FRACTIONATIONS OF SOIL ORGANIC MATTER IN LONG TERM FERTILIZER EXPERIMENT
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Date
2005-03
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The study has been carried out for fractionation of soil organic matter in groundnut-wheat- jowar (fodder) cropping sequence under long-term fertilizer experiment (1979-2000) on a medium black calcareous clay soil at Instructional Farm, College of Agriculture, Junagadh Agricultural University, Junagadh. There were six treatments viz., control, FYM @ 25 t ha-1, ½ NP, ½ NP + K, NP and NP + K and from each treatment soil samples were collected in the years 1980, 1990 and 2000 analysed for active, passive and slow pools. The data were analysed for correlation, regression and path co-efficient statistical tools. The pools of soil organic matter concentrate as soil organic carbon under the treatments application of FYM @ 25 t ha-1 followed by NP + K treatment in the year 1990.
In the context of active pools of SOM, maximum of water soluble carbon and water soluble carbohydrates were recorded under FYM application @ 25 t ha-1 in the years 1990 and 2000, respectively. Vigorous flush of carbon mineralization was achieved under application of FYM @ 25 t ha-1 in the year 1980. Both the SMBC and SMBN were found low under application of full doze of N and P along with potassium in the year 1990 whereas SMBP in the same year were low with N and P without potassium. Maximum activity of dehydrogenase was observed in the year 1990 under NP treatment. Among the passive pools, maximum humic
acid, brown humic acids, gray humic acid, fulvic acid, hymatomelanic acid and humin were observed in the year 1990 with application of FYM @ 25 t ha-1. The slow pools of SOM, improved percent of water stable aggregates and organic carbon application of FYM @ 25 t ha-1.
Positive association among humic acid, brown humic acid, gray humic acid, fulvic acid, hymatomelanic acid and humin was observed under the treatments namely FYM @ 25 t ha-1, NP, ½ NP, ½ NP + K, NP + K. Positive association of soil microbial biomass carbon with dehydrogenase activity and water soluble carbohydrates was observed under control, ½ NP and NP + K treatments. Positive association of soil microbial biomass nitrogen was observed with soil microbial biomass phosphorus under control and with water-soluble carbohydrates under treatments ½ NP + K and NP + K.
Regression of passive pool was significant in three treatments Viz., control, FYM @ 25 t ha-1 and NP + K. During the year 1980, a combine impact of passive pools of humic acid and humin over soil organic carbon contributed to a maximum level in the three treatments. During the year 1990, a combine impact of passive pools of humic acid and humin over soil organic carbon was contributed to a maximum level under NP + K treatment whereas combine influence of humic acid and hymatomelanic acid over soil organic carbon to the maximum tune under FYM @ 25 t ha-1. During the year 2000, a combine impact of passive pools of humic acid and fulvic acid over soil organic carbon contributed to a maximum level in the three treatments. During the year 1980, a combine impact of active pools viz., SMBC and SMBP over soil organic carbon contributed to a maximum level in all the three treatments. During the year 1990, a combine impact of active pools of SMBC and SMBN over soil organic carbon contributed to a maximum level under control treatment whereas combined influence of SMBC and SMBP over soil organic carbon to the maximum tune under FYM @ 25 t ha-1. During the
year 2000, a combine impact of active pools of SMBN and SMBP over soil organic carbon contributed to a maximum level in the three treatments.
Path analysis of active as well as passive pools of soil organic matter have generated useful information. The maximum direct effect was contributed by humin and their indirect effect via fulvic acid under FYM treatment. The humic acid and their indirect effect via humin was observed under NP + K on soil organic carbon. Residual variation was maximum under NP + K treatment. The maximum direct contribution of DHA and indirect effect via SMBN under the FYM and NP + K treatment was observed on soil organic carbon. The maximum direct effect on SOC was contributed by GHA and their indirect effect via humin under FYM treatment. Humin and their indirect effect via GHA was observed under NP + K treatment on soil organic carbon. The maximum direct effect was contributed by SMBC under FYM treatment and by WSC under NP + K treatment on soil organic carbon. The maximum direct effect was contributed by HA and their indirect effect via BHA under FYM treatment. The BHA and their indirect effect via humin followed by HA under NP + K treatment on fulvic acid. The organic and inorganic treatments produced maximum direct effect by SMBC and its indirect effect via SMBN under FYM; and by SMBC and its indirect effect via DHA under NP + K treatments on fulvic acid. The maximum direct effect on SOC was contributed by humin under FYM and by HA under NP + K treatments and their indirect effect via FA on fulvic acid in both the treatments. Residual variation was observed maximum under NP + K treatment. The maximum direct effect was contributed by SMBN and their indirect effect via WSC under both the treatments. In this path, highest residual variation was contributed under FYM application @ 25 t ha-1 compared to application of full doze of NP along with K. Maximum direct effect of the organic and inorganic treatments was contributed by humin in both the treatments and their indirect effect via FA under FYM and via HA under NP + K treatments. In this path, highest residual variation was contributed under
application of full doze of NP along with K comparative to FYM application @ 25 t ha-1. The maximum direct effect was contributed by WSC and their indirect effect via SMBN under FYM and by SMBN and their indirect effect via WSC under NP + K treatments. In this path, highest residual variation was contributed under application of full doze of NP along with K comparative to FYM application @ 25 t ha-1.
Thus FYM application @ 25 t ha-1 improved active, passive and slow pools of SOM. Also, improvement of SOM pools was very slow during 1980, highest during 1990 and further decreased during 2000 but still higher than that of year 1980 in the long-term fertilizer experiments.