Pedosphere 29(4): 483--491, 2019
ISSN 1002-0160/CN 32-1315/P
©2019 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Short-Term Effect of Nitrogen Intensification on Aggregate Size Distribution, Microbial Biomass and Enzyme Activities in a Semi-Arid Soil Under Different Crop Types
Rajasekaran MURUGAN1, V. R. Ramakrishna PARAMA2, Beate MADAN3, R. MUTHURAJU4, Bernard LUDWIG1
1Department of Environmental Chemistry, University of Kassel, Nordbahnhof str. 1a, Witzenhausen 37213(Germany)
2Department of Soil Science and Agricultural Chemistry, University of Agricultural Sciences(GKVK), Bangalore 560065(India)
3Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics, University of Kassel, Stein str. 19, Witzenhausen 37213(Germany)
4Department of Agricultural Microbiology, University of Agricultural Sciences(GKVK), Bangalore 560065(India)
Corresponding Author:Rajasekaran MURUGAN
ABSTRACT
      There is a lack of quantitative assessments available on the effect of agricultural intensification on soil aggregate distribution and microbial properties. Here, we investigated how short-term nitrogen (N) intensification induced changes in aggregate size distribution and microbial properties in a soil of a hot moist semi-arid region (Bangalore, India). We hypothesised that N intensification would increase the accumulation of macroaggregates > 2 mm and soil microbial biomass and activity, and that the specific crop plant sowed would influence the level of this increase. In November 2016, surface (0-10 cm) and subsurface (10-20 cm) soil samples were taken from three N fertilisation treatments, low N (50 kg N ha-1), medium N (75 and 100 kg N ha-1 for finger millet and maize, respectively), and high N (100 and 150 kg N ha-1 for finger millet and maize, respectively). Distribution of water-stable aggregate concentrations, carbon (C) and N dynamics within aggregate size class, and soil microbial biomass and activity were evaluated. The high-N treatment significantly increased the concentration of large macroaggregates in the subsurface soil of the maize crop treatment, presumably due to an increased C input from root growth. Different N fertilisation levels did not significantly affect C and N concentrations in different aggregate size classes or the bulk soil. High-N applications significantly increased dehydrogenase activity in both the surface soil and the subsurface soil and urease activity in the surface soil, likely because of increased accumulation of enzymes stabilised by soil colloids in dry soils. Dehydrogenase activity was significantly affected by the type of crop, but urease activity not. Overall, our results showed that high N application rates alter large macroaggregates and enzyme activities in surface and subsurface soils through an increased aboveground and corresponding belowground biomass input in the maize crop.
Key Words:  agricultural intensification,biomass input,C and N dynamics,large macroaggregate,microaggregate,N application,small macroaggregate,water-stable aggregates
Citation: Murugan R, Parama V R R, Madan B, Muthuraju R, Ludwig B. 2019. Short-term effect of nitrogen intensification on aggregate size distribution, microbial biomass and enzyme activities in a semi-arid soil under different crop types. Pedosphere. 29(4):483-491.
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