Crop residues are the waste materials left over after a crop harvest in the form of leaves, stalks, stems, seeds, etc.
The amount of crop residue depends on the crop type, its growth, its method of tillage, and its method of harvesting.
Cereal crops like paddy, Sorghum (jowar), and wheat produce significant residues.
Crop residues are extremely helpful in adding organic matter to soil.
They are generally used as feed, fodder, fiber, and construction material.
They increase the soil’s water infiltration and retention capacity, buffer the pH, and facilitate the availability of nutrients in the soil.
Types of crop residues
Crop residues are categorized into
- Field residues
- Post-harvest residues
Field residues
The residues left in the field after the main crop is harvested are called field residues. When left in the field, these residues increase water-holding capacity, control erosion, and add nutrients. They can be tilled back into the same soil.
Ex- stem, leaves, stalks, etc.
Post-harvest residues
Post-harvest residues are the materials left after processing. These residues are used as animal feed and soil amendments. Ex- husk, seeds, molasses, bagasse, etc.
Advantages of crop residues
- Sustain soil organic matter
- Increase crop yield
- Control soil erosion
- Reduce surface runoff and evaporation
- Recycle plant nutrients
- Increase soil infiltration rate
- Decrease sedimentation
Disadvantages of crop residues
- Higher costs for removing residues
- Difficulty in land preparation for the succeeding crop
- Cause pollution if used as household fuel
Burning of crop residues
Climate change has become a significant threat at present.
Melting of glaciers, forest fires, and pollution are becoming the current concern. Burning of crop residues or stubble burning is one of the innumerable causes.
Crop residues are burnt in the agricultural field after harvesting. This smoke affects the air quality extensively and has become a significant issue in many countries.
The non-availability of labor and the high costs of removing residues are the primary reasons behind burning them.
Farmers justify their actions by stating that crop residues are burnt to make their work more accessible as it helps to inhibit the occurrence of pests and diseases.
Though this is true to some extent, it won’t neutralize its impact on the environment.
They can overcome the issues by using machines to chop straws and disperse them evenly in the field.
Farmers can use and recycle the residues to various extents or sell them to industries to reduce their harmful environmental effects.
This, in turn, helps them to generate additional revenue.
Crop Residue Management
Though crop residues provide tremendous environmental services, they are considered waste materials. They have to be recycled by acknowledging their importance as a natural resource.
Recycling of crop residues
Conventional farming methods have led to declining soil organic matter, increased soil erosion, and surface and groundwater contamination.
Good crop residue management in agricultural lands positively impacts soil quality.
Using crop residues in the field, either by leaving them directly in the open field or incorporating them with plowing or other field operations, is an age-old practice.
This provides several benefits to the soil by adding organic manure, decreasing soil erosion and weeds, increasing the activity of microorganisms in the soil, and enhancing the water-holding capacity.
The enhancement of organic matter in the soil through crop residues also improves the structure and quality of the soil.
- Enhancing soil organic matter
Modern agriculture practices have resulted in the reduction of soil organic matter. The decline in water infiltration and plant residues has reduced microbial and invertebrate activities in soil.
We can especially see the decrease in the earthworm population in the soil due to the absence of organic residues and the burning of these residues.
If not taken seriously, this will hinder the crop yield and create an imbalance in soil nutrients.
Using the crop residues might help maintain a considerable amount of organic matter in the soil, essentially where crop rotation is included, and green manure or green leaf manure is incorporated for a short period.
Biological nitrogen fixation by leguminous crops and the recycling of fixed N when leguminous crop residues are returned to the soil are the best examples of how residues can benefit the soil to uphold nutrients.
Although crop residues contain macro and micronutrients, macronutrients like nitrogen, phosphorus, potassium, and sulfur are economically significant.
It is considered that 1 ton of straw contains 16 % nitrogen, 5 % phosphorus, and 35 % potassium.
- Protecting soils against soil erosion and improving water retention
Soil erosion is a significant threat to agriculture as it abundantly removes nutrients in the soil.
Soil or wind erosion can be controlled through crop residues by reducing wind speed for soil particle movement and reducing soil surface runoff by increasing infiltration rate.
Reduced erosion and increased water-holding capacity help to boost crop yields.
- Soil Aeration
Crop residue cover improves soil aeration by promoting a free exchange of gases between the soil and the atmosphere. This is facilitated by increasing structural stability, porosity, and soil drainage, further decreasing surface crusting.
- Weed control
Crop residues can suppress weed growth by acting as a mulch in the soil. This layer restricts nitrogen availability and sunlight near the soil and inhibits the growth of weeds.
Other uses of crop residues
Since the beginning of civilization, crop residues have been used in many ways. They are popularly used as household fuel, animal feed, and composting material in many developing and underdeveloped countries.
As Household fuel
Crop residues are an essential energy source in some parts of the world. Pruned leaves, dried stems, and stubble are generally used as fuel for cooking and lighting. However, it is a cheap fuel source and beneficial to low-income families; the smoke released while burning causes health hazards and pollution.
For Mushroom cultivation
The straw is widely used in mushroom production.
Rice and wheat straw are popularly used as a substrate in producing button, oyster, and paddy straw mushrooms.
This can further be used for composting after harvesting mushrooms.
Using inedible Phyto mass in edible mushrooms can add economic value and is densely nutritious.
Biofuel production
In recent years, awareness among the people of the need to use clean fuels has risen exponentially.
There is an increase in the usage of crop residues for energy generation and as a substitute for fossil fuels.
Some crops, like sugarcane and Sorghum, are considered best for biofuel production due to their high carbohydrate content.
Compared with other renewable energy sources like solar and wind, biofuels are more accessible to store, inexpensive, and environmentally friendly.
However, transporting large volumes of straw and infrastructural development for biofuel production is costlier.
Building materials
The conventional method of using cereal straw for roofing and straw-clay mixture to make bricks and walls is still used in some areas to construct sheds and houses. Contrary to this, a modern approach of using clean shredded straws to make boards for interior partitioning can be seen popularly in many areas. This shows the efficient repurposing of the residues.
Feed and Bedding
- As Animal feed
Crop residues are used as feed for domestic animals in most parts of the world. The animals graze directly in the harvested grain field or are given husk or chopped residues with additives like pellets or other nitrogen-rich compounds.
Most crop residues are poor in nutrition and high in fiber content. Lignin present in residues makes them difficult to digest. So, feeding these residues untreated could impede animal digestibility, further affecting their performance.
Here is the list of the residues from different crops used as animal feed
| Sl. No | Crop | Residue used as feed |
|---|---|---|
| 1 | Rice, wheat, barley, sorghum, millets, | Straw |
| 2 | Maize, rice, wheat | Barn |
| 3 | Maize | cobs and Stover |
| 4 | Sugarcane | Bagasse, molasses |
| 5 | Pulses | Hay |
| 6 | Sunflower, olive, linseed, mustard | Cakes |
- Bedding
Cereal straw’s high water absorption property is an excellent material for animal bedding. Using straws further to keep animals clean makes it easier to manage manure and limit the leaching of nutrients. This can be later used as organic waste for plants.
Composting
Straw from crops, especially paddy and wheat, is used in compost preparation along with cow dung and kitchen waste. This compost serves as an organic manure for the soil.
Crop residues should be treated as valuable to enhance productivity and improve soil quality and sustainability.
Agricultural crop residues and their proper management can also play an essential role in helping society cope with increased greenhouse gas emissions from the burning of fossil fuels.
It is seen that with intense modernization, there is a steep decline in the use of crop residues as household fuel in bedding and composting.
This is due to the increasing use of biofuels, labor-intensive techniques for composting, advanced construction materials, and decreased crafting. A few countries have also stopped using residues as feed for animals. For sustainability, residue recycling must be promoted.
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