Partial substitution of manure reduces nitrous oxide emission with maintained yield in a winter wheat crop

Bacillus Bio-Organic Fertilizer Altered Soil Microorganisms and Improved Yield and Quality of Radish (Raphanus sativus L.)

Excessive use of fertilizers will not only cause the enrichment of soil N nutrients, soil secondary salinization, soil acidification, and an imbalance of the soil microbial community structure, but will also lead to the nitrate content of vegetables and the ground water exceeding the standard. The application of bio-organic fertilizer could reduce the amount of mineral fertilizer used. However, the effects of nitrogen reduced with different bio-organic fertilizers on soil chemical properties, microbial community structure, and the yield and quality of radish are not clear. In a field experiment, we designed six fertilization treatments: no fertilization (CK), conventional fertilization (T1), a total nitrogen reduction of 20% (T2), and a total nitrogen reduction of 20% with "No. 1", "Seek" or "Jiajiapei" bio-organic fertilizers. The results showed that nitrogen reduction of 20% with Bacillus bio-organic fertilizer (N1) significantly increased the organic matter, pH, total nitrogen content, and the relative abundance of Bacillus and Streptomyce in the soil compared with T1. RDA analysis showed that the pH, organic matter content, invertase and fluorescein diacetate enzyme activity of the soil were significantly correlated with the soil microbial community structure. In addition, the yield and Vc content in radish were increased with the application of bio-organic fertilizers, while on the contrary, the nitrate and cellulose content were decreased, and the N1 treatment showed the best effect. Moreover, the yield had a significant positive correlation with Bacillus. Overall, nitrogen reduction with bio-organic fertilizers, especially full-effective "No. 1" enriched with Bacillus, could alter the soil microbial community structure and effectively improve soil fertility, which in turn enhanced the yield and quality of radish. An application of Bacillus bio-organic fertilizer was an effective strategy to improve soil quality and vegetable safety.

Partial organic substitution for chemical fertilizer reduces N2O emissions but increases the risk of N loss through nitrification in Tibetan farmland

The combination of organic fertilizers (OFs) and chemical fertilizers (CF) is a promising agricultural management strategy to improve soil fertility while mitigating N2O emissions in croplands. However, there is still lacking of in-depth understanding of the effects of different OF and CF blends on N2O emissions and the underlying drivers. To this end, we conducted a short-term soil incubation to address the influences of partial OF substitutions for CF, i.e., 40% substitution of compost (CP), Yak dung (YD), Qingke straw (QS), and sheep dung (SD) on the processes of nitrification and denitrification in sandy loam soils in the Lhasa Valley. We found that CP, QS, and SD reduced cumulative N2O emissions by 53.43%, 25.96% and 16.64%, respectively compared to pure chemical fertilizer (N), except YD caused a significant higher in total N2O emissions. Fertilization treatments primarily regulate potential N2O emissions by affecting denitrification processes. While ammonia-oxidizing archaea (AOA amoA) could be the main driver of nitrification, and nirS abundance explained most of the cumulative N2O emissions. In addition, NO3--N tends to accumulate in the farmland soils, indicating an increase in the risk of leaching and nutrient loss. Overall, soil N2O emission reduction was favored by applying partial organic fertilizer substitution especially after through compost. Co-composting of animal manure and crop residue has more impressive potential for mitigating farmland N2O emissions.

Nitrous oxide emissions and soil profile responses to manure substitution in the North China Plain drylands

Substituting synthetic fertilizers with manures in agriculture enhances soil properties and crop yield. However, the impact on nitrous oxide (N2O) emissions, especially from the soil profile, remains poorly understood. This study examined emissions from 2017 to 2019 on a well-established (>10-year) maize field site in the North China Plain. Three treatments were compared: 100 % synthetic nitrogen (NPK), 50 % synthetic fertilizer N + 50 % manure N substitution (50%MNS), and 100 % manure N substitution (100%MNS). N2O emissions were monitored for three years, and in 2019, N2O concentrations at 20 cm and 40 cm soil depths were analyzed in relation to surface N2O fluxes and environmental factors. The results showed manure substitution resulted in about 13.8 %-25.2 % (50%MNS) and 40.3 %-72.2 % (100%MNS) reduction in N2O emissions over the 3-year period compared with the NPK treatment. Throughout the maize growing season, the top-dressing accompanied by rainfall was responsible for the N2O emissions. The difference in N2O concentrations between all the treatments at 20 cm depth was insignificant, but at 40 cm depth the N2O concentrations were significantly higher for the 50%MNS treatment than the other treatments. The N2O fluxes and N2O concentration were not synchronized especially in NPK. The decoupled relationship between the N2O fluxes and the N2O concentration in the soil profile depth suggested the contribution of N2O produced in the soil profile to the surface N2O fluxes is limited. This study highlights that manure substitution is an efficient measure to reduce N2O emissions.

Bio-manure substitution declines soil N2O and NO emissions and improves nitrogen use efficiency and vegetable quality index

Substituting mineral fertilizer with manure or a combination of organic amendments plus beneficial soil microorganisms (bio-manure) in agriculture is a standard practice to mitigate N2O and NO emissions while enhancing crop performance and nitrogen use efficiency (NUE). Here, we conducted a greenhouse trial for three consecutive vegetable growth seasons for Spinach, Coriander herb, and Baby bok choy to reveal the response of N2O and NO emissions, NUE, and vegetable quality index (VQI) to fertilization strategies. Strategies included solely chemical nitrogen fertilizer (CN), 20 (M1N4) and 50% (M1N1) substitution with manure, 20 (BM1N4) and 50% (BM1N1) substitution with bio-manure, and no fertilization as a control and were organized in a completely randomized design (n = 3). Manure decreased N2O emissions by 24-45% and bio-manure by 44-53% compared to CN. Manure reduced NO emissions by 28-41% and bio-manure by 55-63%. Bio-manure increased NUE by 0.04-31% and yields by 0.05-61% while improving VQI, attributed to yield growth and reduced vegetable NO3- contents. Improvement of root growth was the main factor that explained the rise of NUE; NUE declined with the increase of N2O emissions, showing the loss of vegetable performance under conditions when denitrification processes prevailed. Under the BM1N1, the highest VQI and the lowest yield-scaled N-oxide emissions were observed, suggesting that substitution with bio-manure can improve vegetable quality and mitigate N-oxide emissions. These findings indicate that substituting 50% of mineral fertilizer with bio-manure can effectively improve NUE and VQI and mitigate N-oxides in intensive vegetable production.

Manure replacing synthetic fertilizer improves crop yield sustainability and reduces carbon footprint under winter wheat-summer maize cropping system

Manure replacing synthetic fertilizer is a viable practice to ensure crop yield and increase soil organic carbon (SOC), but its impact on greenhouse gas (GHG) emissions is inconsistent, thus remains its effect on CF unclear. In this study, a 7-year field experiment was conducted to assess the impact of replacing synthetic fertilizer with manure on crop productivity, SOC sequestration, GHG emissions and crop CF under winter wheat-summer maize cropping system. Five treatments were involved: synthetic nitrogen, phosphorus, and potassium fertilizer (NPK) and 25%, 50%, 75%, and 100% of manure replacing synthetic N (25%M, 50%M, 75%M, and 100%M). Compared with NPK treatment, 25%M and 50%M treatments maintained annual yield (winter wheat plus summer maize) and sustainable yield index (SYI), but 75%M and 100%M treatments significantly decreased annual yield, and 100%M treatment also significantly reduced annual SYI. The SOC content exhibited a significant increasing trend over years in all treatments. After 7 years, SOC storage in manure treatments increased by 3.06-11.82 Mg ha-1 relative to NPK treatment. Manure treatments reduced annual GHG emissions by 14%-60% over NPK treatment. The CF of the cropping system ranged from 0.16 to 0.39 kg CO2 eq kg-1 of grain without considering SOC sequestration, in which the CF of manure treatments lowered by 18%-58% relative to NPK treatment. When SOC sequestration was involved in, the CF varied from -0.39 to 0.37 kg CO2 eq kg-1 of grain, manure treatments significantly reduced the CF by 22%-208% over NPK treatment. It was concluded that replacing 50% of synthetic fertilizer with manure was a sound option for achieving high crop yield and SYI but low CF under the tested cropping system.

Exploring site-specific N application rate to reduce N footprint and increase crop production for green manure-rice rotation system in southern China

Milk vetch (Astragalus sinicus L.) is leguminous green manure (GM) which produces organic nitrogen (N) for subsequent crops and is widely planted and utilized to simultaneously reduce the use of synthetic N fertilizer and its environmental costs in rice systems. Determination of an optimal N application rate specific to the GM-rice system is challenging because of the large temporal and spatial variations in soil, climate, and field management conditions. To solve this problem, we developed a framework to explore the site-specific N application rate for the low-N footprint rice production system in southern China based on multi-site field experiments, farmer field survey, and process-based model (WHCNS_Rice, soil water heat carbon nitrogen simulator for rice). The results showed that a process-based model can explain >83.3% (p < 0.01) of the variation in rice yield, aboveground biomass, crop N uptake, and soil mineral N. Based on the scenario analysis of the tested WHCNS_Rice model, the simple regression equation was developed to implement site-specific N application rates that considered variations in GM biomass, soil, and climatic conditions. Simulation evaluation on nine provinces in southern China showed that the site-specific N application rate reduced regional synthetic N fertilizer input by 29.6 ± 17.8% and 65.3 ± 23.0% for single and early rice, respectively; decreased their total N footprints (NFs) by 23.4% and 49.3%, respectively; and without reduction in rice yield, compared with traditional farming N practices. The reduction in total NF was attributed to the reduced emissions from ammonia volatilization by 35.2%, N leaching by 28.4%, and N runoff by 32.7%. In this study, we suggested a low NF rice production system that can be obtained by combining GM with site-specific N application rate in southern China.