DYNAMICS OF MICRONUTRIENTS IN CALCARIOUS VERTIC USTOCHREPTS SOILS UNDER AICRP-LTFE
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Date
2009-01
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Abstract
Micronutrients play a vital role in enhancing crop productivity and improving quality of crops. Intensification of agriculture with high yielding crop varieties, continuous use of highly analysed fertilizer restricting supply of organic matter, negligible use of crop residuals and increasing cropping intensity, all together exhausted micronutrients from soils. The deficiencies of micronutrients in Indian soils as well as Gujarat soils were very well recognized with special reference to Cu, Mn, Zn and Fe. Further, different pools were recognized and a number of sequential fractionation procedures were developed to study the relative abundance and importance of different fractions in the soil. Junagadh is one of the centers representing medium black calcareous soil (Vertic ustocrepts). These sub soils are difficult to manage from fertility point of view. Further most of our research information is largely emanated from short term study and unable to answer critical questions about how the
intrinsic properties of soils being changed by anthropogenic activities affect the micronutrient resource. In view of above following broad objectives were set :
To study the status of micronutrient (Fe, Zn, Mn, Cu) fractions in calcareous Vertic ustrochrepts soils under AICRP-LTFE.
To investigate the depletion of micronutrients fractions in the soils under investigation.
Modeling the dynamics of micronutrient fractions in the AICRP-LTFE soils.
To achieve the forgoing objectives, this investigation initiated which comprised of samples derived from long term fertilizer experiment started 8 years back on Vertic ustocrept calcareous medium black clayey soils of Junagadh. The samples were subjected to fractionation of micronutrients viz., Cu, Mn, Zn and Fe. The micronutrients, their fractions and soil properties were related to various yields and NPKS content from plants. In this part also the data were subjected to correlation analysis, stepwise regression, multiple correlation and path analysis. The LTFE experiment involved twelve treatments including untreated control which was subjected to analysis of variance in order to find out the effect of various treatments on yield, NPKS content and micronutrient fractions and also depletion in a long term cycle of 4 and 8 years.
In a long run, treatment differences in groundnut yield diminished while wheat yield showed significantly higher values in T8 after long spell of 8th year. The treatment T3 registered the highest N concentration and T8 the lowest in groundnut pod while T2 recorded highest concentration and T9 the lowest in groundnut haulm. The T8 registered
the highest concentration while control the lowest both in wheat grain and straw. In groundnut pod phosphorus concentration decreased while in haulm increased like wise in wheat grain phosphorus concentration was increased but in straw decreased after a period of 8 years. The concentration of potash after 4th year of cycles showed increase while after 8th year cycle it was declined in groundnut and wheat. In groundnut sulphur concentration increased after 4th year while declined after 8th year. In wheat, sulphur concentration decline after 4th and 8th year. From the overall picture with respect to various forms of Cu it can be deduced that there was a decline in the soil Cu levels where a significant decline in most of all important forms. There was a decline in the soil Mn status in the LTFE soils in different form and these was a significant decline in the important forms such as exchangeable Mn, total Mn and residual Mn. Overall mean DTPA available Mn recorded medium values (6.297 ppm) as compared to the critical values. The DTPA available Zn was maintained high quite above critical values (0.5 to 1.0 ppm) and did not indicate any need to supplement Zn nutrient in near future. Particularly DTPA available ferrous showed considerable depletion over time and chemical fertilizers triggered utilization thereby the levels reaching below critical values. Although iron is the most abundant element, its availability needs suitable management practices. The DTPA available nutrients were the predominant form in copper, manganese, zinc and iron. Chemical fertilizers supplemented and enhanced utilization of DTPA available Mn and Cu along with a shift in inter-conversion among forms, over the 4 and 8 years cycles.
Correlations Groundnut pod yield and haulm yield exhibited significant positive relationship with DTPA available Cu, exchangeable Mn, per cent available Mn, residual Mn, residual Zn, per cent available Zn, water soluble Fe, residual Fe and per cent available Fe. Obviously wheat grain yield showed significant negative relationship with available Cu, while significant positive relationship with all forms of Mn and Zn and exchangeable Fe, DTPA available Fe, total Fe and available total Fe. Available form of Cu showed positive relationships with nitrogen concentration particularly in wheat grain (cereals), P concentration in groundnut pod and K concentration in groundnut haulm and S concentration in wheat grain and straw. Available Mn facilitated the partitioning of nitrogen towards wheat grain and groundnut pods. Available Mn favored accumulation of K in wheat gain and groundnut pod over the vegetative parts in both the crops. Phosphorus accumulation was promoted in legumes while it diminished in cereals by Zn. The Fe was found to indirectly regulate partitioning between vegetative and reproductive parts via regulating P concentration which was known to influence the osmotic relations.
The total Cu was predominantly reflected by DTPA available Cu followed by residual, per cent available and residual. The DTPA available copper showed significant positive correlation with soil pH. The data from correlation studies indicated strong association between DTPA-Mn and its reducible, total, residual, and available total. The DTPA available Mn showed significant positive relationship with many soil properties viz., soil pH, O.C. and available K2O. The DTPA available Zn showed highly significant positive relationship with available total and percent available Zn. The DTPA available Zn also showed significant
positive relationship with various soil properties viz., soil pH, EC, O.C., available N, available P and available K2O. The DTPA available Fe displayed a highly significant positive relationship with available total, total and exchangeable forms. The DTPA available Fe recorded significant positive relationship with most of the soil properties viz., Soil pH, EC, O.C., available N and available P. The interactions viz., zinc x iron, manganese x zinc and copper x zinc showed more conspicuous relationships. Regressions The DTPA available micronutrients as influenced by other forms were subjected to stepwise regression and multiple correlation and regression analysis. The prediction models were based on multiple and correlation analysis over a cycle of 1, 4 and 8 years. The stepwise regression analysis indicated that total form in copper, manganese, zinc and ferrous had the maximum impact on DTPA available micronutrients. The stepwise regression analysis of DTPA available micronutrient as the dependent variable and soil properties as the independent variables indicating a low degree of influence. Nevertheless, Properties utilized for analysis soil pH influenced DTPA available Cu, soil O.C. to DTPA Mn and Zn, soil EC and O.C. to DTPA Fe, to the maximum extent. Path Co-efficients The residual Cu form exhibited significant positive correlation with DTPA available Cu. Total and per cent available form of Mn had a direct positive effect on DTPA Mn. The residual Zn and total Zn had a high direct effect on DTPA available Zn. The total ferrous showed a direct positive effect, while reducible ferrous showed a direct negative effect on DTPA available ferrous.
spatiotemporal variations according to soil type, land use, agronomic package, cropping patterns and agro-ecological situations. Most of all micronutrients with their forms exhibited in general a negative trend in the long term fertilizer experiment after 8 years.
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USTOCHREPTS SOILS