Elsevier

Applied Soil Ecology

Volume 166, October 2021, 103992
Applied Soil Ecology

Responses of soil bacterial community and enzyme activity to organic matter components under long-term fertilization on the Loess Plateau of China

https://doi.org/10.1016/j.apsoil.2021.103992Get rights and content

Abstract

Soil bacterial community structure, enzyme activities and their relationships to soil carbon and nitrogen in response to long-term fertilization remain poorly understood. Therefore, the objective of this study was to evaluate soil carbon and nitrogen fractions, enzyme activity, and bacterial community structure at 0–15, 15–30, and 30–60 cm depths after 34-yr of continuous application of manure and inorganic fertilizers. The study had a randomized complete block design with six treatments and three replications. Treatments were inorganic nitrogen fertilizer only (N), nitrogen plus phosphrous fertilizers (NP), manure (M), nitrogen plus manure (NM), nitrogen plus phosphorus plus manure (NPM), and unfertilized control (CK) in a winter wheat (Triticum aestivum L.) monoculture system. Most soil carbon and nitrogen fractions at 0–15 and 15–30 cm were greater with M, NM, and NPM, and winter wheat yield was greater with NPM than other treatments. The NPM increased β-glucosidase, β-xylosidase, and β-N-acetylglucosidase compared to other treatments at all depths. Soil bacterial Shannon index was similar among treatments at 0–15 and 15–30 cm and lower in N and NP than other treatments at 30–60 cm. Compared to CK, inorganic and manure fertilization increased relative abundances of Gemmatimonadetes and Bacteroidetes but decreased those of Nitrospirae, Planctomycetes, and Latescibacteria. Increases in soil enzyme activities and bacterial communities after long-term application of inorganic N and P fertilizers and manure was related to increased substrate availability. Overall, a combination of chemical fertilizers and manure can enhance soil health and quality through increased soil organic matter component, enzyme activity, and bacterial abundance.

Introduction

Inorganic fertilizers have been widely used to improve soil fertility and crop yields across the world. However, long-term fertilizer application has become a significant environmental challenge because it increased soil acidity, nutrient runoff and leaching, and greenhouse gas emissions (Liu et al., 2013; Dou et al., 2016). The overuse of inorganic fertilizers in intensive agriculture is often associated with low nutrient use efficiency and high off-site environmental impacts (Fan et al., 2012). Studies show that excess nitrogen fertilizer that can not be retained in soil or utilized by a crop is lost to the atmosphere as NH3, N2O, NOx, and N2, or lost through leaching and runoff as NO3-N (Robertson et al., 2013). Although inorganic fertilizers increase the labile fractions of soil organic matter in short-term (Brar et al., 2013; Sainju et al., 2000), long-term soil carbon storage may decrease due to the increased microbial activity and carbon mineralization (Manna et al., 2007; Jiang et al., 2014). Studies also reported neutral or adverse effects of inorganic fertilizers on microbial biomass and functional diversity (Lupwayi et al., 2012; Wang et al., 2019).

Compared to inorganic fertilizers, manure and compost applications can increase soil carbon and nitrogen sequestration (Guo et al., 2015) and lead to increased microbial biomass, bacterial abundance, and enzyme activities (Böhme et al., 2005; Ge et al., 2010; Pauline et al., 2011; Zhang et al., 2015; Gai et al., 2018). The addition of organic residues such as green manure, compost, and biosolids application maintained a higher soil carbon level than a control system that involved no organic residue addition (Ghimire et al., 2018; Wuest and Gollany, 2013). Compost addition also increased the microbial biomass, abundance of cultivable microorganisms, soil respiration, and enzyme activities (Zhen et al., 2014). Using manure and compost alone may not produce sustainable high crop yields. Therefore, in subsistence agriculture in developing countries that relies on small landholding and involves crop-livestock integrated systems, inorganic fertilizers are often applied to supplement the compost. Combining organic and inorganic fertilizers improve soil fertility and increase crop yields and soil extracellular enzyme activities compared to inorganic fertilizer alone (Cai and Qin, 2006; Miao et al., 2019). However, there is inconsistency in response to fertilizer and compost application because of inherent variability in the nutrient content of composts.

Long-term fertilization experiments are established to evaluate the agronomic and environmental benefits of fertilizer management. For example, a long-term N fertilization study reported the benefits of N addition on nutrient use and conservation, soil C accumulation, and crop production (Khan et al., 2007). According to Brar et al. (2013), the addition of manure and inorganic fertilizers can enhance soil C fractions and microbial community up to a 60 cm depth. Crop root depth can exceed 1 m, and root residue and exudates can enhance microbial community structure and functions throughout the soil profile. However, most of the studies discussing the influence of fertility management practices on soil microbial community, enzyme activities, and nutrient cycling are limited to the surface soil layer (Coonan et al., 2019). Comparing soil carobon and nitrogen in surface and sub-surface soils, Ghimire et al. (2018) highlighted the role of subsoil fertility in improving crop yields. Information on the impact of fertilization strategy on microbial dynamics at subsurface layers will further advance our understanding of subsoil carbon and nutrients cycling.

This study aimed to evaluate the impacts of long-term fertilization on soil health, specifically, soil bacterial community responses, enzyme activities, and organic matter components on the Loess Plateau of China. We measured soil carbon and nitrogen fractions, enzyme activities, and bacterial community composition at 0–15, 15–30, and 30–60 cm soil depths after 34-yr annual application of inorganic fertilizers, organic manure, and the combination of them under winter wheat monoculture system. A mixture of manure and inorganic fertilizers was expected to enhance soil carbon and nitrogen fractions, enzyme activity, and bacterial abundance compared to those under inorganic fertilizers alone or the control without fertilization.

Section snippets

Site description

A long-term field experiment was established in 1984 at the Shaanxi Changwu Agro-Ecological Station of China (107°44.70′E, 35°12.79 N), aiming to test the effects of fertilization and rotation on soil fertility and crop production under dryland cropping systems (Guo et al., 2008). The site has a sub-humid temperate climate, and the mean annual temperature and precipitation were 9.1 °C and 584 mm, respectively. The soil is Heilutu silt loam (Calcarid Regosol, FAO World Reference Base Soil

Soil carbon and nitrogen fractions and crop yield

Soil carbon and nitrogen fractions were significant with treatments, soil depth, and treatment × depth interaction. At 0–15 cm, SOC, MBC, PCM, STN, PNM, and NH4+-N were greater with M, NM, and NPM than CK and N (Table 1). The POC and PON were greater with M than NP and CK. The MBN was greater with NM and NPM than other treatments, and NO3-N was greater with NP than N and CK. At 15–30 cm, SOC, POC, PCM, STN, PON, and NO3-N were greater with NM and NPM than most other treatments. The MBC was

Long-term fertilization effect on soil organic carbon and nitrogen

Maintenance of soil organic carbon and nutrients in agroecosystems depends on carbon and nitrogen inputs and soil biogeochemical cycling. This study revealed an increase in soil carbon and nitrogen storage with manure application because they enhance SOC, STN, and POC. Manure alone or in combination with inorganic fertilizers increased soil carbon and nitrogen fractions compared to inorganic fertilizer alone, possibly due to increased organic matter inputs from organic manure. Organic manures

Conclusions

This study evaluating soil carbon and nitrogen fractions, enzyme activity, and bacterial community structure in long-term fertility management plots reinforced the importance of organic manure and integrated nutrient management in maintaining carbon and nitrogen in the soil profile and microbial growth. Long-term application of chemical fertilizers decreased most of soil carbon and nitrogen fractions, extracellular enzyme activities, and soil bacterial abundance. Manure alone or manure plus

Declaration of competing interest

We state that all authors in the manuscript have agreed to submit to your journal, and there is no conflict of interest for all authors.

Acknowledgments

This study was supported by the CAS “Light of West China” Program for Introduced Talent in the West, the National Natural Science Foundation of China (Grant No. 31570440, 31270484), and the Key International Scientific and Technological Cooperation and Exchange Project of Shaanxi Province, China (2020KWZ-010).

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