Thursday, 26 April 2012

Need For Nutrient Budgeting For Sustainable Agriculture

In India, diversity exists in the quality and quantity of natural resources and their distribution with respect to time and space. For example, India hosts 15% of the animal population, which, apart from supplying milk and draught power in agricultural operations, contributes valuable plant nutrients as supplement to the fertilizer nutrients. Indian cattle, however, have different genetic make up compared to the those in developed countries. They are smaller in size with lower body weight, low in milk production and adapted to the different climatic conditions and different feeding habits besides their different heritage. Consequently, the different types of manures, derived under such varying environments do differ in their physical and chemical composition due to the differences in the type of animal used to produce dung, animal density, nutrient density of the feed material, type of work an animal is put to use and management factors. IISS, Bhopal developed a database at district level of dung produced and manure availability alongwith its composition.
Even though the human population is increasing at an alarming rate, the cattle population growth is almost stagnant. This is evident from the animal census data of 1997 and 2003 which show a cattle population of 198 and 185 million, respectively. This decrease is primarily due to a decrease in indigenous cattle. The buffaloes population has increased from 89 to 98 million but this is not sufficient to compensate the decrease in cattle population. This shows that the dung manure availability in the country is also not increasing and is estimated to be at around 1.5 tonnes/ha of net cultivated area. An allowance of 15% could be made in this if the dung manure available from other animals like goats, sheep, poultry, horses, pigs etc are included. The total dung manure available would be around 1.7 t/ha. The total N, P2O5, and K2O supply is estimated to be around 1.5, 1.0, and 1.8 million tonnes, respectively for the whole country. In addition, based on 2006-07 crop year data, we have estimated an availability 0.22, 0.16, 0.36 million tonnes of N, P2O5, and K2O respectively from crop residues, assuming only 5% of the residue would be recycled in agriculture and rest would be consumed as cattle feed, burnt or in future might go in for energy generation. Also, some N would be added through symbiotic and free living nitrogen fixers. The addition through green manure crops is estimated to be 0.11 million tonnes. It is estimated that 5-14 million tonnes of compost can be prepared from municipal solid waste depending upon the method of composting. This could at maximum add 0.1,0.06, and 0.09 million tonnes of N, P2O5, and K2O.
The first estimate of nutrient removal by crops was made by National Commission on Agriculture (NCA). At a foodgrain production of 82 million tonnes in 1961, the total N+P205+K20 removal was estimated to be 9.5 million tonnes, including the nutrient removal by other crops. The figure of nutrient removal for 1971 was 12.3 million tonnes at a production level of 108 million tonnnes of foodgrain. Based on these nutrient removal data, it was found that there was a net negative balance of N, P2O5, and K2O to the tune of 8-10 million tonnes during 60s, 70s, and 80s if only the additions through fertilizers are taken in computation. This was true for the three decades. However, this got slightly changed thereafter, owing to a lesser growth rate in the agricultural production than was projected but, the application of fertilizer nutrients continued to increase at a higher rate. For the year 2006-07, we estimated a total nutrient removal of 10, 4.2. and 12.4 million tonnes of N, P2O5, and K2O, respectively at a foodgrain of 217 million tonnes. The additions through fertilizers were 13.8, 5.5, and 2.3 million tonnes of N, P2O5, and K2O, respectively. This leaves a net negative balance of 5.0 million tonnes of N, P2O5, and K2O and this again is due to a heavy negative balance in case of potassium. The total nutrient imbalance would be corrected to some extent if we include the nutrient additions through dung manures (4.3 million tonnes of N, P2O5, and K2O from cattle and buffaloes) and crop residues (0.74 million tonnes). However, this does not mean that our soils are adequately fertilized/manured. There are several areas in Rajasthan, Gujarat, and Madhya Pradesh where the balancc is negative in case of N. Similarly, even P balance is negative in some districts of Uttar Pradesh, Madhya Pradesh and Kerala and K balance is negative in almost 80 per cent districts in India. A higher growth rate in agriculture is expected in future which would accentuate the problem further if careful attention is not paid in the areas where the net budget is negative. These nutrient budgets are only apparent in nature because they do not take into consideration the nutrient additions through natural processes like rainfall, irrigation water, sedimentation from upper reaches and also the losses of nutrients through leaching, volatilization, run off etc. It is important that work is initiated in this direction to compute such additions and deletions so that we could reach to a better understanding of region specific nutrient budgets to guide us in managing the plant nutrients.
India is endowed with variable climates, different strata of farmers ranging from marginal to large practicing variable crop and nutrient management options. These factors change the nutrient recovery from the applied manure. There is a need to compile the manure preparation and handling practices in different parts of the country specific to different situations. The amount and type of the animal feed is important w.r.t. the milk yield and manure nutrient composition. A compilation of the crop residues and its composition used as cattle feed, the availability of concentrated feed material (manufactured and imported) and composition of different cattle feed, the region- specific availability of grazing land and amount and type of pasture, the amount of feed depending upon the type and age of animal is important for determining not only the quantity and quality of manure but also will be helpful in computing enteric methane emission coefficients from animals and methane emission potential of manures.
The availability of fertilizer nutrients (both major and micro) is important for making an overall assessment of region-specific nutrient availability in India. Also, the nutrient requirement of crops vary depending upon the crop species, varieties (hybrid vs. local) and also with the change in climatic and management conditions. The region specific nutrient mining data taking into account type of crop, yields obtained, the amount of residues removed and the partitioning of nutrients into the above and below ground plant parts will help in assessing the nutrient balances in different agro-ecoregions. There is need to establish a connectivity by compiling all the information of nutrient management with the quantity and quality of nutrients available from different sources in different regions and management practices so as to suggest the possible guidelines in the direction of improved nutrient management. It is important to compile, synthesize and process the nutrient region- specific information and present it into a user friendly database as also in the form of spatial maps so that the information could be used by many.
A. Subba Rao
  IISS

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