Residues are the by-products of crops plants and other vegetative products of plants are which are organic in nature and has vital importance for agricultural production. The monotonous use of inorganic fertilizers devoid of balanced NPK and micronutrients has resulted in decreasing soil organic carbon (SOC) and fatigued crop production.
Soil organic matter (SOM) mostly obtained from organic residues facilitates the aggregation and structural stability of soils and responsible for air-water relationship for root growth and protection of soil from wind and water erosion. The composting, in-situ incorporation or retention as stubble mulch are the common methods of residue management.
Residues in general are C-rich materials but contain sufficient amounts of essential plant nutrients. Therefore, their recycling in crop production is an important means of meeting nutrient requirements of the crop plants. Hence, residue application is useful to enhance crop productivity, soil health and profitability both in irrigated and rainfed ecosystems.
Scope of Crop residues recycling
Indian agriculture is entering a new phase. With time the growing concerns for sustainable agriculture have shown a positive response with the advance of conservation agriculture and it has come as a new paradigm to achieve goals of sustained agricultural production. The residue recycling is more common in conservation agriculture.About 675 Mt crop residues are produced annually in India of these, 70% constitute cereal residues.
Crop residues are a tremendous natural resource, not waste materials, is good source of organic matter. Organic matter has very low salt index compared with some chemical fertilizers. About 25% of N and P, and 50% of S and 75% K uptake by cereal crops are retained in the crop residues, making them valuable nutrients.
The critical N content of the organic matter for appropriate mineralization will be 1.7-1.8% N. But in cereal straw it remains 0.3-0.5% and in legumes from 1-1.5% and in green manure crops it is 2.0-2.5%.
Crop residue management in crop production
In India, residue management is very important in rice-wheat cropping system because large quantities of crop residues are left on soil surface, especially where combines are used for crop harvest. Farmer generally burns the crop residues which not only creates pollution to environments but also deteriorates the soil health.
It has been reported that the rice-wheat system producing about 10.0 t/ ha yield exhausts about 500 kg/ha of NPK and other trace elements from soil.
Composting is the controlled decomposition ofcrop residue under aerobic condition.Bio accelerators such as P solubilizer, N fixers and SSP can be added during composting to increase the rate of decomposition and nutrient enrichment. Composting reduces the C:N ratio of composting which help in better mineralization when applied to field.
2. Residues incorporation:
under this, residues are directly applied to soil and incorporated through tillage. Legume residues are better to incorporate but cereal residues may cause immobilization due to high C:N ratio.
3. Direct drilling under residues mulching:
residues are retained on soil surface and specialized seed drill (Happy Seeder/Turbo Seeder) can be used to sow the crops particularly wheat in rice residues uniformly spread over surface. This Prevents splash erosion by heavy rains and surface runoff andimproves soil texture by adding organic matter.
Factors affecting residue decomposition
The effect of residue incorporation on the succeeding crop depends on the amount of residues and time and method of incorporation. Though the long-term effects of crop residue incorporation are generally expected to be beneficial, the effect on crop yields in the short-term is often unpredictable.
Several factors such as residue quality, edaphic factors, and the health of the previous crop and their complex interactions with various management practices are involved in determining the ultimate yield of crops.
The evaluation of crop residues in terms of agronomic effects is complicated by the variable nutrient contents of the materials and a host of other factors.
Advantages and limitations of residue recycling
In general the crop residue recycling will have the agronomic, environmental and economic advantages, however sometime its mis-managements and other technical problems may result its limited uses in farmer’s field.
In general, reducing fuel and labour costs required for intensive cultivation/ ploughing, reducing sediment and fertilizer pollution of lakes and streams and. sustaining the soil fertility and productivity by the continuous mineralization processes are the major advantages of residues recycling with conservation tillage.
The specific advantages and disadvantages are:
- Soil productivity improvement
- Increase in organic matter
- Soil water conservation Improvement in soil structure
- Reduction in soil erosion
- Improvement of water quality
- Improvement of air quality
- Biodiversity increase
- Carbon sequestration
Constraints of residue recycling and its adoption:
- Wide spread use of crop residues for livestock feed and as fuel
- The lack of appropriate seeder/ planters especially for small and medium-scale farmers
- Can slow germination and reduce yields in initial year
- Prevalence of weeds, disease and other pests may shift in unexpected way
- May initially require more nitrogen fertilizer to increase mineralization
- Immobilization of nutrients (with high C: N ratio residues) and fear of attack of several insect pests and diseases
- Lack of knowledge about the potential of recycling, and conservation agriculture to agricultural leaders, extension agents and farmers
Kailash Prajapat*, Gopalareddy K.1 and RamkishorFagodiya
ICAR-Central Soil Salinity Research Institute, Karnal (Karyana) 132001
1ICAR-Indian Institute of Wheat and Barley Research, Karnal (Haryana) 132001