Effect of shallow groundwater table on crop water requirements and crop yields

doi:10.1016/j.agwat.2005.01.005

Agricultural Water Management

Volume 76, Issue 1, 30 July 2005, Pages 24-35

https://doi.org/10.1016/j.agwat.2005.01.005 Get rights and content

Abstract

Due to the increasing demand for food and fiber by its ever-increasing population, the pressure on fresh water resources of Pakistan is increasing. Optimum utilization of surface and groundwater resources has become extremely important to fill the gap between water demand and supply. At Lahore, Pakistan 18 lysimeters, each 3.05 m × 3.05 m × 6.1 m deep were constructed to investigate the effect of shallow water tables on crop water requirements. The lysimeters were connected to bottles with Marriotte siphons to maintain the water tables at the desired levels and tensiometers were installed to measure soil water potential. The crops studied included wheat, sugarcane, maize, sorghum, berseem and sunflower. The results of these studies showed that the contribution of groundwater in meeting the crop water requirements varied with the water-table depth. With the water table at 0.5 m depth, wheat met its entire water requirement from the groundwater and sunflower absorbed more than 80% of its required water from groundwater. Maize and sorghum were found to be waterlogging sensitive crops whose yields were reduced with higher water table. However, maximum sugarcane yield was obtained with the water table at or below 2.0 m depth. Generally, the water-table depth of 1.5–2.0 m was found to be optimum for all the crops studied. In areas where the water table is shallow, the present system of irrigation supplies and water allowance needs adjustments to avoid over irrigation and in-efficient use of water.

Introduction

Irrigated agriculture in the Indus basin is the major user of water in Pakistan. About 93% of the total water resources are used by agriculture (Latif, 2002). The gap between water demand and supply has increased manifolds, due to increased agricultural activities and reduced river flows. Availability of adequate good quality water is one of the most important inputs in successful crop production. Distribution of water among the canals in Pakistan is generally based on historical allocations and does not consider crop water requirements, water-table depth, and soil physico-chemical conditions. About a century ago, water allowances were fixed for different canals depending upon the surface water availability and the area to be covered. Since then many changes have taken place.

Due to seepage from the irrigation network and non-functional drainage systems, water table in many areas had risen to near the soil surface. Rafique (1990) reported that in Pakistan 1.47 million hectars (Mha) has a water table within 1.5 m of the surface. Out of this, 0.13 Mha is covered by severely saline, uncultivated soils. In non-saline soils, 0.32 Mha has water table at 1.0–1.5 m, 0.28 Mha at 0.5–1.0 m depth and 0.74 Mha within 0.5 m. By the end of the dry season, 13% of the irrigated land had water tables less than 1.5 m from the surface. However, after the monsoon, 26% of the irrigated area had the water table less than 1.5 m (Qureshi and Barrett-Lennard, 1998).

Groundwater is a flexible and reliable source of water. However, excessive pumping by deep public and private tubewells is often pulling up water with substantial salinity and is causing secondary soil salinization, whereas shallow fresh groundwater is not utilized. Therefore, there is a need for more judicious use of this precious water. Shallow groundwater could also be used as sub-irrigation by adopting proper irrigation scheduling to help bridge the gap between water demand and supply.

Ayars and Schoneman (1986) showed that during 3 years of cotton growth, for a water-table depth of 1.7–2.1 m, with the water having an ECe = 10 dS m⁻¹, the evapotranspiration (ET) contributed by the groundwater ranged from 0 to a maximum of 37% whereas Wallender et al. (1979) found that cotton extracted 60% of its ET from a saline (EC = 6.0 dS m⁻¹) water table. Pratharpar and Qureshi (1998) observed that in areas where shallow water tables exist, the irrigation requirements can be reduced to 80% of the total crop ET without reducing crop yield and increasing soil salinization. This practice not only produced good yields but also kept the soil salinity and water-table depth within the acceptable limits. Kahlown et al. (1998) showed that there was an inverse relationship between the water-table depth and the groundwater contribution despite the brackish nature of the groundwater. They found that groundwater contribution was maximum at depth less than 1.0 m and was negligible when water-table depths exceeded 2 or 3 m. Soppe and Ayars (2003) studied the soil water fluxes in the presence of saline, shallow groundwater (EC = 14 dS m⁻¹) by maintaining water level at 1.5 m depth under a safflower crop and found groundwater contribution of up to 40% of daily crop water used. On a seasonal basis, 25% of the total crop water used originated from groundwater. The largest groundwater contribution occurred at the end of the growing season when roots were fully developed. The irrigation applied was 46% less when the water table was maintained at 1.5 m depth than when the water table was too deep to be reached by the crops.

It is therefore obvious that the groundwater contribution is a significant component of water balance and should be recognized as providing part of the water needed by the crop for evapotranspiration. This will save water, energy, and labour and will also reduce the drainage effluent and help keep the water table at the desired depth.

A series of studies were carried out in lysimeters to investigate the optimum utilization of water resources under shallow water-table conditions.

Section snippets

Objectives

The main objectives of these studies were to determine (i) the irrigation requirements and evapotranspiration of various crops under different water-table depths, (ii) groundwater contribution to the crop water requirement under different water-tables depths, (iii) effect of different water table-depths on crop yields.

Material and methods

In order to evaluate the contributions of groundwater to meet the water requirements of various crops, a study was initiated in Lahore Pakistan (31° 34′ N, 74° 20′E) an area with arid climate (average maximum and minimum temperatures of 22.7 °C and 8.3 °C in winter, respectively; 36.5 °C and 24.7 °C in summer, respectively and with an average annual rainfall of 51 cm. The average rainfall during the cropping period of wheat, maize, berseem, sunflower, sugarcane and sorghum was 5, 34, 1.5, 0.6, 57

Results and discussion

The results of these studies are presented and discussed in the following sections.

Conclusions

In areas with shallow water table (generally less than 3 m), some crops can draw water from the groundwater, crop yields can often be enhanced and the amount of irrigation applied can be reduced significantly. Under very shallow water-table conditions (0.5 m depth), wheat extracted almost all its required water from the groundwater whereas sunflower extracted more than 80% of its requirement. It was concluded that 1.5–2.0 m was the optimum water-table depth for all the crops studied. The present

Acknowledgements

The authors would like to thank Ch. Talib Ali, Ex- Director, Mr. Abdur Raoof Regional Director and Mr. Noor Ullah, Field Assistant, Pakistan Council of Research in Water Resources Lahore for their help in data collection. The authors are also thankful to Dr. W.D. Kemper for reviewing the manuscript.

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Effect of shallow groundwater table on crop water requirements and crop yields

Abstract

Introduction

Section snippets

Objectives

Material and methods

Results and discussion

Conclusions

Acknowledgements

Agri. Water Manage.

Agri. Water Manage.

Irrigation requirements of wheat and cotton under different water-table conditions

Sarhad J. Agric.

Use of saline water from a shallow water table by cotton

Trans ASAE

Realizing the potential of integrated irrigation and drainage water management for meeting crop water requirements in semi-arid and arid areas

Irrig. Drain. Syst.

Effect of shallow drainage on crop water requirements