Manure Substitution Research Articles

Bio-organic substitution in tobacco (Nicotiana tabacum L) cultivation: Optimum strategy to lower carbon footprint and boost net ecosystem economic benefit

The partial substitution of organic manure for chemical nitrogen fertilizers, known as organic substitution, is widely regarded as a cleaner and more sustainable production strategy. However, few studies have quantified greenhouse gas emissions, product income and net ecosystem economic benefit (NEEB) using a life cycle assessment (LCA) approach, particularly for typical tobacco (Nicotiana tabacum L.) production. Here, we quantified the yield and quality of a typical tobacco production in Qujing, Yunnan, China, through field experiments and calculated its carbon footprint and NEEB using the LCA approach. Four organic substitution strategies were established with equal nitrogen inputs, including synthesized chemical fertilizer (SN), farmyard organic manure (NF), commercial organic manure (NC), and bio-organic (Trichoderma viride Pers.) manure (NT), each substituting 15% of synthesized nitrogen fertilizer. Compared to the SN strategy, the NT strategy significantly increased yield and income by 10.3% and 9.6%, respectively. In contrast, the NF strategy significantly reduced income, while the NC strategy showed no significant difference. Both the NC and NT strategies significantly reduced N2O cumulative emissions (by 15.9% and 8.0%, respectively), increased δSOC (by 38.4% and 15.0%, respectively), and decreased carbon footprint compared to the SN strategy. However, the NF strategy significantly increased the income-scaled carbon footprint, even though it also notably reduced N2O cumulative emissions (by 22.6%) and increased δSOC (by 7.9%). The NT strategy achieved a win-win scenario of low environmental risk and high economic returns of tobacco production with significantly increased NEEB (by 10.6%) compared to the SN strategy (37.60 × 103 CNY yr−1). This suggests that the bio-organic Trichoderma manure substituting 15% synthesized nitrogen fertilizer is the best organic substitution strategy for sustainable tobacco production.

Energy, environmental footprints and economic benefit of substituting inorganic fertilizer with organic manure for winter wheat in Huanghuaihai Plain

Manure substitution shows promise for nitrogen (N) management, food security, energy balance and environmental costs reduction. However, there is limited research on this practice in the Huanghuaihai Plain. This study aimed to investigate the energy use efficiency, economic benefits, carbon and nitrogen footprint under two types of N fertilizer (U, urea and M, organic manure), two application rates of N (180 kg N ha−1, U1 for 100 % urea and M1 for 100 % organic manure; 90 kg N ha−1, U2 for 50 % urea and M2 for 50 % organic manure) and no fertilizer application treatment (CK) for winter wheat from 2017 to 2019. Results showed that grain yield and agricultural input cost under N application rate of 90 kg N ha−1 was 15.5 % and 7.8 % lower than that of 180 kg N ha−1, respectively, leading to a significant decrease in economic benefit. Under the same N rate, M1 obtained higher grain yield than U1, grain yield of M2 did no differ in that of U2. Total energy inputs and agricultural input costs of M were 9.5 % and 3.6 % lower than U, resulting in higher energy use efficiency and economic benefit. The reduced agricultural input for M was primarily due to a decrease in the application of inorganic fertilizer. Compared with other treatments, U2+M2 obtained higher grain yield, energy use efficiency, and economic benefit. The carbon and nitrogen footprint on unit grain yield of U1 was increased by 13.7 %-24.1 % and 3.9 %-19.6 %, which was attributed to the increase in direct N2O emissions, indirect carbon emission and losses of reactive N from agricultural inputs. Overall, U2+M2 sustained high productivity and reduced the environmental impact. Substituting inorganic fertilizer with organic manure was a promising strategy to improve agricultural production with less agricultural inputs and environmental footprints in the Huanghuaihai Plain.

How to effectively reduce sloping farmland nutrient loss and soil erosions in the Three Gorges Reservoir area

Fertilization and soil conservation measures play crucial roles in influencing nutrient loss and soil erosion on sloping farmlands. However, the long-term effects of these measures and the characterization of nutrient loss and sediment yield under different rainfall types and crop growth stages were not well studied. Therefore, we designed six treatments for sloping farmlands in the Three Gorges Reservoir Area with a field experiment. A field experiment included downslope cultivation with chemical fertilizer (DF), downslope cultivation with chemical fertilizer plus manure (DFM), cross-slope cultivation with chemical fertilizer plus manure (CFM), no-till straw cover with chemical fertilizer plus manure (NSFM), ridge plant hedges with chemical fertilizer plus manure (RFM), and biochar interception ditches with chemical fertilizer plus manure (BFM). The results indicated that soil and water conservation measures in association with manure substitution significantly reduced runoff depth (14.3–22.5 %), sediment yield (10.3–46.5 %), and total nitrogen (TN) loss (13.5–36.5 %) compared to DF. NSFM significantly reduced total phosphorus (TP) loss by 17.4 % and the TP loss from the other treatments did not show significant differences compared to DF. Rainfall intensity and runoff depth were identified as critical factors influencing nutrient loss and soil erosion. NSFM showed maximal nutrient reduction performance under different rainfall intensities, while DFM was not significantly effective. NO3--N and particulate P dominated the loss of TN and TP. The first 30 minutes of runoff generation and the seedling stage were identified as risk periods for N and P loss. The study suggests that the NSFM treatment was the appropriate method to prevent soil and water nutrient loss. This provides important insights for the precise control of nutrient loss and soil erosion on sloping farmlands.

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.

Organic substitution regime with optimized irrigation improves potato water and nitrogen use efficiency by regulating soil chemical properties rather than microflora structure

Context or problemImproving water and fertilizer use efficiency is an inevitable choice for sustainable potato production in North China. However, the regulation mechanism of potato water and nitrogen use efficiency under water-nitrogen coupling (W-N) regime is still unknown. Objective or research questionThe objectives from a 3-year field experiment were (1) to assess the impact of W-N regimes on potato yield and water and nitrogen use efficiency, (2) to elucidate the soil microflora structure under W-N regimes, and (3) to determine the relationship between soil chemical properties, microflora structure, and potato water and nitrogen use efficiency. MethodsA three-year two-factor split-zone potato field experiment was conducted in arid and semi-arid regions of the Inner Mongolian Plateau, with irrigation [(rainfed (W0), optimized (soil-based) irrigation (W1), conventional irrigation (W2)] as the primary treatment and N fertilizer [no N (N0), chemical N (N1), 25 % manure substitution (N2)] as the secondary treatment. ResultsPotato yield and water productivity followed N2 > N1 > N0, and partial nitrogen productivity and nitrogen agronomic efficiency followed N2 > N1 at the same irrigation level. Potato yield, nitrogen internal efficiency, partial nitrogen productivity and nitrogen agronomic efficiency first increased and then decreased, whereas water productivity gradually decreased with increasing irrigation levels under the same fertilization regime. Moreover, potato yield, soil total nitrogen, organic carbon, and microbial biomass carbon and nitrogen content peaked with the W1N2 regime. W-N regimes significantly influenced soil microbial community structure. Soil microbial α-diversity was less variable under W1 and N2 conditions. Soil bacterial network complexity and robustness were higher in W1 and W2 than in W0 regimes, whereas the opposite was true for fungi. The complexity and robustness of the soil bacterial and fungal network demonstrated for three fertilization regimes were higher in N1 and N2 than in N0 regimes. Neutral community model showed that soil microflora in W-N regime was mainly influenced by stochastic processes. PLSPM showed that organic substitution regime with optimized irrigation improves potato water and nitrogen use efficiency by regulating soil chemical properties rather than microflora structure. ConclusionsW1N2 regime synergizes well to improve potato water and N use efficiency and soil microflora stability, and organic substitution regime with optimized irrigation improves potato water and nitrogen use efficiency by regulating soil chemical properties. Implications or significanceOur findings initially clarified the regulatory mechanisms of potato water and nitrogen use efficiency in North China, offering theoretical guidance for further optimizing irrigation and fertilization management.

Lime Application Reduces Methane Emissions Induced by Pig Manure Substitution from a Double-Cropped Rice Field

Abstract: The substitution of chemical fertilizers with organic manure plays a critical role in sustainable crop production. Nevertheless, organic amendments promote the global warming potential (GWP) in rice paddies due to increased methane (CH4) emissions. Increasing evidence shows that lime application can reduce CH4 emissions from acidic paddy soils; however, it is still not clear whether liming can reduce the GWP in rice fields under organic manure substitution. A two-year field experiment was conducted to investigate the impacts of pig manure substitution and lime application on grain yield, CH4 and nitrous oxide (N2O) emissions in a subtropical double-cropped rice field in China. The experiment consisted of three treatments: CF (100% chemical nitrogen fertilizer), 1/2N + M (50% of the applied nitrogen substituted by pig manure, M represents manure), and 1/2N + M + L (lime amendment with 50% of the applied nitrogen substituted with pig manure, L represents lime). On average, 1/2N + M reduced rice yield by 5.65% compared to CF, while the lime application had no effect on rice yield. Mean cumulative CH4 emissions were 218.8% higher in 1/2N + M than in CF, whereas 1/2N + M + L reduced CH4 emissions by 36.6% compared to 1/2N + M. Neither pig manure substitution nor lime application affected N2O emissions. Consequently, 1/2N + M increased the GWP and greenhouse gas intensity (GHGI) by 214.6% and 228.3%, respectively, compared to CF. In contrast, 1/2N + M + L reduced the GWP and GHGI by 36.4% and 36.5% compared to 1/2N + M. Lime application can mitigate CH4 emissions and GWP induced by pig manure amendment in double-cropped rice fields.

High-rate pig manure substitution enhances comammox Nitrospira abundance and diversity in the Cinnamomum camphora coppice planting soils

Comammox Nitrospira represents a groundbreaking discovery in nitrogen cycle research, showcasing its remarking ability for complete ammonia oxidation, which challenges prior conceptions of nitrification. In this study, we examined the response of comammox Nitrospira gene abundance, diversity, and community structure to different rates of pig manure substitution (0 %, 25 %, 50 %, 75 %, and 100 %) in subtropical agroforestry soils. The abundance of ammonia-oxidizing microorganisms was assessed by qPCR, whereas the diversity and structure of comammox Nitrospira were determined by high-throughput sequencing. Our findings revealed that pig manure substitution led to an increase in soil pH, available phosphorus (AP), comammox Nitrospira abundance, and diversity within soils under Cinnamomum camphora coppice planting. Soil pH and AP were the primary factors influencing the diversity and community structure of comammox Nitrospira. Moreover, pig manure substitution significantly influenced the composition of comammox Nitrospira, notably by increasing the relative abundance of clade A.2.1 while reducing that of clade A.2.2. However, pig manure substitution did not exert a significant impact on net nitrification rates, suggesting bacterial relative abundances were more sensitive to manure substitution compared to the underlying biogeochemical processes. Overall, our results offer new insights into the response of comammox Nitrospira to different rates of pig manure substitution in Cinnamomum camphora coppice planting soils, highlighting the pivotal role of soil AP and pH as the key determinants shaping comammox Nitrospira diversity and community structure.

Synergistic Effects of Soil-Based Irrigation and Manure Substitution for Partial Chemical Fertilizer on Potato Productivity and Profitability in Semiarid Northern China.

Soil-based irrigation and the partial substitution of chemical fertilizers with manure are promising practices to improve water and nitrogen (N) use efficiency. We hypothesize that their combination would simultaneously benefit potato production, tuber quality and profitability. A two-year experiment was conducted in semiarid northern China to investigate the combined effects of three water treatments [rainfed (W0), soil-based irrigation (W1), conventional irrigation (W2)] and three N treatments [no N (N0), chemical N (N1), 25% manure substitution (N2)] on these indicators, and to perform a comprehensive evaluation and correlation analysis. The results showed that water and N treatments separately affected all indicators except vitamin C content. Compared to W2, W1 significantly increased water productivity by 12% and irrigation water use efficiency (IWUE) by 30% due to 10% lower evapotranspiration and 21% lower water use. However, W1 and W2 negatively affected crude protein content. Conversely, this was compensated by the combination with N1 and N2. There were slight differences between N1 and N2 for all indicators on average across water treatments, while under W1, N2 significantly increased leaf area index (LAI) and N recovery efficiency (REN) by 18% and 29.4%, respectively, over N1. Also, comprehensive evaluations showed that W1N2 performed best, with the highest tuber yield, profit and acceptable quality. This can be explained by the increase in LAI, IWUE and REN due to the positive correlations with tuber yield and net return. Consequently, soil-based irrigation combined with 25% manure substitution had complementary effects on tuber quality and synergistic effects on potato productivity and profitability.

The effect on the carbon footprint of the rice-wheat system of substituting chemical fertilizers by pig manure: The results of a field experiment

Livestock manure is widely recycled to enhance intensive agricultural production. Nevertheless, the environmental and agronomic benefits of liquid manure, such as biogas slurry, have rarely been comprehensively evaluated. To boost food production while maintaining environmental sustainability, a field experiment was performed to assess the effects of solid and liquid manure substitution for chemical fertilizer on direct greenhouse gas (GHG) emissions, soil organic carbon (SOC), grain yield, and carbon footprints (CF) in a rice-wheat system. The treatments involved only chemical fertilizer (NPK), 50 % NPK + 50 % pig manure (50 % PM), 100 % pig manure (100%PM), 50 % NPK + 50 % biogas slurry from PM (50 % PS), and 100 % biogas slurry from PM (100 % PS) in the circumstances of equal nitrogen fertilization. The results showed that rice CH4 emissions dominated the direct GHG emissions, and followed the order of 100%PM > 50%PM > 50%PS = NPK = 100%PS on average of three years. The 100%PM had the highest area-scaled CF with 11.84 Mg CO2-eq ha−1 due to high CH4 emissions and carbon emissions from pig manure production and compost indirectly without considering the changes in SOC stock. Meanwhile, 100%PM significantly increased SOC stock at 0–30 cm depth by 49.1 %, 11.8 %, 44.8 %, and 56.5 % compared with NPK, 50%PM, 50%PS, and 100%PS, respectively (P < 0.05). Notably, 100 % PM had the lowest area-scaled CF with 0.99 Mg CO2-eq ha−1 when considering the changes in SOC stock, followed by 50%PM. The 50%PM significantly increased the annual grain yield of rice and wheat from 2010 to 2018, with an average of 4.9 %, 4.5 %, and 5.7 % compared with NPK, 100%PM, and 100%PS, respectively (P < 0.05). Overall, although there was a trade-off between SOC sequestration and CH4 emissions under pig manure, pig manure substitution for chemical fertilizer significantly decreased yield-scaled CF, followed by biogas slurry substitution relative to NPK (P < 0.05). Thus, pig manure substitution for chemical fertilizer is recommended for environmental and yield benefits simultaneously considering the whole chain of production process in a rice-wheat system. In future, strategic fertilizer management based on PM and PS could potentially offer a sustainable solution to mitigate the trade-off and sustain the respective benefits of PM (i.e. SOC and grain yield) and PS (i.e. CH4 emissions).

Impact of biological manure substitution on grain yield, nitrogen recovery efficiency, and soil biochemical properties.

Fertilization plays a crucial role in ensuring global food security and ecological balance. This study investigated the impact of substituting innovative biological manure for chemical fertilization on rice (Oryza sativa L) productivity and soil biochemical properties based on a three-year experiment. Our results suggested rice yield and straw weight were increased under manure addition treatment. Specifically, 70% of total nitrogen (N) fertilizer substituted by biological manure derived from straw, animal waste and microbiome, led to a substantial 13.6% increase in rice yield and a remarkable 34.2% boost in straw weight. In comparison to the conventional local farmer practice of applying 165 kg N ha-1, adopting 70% of total N plus biological manure demonstrated superior outcomes, particularly in enhancing yield components and spike morphology. Fertilization treatments led to elevated levels of soil microbial biomass carbon and N. However, a nuanced comparison with local practices indicated that applying biological manure alongside urea resulted in a slight reduction in N content in vegetative and economic organs, along with decreases of 10.4%, 11.2%, and 6.1% in N recovery efficiency (NRE), respectively. Prudent N management through the judicious application of partial biological manure fertilizer in rice systems could be imperative for sustaining productivity and soil fertility in southern China.

Deciphering the crop-soil-enzyme C:N:P stoichiometry nexus: A 5-year study on manure-induced changes in soil phosphorus transformation and release risk

Carbon:nitrogen:phosphorus (C:N:P) stoichiometry plays a vital role in regulating P transformation in agriculture ecosystems. However, the impact of balanced C:N:P stoichiometry in paddy soil, particularly regarding relative soil P transformation, remains unknown. This study explores the response of C:N:P stoichiometry to manure substitution and its regulatory role in soil P transformation, along with the associated release risk to the environment. Based on a 5-year field study, our findings reveal that replacing 30 % of chemical P fertilizer with pig manure (equal total NPK amounts with chemical P fertilizer treatment, named CFM) increased soil total C without altering soil total P, resulting in an elevated soil C:P ratio, despite the homeostasis of crop stoichiometry. This increase promoted microbial diversity and the accumulation of organic P in the soil. The Proteobacteria and Actinobacteria produced lower C:PEEA metabolism together, and enhanced in vivo turnover of P. Additionally, by integrating high-resolution dialysis (HR-Peeper), diffusive gradients in thin films (DGT), DGT-induced fluxes in the soil (DIFS), and sediment P release risk index (SPRRI) models, we observed that, in addition to organic P, CFM simultaneously increased soil Al-P, thereby weakening the diffusion and resupply capacity of P from soil solids to the solution. Consequently, this decrease in P release risk to the environment was demonstrated. Overall, this study establishes a connection between crop-soil-enzyme C:N:P stoichiometry, soil microorganisms, and soil P biogeochemical processes. The study further evaluates the P release risk to the environment, providing a novel perspective on both the direct and indirect effects of manure substitution on soil P cycling.

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.

Effect of Mild Organic Substitution on Soil Quality and Microbial Community

Mild organic substitution is advantageous for sustainable agricultural development. In order to determine the proper fertilization strategy, it is essential to investigate the impact of substituting chemical fertilizers with varying levels of organic manure on soil nutrients, microbial communities, and crop productivity. Four treatments were implemented: no fertilizer, sole chemical fertilizer, 20% organic manure substitution, and 40% organic manure substitution. Bacterial and fungal communities were characterized through high-throughput sequencing of the 16S rRNA gene V3–V4 region and the V4 region, respectively. The 20% and 40% organic manure substitutions increased soil organic matter (SOM) content, total nitrogen (TN) content, and reduced soil pH compared to the control (CK). The 20% organic manure substitution showed the most significant improvements in soil alkaline phosphatase, urease, and invertase activities. Soil nutrient enhancement increased bacterial alpha diversity, with a milder impact on fungal alpha diversity compared to bacteria. Different fertilization treatments elevated the relative abundance of bacterial Bacteroidetes (8.11%, 21.25%, and 1.88%), Actinomycetes (12.65%, 26.36%, and 15.33%), and fungal Ascomycota (16.19%, 10.44%, and 12.69%), known for degrading recalcitrant organic matter. The sole chemical fertilizer treatment increased the pathogenic Cheatotryiales. Shared species, primarily from bacterial Actinomycetes, Firmicutes, Proteobacteria, and fungal Ascomycota phyla, were found at 20% and 40% organic manure substitution levels. Specifically, the 20% organic manure substitution level promoted the relative abundance of beneficial plant growth-promoting taxa, Oxalobacteraceae and Massilia, and suppressed pathogens, with an increase in the relative abundance of the Purpureocillium genus and Mortierellomycota. These findings suggest that a 20% OF substitution can maintain crop yield, enhance soil nutrients and enzyme activities by fostering beneficial soil bacteria, inhibiting soil-borne pathogens, and refining microbial community structure.

Nitrogen substitution practice improves soil quality of red soil (Ultisols) in South China by affecting soil properties and microbial community composition

Substituting synthetic nitrogen (N) fertilizer with organic amendments is considered an effective practice to improve soil quality. However, information on the effects of N substitution practices on soil quality in the red soil area in South China is still limited. In this study, therefore, four kinds of organic materials, including maize straw, cow manure, biochar and biogas residue, were applied to sweet maize farmland for six consecutive cropping seasons to substitute 20% synthetic N fertilizer in the Pearl River Delta Plain, which is a typical red soil area in South China. We compared the effects of different N substitution practices with conventional fertilization (CK) on the soil physical, chemical and biological properties and the microbial community structure. A minimum dataset method was utilized to calculate the soil quality index (SQI) under different treatments. The results demonstrated that the N substitution practice improved the SQI by 55%−70% compared to the CK in the red soil of South China by improving the soil physicochemical properties and biological characteristics. Meanwhile, the N substitution practice showed positive effects on changing the microbial community structure. Cow manure substitution showed the best effect due to the increased relative abundance of beneficial phyla in the soil microbiota, such as Proteobacteria, Chloroflexi and Ascomycota, and the decreased relative abundance of Basidiomycota. Finally, the structural equation model illustrated that the N substitution practice greatly improved the SQI in red soil by improving the soil bulk density, pH, β-glucosidase activity, urease activity and microbial community composition. Collectively, all four N substitution practices significantly improved soil quality, and cow manure substitution was the most effective way to improve soil microbial community composition and soil quality. This study provides a research basis for improving soil quality in the red soil region in South China and valuable information for the development of clean agricultural production in typical subtropical areas in East Asia.

Optimizing the manure substitution rate based on phosphorus fertilizer to enhance soil phosphorus turnover and root uptake in pepper (Capsicum).

In contemporary agriculture, the substitution of manure for chemical fertilizer based on phosphorus (P) input in vegetable production has led to a significant reduction in P fertilizer application rates, while, the effect of manure substitution rates on soil P transformation and uptake by root remain unclear. This research conducts a pot experiment with varying manure substitution rates (0%, 10%, 20%, 30%, 40%, 50%, 75% and 100%) based on P nutrient content to elucidate the mechanisms through which manure substitution affects P uptake in pepper. The result showed that shoot and root biomass of pepper gradually increased as manure substitution rate from 10% to 40%, and then gradually decreased with further increases in the substitution rate. Soil alkaline phosphatase activity and arbuscular mycorrhizal (AM) colonization gradually increased with manure substitution rates improvement. Specifically, when the substitution rate reached 30%-40%, the alkaline phosphatase activity increased by 24.5%-33.8% compared to the fertilizer treatment. In contrast, phytase activity and the relative expression of phosphate transporter protein genes in the root system was declined after peaking at 30% manure substitution. Additionally, soil available P remained moderate under 30%-40% substitution rate, which was reduced by 8.6%-10.2% compared to that in chemical fertilizer treatment, while microbial biomass P was comparable. In the current study, soil labile P similar to or even higher than that in chemical fertilizer treatment when the substitution rate was ≤40%. Correlation heatmaps demonstrated a significant and positive relationship between soil available P and factors related to labile P and moderately labile P. This finding suggested that substituting 30%-40% of chemical P with manure can effectively enhance root length, AM colonization, soil enzyme activity, soil labile P, and consequently improve P uptake in pepper. These findings provide valuable insights for future organic agricultural practices that prioritize P supply, aiming to standardize organic P management in farmland and achieve high crop yields and maintain soil health.

Mitigation of N2O emissions in water-saving paddy fields: Evaluating organic fertilizer substitution and microbial mechanisms

Water-saving irrigation strategies can successfully alleviate methane emissions from rice fields, but significantly stimulate nitrous oxide (N2O) emissions because of variations in soil oxygen level and redox potential. However, the relationship linking soil N2O emissions to nitrogen functional genes during various fertilization treatments in water-saving paddy fields has rarely been investigated. Furthermore, the mitigation potential of organic fertilizer substitution on N2O emissions and the microbial mechanism in rice fields must be further elucidated. Our study examined how soil N2O emissions were affected by related functional microorganisms (ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), nirS, nirK and nosZ) to various fertilization treatments in a rice field in southeast China over two years. In this study, three fertilization regimes were applied to rice cultivation: a no nitrogen (N) (Control), an inorganic N (Ni), and an inorganic N with partial N substitution with organic manure (Ni+No). Over two rice-growing seasons, cumulative N2O emissions averaged 0.47, 4.62 and 4.08 kg ha−1 for the Control, Ni and Ni+No treatments, respectively. In comparison to the Ni treatment, the Ni+No fertilization regime considerably reduced soil N2O emissions by 11.6% while maintaining rice yield, with a lower N2O emission factor (EF) from fertilizer N of 0.95%. Nitrogen fertilization considerably raised the AOB, nirS, nirK and nosZ gene abundances, in comparison to the Control treatment. Moreover, the substitution of organic manure for inorganic N fertilizer significantly decreased AOB and nirS gene abundances and increased nosZ gene abundance. The AOB responded to N fertilization more sensitively than the AOA. Total N2O emissions significantly correlated positively with AOB and nirS gene abundances while having a negative correlation with nosZ gene abundance and the nosZ/nirS ratio across N-fertilized plots. In summary, we conclude that organic manure substitution for inorganic N fertilizer decreased soil N2O emissions primarily by changing the soil NO3−-N, pH and DOC levels, thus inhibiting the activities of ammonia oxidation in nitrification and nitrite reduction in denitrification, and strengthening N2O reduction in denitrification from water-saving rice paddies.

Optimization of fertilization scheme based on sustainable wheat productivity and minor nitrate residue in organic dry farming: An empirical study

The substitution of chemical nitrogen fertilizer with manure holds the potential for a synergistic rise in wheat grain yield and protein concentration, while minimizing residual nitrate in soil. We conducted a 6-year field fertilization experiment including two manure treatments (with or without) and five nitrogen applications rates (0, 60, 120, 180 and 240 kg ha−1). The study investigated the impact of single chemical nitrogen (CN) and manure substitution for nitrogen fertilizer (MN) on the grain yield (GY), grain protein concentration (GPC), plant nitrogen uptake (PNupt) and plant nitrogen requirement (PNR) of wheat, and the dynamic change of soil nitrate-N. The findings revealed that: (1) the MN demonstrated a greater advantage over CN, as evidenced by a 13.4–16.0 % increase in GY, a 2.6–3.8 % increase in GPC, a 7.2–15.7 % increase in PNupt and a 1.5–4.7 % reduction in PNR. (2) Soil nitrate accumulation (SNA) significantly increased when fertilizer rates ≥180 kg ha−1 and the peak annually shifted to deeper layer. The MN increased the SNA0–100 by 20.9–21.8 %, but significantly reduced SNA0–200 by 11.8–13.5 % compared with the CN. Topsoil nitrate content (SNC0–20) can be adopted as a substitute for SNA0–100 to make the fertilization schedule convenient. (3) Regression analysis revealed (taking the MN for example) that the optimum N rates for the maximum GY (5417 kg ha−1) and GPC (15.3 %) were 164 and 211 kg N ha−1, respectively. The nitrate-N safety threshold was 62 kg ha−1 at the fertilizer rate of 89 kg N ha−1. Based on this, nitrogen fertilizer input reduced by 44.8–57.2 % and SNA0–200 by 17.9–33.6 %, with achieving 91.8–95.0 % of maximum GY and 89.7–92.9 % of maximum GPC. Substituting manure for nitrogen fertilizer achieved the potential of maintaining the grain yield and protein concentration while the minimization in soil nitrate residue. This study offers a feasible way for fertilization recommendation and nitrate residue controlling in dry farming.

Manure substitution with appropriate N rate enhanced the soil quality, crop productivity and net ecosystem economic benefit: A sustainable rainfed wheat practice

Partial substitution of organic fertilizer is adopted to increase production and alleviate farmland greenhouse gas (GHG) emissions. However, there is a lack of integrated assessment of soil quality, crop productivity, and environmental benefits through organic fertilizer substitution. Therefore, an in-situ experiment was conducted with the single nitrogen (N) treatments (120, 180, 240 kg N ha−1, expressed with N120, N180, N240, respectively) and partial substitution with manure fertilizer (each N treatment decreased by 30 kg N ha−1 and plus 2 t ha−1 pig manure, expressed with NM120, NM180, NM240, respectively) for rainfed wheat production on the Loess Plateau. A comparison between N and NM treatments showed that manure substitution treatments: 1) increased soil quality index by 50.9 − 57.4%, grain yield by 9.0 − 42.9%, total N accumulation by 8.6 − 31.1% and nitrogen recovery efficiency by 10.7 − 76.9%; 2) decreased N2O emission by 10.6 − 15.3% and CH4 uptake by 2.9 − 3.6%, whereas increased CO2 emission by 5.1 − 6.7%; 3) reduced the carbon footprint by 1.7 − 2.3 time mainly by the soil organic carbon sequestration. The global warming potential (GWP), Greenhouse gas emission intensity (GHGI), grain yield and net ecosystem economic benefit (NEEB) increased as the fertilizer rates increasing. NM180 had higher yield (average 6022 kg ha−1) and lower GWP (16489 kg CO2-eq ha−1) than N180, which obtained the smaller GHGI (2.67 kg CO2-eq kg−1) and maximum NEEB (4150 RMB ha−1). Overall, manure partial substitution with appropriate N rate enhances soil quality, crop productivity and environment benefit, which is a sustainable rainfed wheat practice.

Full substitution of chemical fertilizer by organic manure decreases soil N2 O emissions driven by ammonia oxidizers and gross nitrogen transformations.

Replacing synthetic fertilizer by organic manure has been shown to reduce emissions of nitrous oxide (N2 O), but the specific roles of ammonia oxidizing microorganisms and gross nitrogen (N) transformation in regulating N2 O remain unclear. Here, we examined the effect of completely replacing chemical fertilizer with organic manure on N2 O emissions, ammonia oxidizers, gross N transformation rates using a 13-year field manipulation experiment. Our results showed that organic manure reduced cumulative N2 O emissions by 16.3%-210.3% compared to chemical fertilizer. The abundance of ammonia oxidizing bacteria (AOB) was significantly lower in organic manure compared with chemical fertilizer during three growth stages of maize. Organic manure also significantly decreased AOB alpha diversity and changed their community structure. However, organic manure substitution increased the abundance of ammonia oxidizing archaea and the alpha diversity of comammox Nitrospira compared to chemical fertilizer. Interestingly, organic manure decreased organic N mineralization by 23.2%-32.9%, and autotrophic nitrification rate by 10.5%-45.4%, when compared with chemical fertilizer. This study also found a positive correlation between AOB abundance, organic N mineralization and gross autotrophic nitrification rate with N2 O emission, and their contribution to N2 O emission was supported by random forest analysis. Our study highlights the key roles of ammonia oxidizers and N transformation rates in predicting cropland N2 O.

Effects of partial substitution of chemical fertilizer with organic manure on the activity of enzyme and soil bacterial communities in the mountain red soil.

The partial substitution of chemical fertilizer with organic manure takes on a critical significance to enhancing soil quality and boosting sustainable agricultural development. However, rare research has studied the effects of partial substitution of chemical fertilizer with organic manure on soil bacterial community diversity and enzyme activity in maize field in the mountain red soil region of Yunnan. In this study, four treatments were set up in which chemical fertilizer (the application rates of N, P2O5 and K2O were 240, 75 and 75 kg·ha-1, respectively) was substituted by 10% (M10), 20% (M20), 30% (M30) and 40% (M40) of organic manure with equal nitrogen, as well as two control treatments of single application of chemical fertilizer (M0) and no fertilization (CK). The maize (Zea mays L.) crop was sown as a test crop in May 2018. The effects of partial substitution of chemical fertilizer with organic manure on soil physicochemical properties, soil bacterial community diversity and enzyme activity were studied. The activities of Cellulase (CBH), Invertase (INV) and β-glucosidase (BG) increased with the increase of organic manure substitution ratio. The activities of β-1,4-N-acetylglucosaminidase (NAG), Urease (URE), and leucine aminopeptidase (LAP) also had the same trend, but the highest activities were 159.92 mg·g-1·h-1, 66.82 mg·g-1·h-1 and 143.90 mg·g-1·h-1 at 30% substitution ratio. Compared with CK and M0 treatments, Shannon index increased notably by 82.91%-116.74% and 92.42%-128.01%, respectively, at the organic manure substitution ratio ranging from 10% to 40%. Chao1 and ACE index increased significantly at the organic manure substitution ratio ranging from 10% to 30%. Proteobacteria was the dominant phylum in all treatments, the relative abundance of Proteobacteria decreased as the organic manure substitution ratio increased. Redundancy analysis showed that microbial biomass C was the main factor affecting the bacterial community composition under partial replacement of chemical fertilizer treatment, while Actinobacteria was the main factor affecting the enzyme activity. In addition, the maize yield of M30 and M40 treatments was significantly higher than that of CK and M0-M20 treatments, and the yield of M30 treatment was the highest, reaching 7652.89 kg·ha-1. Therefore, the partial substitution of chemical fertilizer with organic manure can improve soil biological characteristics, while increasing bacterial community diversity and soil enzyme activity. Therefore, a thirty percent organic manure substitution was determined as the optimal substitution ratio for maize farmland in the mountain red soil area of Yunnan, China.