A crop residue is as any vegetative material remaining in the field after harvest and thrashed. Crop residues are good sources of plant nutrients as about 25% of nitrogen (N) and phosphorus (P), 50% of sulfur (S), and 75% of potassium (K) uptake by cereal crops are retained in crop residues, making them valuable nutrient sources. Crop residue is not a waste but rather a tremendous natural resource and is important components for the stability of agricultural ecosystems.
Burning of crop residues
In areas with high yield potential and with the advent of mechanized harvesting, farmers prefer to burn the residues left in the field as the crop residues may interfere with tillage and seeding operations for the next crop.
The burning of crop residues leads to the following:-
• Air pollution due to the release of carbon dioxide, nitrous oxide, ammonia, and particulate matter in the atmosphere, which harms environment and contributes to global climate change.
• Substantial waste of precious nutrient resources and organic matter in the soil, especially nitrogen as it is reported that 40 to 80% of the nitrogen in wheat crop residue is lost as ammonia when it is burned in the field and also the ash left on the soil surface after burning crop residues causes an increase in urease activity and may cause N losses from soil and applied fertilizer.
• Deterioration of soil physical properties as burning residues leads to a corresponding loss in soil fertility.
• Residue burning can have a beneficial short-term effect on the N supply to subsequent crops, but has negative long-term effects on overall N supply and soil carbon levels.
Crop residues as animal feed
In areas with low yield potential, crop residues are use as animal feeds where animals are left to graze freely on harvested fields or straw is collected off the land and taken to the pen to feed livestock or silage and also use as a bedding material for the animals. This scenario, if not managed sustainably, often results in deteriorating soil fertility as nutrients are removed from the land and not returned and the bare soil is exposed to wind and water erosion. An adequate amount of residue must be left on the field to provide soil surface protection.
Crop Residue Management (CRM) practices comprises of:-
• CRM systems include conservation tillage practices such as zero-till, reduced till, bed planting, and other practices that provide sufficient residue cover to protect the soil surface from the erosive effects of wind and rain. Also, successive crops can be sown using zero-tillage after straw is left on the soil surface.
• CRM is a year-round system, which includes all field operations that affect the amount of residue, its orientation to the soil surface and prevailing wind and rainfall patterns, and the evenness of residue distribution throughout the period requiring protection.
• Crop residues and their appropriate management suppress the weeds: through their physical presence on the soil surface as mulch; by restricting solar radiation reaching below the mulch layer; by direct suppression; and by controlling N availability.
• CRM and tillage practices also influence the efficiency of soil-applied pre-emergence herbicides. Because pre-emergence herbicides are applied to the soil and the amount and quality of residues left might affect their effectiveness. This means that a higher rate of herbicide application is often needed to achieve effective weed control.
Thus, the main advantages of crop residue management over conventional systems include fuel and labour savings, as well as long-term benefits as crop residue, being an organic material, leads to an improvement in soil structure and fertility status of soil.
