Suwardi 1 and Itsuo Goto 2
1Department of Soil Science,
Jl. Raya Pajajaran
2 Department of Agricultural Chemistry,
Sakuragaoka 1-1-1, Setagaya-ku,
Nitrogen (N) is the most important nutrient element and the key to increase rice production. However, the efficiency of this nutrient is very low due to ammonia volatilization and denitrification. Efforts to minimize the loss of ammonia from N fertilizers have been conducted including by addition of slow-release agents. Among these materials, zeolites were possibly used in large scale as slow-release agents because of their capability to capture ammonium ion (NH4+) and availability in abandon amount as natural resources. Pot experiments were conducted in green house to evaluate the optimum ratio of N fertilizers and zeolites, the effect of different sorts of N fertilizers, and pelletizing on yield of rice.
The results showed that addition of zeolites DAP in the ratio of 1:5 increased slightly the grain weight of rice and the increasing yield become 17% when the mixture was pelletized. In urea, the optimum yield was obtained in the ratio of urea and zeolites in 1:10. When the mixture was pelletized, the optimum yield was obtained in the ratio of 1:5. Compared to without zeolites, the increasing grain weight in the soil applied by pelletized zeolite and urea was 20%. Increasing grain weight was due to the increasing panicle number. The mechanism of increasing N fertilizer efficiency might as follows. When the concentration of NO3-N in the soil solution decrease, NH4-N absorbed by zeolites is released to the soil solution. The addition of too much zeolites on the contrary, decreases N availability because of the strong retain of N on zeolites.