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Sub-irrigation and Shallow Groundwater as a Resource for Crop Water Use; a Review

A. A. Hassan
Agricultural Engineering Division, Bangladesh Institute of Nuclear Agriculture, P. O. Box 4, Mymensingh 2200, Bangladesh.

Abstract/ Executive Summary:

Part of evapotranspiration demand is fulfilled from shallow groundwater through the use of sub-irrigation. which in turn reduces frequency and quantity of supplemental irrigation. Recent research contributions have improved the methodology for exploiting shallow groundwater for crop water use. Where there is no surface water application. capillary movement will be only towards upward direction controlled by zero-flux plane and hydraulic gradient. Even in presence of shallow groundwater. some of the crops may need surface water additions. In such case, most of the additional water is lost through deep percolation. To minimize losses, it needs further investigation for judicial use of costly irrigation water to save energy. There are different approaches to estimate, measure, and model groundwater contribution due to capillary movement and upward flux. Model studies agree with direct measurements where there is a fixed water table. Direct measurements are not made where there is moving water table and further investigation is warranted.

Keywords: Sub-irrigation, Shallow groundwater, Crop water use

Location: BINA, Mymensingh

Start Date: 00-01-1997

End Date: 31-12-1997

Program Area: Crop-Soil-Water Management

Commodity: Water management

Objectives:

1. To evaluate shallow groundwater as a resource for crop water use.

Methodology:

At the early stage of a crop (under partial cover), the process of evaporation predominates and this reduces soil wetness and thus increase the soil water suction at the surface. This, in turn, causes soil water to be drawn upward from the lower layers which have been wetted by the capillary upward flux from the shallow groundwater. At a later stage (under full cover), transpiration predominates and the soil starts drying because water is taken up by roots. As the surface layers have become direr from the initial evaporation process, so the crop roots penetrate lower layers to extract water for its demand. Sometime, when there is a shallow groundwater, the roots of deep- rooted crops approach the water table depending on the location of the zero-nux plane. In the presence of a shallow groundwater, water uptake is not necessarily related to root distribution, and a small quantity of roots near the capillary fringe can absorb most of the water. The uptake of water required to meet crop water demand can be limited by many soil and crop related factors. It is well known that soil-transmitting property decreases as water content decreases, but few data are available on the actual magnitude or this effect of water uptake by plant roots. Unsaturated hydraulic conductivity is one or the majors limiting factors in water uptake by plant roots. The amount or water absorbed from the upper part of the soil is negligible compared with that absorbed from lower layers. Therefore, downward root growth becomes important for transporting water from the capillary fringe to roots.

Source of Information: Journal or the Institution of lngiucers. Bangladesh,Agricultural Engineering Division, Vol. 25/AE, No. I, Dec. 1998

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

A properly managed shallow groundwater of good quality is a potential resource for sub-irrigation in shallow groundwater management schemes. Again, some soil water models would help to calculate the groundwater contribution from shallow groundwater to reduce the frequency of supplemental irrigation, and would also help to control salt accumulation in the soil profile.

Knowledge Management: Journal