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On the Chemical Properties of Some Deep Water Rice Soils of Bangladesh

A. Islam
Department of Soil, Water and Environment, University of Dhaka, Bangladesh

M. Sultan Hussain
Department of Soil, Water and Environment, University of Dhaka, Bangladesh

W. Islam
Department of Soil, Water and Environment, University of Dhaka, Bangladesh

Abstract/ Executive Summary:

Changes in chemical properties due to submergence were studies on deep-water rice soils of Bangladesh. On submergence there was an initial drop in pH values which again increased and stabilized at pH 6.4 to 7.1 redox potential decreased gradually on submergence showing a minimum value of -100mv. Nitrate showed a gradual decrease on submergence and ultimately, disappeared, while ammonia showed an increasing trend. Soluble P, Ca, Mg and K in soils were found to increase in concentration with flooding. Soluble iron and manganese also increased gradually on submergence and peak values were obtained at the end of the thirteenth week.

Keywords: Chemical and physic-chemical changes, Deep and shallow water, Rice, Soil, Bangladesh.

Location: Department of Soil, Water and Environment, University of Dhaka, Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Rice

Objectives:

To present chemical and physic-chemical changes which took place, due to submergence, on deep and shallow water rice soils of Bangladesh.

Methodology:

Soil samples representing 0 to 15 cm depths and differing in pH, texture and chemical properties were collected from six different deep-water rice zones of Bangladesh. Locations and series names of six soils employed in the present investigation. Experiments were conducted in pots in the Dhaka University greenhouse. Soils were kept both at submerged and field capacity. The soils in pots at field capacity received sufficient distilled water to bring soil just to field capacity by adding distilled water whenever needed. Soils under submerged conditions were kept continuously submerged at 5 cm of standing water by the daily addition of distilled water. The soil solution was collected anaerobically, as followed by Ponnamperuma, at intervals of 0, 1, 3, 5, 9 and 13 weeks. The mechanical analysis of soils was carried out by the hydrometer method. The organic matter was determined volumetrically by wet oxidation method as devised. Exchangeable calcium, magnesium and potassium were determined from the normal neutral ammonium acetate leachate of soils by a flame photometer. pH was determined by a pye pH meter. Nitrate and ammonium from of nitrogen were determined separately from the soil solutions following the method described by Piper. Iron was estimated by the method followed by Fortune and Mellon. Manganese was determined by the methods outlined by Willard and Greathouse and, later modified by Peech. Phosphate was analyzed by a modification of the benzene-isobutanol method described by Martin and Doty. Calcium, magnesium and potassium were determined directly from the soil solutions by using a flame photometer (sp.900).

Source of Information: Intl. Seminar on Deep-water Rice. Dhaka, Bangladesh. 1974

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

On submergence the pH of soil solutions showed a slight decrease, but later gradually increased and attained as stable pH in the large range of 6.4 to 7.1. The initial decrease in pH value is thought to be due to an accumulation of CO₂ and also to the production of organic acids in soils. Soils containing high organic matter and low iron and manganese showed a pronounced decrease in pH values. The final increase in pH on continued submergence was due to soil reduction. The pH values of soil solutions at field capacity were generally similar to those of submergence. In the present soils calcium concentration increased rapidly with time of submergence and then decreased. The velocity and magnitude of increase in calcium content varied in different soils. In all soils, however, the peak values were obtained in the ninth week of submergence followed by a gradual decrease. The increase was much pronounced on the solution from Chanchora soil with a maximum of 200 ppm. Similar trends could be detected at field capacity. The changes, however, were much less pronounced as compared to those under submerged conditions. The peak values ranged between 82 and 234 ppm attained on the thirteenth week, the highest and the lowest being in Parbata and Chanchora soils respectively. Ponnumperuma observed a concentration of 380 ppm Fe⁺⁺ in the soil solution after 4 weeks of submergence in an acid latosolic soil containing high organic matter and attributed the increase in the content of water soluble Fe⁺⁺ to the reduction of ferric hydroxide. Changes in iron contents at field capacity were only slightly noticeable in Parbata soil. In the other soils, percolates failed to extract any amount of detectable iron. Nitrate showed a gradual decrease on submergence and ultimately, disappeared, while ammonia showed an increasing trend. Soluble P, Ca, Mg and K in soils were found to increase in concentration with flooding. Soluble iron and manganese also increased gradually on submergence and peak values were obtained at the end of the thirteenth week.

Knowledge Management: Report/Proceedings