Introduction
Soil and water conservation (SWC) engineering involves application of suitable engineering measures for conservation of rainwater with reduced soil erosion and judicious management of available land and water resources in the watershed. The implementation of suitable SWC measures in the watershed depend on soil type and depth, land slope, rainfall, infiltration, runoff and land use. It helps in breaking the slope, control of flow velocity and soil erosion, reducing the volume of surface runoff, increased infiltration, retention of soil moisture and fertility, maintaining good soil cover by vegetation and safe drainage of excess rainwater from the field.
The arable land in watershed is always under high pressure due to continuous soil erosion with rainwater every year and it should be curbed with appropriate treatment measures. From a study in eastern ghat region of India, Naik et al., (2015) reported annual soil loss of 13.34 million tonnes from the cultivable area at the rate of 43.86 t ha-1 yr-1 and they mentioned that soil loss is a menace to agriculture and it is to be tackled properly with the adoption of suitable conservation measures. In this context, the following SWC engineering measures are scientifically found very much effective and can be suitably implemented in arable lands in watershed for erosion control and minimizing the land degradation.
SWC engineering treatment measures suitable for arable land
Soil and water conservation engineering measures in arable land mainly includes bunding/trench cum bund, trenching, conservation bench terracing (Sharda et al. 2007), bench terrace, conservation ditching, contour stone wall, vegetative filter strips and moisture conservation pits.
Bunding/Trench cum bund
There are two types of bunding viz contour bunding and graded bunding. Contour bunds are small earthen embankment type structures constructed on contour lines and adopted in low rainfall areas with annual rainfall less than 800 mm and land slope 2 to 6%. Graded bunds are adopted in high rainfall areas with more than 800 mm annual rainfall and land slope up to 10% with low infiltration rate (< 8 mm/hr). Graded bunds are laid along pre-determined longitudinal grade instead of along the contours for safe disposal of excess runoff from the field. The gradient may vary from 0.4 to 0.8 %.( 0.4 for light soils and 0.8 for heavy soils).
The bunds control the velocity of flow, store the excess runoff and allow excess runoff to drain safely to downstream. Bunding increases the time of concentration of rainwater and permit more infiltration and maintains healthy soil moisture and fertility for better crop growth.
Trenching
These are trenches constructed along the contour by excavating the soil. Contour trenches are effective measure for soil and moisture conservation in varying rainfall, soil types and depths, and sloping conditions. The trenches break the slope, reduce the velocity of surface runoff and store the excess runoff. These are of two types:
1.Continuous contour trench
When the land slope is below 8%, such trenches are constructed without break in their length i.e. 10 to 20 m long across slope with 30-50 cm depth and bottom width, and trapezoidal in shape.
2. Staggered trench
It is preferred in varied land sloping conditions (8-33%). In this case, the length of trench is kept short i.e. 2-3 m and row spacing vary from 3-5 m. It is mostly suitable for hilly areas with undulating topography.
Conservation bench terracing (CBT)
The CBT system is most suitable in gentle land slopes (up to 10%) for reduction of slope length, minimizing the velocity runoff, more infiltration and control of soil erosion. In this case, land is divided along the slope into 2:1 ratio. The lower 1/3rd area is levelled for collecting the runoff from the upstream 2/3rd area with natural sloping condition. Upper 2/3rd area is cultivated with less moisture requiring crops i.e. maize, millets etc. and the lower 1/3rd levelled terraces is cultivated with more moisture requiring crops i.e. paddy, mustard, vegetables etc.
Bench terracing
Bench terraces are constructed on steep sloping lands with relatively deep soils for cultivation purposes. It includes construction of series of level steps or benches by cutting and filling method in hills up to 60% land slopes. Bench terracing reduces slope, controls the velocity of runoff and erosion, and retains soil moisture for crop growth.
Conservation ditching
These are inverted form of bunds specially dugout in black soils to break the land slope, storing runoff, controlling erosion, avoiding cracks and breaching of bunds. The moisture conserved in the ditch helps in healthy crop growth during dry spells. The eroded soils also get deposited in the ditch and soil loss is reduced.
Contour stone wall
In high rainfall area with lateritic and gravelly soil, and having land slope varying from 15 to 40%, this treatment measure is practiced. It is constructed of locally available loose stones so it is called stone wall. In some places only stone pitching is done in downstream side along with contour bunding due to less frequency of intense rainfall and non-availability of more loose stones. It may be done with planting of local grass in upstream side for the better performance and durability. This helps in breaking the land slope, reducing the runoff velocity and controlling the soil erosion.
Vegetative filter strips (VFTs)
It involves plantation of suitable grass/fodder species in rows in staggered way across the land slope to act as a barrier for controlling the runoff velocity and erosion. The fibrous root system of grass binds the soil and the grass cover filter the run off, arrest the sediments and thus infiltration is increased. The fodder can also be used for feeding the livestock to have an alternate source of income for the farmer.
In-situ moisture conservation pits
Small pits of suitable dimensions are constructed over the land surface by excavating the soil to arrest surface runoff and silt and thus leading to storage of runoff and ground water recharge. The pits constructed in the field impounds the rainwater during rainy period and results in healthy soil moisture and nutrient status for the plant growth.
Conclusion
The arable land in the watershed is the most fertile and productive land and its conservation is very much needed by controlling the soil erosion particularly. The suitable soil and water conservation engineering measures viz, bunding/trench cum bund, trenching, conservation bench terracing, bench terrace, conservation ditching, contour stone wall, vegetative filter strips etc. can be adopted and implemented to reduce the slope length, control of velocity of runoff with less soil erosion and simultaneously conserving the soil moisture in arable land in watershed. These treatment measures should be scientifically executed keeping in view the requirement of field conditions and it may definitely help farmers’ community for sustainable agricultural growth and their social life as well.
Reference
Naik, B. S., J. C. Paul, B. Panigrahi, and B. C. Sahoo. 2015. Soil erosion assessment from farming lands of Eastern Ghat Region of Odisha. Ind. J. of Soil Cons., 43: 33-37.
Sharda V. N, G. P. Juyal, C. Prakash and B. P. Joshi. 2007. Training Manual Soil conservation and watershed management, Vol-II, (soil water conservation engineering).Central Soil and Water Conservation Research and Training Institute (CSWCRTI), Dehradun, Uttaranchal, pp. 1-410.
Authors
Dr. Bhupendra Singh Naik, Dr. Dhruba Charan Sahoo, Dr. Praveen Jakhar, Dr. Partha Pratim Adhikary, Hombe Gowda, H.C. and Dr. Ravi Dupdal
Corresponding Author: naikbsn@gmail.com
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