नाइट्रोजन उर्वरकों के सुरक्षित और लाभदायक उपयोग के लिए सर्वश्रेष्ठ प्रबंधन पद्धतियां

Indian agriculture has witnessed a tremendous fourfold increase in food production over the past three decades. This enhanced food grain production later known as ‘green revolution’ could be mainly attributed to the introduction of high-yielding, input responsive cultivars of wheat and rice in the mid-1960s and to the increased availability and use of chemical fertilisers, especially the nitrogenous (N) fertilizers.

Nitrogenous fertilizers supply N which is very essential for plant growth and development and mainly supplied to the crop plants in the form of urea, Diammonium phosphate (DAP) etc. When N fertilizers are used correctly they are very beneficial, but unscientific practices of their usage could lead to large scale pollution and harmful effects on environment. Both surface and groundwater are very vulnerable to No₃^- contamination by excess use of N fertilizers. Protecting the water bodies in particular and environment in general from No₃^- contamination is major concern. Therefore here we discuss the best management practices for safe and economic use of Nitrogenous fertilizers.

Always apply fertilizers based on soil nutrient status

Fertilizers should be applied only based on the soil nutrient status, which can be known by testing the soil at a laboratory. Nowadays all state department of agriculture district headquarters are having free soil testing facilities. Proper care should be taken while collecting soil samples.

Always supply recommended dose of fertilizers

Dosage of fertilizer should be as per the dose recommended for the region. These recommendations in India are normally made by State Agricultural Universities, State Departments, crop specific Research Institutes etc.

Table 1. Recommended dose of fertilizers and specific crop growth stages of maximum N demand for split application of N in different crops of India.

Selection of suitable fertilizer source

Selection of fertilisers should be done according to the soil reaction viz., acidic fertiliser for alkaline soils and basic fertilisers for acidic soil reactions. Slow-release nitrogen fertilizers coated with nitrification inhibitors and urease inhibitors can be chosen in rice, which will help in reduction of N losses due to leaching. Nitrogen in the form of organic manures is also less prone to short-term loss by leaching. Details of different fertilizers (Major and Micronutrients) available in the market and their % nutrient content is given in table 2 & 3.

Table 2. Fertilizers available in the market and their % nutrient content

Table 3. Micronutrient Fertilisers and their nutrient content

Proper method of application

The widely practiced method of fertilizer application in India is by surface application through broadcasting where fertilizers are uniformly distributed over the whole cropped field. Broadcasting is preferred under conditions such as, crops with a dense stand and not sown in rows; for application of readily soluble nitrogenous fertilizers; when high rate of fertilizers are used and in crop plants whose roots spread widely in the soil.  Some of the drawbacks of broadcasting are that it stimulates excess weed growth and fertilizers especially P may come in contact with a large volume of soil and are likely to be fixed and unavailable for crop.

Band application

Band application of fertilizer is done by placing a band of about 3 - 4 cm by the side or below the seed as shown in fig-1. Band application is practiced when a) small quantities of fertilizers are to be supplied; 2) when phosphatic fertilizers are applied in acidic soils 3) where fixation of phosphorus is a problem; 4) in the case of crops sown in wide rows; 5) on soils with low fertility and 6) for application of fertilizers to shallow rooted crop plants.

Figure 1. Band application of Fertilizers by the side of crop rows

Fertigation

Recent methods of application like fertigation would help in increasing the nutrient use efficiency along with reducing the losses. Fertigation is a method of fertilizer application in which fertilizer is incorporated within the irrigation water by the drip system. In this system fertilizer solution is distributed evenly in irrigation. The availability of nutrients is very high therefore the efficiency is more. In this method liquid fertilizer as well as water soluble fertilizers are used. By this method, fertilizer use efficiency is increased from 80 to 90 per cent. Practicing fertigation is beneficial to farmers in timely and site specific application of nutrients in addition to reducing quantity of fertilizer to be supplied as nutrients are directly supplied to root zone.

Figure 2. Layout of fertigation system and photographs showing fertigation/drip irrigation in Potato, Sugarcane and carnation.

Split application of fertilizer N

Split application of N to meet the immediate crop growth stage specific N needs is recommended for maximum N use efficiency with reduced losses. Splitting the total N into two doses, half as basal dose and rest as top-dressing in case of heavy soil types is recommended. In case of light soils, nitrogen should be applied in three equal splits i.e 1/3 as basal, 1/3 after 30 days of sowing and the balance 1/3 about 50-60 days after sowing. Finally splitting should be crop specific and crop stage specific to match the growth stage specific N demand. To know these specific crop growth stages of maximum N demand leaf colour chart can be useful. The leaf colour chart (LCC) primarily developed for rice, is a tool to rapidly assess leaf N status and thereby guide the application of fertilizer N to maintain optimal leaf N content, which is vital for achieving higher yields. A detail of specific crop growth stages along with the amount of recommended N to be supplied as split dose in different crops is given in table 1.

In addition to above practices some of the following measures can be adopted for economic and safe use of fertilizers

• For at least a week, flooding with too deep water or poor drainage should be avoided after application of the fertilisers.
• Top dressing should be done after draining out the water and weeding so that the loss of nutrient is minimum. Paddy fields, used for transplanting, should be puddled and fertilisers should be applied at the time of puddling. This will help fertilisers to penetrate and get stored in the soil.
• The acidic soils should be treated with liming materials as and when required.
• Deep placement of fertiliser, along with foliar feeding of nitrogen (i.e., urea) through spraying of nitrogenous fertiliser in place of top dressing should be done in case of dry lands.
• Addition of organic manures or green manuring should be done at least once in 3-5 years. Weed growth should not be permitted in cropped areas, during any part of the year.
• In case of flooded fields or calcarious soils, use of slow release nitrogenous fertilisers like sulphur coated urea, urea super granules, neem coated or neem blended ureas should be used so that loss of nitrogen can be minimised.
• Mud bolls, contain urea and should be used in case of deepwater crops because they help in proper placement and also reduce the loss of nitrogen from the field.
• Appropriate plant protection measures and proper tillage practices should be adopted so that plants remain healthy and absorb the applied nutrients from the field.

Authors:

Venkatesh K.*¹, Singh S.K.¹, Mamrutha HM¹, Tiwari V.¹, Gupta O.P.², and Sharma I³

¹Division of Crop Improvement, ²Division of Quality and Basic Sciences^,

³The Project Director, Directorate of Wheat Research, Karnal-132 001, Haryana-India

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