Course Content
Crop Production (Unit 6)
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ASRB NET / SRF / Ph.D. Agronomy
Agricultural and Agro-Industrial Residues and Their Recycling

Definition and Significance

  • Agricultural Residues:These are the non-edible plant parts left in the field after harvesting the primary economic product (grain, fruit, etc.). They are by-products of crop cultivation and harvest. Examples: Straw (rice, wheat), stover (maize, sorghum), husks, shells, stalks, and vines.
  • Agro-Industrial Residues:These are the wastes generated during the processing of primary agricultural produce in mills, factories, and processing units. Examples: Bagasse from sugar mills, rice bran from rice mills, oilseed cakes from oil mills, fruit pomace from juice industries.
  • Significance of Recycling:If not managed properly, these residues can lead to:
    • Environmental Pollution: Open burning causes severe air pollution (smog, PM2.5, GHGs).
    • Nutrient Loss: Valuable nutrients locked in the biomass are lost forever.
    • Waste of Resources: They represent a massive underutilized resource for energy, feed, and soil health.

 

  1. Major Types of Residues

Category

Examples

Key Characteristics

Agricultural Residues

 

Field-based, Lignocellulosic, Bulky

Cereal Crops

Rice straw & husk (largest vol. in India), Wheat straw, Maize stover/cobs, Sorghum & Millet stalks

High C:N ratio, high silica (esp. rice), slow decomposition.

Pulse Residues

Pigeonpea stalks, Chickpea husk

Relatively higher nitrogen content.

Oilseed Residues

Groundnut shells, Mustard straw & husk, Sunflower heads

 

Horticultural Residues

Banana pseudostems, Vegetable peels & vines, Fruit trimmings, Coconut coir & pith

Often high moisture content, perishable.

Agro-Industrial Residues

 

Factory-based, Processed, Concentrated

Sugar Industry

Bagasse (fibrous residue), Molasses (viscous syrup), Press mud

Bagasse is fibrous; molasses is rich in sugars.

Cotton Industry

Cotton stalks, Cotton linters (short fibers), Cottonseed cake (after oil extraction)

Stalls are woody; cake is a protein-rich feed.

Oil Mills

Oilseed cakes (e.g., Mustard cake, Groundnut cake), De-oiled bran

Rich in protein and minerals, used as feed/fertilizer.

Rice Mills

Rice husk (high silica), Rice bran

 

Breweries/Distilleries

Spent wash, Distillery sludge

High organic load, can be a major pollutant.

Dairy Industry

Whey, Dung, Slurry from biogas plants

High Biological Oxygen Demand (BOD).

Food Processing

Fruit & vegetable waste, Coffee husk, Tea waste

Perishable, can be composted easily.

 

  1. Problems with Unscientific Management; Open Field Burning:Prevalent in the Rice Wheat systemof Punjab, Haryana, and Western UP due to short window between crops.
  • Nutrient Loss:Burning 1 tonne of rice straw causes approx. loss of: 5 kg N, 2.3 kg P₂O₅, 25 kg K₂O, 1.2 kg S.
  • Air Pollution:Releases massive amounts of PM₂.₅, PM₁₀, CO₂, CO, NOx, and SO₂, contributing to smog and health hazards.
  • Soil Health Degradation:Kills beneficial soil microbes, reduces soil organic matter (SOM), and leads to loss of biodiversity.

 

Challenges in On-Farm Recycling:

  • Bulkiness:High volume makes handling and transportation difficult.
  • Slow Decomposition:High C:N ratio and lignin content delay breakdown.
  • Silica Content:Especially in rice straw, impedes decomposition and feeding value.

 

Recycling and Management Strategies

i) On-Farm Management (In-Situ)

  • Soil Incorporation:Using implements like Rotavators or Happy Seeders. The Happy Seeder is a key technology for zero-till sowing of wheat into rice stubble. Benefits:Improves Soil Organic Carbon (SOC), microbial biomass, water holding capacity (WHC), and recycles nutrients (e.g., rice straw adds ~300-350 kg K/ha).
  • Composting/Vermicomposting:Converting residues into nutrient-rich organic manure by mixing with animal dung and microbial inoculants (e.g., TrichodermaPleurotus fungi).
  • Mulching:Using straw as a soil cover in horticultural crops to conserve moisture, suppress weeds, and moderate soil temperature.

 

ii) Livestock Feed

  • Cereal Straws/Stovers:Used as roughage for cattle. Treated with 4% Urea or NaOH to break lignin bonds and improve digestibility.
  • Agro-Industrial Byproducts:Oilseed cakes, bran, molasses, and distillery grains are concentrated sources of protein and energy, used as feed supplements.

 

iii) Energy Generation (Bioenergy)

  • Biogas Production:Using dung, press mud, and food waste in anaerobic digesters to produce methane for cooking and electricity.
  • Bioethanol:Fermenting sugar-rich (molasses) or starchy residues (spoilt grains) into ethanol.
  • Briquetting/Pelleting:Compressing loose residues (rice husk, sawdust) into dense solid fuels for industrial boilers.
  • Gasification:Thermochemical conversion of biomass into a combustible gas (producer gas) for power generation.

 

iv) Industrial Uses

  • Rice Husk:Source of high-quality silica, used in cement, insulation, and steel industries. Husk ash (RHA) contains 85-90% silica.
  • Bagasse:Primary raw material for paper, cardboard, and bio-plastics.
  • Cotton Stalks:Used for making particle boards and paper pulp.
  • Coconut Coir:Used for making ropes, mats, geotextiles, and horticultural growing media.

 

v) Innovative Uses

  • Mushroom Cultivation:Paddy straw is an excellent substrate for cultivating oyster mushrooms.
  • Biochar Production:Pyrolysis of residues under low oxygen produces biochar, a stable carbon amendment that enhances soil fertility and carbon sequestration.
  • Green Manuring & Enriched Composts:Agro-industrial wastes like press mud (contains ~2-3% N, 1.5-2% P₂O₅, 2-3% K₂O) can be composted with rock phosphate to create valuable soil amendments.

 

Benefits of Scientific Recycling

  • Soil Health:Returns essential macro and micronutrients, improves SOC, soil structure, porosity, and water retention.
  • Resource Efficiency:Provides low-cost feed, fuel, and raw materials for industries, reducing reliance on imports.
  • Pollution Abatement:Eliminates the need for burning, drastically reducing GHG emissions and air pollution.
  • Circular Economy:Transforms waste into wealth, closing the nutrient and energy loop in agriculture.

 

Key Facts for ASRB NET & Exams

  • India generates ~500-600 million tonnesof crop residues annually.
  • The Rice-Wheat cropping systemalone contributes 120-150 MT of this residue.
  • The sugar industry produces ~90-100 million tonnesof bagasse annually.
  • Happy Seeder technologyis a cornerstone of the “Happy Seeder Technology” for sustainable residue management in North-West India.
  • Nutrient composition of key residues:
    • Press Mud:2-3% N, 1.5-2% P₂O₅, 2-3% K₂O.
    • Rice Husk Ash:85-90% Silica.
    • Rice Straw:~0.5% N, 0.1% P, 1.5% K.
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