PH and salinity are the dominant limiting factors for the application of mariculture sludge to paddy soil

Abstract

With the rapid development of mariculture industry, the disposal of mariculture sludge (MS) has become a serious environmental problem. Despite MS containing abundant organic matter, there may be some risks following MS application in agricultural practice. Many studies focus on the effects of sewage sludge application on crops. The potential of MS application on the microbial ecosystem and the above ground rice growth has not been systematically analyzed. We used 16S rDNA high-throughput sequencing to investigate the effects of MS application on soil microbial community and the rice growth. Soil samples were collected during rice growth under a pot experiment comprised of three treatments: without sludge (CK), native soil: sludge = 20:1 (LS) and native soil: sludge = 10:1 (HS). Application of MS enhanced soil nutrient content, but a high level of soil pH and salinity remained in the initial phase. Soil microbial biomass and extracellular enzyme activity were inhibited. The microbial diversity was decreased, including Chao1, Richness and Shannon index. Moreover, the specific bacterial taxa (Rhodobacteraceae, Flavobacteriaceae and Synergistales) were enhanced. The relative abundance of bacterial genes related to process of nitrification and denitrification were reduced, while the relative abundance of genes involved in N-fixation were increased. Partial Least Squares Path Modeling (PLS-PM) showed that soil pH and salinity were the dominant limiting factors during rice growth by indirectly affecting bacterial diversity. These findings strengthen the understanding of direct application of mariculture sludge in agriculture and provide a theoretical basis for resourceful utilizations of mariculture sludge.