Organic Amendments Alleviate Salinity Effects on Soil Microorganisms and Mineralisation Processes in Aerobic and Anaerobic Paddy Rice Soils

Abstract

Sea-water level rise leads to increased saltwater intrusion causing soil salinity on arable land with negative effects on soil microbial processes. Organic amendments are known to reduce the effects of salinity on soil microorganisms, therefore positively influencing microbial activity and nutrient cycling. However, the extent of this effect in paddy rice soils under aerobic compared to anaerobic conditions is unknown. Consequently, benefits of organic matter addition on carbon (C) and nitrogen (N) mineralisation under saline conditions were evaluated in a short-term laboratory incubation experiment. Two soils from Bangladesh were incubated with rice straw, manure or a manure-rice straw mixture at 50 and 100% water holding capacity (25 • C, 27 days). In addition, NaCl was added to half of the samples, which resulted in a set of non-saline (EC e = 1.1-1.3 dS m −1 ) and saline (EC e = 24.0-32.4 dS m −1 ) soils. Soil respiration (CO 2 -release) was measured throughout the experiment. At the end of the experiment, dissolved organic C, inorganic N, microbial biomass as well as bacterial, archaeal, and fungal domains were determined. Overall, effects of substrate addition overruled effects caused by salinity and water content. Microbial activity and biomass in particular fungi increased most strongly after rice straw addition and resulted in N immobilisation independent of moisture level. Rice straw and manure alleviated the effects of salinity on microorganisms; these were therefore mainly detectable in the non-amended soils. The reason for this is likely a higher C availability for soil microorganisms after amendment of organic materials, which allows them to produce osmolytes, counteracting the osmotic effects of increased salinity. However, the microbial communities of the two soils under investigation showed different response patterns to salinity reflected by a substantially higher fungi-bacteria ratio in soil B prone to salinity at 50% WHC as compared to soil A. Likewise, the metabolic quotient Wichern et al. Salinity Alleviation and Soil Microorganismswas higher in soil B and not affected by any of the short term treatments, revealing a soil legacy. Our results highlight the importance of organic amendments, such as rice straw to paddy soils under saline conditions to reduce negative effects on soil microbial processes, allowing them to maintain their major functions.

Deficit saline water irrigation under reduced tillage and residue mulch improves soil health in sorghum-wheat cropping system in semi-arid region

“…Decreased survival of microorganisms because of increased salinity and moisture stress prevailing in March–April at the experimental site was mainly responsible for lower MBC values after wheat compared to sorghum harvest. This finding conforms with others 34 , 48 those recorded lower values of MBC in the soil after harvest of wheat compared to sorghum in saline soils. The 100CWR saline-water irrigation imported more salts compared to deficit saline-water irrigation (60 and 80CWR) and showed lower values of MBC.…”

“…Measuring the activities of phosphatase, dehydrogenase, urease and glucosidase serve as an early indicator of changes in soil health of saline soil brought under cultivation 43 , 48 . Activities of these enzymes increased with a gradual decline in EC e after every crop cycle.…”

Salt Stress in Plants and Amelioration Strategies: A Critical Review

“…Several studies reported a significant increase in the soil microbial and enzymatic activities as a result of organic matter incorporation. The incorporation of organic amendments resulted in enhanced enzymatic activities [31,33,140,161,164,172], microbial biomass C [32,143,161,164,173], microbial biomass N [32,161], soil microbial activity as expressed by basal respiration [32,174], and nematode abundance [143]. However, the response of microbial and enzymatic activities to organic amendments differs depending on the kinds of amendments, rates of incorporation, the types of crops grown, etc.…”

Grazing exclusion regulates bacterial community in highly degraded semiarid soils from the Brazilian Caatinga biome

“…Thus, although the analyzed soil was not included in the saline soil classes, that is, EC <2 dS m −1 (Castro & dos Santos, 2020), the bacterial community in the natural and exclusion treatments may drive nutrient cycles more efficiently at lower salt concentrations because of their increased soil organic matter and CN availability (Table 1). Elevated salt concentrations in the soil can change the nutrient availability for plants and microbial communities, and it affects the quantity and quality of soil organic matter (Wichern, Islam, Hemkemeyer, Watson, & Joergensen, 2020). In addition, previous studies have shown that salt contents influenced the size and the activity of soil microbial biomass, which in turn plays an important role in soil biogeochemical cycles (Mavi, Sanderman, Chittleborough, Cox, & Marschner, 2012; Rietz & Haynes, 2003; Tripathi et al, 2006).…”