Nitrification and Denitrification Gene Abundances under Stable Soil Chemical Properties Established by Long-Term Compost Fertilization

Abstract

Rice paddies are dynamic areas for microbe-mediated nitrogen cycling and this could be driven by the long-term alteration of paddy soil edaphic factors. The objective of this study is to evaluate the lasting impact of long-term compost fertilization on the soil chemical properties of paddy fields, determining the size of the microbial guilds involved in nitrification and denitrification. Soil sampling was done on paddy fields without fertilizer, with NPK + compost, and with compost application, and the soil chemical properties of the fields were determined from 2018 to 2021. The abundance of genes related to nitrogen cycling was measured using quantitative PCR (qPCR). Annual analyses showed that the studied soils have attained stable, baseline chemical properties with significantly increased phosphorus (P2O5), potassium (K), SOM, and total nitrogen (TN) due to decades of fertilization with NPK + compost and compost. Consequently, the genes related to bacterial amoA, nosZI, and nosZII were significantly increased in Com- and NPKCom-amended soils compared to the NF paddy field. The nirK gene abundance was unaffected after long-term amendment with compost. A positive correlation was found between the archaeal amoA gene abundance and DOC, while SOM and TN were consistently positively correlated with the abundances of bacterial amoA, nosZI, and nosZII genes, in addition to interactions with potassium and DOC. Principal component analysis (PCA) indicated soil variabilities across treatments, where the unfertilized paddy field contained lower SOM and nutrient contents with a characteristic nirK gene abundance. Similar variabilities in terms of the SOM, TN, K, nosZI, and nosZII gene abundances were observed in the Com and NPKCom paddy fields. Long-term amendment with NPK + compost and compost created soil paddy fields with stable soil chemical properties with higher SOM and nutrient contents, which established higher abundances of genes associated with denitrification and nitrification that were observed during the fallow period.

Changes in Soil Chemical Properties and Bacterial Community Composition of Jujube Orchard Due to Oil Cake Fertilization

“…The application of organic fertilizers in agroecosystems can bring significant alterations in soils including both chemical and physical properties [28,29]. This is exemplified in long-term continuous applications either only as organic fertilizer amendment or mixing of organic and inorganic chemical fertilizers changing soil chemistry and ultimately affecting functional and structural soil microbiomes [10,11]. The most commonly used organic fertilizer amendment at least in paddy fields are fresh or composted animal manure singly, composted crop residues such as rice straw or a combination of both types [6].…”

“…There is also a cladespecific changes related to nitrogen cycling microbial communities as influenced by nitrogen fertilization [37]. The differing responses of diverse microbial guilds may show common trends as well as taxon-specific or clade-specific microbial responses to different types of fertilization input in agricultural lands which could be better elucidated under long-term fertilization studies [6,10,11].…”

“…As observed in our study, the clear clustering of the OC and NPK amended soils mainly influenced by soil chemical parameter and different microbial guilds indicates significant variabilities that exist between the two jujube orchard soils treated with different fertilizer regimes. These differences in terms of soils become prominent particularly in long-term application of compost, NPK, and compost plus NPK treatments compared to the control creating characteristic soils with different soil physicochemical properties and varying microbial community composition, diversity and abundances which eventually lead to changes in functional activities and services occurring in the soils [6,10,11]…”

“…The application of organic fertilizers especially long-term application has led to changes in physicochemical components of the soil concurrently changing its microbial components leading to overall changes that distinctly separates soils with and without fertilizer application. These changes ultimately change biochemical features of the soil affecting their overall function and services [10,11].…”

“…There are various studies that concentrated on unraveling the soil microbial community profiles in different agricultural fields treated with conventional organic fertilizers [20][21][22][23][24]. The application of organic fertilizer could alter soil properties [10,11,15], soil microbial communities [20][21][22][23], soil function [20][21][22][23] and even crop yield and quality [24]. Although there are numerous studies on the effect of organic fertilization on agroecosystems, there have been less studies focusing on the effect of oil cake-based fertilization on the communities of microbes in jujube orchards.…”