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Rainfall Induced Saline Soil Management Through Leaching

Palash Kumar Kundu*
SO
Scientific Officer, Bangladesh Rice Research Institute, Gazipur, Bangladesh

Md. Ferdous Parvez
Lecturer, EXIM Bank Agricultural University Bangladesh, Bangladesh

Dr. Tapos Kumar Acharjee
Associate Professor, Bangladesh Agricultural University, Mymensingh, Bangladesh

Sheikh Maniruzzaman
Scientific Officer, Bangladesh Rice Research Institute, Gazipur, Bangladesh

Sanjoy Kumar Debsharma
Scientific Officer, Bangladesh Rice Research Institute, Gazipur, Bangladesh

Golam Sarwar Jahan
Scientific Officer, Bangladesh Rice Research Institute, Gazipur, Bangladesh

Hasibur Rahaman Hera
Scientific Officer, Bangladesh Rice Research Institute, Gazipur, Bangladesh

Aishik Debnath
Scientific Officer, Bangladesh Rice Research Institute, Gazipur, Bangladesh

Md. Rezoan Bin Hafiz Pranto
Scientific Officer, Bangladesh Rice Research Institute, Gazipur, Bangladesh

Abstract/ Executive Summary:

Five treatments - I1: soil irrigated with fresh water, I2: soil irrigated with saline water EC = 4 dS/m, I3: EC = 7 dS/m, I4: EC = 10 dS/m, and I5: EC = 13 dS/m. Soil samples were collected from each plot at 0?20, 20?40, 40?60 cm soil profiles at, usually, 15 days interval. At the end of the rainy season, the salt accumulated due to irrigation completely leached out of the top 0?20 cm soil profile in all treatments. The salt from the upper soil profile (0?20 cm) leached down and increased the salinity of the lower soil profiles. At the end of the rainy season, the salinity in the lower soil profile did not reduce to its initial value, implying that the rainfall was not enough to wash out the imposed salinity from the entire root zone soil. At the early period of rainy season, the rainfall was relatively little, but the rate of EC reduction was high, especially in the soil with high salinity . It is concluded that, irrigation with high saline water (EC ≥7 dS/m) caused accumulation of salt in excess of that washed out by monsoon rainfall.

Keywords: Rainfall, Leaching, Salinity, pH, Saline soil management

Location: Bangladesh Agricultural University (BAU)

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Non-commodity: Rainfall

Objectives:

To quantify rainfall-induced leaching of salt through field soil, to correlate salt leaching with rainfall, and to identify depth variation salt leaching due to rainfall

Methodology:

The experiment was done at the experimental field of the Department of Irrigation and Water Management (IWM) of Bangladesh Agricultural University (BAU), Mymensingh, during the month of March to October, which is located in the Old Brahmaputra Floodplain (Agro Ecological Zone 9) that lies at 24.75oN latitude and 90.50o E longitude. The elevation of the experimental site was 18 m above mean sea level. The soil the soil was silt loam underlain by sandy loam texturally. The top soils were moderately acidic but sub-soils were neutral in reaction. The organic matter content of the experimental soil was low (0.48%). The sub-tropical climate of the experimental site is characterized by high temperature, high humidity and an above average rainfall of 2451 mm with occasional gusty winds in kharif season (April-September). The rabi season (October-March) is characterized with occasional and less rainfall associated with moderately low temperature. In a previous field experiment, saline water of different salinity levels, prepared by mixing sodium chloride (NaCl) salt with water from a deep tube well, was applied in an experiment with wheat cultivation during the period from November to March. The experiment consists with only one factor, soil with different salinity levels, which had five treatments and three replications. The treatments (replicated three times consecutively) were: (i) I1: Soil irrigated with fresh water, (ii) I2: Soil irrigated with saline water of EC=4 dS/m, (iii) I3: Soil irrigated with saline water of EC=7 dS/m, (iv) I4: Soil irrigated with saline water of EC=10 dS/m, and (v) I5: Soil irrigated with saline water of EC=13 dS/m. Each block was divided into 5 unit plots having 3m x 2m size. A buffer of 1m between the adjacent blocks, and 0.5 m between the adjacent unit plots were maintained. There were total 15 unit plots. The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications (R1, R2 and R3). The five irrigations treatments (irrigation water of different salinity levels) were employed. Soil samples were collected from each plot by using a hand auger. The samples were collected at 20 cm increments to a depth of 60 cm considering the effective root zone of wheat as 60 cm. The samples were collected, in general, at 15 days interval, starting from just after harvesting of wheat until the end of rainy season ( March?October); there was no rainfall between harvesting and first soil sampling. During heavy rainfall in July?August, there was standing water in the field, soil samples were collected at one month interval. These samples were transferred to the soil and water engineering laboratory of IWM department, dried in air and sieved through a 2-mm square mesh sieve. The samples were stored in separate polythene papers for analysis. Undisturbed soil samples were also collected in 5 cm × 5 cm core samplers to determine bulk density and field capacity. The textures of the soils at the three depth intervals were determined by Hydrometer method. The bulk density and field capacity of the soils were determined in this study. The EC and pH of the soils were determined by using a combine electrical conductivity and pH meter. For this determination, 30 g of air-dry soil was taken into separate conical flasks of 100 ml capacity, and 75 ml distilled water was added with each soil. The ratio of soil and water was 1:2.5. The soil-water mixture was shaken by using a shaker at 250 rpm for 15 minutes. Then, the conical flasks were kept undisturbed for six hours for sedimentation in a control room at 25°C. The saturation extract were separated from the saturation paste carefully by filtration. The EC and pH of the saturation extract were measured by the combined conductivity and pH meter. There were different amount of salts in the soil under different treatments. Due to rainfall, the soil salinity changed over time as a function of depth. By analyzing the measured EC and pH, the temporal and spatial dynamics of the salt in the soil were evaluated.

Source of Information: North American Academic Research , Volume 3, Issue 07; July, 2020; 3(07) 208-222

Article Link (Online Journal): http://twasp.info/journal/home

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

From the results of this study the following conclusions were drawn: (i) At the end of the rainy season, the salt accumulated due to irrigation completely leached out of the top soil profile in all treatments. (ii) Salinity at the lower layers was not leached out completely. (iii) Soil salinity in the upper soil layers decreased rapidly than the lower layers. (iv) Salinity at the lower layers increased as the leached out salt from the upper soil profiles accumulated in the lower layers. (v) Irrigation with high saline water (≥7 dS/m) caused accumulation of salinity in excess of that washed out by monsoon rainfall. High saline water (≥ 7 dS/m) is recommended to be avoided for irrigation.

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