Effects of Temperature and Soil Type on N Release and Nitrification during the Incubation of Slow Release Fertilizers.

Abstract A soil incubation was conducted to evaluate the effects of soil temperature and soil type on the degradation (mineralization) rate of a slow release N fertilizer (Urea Form, a condensation product of urea and formaldehyde) and nitrification of release N. Four types of ureaform selected for the incubation experiments were: Nitamin 30L (liquid) (L30), Nitamin RUAG 521G30(liquid) (G30), Nitamin 42G (granular) (N42) and Nitroform (granular) (NF).The two soils used were a sandy soil and a loam soil. Four fertilizers were incubated in sand soil with 3 temperatures (20, 25 and 30 0C) and in loam soil with one temperature (25 0C). Differential N release kinetics of the N sources was determined by measuring ammonium-N and nitrate-N continents during the incubation period of 78 days. Net N released, as percentage of organic N in the fertilizer (net N %), was significantly affected by N sources, incubation temperature, incubation time and soil types. Increasing temperature increased net N release. In the sand soil, the net N% in N42 was 85% at 35d in 20 0C, 90% at 35d in 25 0C and 94% at 21d in 30 0C respectively; the net N% in L30 was 67% at 63d in 20 0C, 82% at 63d at 25 0C and 87% at 49d at 30 0C respectively; the net N% in G30 was 88% at 78d in 200C, 102% at 49d in 250C and 93% at 35d in 30 0C respectively and the net N% in NF at 78d was 16% in 20 0C, 24% in 25 0C and 28 in 30 0C respectively. The N release rate in sand soil was N42> G30>L30>NF. The release rates from fertilizers were enhanced in loam soil. The net N% in N42, L30 and G30 at 25 0C in loam soil was over 61% in first 4d and over 95% at 49d. The net N% at 25 0C in loam soil was 97% in N42 at 35d, 102% in L30 at 49d, 99% in G30 at 28d and 25% in NF at 63d, the release rate in loam soil was G30>N42 >L30>NF. Nitrification in sand soil was very low and very high in loam soil at 25 0C, a high concentration of NO3-N accumulated in the loam soil after SRFs application may be a concern for Nitrate leaching.