First results from on-farm studies in seven regions indicate significant opportunities to increase maize production in the Philippines. Farmer fertilizer use was insufficient to achieve high, profitable yield. Attainable yield in farmer’ fields with ample supply of fertilizer N, P, and K was 2.4 t/ha or 41% greater than with farmer fertilizer practice (FFP) (8.3 vs. 5.9 t/ha).

The contribution of fertilizer N, P, and K to these significant yield increases were separately estimated using the omission plot technique. This information on nutrient related yield gaps was crucial in improving a preliminary Site Specific Nutrient Management (SSNM) strategy, developed using previously available information that included soil test results, which provided a limited yield advantage of only about 1 t/ha compared to the farmer practice. Using the newly available information on nutrient related yield gaps, the SSNM strategy was revised for evaluation in the next maize cropping season to fully exploit attainable yield while making efficient use of applied fertilizers. This also includes the use of the leaf color chart (LCC), originally developed for rice, as a diagnostic tool to detect N deficiencies in maize.