Microbial response of distinct soil types to land-use intensification at a South-Indian rural-urban interface

Abstract

Aims Rural-urban dynamics are leading to agricultural intensification practices, which affect microbial ecosystem functions in a soil-specific way. This study aimed to investigate what effects agricultural intensification has on soil microbial communities. Methods The effects of N fertilization level (low and high) and crop type (maize and finger millet) on microbial communities were investigated, using a two-factorial split-plot design, at two fields (irrigated and rainfed) on typical soil types (Nitisol and Acrisol) mimicking an intensification gradient in the rural-urban interface of the Indian Megacity Bangalore. Results The Nitisol had higher pH and clay content than the Acrisol. In combination with irrigation, this led to higher aboveground plant biomass (APB), soil organic carbon (SOC), microbial biomass (MB), fungal ergosterol and microbial necromass. High APB resulted in low total P content, due to P export in APB and high soil C/P and MB-C/P ratios in the Nitisol. Crop type and N fertilization level did not affect microbial parameters in the irrigated Nitisol, whereas crop type affected ergosterol and MBP and N fertilization level affected basal respiration in the rainfed Acrisol. Particulate organic matter (POM) was a major explanatory factor for most microbial parameters in both soils. In the Acrisol, drought reduced metabolic demand, which counteracted negative effects of low pH and clay on the MB. This was indicated by similar metabolic quotients and MBC/SOC ratios in both soils. Conclusions These results indicate the current need for water and high-quality fresh plant inputs to improve the microbial contribution to soil fertility at Bangalore.

Soil respiration under different N fertilization and irrigation regimes in Bengaluru, S-India

“…Development of root and shoot growth in plants also induces increased CO 2 emissions (Magill et al 1997). On our experimental plots, high N plots had significantly higher aboveground plant biomass than low N plots (Moran-Rodas et al 2022;Buerkert et al 2023). Higher CO 2 emissions from the high N plots align with the results of previous studies.…”

Agricultural Management Practices and Decision-Making in View of Soil Organic Matter in the Urbanizing Region of Bangalore

“…Nitrogen and lignin contents are major determinants of decomposition rates [28], with N 2 -fixing plants playing important roles in a substitution of mineral N fertilizer. Highquality residues increase microbial anabolic activity [12,29,30], promoting the production of microbial residues, thus increasing the C sequestration in soils [31]. Furthermore, crops differing in root traits may impact SOC dynamics via various processes, e.g., finer roots and more branched root systems as well as mycorrhiza infections increase the aggregate stability mainly through the physical enmeshment of soil particles, which increases resistance to soil erosion [32].…”

“…Furthermore, crops differing in root traits may impact SOC dynamics via various processes, e.g., finer roots and more branched root systems as well as mycorrhiza infections increase the aggregate stability mainly through the physical enmeshment of soil particles, which increases resistance to soil erosion [32]. In annual cropping systems, species with high root to shoot ratios, such as pigeon pea and finger millet, which are traditionally grown in Bangalore, show higher contributions to SOC compared to plants with lower root shoot ratios, such as maize [30,33]. Perennial crops generally deposit more C than annual species due to their permanent and deeper root systems, promoting the stabilization of SOC [8,10].…”

“…The application of mineral fertilizers and combinations with organic amendments are recommended to counteract nutrient exports with harvested crops and nutrient losses during cultivations, while increasing soil aggregations, SOC contents, and water retentions of soils [8,13,54]. An N fertilization effect on SOC fractions has not been observed in the short term [30,55,56], whereas long-term individual studies demonstrated positive effects of N fertilization on SOC. However, the positive effects may be outweighed by negative effects due to increased N 2 O emissions at high fertilization levels [57].…”

Effects of land uses and soil types on microbial activity and community structure

“…A decline in the soil microbial community in anthropogenic cases was driven by organic carbon, total nitrogen and the C:N ratio, while in the case of natural changes the following factors played key roles; total nitrogen, phosphorus and the C:N ratio (Chen et al, 2022). According to Moran-Rodas et al (2022), who investigated two soil types under different land uses, the highest impact factor on the soil microbial community was particulate soil organic matter content.…”