Green manure removal with reduced nitrogen improves saline-alkali soil organic carbon storage in a wheat-green manure cropping system

The incorporation of green manure into cropping systems is a potential strategy for sequestering soil carbon (C), especially in saline-alkali soil. Yet, there are still unknown about the substitution impacts of green manure on nitrogen (N) fertilizer in wheat-green manure multiple cropping system. Herein, a five-year field experiment was performed to determine the impact of three levels of N fertilizer inputs [i.e., N fertilizer reduced by 0 % (100N), 10 % (90 N), and 20 % (80 N)] with aboveground biomass of green manure removal (0GM) and return (100GM) on soil organic carbon (SOC) storage and its primary determinants. The results demonstrated that no significant interaction on SOC storage was detected between green manure and N fertilizer management. 80 N enhanced SOC storage in bulk soil by 7.4 and 13.2 % in 0-20 cm soil depth relative to 100 N and 90 N (p < 0.05). Regardless of N fertilizer levels, compared with 100GM, 0GM increased SOC storage in bulk soil by 14.2-34.6 % in 0-40 cm soil depth (p < 0.05). This was explained by an increase in soil macro-aggregates (>2 and 0.25-2 mm) proportion contributing to SOC physical protection. Meanwhile, the improvement of SOC storage under 0GM was due to the decrease of soil C- and N-acquisition enzyme activities, and microbial resource limitation. Alternatively, the variation partitioning analyses (VPA) results further suggested that C- and N-acquisition enzyme activities, as well as microbial resource limitation were the most important factors for SOC storage. The findings highlighted those biological factors played a dominant role in SOC accumulation compared to physical factors. The aboveground biomass of green manure removal with N fertilizer reduced by 20 % is a viable option to enhance SOC storage in a wheat-green manure multiple cropping system.

Green manuring alters reactive N losses and N pools in arable soils: A meta-regression study

Green manuring is a conservation agricultural practice that improves soil quality and crop yield. However, increasing the active nitrogen (N) and carbon (C) pools during green manure (GM) amendment may accelerate soil N transformation and stimulate N loss. Previous studies have reported the effects of cover crop incorporation on N2O emission; however, the driving mechanisms and other N losses remain unclear. Therefore, we conducted a comprehensive meta-analysis of 109 published articles (517 paired observations) to clarify the effects of GM amendment on soil reactive N (Nr) losses (N2O emissions, NH3 volatilization, and N leaching and runoff), N pools, and N cycling functional gene abundance. The results showed that green manuring increased soil microbial biomass N (MBN) and NO3--N concentrations and stimulated N2O emission but significantly lowered N leaching and yield-scaled NH3 volatilization. Practices of green manuring made a dominant contribution to the variation in N2O emissions and NH3 volatilization after GM application. Furthermore, applying legume-based GM, using N derived from GM (GMN) as an additional input, and short-term GM amendment each stimulated N2O emissions. In contrast, adopting non-legume GM, using GMN to partially substitute mineral N, and applying GM to the soil surface or paddy field mitigated NH3 loss during GM amendment. Additionally, the variation in NH3 volatilization was positively related to soil pH and N application rate (NAR) but had a negative relationship with mean annual precipitation (MAP). This study highlighted the marked effects of green manuring on soil N retention and loss. Agricultural operations that adopt GM amendment should select suitable GM species and optimize mineral N inputs to minimize N loss.

Green manuring reduces cadmium accumulation in rice: Roles of iron plaque and dissolved organic matter

In southern China, winter green manure is widely used in rice cropping systems for improving grain yields and soil fertility. Cd pollution has recently been reported in some of these paddy fields. Research on the in-depth understanding of how green manuring affects Cd absorption in rice is limited. This study aimed to investigate the impacts of different green manures, including single plantation and mixed plantation on the absorption of Cd by rice and explore the underlying mechanisms. Pot experiments demonstrated that compared with winter fallow-rice, green manuring treatments considerably decreased rice Cd content, promoted the conversion of bioavailable Cd fraction into a more stable form, induced the formation of iron plaque, and increased the content of humic-like fraction (HF) in soil dissolved organic matter (DOM). Treatment with mixed plantation resulted in a greater decrease in rice Cd content and an increase in HF and iron plaque contents than single plantation. Hydroponic experiments confirmed that both iron plaque and green manure-derived DOM significantly reduced the Cd content in rice seedlings. In conclusion, green manure incorporation is an efficient measure for the safe utilization of Cd-contaminated soil, and mixed plantation of different green manures exerts stronger effects.

Adaptive evaluation for agricultural sustainability of different fertilizer management options for a green manure-maize rotation system: Impacts on crop yield, soil biochemical properties and organic carbon fractions

Green manure planting can reduce the intensity of soil use, while improving farmland productivity in double-cropping systems. However, only few studies have focused on the impacts of green manure application under different fertilization management options on succeeding crop yield and soil organic carbon (SOC) process. A three-year field experiment was conducted with a winter smooth vetch-summer maize cropping system to evaluate the effects of green manure with different chemical fertilizers on soil physiochemical properties, SOC fraction, enzyme activities and maize yield. Total eight treatments were compared including different combinations of green manure and chemical fertilizers (i.e., nitrogen and phosphorus fertilizers) in the smooth vetch phase and maize phase. The results showed that compared to the control, green manure incorporation increased the soil moisture, total nitrogen, total phosphorus, basal respiration, SOC and its labile fractions, and enzyme activities, especially for the treatments of green manure with fertilization. However, the soil pH and bulk density decreased due to green manure application. Maize yield increased 34 %-53 % after green manure application, and was found to be significantly and positively correlated with soil carbon process (P < 0.05). Moreover, SOC and its labile fractions, and total nitrogen were observed as the main drivers of the maize yield. Variation partition analysis demonstrated that soil biochemical properties and their interaction with green manure by fertilization caused variations in SOC fractions. Further, structural equation models indicated that both balanced fertilization practices had positive effects on maize yield and soil carbon process via changes in SOC fractions and C cycling-related enzyme activities, respectively. In addition, the amount balance of chemical fertilizer positively impacted the soil carbon process by regulating SOC fractions through enzyme activities. These findings provide important guidance for applying optimal fertilization management in the green manure phase to improve succeeding crop yield and soil quality as well as to mitigate the adverse impacts of chemical fertilizers. The study will be equally illuminating for other green manure-crop rotation systems.

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.

Tillage, green manuring and crop residue management impacts on crop productivity, potassium use efficiency and potassium fractions under rice-wheat system

The conventional crop production practices including intensive tillage and open field crop residue burning in world' largest rice-wheat system (RWS) are adversely affecting crop productivity besides deteriorating natural resources and ecosystems' sustainability. In order to improve system productivity, potassium (K) use efficiency and apparent K balance, adoption of conservation tillage in a RWS with residue management is considered highly effective. We therefore, studied the effect of wheat straw retention and green manure (GM) in rice (main plot treatment), and tillage and rice residue management in subsequent wheat (sub-plot treatments) on crop productivity, K use efficiency and its transformation amongst different fractions of variable solubility. These results revealed that rice straw retention along with GM significantly (p < 0.05) increased the rice yields by ∼5.3-6.7% and wheat yields by ∼10.2-16.9%, compared to the conventional tillage (CT) without GM. Green manuring during the intervening period (CTR_W0+GM) significantly increased the rice grain K uptake by ∼36.2% than in plots with no-GM (CTR_W0). However, it increased by ∼29.8% under CTR_W25+GM, compared with CTR_W25-GM treatment. As compared with CTR_W0, CTR_W0+GM significantly increased the reciprocal internal use efficiency of K of rice by 3.8 kg Mg^-1 grain yield (∼29.5%). However, CTR_W25+GM increased the RIUE_K of rice by 3.3 kg Mg^-1 grain yield (∼22.4%), compared with no-GM (CTR_W25). Although, apparent K balance was net negative for CTR_W25, ZTW_R100 treatments, yet there was decreased K mining of 56-262 kg K ha^-1 (∼11.9-61.2%) for CTR_W25 and ZTW_R100 over CTR_W0 and ZTW_R0. The increased crop yield, K uptake and K use efficiency were significantly related to K enrichment in water soluble K, exchangeable K, non-exchangeable-K, hydrochloric acid extractable-K, lattice-K and total K fractions by ∼1.3, 3.4, 18.6, 11.0 and 34.1%, respectively due to residue retention, compared with no residue. Therefore, conventional tillage with puddled transplanted rice (CTR) with wheat residue and green manure during intervening period (CTR_W25+GM), and zero tillage wheat with rice residue retention (ZTW_R100) were emerged as highly valuable technological options for mitigating soil degradation effects under intensive RWS for food grains in north-western India.

Cover crop response to increased concentrations of copper in vineyard soils: Implications for copper phytoextraction

The use of cover crops (CCs) in viticulture is threatened by the contamination of vineyard soils by copper (Cu). This study investigated the response of CCs to increased concentrations of Cu in soil as a way to assess their sensitivity to Cu and their Cu phytoextraction ability. Our first experiment used microplots to compare the effect of increasing soil Cu content from 90 to 204 mg kg^-1 on the growth, Cu accumulation level, and elemental profile of six CC species (Brassicaceae, Fabaceae and Poaceae) commonly sown in vineyard inter-row. The second experiment quantified the amount of Cu exported by a mixture of CCs in vineyards with contrasted soil characteristics. Experiment 1 showed that increasing the soil Cu content from 90 to 204 mg kg^-1 was detrimental to the growth of Brassicaceae and faba bean. The elemental composition of plant tissues was specific to each CC and almost no change in composition resulted from the increase in soil Cu content. Crimson clover was the most promising CC for Cu phytoextraction as it produced the most aboveground biomass, and, along with faba bean, accumulated the highest concentration of Cu in its shoots. Experiment 2 showed that the amount of Cu extracted by CCs depended on the availability of Cu in the topsoil and CC growth in the vineyard, and ranged from 25 to 166 g per hectare. Taken together, these results emphasize the fact that the use of CCs in vineyards may be jeopardised by the contamination of soils by Cu, and that the amount of Cu exported by CCs is not sufficiently high to offset the amount of Cu supplied by Cu-based fungicides. Recommendations are provided for maximizing the environmental benefits provided by CCs in Cu-contaminated vineyard soils.

Green manure increases peanut production by shaping the rhizosphere bacterial community and regulating soil metabolites under continuous peanut production systems

BACKGROUND

Green manure (GM) is a crop commonly grown during fallow periods, which has been applied in agriculture as a strategy to regulate nutrient cycling, improve organic matter, and enhance soil microbial biodiversity, but to date, few studies have examined the effects of GM treatments on rhizosphere soil bacterial community and soil metabolites from continuous cropping peanut field.

RESULTS

In this study, we found that the abundances of several functionally significant bacterial groups containing Actinobacteria, Acidobacteria, and genus Sphingomonas, which are associated with nitrogen cycling, were dramatically increased in GM-applied soils. Consistent with the bacterial community results, metabolomics analysis revealed a strong perturbation of nitrogen- or carbon-related metabolisms in GM-applied soils. The substantially up-regulated beneficial metabolites including sucrose, adenine, lysophosphatidylcholine (LPC), malic acid, and betaines in GM-applied soils may contribute to overcome continuous cropping obstacle. In contrast to peanut continuous cropping, planting winter wheat and oilseed rape in winter fallow period under continuous spring peanut production systems evidently improved the soil quality, concomitantly with raised peanut pod yield by 32.93% and 25.20%, in the 2020 season, respectively.

CONCLUSIONS

GMs application is an effective strategy to overcome continuous cropping obstacle under continuous peanut production systems by improving nutrient cycling, soil metabolites, and rhizobacterial properties.

Winter crop rotation intensification to increase rice yield, soil carbon, and microbial diversity

Crop rotation has widely contributed to increasing farmland biodiversity as well as to improving soil carbon pools and microbial diversity. However, there is a weak understanding of the suitability of winter crop rotation intensification in double rice fields, especially rotation with various winter crops. For this task, a long-term field experiment based on one from 2012 was conducted with five winter crop systems for double rice: winter fallow (T0), winter milk vetch (T1), winter rape (T2), winter garlic (T3), winter rotation intensification with potato, milk vetch, and rape (T4). Parameters such as crop yield, soil carbon, nitrogen, and soil microorganism were measured. It was found that compared to winter fallow, winter milk vetch, rape, garlic, and crop rotation intensification practices increased the late rice yield by 2.5%, 2.3%, 4.5%, and 3.7%, respectively; winter garlic and crop rotation intensification also increased the early rice yield by 4.6% and 3.5%, respectively. This is associated with the promotion of rice tillering. At the same time, for winter crop rotation, compared to winter fallow, the soil organic carbon increased by 21%. With the input of diversified crop residues, winter crops were effective in soil carbon sequestration, improving soil microbial structure, and increasing soil microbial diversity. The Shannon diversity index of winter crops ranged from 9.75 to 9.91, while winter fallow was 9.38. The Simpson's diversity index of winter crops ranged from 0.997 to 0.998, while winter fallow was 0.996. In conclusion, winter crop practices, especially winter crop rotation intensification, can enhance soil health and sustainability in double rice fields through its positive feedback on crop yield, soil carbon sequestration, and microorganisms.

Ability of aerated compost tea to increase the mobility and phytoextraction of copper in vineyard soil

Aerated compost tea (ACT) contains soluble humic substances (SHS) that are expected to alter the dynamics and ecotoxicity of Cu in soil. This study investigated the efficiency of ACT in enhancing the mobility and phytoextraction of Cu in vineyard soil. Crimson clover (Trifolium incarnatum L.) was grown on a vineyard soil at three concentrations of Cu (90, 261 and 432 mg kg^-1), and supplied (or not) with ACT, then sampled after 56 days to determine the amount of Cu phytoextracted. Soil was extracted with 0.01 M KCl and potentiometric analyses were performed to measure the impact of ACT on the speciation of Cu in the extraction solution. ACT was found to increase the mobility of Cu in the soil by a factor of 3-14 depending on the soil Cu content and on the soil extraction date. The increase in Cu mobility was associated with an increase in absorbance at 254 nm and with a decrease in the free ionic fraction of Cu in the KCl extract, suggesting that Cu was mainly mobilized by the SHS present in the compost tea, and through a ligand-controlled dissolution process. ACT increased Cu phytoextraction at Cu90 and Cu261 by on average 80% thanks to its positive impact on plant growth, and on Cu accumulation in plant shoots, whereas it reduced Cu phytoextraction at Cu432 due to its deleterious effect on plant growth at this soil Cu content. ACT is thus an efficient way to increase the phytoavailability of Cu in soil, but probably should not be used in vineyard soils that are highly contaminated by Cu. To obtain Cu phytoextraction yields in line with the needs of the wine sector, the use of ACT needs to be associated with the cultivation of a Cu-accumulating plant.

Altering microbial community for improving soil properties and agricultural sustainability during a 10-year maize-green manure intercropping in Northwest China

Maize is a crop that is cultivated worldwide. The Hexi Oasis is one of the most important areas for high-yield maize seed production in China. Green manure, a plant fertilizer, has great potential for increasing crop yield and agricultural sustainability. However, the role of microorganisms in soil health and the microbiological mechanism of green manure in improving soil fertility and crop production in the Hexi Oasis area remain unknown. The effects of maize-green manure intercropping on the soil microbial community structure and diversity and the mechanism of soil improvement were investigated in a 10-year field experiment. The study revealed that microbial phylotypes were grouped into four major ecological clusters. Module #2 is a soil core ecological cluster enriched with many plant growth-promoting rhizobacteria and arbuscular mycorrhizal fungi. The application of green manure led to significantly increased soil pH, nutrient contents, and enzyme activities, and significantly reduced the relative abundance of potential plant pathogens compared with monocropping, which should ensure high and stable maize yield under long-term continuous cropping. It also increased the economic benefits by 56.39% compared with monocropping, owing to the additional products produced by the green manure. These improvements were associated with changes in the microbial community structure and activity, consistent with the structural equation model results. Therefore, soil microorganisms are the key drivers of the potential benefits of maize-green manure on agricultural sustainability.

Combined effects of green manure and zinc oxide nanoparticles on cadmium uptake by wheat (Triticum aestivum L.)

Cadmium (Cd) toxicity in agricultural soils is serious concern these days which needs continuous attention. Little is known about the combined use of berseem and/or maize residues soil applied as a green manure alone or along with foliar dressing of zinc oxide nanoparticles (ZnONPs) on Cd accumulation in wheat (Triticum aestivum L.). A pot experiment under ambient conditions with wheat grown in Cd-contaminated soil was performed after soil applied different green manure amendments and foliar dressing of ZnONPs was done during plant growth and plants were harvested at full maturity. Compared with control, plant growth attributes and biomass of above ground parts substantially increased with applied amendments being maximum with combined use of ZnONPs + B75 (berseem residue, 75 mg/kg) followed by ZnONPs + M75 (maize residue, 75 mg/kg). All the treatments improved the leaf chlorophyll contents and improved the leaf antioxidant enzyme activities thereby reduced the leaf electrolyte leakage. The Cd accumulation in roots and aboveground parts of the wheat was reduced especially in ZnONPs + B75 followed by ZnONPs + M75. The higher rate of soil applied amendments along with NPs minimized the available Cd in soil extracts but soil post-harvest pH was not much affected by the applied amendments. In conclusion, incorporation of berseem and maize residues as a green manure applied in Cd-contaminated soil combined with foliar NPs may decrease Cd phytoavailability and its accumulation in wheat grains. However, substantial field studies are required under various environmental conditions before final recommendations at field levels.

Green manure incorporation accelerates enzyme activity, plant growth, and changes in the fungal community of soil

Green manure can sustain agricultural production, preserve biodiversity, and mitigate soil degradation caused by long-term application of chemical fertilizers. Moreover, the application of green manure can improve soil health through increased soil biological activities. Nevertheless, little attention has been paid to the effects of leguminous and non-leguminous plants on phosphorus- and carbon-related enzyme activities and fungal community composition in soil. In this study, a pot experiment was carried out to elucidate the effects of two green manures on plant growth promoting potential, phosphorus- and carbon-related enzyme activities, and soil fungal community composition. Two green manure treatments (Brassica juncea and hairy vetch), poultry compost and control (no amendment) were applied and soil samples were collected after incorporation of green manure and after plant harvest. The results revealed that plant growth with hairy vetch was significantly higher than that with B. juncea and poultry compost, and soil enzyme activities were markedly higher with hairy vetch than with B. juncea. Both green manure amendments altered the soil fungal community composition. It is possible that the incorporation of green manure into soil and their mineralization and decomposition were controlled by the carbon: nitrogen ratio of the manures and that these manures were easily degradable by soil fungi. In particular, the incorporation of leguminous (hairy vetch) green manure with a low carbon: nitrogen ratio resulted in better plant growth through fast mineralization. Our findings suggest that green manure incorporation is an effective practice and provides substantial benefits to the soil-plant system.

Mitigation of global warming potential and greenhouse gas intensity in arable soil with green manure as source of nitrogen

This study was conducted to determine the effect of different green manure treatments on net GWP and GHGI in upland soil. Barley (B), hairy vetch (HV), and a barley/hairy vetch mixture (BHV) were sown on an upland soil on November 4, 2017 and October 24, 2018. The aboveground biomass of these green manures was incorporated into soil on June 1, 2018 and May 8, 2019. In addition, a fallow treatment (F) was installed as the control. Maize was transplanted as the subsequent crop after incorporation of green manures. Green manuring significantly affected CO₂ and N₂O emission, but not CH₄. Average cumulative soil respiration across years with HV and BHV were 37.0 Mg CO₂ ha^-1 yr^-1 and 35.8 Mg CO₂ ha^-1 yr^-1, respectively and significantly higher than those with under F and B (32.7 Mg CO₂ ha^-1 yr^-1 and 33.0 Mg CO₂ ha^-1 yr^-1, respectively). Cumulative N₂O emissions across years with F and HV were 6.29 kg N₂O ha^-1 yr^-1 and 5.44 kg N₂O ha^-1 yr^-1, respectively and significantly higher than those with B and BHV (4.26 kg N₂O ha^-1 yr^-1 and 4.42 kg N₂O ha^-1 yr^-1, respectively). The net ecosystem carbon budget for HV (-0.5 Mg C ha^-1 yr^-1) was the greatest among the treatments (F; -1.61 Mg C ha^-1 yr^-1, B; -3.98 Mg C ha^-1 yr^-1, and BHV; -0.91 Mg C ha^-1 yr^-1) because of its high biomass yields and the yield of maize after incorporation of HV. There was no significant difference of GHGI among F, HV, and BHV. Incorporation of HV or BHV could reduce net CO₂ emissions per unit of maize grain production as well as F.

Sustained rice yields and decreased N runoff in a rice-wheat cropping system by replacing wheat with Chinese milk vetch and sharply reducing fertilizer use

Pollution from the paddy fields has posed a threat to surface water quality, and the reactive N in runoff has been recognized as the dominant contributor. In the rice-wheat systems of eastern China, replacing wheat (Triticum aestivum) with Chinese milk vetch (CMV) (Astragalus sinicus) is known to reduce total fertilizer N use and associated N losses during winter; however, the function of the rice-CMV system in controlling the N runoff loss was overlooked during the summer rice-growing season. Over 6 years, we monitored soil mineral N, plant N accumulation, rice grain yield, N agronomic efficiency (AE_N), and N runoff in rice-CMV fertilizer N rate-response experiments and made comparisons with the conventional N inputs in rice-wheat rotation. Aboveground CMV residues added 65-116 kg N ha^-1 yr^-1; therefore, by adjusting the fertilizer time, the rice in this system required 44-56% less N fertilizer to produce rice yields equivalent to the 270 kg N ha^-1 (district average, C270) used in the rice-wheat system. In all fertilizer N application treatments, 120 kg ha^-1 seemed to be the threshold that ensured the soil N supply, the N accumulation at rice critical stages, and consequently, the current level rice yield. The corresponding runoff N averaged 9.3 kg ha^-1 season^-1, which was 51.8% less than that in C270 (19.3 kg ha^-1 season^-1). Cumulative N runoff (total N and NH₄⁺-N) correlated strongly with fertilizer N input for any single year (sample size = 108, P < 0.01). Application of 30-120 kg fertilizer N ha^-1 gave an equivalent AE_N, which indicated that the integration of CMV and fertilizer N could increase the agronomic efficiency of N fertilizer applied to the rice. Rotating paddy rice with CMV instead of wheat, together with the suitable adjustment of N fertilizer, could sustain rice yield and gain the utmost environmental benefits from rice-based agroecosystems.

Organic farming practices change the soil bacteria community, improving soil quality and maize crop yields

Background

The importance of organic farming has increased through the years to promote food security allied with minimal harm to the ecosystem. Besides the environmental benefits, a recurring problem associated with organic management is the unsatisfactory yield. A possible solution may rely on the soil microbiome, which presents a crucial role in the soil system. Here, we aimed to evaluate the soil bacterial community structure and composition under organic and conventional farming, considering the tropical climate and tropical soil.

Methodology

Our organic management treatments were composed by composted poultry manure and green manure with Bokashi. Both organic treatments were based on low nitrogen inputs. We evaluated the soil bacterial community composition by high-throughput sequencing of 16S rRNA genes, soil fertility, and soil enzyme activity in two organic farming systems, one conventional and the last transitional from conventional to organic.

Results

We observed that both organic systems evaluated in this study, have higher yield than the conventional treatment, even in a year with drought conditions. These yield results are highly correlated with changes in soil chemical properties and enzymatic activity. The attributes pH, Ca, P, alkaline phosphatase, and β- glucosidase activity are positively correlated with organic systems, while K and Al are correlated with conventional treatment. Also, our results show in the organic systems the changes in the soil bacteria community, being phyla Acidobacteria, Firmicutes, Nitrospirae, and Rokubacteria the most abundant. These phyla were correlated with soil biochemical changes in the organic systems, helping to increase crop yields.

Conclusion

Different organic management systems, (the so-called natural and organic management systems, which use distinct organic sources), shift the soil bacterial community composition, implying changes in their functionalities. Also, our results contributed to the identification of target bacterial groups and changes in soil chemical properties and enzymatic activity in a trophic organic farming system, which may contribute to higher crop yields.

Effect of plastic film mulching on maize productivity and nitrogen use efficiency under organic farming in South Korea

Winter cover crop cultivation and its biomass recycling as green manure (GM) were accepted as an ideal nutrient management practice in temperate organic farming fields. Since its biomass growth was boosted with air temperature rising from late Spring to early Summer, this stage overlapped with cash crops' seeding or transplanting. Thus, organic farmers were suffering from low crop productivity, due to delayed mineralization of incorporated biomass. To accelerate the mineralization of biomass nutrients and control weeds, plastic film mulching (PM) was broadly utilized in organic farming fields of temperate-monsoon climate region. However, the effect of PM on increasing nutrient use efficiency was not properly quantified in GM amended soil. To determine the effect of PM on crop productivity and nutrient use efficiency in GM amended soils, PM and no-mulching treatments were installed under different levels of GM biomass amended soils (0, 25, 50 and 100% of harvested aboveground biomass). The biomass productivity of barley and hairy vetch mixture as cover crop and biomass nitrogen productivity were dramatically increased from the mid May to the early June. PM significantly improved soil temperature and moisture regimes during maize cropping seasons, and then increased inorganic N (NH₄⁺ and NO₃^-) contents in soils. These improved soil properties under PM highly increased maize productivity and nitrogen use efficiency (NUE). Comparing with no-mulching, as GM application level was increased, the effect of PM on increasing maize productivity became greater, but its effect on increasing NUE became smaller. In conclusion, PM could be very useful tool to improve productivity and NUE of cash crop maize in organic cropping fields, in which the harvesting time of GM biomass might be sustained to increase GM biomass productivity.

Paddy-upland rotation with Chinese milk vetch incorporation reduced the global warming potential and greenhouse gas emissions intensity of double rice cropping system

It is a common practice to maintain soil fertility based on the paddy-upland rotation with green manure in the subtropical region of China. However, rare studies are known about greenhouse gas (GHG) emissions from the paddy-upland rotation with green manure incorporation. Therefore, we conducted a field experiment of two years to compared with the effect of two kinds of green manure (CV: Chinese milk vetch and OR: Oilseed rape), and two kinds of cropping system (DR: double rice system and PR: paddy-upland rotation) on greenhouse gases emissions. We have found that the annual accumulation of CH₄ of Chinese milk vetch-rice-sweet potato || soybean was significantly reduced by 32.95%∼63.22% compared with other treatments, mainly because Chinese milk vetch reduced the abundance of methanogens by reducing soil C/N ratio. Meanwhile increasing soil permeability resulting from paddy-upland rotation also reduced soil CH₄ emission. However, The annual accumulation of N₂O of Chinese milk vetch-rice-sweet potato || soybean was increased by 17.39%∼870.11% compared with other treatments, mainly attributed to paddy-upland rotation decreased soil pH and nosZ abundance and increased nirK and nirS, thus enhancing N₂O emission, meanwhile the Chinese milk vetch incorporation and its interaction with the paddy-upland rotation has greatly enhanced the contents of NO₃^--N and abundance of ammonia-oxidizing archaea (AOA). The area-scaled global warming potential (GWP) and the biomass-scaled greenhouse gas emissions intensity (GHGI) of Chinese milk vetch-rice-sweet potato || soybean was reduced by 19.01%∼50.69% and 5.38%∼35.77% respectively. Thereby, the Chinese milk vetch-rice-sweet potato || soybean cropping system was suitable for agricultural sustainable development.

First Report of 16SrII-V Phytoplasma Associated with Green Manure Soybean (Glycine max L.) in Taiwan

QING PI DOU, a local variety of soybean (Glycine max (L.) Merrill) with small seed size, is primarily cultivated in the southern region of Taiwan. Due to the advantage of high germination rate, fast growth and high nitrogen fixation capacity, QING PI DOU has widely used as green manure in rotation with rice to increase soil fertility in Taiwan. In the summer of 2020, phytoplasma-induced disease symptoms were observed in QING PI DOU with 23% (18/78) disease incidence in Yunlin County, Taiwan. These plants exhibited severe disease symptoms such as little leaf, yellowing, phyllody, virescence, and witches' broom compared to healthy plants. Leaf samples of the symptomatic plants were subsequently collected and examined through transmission electron microscopy (TEM), PCR, and western blotting analyses. The ultrathin sections of the diseased QING PI DOU were double-stained with uranyl acetate and lead citrate. The typical phytoplasma-like pleomorphic bodies were observed in sieve elements of leaf veins by TEM. To investigate the association of phytoplasma with the diseased QING PI DOU, total DNA extracted by the Plant Genomic DNA Purification Kit (DP022, Genemark, Taiwan) was examined by nested PCR using the phytoplasma universal primer pair P1/P7 followed by R16F2n/R16R2 (Lee et al. 1993). The 1.2 kb PCR product specific for 16S ribosomal RNA (16S rRNA) gene was only amplified from symptomatic plants but not from healthy plants. BLAST analysis demonstrated that the sequence (accession no. MW393690) of amplified DNA fragment of 16S rRNA is identical to that of GenBank accession no. NZ_AMWZ01000008 (complement [31109 to 32640]) of peanut witches' broom (PnWB) phytoplasma, a 'Candidatus phytoplasma aurantifolia'-related strain (Firrao et al. 2004). Further analysis on the virtual RFLP pattern of MW393690 generated by iPhyClassifier confirmed that the phytoplasma identified in the diseased QING PI DOU can be classified into the 16SrII-V subgroup. Samples examined by nested PCR were further selected for total cell extracts preparation and characterized by western blotting using the polyclonal antibody raised against the immunodominant membrane protein (Imp) of PnWB phytoplasma (Chien et al. 2020). An expected signal of 19 kDa specific for Imp was only detected in symptomatic plants but not in healthy plants. Moreover, the PCR products encoding SAP11 and phyllogen, the virulence factors responsible for phytoplasma-induced witches' broom and phyllody symptoms (Namba 2019), were also amplified from symptomatic QING PI DOU by PCR using the primer pairs 5'-ATGGCTCCCGAAAAAAATGATAAAGG-3'/5'-TTTTTTAGAATCATCAGGCTTTTTAG-3' (0.28 kb) and 5'-ATGGATCCAAAACTTCCAGAAACT-3'/5'-GTTTTTTTCATCATTTAAATCAT-3' (0.27 kb), respectively. Further analysis by BLAST revealed that SAP11 and phyllogen identified in symptomatic QING PI DOU are identical with those of PnWB phytoplasma. To the best of our knowledge, this report is the first to describe phytoplasma-associated soybean (Glycine max L.) witches' broom disease in green manure soybean in Taiwan.

Precomposting and green manure amendment for effective vermitransformation of hazardous coir industrial waste into enriched vermicompost

Vermitransformation of coir pith (CP) into enriched vermifertilizer has been achieved by amending a green-manure plant, Sesbania sesban (SS) for the first time, and cow dung (CD) in five different combinations: T1_(1:0:1), T2_(4:3:3), T3_(5:3:2), T4_(5:4:1) and T5_(1:1:0). The substrates were 28 days precomposted with Pleurotus sajor-caju followed by 50 days vermicomposting with Eisenia fetida and Eudrilus eugeniae. Results showed a significant reduction in cellulose, lignin, organic carbon, C/N ratio, C/P ratio and an increase in plant nutrients compared to control. The fertilization index and efficiency of nutrient recovery rate were higher in SS and CD amended CP vermicompost, with a maximum in T2_(4:3:3) for E. fetida and T3_(5:3:2) for E. eugeniae. The activity of dehydrogenase, urease and cellulase, and phytotoxicity assays further revealed vermicompost stability. The study concludes that T2_(4:3:3) and T3_(5:3:2) combinations respectively for E. fetida and E. eugeniae is suitable for vermitransformation of CP into enriched vermicompost.

Using of indigenous bulking agents (IBAs) in complementary stabilization and enhancing of dewatered sludge class B to class a on a full scale

BACKGROUND

Different bulking agents are used in the compost of dewatered sludge (DWS). The aim of this study has been using of indigenous bulking agents (IBA_s) in the enhancing of the DWS class of municipal wastewater from class B to class A and complementary stabilization of it for production of green manure in Sari city, Iran.

METHODS

Three IBAs including the Saccharum Wastes (SW), Citrus Purning Wastes (CPW) and Phragmites Australis (PA) from eight IBAs were selected to be compared with the sawdust (SD) that was as a control bulking agent. Five turned windrow piles were constructed on a full scale and on base of optimal C/N equal 25.All experiments were performed on the base of the standard methods on initial mix and final compost.

RESULTS

Among five windrow piles, P5 was been the best pile with a weighting ratio of DWS to IBAs (DWS: SW: CPW: PA) equal 1: 0.2: 0.24: 0.28. Pile P1 with weighting ratio DWS: SW equal 1: 0.6, Pile P3 with weighting ratio DWS: PA equal 1: 0.84, Pile P2 with weighting ratio DWS: CPW equal 1: 0.73 and Pile P4 with weighting ratio DWS: SD equal 1: 0.57 were placed in the next rounds. The results showed that the class of DWS enhanced to Class A for about 80 to 97 days and complementary stabilization of DWS by IBAs was done well and produced green manure in term of organic matter, potassium, germination index, PH, C/N and electrical conductivity had reached to the Grade 1 of Iran's manure 10716 standard and in term of phosphorus and moisture had reached to the Grade 2 of this standard. Also heavy metals were below the maximum permissible of standards.

CONCLUSION

Using of IBAs, had a higher efficiency than the control bulking agent (sawdust) in enhancing sludge class and its stabilization, so that using of them in combination (mix of IBA_s) had the highest efficiency and respectively, Saccharum Wastes (SW), Phragmites Australis (PA), Citrus pruning wastes (CPW) were placed in the next round, and sawdust was placed after them. By adding suitable IBA_S, with an optimal ratio in turned windrow method, the class of DWS of sari WWTP enhanced to Class A and complementary stabilization of DWS has been well done and the produced green manure has been reached to agricultural standards and can be safely used in agriculture.

Green manuring effects on crop morpho-physiological characters, rice yield and soil properties

A field experiment was carried out to evaluate the effect of green manure and nitrogen fertilizer on morpho-physiological traits, yield and post-harvest nutrient status of the soil during kharif season of 2017. The experiment was laid out with a randomized complete block design with twelve treatments, and was replicated thrice. The treatments were T1 [Control (no green manure + no fertilizer)], T2 (Sesbania aculeata + N0), T3 (Sesbania aculeata + N15), T4 (Sesbania aculeata + N30), T5 (Sesbania aculeata + N45), T6 (Sesbania aculeata + N60), T7 (Crotalaria juncea + N0), T8 (Crotalaria juncea + N15), T9 (Crotalaria juncea + N30), T10 (Crotalaria juncea + N45), T11 (Crotalaria juncea + N60), and T12 (N60). Incorporation of green manure with nitrogen fertilizer generated consistently positive responses in important morpho-physiological traits such as chlorophyll content (SPAD value), leaf area index (LAI), light interception percent (%LI), and net assimilation rate (NAR), which may result in higher grain yield compared to control, and N60 due to greater contribution of yield determining traits. Treatment comprising green manure with N60 produced significantly the higher grain yield even over the N60. The results of this research indicated that balanced nutrients supply increased leaf chlorophyll content, LAI, %LI, NAR, and finally led to higher dry matter production and yield of rice. Incorporation of green manure also had significantly increased the macro- and micronutrient content of post-harvest soil. These results suggest that continuous use of fertilizer might lead to a yield loses of rice, and that situation could be escaped by a combined application of green manure and judicial nitrogen fertilizer management.

Metagenomic assessment of methane production-oxidation and nitrogen metabolism of long term manured systems in lowland rice paddy

Biochemical pathways of methanogenesis and methanotrophy coupled with carbon (C)-nitrogen (N) metabolism were studied in long term (13years) manured systems in lowland rice paddy through metagenomics approach. Manured systems included in this study were, control (exclusion of application of any manure), farm yard manure (FYM, @5Mgha^-1yr^-1) and green manuring (GM with Sesbania aculeata). Metagenomic sequence data revealed the dominance of C decomposing bacterial communities' like Proteobacteria, Planctomycetes, Actinobacteria, Firmicutes, Acidobacteria, in manure amended soils as compared to control. Diversities for assimilatory and dissimilatory N-fixing microorganisms at phylum level were found higher under GM as compared to rest. Two genera responsible for methanogenesis, viz. Methanolobus and Methanotorris were absent in manured systems as compared to control. The acetoclastic and serine pathway was found as the predominant pathway for methanogenesis and methanotrophy, respectively, in tropical lowland rice paddy. Abundance reads of enzymes were in the range of 254-445 in the acetoclastic methanogenesis pathway. On the other hand, these were varied from 165 to 216 in serine pathway of methanotrophy. Lowland paddy soil exhibited higher functional and structural diversities in manured systems as compared to unamended control in respect to labile C pools and CH₄ production. Methane (CH₄) emission was 31% higher in FYM system than GM. However, nitrous oxide (N₂O) emission was found 25% higher in GM as compared to FYM. As a whole, bacterial diversities were higher under FYM system in tropical lowland rice paddy as compared to GM and unamended systems.

Potential role of compost and green manure amendment to mitigate soil GHGs emissions in Mediterranean drip irrigated maize production systems

Organic fertilization can preserve soil organic matter (SOM) and is foreseen as an effective strategy to reduce green house gases (GHGs) emissions in agriculture. However, its effectiveness needs to be clarified under specific climate, crop management and soil characteristics. A field experiment was carried out in a Mediterranean drip irrigated maize system to assess the pattern of soil CO₂ and N₂O fluxes in response to the replacement of a typical bare fallow-maize cycle under urea fertilization (130 kg N ha^-1 y^-1) (CONV) with: (i) bare fallow-maize cycles under two doses of compost (COM1 and COM2, 130 and 260 kg N ha^-1 y^-1, respectively) and (ii) a vetch-maize cycle, with vetch incorporation as green manure (130 kg N ha^-1 y^-1) (GMAN). Along the maize period (MP), reduced daily N₂O emissions were detected in organic treated soils compared to CONV, mainly in the first stages of the cultivation, thanks to the slow release of available nitrogen from the organic substrates. Cumulative N₂O fluxes (kg N₂O-N ha^-1) in MP scored to 0.24, 0.14, 0.12 and 0.085 for CONV, COM1, COM2 and GMAN, respectively, with significantly lower emissions in GMAN respect to CONV. CO₂ fluxes partially reflected the ranking observed for maize yields, with cumulated values (Mg CO₂-C ha^-1) of 2.2, 1.5, 2.1, 2.1 for CONV, COM1, COM2 and GMAN, respectively, and significantly lower in COM1 respect to the other treatments. During the fallow period (FP), compared to CONV (0.77 Mg CO₂-C ha^-1 and 0.25 kg N₂O-N ha^-1), enhanced GHG fluxes were detected in COM treatments (about 0.90 Mg CO₂-C ha^-1 and 0.37 kg N₂O-N ha^-1, as averaged values from COM1 and COM2), likely driven by the slow prolonged mineralization of the added organic matter. GMAN showed comparable CO₂ (0.82 Mg CO₂-C ha^-1) and N₂O emissions (0.30 kg N₂O-N ha^-1), in consequence of restrained post-harvest residual N coupled with the counteracting effect of vetch uptake. Respect to the total yearly GHG emissions in CONV (about 194 kg CO₂ eq ha^-1 y^-1), the overall results showed commensurate slightly higher GWP in COM treatments (+11% as averaged value from COM1 and COM2). The yield-scaled global warming potential (GWP) resulted 60% higher and nearly doubled for COM2 and COM1 respectively, according to the lower COM yields, markedly dampening at halved compost dose. GMAN appeared the best performing organic treatment, with lower GWP (-27%) and competitive yields respect to CONV. All treatments showed N₂O emission factors consistently lower compared with the default IPCC 1% value.

Sewage sludge as an initial fertility driver for rapid improvement of mudflat salt-soils

Sewage sludge is by-product in the process of centralized wastewater treatment. Land application of sewage sludge is one of the important disposal alternatives. Mudflats in the interaction zone between land and sea can be important alternative sources for arable lands if amended by large amount of organic fertilizers. Rich in organic matter and other nutrients, sewage sludge has been considered as the economic choice for an initial fertility driver. However, sewage sludge amendment has been greatly hampered due to availability of potential toxic metals. Using sewage sludge in compliance with the national standards for agricultural usage could avoid the accumulation of heavy metals. Nevertheless, it is not clear whether massive input of sewage sludge would increase heavy metals concentration in crops. The objective of this study was to investigate impact of sewage sludge amendment (SSA) as an initial fertility driver by one-time input, with the rates of 0, 30, 75, 150, and 300tha^-1, on biomass of green manures, soil chemical properties, and growth and heavy metals uptake of maize (Zea mays L.) grown in mudflat soil. Results showed that one-time sewage sludge amendment promoted an initial fertility for infertile mudflat soil, supported growth of ryegrass as the first season green manure. By tilled ryegrass, it modified the chemical properties of mudflat soil by increasing soil organic carbon, total and available N and P, and decreasing soil salinity and pH, which promoted subsequent growth of two green manures for sesbania and ryegrass. The sewage sludge as an initial fertility driver combined with planting and tilling green manures, increased dry matter of the aerial part and grain yield of maize grown in mudflat soil. Cd and Ni concentrations in grain of maize were positively correlated with sewage sludge amendment rates. Importantly, heavy metal concentrations in grain of maize at all SSA rates did not exceed the safety standard for food in China (GB 2762-2012). The study suggests that sewage sludge can be applied as an initial fertility driver for mudflat soil amendment, which provides an innovative solution for arable land resources and solid waste disposal.

The rotation of white lupin (Lupinus albus L.) with metal-accumulating plant crops: a strategy to increase the benefits of soil phytoremediation

Most of the plants employed to remove metals from contaminated soils are annuals and have a seed-to-seed life cycle of a few months, usually over spring and summer. Consequently, for most of the year, fields are not actively cleaned but are completely bare and subject to erosion by water and wind. The objective of this study was to evaluate the benefits of using Lupinus albus as a winter crop in a rotation sequence with a summer crop ideally selected for phytoextraction, such as industrial hemp. Lupin plants were grown in two alkaline soil plots (heavy metal-contaminated and uncontaminated) of approximately 400 m(2) each after the cultivation and harvest of industrial hemp. A smaller-scale parallel pot experiment was also performed to better understand the lupin behavior in increasing concentrations of Cd, Cu, Ni and Zn. White lupin grew well in alkaline conditions, covering the soil during the winter season. In few months plants were approximately 40-50 cm high in both control and contaminated plots. In fields where the bioavailable fraction of metals was low (less than 12%), plants showed a high tolerance to these contaminants. However, their growth was affected in some pot treatments in which the concentrations of assimilable Cu, Zn and Ni were higher, ranging from approximately 40-70% of the total concentrations. The lupin's ability to absorb heavy metals and translocate them to shoots was negligible with respect to the magnitude of contamination, suggesting that this plant is not suitable for extending the period of phytoextraction. However, it is entirely exploitable as green manure, avoiding the application of chemical amendments during phytoremediation. In addition, in polluted fields, white lupin cultivation increased the soil concentration of live bacteria and the bioavailable percentage of metals. On average live bacteria counts per gram of soil were 65×10(6)±18×10(6) and 99×10(6)±22*10(6) before and after cultivation, respectively. The percentages of bioavailable Cu, Pb, Ni, Zn and Cr, which were 5.7±0.7, 5.3±1.7, 1.2±0.1, 12±1.5 and 0.1±0.02%, respectively, before lupin growth, increased to 9.6±1.6, 7±2, 2±0.3, 14±1.5 and 0.1±0.02% after lupin harvest. On the whole, our results indicate that the winter cultivation of white lupin in sequence with a metal-accumulator summer crop can improve the recovery of soil quality during the phytoextraction period. It improves the safety of the area, limiting additional ecological and human health problems, and enhances soil health by avoiding the use of chemical amendments and by increasing the levels of viable microorganisms.

Do cover crops enhance N₂O, CO₂ or CH₄ emissions from soil in Mediterranean arable systems?

This study evaluates the effect of planting three cover crops (CCs) (barley, Hordeum vulgare L.; vetch, Vicia villosa L.; rape, Brassica napus L.) on the direct emission of N₂O, CO₂ and CH₄ in the intercrop period and the impact of incorporating these CCs on the emission of greenhouse gas (GHG) from the forthcoming irrigated maize (Zea mays L.) crop. Vetch and barley were the CCs with the highest N₂O and CO₂ losses (75 and 47% increase compared with the control, respectively) in the fallow period. In all cases, fluxes of N₂O were increased through N fertilization and the incorporation of barley and rape residues (40 and 17% increase, respectively). The combination of a high C:N ratio with the addition of an external source of mineral N increased the fluxes of N₂O compared with -Ba and -Rp. The direct emissions of N₂O were lower than expected for a fertilized crop (0.10% emission factor, EF) compared with other studies and the IPCC EF. These results are believed to be associated with a decreased NO₃(-) pool due to highly denitrifying conditions and increased drainage. The fluxes of CO₂ were in the range of other fertilized crops (i.e., 1118.71-1736.52 kg CO₂-Cha(-1)). The incorporation of CC residues enhanced soil respiration in the range of 21-28% for barley and rape although no significant differences between treatments were detected. Negative CH₄ fluxes were measured and displayed an overall sink effect for all incorporated CC (mean values of -0.12 and -0.10 kg CH₄-Cha(-1) for plots with and without incorporated CCs, respectively).