In 2004, the Southeast Asia Program of IPNI and IPI launched a new maize project on site-specific nutrient management (SSNM) for maize in Southeast Asia. The key objective was to assess opportunities and provide maize farmers with management options for increasing productivity and profitability. The identification of major production constraints in key maize growing areas and the development of tools to overcome those constraints using scientific principles and site-specific approaches are the main focus of this project. Improved crop and nutrient management strategies have been developed, evaluated, and refined and their delivery facilitated in partnership with national agricultural research and extension systems in the region.

Development and evaluation of SSNM in 2004-2007

The principles of SSNM for maize were developed through a series of researcher managed on-farm and on-station experiments covering a wide range of bio-physical and socio-economic conditions. On-farm trials were conducted for at least two seasons to estimate yield responses to the application of fertilizer N, P, and K and associated agronomic efficiencies (AE, kg grain per kg fertilizer nutrient applied). Additional on-station experiments were conducted by researchers of the Cereals Research Institute in Maros, Indonesia, to develop real-time N management strategies using a 4-panel leaf color chart (LCC) that was originally developed for rice (Witt et al., 2004; Witt et al., 2005) and to investigate the interaction of planting densities and N management. The principles of SSNM were frequently updated as more experimental data became available and used to develop site-specific fertilizer recommendations for evaluation at project sites.

In the first year, a total of 120 on-farm experiments were set up in farmers' fields at 19 key maize growing sites in Indonesia, the Philippines, and Vietnam. Experimental treatments established in the on-farm trials included nutrient omission plots (-N, -P, and -K) to estimate nutrient-limited yield, a fully-fertilized treatment with ample application of fertilizer N, P and K to estimate attainable yield, and a farmer's fertilizer practice (FFP) to obtain the actual yield in farmers fields' as benchmark for comparison. Improved crop management (iCM) treatments were established at all sites but varied from site to site, depending on expected constraints to improving yield in farmers' fields. These treatments included manure application, lime application, or increased planting density (iPD). Varieties grown always included farmer-selected hybrids and, in some cases, open-pollinated varieties (OPV).

Fig. 1 provides an overview of yield responses to fertilizer application across sites in Indonesia, the Philippines, and Vietnam. In general, yield responses followed the order N >> P > K. In 75% of the cases, average yield responses to fertilizer N were <6 mt/ha in Indonesia, <4 mt/ha in the Philippines, and <5 mt/ ha in Vietnam. Yield responses for fertilizer P and K were commonly in the range of 1 mt/ha. The measured yield responses to fertilizer application were used to calculate the site-specific fertilizer N, P, and K requirements to achieve optimal yields. Fertilizer P and K rates were further adjusted to avoid soil nutrient depletion.

As shown in Fig. 2, SSNM improved yield by about 1 mt/ha compared with the farmers' fertilizer practice (FFP) in each country and across all sites, but the full yield advantage with SSNM could often only be achieved once other constraints to yield improvement were addressed (SSNM+iCM and SSNM+iPD). One such constraint in Indonesia and Vietnam was low planting density.

The agronomic and economic performance of SSNM was evaluated in detail at all project sites as shown in the example for Indonesia in Table 1. In 2005/06 and across all sites except for drought prone sites in South Sulawesi, attainable yields ranged from 7 to 11 mt/ha with ample NPK supply, available hybrid cultivars, and current farmers' management practices (data not shown). Yield responses followed the order N >> P = K with yield responses of 3 to 5 mt/ha to fertilizer N, 1 to 1.5 mt/ha to fertilizer P, and 0.5 to 1.5 mt/ha to fertilizer K application. Table 1 shows that significantly greater yield (+17%) and net benefit (+19%) were achieved with SSNM compared to farmers' practice despite larger investments in seeds (+10%) and fertilizer (+6%). Note that fertilizer P and particularly K was increased with SSNM at the expense of fertilizer N. Adjustments in fertilizer N, P, and K rates and better timing of fertilizer N applications were the key to achieving greater yield with SSNM.

Participatory evaluation in 2007/08
In 2007, the regional initiative on the development of Site-Specific Nutrient Management (SSNM) for Maize by the IPNI Southeast Asia Program and its partners entered a new phase. With sufficient evidence and promising results collected from researcher managed on-farm trials, SSNM has proven a reliable technology ready for wider-scale, participatory evaluation in partnership with farmers at project sites in Indonesia, the Philippines, and Vietnam.

Baseline agronomic surveys were conducted at project sites with significant opportunities for increasing productivity to obtain crucial information on current farmers' practices and serve as a reference for future impact analysis. Participatory evaluation of local SSNM guidelines commenced with farmer groups at project sites. Before the start of the season, farmers and researchers share their experiences, discuss management options, and agree on practices for participatory evaluation. Frequent meetings are held throughout the season in farmers' fields to refine SSNM through a dialogue between researchers and farmers. The final guidelines are discussed and approved by farmers and researchers for wider scale dissemination. Farmer participatory evaluation is an important step towards wider scale delivery of more knowledge intensive technologies like SSNM for maize in the research-extension continuum of IPNI-IPI and its partners in Southeast Asia.

Planning for wider scale dissemination of SSNM in 2008-2010 has begun involving existing collaborators and new stakeholders.

References

• Witt, C., Pasuquin, J.M.C.A., and R. Mutters. 2004. Spectral reflectance of rice and maize leaves and leaf color charts for N management [online]. In: New directions for a diverse planet: Proceedings of the 4th International Crop Science Congress Brisbane, Australia, 26 Sep - 1 Oct 2004. Available at www.cropscience.org.au/icsc2004 (last update 2004; accessed 15 July 2005).
• Witt, C., Pasuquin, J.M.C.A., Mutters, R., and R.J. Buresh. 2005. New leaf color chart for effective nitrogen management in rice. Better Crops. 89(1):36-39.

Acknowledgements
Funding for the project on Site-Specific Nutrient Management for Maize in Southeast Asia is provided by the International Fertilizer Industry Association (IFA), Canpotex International Pte. Ltd., the International Plant Nutrition Institute, and the International Potash Institute. Additional direct and indirect support is provided by the collaborating national agricultural research and extension systems which are gratefully acknowledged. On behalf of all stakeholders involved in the project, we wish to thank all donors for supporting our work since 2004.

The authors wish to thank the following scientists and their institutions for their invaluable contributions to this project.

Indonesia: Mrs. Sari S. Girsang (AIAT North Sumatera), Mr. Andarias M. Murni (AIAT Lampung), Mr. Supadmo (AIAT Central Java), Mr. Suwono (AIAT East Java), Mr. P. Tandisau (AIAT South Sulawesi), Dr. S. Saenong ( ICRI), Dr. Subandi ( ICRI), Dr. D. Setyorini and Dr. F. Agus (ISRI), and Dr. S. Kartaatmadja (IPNI-IPI).

Philippines: Dr. R. Labios (UPLB), Dr. A. Ocampo (IPB), Mrs. J. Labios (UPLB), Mr. H.C. Gines (PhilRice), Mr. C. Lapoot (NOMIARC), Mr. S. Tumamang (CVIARC).

Vietnam: Dr. P.S. Tan (CLRRI), Dr. T. T. Son (NISF), Dr. D.T. Binh (IAS), Dr. Nguyen My Hoa and Dr. Ngo Ngoc Hung (Cantho University), Dr. Ton Nu Tuan Nam (WASI).

We are very grateful to Dr. Achim Dobermann for his advice and guidance in the development and implementation of this project. Dr. Roland Buresh provided valuable comments on the development of SSNM for maize which is gratefully acknowledged.

The following institutes and organizations are collaborating partners and stakeholders in the project on Site- Specific Nutrient Management for Maize in Southeast Asia.

Indonesia:

• Indonesian Agency for Agricultural Research & Development (IAARD)
• Indonesian Center for Food Crops Research and Development (ICFORD)
• Indonesian Center for Soil & Agro-climate Research and Development (ICSARD)
• Indonesian Center for Agriculture Technology Assessment and Development (ICATAD)
• Indonesian Cereals Research Institute (ICRI)
• Indonesian Soil Research Institute (ISRI)
• Indonesian Agro-climate and Hydrology Research Institute (IAHRI)
• Assessment Institutes for Agricultural Technology (AIAT) East Java, North Sumatra, Central Java, Lampung, South Sulawesi

The Philippines:

• University of the Philippines Los Baños (UPLB)
• Bureau of Agricultural Research (BAR)
• Philippine Rice Research Institute (PhilRice)
• Department of Agriculture (DA) in Cagayan Valley Integrated Agricultural Research Center (DACVIARC) and in Northern Mindanao Integrated Agricultural Research Center (NOMIARC)

Vietnam:

• Vietnamese Academy for Agricultural Sciences (VAAS)
• Soils and Fertilizer Research Institute (SFRI)
• Western Highlands Agro-Forestry Scientific & Technical Institute (WASI)
• Institute of Agricultural Science of South Vietnam (IAS)
• University of Cantho
• Cuu Long Delta Rice Research Institute (CLRRI)

Linkages with Universities and International Organizations:

• University of Nebraska, Lincoln
• International Rice Research Institute (IRRI)
• International Maize and Wheat Improvement Center (CIMMYT)

The project on Site-Specific Nutrient Management for Maize in Southeast Asia is an initiative of the International Plant Nutrition Institute (IPNI) Southeast Asia Program, a join mission with the International Potash Institute (IPI).