Assessment of soil degradation and water quality in areas of small scale brick production and management of the degraded soil

Abstract

The utilization of clay for construction of habitations and buildings dates back to the period of ancient civilizations. Even though centuries had passed and civilizations changed, the basic raw material for brick production remained the same. Brick production requires fine clayey loam soil with plenty of water supply. With the increasing demand for construction material, clay mining had shifted from river banks to fertile agricultural lands. This change in land use had resulted in the deterioration of soil health and decrease in crop production. The entry of large number of small scale brick production units is causing irreversible damages to the soil, hydrology and ecosystem. Hence, this study was taken up to characterise the desurfaced (mined) soils and water resources and to identify suitable management methods of these soils. A comprehensive survey was conducted at Alathur Taluk of Palakkad District to identify locations with resurfaced soils. Soil and water samples were collected from 11 locations including a control location without mining activities during August to September, 2017. A total of 88 soil samples (eight samples per location) and 11 water samples (one sample per location) were collected for the study. Both soil and water samples were analysed for various physico- chemical properties. Biological properties of soil samples were also analysed. The physical properties of soil such as temperature and bulk density were found to be higher in desurfaced soils when compared to control. The water holding capacity, porosity and moisture content were found to be reduced in desurfaced soils. The texture of the soil changed from clay loam to sandy loam. The organic carbon content of desurfaced soils were in the range of 0.08 – 0.46 per cent with a reduction of 61 per cent when compared with control soil. The content of available nitrogen, phosphorus and potassium were also reduced to the extent of 43.70, 74.50 and 43.36 per cent respectively. The available magnesium content was found to be lower in desurfaced soils (55.6 per cent reduction). The content of plant available micronutrients (Fe, Mn, Cu and Zn) and heavy metals (Ni, Cr and Pb) were high in desurfaced soils. The presence of earthworms (13 nos. per m2) and termite mound were observed only in the xi

control soil. The microbial biomass carbon and dehydrogenase enzyme activity were highly reduced in desurfaced soils. Water samples were also affected by small scale topsoil mining activity. The pH, electrical conductivity and TDS were in the safer limits for all water samples. The concentrations of sodium (W1 andW10) and calcium (W1 andW5) in certain water samples collected from mined areas were high and they were above safe limits to be used for irrigation purposes. Similarly the higher levels of nitrate, phosphate, bicarbonate and chloride in water samples from mined areas denote the possibility of the water bodies being polluted by mining activities. Based on the status of organic carbon and major nutrients, the soil with the lowest nutrient status (S5) was selected for pot culture study. The pot culture study was conducted with chilli (var. Anugraha) as the test crop. The effect of various organic and inorganic amendments on the properties of desurfaced soils were evaluated in this experiment. The treatment T2 (soil test based NPK + poultry manure) recorded the highest plant height (50.42 cm), number of leaves (221.78) and number of branches (6.11) at 60 days after transplanting. The yield attributes such as total number of flowers (95.33), total number of fruits (31.33) and per cent fruit set (32.95 per cent) were found to be higher for the same. The highest yield was obtained for the treatment T2 (soil test based NPK + poultry manure). The soils were also analysed after the harvest of the crop. The bulk density of soil after harvest was the lowest in treatment T3 (soil test based NPK + vermicompost) and was on par with T4 (soil test based NPK + coirpith compost). The content of organic carbon, available nitrogen, phosphorus and potassium recorded higher values in treatment T2 (soil test based NPK + poultry manure) than the other treatments. The biological properties such as microbial biomass carbon (374.133 μg g-1 soil) and dehydrogenase activity (3.630 μg TPF g-1 day-1) were the highest in treatment T2 (soil test based NPK + poultry manure) and T4 (soil test based NPK + coirpith compost) respectively. The study revealed that top soil mining for brick production predominantly affected bulk density, soil temperature and water holding capacity of the soils. The content of organic carbon and available nutrients such as N, P and K were also reduced. The biological properties like dehydrogenase enzyme activity and microbial biomass xii

carbon reduced to a greater extent. Water samples from mined areas were polluted by cations like sodium and calcium and anions like nitrate, phosphate, bicarbonate and chloride to limited extent. Poultry manure application as an integrated nutrient management technique, followed by vermicompost application were found to be beneficial for the management of such desurfaced soils.