Status of Zinc Content in Soils and Rice Genotypes and its Relationship with Soil Chemical Properties across different Agro-Climatic Zones of Karnataka, South India

Micronutrient malnutrition has affected lives of billions as evident by 2.7 billion suffering from Zn deficiency allover the world (Anon 2004). In India, 27 percent of total population is affected by Zn deficiency related disorders such as poor immune system, diarrhoea, poor physical and mental health (WHO 2007). Zn deficiency claims about 4.4 percent of the total child deaths in the world (Black 2003).

Rice is the important staple food for more than half of the world population and provides 60 to 70 percent body calorie intake to the consumers and is consumed in large amounts. Rice is the staple food of nearly 65 percent of the total population in India (Barah 2005). Because of the high consumption of rice in developing countries and its inherent low Zn content, the extra Zn would have meaningful impact on human nutrition and health. A little increase ingrain nutritive value of rice will produce a cumulative effect on total nutrient intake (Chandel et al. 2010). Nutritional requirement of micronutrient should be met from micronutrient output of modern agricultural systems. Accordingly, knowledge on micronutrient status in soil and crop edible tissues is necessary. Katyal and Sharma (1991) indicated the variation in Zn content of different major soils forming rocks of India. Available Zn content in surface soils of India ranged from 0.08 to 20.5 ppm. There is a wide variation in agricultural soils across the globe in Zn content and their capacity to supply Zn for optimal crop growth (White and Zasoki 1999). Alloway (2008) reported worldwide deficiency of Zn in soils. Zinc deficiency was reported in the soils of Turkey (Cakmak 2002), China (Liu 1991), Java (Soepardi 1982), Australia (Sillanpaa 1990) and in India (Takkar 1996; Singh 2001; Behera et al. 2009). About 48 percent of Indian soils are deficient in Zn (Sakal 2001). Zn deficiency in soils of Karnataka is up to the extent of 78 percent (Singh and Saha 1995). It is generally prevalent in high pH calcareous soils (Liu et al. 1983; Katyal and Vlek 1985). But it has also been reported in acid soils which are leached and heavily weathered (Alloway 2008 and Behera 2011).

Plant availability of Zn in soils is influenced by many factors (Shuman 1986). Besides soil organic carbon (OC) content, one of the most important soil properties influencing Zn availability in soil is soil pH (Anderson and Christensen 1988). Usually extractable Zn decreases with an increase in soil pH due to increased absorptive capacity, the formation of hydrolyzed forms of Zn, possible chemisorptions on calcium carbonate and co-precipitation as iron oxides (Cox and Kamprath 1972; Alloway 2008).

The incidence of Zn deficiencies in crops has increased markedly in recent years due to intensive cropping, loss of top soils by erosion, losses of micronutrients through leaching, liming of acid soils, decreased proportions of farmyard manure compared to chemical fertilizers, increased use of high analysis NPK fertilizers coupled with use of Zn free fertilizers and use of marginal lands for crop production. Micronutrient deficiency problems are also aggravated by the high demand of modern crop cultivars (Fageria et al. 2002). As a result, Zn content in plant dry matter is low particularly in grain. Since all of the micronutrients that human consume are derived from the soil-plant system. Therefore, identification of high grain Zn containing rice genotypes is needed to ensure adequate attainment of mineral element in daily diet.

In the context of the above facts, the present study was carried out to (i) access the status of Zn in soils and rice genotypes (ii) study the relationship of selected soil chemical properties such assoil pH, OCand DTPA-Zn with Zn content ingrain and straw of rice.