«Abstract Tanks were an integral part of rural life in India traditionally. However, with decreasing collective action by the community inappropriate ...»
4.0 Impact on Soil The clay content of the tank silt ranged from 60 to 80%, while its application to the field reduced the bulk density of the soil from 1.5 to 1.25 g cc-1. Addition of tank silt at the rate of 50, 100, 150 and 375 tractor loads per hectare improved the available water content by 0.002, 0.007, 0.012 and 0.032 g g-1 soil, respectively. All the farmers were in agreement that the moisture retention had gone up by 4 to 7 days, which plays an important role during the period of prolonged dry spells. This was confirmed through gravimetric studies that the available water content in the root zone increased by one per cent, i.e., from a normal 6% to 7% with addition of 100 tractor loads per hectare. Farmers believe that once applied, the impact on crop yield will remain for three years, but the invisible aspect is the permanent change in physical and chemical properties of soil. A change in the clay percent was noticed from 20 to 40 in the root zone, while there was no change in the silt content. A decrease in coarse sand and fine sand was noticed. No change in pH, EC and organic carbon was noticed, while an appreciable change was observed in available N, P and K and moderate reduction in sulphur. Improvement in clay content will not only retain higher moisture but will also reduce the losses of nutrients through leaching because of improved cation exchange capacity (CEC).
5.0 Impact on Crop Growth and Yield In an observation made on plant population and growth of rabi maize 45 days after sowing (DAS), indicated that not only silt-received-plot had higher plant population but also higher plant height (Table 5). Most of the farmers interviewed reported savings on fertilizers ranging from Rs. 2500 to Rs. 3750 per hectare in case of cotton, which is a major crop grown in this area. The increase in the yield of cotton was to the tune of 1000 kg ha-1. Farmers could achieve this kind of response with the application of 100 tractor loads per ha. Farmers paid Rs. 50-60 for each trip of tractor depending upon the distance plus Rs. 10 towards contribution. A farmer for 100 tractor loads paid Rs. 6000 towards transport and contribution while the project borne the rest of Rs. 6000.
The maximum benefit was obtained in chillies and cotton and the gain was negligible in turmeric and no gain was observed for maize (Fig. 2). A detailed cost of cultivation with and without application of silt for different crops is set out in Annex-I. An additional environmental benefit was obtained through less use of pesticides through application of tank silt. Farmers reported less number of sprays in various crops that received tank silt (Fig. 3). The number of sprays reduced by two compared to the normal, which resulted in saving of Rs. 2500 ha-1 in cotton, chilli and turmeric, respectively while Rs. 1750 ha-1 in maize.
31215 31075 30000 24620 20000 10210 10128 10000 7720
Figure. 3. Savings on pesticides with application of tank silt in various crops.
6.0 Economic Evaluation The economic feasibility of the removal of silt was estimated. The quantity of silt removed from different tanks amounted to 76393 tons. The total cost incurred in the removal of silt amounted to Rs. 11,33,190. The value of silt was quantified in terms of fertilizer equivalent costs for different nutrients. The nutrients retrieved from silt were considered to be beneficial as against the expenditure (cost) incurred in removing the silt from the tanks. The value for various nutrients is presented in Table 6. Additionally, the process of silt application to farm lands that is rich in organic C resulted in C mineralisation and higher nutrient availability, thereby helping plant growth and greater fixation of C through photosynthesis.
The benefit-cost ratio was found to be highly variable and ranged from 0.44 to 1.11, which is lower than the B:C ratio reported earlier for tank de-silting in Medak district (Padmaja et al. 2008). Average benefit-cost ratio of 0.72 is not reflecting the true picture as physical and other ecosystem benefits are not accounted. It is worth noting that fertilizers are supplied at 50% of the production cost and the government meets the rest as subsidy. If subsidy is accounted, the average B:C ratio will become 1.44 and recycling of silt back to the farm lands will become highly economical proposition. Indirect benefits are many and difficult to account in rupee terms. Application of the silt back to the agricultural fields forms an improved agricultural management practice that enhances and protects the soil quality, resulting in improved production capacity of the soil and reverses the process of land degradation. The impacts of recycling will be long lasting and need to be studied for longer period.
11 Estimation of silt requirement based on silt quality and crop need A simple formula has been devised to meet the crop nutrient requirement in terms of nitrogen equivalent. In general, tractors are used for transport of tank silt, therefore, estimation need to be made in terms number of tractor loads required to meet the need of a particular crop. The impact will be there on the successive crops too. An example of cotton is given below which has a recommended dose of 120 kg N ha-1. About 117 tractor loads are needed to meet N requirement of cotton using Koppula tank silt, having 0.0412% available N. Any increase in N content of tank silt will reduce the number of tractor loads needed per unit area. Therefore, preference may be given for de-silting of tanks having high fertility.
7.0 Policy Implications The past experiences of de-silting in Medak and Warangal indicate the presence of all the valuable nutrients required for plant growth in adequate quantities. Recycling of tank silt will overcome the deficiency of nutrients observed in many soils, particularly that of zinc, boron and sulphur and will also improve organic carbon content of soil, resulting in improved soil physical properties. The following interventions should be planned and implemented in view of economic viability, social acceptability and eco-friendliness of tank de-silting.
• Tank silt to be considered as a substitute for the fertilizer and a part of subsidy given to fertilizers need to be diverted for tank de-silting and recycling of nutrients to farm lands. Fertilizers provide one or two nutrients, while silt provides all the nutrients in adequate quantities and also improves soil health and water-holding capacity essential for drought-proofing in rain-fed areas.
• De-silting operations of the existing tanks could be included in the National Food for Work Programme, which creates employment as well as restores the asset for harvesting rainwater.
• Provide soft credit line to farmer to apply tank silt to the fields and credit support to various government programs/panchayats for undertaking de-silting operation.
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Note: Varieties: RCH-2, Bollguard, Price: Rs. 18.0 kg -1 Cost of urea Rs. 255 per 50 kg, DAP Rs. 485 per 50 kg, MoP Rs. 232 per 50 kg Chillies
Note: Varieties grown: Bioseed, Kargil, Monsanto double, Price Rs. 4.90 kg-1 Cost of urea Rs. 255 per 50 kg, DAP Rs. 485 per 50 kg, MoP Rs. 232 per 50 kg 16 About ICRISAT The International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) is a non-profit, non-political organization that does innovative agricultural research and capacity building for sustainable development with a wide array of partners across the globe. ICRISAT’s mission is to help empower 600 million poor people to overcome hunger, poverty and a degraded environment in the dry tropics through better agriculture. ICRISAT is supported by the Consultative Group on International Agricultural Research (CGIAR).