Title : Glomalin content of soil in relation to soil organic carbon under long term fertilizer studies in finger millet – maize cropping system
An experiment conducted in an ongoing Long Term Fertilizer Experiment at Zonal Agricultural Research Station, UAS, GKVK, Bengaluru, Karnataka, India to study the dynamics of soil organic carbon and glomalin content of soil under finger millet-maize cropping system. Glomalins are a thermo stable, water-insoluble soil glycoproteins produced by arbuscular mycorrhizal fungi measured in soil as glomalin related soil protein. These proteins perform a fundamental role in making soil structure and they live relatively long in soil and play a structural role in soil carbon dynamics. The results of two years study (2013 and 2014) revealed that continuous application of inorganic fertilizers along with organic manure had significant effect on glomalin content which was significantly higher in 100 % NPK + FYM + Lime (3.83 g kg-1) applied plot followed by the treatment receiving 100 % NPK + FYM (3.72 g kg-1) as compared to the treatments receiving only inorganic fertilizers, while lower glomalin content was recorded in control (1.21 g kg-1). Among different depths, surface layer (0 to 15 cm) recorded significantly higher glomalin content in soil (2.53 g kg-1). Generally in cultivated land plant roots were more heavily colonized with almost the whole root filled with mycorrhizal material (hyphae, arbuscules, vesicles or spores). The content of glomalin in the soil is something that builds up over time and is not always measurable in the first year after treatment imposition. Therefore, long term application of fertilizers had significant impact on glomalin content. Total organic carbon was also significantly higher in the treatment receiving 100 % NPK + FYM + Lime (5135 mg kg-1). The pooled data of two years revealed that irrespective of depth soil organic carbon content was significantly higher in the treatment receiving 100 % NPK + FYM + Lime (4.99 g kg-1) followed by treatment receiving 100 % NPK + FYM (4.85 g kg-1)). In the present study it was observed that the values of glomalin content had a positive and significant relation with soil total organic carbon. Application of FYM increased the soil organic carbon content to a greater extent than that of inorganic fertilizer alone. This may be attributed to enhanced crop growth which in turn, resulted in increased above and below-ground organic residues and thus raised the organic carbon content. Aggregate stability of soil was also significantly higher in 100 % NPK + FYM + Lime (79.53%) followed by 100 % NPK + FYM (77.98%) as compared to treatments receiving only inorganic fertilizers and unfertilized control. Significantly higher maize yield was recorded in 100 % NPK + FYM + Lime (50.49 q ha-1) and finger millet in 150 % NPK (34.51 q ha-1) was mainly due to more organic carbon and improved glomalin content which enhanced the good soil aggregates which helped in better moisture and nutrient supply there by enhanced the crop yield.
Take away notes:
• Can know the significance of glomalin content in soil aggregate formation, maintaining soil fertility and soil organic carbon content in soil.
• The data generated is only after 28 years of experimentation. Long term impact of organic manure and fertilizers on glomalin content and carbon sequestration can be studied over the years.
• Long term impact of organic manure and fertilizers on annual C input required to maintain SOC in equilibrium can be studied by carbon modeling.