SUMMARY
Nitrogen (N) and potassium (K) are macronutrients that plants need for better growth and yield, but which are readily lost from the soil through volatilization, denitrification, and leaching, aside from being absorbed by plant roots. At the same time, when they are present in the soil in too large quantities, they may cause some detrimental effects on the plants themseves. Thus, to maximize the beneficial effects of N and K fertilization, the formulation and application of a Controled Release Fertilizer (CRF) may be carried out. Hence, this study aimed to describe the release pattern of ammonium nitrogen (NH4-N) and nitrate nitrogen (NO3-N), as well as K from CRF through laboratory incubation method. Two types of CRF - CRF A (16-16-16) and CRF B (30-6-8), with a non-CRF (Mutiara NPK16-16-16) as Control – were used. Each fertilizer was tested at doses corresponding to 600 and 1200 kg/ha. The results showed that the rate of release of NH4-N decreased with incubation time; on the other hand, the release rate of NO3-N and potassium increased, respectively. Initially, the NH4-N release was very high at 40 – 60%, but proceeded to decline to almost 0% after 14 weeks. In comparison, the NO3-N release rate was 17 – 40% during the first week followed by steady increase up to nearly 100% by the 14th week of incubation. Potassium release ranged from 20 to 30% in the first week, then rose to 30 – 70% at Week 14. Overall, CRF (30-6-8) at a dose of 1200 kg/ha showed the slowest rate of nitrogen release.