Natural Nitrification Inhibitors for Augmenting Nitrogen Use Efficiency in Soil-Plant System
Agriculture in the Indian sub-continent aims at competitive production of higher level of food, vegetables and fruits and industrial raw materials from the existing cultivable land through innovative research and development applications. The land holdings with the farmers are small, not amendable to the mechanized agricultural practices responsible for high crop yields, such as obtained in the developed part of the globe. Production of agriculture per unit area and time is largely dependent on provision of fertilizers and irrigation in ample measure for the adequate expression of genetic potential of improved varieties of food grain, vegetable crops and industrial crops. Urea is the widely used nitrogenous fertilizer. However, it appears that benefits from large level of urea fertilizer can be expanded by increasing the effectiveness of fertilization. Recovery of applied fertilizer urea-N seldom exceeds 50% in many crops; it is yet low in waterlogged paddies. The products of hydrolysis and nitrification are prone to losses through volatilization, and denitrification and leaching. Arrest of N-loss in the crop fields can help increase N utilization. This, if achieved, will provide several advantages: decrease the cost of agricultural production and increase profits to farmers, expand the use of urea in optimal amount over larger cultivated area and contain N- pollution that results from inefficient use of urea-N. Regulation of urea transformation reactions that occur in soil for better utilization of its N by crops has been an active R& D area. Several classes of compounds viz. phosphorodiamidates and triamidates, sulphahydryl reagents, dihydric phenols, aminocresols, catechol, p-benzoquinones, dihydric phenols etc, have been found to restrict hydrolysis of urea in soil. Ammonium polyphosphate and phosphoric, boric and nitric acid have been found to reduce volatilization of ammonia generated from urea. Rapid nitrification or oxidation of ammonium to nitrate in soil catalysed by microbes has been founds to be inhibited by nitrapyrin (2-chloro -6- tricholoro methyl pyridine), BHC, sodium azide, sodium chlorate, dicyandiamide (DCD), ATC (4-amino-1-2-4 triazole), N-serve and certain other compounds. The use of many of these chemicals has been restricted to academic experimental levels because of high cost, lack of availability and adverse side effects. Nitrification inhibitory properties of several plants materials like Karanj (Pongamia glabra), Neem (Azaddirachta indica), and tea (Camellia sinensis) waste have been evaluated by many researchers and their advantages and disadvantages have been reported. Commercial use of these materials has not been possible due to lack of their availability, cumbersome coating process with urea, inefficient promotional activities etc. The recent inclusion of botanicals in the list of plant based materials is the natural essential oils and their by- products. The advantages of these materials are that they are easily available, cheap, eco-friendly and can be cultivated as per their requirement. This paper deals with the different aspects of plants based materials as nitrification inhibitors.