SOIL HYDRO-PHYSICAL PROPERTIES AND PRECIPITATION CONCENTRATION INDEX IN ENHANCING RUNOFF UNDER VETIVER GRASS STRIPS
As human populations have grown and living standards have raised, the requirement for agricultural products have increased enormously. More land have been brought under cultivation, including marginal lands that are particularly vulnerable to degradation (Johnson and Douglas, 2007) by such process as Erosion, depletion of organic matter and nutrients, pollution, water-logging, and salinization.
Consequently, the domain remaining for natural ecosystems has shrunk and has been divided into smaller enclaves, to the detriment of numerous species. Two alternative approaches have been proposed to prevent further destruction of the remaining natural ecosystems and to relieve pressure on fragile marginal lands (Hillel, 2004). One way is to restrict human activities to choice areas, where production can be intensified e.g. optimizing maximum efficiency in the utilization of soil, water, energy and other necessary inputs.
Another approach is to devise naturalistic modes of production that are compatible with the environment, soil hydro-physical properties conservation. Here vetiver grass technology becomes handy. Vetiver grass is a tropical plant from Thailand (Truong and baker, 2007) that is adopted to different environmental conditions and aimed at improving and conserving highly porous, hard or friable dispersed and eroded soil to favour various types of plants and other living organisms in production optimization.
According to Herber (2009) any practice that improves soil hydro-physical properties will enhance water entry into the soil. Therefore, the present study is carried out using erosion prone soil to determine the effect of Vetiver grass strip intervention at different spacing on the water and physical properties of the soil.
Vetiver grass is found in a wide range of areas from the highlands to lowlands, but is found only scantily in the wild in Nigeria. It appears in dense clumps and is fast growing through tillening. The clump diameter is about 30cm with a height of 50 – 150 cm; the narrow, erect and rather stiff leaf is about 75 cm long and 8 mm wide. There horizontal expansion of the root system being limited to only 50 cm imposes no obstacle to nearly plants and in particular is considered and effective measure for soil and water conservation (World Bank, 1995). In other to improve soil physical properties, the use of vetiver grass was considered to be a major breakthrough in soil conservation (Blanco, 2009) when planting across the contour on slopes, it holds back eroded soil, while the clump stands above the ground and produces tillers forming a green hedges. Hence, this makes it capable to trapping eroded sediment, residues and runoff associated with heavy tropical rains, dispersing runoff and leading to the formation of natural earth terraces that eliminate the erosive power of the runoff.
Study in Nigeria and elsewhere have shown a reduction in runoff, soil loss and increase crop yield with the use of vetiver grass buffer strip (VGBS). Knowledge of soil water intake (infiltration) is required as an indicator in determining the vulnerability of an area to flood. Infiltration in soils is governed by other primary soil properties such as bulk density, porosity, soil permeability, hydrologic conductivity.
There is little or no information about the use of vetiver grass strip in Uyo, Soutern Nigeria; hence the study aim at determining the effect of vetiver grass strips intervention at different spacing on the water and physical properties of the soil.
Infiltration – the entry of water into the soil is an important property of the soil that determines whether a soil is easily flooded or flood water is easily absorbed when flood occurs. The ease or difficulty in the movement of water into the soil determines to a large extent whether land flow will occur. When the rate at which water is supplied to the soil has exceeded the rate of absorption by the soil (infiltration), there would be enough water accumulation on the surface to cause floods on flat and valley areas and runoffs will occur following the slope gradient in the landscape. Infiltration is the important property of the soil that can be explored to reduce flooding or overland flow and enhance ground water reserves.
1.1 Objectives of the Study