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Effect of Irrigation and Intensive Cultivation on Soil Properties: a Case Study on Calcareous Soils in Ganges-kobadak (g-k) Irrigation Project in Bangladesh.

M. H. RAHMAN
Faculty of Biological Science, Dhaka University, Dhaka, Bangladesh

M. ITO
Faculty of Agriculture, Iwate University, Japan

A. TANAKA
Faculty of Agriculture, Iwate University, Japan

S. Hoque
Faculty of Biological Science, Dhaka University, Dhaka, Bangladesh

T. H. KHAN
Faculty of Biological Science, Dhaka University, Dhaka, Bangladesh

Abstract/ Executive Summary:

The effect of long-term irrigation and intensive cultivation on three soil series was investigated. These soils were from a calcareous belt in the G-K irrigation project area in Bangladesh, which had experienced declining crop yields. In order to evaluate the effect, if any, of irrigation and intensive cultivation on soil properties, three soil series from irrigated and adjoining non-irrigated areas located in the same catena were studied. Soil properties such as organic carbon, CEC, electrical conductivity, potassium adsorption ratio, exchangeable sodium percentage, and ionic strength did not show any distinct changes between the investigated areas. The major changes identified between the irrigated and non-irrigated soils were pH, void ratio, maximum water holding capacity, water-soluble Na, ferrous iron, sodium adsorption ratio, available nitrogen, and free carbonate content. In this study, the correlations between the following soil properties were demonstrated in all the series: (i) exchangeable and water-soluble sodium, (ii) exchangeable and water-soluble potassium, (iii) void ratio and maximum water holding capacity. By applying t-test, the effects of cations on other cations, sodium adsorption ratio on free carbonate, and water-soluble sodium on water-soluble potassium were found to be insignificant. The present study indicated the necessity of further investigation of the relationship between the declining fertility and changes in soil carbonate.

Keywords: Soil properties, Irrigation, Intensive cultivation, Calcareous Soils

Location: Kushtia, Chuadanga, Meherpur, Iessore, Magura, and Jhenaidah districts, Bangladesh.

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Water Conservation

Objectives:

1.To analyze and identify the changes of soil properties for long-term irrigation and intensive cultivation

2.To examine the quantitative relationships among the soil properties.

Methodology:

The Ganges-Kobadak (G-K) irrigation project (latitude 23°11 'N to 24°08'N; longitude 89°03' E to 89°10' E; altitude 7-14 m) in Bangladesh was established with the objectives of developing irrigation and road systems, improving drainage, navigation and for controlling river floods. The whole G-K project is divided into two units: Kushtia unit, covering Kushtia, Chuadanga, and Meherpur districts, and Iessore unit, covering Iessore, Magura, and Ihenaidah districts. The Kushtia unit is divided into two parts: phase I which was completed in 1969-70, and phase II, which was put into operation by the end of 1980. The command area is 85,020 and 117,813 hectares for phase I and phase II, respectively. The total area of the G-K project is about one fifth of the total cultivable land of Bangladesh. The studied irrigated soils are plowed and harrowed in water-saturated condition. A height of standing water is maintained during the crop (T. Aus-T. Aman) and after draining, rabi crops are grown, and the field is then kept fallow and dry after harvest. But most of the non-irrigated soils are plowed in unsaturated condition. The major soil series namely, Sara, Gopalpur and Ishurdi were selected for study because they cover a vast project area and are located in the same catena. These soils developed on different parent materials on Calcareous Brown Floodplains. Soils developed on this floodplain differ in their physical and chemical properties mainly due to their mineralogy, age of sedimentation, relief, drainage and biotic activity. In general the G-K project area, like the rest of the country, has a tropical monsoon climate. Soil for analysis was collected from three locations, namely, phase I, phase II and adjoining non-irrigated area, considering soil series. At each selected site, soil characteristics and soil management practices were recorded, the pits were opened, and macromorphological characteristics of the soils were studied. Undisturbed core samples (triplicate) and disturbed soil samples were collected on a profile basis from each genetic horizon up to a depth of 120 cm. Soil pH was determined electrochemically by using a corning glass electrode pH meter. The soil-water ratio was 1: 2.5, and the shaking time was 30 minutes. Soil organic carbon (OC) content was estimated wet oxidation method. Ferrous iron contents of the moist soil samples were determined by the method m. Sodium Adsorption Ratio (SAR), Potassium Adsorption Ratio (PAR), and Exchangeable Sodium Percentage (ESP) were determined according to U.S. Salinity Laboratory Staff (1954) by using the following formulae: SAR = (Na⁺) I [l/2(Ca⁺⁺ + Mg⁺⁺)]^1/2; PAR = (K⁺) I [l/2(Ca⁺⁺ + Mg⁺⁺)]^1/2 and ESP = (Na⁺ /CEC)100 Ionic strength (1) was estimated from using the following equation: Ionic strength = 0.013EC. Data were subjected to analysis of variance (ANOVA), and t-test was used to determine significant changes of soil properties due to different durations of irrigation and intensive cultivation. t-test was used for comparison of two regression coefficients. Simple linear regression correlation was used to show the relation between some soil properties.

Source of Information: Journal of Irrigation Engineering and Rural Planning, No. 29, (1995. 8) pp. 78-94

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The findings presented in this paper are a comprehensive investigation of changes in the soil properties of the studied soils under irrigation and intensive cultivation. Soil properties have been discussed and statistical correlations have been made where deemed necessary. The findings of the present study indicated that (1) Changes were observed in the pH, void ratio, maximum water holding capacity, water-soluble Na, ferrous iron, sodium adsorption ratio, available nitro- gen, and free carbonate content due to irrigation and intensive cultivation. (2) Changes in soil properties were not consistent possibly because of the alluvial nature of the soil. (3) The soils of the G-K project area are suitable to moderately suitable for rice cultivation. (4) Soils of the investigated area had no limitation in terms of salinity or alkalinity. (5) The decline in soil fertility needs further investigation. As the soils are calcareous in nature, the effect of changes in carbonate content on soil fertility needs detail study. Though some changes were detected between irrigated and non-irrigated soils, they were not so big as to be major problems requiring a solution. The various aspects covered by this study will have important implications in land use planning and management practices.

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