Many countries in Asia have started replacing blanket fertilizer recommendations for vast areas of rice, maize, or wheat with more site-specific guidelines adapted to local needs. This process has been accompanied with a shift from traditional on-station research to on-farm development and evaluation of novel practices. A key challenge faced by the local extension agencies remains the complex nature of factors influencing nutrient requirements.  To aid in this process, the International Plant Nutrition Institute has developed Nutrient Expert (NE), a nutrient decision support software, which uses the principles of site-specific nutrient management (SSNM). NE enables crop advisors to develop fertilizer recommendations that are tailored to a specific field or growing environment. NE takes into account important factors affecting nutrient management recommendations and uses a systematic approach of capturing information to develop location-specific recommendations. Nutrient Expert does not require a lot of data nor very detailed information as in the case of many sophisticated nutrient decision support tools, which can overwhelm the user. Nutrient Expert allows the users to draw the required information from their own experience, the farmers’ knowledge of the local region, and the farmers’ practices. NE can use experimental data, but it can also estimate the required SSNM parameters using existing site information.

 

NE provides fertilizer recommendations that are based on the relationship between the balanced uptake of nutrients at harvest and grain yield, called internal nutrient efficiency, which are predicted using the quantitative evaluation of the fertility of tropical soils (QUEFTS) model. The fertilizer requirement for a field or location is estimated from the expected yield response to each fertilizer nutrient, which is the difference between the attainable yield and the nutrient-limited yield. These parameters are determined from nutrient omission trials in farmers’ fields, while attainable yield is the yield for typical year at a location using best management practices without nutrient limitation. Nutrient-limited yield is that when only the nutrient of interest is omitted. The amount of nutrients taken up by a crop is directly related to its yield so that the attainable yield indicates the total nutrient requirement and the nutrient-limited yield indicates the indigenous nutrient supply. The yield response indicates the nutrient deficit, which must be supplied by fertilizers.

 

As a computer-based decision support tool, NE combines all the steps and guidelines in SSNM into simple software tailored for crop advisors especially the not-so-technical users such as the extension agents in developing countries. In such countries, many crop advisors from both public and private companies do not have the data nor facilities needed to run sophisticated models. The parameters needed in SSNM are usually measured in nutrient omission trials installed in farmers’ fields, which require at least one crop season. With NE, parameters can be estimated using proxy information, which allows crop advisors to develop fertilizer guidelines for a location without data from field trials.