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Green manure application is a feasible agricultural practice to effectively improve soil fertility. However, our understanding of the effects and mechanisms of different green manure residue amounts on soil fertility improvement remains insufficient. Regarding a new type of Italian ryegrass (Lolium multiflorum L.)-rice (Oryza sativa L.) rotation (IRR) system in Southern China, the effects of six Italian ryegrass residue amounts (IRR0: 15,700 kg·ha−1, IRR1: 30,700 kg·ha−1, IRR2: 35,400 kg·ha−1, IRR3: 40,100 kg·ha−1, IRR4: 44,800 kg·ha−1, IRR5: 49,500 kg·ha−1) on the soil nutrient contents, soil enzyme activities, and bacterial communities were evaluated. Compared to the CK, appropriate amounts of Italian ryegrass residue application increased total nitrogen (36.45–37.38 %), soil organic carbon (15.34–26.55 %), microbial biomass carbon (14.07–33.93 %) and microbial biomass nitrogen (30.20–47.65 %) (P < 0.05). The activities of soil polyphenol oxidase, urease, β-glucosidase, peroxidase, cellulase, and total enzyme were also improved significantly in comparison with the CK (P < 0.05). Bacterial community structures in response to IRR were different from those in the CK. The application of Italian ryegrass residue significantly enhanced the relative abundance of beneficial taxa, including Acinetobacter , Pseudomonas , and Arenimonas (P < 0.05). The 30,700–35,400 kg·ha−1 Italian ryegrass residue exhibited the most practical amounts for enhancing soil fertility, soil enzyme activities, and altering soil microbial communities, suggesting that the improvement effects of green manure application on soil were dependent on the residue returning amounts. These findings suggest that the returning of Italian ryegrass residue is an effective land management measure to realize efficient and sustainable utilization of paddy fields. • Italian ryegrass residue improved the soil properties and bacteria communities in an amount-dependent manner. • The dominant bacteria communities were constructed according to their nutrient utilization capacity. • Relative abundances of the dominant bacteria were associated with soil biochemical properties. • Application of 30,700-35,400 kg·ha-1 Italian ryegrass residue was recommended. [ABSTRACT FROM AUTHOR]

The dominant ammonium bacteria established in different crop rotations are directly related to the conversion and utilization of nitrogen (N) in paddy soil. This study investigated the ammonia oxidation process in the rice rhizosphere of Italian ryegrass (Lolium multiflorum L.)-rice (IRR), celery (Apium graveolens)-rice (CLR) and winter fallow-rice (WFR) rotations in South China through the amoA functional gene analysis based on Miseq high-throughput sequencing platform and qPCR methods. The abundance of amoA gene in IRR was increased by 116.67 % (P < 0.05) and 42.76 % (P > 0.05) compared with CLR and WFR, respectively. Nitrosomonas became the dominant genus in the rhizosphere of IRR, with the highest relative abundance (59.30 %). The contents of soil organic matter, total N and nitrate nitrogen (NO 3 −-N) in the rice rhizosphere soil in IRR were significantly higher than other two treatments (P < 0.05) by 12.47–14.31 %, 16.88–25.00 %, and 97.48–159.60 %, respectively. Although lower microbial diversity was observed in IRR, the soil fluorescein diacetate hydrolysis enzyme activities and ammonia monooxygenase activities in the rice rhizosphere were higher in IRR than those in CLR and WFR (P < 0.05). Also, the soluble sugar and crude protein of milled rice were highest in IRR among the three rotation treatments (P < 0.05). The ammonia oxidation efficiency of ammonium-oxidizing bacteria was largely dependent on key taxa, such as Nitrosomonas (dominant genus in IRR), rather than the dynamics of AOB community structure. The key amoA- nitrifier taxa of the AOB community developed in IRR are capable of promoting rice production by improving soil N cycle efficiency and reducing the loss of N. Our findings illustrate the regulatory mechanism of IRR on the rice rhizosphere AOB community and reveal the important role of winter ryegrass in promoting soil nitrogen cycling during nutrient transformation of agricultural ecosystems in paddy fields. • Italian ryegrass-rice rotation (IRR) improved N contents and related enzyme activities of rice rhizosphere. • Nitrosomonas was the dominant AOB group in the rice rhizosphere after winter planting of ryegrass. • The ammonia oxidation efficiency of AOB community function mainly depended on Nitrosomonas. • IRR improved soluble sugar and crude protein of rice grains through higher soil nitrogen level. [ABSTRACT FROM AUTHOR]

Highlights • Soil moisture and yield were observed for 6-year grain, forage and bioenergy crops. • Potential bioethanol production and groundwater decline were calculated. • Sorghum rotation produced more bioethanol per unit of groundwater decline. • Net groundwater withdrawal for perennial switchgrass was the smallest. Abstract Managing the complex demands on available energy, food and water is a fundamental challenge for a world with increasingly tenuous resource pools. The North China Plain's groundwater crisis has become increasingly serious due to decades-long over-exploitation for irrigation to pursue high grain yield. This combined challenge motivated investigation of ways to mitigate the groundwater table decline while fostering the use of renewable bioenergy resources. To provide insights about tradeoffs among water, food and energy, we performed a six-year experiment from 2010 to 2015 in the North China Plain where groundwater use, biomass and biofuel production and water use efficiency were compared for four cropping systems. They are winter wheat-summer maize (WM, grains, 1-year cycle), ryegrass–sweet sorghum (RS, forage plus bioenergy crops, 1-year cycle), winter wheat–summer maize→ ryegrass–sweet sorghum (WMRS, forage, bioenergy plus grain crops, 2-year cycle), and perennial switchgrass (SG, bioenergy crop). Actual evapotranspiration (ET a) and recharge to groundwater were calculated and validated using observed soil moisture contents. Results showed ET a of the cropping systems were statistically similar ranging from 694 to 730 mm yr−1 with the exception of switchgrass which was significantly less at 504 mm yr-1. The water table was projected to decline by about 1.3 m yr-1 for all three multi-crop rotations and 0.4 m yr-1 for switchgrass. In terms of bioethanol production per unit land and per unit ET a , the ryegrass-sweet sorghum (RS) rotation performed best with 25.0 m3 ha-1 and 5.7 L m-3 outperforming the yearly winter wheat–summer maize (WM) rotation (11.7 m3 ha-1 and 3.3 L m-3) and switchgrass (11.4 m3 ha-1 and 2.6 L m-3). The multiple year rotation of winter wheat–summer maize→ ryegrass–sweet sorghum (WMRS) yielded 16.9 m3 bioethanol per hectare and 4.3 L m-3 bioethanol per m3 ET a. When optimizing bioethanol against net groundwater depletion, RS and switchgrass outperformed the two grain-based rotations with 15.5 L and 14.4 L of bioethanol per m3 of depleted groundwater, ahead of WMRS at 10.9 L m-3 and WM at 9.1 L m-3. These results are significant for setting governmental policies on sustainable use of groundwater by various crop mixes. [ABSTRACT FROM AUTHOR]

Cd is a heavy metal that contaminates soils. These kinds of heavy metals pose a serious threat to food security, ecosystems, and human health. To improve the phytoremediation efficiency of moderately Cd-contaminated cropland soils and achieve simultaneous production and remediation, intercropping ryegrass (Lolium perenne L.) with hollyhock (Althaea rosea) was investigated using pot experiments, and Bacillus thuringiensis (B. thuringiensis) inoculation was used as a booster to strengthen the absorption and accumulation of Cd in plants. The results showed that intercropping (Int treatment) decreased the Cd concentration in plants compared to hollyhock and ryegrass monocropping. However, the Cd accumulation in ryegrass and hollyhock was promoted by B. thuringiensis addition to intercropping (Int-B treatment), as the biomass of ryegrass and hollyhock was 2.33 and 1.13 times that of the Int treatment, respectively. Compared with the Int treatment, the total Cd concentration in soils of the Int-B treatment decreased by 8.1%, while diethylenetriaminepentaacetic acid solution extracted Cd (DTPA-Cd) increased by 18.2%, indicating that B. thuringiensis increases the available Cd concentration in soils to promote Cd adsorption by hollyhock enrichment plants. High-throughput sequencing results further revealed that the dominant microflora in the soils of the Int and Int-B treatments were consistent with the control, although their abundance and diversity decreased slightly. Overall, intercropping with B. thuringiensis addition effectively increased the hollyhock remediation efficiency in moderately Cd-contaminated soils, and the concentration of Cd in forage crops of ryegrass was lower than the limit value of "Hygienic standards for feeds' (GB 13078–2017) in China. [Display omitted] • Bacillus enhanced the remediation of Cd contaminated soil by plant intercropping. • Intercropping decreased Cd uptake by ryegrass. • Biomass and the Cd accumulation of ryegrass were promoted by Bacillus. [ABSTRACT FROM AUTHOR]

Intensive double cropping in the North China Plain has been challenged by serious environmental problems. Crop rotation is one of the important strategies for sustainable agriculture, which can reduce production risk and environmental impact. Yet, few studies have assessed enhanced crop rotation diversity on GHG emissions in the North China Plain. Carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2 O) emissions and yields were measured from four cropping systems: (1) wheat (Triticum aestivum L.)-maize (Zea mays L.) double cropping (WM); (2) peanut (Arachis hypogaea L.) and WM rotation (PWM); (3) ryegrass (Lolium perenne L.)-cotton (Gossypium hirsutum L.), peanut and WM rotation (RCPWM); and (4) continuous cotton (C), to determine if enhanced crop rotation diversity can reduce greenhouse gas (GHG) emissions and improve yields. The RCPWM, PWM and WM cropping system produced 11.9%, 15.7% and 32.4% higher net greenhouse gas emissions (GHGE), respectively, than the C cropping system each year by the soil-based method assessing the field productive process. From 2017 to 2018, in the same crop planting seasons, RCPWM had lower cumulative N 2 O and CO 2 emissions, and produced similar peanut, wheat, and maize yields when compared to PWM. In 2018, PWM had higher cumulative N 2 O than WM during the wheat period, and they had similar seasonal cumulative N 2 O emissions during the maize period. Meanwhile, PWM produced lower cumulative CO 2 emissions and higher wheat and maize yields. In 2019, RCPWM did not have significantly different seasonal cumulative N 2 O emissions and yield, but slightly higher soil CO 2 emissions than C during the cotton season. The GHG emission intensity (GHGI) of the same crops was lower in RCPWM than in PWM during the peanut, wheat, and maize period or slightly higher than in the C treatment during cotton period. The results demonstrate that RCPWM could reduce soil N 2 O emissions when the same crops in PWM were compared due to less soil CO 2 emissions that the previous cotton brought about. The RCPWM system did not show a lower soil organic carbon (SOC) sequestration rate than the PWM and C systems. Therefore, increasing cotton into the peanut and wheat-maize rotation system (RCPWM) for more diversified system can help reduce soil GHG emissions without sacrificing yields. • PWM, RCPWM and C cropping systems reduced indirect GWP compared to WM. • PWM did not decrease soil N 2 O emissions but improved wheat and maize yield. • The previous cotton lowered soil CO 2 and N 2 O emissions for next crop growing season. • Increasing crop species in rotation could reduce soil GHG emissions without sacrificing yields. [ABSTRACT FROM AUTHOR]

Abstract: Winter cover cropping is a common practice in paddy soils in southern China. This two year study (2008–2010) was undertaken to determine dry matter productivity and N uptake of two winter cover crops: ryegrass (Lolium multiflorum Lam.) and Chinese milkvetch (Astragalus sinicus L.) and their effects on soil properties as well as two subsequent rice (Oryza sativa L.) crops in Dongting Lake Plain in Hunan, China. Cover crops were broadcast sown in October, approximately 10d before the harvest of late rice. Ryegrass was first cut in March and finally harvested in April coincident with the plough of milkvetch. Two consecutive rice crops were grown following the cover crops without application of chemical N. Averaged over two years, ryegrass produced more aboveground dry matter and accumulated higher amounts of N than milkvetch (4.7Mgha−1 vs. 2.4Mgha−1, 128kgha−1 vs. 71kgha−1). Compared to CK (bare fallow without weed), both ryegrass (RG) and milkvetch (CMV) treated plots had lower soil bulk density at 0–15cm and 15–30cm depths. At the harvest of cover crops, CMV increased soil NH4 +-N concentration at 0–10cm, 10–20cm and 20–30cm depths. In contrast, RG decreased soil NH4 +-N and NO3 −-N concentrations in the three depths. Averaged over four sampling dates in the double rice seasons in 2010, soil microbial biomass C was slightly different between RG (257mgkg−1) and CMV (249mgkg−1), and these were significantly higher than CK (218mgkg−1). Soil microbial biomass N was highest for CMV (15.4mgkg−1), followed by RG (11.3mgkg−1) and CK (6.1mgkg−1). Grain yield and total N yield of early rice were 0.6Mgha−1 and 11kgha−1 higher for CMV, respectively, and 1.0Mgha−1 and 20kgha−1 lower for RG as compared with CK averaged over years. Grain yield and total N yield of late rice were not significantly affected by cover crops. [Copyright &y& Elsevier]

• A water-energy-food relative index for cropping systems at the field scale is proposed. • Synergy among water, energy and food in the North China Plain is evaluated. • Sustainable systems can balance crop production while reducing resource depletion. Extreme climate change, rapid population growth and economic development drive a growing demand for resources, which lead to energy, food, water and their intertwined nexus becoming increasingly important. Agricultural decisions considering the interconnections among water, energy, and food are critical. The consumption of large amounts groundwater and non-renewable energy by the predominant traditional wheat-maize cropping system has caused a serious water shortage in the North China Plain (NCP), which is a large food production region in China. This situation has strained the relationship between water/energy consumption and food production. It is important to seek synergy in the water-energy-food nexus. This paper proposed a relative index of water-energy-food (WEF RI) based on different values of resource consumption and use efficiency between treatment systems and control system to analyze the synergy between water utilization, energy consumption and food supply in different cropping systems at the field scale. The goal is to seek a sustainable cropping system to balance crop production while reducing energy consumption and water depletion. In this case, different systems including monocropped maize (Zea mays) (MM), intercropped maize and soybean (Glycine max) (MS), relay cropped of maize with pea (Pisum sativum) (MP) and potato (Solanum tuberosum) (MO), rotation of maize with spinach (Spinacia oleracea) (MI) and ryegrass (Secale cereale) (MR), and using traditional wheat-maize (Triticum aestivum) (MW) as a control. MM, MS, MP and MO were the best systems within a particular range of food supply reduction. The WEF RI of the MM/MS system was the highest (2.96/2.78). Compared to the MW system, the groundwater consumption of MM/MS was reduced by 73.84%/73.84%, and non-renewable energy inputs were reduced by 48.01%/48.30%; however, the food supply decreased by 48.05%/51.70%. The WEF RI of the MP system was 1.98. In comparison with the MW system, the groundwater consumption of the MP system was reduced by 28.46%, and the non-renewable energy inputs were reduced by 42.68%. However, the food supply decreased by 37.13%. The WEF RI of MO system was 1.92. Compared to the MW system, the groundwater consumption of MO was reduced by 11.47%, non-renewable energy inputs were reduced by 32.14%, and the food supply only decreased by 26.27%. In conclusion, we theoretically proposed the following references for cropping systems in the NCP: MM and MS are implemented when the areas has extreme water shortages, MO is implemented when a less than 30% reduction in the food supply capacity is acceptable, and MP is recommended if a 30%–40% reduction in the food supply is acceptable. [ABSTRACT FROM AUTHOR]

• Soil improvements by roots are different for planted and natural vegetation. • Distributions of root systems reached a steady state after 12 years restoration. • Root length density was the best root predictor for rill detachability and erodibility. • Rill erodibility of rooted-soils decreases exponentially as root length density increases. The objectives of this study were to evaluate different root parameters for estimating rill detachment, and to compare and quantify the effectiveness of planted and natural vegetation on soil physical characteristics and in reducing rill detachment and erodibility. Laboratory-concentrated-flow flume tests were performed under a flow discharge of 3 L min−1 and a slope of 15° with intact soil samples. A silt loam soil (Calcic Cambisol , in Loess Plateau in China) was sampled in 2015 from laboratory with planted ryegrass (Lolium perenne L.) and in 2014 from natural vegetation fields under 12 to 36-a restoration. The results indicated that root length density was the best parameter for estimating the effects of roots on rill detachment and erodibility for both planted ryegrass and natural vegetation, with exponential reduction equations. The exponents were more negative for natural vegetation (−0.411) than for planted species (−0.217) because of the existence of more complex root networks under more diverse natural vegetation. Rill erodibility of soil samples with roots decreased exponentially from the baseline erodibility of the root-free soil as RLD increased. Root systems of the restored natural vegetation ameliorated soil characteristics (bulk density, aggregate stability and organic matter content) more profoundly than those of the laboratory tests due to stronger bonding and binding effects, resulting in a lower absolute soil detachment rate for a given root density. There existed a vertical decay distribution pattern of root densities with soil depth for natural vegetation and planted ryegrass, and this distribution of root systems reached a steady state after 12 years natural vegetation restoration. More vegetation types under more different hydraulic conditions should be evaluated in future studies to provide better scientific bases for modelling their impacts on rill detachment and erodibility. [ABSTRACT FROM AUTHOR]