SITE-SPECIFIC NUTRIENT MANAGEMENT (SSNM)

Initial Concept of SSNM

The concept of SSNM for rice was developed in the mid-1990s and then evaluated from 1997 to 2000 in about 200 irrigated rice farms at eight sites in six Asian countries. SSNM aimed at dynamic field-specific management of N, P, and K fertilizers to optimize the supply and crop demand for nutrients. The crop’s need for fertilizer N, P, or K was determined from the gap between the crop demand for sufficient nutrient to achieve a yield target and the nutrient supply from indigenous sources. A modification of the QUEFTS model (Janssen et al. 1990) was used to predict the amount of fertilizer N, P, and K required for a specific yield target as follows:

1. Establish a yield target for average climatic conditions.

   • This yield target could be based either on a percentage (for example 70–80%) of the potential yield estimated with a crop growth model or on yields currently achievable by farmers practicing good crop management.

2. Estimate crop demand for N, P, and K for a target yield.

   • Based on a large database of modern rice varieties with harvest indices of 0.45 to 0.55, the balanced plant nutrient requirement to produce a metric ton (1,000 kg) of unmilled rice was estimated as 15 kg N, 2.6 kg P (6 kg P₂O₅), and 15 kg K (18 kg K₂O) for the linear portion of the relationship between grain yield and nutrient accumulation in the mature crop.

3. Estimate field-specific indigenous supply of N, P, and K.

   • The indigenous supply is the cumulative crop uptake of a nutrient from all sources other than fertilizer (that includes soil, crop residues, manures, irrigation water, rainfall, and atmospheric deposition). It is determined by the nutrient omission plot technique, whereby the indigenous supply of a nutrient is estimated by its accumulation in a crop not fertilized with the nutrient of interest but fertilized with sufficient amounts of other nutrients to ensure they do not limit yield. Indigenous K supply, for example, is determined in a K omission plot receiving no K fertilizer but sufficient N and P to ensure they do not limit yield.

4. Establish recovery efficiencies for fertilizer N, P, and K.

   • Crop recovery efficiencies of 0.4 to 0.6 kg ^kg−1 for fertilizer N, 0.2 to 0.3 kg ^kg−1 for fertilizer P, and 0.4 to 0.5 kg ^kg−1 for fertilizer K were used as targets.

5.  Estimate optimal N, P, and K fertilizer rates.

   • The estimated crop demand for N, P, and K to optimally achieve the yield target; the estimated indigenous supply of N, P, and K; and targeted recovery efficiencies for fertilizer N, P, and K were used to determine optimized fertilizer N, P, and K rates for filling the gap between crop demand for a yield target and indigenous supply. 

    

The achievements in the initial conceptualization and development of SSNM before 2001 are documented in a book by Dobermann et al. (2004).

Evolution of SSNM (2001 to present)

From 2001 to 2004, the Reaching Toward Optimal Productivity (RTOP) workgroup of the Irrigated Rice Research Consortium (IRRC) collaborated with national agriculture research and extension systems in eight Asian countries to systematically transform the initial SSNM concept into an inclusive, simplified framework for the dynamic plant-need-based management of N, P, and K. The SSNM approach now enables:

·         Dynamic adjustments in fertilizer N, P, and K management to accommodate field- and season-specific conditions.

·         Effective use of indigenous nutrients.

·         Efficient fertilizer N management through the use of the leaf color chart (LCC), which helps ensure that N is applied at the time and in the amount needed by the rice crop.

·         Use of the nutrient omission plot technique to determine the requirements for P and K fertilizers.

·         Use of micronutrients based on local recommendations.

References

Janssen BH, Guiking FCT, van der Eijk D, Smaling EMA, Wolf J, van Reuler H. 1990. A system for quantitative evaluation of the fertility of tropical soils (QUEFTS). Geoderma 46: 299-318.

Dobermann A, Witt C, Dawe D (eds). 2004. Increasing the 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).

Site Specific Nutrient Management