Soil fertility evaluation and improvement for sustained high corn yields in major corn growing areas

This investigation helps address the national concern on low corn production due to poor crop nourishment and the perennial corn importation due to insufficient production to meet local demands and buffer stocks. The conclusions and recommendations are as follows: 1) On an alluvial silt loam with a very low OM (0.35%) at Enrile, Cagayan, 145 kg N/ha is needed for optimum yield. The P2O5 and K2O requirements are (kg/ha): 110 and 67, respectively. This silt loam also needs one kg/ha each of Zn and Cu; 2) On Adtuyon clay at Impasugong, Bukidnon, the hybrid corn did not respond to N fertilization rates of 0-180 kg/ha since the OM content was 4.0% and the total N was 0.18%. There is no N recommendation for this particular site. To support optimum yield 48 kg PsO5 and 92 kg K2O/ha are needed since the soil is slightly acidic. One kilogram Cu/ha is also recommended. 3) The extremely acidic soil at Benito Soliven, Isabela requires 3.6 tons CaCo3/ha to attain the optimum pH and suitable nutrient solubility. The nutrient yield of corn producing 9.81 tons/ha are as follows (kg/ha): 202 N, 38 P, 151 K, 38 Mg, 26 Ca, 05 Zn, and 0.1 Cu. These amounts should be used as basis for developing treatments for maximum yield research. The nutrients contained in the grains only are (kg/ha): 104 N, 22 P, 25 K, 14 Mg, 9 Ca, 0.3 Zn and 0.03 Cu. For plant fertilization and fertility maintenance purposes in high yield production, these are important considerations, 5) Spatial variability existed for pH, OM, P, K, Zn, Cu and B. In ten towns of Cagayan inclusive of the soil types present, the number of test classes ranged as follows: 1-3 pH and OM, 1-4 P and K, and 1-3 Zn and Cu. In eight towns of Isabela inclusive of the soil types, the number of test classes for the fertility components are: 1-4 pH, 2 OM, 1-4 P and K, 1-3 Zn, 1-4 Cu and 1-3 B. Spatial variation in six towns of Bukidnon is evidenced by the following range of test classes: pH 1-3, OM 1-3, P and K 1-3, Zn 2-3, Cu 1-3 and B 1-2. For Misamis Oriental, the number of test classes in four towns are: pH 1-4, OM 2-4, P 3-4, K and Zn 2-3, and B 1-2. The numbers of test classes in wide areas of the provinces provide strong justification to adjust fertilizer and lime recommendations according to the class or test value. This is simply site-specific fertilization and liming or variable-rate fertilization and liming. The frequency of occurrence of a test class reflects also the extent of occurrence of spatial variability of a constraint in a wide area. The range of the frequency of occurrence extent of the test classes in four provinces are as follows: Cagayan 16.2-98.0%, Isabela 31.0-97.0%, Bukidnon 9.1-98.0%, and Misamis Oriental 38.5-5.90%. The spatial distribution map of the test values and corresponding interpolated maps for pH, OM, PK, Zn, Cu and B are presented in seventy three figures for the four provinces. The maps provide clearer dimension and perspective of the soil test categories in different farms of the four provinces. The site-specific recommendaitons for N, P2O5, K2O, Zn, Cu, B and lime for 144 farms in Cagayan, Isabela, Bukidnon and Misamis Oriental are presented. The total number of recommendations given for each nutritional constraint is as follows: 144 N, 107 P2O5, 52 K2O, 71 Zn, 50 Cu, 79 B and 46 CaCO3. Clearly, not all of the sites require P, K, Zn, Cu, B and lime.