Anjali Patel1, Sakina Begam2 and Kailash Vishal3
1Department of Agronomy, Indira Gandhi Krishi Vishwavidyalaya, Raipur, Chhattisgarh 492001.
2Department of Plant Physiology, Indira Gandhi Krishi Vishwavidyalaya, Raipur, Chhattisgarh 492001.
3Department of Plant Pathology, Jawaharlal Nehru Krishi Vishwavidyalaya, Jabalpur, Madhyapradesh 482004.

‘Feeding of crop with nutrients as and when needed’
“Site-specific nutrient management (SSNM) is the dynamic, field-specific management of nutrients in a particular cropping season to optimise the supply and demand of nutrients according to their differences in cycling through soil-plant systems.”
  • SSNM is a relatively new approach of nutrient recommendations, is mainly based on the indigenous nutrient supply from the soil and nutrient demand of the crop for achieving targeted yield.
  • The SSNM helps in improving NUE as it provides an approach for feeding crops like rice, maize, wheat etc. with nutrients as and when needed.
  • 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.

  • Provide a locally-adapted nutrient best management practice tailored to the field- and season-specific needs for a crop
  • Increase in yield
  • High efficiency of fertiliser use
  • Improve profitability
  • Improve marketable crop quality
  • Improve environmental stewardship

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 colour 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 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.

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.
  • Five key steps for developing field-specific fertilizer NPK recommendations have been developed.

1. Selection of the Yield Goal:-
  • A yield goal exceeding 70-80 % of the variety-specific potential yield (Ymax) has to be chosen.
  • Ymax is defined as the maximum possible grain yield limited only by climatic conditions of the site, where there are no other factors limiting crop growth.
  • The logic behind selection of the yield goal to the extent of 70-80% of the Ymax is that internal NUEs decrease at very high yield levels near Ymax.
2. 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) model.
  • Nutrient requirements for a particular yield goal of a crop variety may be smaller in a high yielding season than in low yielding one.
3. 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 no-limiting.
  • The INS is derived from soil, incorporated crop residues, irrigation water and BNF.
4. Computation of Fertilizer Nutrient Rates:-
  • Field-specific fertilizer N, P & K recommendations are calculated on the basis of above steps (1-3) and the expected fertilizer recovery efficiency (RE- kg of fertilizer nutrient taken up by the crop per kg of the applied nutrient).
  • Studies indicated RE values of 40-60 % for N, 20-30 % for P, 40-50 % for K in rice under normal growing conditions.
5. Dynamic Adjustment of N Rates:-
  • Whereas, fertilizer P and K are applied basally (at the time of sowing), the N rates and application schedules can be further adjusted as per the crop demand by using chlorophyll meter (SPAD), Green seeker and Leaf Colour Chart (LCC).
  • Recent on farm studies in India have revealed a significant SPAD/LCC based N management schedules in rice and wheat in terms of yield gain, N use efficiency and economic returns over the conventionally recommended N application involving 2-3 splits during crop growth.
  • SPAD based N application resulted in a saving of 55 kg N/ha as compared to Soil Test Crop Response (STCR) based N application.

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 RE of applied nutrients are considered for developing fertilizer use schedule to achieve maximum economic yield of a crop variety.
  • In order to ascertain desired crop growth, not limited by apparent or hidden hunger of nutrients, soil is analyzed for all macro and micronutrients well before sowing/planting.
  • Total nutrient requirement for the targeted yield and RE are estimated with the help of documented information available for similar crop growing environments. “SSNM is a component of site-specific crop management or precision farming”

Precision Agriculture
“Precision agriculture can be defined as the application of principles and technologies to manage spatial and temporal variability associated with all aspects of agricultural production for the purpose of improving crop performance and environmental quality.”

Concept is simple…
1) Right Product
2) At right time
3) In right Place
4) At right Rate

Why is Precision Nutrient Management Important?
  • Nutrient variability within a field can be very high (graphs to follow), affecting optimum fertiliser rates.
  • Yield potential and grain protein can also vary greatly even within one field, affecting fertiliser requirements.
  • Increasing fertilizer use efficiency will become more important with increasing fertilizer costs and environmental concerns.

Site-Specific Equipment and Technology

  • Special equipment is not required for site-specific management.
  • Identifying areas requiring specific management can be done with conventional soil testing and scouting techniques.
  • Different fertilizer rates can be applied to different areas by staking or flagging them, and then spreading the different areas separately.

Technology tools include:

1. Global Positioning System (GPS)
GPS is a satellite based signal broadcast system that allow GPS receivers to determine their position. GPS provides the accurate positional information, which is useful in locating the spatial variability with accuracy.

2. Geographical Information System (GIS)
GIS is a computer based system or a type of computerised map, provides information on field topography, soil types, surface drainage, subsurface drainage, soil testing, irrigation, chemical application rates and crop yield.

3. Remote sensing
Remote sensing is a tool which gather information in the form of map with the help of satellites. RS is used for collection, processing and analysing data to extract information from earth surface without coming in to physical contact with it.

4. Variable Rate Applicator
It is the implementation of gathered information for site specific agriculture. It consists of farm field equipment with the ability to precisely control the rate of application of crop inputs and tillage operations.

5. Yield Monitoring (YM)
Yield monitors are attached to conveyors or combines to measure grain yield and moisture content. Coupled with a GPS logging location, data can be mapped.

6. Farmer
Farming cannot be imagined without farmer. For assessing and managing the variability, decision-making is the key factor, and it is to be done in consultation with the farmer.

7. Laser Land Leveling
  • Saves 25-30% of water.
  • Reduces the amount of water required for land preparation.
  • Reduces labor requirement for irrigation by 35 %.
  • Improves uniformity of crop maturity.
8. Leaf Color Chart (LCC)
The leaf color chart (LCC) is an easy-to-use and inexpensive diagnostic tool for monitoring the relative greenness of a rice leaf as an indicator of the plant N status.

9. Green seeker sensor
A green seeker handheld crop sensor can detect wavelengths of reflected light from the crop canopy and produce a normalized difference vegetation index value called NDVI that is correlated with leaf chlorophyll. Based on this information, side dress nitrogen rates that are aligned with site specific crop needs can be prescribed.

10. Chlorophyll meter
The soil plant analysis development (SPAD) chlorophyll meter is one of the most commonly used diagnostic tools to measure crop nitrogen status. Released in 1984 (Minolta Co. ltd., Japan). When SPAD value fell to between 29 and 32, indicating that additional fertilizer is necessary.

11. Software for SSNM
Computer or mobile phone-based tools are increasingly used to facilitate improved nutrient management practices in farmers’ fields, especially in geographies where blanket fertilizer recommendations prevail. Nutrient Expert® and Crop Manager are examples of decision-support systems developed for SSNM in cereal production systems.

Nutrient Expert®
Nutrient Expert® is an interactive, computer-based decision-support tool that enables smallholder farmers to rapidly implement SSNM in their individual fields with or without soil test data.

Crop Manager
Crop Manager is a computer and mobile phone based application that provides small-scale rice, rice-wheat, and maize farmers with site- and season-specific recommendations for fertilizer application. The software is freely downloadable at

Problems in Adoption of SSNM
  • Fragmented land holding
  • Lack of continuously monitoring the health and availability of the natural resources.
  • Climatic aberrations.
  • Operational constraints.
  • Uncertainty in getting the various inputs.
  • Absence of a long standing and uniform agricultural policy.
  • Lack of success stories.
  • Lack of local technical expertise.
  • Land ownership, Infrastructure and Institutional constraints.

Probable Strategies
  • Farmer’s co-operatives.
  • Pilot projects.
  • Agricultural input suppliers, Extension advisors and consultant play important role in the spread of the technology.
  • Combined effort of Researchers and Government.
  • Public agencies should consider supplying free data such as remotely sensed imagery to the universities and research institutes involved in Precision farming research.

Site-specific nutrient management is gaining popularity with the passage of time obviously due to its in-built advantages over other contemporary approaches. With an increase in understanding of SSNM, decision support tools on fertilizer, best management practices will be developed for different crops and farming situation.