybean. As regard to wrinkle seeds, percentage of side wrinkle was higher in CU+K treatment compared with other treatment. The percentage of turtle wrinkle was positively correlated with pealed seeds (R(2)=0.707), broken coat (R(2)=0.399) and side wrinkle (R(2)=0.294), and negatively correlated with the percentage of good seed (R(2)=0.587).