Critical limits of zinc in soil and rice plant grown in alluvial soils of West Bengal, India

SAARC J. Agri., 10(2): 137-146 (2012) CRITICAL LIMITS OF ZINC IN SOIL AND RICE PLANT GROWN IN ALLUVIAL SOILS OF WEST BENGAL, INDIA M. K. Mahata1, P. Debnath 2* and S. K. Ghosh3 1 Assistant Director of Agriculture, Dinhata-736135, Coochbehar, West Bengal, India ABSTRACT A study was conducted in 22 alluvial soils of West Bengal, India to estimate the critical limit of Zn in soil and rice plant for predicting the response of rice (Oryza sativa) to zinc application. The DTPAextractable Zn was positively and significantly correlated with CEC, organic carbon and clay contents and negatively correlated with pH, silt and sand contents of soil. The DTPA-extractable Zn also showed a positive correlation with dry matter yield and plant Zn content. The critical concentration of Zn in these soils was established at 0.75 mg kg-1 for rice and that of 28.0 mg kg-1 in the plant tissue. Soil containing Zn below the critical limit responded appreciably to Zn fertilization. A negative response to Zn application was also observed at its higher level. The average dry matter yield increases with increasing level of Zn application up to 2.5 mg kg-1 in Zn deficient soils. The average response to Zn application in rice in Zn deficient soils was found to be 68.5% and 19.9% in Zn adequate soils. Key words: Zinc, bray’s percent yield, critical limits, alluvial soil, physico-chemical properties of soil, rice. INTRODUCTION Rice is one of the most important food crops and a primary food source for more than one third of world’s population (Prasad et al., 2010). In Asia, India has the largest area under rice cultivation (44.3 million ha) accounting for 29.4 per cent of the global rice area. The productivity level in India is low (2.04 t ha-1) as compared to Japan (6.25t ha-1), China (6.24t ha-1) and Indonesia (4.25t ha-1). In India, West Bengal is one of the leading states for rice cultivation. Productivity of rice depends upon balance application of nutrients. The soils of West Bengal are poor in micronutrients * Corresponding author email: ; Department of Soil Science and Agricultural Chemistry, College of Horticultural and Forestry, CAU, Pasighat7991102, Arunachal Pradesh, India 3 Department of Soil Science and Agricultural Chemistry, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur741252, Nadia, West Bengal, India 2 Received: 04.06.2012 138 M. K. Mahata et al. due to continuous growing of high yielding varieties and only incorporation of macronutrients in cropping system. The deficiencies of micronutrients are of critical importance for sustaining high productivity of rice in India. Zinc is one of the essential plant micronutrients and its importance for crop productivity is similar to that of major nutrients (Rattan et al., 2009). Zinc plays an important role in different plant metabolism processes like development of cell wall, respiration, photosynthesis, chlorophyll formation, enzyme activity and other bio-chemical functions (Das, 2003 and Singh, 1984). Widespread and extensive Zn deficiency has been reported in the soils of lowland rice cultivation of India, Bangladesh, Pakistan, Philippines, Myanmur, Indonesia, Japan, Korea, Taiwan and Thailand (IRRI, 1978). In West Bengal, 55% of the soils are found to be deficient in Zn (Takkar et al., 1989). Studies on Zn fertilizer proved that the application of Zn greatly influences growth, yield and quality of rice (Patnaik et al., 2011 and Rahman et al., 2007). The symptoms of Zn deficiency have been recorded on rice and other field crops including vegetables crops grown in soils of alluvial zone of West Bengal. Realising the importance of Zn in plant growth and at the same time seriousness of its deficiency in soils and plants, an attempt was, therefore, made to study the critical concentration of Zn in soils and rice crop which is widely grown in the region of West Bengal for making Zn application more rational. MATERIALS AND METHODS Twenty two soil samples in bulk from plough layer (0-20 cm) were collected from different locations of alluvial zone of West Bengal. This zone comprised of four districts viz, Nadia, Burdwan, Murshidabad, and Hoogly of West Bengal, India (Table 1), lying between 220 34/ to 230 24 / N latitude and 88024/ to 880 33/ Longitude. These soils belong to order Inceptisols, Entisols and Alfisols (Soil Survey Staff, 2006). The collected soil samples were separately air dried ground and passed through 2 mm size sieve for laboratory analysis. Particle size distribution was done by the standard Bouyoucos hydrometer method (Gee and Bauder, 1986). Soil pH was determined by glass electrode with calomel as standard (Jakson 1973). Organic carbon was estimated by wet digestion method of Walkey and Black (Jackon, 1973). The cation exchange capacity was determined by leaching the soil with 1 N NH4+OAC and subsequently displacing the adsorbed NH4+ methods (Gupta, 2007). Available zinc content of the soil samples was extracted with DTPA-TEA (pH 7.3) extractant following the method of Lindsay and Norvell (1978) and the concentration of Zn in the extracted solution was estimated with the help of Atomic Absorption Spectrophotometer (AAS). A pot culture experiment was conducted in a greenhouse in polythene lined pots at the Instructional farm (22057/ N Latitude and 88020/ E Longitude), Mohanpur, West Bengal. The polythene lining was rinsed in 0.1N HCI followed by deionized water. Four kg of each soil was transferred into each pot. Recommended doses of CRITICAL LIMITS OF ZINC IN SOIL 139 nitrogen, phosphorus and potassium @ 50, 11 and 21 mg kg-1 N, P and K, respectively were applied as reagent grade i.e. Urea, KH2PO4 and KCl. Three 21 day old rice seedlings (var. IR 36) were transplanted in each pot. Zinc was applied @ 0, 1.25, 2.5 and 5.0 mg kg-1 soil as reagent grade of Zinc sulphate (ZnSO4, 7H2O) after 7 days of transplanting of rice seedling. Each treatment was replicated thrice in completely randomized design. Watering with deionized water and intercultural operations like weed control and plant protection measures were adopted uniformly in each pot as and when required. Rice plants of above ground portion were harvested after 30 days of transplanting and washed in acidified solution, rinsed with deionized water, dried at 65 0C in a hot air oven and dry-matter yield was recorded. The dried rice plant and dried 3rd leaf samples of each pot were separately powdered in a warring stainless steel grinder. The dry powdered plant samples were digested in a mixture of 10:4:1 of HNO3: HClO4: H2SO4 on a hot plate and filtered through Whatman No.42 for estimation of Zn with the help of Atomic Absorption Spectrophotometer (AAS). The critical value of DTPA-extracted zinc in soil and in plant were determined by plotting the Bray’s percent yield against soil DTPAextracted zinc content and separately against plant tissue zinc content respectively, following the method of Cate and Nelson (1965). Bray’s percent Yield = x100 Simple correlation an (...truncated)