Maize is the most important crop in upland areas in the Philippines, but production lags behind potential in many areas, especially those with acid soils. The Nutrient Management Support System (NuMaSS), a computer-based decision aid, provides soil and crop-based recommendations for nutrient amendments and lime. Development and trials of the NuMaSS were carried out on upland maize farms in Isabela province in the northern Philippines from 1998 to 2006. While local practices and standardized government recommendations had included applying N, P, and K, the application of lime to correct soil acidity had not been practiced locally and lime was not commercially available in local markets. Based on data from 39 field trials on 13 different farms over four years, we calculate that liming increased maize grain yield on the average by 1.5Â t/ha. A farmer purchasing and applying lime would realize a single-season marginal rate of return on investment of about 160%. Because of the positive results of the on-farm trials of the NuMaSS, and in particular the positive result of liming acid soils, the Philippine Department of Agriculture began a lime promotion program in four provinces in Region II in 2006. The program includes field days, farm-level demonstrations, and distribution of subsidized lime to farmer-cooperators. We estimate the economic value of the NuMaSS and lime promotion program to have an NPV of $8 million or an IRR of 25%. We base our calculations on the costs for the research program itself, the costs of the extension program, the costs of the subsidized inputs for the first four years, and the benefits of improved maize production over a 40Â year horizon over 12,000Â ha (out of a potential 90,000Â ha of acid soils in maize production). Our calculations show that the NPV of the lime promotion increases with increasing adoption but the program has a positive NPV even if adoption is negligible after the initial promotional program ceases. Our results document the adoption and farm level and regional economic impact of a decision aid. As agriculture in the Philippines and other developing countries expands with increasing food prices and other demands such as bioenergy production, farmers will need better decision tools such as the NuMaSS to manage crop production on problem soils and marginal sites.