The plant nutrients may be supplied through mineral fertilisers and organics including inputs through biological processes. Nevertheless, the results of a large number of experiments on manures and fertilisers conducted in the country have revealed that neither the mineral fertilisers alone nor the organic sources exclusively can achieve the production sustainability of soils and sugarcane under a highly intensive cropping system. Therefore, an integrated nutrient supply system (INSS) involving the use of mineral fertilisers in conjunction with organic manures/wastes coupled with inputs through biological processes, discussed below, will be essential to achieve higher productivity and sustainability of soils and sugarcane. The use of organics and biofertilisers will further help to bridge the increasing gap between demand and supply of fertilisers. Legumes: The legumes in sugarcane farming system are grown either in sequence or as intercrops for green manuring/grain/fodder. Green manure legumes preceding sugarcane give a benefit of 19-43 percent increase in the yield of spring sugarcane and contribute 41-85 kg nitrogen/ha through biological nitrogen fixation. An integrated use of different green manure crops with mineral fertilisers reduces N requirement of sugarcane besides increasing availability of micronutrients and nutrient – use efficiency. However, this practice has almost disappeared from sugarcane farming due to population pressure on land for other food crops. Nevertheless, growing of legumes in interrow spaces as intercrops or companion crop for grain/fodder/green manuring with autumn/spring/late planted sugarcane is considered a very useful innovation in economising the resources. This practice has shown promise for fertiliser – N economy in terms of 10-15% increase in the yield of sugarcane ratoon. Organic manures: The organic manures play a direct role by supplying macro-and micro-nutrients and an indirect role by improving the physico-chemical and biological environment of the soils. The long term soil studies on sugarcane for 30 years have established the superiority and necessity of the application of FYM/compost as a basal manure for obtaining soil fertility of an optimum level. The decline in cane yield observed with time can be arrested to some extent by the application of FYM/compost and more so by an integrated application of mineral fertilisers with organic manures. In fact, with an increasing deterioration in soil fertility /productivity, there is, and in future will be, a greater need to reintroduce the practice of supplying a part of the total fertiliser-N to sugarcane in the organic form. Crop residues: Addition of green leaves from outside has the similar effect to that of above ground portion of a green manure crop incorporated into the soil. The tops of a green manure crop may contribute about 63 percent of the total benefits accrued by green manuring the whole crop. The green manuring of potato foliage having 2.59 to 2.68 per cent N may economise 46 kg/ha N whereas potato inter-cropping with sugarcane saves 66 kg/ha N for sugarcane. An integrated use of 5 t cane trash/ha with 75 kg/N/ha in sub-tropics and with 175 kg N/ha in tropics economises nearly half of the N applied to sugarcane. The positive value of trash lies in its capacity to minimise N losses from the soil and to increase organic matter level in the soil. The cane trash obtained at 10-20% of the cane produced contains 0.42 per cent n, 0.15 per cent P and 0.57 percent K besides 25.7, 2045, 236.4 and 16.8 ppm Zn, Fe, Mn and Cu, respectively. At the rate of 10 percent of the cane produced, at least 38 million tonnes of trash will be available during 2010A.D. This much trash will have the potential to supply 0.16 and 0.22 million tonnes of N and K, respectively besides 57.0, 77.7, 8.98,1.0 and 0.68 thousand tonnes of P, Fe, Mn, Zn and Cu , respectively. Factory wastes: Filter cake/pressmud cake, a by-product of sugar industry, is produced at 3-7 percent of the cane crushed in a sugar factory. On an average, each tonne of oven dry sulphidation pressmud cake (SPMC), contains 17,36, 14 and 23 kg of N, P, K and S respectively besides secondary and trace elements. Thus, the fresh SPMC having 80 percent moisture likely to be produced at 3 percent of 249 million tonnes of cane crushed will have the capacity to recycle 25.3, 53.7, 20.9 and 34.3 thousand tonnes of N,P, K and S, respectively besides secondary and trace elements during 2010 A.D. An economy of 50-75 kg N/ha has been reported in sugarcane cropping system by several research workers by an integrated use of SPMC with mineral fertilisers. The N-use efficiency by 4-8 percent is also increased in sugarcane due to integrated use of SPMC and fertiliser-N. The SPMC has been reported to increase organic carbon content and the availability of N, P,K.S, Zn,and Mn in the soils. It has also proved itself a good sulphur source in sugarcane. Biofertilisers: Some of the species of Azotobacter, Azospirillium, Acetobacter and Bacillus have been found to economise fertiliser N by 25 percent of its quantity applied to sugarcane. Therefore, biofertilisers have a promise for N economy in sugarcane farming. The foregone discussion suggests that a judicious combination of both the organic manures/materials and mineral fertilisers may serve a potential tool for sustaining the productivity of soil and sugarcane in sugarcane-based intensive cropping system on a long term basis. Effect of Cropping Systems on Yield of Sugarcane: The results of an experiment conducted for 40 years at Mandya (Karnataka) on the long term effects of manuring sugarcane in different cropping systems on cane yield indicate that the yield of unmanured –sugarcane decreased considerably in cereal –based cropping systems. The inclusion of legumes such as sunnhemp and lucerne in the cane culture not only sustained the yield of unmanured sugarcane but also improved the productivity of manured sugarcane. Efficiency of Plant Nutrients: Inadequate replenishment of plant nutrients has turned most of the Indian soils deficient in N and has also resulted in the emergence of deficiencies of P, K, S, Zn, Fe, Mn, and Cu in soils and plants on a large scale. Consequently, each kilogram of soil-applied N,P,K,NPK, S,Zn, Fe and Mn have given yield responses of 0.07 to 0.35, 0.06 to 0.13, 0.01 to 0.28, 0.06 to 0.16, 0.35, 2.18, 2.08 and 2.51 t cane, respectively. The yield responses were 5.52, 5.80, 2.34 and 2.40 t cane for each kilogram of foliar applied Zn, Fe, Mn and Cu, respectively. Every kilogram of soil-applied P produced 0.12 and 0.04 t cane in first and second ratoons, respectively whereas that of S produced 0.29 t cane in the first ratoon. The use efficiency of nitrogenous fertilisers on farmer’s fields generally ranges from 30-40 per cent. It can be increased to 60-65 percent as obtained in experimental fields. |
|
|
