Response of coconuts grown on three soils of Leyte, Philippines to organic and inorganic sources of nitrogen

Results of the study showed that the bearing percentage, nut per tree, copra per nut, and copra yield were significantly higher in plots applied with inorganic than organic N fertilizers. Neither the application of ipil-ipil herbage nor the planting of Kudzu mixed with calopogonium as source of organic nitrogen fertilizer plus 2 kg KCl per palm per year was totally able to replace the inorganic N levels used in the study. However, an increase of 132 percent-152 percent and 26 percent-36 percent in copra yield per hectare per year was observed in the unfertilized treatment and in those applied with only 2 kg KCl per palm per year, respectively. The application of 2 kg ammonium sulfate per palm per year gave the most number of harvested nuts and corresponding copra yields, although it is not statistically different from other levels of inorganic sources such as 1.5 kg ammonium sulfate or 0.66 kg urea per palm per year. Treatment effect was observed starting 2 yr after treatment implementation. Copra yield being higher in Maasin clay was statistically comparable to either Mandaue clay or Palo clay loam. Coconut leaf N significantly increased in plots planted with kudzu mixed with calopogonium in addition to 2 kg KCl per palm per year compared to ipil-ipil organic N source. However, the result was comparable to other levels of inorganic N fertilizer. Unfertilized palms and those applied only with 2 kg KCl obtained the highest leaf K value. Phosphorus, calcium, and magnesium were not influenced by the different sources of N fertilizers. Coefficients of correlation between leaf nutrient levels and copra production apparently responded only to N and K. Although leaf K in all soil types was above the critical level, KCl application as source of K fertilizer possibly increased the leaf chlorine (C1) content which was initially below the desired level as shown in the leaf analysis