STUDIES ON FERTILITY EVALUATION OF SOILS OF GUNTUR REVENUE DIVISION, AP WITH SPECIAL REFERENCE TO ZINC
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Date
2014
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ACHARYA N.G. RANGA AGRICULTURAL UNIVERSITY
Abstract
The present study was conducted to evaluate fertility status of soils of Guntur revenue division, Guntur district, AP with special reference to zinc. One hundred and three representative surface soil samples were collected from nineteen mandals of study area by following random sampling technique. The soil samples were analysed for various physical, physico-chemical and chemical properties to evaluate the fertility status of soils and for assessing the ability of chemical extractants viz., AB-DTPA, Mehlich-3 and NH4OAc in extracting soil available zinc. Pot culture and incubation experiments were also conducted to study the performance of rice crop and efficiency of extractants with different levels of zinc application. The suitability of AB-DTPA, Mehlich-3 and NH4OAc in extracting zinc was evaluated in comparison with the DTPA extraction (conventional method) and the amount of zinc taken up by rice crop.
The soils were classified into five different textural classes viz., loamy sand, sandy clay loam, sandy clay, silty clay and clay. Out of which, clay was the dominant texture. The soils were neutral to moderately alkaline in reaction, non saline, non sodic and moderately calcareous in nature. The cation exchange capacity of the soils ranged from 8.91 to 51.23 cmol (p+) kg-1 with high base saturation values varying from 77.83 to 99.84 per cent. The exchangeable bases on the exchange complex were found to be in the order of Ca2+ > Mg2+ > Na2+ > K+.
The soil nutrient index values in respect of organic carbon and nitrogen were low and fertility status was high with respect to phosphorus and potassium.
The micronutrient status of soils was exhibited in the form of DTPA extractable Zn, Fe, Mn and Cu. The soils were deficient in zinc (80.58 %) and sufficiently rich in iron (76.70 %), manganese and copper. Soil organic carbon content of the soils significantly and positively affected while pH and calcium carbonate content negatively affected the availability of Zn, Fe, Mn and Cu in soils.
To explore the feasibility of adoption of AB-DTPA as a multi nutrient extractant, P, K, Zn, Fe, Mn and Cu content of soils were also extracted with ABDTPA. It was observed that the contents of P and K extracted by AB-DTPA were comparatively lower whereas the amounts of Zn, Fe, Mn and Cu were higher when compared to their respective conventional method of extraction. Though there was a variation in extracted amounts of nutrients but it showed significant and positive correlation with the conventional methods of extraction of P, K, Zn, Fe, Mn and Cu. This indicated the feasibility of using AB-DTPA as multi nutrient extractant for the soils of Guntur revenue division.
Among the chemical extractants tested for zinc availability, the mean available zinc content was the highest in Mehlich-3 followed by AB-DTPA, DTPA and NH4OAc and their efficiency in extracting available zinc content of soils was in the order of AB-DTPA > DTPA > Mehlich-3 > NH4OAc based on correlation values in the Neubauer experiment. Highest positive and significant correlation was observed between zinc uptake and AB-DTPA (0.654**) followed by DTPA (0.635**), Mehlich-3 (0.436**) and such relation was not significant with NH4OAc (0.124).
Irrespective of the soil type, increasing levels of zinc application increased the zinc content, dry matter yield and zinc uptake by rice. The highest values of biological indices were observed in clayey soils with higher level of zinc application (10 mg kg-1) while the lowest values were observed in sandy clay loam soils (0 mg kg-1).
Application of zinc to soil increased the zinc extracted by each method of chemical extraction at the end of 15 days after incubation when compared with the native soil zinc extraction. The amount of zinc extracted by different chemical extractants in different textural groups of the soils were in the order of clay (paddy) > clay (non paddy) > silty clay > sandy clay > sandy clay loam. At all the levels of zinc application, the amount of zinc extracted with AB-DTPA at 15 DAI in all the five groups of soils was positively related with the uptake of zinc by rice indicating it’s efficiency of extraction in soils of the study area.
Since DTPA and AB-DTPA extractants showed significant positive correlation (r = 0.993**) with each other and with that of rice uptake (0.899** and 0.861**, respectively) at different levels of zinc application, suggested that AB-DTPA could be used effectively for estimating available zinc in soils.
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