Partial substitution of manure increases N2O emissions in the alkaline soil but not acidic soils.

The fertilization regimes of combining manure with synthetic fertilizer are benefits for crop yields and soil fertility in cropping systems as compared to sole synthetic fertilization, but the responses of nitrous oxide (N2O) emissions to these practices are inconsistent in the literatures. We hypothesized that it is caused by different proportions of nitrogen (N) applied as manure and various soil properties. Here, we conducted a microcosm experiment, and measured the N2O emissions from control (no N) and five manure substitution treatments (supplied 100 mg N kg-1 using the combination of urea with manure) with a range of proportions of N applied as manure (0, 25%, 50%, 75%, and 100%) in three different soil types (fluvo-aquic soil, black soil, and latosol) under aerobic condition. The stimulated effect on N2O emissions was more pronounced after manure application in an alkaline soil with high nitrification rate, due to relatively rapid soil DOC depletion and N mineralization of manure. N2O emissions from partial substitution of urea with manure were significantly higher than manure-only addition under high soil pH due to abundant labile C from manure. However, there was no difference between manure substitution treatments under acid soils. Nitrification inhibitor substantially decreased N2O emissions with increasing soil pH, but it was less effective in mitigating N2O emissions with larger proportion of manure. This is likely due to the slow nitrification under low soil pH, and denitrification derived N2O increased with increasing manure application rate. Collectively, our study shows that the application of manure substitution to alkaline soils requires careful consideration, which might have rapid nitrification potential and hence trigger significant N2O emissions. The knowledge gained in this work will help the decision-makers in optimizing a sound N fertilization regime interacted with soil properties for sustainable crop production and N2O mitigation.

Digestate induces significantly higher N2O emission compared to urea under different soil properties and moisture.

Digestate is considered as an option for recycling resources and a part of the substitution for chemical fertilizers to reduce environmental impacts. However, its application may lead to significant nitrous oxide (N2O) emissions because of its high concentration of ammonium and degradable carbon. The research objectives are to evaluate how N2O emissions respond to digestate as compared to urea application and whether this depends on soil properties and moisture. Either digestate or urea (100 mg N kg-1) was applied with and without a nitrification inhibitor of 3,4-dimethylpyrazole phosphate (DMPP) to three soil types (fluvo-aquic soil, black soil, and latosol) under three different soil moisture conditions (45, 65, and 85% water-filled pore space (WFPS)) through microcosm incubations. Results showed that digestate- and urea-induced N2O emissions increased exponentially with soil moisture in the three studied soils, and the magnitude of the increase was much greater in the alkaline fluvo-aquic soil, coinciding with high net nitrification rate and transient nitrite accumulation. Compared with urea-amended soils, digestate led to significantly higher peaks in N2O and carbon dioxide (CO2) emissions, which might be due to stimulated rapid oxygen consumption and mineralized N supply. Digestate-induced N2O emissions were all more than one time higher than those induced by urea at the three moisture levels in the three studied soils, except at 85% WFPS in the fluvo-aquic soil. DMPP was more effective at mitigating N2O emissions (inhibitory efficacy: 73%-99%) in wetter digestate-fertilized soils. Overall, our study shows the contrasting effect of digestate to urea on N2O emissions under different soil properties and moisture levels. This is of particular value for determining the optimum of applying digestate under varying soil moisture conditions to minimize stimulated N2O emissions in specific soil properties.

Once-middle amount of straw interlayer enhances saline soil quality and sunflower yield in semi-arid regions of China: Evidence from a four-year experiment.

Straw deep returning as an interlayer is a novel practice to enhance soil carbon and nutrients. However, the impact of applying various amounts of straw as an interlayer on soil quality still remain unclear in the saline soil. Therefore, a field experiment was carried out over four years (2015-2018) in Hetao Irrigation District, China. The aim was to evaluate the impact of four straw interlayer rates (i.e., 0, 6, 12, and 18 Mg ha-1) applied at 40 cm depth on soil quality index (SQI) and its relationship to sunflower yield in saline soil. Our results showed that, in comparison to no straw interlayer (CK), straw interlayers applied at rates of 6, 12, and 18 Mg ha-1 improved SQI on average by 2.0, 2.7, and 3.0 times in four years, respectively (p < 0.05). This suggested that straw deep returning as an interlayer improved SQI, especially for middle and high amounts (12 and 18 Mg ha-1). Partial least squares path model (PLSPM) illustrated that the improvement of SQI was due to the high-moisture and low-salt environment created by straw interlayer in the early two years (2015-2016), while the higher soil nutrients released from straw decomposition in the subsequent years (2017-2018). The improvement of SQI contributed to sunflower yield, which was related to the decrease of soil salinity, the increase of soil moisture, soil organic carbon (SOC), total nitrogen (TN), and available nutrients under straw interlayers. The sunflower yield was increased by 8.7-13.4% under straw interlayers (p < 0.05), following the order of 18 = 12 > 6 >0 Mg ha-1. The greater increment of yield was detected during the initial phase of burying straw interlayers, which indicated that straw as an interlayer played a more important role than nutrient supply from straw decomposition. The findings highlighted that appropriate straw return amount (i.e., 12 Mg ha-1) as an interlayer is an economic practice to benefit soil quality and crop yield synchronously in salt-affected soils.

Secondary structure construction and molecular identification of rRNA 18S V4 region E23-5-E23-6 of parasitic lice of Hominidae.

The parasitic lice of Hominidae are a class of blood-sucking insects, having a large fragment expansion region in ribosome 18S V4 region. In this study, the value of the E23-5-E23-6 stem-loop structure in the insertion region for molecular identification of lice were explored through motif analysis and secondary structure construction. Five pubic lice samples from China were morphologically identified, and primers for the rRNA 18S V4 region were designed for molecular identification. The V4 sequence of the parasitic lice of Hominidae was retrieved from GenBank for sequence analysis. The five samples were identified as pubic lice based on V4 region, which were of the same specie but geographically different from Australian strains in Genbank, with the identity of 99.06-99.46%. Compared with the human lice, both the chimpanzee lice and pubic lice had large indel fragments in the V4 region. Comparison results showed that Muscle and MAFFT had better alignment and phylogeny results than Clustal. The large expansion region, comprising E23-5 and E23-6, was located between E23-4 and E23-7. The V4 secondary structure showed that the stem-loop structures of the lice parasitizing on pubic area, human, and chimpanzee were different in the E23-5 and E23-6, which could effectively distinguish the three parasitic lice and divide the human lice into five genotypes. This is suitable not only for the identification of three lice species in higher taxonomic ranks but also for genotype identification of human lice in lower taxonomic ranks. The difference between the stem-loop structure is more intuitive than that between the primary sequences.

Effect of Ag Nanoparticles on Denitrification and Microbial Community in a Paddy Soil.

The extensive application of Ag nanoparticles (AgNPs) in industry, agriculture, and food processing areas increases the possibility of its release and accumulation to agroecosystem, but the effects of AgNPs to denitrification and the microbial community in paddy ecosystems are still poorly studied. In this study, microcosmic simulation experiments were established to investigate the response of soil denitrification to different levels of AgNPs (i.e., 0.1, 1, 10, and 50 mg/kg) in a paddy soil. Real-time quantitative PCR and high-throughput sequencing were conducted to reveal the microbial mechanism of the nanometer effect. The results showed that, though 0.1-10 mg/kg AgNPs had no significant effects on denitrification rate and N2O emission rate compared to CK and bulk Ag treatments, 50 mg/kg AgNPs significantly stimulated more than 60% increase of denitrification rate and N2O emission rate on the 3rd day (P < 0.05). Real-time quantitative PCR revealed that 50 mg/kg AgNPs significantly decreased the abundance of 16S bacterial rRNA gene, nirS/nirK, cnorB, and nosZ genes, but it did not change the narG gene abundance. The correlation analysis further revealed that the cumulative N2O emission was positively correlated with the ratio of all the five tested denitrifying genes to bacterial 16S rRNA gene (P < 0.05), indicating that the tolerance of narG gene to AgNPs was the key factor of the increase in denitrification in the studied soil. High-throughput sequencing showed that only the 50-mg/kg-AgNP treatment significantly changed the microbial community composition compared to bulk Ag and CK treatments. The response of microbial phylotypes to AgNPs suggested that the most critical bacteria which drove the stimulation of 50 mg/kg AgNPs on N2O emission were Firmicutes and ß-proteobacteria, such as Clotridiales, Burkholderiales, and Anaerolineales. This study revealed the effects of AgNPs to denitrification in a paddy ecosystem and could provide a scientific basis for understanding of the environmental and toxicological effects of Ag nanomaterials.