Micronutrient status of soils of Taluka Malir under different sources of irrigation

The study was carried out to determine the micronutrient status of the soils irrigated with different sources of water such as T1=underground water, T2=sewage water and T3=underground + sewage water. The soil samples were collected from 30 different selected locations from the Rasheed Farm, deh Sanhro, Taluka Malir Karachi where vegetables are cultivated. The samples were taken from two depths (0-20-20-40 cm). Majority of the soil samples of surface and subsurface soils in both sites were sandy loam to sandy clay loam in texture. Soils were slightly saline to non-saline in soil irrigated with underground water, whereas, non-saline to slightly saline in irrigated with sewage water and mixed water. Average EC value at 0-20cm soil depth was 2.417, 1.488 and 1.818 dS/m, while at 20-40 cm was 2.359, 1.473 and 1.827 dS/m in soil irrigated with T1, T2 andT3. Majority of soil samples at both depths was moderitely alkaline in reaction. The average pH value at 0-20 cm soil depth was 8.04, 7.84 and 8.18, while at 20-40 cm soil depth was 8.02, 7.84 and 8.19 in soil irrigated with T1, T2 and T3, respectively. All the soil samples were found highly calcareous in nature. The average lime content at 0-20cm soil depth was 20.25, 20.26 and 20.3 percent while at 20-40 cm soil depth was 20.15,-19.78 and 20.2 percent in soil irrigated with T1, T2 and T3 respectively. The organic matter (O.M) in the soil irrigated with underground water at surface soil layer was poor to medium in O.M content while at subsurface layer the soil was poor. In case of sewage water and mixed water irrigated soil, the O.M. content at 0-20 cm soil depth was adequate to medium, while at the sub-surface soil layer was poor in O.M respectively. The results showed that most of the soils were high in Zinc content in both sites, while at sub-surface soil irrigated with underground water were mostly found low in Zinc availability. The average Zn content at 0-20 cm soil depth was 1.824, 166.99 and 69.583 ppm while at 20-40 cm soil depth was 0.491, 119.29 and 23.915 ppm in soil irrigated with T1, T2 and T3. Most of the soils were high in iron content in both sites. The subsurface soils irrigated with underground water were mostly found medium to low in iron availability. The average Fe concentration at 0-20 cm soil depth was 6.456, 103.67 and 46.975 ppm, while at 20-40 cm soil depth was 3.785, 35.80 and 19.635 ppm in soils irrigated with T1, T2 and T3 respectively. The data revealed that both sites at 0-20 and 20-40 cm depths 100% soils samples were highly riched in Cu content. The average Cu concentration at 0-20 cm soil depth was 6.456, 103.659 and 46.975 ppm, while at 20-40 cm soil depth was 3.785, 35.799 and 19.635 ppm in soils irrigated with T1, T2 and T3, respectively. The data revealed that both sites at 0-20 and 20-40 cm depths 100% soils samples were highly riched in Mn content. The average Mn concentration at 0-20 cm soil depth was 4.900, 96.091 and 46.914 ppm, while at 20-40 cm soil depth it was 2.939, 49.578 and 24.387 ppm in soils irrigated with T1, T2 and T3 respectively. The average Zinc concentration was 78.336, 361.716 and 194.971 ppm in T1, T2 and T3 respectively. It was observed that Zn concentration was remarkably higher in sewage water and underground+sewage (mixed) water samples as compared to underground water, which clearly indicates the availability of heavy metals in the sewage water in higher quantities. The average Mn content was 404.465, 680.553 and 586.051 ppm in T1, T2 and T3 respectively. It was observed that the situation was similar for Fe concentration in the water and micronutrient level considerably higher in sewage water as well as in the mixed (underground water + sewage water) water as compared to underground water. The average Cu concentration in water samples was 12.1, 31.274 and 21.390 ppm for T1, T2 and T3 respectively. This clearly indicates that the heavy metal concentrations in the sewage water are in greater quantities than underground water. The average Mn content in water samples was 197.389, 457.442 and 334.362 ppm in T1, T2 and T3 respectively. This showed that both sources of irrigation water were highly contaminated with heavy metals. It is concluded that the high levels of micronutrients found in the vegetables grown in the Rasheed Farm is due to the continuous use of untreated industrial effluents.