ASSESSMENT OF CHEMICAL AND BIOCHEMICAL INDICES FOR DIAGNOSING ZN DEFICIENCY AND SOIL ASSOCIATED FACTORS OF CITRUS (CITRUS SINENSIS L. OSBECK) NUTRITION

Abstract

A three phase research programme was planned to assess the chemical and biochemical indices for diagnosing Zinc (Zn) deficiency and soil associated factors of citrus nutrition in Marathwada region of Maharashtra state of India. In the first phase a survey of sweet orange orchards was carried out to evaluate the nutritional status and determine constraints in fruit production. In the second phase a pot culture experiment was conducted to evaluate the critical concentration of Zn in soil and leaf. Similarly biochemical indices the CAA (Carbonic Anhydrase Activity) and chlorophyll was also studied. While in third phase, another pot culture experiment was conducted to determine the effect of lime, organic manure and Zn on growth of sweet orange seedlings. Phase I revealed that sweet orange orchards (Citrus sinensis L. Osbeck) of the region are grown on variety of soils (Entisol, Inceptisol and Vertisol) without considering their suitability. Similarly intercrops are planted without testing compatibility. Analysis of orchard soils showed they were calcareous and predominantly clay in texture. Leaf analysis confirmed wide spread deficiency of N and Zn followed by P. Biochemical indices viz. CAA and chlorophyll content of sweet orange leaf were found to be a sensitive and indicator of Zn deficiency. Sweet orange orchards established on Inceptisols performing better than the orchards established on other soil types. Improvement in sweet orange seedling was recorded with high Zn soils supplied with 5 mg Zn, marginal Zn status soils with 10 mg Zn and low Zn status soils with 15 mg Zn kg-1. Reduction in sweet orange growth was noticed with 15 to 20% CaCO3 level. It was further concluded that detrimental effect of high CaCO3 content (up to 20%) on growth can be alleviated to some extent by applying double or triple (10 to 15 g organic manure kg-1) the recommended dose of organic manure. Organic manure in combination with Zn application performed best in improving growth, uptake of Zn, CAA, chlorophyll content and dry matter production of sweet orange seedlings. Critical soil Zn concentration under different levels of CaCO3 and organic matter content for sweet orange varied from 1.04 to 1.17 mg kg-1, while critical leaf Zn con¬centration varied from 28.80 to 36.40 mg kg-1. The variations in critical concentration of Zn in soil and sweet orange leaf are attributed to the variability of CaCO3 and organic matter in soil.