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Singh S.R.,CSSRI Regional Research Station | Verma C.L.,CSSRIRegional Research Station
Proceedings of the Indian National Science Academy | Year: 2010

A pore shape neutral viscous resistance model for analyzing flow through soils to estimate its saturated hydraulic conductivity in terms of routinely measured porous matrix and fluid properties has been developed. The model for saturated hydraulic conductivity requires porosity, specific surface area and soil dependent matching parameter (1/Ts) as the three soil properties, and specific weight and viscosity as the two water properties. The Ts in the matching parameter is a coefficient which has been named tortuousity in accordance with the historical nomenclature, but has a different meaning than the one propounded by Carman. Using observed hydraulic conductivity of 30 UNSODA soils, an empirical relationship between tortuousity and {(porosity/(6(1-porosity))) (clay fraction/non-clay fraction)} has been developed. The tortuousity in the proposed model is greater than unity only when {(porosity/(6(1-porosity))) (clay fraction/non-clay fraction)}< 0.01303. Individually, when the clay fraction is less than 0.0766 or porosity is less than 0.38, tortuousity is greater than unity. The viscousresistance model without tortuousity for computing hydraulic conductivity under-estimates the true hydraulic conductivity values. However, incorporation of the computed value of tortuousity in the model improves the estimates of saturated hydraulic conductivity of soils. The minimum, maximum, and average values of the matching parameter computed from the empirical model for tortuousity were found to be 0.6636, 21.2314, and 1.3706, respectively. Source

Saha R.,ICAR Research Complex for the NEH Region | Saha R.,Indian Institute of Science | Ghosh P.K.,ICAR Research Complex for the NEH Region | Ghosh P.K.,Indian Institute of Pulses Research | And 4 more authors.
Outlook on Agriculture | Year: 2010

In the north-eastern regions of India, shifting cultivation is traditional and a dominant land use practice, leading to heavy soil erosion and severe degradation of biodiversity. Agroforestry systems (AFS), which have great potential for crop and livestock production, are the best alternative to overcome the adverse effects of shifting cultivation. Agroforestry is an ecologically based, natural resource management system that sustains production and benefits all those who use the land by integrating trees on farms and in the agricultural landscape. In addition to timber, fodder, fuelwood, medicines, etc, it conserves natural resources. In this paper, the authors discuss the role of promising agroforestry systems and various multipurpose trees (MPTs) in the conservation of natural resources. These systems improved soil physical health through checking soil erosion and run-off, maintained soil organic matter, enhanced soil chemical and biological properties, added nitrogen input by trees and shrubs, and helped in the mining of minerals from lower horizons by roots and their recycling through litter fall on the ground. Of the systems studied, multistoreyed AFS [alder + tea + black pepper + annual agricultural crops], silvi-horti-pastoral [alder + pineapple + fodder grasses] and natural forest systems with suitable soil conservation measures are the most viable alternatives for natural resource management and could sustain long-term soil productivity in the highly degraded soil of this region. Source

Singh A.,Indian Institute of Technology Kharagpur | Panda S.N.,Indian Institute of Technology Kharagpur | Saxena C.K.,CIAE | Verma C.L.,CSSRI Regional Research Station | And 3 more authors.
Journal of Irrigation and Drainage Engineering | Year: 2016

The continuous increase in global population and simultaneous decrease in good-quality water resources emphasize the need of conjunctive use of groundwater and surface-water resources for irrigation. The optimal allocation of water resources can be achieved by employing an appropriate optimization technique. This paper presents an overview of the different programming techniques used for the conjunctive use planning and management of irrigated agriculture. Past papers on the applications of different programming techniques for the conjunctive use of different water sources are grouped into four categories: linear programming, nonlinear programming, dynamic programming, and genetic algorithms. Conclusions are provided based on this review, which could be useful for all stakeholders. © 2015 American Society of Civil Engineers. Source

Singh S.R.,CSSRI Regional Research Station | Verma C.L.,CSSRI Regional Research Station
Proceedings of the Indian National Science Academy | Year: 2010

Theory of drag resistance has been used to derive Darcy's law describing flow through porous media which comprised of granular particles of different diameters and densities. It has resulted in a generalized model for estimating saturated hydraulic conductivity of granular porous materials. The model has been applied to flow through soils, where particles have equal densities, by incorporating an empirical matching factor. Analysis of matching factors of 30 UNSODA (Unsaturated Soil Hydraulic Database) soils has revealed the dependence of the factor on two measurable soil properties, porosity and clay content, in the form of [{porosity2/(1-porosity)}clay fraction]. An empirical linear relationship between the (matching factor)0.1 and [{porosity2/(1-porosity)}clay fraction] has been developed for computing the factor. The model for the saturated hydraulic conductivity in conjunction with the empirical equation for computing the matching factor has reduced the average deviation between the observed and estimated hydraulic conductivity of the soils. The estimated minimum, maximum and average values of the matching factor have been found to be 1.4352, 11.7151, and 3.5683, respectively. The drag resistance model has been compared with the viscous resistance model. The comparison reveals that the drag resistance model without the matching factor is more accurate than the viscous resistance model without tortuousity. Source

Sita Singh R.A.M.,CSSRI Regional Research Station | Chhedi Verma L.A.L.,CSSRI Regional Research Station
Proceedings of the Indian National Science Academy | Year: 2011

A new model for estimating water retention characteristic curve from the routinely measured soil properties - particle size distribution, bulk density and particle density - has been developed. The model is based on the premise of a close similarity between the shapes of the water retention characteristic (WRC) and particle size distribution (PSD) curves. The aforesaid idea enables one to write every Cartesian coordinate of the WRC curve as a multiple of a scale factor and the corresponding Cartesian coordinate of the PSD curve. The approach has resulted into the suction head, hJ = CXj /Dmj, in which Cxj is a scale factor and D . is the mean particle diameter, all corresponding to theth segment of the PSD curve. The scale factor, Cxj , has been found to depend on the particle shape factor, C, volumetric water content, θJ, total porosity, Θ, and residual moisture content, θr. The model has two unknown parameters, θr and C, which have been evaluated from the observed moisture contents at two suction heads. Assuming soil particles to be spherical for which C = 6, the only unknown parameter in the model is θr whose determination requires only one set of measured data on moisture content versus suction head. Estimation of WRC from PSD data of 12 soils have yielded the average and maximum deviations between the estimated and the measured WRC curves to be lesser than two and 3.4 per cents, respectively. An equation for the air entry suction as a function of mean particle diameter and void ratio has also been derived. © Printed in India. Source

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