Promotion effects of salt-alkali on ammonia volatilization in a coastal soil

Coastal ecosystems are highly susceptible to salt-related problems due to their formation process and geographical location. As such ecosystems are the most accessible land resources on Earth, clarifying and quantifying the effects of salt-alkali conditions on N concentration and ammonia(NH_(3)) volatilization are pivotal for promoting coastal agricultural productivity. The challenge in establishing this effect is to determine how salt-alkali conditions impact NH_(3) volatilization through direct or indirect interactions. An incubation experiment using a coastal soil from a paddy farmland, combined with the structural equation modeling(SEM) method, was conducted to reveal the net effects of salt-alkali on NH_(3) volatilization and the role of environmental and microbial factors in mutual interaction networks. The specific experimental design consisted of four salt treatments(S1, S2, S3, and S4: 1‰, 3‰, 8‰, and 15‰ NaCl by mass of soil, respectively), four alkaline treatments(A1, A2, A3, and A4: 0.5‰, 1‰, 3‰, and 8‰ NaHCO_(3)by mass of soil, respectively) and a control without NaCl or NaHCO_(3) addition(CK), and each treatment had three urea concentrations(N1, N2, and N3: 0.05, 0.10, and 0.15 g N kg^(-1) soil,respectively) and three replicates. At the N1, N2, and N3 levels, NH_(3)volatilization increased by 9.31%–34.98%, 3.07%–26.92%, and 2.99%–43.61% as the NaCl concentration increased from 1‰ to 15‰, respectively, compared with CK. With an increase in the NaHCO_(3)concentration from 0.5‰ to 8‰, NH_(3) volatilization increased by 8.36%–56.46%, 5.49%–30.10%, and 30.72%–73.18% at the N1, N2, and N3 levels, respectively, compared with CK. According to the SEM method, salinity and alkalinity had positive direct effects on NH_(3)volatilization, with standardized path coefficients of 0.40 and 0.19, respectively.Considering the total effects(net positive and negative effects) in the SEM results, alkalinity had a greater influence than salinity(total standardized coefficient0.104 > 0.086). Nitrogen concentrations in the incubation system showed a direct positive effect on NH_(3) volatilization(standardized path coefficient = 0.78),with an obvious decrease under elevated salinity and alkalinity levels. Additionally, gene abundances of nitrogen-transforming microbes indirectly increased NH_(3) volatilization(total indirect standardized coefficient = 0.31). Our results indicated that potential NH_(3) emissions from coastal saline areas could be enhanced more by soil alkalization than by salinization.

Partial organic fertilizer substitution promotes soil multifunctionality by increasing microbial community diversity and complexity

Partial substitution of synthetic nitrogen(N)with organic fertilizers(PSOF)is of great significance in improving soil ecosystem functions in systems that have deteriorated due to the excessive application of chemical N fertilizer.However,existing studies typically focus on individual soil functions,neglecting the fact that multiple functions occur simultaneously.It remains unclear how PSOF influences multiple soil functions and whether these impacts are related to soil microbial communities.Here,we examined the impacts of partial substitutions(25%–50%)of chemical N fertilizer with organic form(pig manure or municipal sludge)in a vegetable field on soil multifunctionality,by measuring a range of soil functions involving primary production(vegetable yield and quality),nutrient cycling(soil enzyme activities,ammonia volatilization,N leaching,and N runoff),and climate regulation(soil organic carbon sequestration and nitrous oxide emission).We observed that PSOF improved soil multifunctionality,with a 50%substitution of chemical N fertilizer with pig manure being the best management practice;the result was strongly related to the diversities and network complexities of bacteria and fungi.Random forest analysis further revealed that soil multifunctionality was best explained by the bacterial-fungal network complexity,followed by available phosphorus level and bacterial diversity.The PSOF also shifted the composition of bacterial and fungal communities,with increased relative abundances of dominant bacteria phyla,such as Bacteroidetes,Gemmatimonadetes,and Myxococcota,and fungal phyla,such as Basidiomycota and Olpidiomycota.The observed increases in soil multifunctionality were consistent with significant increases in the relative abundances of keystone taxa such as Blastocladiomycota,Chaetomiaceae,and Nocardiopsaceae.Together,these findings indicate that PSOF can enhance interactions within and among microbial communities and that such practices have the potential to improve soil ecosystem multifunctionality and contribute to the development of sustainable agriculture.

A 2-year study on the effect of biochar on methane and nitrous oxide emissions in an intensive rice-wheat cropping system

The impacts of biochar addition with nitrogen fertilizer(Urea-N)on greenhouse gas(GHG)fluxes and grain yields are not comprehensively understood.Therefore,we designed a field experiment in an intensive rice-wheat cropping system located in the Taihu Lake region of China and measured CH4 and N_(2)O emissions for 2 consecutive years to examine the impacts of biochar combined with N-fertilizer on rice production and GHG flux.Three field experimental treatments were designed:(1)no N-fertilizer application(N0);(2)270 kg N ha^(−1) application(N270);and(3)270 kg N-fertilizer ha^(−1) plus 25 t ha^(−1) biochar application(N270+C).We found that,compared with urea application alone,biochar applied with Urea-N fertilizer increased N use efficiency(NUE)and resulted in more stable growth of rice yield.In addition,biochar addition increased CH4 emissions by 0.5-37.5%on average during the two consecutive rice-growing seasons,and decreased N_(2)O-N loss by~16.7%.During the first growing season,biochar addition did not significantly affect the global warming potential(GWPt)or the greenhouse gas intensity(GHGI)of rice production(p>0.05).By contrast,during the second rice-growing season,biochar application significantly increased GWPt and GHGI by 28.9%and 18.8%,respectively,mainly because of increased CH_(4) emissions.Our results suggest that biochar amendment could improve grain yields and NUE,and increased soil GWPt,resulting in a higher potential environmental cost,but that biochar additions enhance exogenous carbon sequestration by the soil,which could offset the increases in GHG emissions.