Oleh: Suwardi (2000)
Increasing population in the world need to produce greater amounts of foods and fibers through development of appropriate technologies including improvement of soil fertility and land-use strategies resulting in permanent and sustainable agricultural production. Various efforts have been initiated to solve the problems in food and fiber production and these have met with varying degree of success. Many program have been directed to solve the problem of production through crop improvement, fertilizer management maintenance of soil fertility under conditions of low external inputs to maintain and improve the soil fertility, especially to increase the efficiency of fertilizers, various approaches have been used, including alternative methods of fertilizer application (Mengel et al., 1982; Touchton and Hargrove, 1982), fertilizers technology, such as coating urea granule (Prasad, 1976; Vlek and Craswell, 1979), and improvement of soil pH by liming it concluded that fertilizer alone or even in conjunction with improving crop varieties and pest and disease control, will not preserve productivity if significant soil chemical and physical properties were not improved.
It is well known that among the nutrient elements often with the great effect on crop production, nitrogen (N) is the most important besides phosphorus (P) and potassium (K). Unfortunately, N is not efficient because only 20 to 40% of the applied N is absorbed by rice crop (Vlek and Byners 1986). Fenn and Kissel (1973) reported that under laboratory condition more than 5% of applied N was loss in 100 hours following the surface application of 550 kg N ha-1 as NH4F and (NH4)2 HPO4 (diammonium hydrogen phosphate=DAP). Ammonia volatilization and denitrification are two major mechanisms of lowering efficiency of fertilizer by N loss in the field even when leaching and runoff are eliminated (Keeney and Sahrawat 1986; Dedatta and Buresh, 1989). The N loss through volatilization and denitrification increases when higher rate of N is applied to the field.
The formulation of slow release fertilizer has been developed since the last decades (Hauke 1972). These slow release fertilizers release N over long period of time, which reduce the susceptibility to excessive losses at any given time. Savant, Clemmons, and James (1982) used sulfur, waxes, and cement for coated urea as slow release fertilizer. Savant and James (1985) used resin-coated urea and Kochba ,Gambash, and Avnimelech (1990) used KNO3-coated for the same purposes. Mixing urea with various organic chemical has shown to reduce of ammonia volatilization. By using the above materials, the efficiency of N fertilizers was in increased.
Zeolites with unique cation-exchange properties, molecular sieving and adsorption make these minerals attractive to the agricultural utilization including for slow release fertilizer (Barbarick and Pirela ,1984; Lewis, et al., 1984; Pirela, et al., 1984; Weber, et al., 1983). Among the materials of slow release fertilizer, zeolites were possibly used in large scale because of the their capability to capture ammonium ion (NH4+) and availability in abandon amount as natural resources. Addition of zeolites to N fertilizers possibly reduce the release of N to soil solution so that the leaching and volatilization can be reduced. Natural zeolites may well play an important role in achieving these goals.