Stop Wasting Money on Urea! Discover the Ultimate Soil-Saving Solution: Green Manuring

The soils in Punjab are naturally deficient in nitrogen supply due to their location in a tropical semi-arid climate that does not allow for the accumulation of soil organic matter, which is a primary source of nitrogen in the soil. In the state, crop intensity is around 190%, which means at least two crops are grown throughout the year. However, the use of high-yielding varieties in this intensive farming can harm soil health, leading to lower crop productivity.

To improve soil quality and achieve high productivity, it is essential to increase the soil organic matter content, which can be done through integrated nutrient management, such as the use of organic manure along with chemical fertilizers. Organic manures like farmyard manure, poultry manure, crop residue incorporation, or green manure can be combined with chemical fertilizers. However, due to the scarcity of farmyard manure in adequate amounts, the high cost of poultry manure, and the wide carbon/nitrogen ratio of straw, green manure could be the more viable option.

Why Choose Green Manuring

It refers to the practice of growing leguminous crops, such as dhaincha, sun hemp, cowpea, and summer moong, which have a narrow C: N ratio. These crops are grown for a specific period (flowering) before being plowed into the soil. It has a beneficial effect on soil health and the subsequent crop that is grown on it. Using green manure in different cropping cycles increases nutrient storage in the soil and nitrogen availability after incorporation.

When there is no crop sown for several months of the year (after the harvesting of wheat and before the sowing of paddy), the use of green manure increases soil fertility and preserves nutrients in the upper layer of the soil. The addition of organic matter from green manure crops also improves the soil's physical properties such as soil structure, soil water infiltration, and water storage capacity. During the decomposition of these manure crops, weak acids are released into the soil which favor the solubilization of few insoluble plant unavailable nutrients, just as the use of green manure in soils with high calcium increases the amount of plant available phosphorus.

Its Nutrient Concentration

Table 1.

The amount of dry matter production and nitrogen availability in different green manure crops is given in Table No. 1. Apart from this, phosphorus in their dry matter is 0.15 to 0.20 percent, potash is 1.5 to 2.0 percent, and minor elements such as zinc, copper, iron, and manganese exist at 25-35, 12-18, 280-320, and 600-700 ppm, respectively.

Selection of Crop

While picking a green manure crop, it is important to choose crops with maximum nodules on their roots so that nitrogen from the air can be stored in the soil. Legumes should also grow quickly and have high yields. The roots should be deep enough to take in elements that have gone beyond the reach of the roots in the soil. Seeds that are cheaper and more effective in reducing the use of water and withstanding drought, such as sunn hemp and cowpea, are easier to use.

Some Key Advantages

Green manuring is an effective and inexpensive way to improve soil health by reducing soil erosion, improving soil physical properties, and increasing the soil's ability to absorb water. Green manure saves 25 kg of nitrogen (55 kg urea fertilizer) per acre in paddy and reduces the chances of iron deficiency in the paddy crop.

There is no need to add urea fertilizer to basmati by sowing green manure in the field. After plucking the summer moong beans sown after the wheat, plowing the remaining vegetative part of the moong a day or two before planting the paddy increases the yield of the paddy and reduces one-third of the nitrogen.

Green manure significantly increases soil fertility, as it increases the amount of nitrogen, phosphorus, potash, and other minor elements in the soil. The problem of weeds in the crop sown after green manure is reduced because the green manure crop suppresses the weeds due to early growth, and the weeds growing in the field are buried during the sowing of green manure before the seeds form. The method also helps in solving the problem of nematodes by increasing the number of beneficial bacteria in the soil. Saline lands can be retreated with the use of green manure.

A Fit Practice for Punjab

In Punjab, crops such as jantar/dhaicha, sunn hemp, cowpea, etc., are mainly used as green manure. Further, Punjab Agriculture University Ludhiana has recommended Punjab Dhaicha-1, PAU 1691, and Narinder Sanai-1 varieties of sunn hemp for green manure, CL 367 of cowpea. For green manure crops, sow the 20 kg seed rate.

For optimal results with green manure, it is recommended to sow dhaincha/sunn hemp at a rate of 20 kg/acre or cowpea at 12 kg/acre, after they have been soaked for eight hours. If the fields are deficient in phosphorus, it is suggested to add 75 -100 kg of single super phosphate fertilizer per acre as it boosts the growth of green manure, and removes the need for phosphorus fertilizer in the paddy crop.

The green manure crop requires 2-4 irrigations depending on prevailing weather conditions. If grown for seed, it should not experience water stress during flowering and grain development stages. The green manure crop flowers within 40-50 days of sowing and is ready to be plowed into the soil. The green manure crop should be plowed or tilled ten days before sowing maize and one day before planting paddy.

Generally, incorporation of dhaincha\ sunnhemp\cowpea into the field can save 25 kg of nitrogen (55 kg of urea fertilizer). It is recommended to incorporate sunn hemp or dhaincha in saline, sodic, or newly cultivated soils. Plowing summer moong leftovers, in the field, a day before planting paddy seedlings can save one-third of the N fertilizer. Moreover, green manuring in paddy prevents deficiency of cationic micronutrients (Zn, Fe, Cu, and Mn).

In maize, 40-50 days of green manure and 50 kg of N per acre boost crop grain yield and improve soil health. In case there is an issue of pest attack in the green manure crop, it is recommended to seek advice from experts at Krishi Vigyan Kendras or Farm Advisory Service Centers of Punjab Agricultural University.