Indicative spatial soil fertility mapping of land management units (LMU's) for rice using quantum GIS[Geographical Information Systems in the Philippines]

The application of fertilizers is one important intervention in raising crop yield such as in rice. Generally, soil test and/or plant tissue analyses are used as basis to determine appropriate rate of fertilizer to apply on individual crop. Unfortunately, data on soil analysis especially at the Land Management Unit (LMU) level are unavailable. If ever they are obtainable, many farmers do not know how to use soil and/or tissue test results. Indicator-based mapping can generate maps that can be made easy for both ordinary farmer and technicians to use. The Geographic Information System (GIS) is one valuable tool that can help generate databases of soil properties at the same time present the spatial data into simple maps. The study utilizes Free and Open Source Software for Geomatics (FOSS4G) tools such as Quantum GIS and Open Office to develop soil databases and LMU-based indicative spatial soil fertility maps. The study utilized soil survey reports to gather basic soil information. Meanwhile, provincial production data were obtained from the Bureau of Agricultural Statistics to match rice performance record with soil data. Random key informant interviews were conducted to gather additional data (e.g. farmer profiles, rice varieties, and yield). In order to update soil information, soil samples were collected from each representative LMUs which were qualitatively analyzed for NPK and salinity level using the ASC-UPLB [Agricultural Science Cluster-University of the Philippines Los Banos, College, Laguna, Philippines] Soil Test Kit (STK). Nutrient Manager (NM) was utilized to find out what and how much fertilizer must be added for rice varieties planted in the sample farms. Overall, the LMU's with clayey soil texture has high potential to supply essential nutrients to rice crop as indicated by the 24 cmol/kg CEC values and the medium base saturation ( 20%) level. However, it was noted that several farms have very low (1-2%) organic carbon. This means N is generally limiting in most rice fields included in the study and therefore would require regular application of N fertilizer in order to maintain high and sustainable yield level. Further, the observed variability of fertilizer recommendations based on NM for different rice variety and under different LMUs would suggest that blanket fertilizer recommendations are not advisable to improve rice yield. It will not also help increase fertilizer use efficiency.