The Nutrient Decision Support System (NuDSS) for irrigated rice is part of an initiative by the Irrigated Rice Research Consortium (IRRC) to provide decision support on Site-Specific Nutrient Management (SSNM) in the irrigated lowlands (Witt et al., 2005). The content of the software is consistent with earlier publications on SSNM including a handbook and practical guide. The NuDSS software adds value to these materials by combining various models into one user-friendly software package to assist in the development of improved fertilizer strategies for effective fertilizer use, high and sustainable yields, and increased farmers' profit.

The software was developed recognizing the need for decision aids providing assistance in complex mathematical calculations (e.g., though optimization routines) that would be difficult to perform otherwise.

NuDSS is a generic decision support system for irrigated rice capturing the most important cropping conditions in tropical and sub-tropical Asia. The underlying principles of plant nutrition are valid for all modern, high-yielding rice varieties with a harvest index of about 0.50 kg kg^-1. Crop- and site-specific conditions are specified in a general settings menu, including guidelines for local adaptation when conditions divert from the standard situations.

Decision framework

Based on the general framework for decision support depicted in Fig. 1, the development of improved fertilizer recommendations may include six major steps with the following outputs:

1. Estimate recommendation domains and indigenous nutrient supplies. Larger areas are divided into smaller agro-ecological recommendation domains. Domain sizes determine the required number of nutrient omission plots that are used to obtain average N, P and K limited yields (estimates of indigenous nutrient supplies) valid for the domain (Dobermann et al., 2003a; Dobermann et al., 2003b).

2. Select a yield target. Season-specific yield targets are set to be about 10% greater than currently achieved in farmers' fields but not more than 80-85% of the yield potential (Witt et al., 2002).

3. Calculate fertilizer nutrient requirements. Total fertilizer N, P and K requirements are calculated based on expected fertilizer nutrient requirements of 40-50 kg N, 20 kg P₂O₅, and 30 kg K₂O per ton of required yield increase. Requirements for P and K are adjusted using an input-output balance to prevent soil nutrient depletion due to nutrient removal with grain and straw (Witt et al., 2002; Witt and Dobermann, 2004).

4. Select meaningful fertilizer material. Fertilizer rates of elemental nutrients (kg ha^-1) are expressed in nutrient sources per local area unit to facilitate wider-scale promotion.

5. Obtain profit estimate.The existing practice is compared with the newly developed alternative nutrient management strategy to obtain an estimate of the expected profit increase (ex-ante analysis). Fertilizer strategies are adjusted depending on the outcome of the economic analysis (Witt and Dobermann, 2004).

6. Simple guidelines and strategies for promotion. Where farmers' fertilizer use is inadequate, it may be most effective and economic to develop, evaluate and locally adapt improved fertilizer recommendations through farmer participation and then promote new guidelines in suitably large areas, including guidelines for further adjustments (Buresh et al., 2005). The NuDSS software aims to facilitate this process.

Software, tutorial, and background information on the principles of SSNM can be downloaded at the websites of PPI/PPIC-IPI (www.seap.sg) and IRRI (www.irri.org/science/software).

References
Buresh, R.J., Witt, C., Ramanathan, S., Mishra, B., Chandrasekaran, B. and R. Rajendran. 2005. Site-specific nutrient management: Managing N, P, and K for rice. Fert. News. 50(3):25-28; 31-37.

Dobermann, A., Witt, C., Abdulrachman, S., Gines, H.C., Nagarajan, R., Son, T.T., Tan, P.S., Wang, G.H., Chien, N.V., Thoa, V.T.K., Phung, C.V., Stalin, P., Muthukrishnan, P., Ravi, V., Babu, M., Simbahan, G.C. and M.A. Adviento. 2003a. Soil fertility and indigenous nutrient supply in irrigated rice domains of Asia. Agron.J. 95:913-923.

Dobermann, A., Witt, C., Abdulrachman, S., Gines, H.C., Nagarajan, R., Son, T.T., Tan, P.S., Wang, G.H., Chien, N.V., Thoa, V.T.K., Phung, C.V., Stalin, P., Muthukrishnan, P., Ravi, V., Babu, M., Simbahan, G.C., Adviento, M.A. and V. Bartolome. 2003b. Estimating indigenous nutrient supplies for site-specific nutrient management in irrigated rice. Agron.J. 95:924-935.

Witt, C., Balasubramanian, V., Dobermann, A and R.J. Buresh. 2002. Nutrient management. In: Fairhurst, T.H. and C. Witt (eds.). Rice: a practical guide for nutrient management. Singapore and Los Baños: Potash and Phosphate Institute & Potash and Phosphate Institute of Canada and International Rice Research Institute. p 1-45.

Witt, C. and A. Dobermann, A. 2004. Towards a decision support system for site-specific nutrient management. In: Dobermann A, Witt C, Dawe D, editors. Increasing productivity of intensive rice systems through site-specific nutrient management. Enfield, NH (USA) and Los Baños (Philippines): Science Publishers, Inc., and International Rice Research Institute (IRRI).

Witt, C., Fairhurst, T.H., Sheehy, J.E., Dobermann, A. and A. Gfroerer-Kerstan. 2005. A nutrient decision support system software for irrigated rice. Better Crops. 4:26-28.