Indian farmers have traditionally used de-oiled Neem cake as a fertilizer in their fields. The dual activity of Neem cake as fertilizer and pest repellent, has made it a favored input. Neem leaves have also been used to enrich the soil. Together, they are widely used in India to fertilize cash crops. When Neem cake is ploughed into the soil it also protects plant roots from nematodes and white ants. Farmers in southern parts of India puddle neem leaves into flooded rice fields before the rice seedlings are transplanted.
Application to the Neem seed cake to crops provides them with various nutrients. Besides the Neem seed cake also reduces the number of soil insect pests, fungi, bacteria and nematodes and protects the crop from damage caused by these organisms. Neem seed cake can also reduce alkalinity in the soil by producing organic acids when mixed with the soil. The calcium and magnesium present in Neem cake also aid in removing alkalinity.
For cash crops such as turmeric, sugarcane, banana and cardamom, 200 kg per hectare of Neem cake is applied. For black pepper and betel vine 250 g per plant is applied. Neem cake is also extensively used for citrus trees, jasmine, roses and vegetable crops as an organic manure.
Neem for Soil Fertility & Nutrient Management.
Good soil fertility means good crop yields. Preventing the loss of plant nutrients from an ecosystem is important for soil-fertility management. Nitrogen, phosphorus, and potassium (N,P,K) are the three major elements which determine soil fertility and should be ideally present in 4:2:1 ratio; aberrations affect fertility and therefore crop yield. Urea, containing 46% of N, is applied to crops in the largest amounts; but less than half of this N, in the form of nitrate, is available to the crops.
The rest is lost through ‘leaching’ or by ‘volatilization’, or by surface run-off after a heavy shower, (Prasad and Power 1995). Leaching of soluble nitrates into the subsoil and, eventually into ground water, is well known. Nitrate losses of 50 to 70% through leaching were observed in rice crops in India.
Leaching not only depletes precious nitrate but also takes away clay, soil, and organic matter, leading to low chemical soil fertility and low plant-available water reserves. Ammonia volatilization also can contribute to a nearly 60% nitrate loss. Loss through volatilization occurs when the denitrifying bacteria reduce the nitrate to elemental nitrogen and nitrous oxide which escape to the stratosphere and cause ozone depletion and also contribute to greenhouse warming. On the other hand, nitrate build-up in drinking water can reduce the blood’s ability to transport oxygen, especially if the nitrates are converted into nitrites (blue-baby syndrome). Even ruminants are vulnerable to nitrate or nitrite poisoning, leading to poor growth rates, reduced milk production, and increased susceptibility to infections, and even abortions.
One way to minimise nitrate loss is to apply the urea more than once in smaller quantities or, alternatively, to use a slow-release urea which makes the urea available in the soil for a longer time. Bains et al. (1971) in field trials in India found that an acetone extract of neem kernel was an excellent nitrification inhibitor, even better than sulfur-coated urea. Ammonia volatilization, urea hydrolysis, and leaching, were all reduced when urea was blended or coated with neem cake.
Results from several field experiments show that neem cake coating of prilled urea increased nitrogen uptake by 4.5 to 19.4%. The increase in rice yield due to neem cake coating/blending of prilled urea ranged from 1 to 54%, the average being 9.6%. Neem cake coated urea applied to rice or sugarcane also left a carryover effect and increased sugarcane yield by 7% in the ratoon sugarcane crop.
Ready-to-use, neem-based urea-coating agents, such as ‘Nimin’ (containing ca. 5% neem bitter tetranortriterpenoids) are now commercially available in India.
Application of Nimin-coated urea (1 part Nimin: 100 parts urea, wt/wt) reduced losses of fertiliser N through leaching and de-nitrification by 30-35% and increased yields in treated crops by up to 25% (Vyas et al. 1996). The bitters in Nimin delay the de-nitrification process up to 30 d by either killing nitrifying bacteria or suppressing their activity. Coating urea with Nimin could bring a saving of up to 20% of urea. The technology is becoming popular with farmers in India where annual Nimin sales are now ca. 700 metric tons.
Neem for Sustainable Agriculture and Environmental Conservation
In the past two decades, “green revolution technologies” have more than doubled the yield potential of rice and wheat, especially in Asia. These high-input production systems requiring massive quantities of fertilisers, pesticides, irrigation, and machines, however, disregard the ecological integrity of land, forests, and water resources, endanger the flora and fauna, and cannot be sustained over generations. Also, we cannot look to the sea in future as fishing stocks in many parts of the world are already in crisis due to overfishing or pollution. To a great extent, future food security and economic independence of developing countries would depend on improving the productivity of biophysical resources through the application of sustainable production methods, by improving tolerance of crops to adverse environmental conditions, and by reducing crop and post-harvest losses caused by pests and diseases.
Environmentally Friendly Agricultural Technologies
Appropriate technologies, which do not assault the nature, would have key roles to play in ensuring food security, in improving human health, and in rehabilitating and conserving the environment to safeguard the well being of the posterity. Instead of striving for more “green revolutions” with emphasis on miracle seeds, hard-hitting, synthetic and engineered pesticides, and increased use of fertilizers, the future must look to natural ways and processes for augmenting agricultural productivity.
In fact, all development efforts and activities should be within well defined ecological rules rather than within narrow economic gains. Sustainable agricultural systems must be ecologically sound for long-term food sufficiency, equitable in providing social justice, and ethical in respecting both future generations and other species. For developing countries, the use of the neem tree may provide a key component in more sustainable agricultural system.