उर्वरक दक्षता और कृषि लाभप्रदता बढ़ाने के लिए साइट विशिष्ट पोषक तत्व प्रबंधन (SSNM)

Agriculture is the major land use across the globe. The sustainability of our world depends fundamentally on nutrients. Most of the agricultural production system worldwide facing the insufficient access to nutrients still limits food production and contributes to land degradation.  Adoption of precision technologies for more efficient use of resources and nutrients becomes more relevant in the current production scenario.

Site-specific nutrient management (SSNM) involving use of inorganic or organic sources along with spatial and temporal soil variability, crop requirements of nutrients and cropping systems, soil capacity to supply nutrients, utilization efficiency of the nutrient and productive capacity of the varieties with improved NUE is the most ideal system that needs to be practiced to achieve the targeted goals.

Principles of SSNM:

SSNM is an approach to feed crops with nutrients as and when needed. The application and management of nutrients are dynamically adjusted to crop needs of location and seasons.

There are five cardinal principles of SSNM:

1. Principle 1- balanced fertilization based on crop requirements
2. Principle 2- plant based estimation of root nutrient supplies

• Principle 3- need based fertilizer N management

1. Principle 4- sustainable P & K management
2. Principle 5- increasing profitability

Important Features of SSNM:

• Optimal use of existing indigenous nutrient sources such as crop residues.
• Application of N, P and K fertilizers is adjusted to the location and season-specific needs of the crop.
• Use of the leaf color chart ensures that nitrogen is applied at the right time and in the amount needed by the crop which prevents wastage of fertilizer.
• Use of nitrogen omission plots to determine the P & K fertilizers required to meet the crop needs. This ensures that P and K are applied in the ratio required by the rice crop.
• Local randomization for application of Zn, S and micronutrients are followed.
• Selection of most economic combination of available fertilizer sources.
• Integration with other integrated crop management (ICM) practices such as the use of quality seeds, optimum plant density, integrated pest management and good water management.

SSNM approaches: 

The SSNM recommendations could be evolved on the basis of solely plant analysis or soil cum plant analysis.

Plant Analysis-Based SSNM

It is considered that the nutrient status of the crop is the best indicator of soil nutrient supplies as well as nutrient demand of the crops. Thus, the approach is built around plant analysis. Witt and Dobermann (2002) proposed five key steps for developing field-specific fertilizer NPK recommendations for rice, through the basic principles remain the same for other crops as well.

Selection of the Yield Goal: A yield goal exceeding 70–80% of the variety-specific potential yield (Ymax) has to be chosen.

Assessment of Crop Nutrient Requirement: The nutrient uptake requirements of a crop depend both on yield goal and Ymax. In SSNM, nutrient requirements are estimated with the help of quantitative evaluation of fertility of tropical soils (QUEFTS) models.

Estimation of Indigenous Nutrient Supplies: Indigenous nutrient supply (INS) is defined as the total amount of a particular nutrient that is available to the crop from the soil during the cropping cycle, when other nutrients are not limiting. The INS is derived from soil incorporated crop residues, water and atmospheric deposition. It is estimated by measuring plant nutrient uptake in an omission plot embedded in the farmers’ field, wherein all other nutrients except the one (N, P or K) in question, are applied in sufficient amounts.

Computation of Fertilizer Nutrient Rates

Field-specific fertilizer N, P or K recommendations are calculated on the basis of above steps and the expected fertilizer recovery efficiency (RE, Kg of fertilizer nutrient taken up by the crop per Kg of the applied nutrient).

Dynamic Adjustment of N Rates: Whereas fertilizer P and K, as computed above, are applied basally i.e., at the time of sowing/planting, the N rates and application schedules can be further adjusted as per the crop demand using chlorophyll meter (popularly known as SPAD) or leaf color chart (LCC).

Soil-cum-Plant Analysis Based SSNM

In this case, nutrient availability in the soil, plant nutrient demands for a higher target yield (not less than 80% of Ymax), and recovery efficiency of applied nutrients are considered for developing fertilizer use schedule to achieve maximum economic yield of a crop variety.

Total nutrient requirement for the targeted yield and recovery efficiency are estimated with the help of documented information available for similar crop growing environments. Field-specific fertilizer rates are then suggested to meet the nutrient demand of the crop (variety) without depleting soil reserves.

Management of macro and micronutrients:

Management of N:

• An estimate of crop demand, potential N supplies from indigenous sources (soil biological N2 fixation) and N recovery from inorganic and organic resources applied. These factors are considered while estimating the total fertilizer N requirement for the crop.
• As estimate of the need for a basal N application according to soil release patterns, crop variety and crop establishment method.
• Plant N status monitoring to optimise the timing of split application of fertilizer N in relation to crop demand and soil N supply.
• Long term soil and crop management practices to optimize the indigenous nitrogen supply.

SPAD:

Chlorophyll meter (SPAD meter) is a simple portable diagnostic tool used for monitoring crop N status in site in field when properly calibrated to locally important crop varieties and crop growing conditions, it serve as efficient tool for developing need based variable rate N application for cereal crops. The method involves measuring a dimensionless ‘SPAD value’ which is then compared with a critical threshold value to decide whether and how much N needs to be applied.

A SPAD threshold value of 35 has been found to work well in transplanted rice. A higher threshold value near 40 is required for semi dwarf wheat varieties. SPAD value is measured 4-5 times in a season at 10 days interval starting from tillering stage. Usefulness of SPAD meter for optimizing N top dressing in rice wheat and maize has been demonstrated by various workers (Dass et al., 2014).

LCC:

Leaf colour chart is another simple, easy to use and inexpensive tool to increase N use efficiency in rice and other cereal crops. The chart contains six green strips with the colour ranging from yellowish green to dark green. It has been calibrated with the chlorophyll meter and has been used to guide N top dressing in rice. The critical leaf colour reading for N top dressing range from 3 for varieties with light green foliage of scented rice varieties to 4 for semi dwarf indica varieties and 5 for hybrid rice varieties.

Management of Phosphorus and Potassium:

• An estimate of crop P and K demand potential indigenous P and K supply and recovery efficiency of applied P and K through inorganic and organic sources.
• A schedule for timing K application depending on soil K buffering characteristics and an understanding of the relationship between K nutrition and
• Knowledge of relationship between the P and K budget, residual effect of P and K fertilizers and changes in soil supply over time.

Management of other nutrients:

• Prevention, diagnosis and treatment are the management tools for other nutrients such as S and micronutrients.
• Over the long term, prevention through general crop management, water management and fertilizer management is important.
• Deficiencies can be alleviated by regular or one time measure as a part of general recommendations.
• Diagnostic tools can be used to identify other nutritional disorders such as salinity, Fe toxicity and B toxicity.

Decision Support Systems

Nutrient Expert® (http://software.ipni.net/article/nutrient-expert)

Nutrient Expert® (NE) is an easy-to-use, interactive, and computer-based decision support tool that can rapidly provide nutrient recommendations for an individual farmer field in the presence or absence of soil testing data. NE is nutrient decision support software that uses the principles of SSNM and enables farm advisors to develop fertilizer recommendations tailored to a specific field or growing environment.

Decision Rules to Estimate Site-Specific Nutrient Management Parameters

NE estimates the attainable yield and yield response to fertilizer from site information using decision rules developed from on-farm trials. Specifically, NE uses characteristics of the growing environment—water availability (irrigated, fully rainfed and rainfed with supplemental irrigation) and any occurrence of flooding or drought; soil fertility indicators - soil texture, soil color and organic matter content, soil test for P or K (if available), historical use of organic materials (if any) and problem soils (if any); crop sequence in farmer’s cropping pattern; crop residue management and fertilizer inputs for the previous crop; and farmers’ current yields.

Yield, profitability and nutrient-use efficiency

As compared to farmers’ fertilizer practice (FFP), overall average yields with SSNM increased by 7% and profitability by 12% (Witt and Dobermann, 2002). A site-specific approach to nutrient management evaluated in 56 on-farm experiments with irrigated wheat and transplanted rice crops in North-West India revealed that field-specific management of macronutrients increased yields of rice and wheat crops by 12 and 17% and profitability by 14 and 13%, respectively, in North-West India (Dass et al., 2014).

In maize, SSNM increased the agronomic efficiency of N fertilizer by 53% than FFP. Abdulrachman (2002) reported that the results of 45 trials conducted on irrigated rice indifferent countries of South Asia, revealed that with SSNM, fertilizer N rates were reduced significantly i.e., by 10–20%.

Chlorophyll-meter based N application (30 Kg basal + 30 Kg N/ha at SPAD value 37.5) saved 30 Kg N/ha and increased rainy season maize grain yield by 10% as compared to soil test-based N application in Semiarid north plain zone of India (Dass et al., 2012).

Table 1. Effect of site-specific nutrient management (SSNM) on wheat productivity (t ha^-1) and economic returns (Rs ha^-1, in parenthesis) at seven locations in India (source: Singh and Bansal 2010)

FP = Farmers’ practice, SR = State fertilizer recommendation

Conclusions

Site specific nutrient management (SSNM) is fundamental to precision nutrient applications in different crops. SSNM provides an approach for need-based feeding of crops with nutrients while recognizing the inherent spatial variability. This makes the efficient utilization of nutrients by crop plants and avoids the wastages of fertilizers. The environmental footprints of chemical fertilizers are also reduced.

Crop yields increase by over 15%, while amount of nutrients applied mostly decrease. Farm profitability and NUE increase convincingly by using this novel concept. For efficient and effective SSNM, use of soil and plant nutrient status sensing devices, remote sensing, GIS, decision support systems, simulation models, and machines for variable application of nutrients play an important role.

Although SSNM proved to be useful in improving yield and NUE indicative of soil health enhancement per se, still the nature of the SSNM approach need to be tailored to specific circumstances under different climatic conditions.

In some areas, SSNM may be site- or farm-specific, but in many areas, it is likely to be just region- and/or season-specific. Thus, a simplified future SSNM approach should combine decisions that are made on a site-specific basis as well as decisions that are valid for somewhat larger regions with similar agro-climatic conditions.

References

1. Abdulrachman, S., Gines, H. C., Nagarajan, R. 2002. Variation in the performance of site-specific nutrient management among different environments with irrigated rice in Asia. Better Crops International. 16(2), 18–23p.
2. Dass, A., Singh, D. K., Dhar, S. 2012. Precise supply of nitrogen and irrigation to hybrid maize using plant sensors In: Proceedings of the International Agronomy Congress: Agriculture, Diversification, Climate Change management and livelihoods; 534–35p.
3. Dass, A., Suri, V. K., Choudhury, A. K. 2014. Site-Specific Nutrient Management Approaches for Enhanced Nutrient-Use Efficiency in Agricultural Crops. Research & Reviews: Journal of Crop Science and Technology, Volume 3(3), 1-6.
4. Dobermann A, Witt C, Dawe D. 2002. Increasing the productivity of intensive rice systems through site-specific nutrient management. New Delhi, India; and Makati City, Philippines: Science Publishers; and International Rice Research Institute (IRRI).
5. Singh, H., Bansal, S. K. 2010. A review of crop productivity and soil fertility as related to nutrient management in the Indo-Gangetic Plains of India. Better Crops 1, 27–29.

Authors

Sunanda Biswas^1*, B. H. Gawade² and Priya Singh¹

¹Division of Soil Science and Agricultural Chemistry, ICAR-IARI, New Delhi-110012

²Quarantine Division, ICAR-National Bureau of Plant Genetic Resources, New Delhi-110012

*email: This email address is being protected from spambots. You need JavaScript enabled to view it.