Mineralization of Urea-Formaldehyde Fertilizer and Its Availability to Oil Palm Seedling under the Tropical Environment

Easily dissolved fertilizers release nutrient in excess amount to be assimilated by plant roots. Some portions these fertilizers leach out from the root zone and adversely impact the environment. Controlled-release fertilizers are more favorable to reduce fertilizer loss, labor cost, and environmental impact. Urea-formaldehyde (UF) was synthesized by polymerization of urea and 40% formaldehyde solution using H3PO4 as a catalyst. Three mole ratios of urea:formaldehyde, namely, 1.0:1.0, 1.5:1.0 and 2.0:1.0 were synthesized. Mineralization of the UF was conducted using eight different mixtures, four different moisture, and four incubation periods. The experiment included soil alone, soil with compost, soil with UF (1.0:1.0), soil with UF (1.5:1.0), soil with UF (2.0:1.0), soil with UF (1.0:1.0) and compost, soil with UF (1.5:1.0) and compost, and soil with UF (2.0:1.0) and compost. Moisture of the mixtures was adjusted to 20%, 40% 60% and 80% water holding capacity (WHC) of the soil. The mixtures were incubated at room temperature for 1, 2, 4 and 8 weeks, the released NH4+ and NO3- were extracted by 1 M KCl and analyzed via a distillation method. Rates of mineralization increased with mole ratio of urea and moisture content of the soil. N loss increased with the moisture content. The best performance for the compromised condition was a mole ratio less than 1.5:1.0 (urea:formaldehyde) at 60% WHC. Availability of UF and serpentine-phosphate for oil palm seedlings was conducted using 10 treatments. The experiment consisted of soil without amendment; soil with Multicote; soil with cow manure; soil with cow manure and urea; soil with cow manure and UF (1.0:1.0); soil with cow manure and UF (1.5:1.0); soil with cow manure, MgHPO4 and UF (1.0:1.0); soil with cow manure, MgHPO4 and UF (1.5:1.0); soil with cow manure, serpentine-phosphate and UF (1.0:1.0); and soil with cow manure, serpentine-phosphate and UF (1.5:1.0). All amended soils increased vegetative growth of oil palm seedlings compared with the non-amended soils. Urea and UF increased the N content in seedling leaves, while Multicote, cow manure, MgHPO4, and serpentine-phosphate increased the Mg content. The best performance was found in the combination of cow manure, serpentine-phosphate and the UF with mole ratio of 1.0:1.0.