Published in: May 2018
Soil fertility is a natural gift for both animals and plants. Soil is fundamental to life, and fertile soil is crucial for good crop yields.
Since crops absorb all their necessary nutrients from the soil, it is essential to maintain soil fertility to ensure they can access these nutrients. Natural fertilizers play a crucial role in maintaining this soil fertility.
In Tamil Nadu, soils generally have low levels of organic matter and nutrients. However, both are essential for improving soil fertility. The biological properties of soil degrade due to reduced levels of organic matter and the destruction of soil microorganisms. To enhance these properties, natural fertilizers should be added during each crop cycle or annually.
Easily accessible and low-cost natural fertilizers include green manure crops and green leaf manure crops. Green manure crops involve growing a crop and then plowing it back into the soil. These crops, such as sunn hemp, dhaincha, sesbania, gliricidia, and indigo, form root nodules that store nitrogen from the air.
Types of Green Manure Crops
Sunn Hemp
Sunn hemp grows quickly and provides both fiber and manure. It is suitable for garden lands but not for areas with high water levels or continuous waterlogging. It can be intercropped with coconut trees due to its ability to grow in shade. This crop reduces soil nematodes and, when plowed during flowering, releases organic acids that reduce soil salinity and convert insoluble nutrients into absorbable forms.
- Seed Requirement: 25-35 kg per hectare.
- Method: Mix seeds with 1 kg rhizobium and 1.5 liters of cooled rice or maida gruel, dry in shade for half an hour, and then sow.
- Irrigation: First watering after sowing, second on the third day, and then once every 10-15 days. Plow back at 45-60 days during flowering to yield 13-15 tons of green manure per hectare.
Dhaincha
Dhaincha is suitable for saline soils and grows quickly, providing 10 tons of green manure per hectare in a short period. It thrives in both waterlogged and drought-prone areas and releases organic acids that improve soil structure.
- Seed Requirement: 50 kg per hectare.
- Method: Mix seeds with 1 kg rhizobium and 1.5 liters of cooled rice or maida gruel, dry in shade for half an hour, and then sow.
- Irrigation: Similar to sunn hemp, with plowing at 45-60 days to yield 25 tons of green manure per hectare.
Indigo
Indigo is not grazed by livestock and grows slowly. After repeated sowing for 2-4 cycles, it self-seeds in the soil. It is drought-resistant and suitable for summer fallows.
- Seed Requirement: 15-20 kg per hectare.
- Method: Soak seeds in 1.5-2 liters of concentrated sulfuric acid for 30 minutes, wash 10-15 times, dry in shade, and then sow.
- Irrigation: Water similarly to sunn hemp, plowing at 60 days for 6-7 tons of green manure per hectare.
Manila Agathi
This tropical leguminous green manure crop, brought to India by the International Rice Research Institute, thrives in wet conditions and waterlogged areas.
- Seed Requirement: 40 kg per hectare.
- Method: Soak seeds in 4 liters of concentrated sulfuric acid for 10 minutes, wash 10-15 times, mix with rhizobium, and sow.
- Irrigation: Similar to other green manure crops, plowing at 45-50 days for 20 tons of green manure per hectare.
Benefits of Green Manure Crops
Green manure crops enrich the soil with essential nutrients and organic matter, improving soil structure, moisture retention, and aeration. They help reduce soil erosion and salinity, enhancing the soil’s ability to support future crops.
Incorporating green manure crops into crop rotations can significantly enhance soil fertility and crop yields, supporting sustainable agriculture practices. By using these natural fertilizers, farmers can protect and improve soil health, ensuring long-term agricultural productivity.
Dr. M. Shanmuganathan, Dr. L. Chitra, Dr. V. Bhaskaran, Sugarcane Research Station, Sirugamani, Trichy – 639 115.
