Development of controlled release phosphate fertilizer

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Basic experiments were performed regarding the development of controlled-release fertilizer (phosphates). Fertilizer gel beads (ca. 3 mm diameter) were made from the same moles of CaHPO_4 and α-cyclodextrin (CD)(abbreviated as α gel : 3 kinds of 4, 40, and 84 mM), or CaHPO_4 only without α-CD (abbreviated as 4, 40, and 84 mM P gel), by co-use of 4 percent of G-type alginate solution as the material to make the gel beads themselves.After these gel beads were bathed with water and stored in incubators at several temperatures (10, 20, 25, and 30 ℃) and at several intervals, the quantities of phosphate ions released in water were measured. Phosphate ions from 4 mM gel were released within ca. 2 months at 10 and 20 ℃ and within ca. 1 month at 25 and 30 ℃. On the other hand, 40 and 84 mM P gels continued to release phosphate ions ascending through out the experimental periods of 90 days, and 40 and 84 mM α gels continued to release phosphate ions showing a peak after the 20th day. Total phos … More phate released ions of every gel reached its peak at 25 and 30 ℃ among the four temperatures.To investigate the mechanism of release, NMR of 4 mM gel was measured by means of a surface probe method, the results showing that water had a longer relaxation time (T_2) of ^1H of water contained in α gel than it did in P gel. These results suggest that the water of α gel existed in a freer not-associative state than it did in P gel and thus dissolved and released phosphate ions more easily than did P gel.Potting cultivation tests using 40 mM gels were performed over a period of 40 or 45 days using 1/10000 a. pots and Brassica campestris (Komatsuna in Japanese). During the vernal summer term, the yields of 60% field capacity pots were higher than those of 40% field capacity pots. As well, the harvest yields at the 40th day of 60% α gel pots exceeded those of P gel pots, with their phosphorus utilization rate reaching a maximum of 40 %. In the autumn/ winter term, the yields of the 60% pots at the 45th day were more than 10 times those of the 35% pots, but the yields were half in comparison to those of the vernal summer term. Further, the phosphorus utilization rate of 60% P gel pots was only a maximum of 8 percent.For the field cultivation test, four ridges were prepared for α gel, P gel, chemical fertilizer, and the blank without phosphate, respectively (N : P_2O_5 : K = 16 : 15 : 16 Kg/10 a.). The soil was mixed at a 15 cm width and 20 cm depth. After a growing period of 60 days in the autumn/winter term, dry weights of Brassica campestris for every ridge were weighed, showing lighter yields in the order of P gel, α gel, chemical fertilizer, and the blank ridge. The dry weights from the P gel ridge and the α gel ridge became 1.76 and 1.66 times that of the chemical fertilizer ridge, respectively.The above results showed that α gel was more effective with an adequate amount of water and with a high temperature, though P gel was more effective with a low amount of water and with a low temperature. Less