Author : Raymundo, Reynaldo L.

Summary : A field experiment was conducted to determine the response to increasing levels of NPK fertilizer of corn grown in three major soil series in Isabela Province, north Philippines. The soil series were San Manuel, Ilagan and Cauayan, which were respectively found in the towns of Gamu, Benito Soliven, and Jones. In each site, 13 levels of NPK fertilizer treatments were used: 0-0-0, 30-30-30, 60-60-60, 90-90-90-, 120-120-120, 60-30-30, 90-60-60, 120-90-90, 90-30-30, 120-60-60, 90-0-0, 90-60-0, and 90-60-60+B kg/ha. The corn crops responded significantly to 30-30-30 NPK kg/ha in Benito Soliven and Jones and to 90-60-60 NPK kg/ha in Gamu. Grain yields increased from 1.55 to 4.79 t/ha in Benito Soliven, 2.90 to 5.10 t/ha in Jones, and 0.41 to 2.50 t/ha in Gamu. Likewise, NPK uptake of grains in the treated corn crops was six times than that of the control in Gamu, three times more than that of the control crop in Benito Soliven, and double that of the control in Jones. Optimum concentration on mineral nutrients in the plant tissue, however, was not obtained. The mineral nutrient uptake of corn in the three sites (53,333 plants/ha) indicated that in Gamu, a yield of 2.50 t/ha required a nutrient uptake of 38 kg N, 6.39 kg P, 14.20 kg K, 0.107 kg Ca, and 2.15 kg Mg. In Benito Soliven, a yield of 4.79 t/ha required 37.49 kg N, 6.92 kg P, 14.59, 14,59 kg K, 0.06 kg Ca, and 2.37 kg Mg. In Jones, the requirement for a yield level of 5.10 t/ha was 59.80 N, 8.47 kg P, 20.22 kg K, 0.14 kg Ca, and 4.06 kg Mg. Application of 90 N kg/ha increased the corn's demand for P and K. However, higher rates of N rendered the plants susceptible to lodging. A survey of 22 corn farmers was conducted to determine their perception of fertilizer technology and the factors affecting its adoption or rejection. The farmers cultivated an average farm size of 3.45 ha; majority of them were share-tenants. They had always obtained credit from non-formal sources. Majority of them felt that the government should improve its services.