DYNAMICS OF MICRONUTRIENT FRACTIONS IN THE CALCAREOUS SOILS OF SAURASHTRA REGION
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Date
2004-11
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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 deficiency 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. The majority of medium black soils of Saurashtra region are calcareous in nature derived from trap basalt in semi-arid climate. The calcareousness is a unique property of soils which affects the physical and chemical properties, nutrient availability and plant growth. Almost 10 agro-ecological situations of
Saurashtra region have been identified which vary in soil resource. Among them, 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 :
1. To determine the turn over of micronutrients fractions in the different soil groups of Saurashtra region.
2. To investigate the status of micronutrients (Cu, Mn, Zn and Fe) fractions in medium black calcareous soils (Vertic Ustocrepts) of Junagadh under LTFE.
3. Modeling the dynamics of micronutrients fractions in these soils.
To achieve the forgoing objectives whole work is divided in two parts. The part one (I) comprised regular monitoring of the fertility since 1990. Sampling were made from the soils of predetermined survey number at ten years intervals. The samples of 1990 and 2000 were subjected to fractionation of micronutrients viz., Cu, Mn, Zn and Fe. Various soil properties such as soil pH, soil EC, soil CaCO3, soil CEC, soil ExCa, soil OC, soil clay, soil ESP, soil available nitrogen, soil available phosphorus, soil available potash and soil-heat soluble sulphur were also analysed. Whole set of data from ten different soil groups of Saurashtra region and changes in a long term cycle of 10 years were subjected to various statistical analyses including correlation among fractions, between the forms and with properties, stepwise regression, multiple
correlations and path analysis with DTPA available micronutrient as the dependent variable to investigate the influence of long term cycle, interaction and soil properties on available form of micronutrients vis-à-vis finding out the depletion of predominant component of available micronutrients and interactions among various forms and fractions of soil groups as well as districts.
Second part (II) of investigation comprised the samples derived from long term fertilizer experiment initiated 20 years back on Vertic Ustocrept calcareous medium black clayey soils of Junagadh. There were no gross additions of micronutrients in this groundnut-wheat-sorghum cropping system. The micronutrients, their fraction and soil properties were related to various yields and NPK 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 six treatments including untreated control which was subjected to analysis of variance in order to find out the effect of various treatments on yield, NPK content and micronutrient fractions and also depletion in a long term cycle of 10 and 20 years.
I. SOIL GROUP ANALYSIS :
Status and Depletion :
In zinc, copper and ferrous the predominant component of available total was DTPA available form while in case of manganese it was reducible form. Considering primarily the predominant component, the status of copper was highest in soil group RAD and SBSS in 1990 and 2000, respectively, manganese in soil group SBTB and DBTB in both years, zinc displayed variable picture while soil group MBTB which
recorded highest values for iron. So far as depletion is concerned soil group SBLS registered maximum depletion in copper and manganese, iron in soil group MBLS and MBTB while zinc displayed a variegated picture. In certain soil groups on the contrary there was an increase over time. Soil group SBSS and DBTB recorded an increase in copper, manganese and iron along with some other groups. In case of zinc almost all groups registered an increase in a span of ten years.
Correlations :
The DTPA available micronutrients showed strong positive relationship with percent availability thereby rendering its predominance in most of the soil groups with some exceptions. Soil properties showed a variegated picture and different relationships were found to vary in direction and magnitude in various soil groups. Soil groups specific interactions were evident but in general copper and manganese with special reference to DTPA available form were correlated maximum while copper and zinc the least between them with exceptions in some soil groups. Ferrous and zinc also showed lesser extent of interactions.
Regressions :
The prediction models were worked out for DTPA available forms as influenced by the other representative forms in the years 1990, 2000 and pooled utilizing the multiple correlation and regression analysis. The pooled data were also subjected to stepwise regression analysis which indicated that DTPA available copper was mostly influenced by total, residual and water soluble, whereas DPTA available manganese by exchangeable form and DTPA available zinc and ferrous by different forms in different soil groups. As in forms, the DTPA available
micronutrients as influenced by various soil properties were also subjected to multiple correlation analysis in the year 1990, 2000 and pooled and prediction models were derived. So far as stepwise regression analysis of pooled data are concerned soil properties could explain the behaviour of DTPA available micronutrients viz., Cu, Mn, Zn and Fe to little extent.
Path Co-efficients :
Path analysis of DTPA available micronutrients as influenced by other forms in the year 2000 revealed that total content of micronutrient had a direct positive effect while residual forms had a direct negative effect which was because of its strong indirect negative effect through the total content. The path co-efficient analysis of DTPA available micronutrients as influenced by various soil properties revealed that the values of residual component were very high in most of soil groups and soil property could explain only a little of the behaviour of DTPA available micronutrients.
II. LONG TERM FERTILIZER EXPERIMENT :
The differences in yield diminished in groundnut while T6 recorded highest values in wheat as well as sorghum all through. The N content were highest in T6 in a long run in groundnut and wheat grain while in straw it declined. Phosphorus in groundnut increased while that in cereals declined over 20 years. Potash also followed more or less same trend.
Particularly manganese exhibited an overall decline with time. Even DTPA available Mn registered below the critical values. If predominant form of bioavailable manganese is reducible one, then only
the deficiency symptoms are not observed. Nevertheless, whole spectrum warrants a need to supply suitable Mn nutrient. Although copper also showed a decline but DTPA available copper was maintained well above the critical value. Zinc also rendered a similar picture and application of chemical fertilizers supplemented as well as enhanced the utilization of zinc. 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, zinc and iron while reducible was predominant in manganese. Chemical fertilizers supplemented and enhanced utilization of DTPA available Mn and Cu along with a shift in inter-conversion among forms, over the 10 and 20 years cycles.
Correlations :
Groundnut pod yield was significantly related with percent available Mn, total and residual zinc and percent available iron and available total iron. Available total of Cu, available Mn, DTPA available zinc and an overall available iron predominantly showed positive relationship with soil properties. Correlation study indicated that Zn regulated partitioning of nitrogen towards grain and of potassium towards the vegetative growth. Phosphorus accumulation was promoted in legume while demoted in cereals by zinc. Available iron regulated concentration of nitrogen toward grain in cereals and phosphorus toward legumes, and potash in wheat grain and groundnut pods. Available copper showed positive relationship with nitrogen and potassium in wheat grains, and phosphorus in groundnut. Available Mn
behaved differently with phosphorus concentration exhibiting positive relationship in groundnut and negative relationship in wheat and sorghum. Available Mn by virtue of reducible forms favoured accumulation of potash in wheat grain and groundnut pod over vegetative parts.
Manganese revealed an overall negative relationship with NPK in groundnut, wheat and sorghum. Copper showed positive relationship with potash in groundnut haulm and inverse relationship with wheat straw. The DTPA Zn was positively related with phosphorus uptake in groundnut haulm while other forms showed negative relationship with N and P in sorghum, wheat straw and groundnut haulm. In iron relationships varied with form. The DTPA available and reducible form showed significant positive relationship with phosphorus uptake in groundnut haulm. The interactions viz., Iron x copper, iron 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 based on multiple regression and correlation analysis over a cycle of 1, 10, 20 years were presented. The stepwise regression analysis indicated that exchangeable form of copper, manganese and zinc along with the total had the maximum impact on DTPA available micronutrients. On the contrary in ferrous reducible forms had the maximum influence. The stepwise regression analysis of DTPA available micronutrients as the dependent variable and soil properties as the independent variable indicated very high residual values thereby indicating a low degree of influence of the soil properties.
Nevertheless, soil EC, soil OC and soil pH influenced DTPA available Cu, Mn, Zn and Fe, respectively, to some extent.
Path Co-efficients :
Zinc was explained the least and copper the most based on the independent variables (various forms) included in the analysis. The total micronutrients had the maximum direct effect on DTPA available micronutrient in Fe, Zn and Mn. Although the relationships of exchangeable and reducible forms with DTPA available form were significantly positive but direct effect were either negative or negligible. This might be due to their high indirect positive effect through total form of zinc and ferrous.
The dynamics of micronutrients with all its form exhibited spatiotemporal variations according to soil type, land use, agronomic package, cropping patterns and agro-ecological situations. Except that of Zn all other micronutrients with their forms exhibited in general a negative trend over a period of 10 years and so also in the long term fertilizer experiment after 20 years.