中国南方稻田绿肥种植和利用已有数千年历史，维持了区域土壤肥力和水稻生产。但目前绿肥对稻区土壤碳固持和碳足迹的定量化研究少有报道。本研究将长期定位试验与Meta分析结合，定量研究了绿肥提高中国南方稻田土壤碳固持和减少碳足迹的潜力。研究表明，与冬闲相比，冬种绿肥处理可在减少40%的氮肥下维持水稻产量，同时土壤表层碳固持速率为1.62 Mg CO₂-eq ha^-1 yr^-1。不同试验站的总碳足迹范围为7.51~13.66 Mg CO₂-eq ha^-1 yr^-1， 其中甲烷是最主要组分，占总量的60.7%-81.3%。绿肥-稻田模式降低了稻田生产系统31.4%的非直接碳足迹排放（主要为氮肥），提高了19.6%的直接碳足迹排放（主要为甲烷）。绿肥的甲烷排放因子（EF_gc）在低和高甲烷排放情景下分别为5.58%和21.31%。在低排放情景下，土壤碳库的增加可抵消增加的稻田甲烷排放；而在高排放情景下，土壤碳库的增加不足以抵消增加的稻田甲烷排放。当EF_gc小于9.20%时，绿肥可同时增加土壤碳库和减少系统碳足迹。EF_gc值的大小主要受绿肥翻压量和稻田水分管理影响，说明优化翻压量和田间水分管理是提高中国南方稻田绿肥田土壤碳固持和减少碳足迹的关键。

紫云英-稻秸联合利用作为一种高效的耕作模式，在我国南方稻区已有广泛应用，然而其对稻田土壤团聚体和土壤有机碳稳定性的影响尚缺乏研究。本文基于田间定位试验，研究了紫云英、稻秸及其联合利用对土壤团聚体分布和有机碳组分的影响。田间定位试验设6个处理，分别为冬闲稻秸不还田（Crtl）、冬闲稻秸半量还田（1/2RS）、冬闲稻秸全量还田（RS）、冬种紫云英稻秸不还田（GM）、冬种紫云英稻秸半量还田（GM1/2RS）、冬种紫云英稻秸全量还田（GMRS）。结果表明，GMRS相比RS处理，土壤细大团聚体（0.25-2 mm）含量和团聚体平均质量直径（MWD）分别增加18.9%和3.41%，粉粘粒（<0.053 mm）含量降低14.4%。GMRS相比GM和RS，提高了微团聚体（0.053-0.25 mm）和粉粘粒中的SOC含量。GMRS处理相比RS显著增加了各粒径团聚体和全土中的轻组有机碳（fLOC）含量及其在碳组分中的占比，降低了细大团聚体、微团聚体和全土中矿质结合态有机碳（MOC）的含量及其在碳组分中的占比。GMRS相比GM提高了颗粒态有机碳（iPOC）在有机碳组分中的占比。GMRS对细大团聚体中的iPOC有强烈的正影响，说明联合利用能够促进fLOC转移到iPOC。综上，紫云英-稻秸联合利用能够通过提高fLOC含量培育土壤有机碳库，并促进有机碳转化为iPOC以物理保护的形式固存而提高其稳定性。

绿肥-作物轮作作为一项可持续农艺措施，具有增强作物抗病、提升作物产量的效果。 然而，绿肥施用对作物相关微生物群落构建的调控机制尚不清楚。 本研究通过烟草与紫云英、黑麦草、肥田萝卜和冬闲（不施绿肥）四种轮作方式的田间试验，研究烟草不同区室（非根际土、根际土、根表及根内）细菌群落水平构建过程。 结果表明：与冬闲处理相比，绿肥各处理相邻区室构建的共现网络具有更多的边，表明其土壤-根界面存在显著的微生物相互作用。绿肥施用提高了土壤各区室间的扩散-生态位连续指数，促进了微生物的水平扩散。 对于不同的绿肥处理，中性群落模型对细菌出现频率的解释为24.6-27.6%，且每种处理至少有一个区室的归一化随机率高于50%边界，表明确定性和随机过程共同塑造了烟草微生物群落。综上所述，绿肥施用促进了不同区室间细菌群落的扩散，增强了相邻区室潜在的相互作用。本研究为了解绿肥-作物轮作条件下微生物群落的构建过程提供了经验依据。

研究西北地区（西宁、武威）玉米间作豆科绿肥系统中豆科绿肥的生物固氮量及其向玉米的氮素转移量，探讨间作条件下玉米利用豆科绿肥生物固氮的可能性。试验处理包括玉米单作、绿肥（箭筈豌豆和毛叶苕子）单作、玉米和绿肥间作。与绿肥单作相比，间作绿肥的生物固氮效率无显著变化（西宁毛叶苕子除外）；但西宁、武威两地箭筈豌豆生物固氮量分别从1.16和1.10 g/盆显著降低至0.77和0.55 g/盆，西宁毛叶苕子生物固氮量从1.02 g/盆显著降低至0.48 g/盆。西宁和武威间作系统中，箭筈豌豆氮素转移量分别为21.54和26.81 mg/盆，占玉米吸氮量的32.9和5.9%；毛叶苕子的氮素转移量分别为39.61和46.22 mg/盆，占玉米吸氮量的37.0和23.3%。路径分析结果表明，绿肥生物固氮量主要与土壤养分与地上部干物质量相关，氮素转移量主要与土壤δ¹⁵N相关。结果表明，玉米吸氮量的5.9～37.0%来自于豆科绿肥生物固氮，毛叶苕子的氮素转移量高于箭筈豌豆。综上所述，与豆科绿肥间作，是玉米有效利用豆科绿肥生物固氮的可能途径。

Received  27 October, 2017    Accepted  11 January, 2018

Dissimilatory Fe(III) reduction is an important process in the geochemical cycle of iron in anoxic environment.  As the main products of dissimilatory iron reduction, the Fe(II) species accumulation could indicate the reduction ability.  The effects of different green manures on Fe(III) reduction in paddy soil were explored based on a 31-year rice-rice-winter green manure cropping experiment.  Four treatments were involved, i.e., rice-rice-milk vetch (RRV), rice-rice-rape (RRP), rice-rice-ryegrass (RRG) and rice-rice-winter fallow (RRF).  Soils were sampled at flowering stage of milk vetch and rape (S1), before transplantation (S2), at tillering (S3), jointing (S4), and mature (S5) stages of the early rice, and after the harvest of the late rice (S6).  The contents of TFe_HCl (HCl-extractable total Fe), Fe(II)_HCl (HCl-extractable Fe(II) species) and Fe(III)_HCl (HCl-extractable Fe(III) species) were measured.  The correlations among those Fe species with selected soil environmental factors and the dynamic characteristics of Fe(II)_HCl accumulation were investigated.  The results showed that TFe_HCl in RRF was significantly higher than those in the green manure treatments at most of the sampling stages.  Fe(II)_HCl increased rapidly after the incorporation of green manures in all treatments and kept rising with the growth of early rice.  Fe(II)_HCl in RRG was quite different from those in other treatments, i.e., it reached the highest at the S2 stage, then increased slowly and became the lowest one at the S4 and S5 stages.  Fe(III)_HCl showed oppositely, and Fe(II)_HCl/Fe(III)_HCl performed similarly to Fe(II)_HCl.  The maximum accumulation potential of Fe(II)_HCl was significantly higher in RRF, while the highest maximum reaction rate of Fe(II)_HCl accumulation appeared in RRG.  Significant correlations were found between the indexes of Fe(II)_HCl accumulation and soil pH, oxidation-reduction potential (Eh) and total organic acids, respectively.  In together, we found that long-term application of green manures decreased the TFe_HCl in red paddy soils, but promoted the ability of Fe(III) reduction, especially the ryegrass; Fe(II)_HCl increased along with the growth of rice and was affected by soil conditions and environmental factors, especially the water and redox ability.

Green manure use in China has declined rapidly since the 1980s with the extensive use of chemical fertilizers. The deterioration of field environments and the demand for green agricultural products have resulted in more attention to green manure. Human intervention and policy-oriented behaviors likely have large impacts on promoting green manure planting. However, little information is available regarding on where, at what rates, and in which ways (i.e., intercropping green manure in orchards or rotating green manure in cropland) to develop green manure and what benefits could be gained by incorporating green manure in fields at the county scale. This paper presents the conversion of land use and its effects at small region extent (CLUE-S) model, which is specifically developed for the simulation of land use changes originally, to predict spatial distribution of green manure in cropland and orchards in 2020 in Pinggu District located in Beijing, China. Four types of land use for planting or not planting green manure were classified and the future land use dynamics (mainly croplands and orchards) were considered in the prediction. Two scenarios were used to predict the spatial distribution of green manure based on data from 2011: The promotion of green manure planting in orchards (scenario 1) and the promotion of simultaneous green manure planting in orchards and croplands (scenario 2). The predictions were generally accurate based on the receiver operating characteristic (ROC) and Kappa indices, which validated the effectiveness of the CLUE-S model in the prediction. In addition, the spatial distribution of the green manure was acquired, which indicated that green manure mainly located in the orchards of the middle and southern regions of Dahuashan, the western and southern regions of Wangxinzhuang, the middle region of Shandongzhuang, the eastern region of Pinggu and the middle region of Xiagezhuang under scenario 1. Green manure planting under scenario 2 occurred in orchards in the middle region of Wangxinzhuang, and croplands in most regions of Daxingzhuang, southern Pinggu, northern Xiagezhuang and most of Mafang. The spatially explicit results allowed for the assessment of the benefits of these changes based on different economic and ecological indicators. The economic and ecological gains of scenarios 1 and 2 were 175 691 900 and 143 000 300 CNY, respectively, which indicated that the first scenario was more beneficial for promoting the same area of green manure. These results can facilitate policies of promoting green manure and guide the extensive use of green manure in local agricultural production in suitable ways.

On the basis of a long-term (30 years) field experiment that involved four rotation systems, rice-rice-winter fallow (RRF), rice-rice-ryegrass (RRG), rice-rice-rape (RRP), and rice-rice-milk vetch (RRV), this study described the effects of green manure on the microbial communities in the red paddy soils using 454 pyrosequencing for the 16S rRNA gene. The Chao1 richness and non-parametric Shannon’s index increased in all soil samples that received green manure treatments. The communities’ structures with the green manure applications were significantly dissimilar from that under the winter fallow. Using Metastats tests, many genera in the RRG, RRP and RRV soils were significantly different from those in the RRF soil, including a number of genera that functioned in the nitrogen and sulfur cycles. Analyses of the genera with these functions revealed the shifts in microbial ecosystem functions after long-term green manuring. Changes in the microbial communities increased the ammonium supply and decreased the soil acidification in green-manure-amended soils. Together, these data suggested powerful effects of green manure on both the microbial communities and the biogeochemical cycle driven by the shifts in bacterial functional groups.

The development of more efficient management systems is crucial to achieving high grain yields with high nitrogen use efficiency (NUE). February Orchid-spring maize rotation system is a newly established planting system with the benefits of ground cover and potential wind erosion in northern China. A field experiment was conducted to evaluate the effects of integrated application of February Orchid as green manure with reduction of chemical fertilizers (INTEGRATED) on spring maize yield, N uptake, ammonium volatilization, and soil residual mineral N in northern China. Compared to farmers’ traditional fertilization (CON), integrated application of February Orchid as green manure with 30% reduction of nitrogen fertilizers (INTEGRATED) increased maize grain yield and biomass by 9.9 and 10.2%, respectively. The 0–100 cm soil residual Nmin at harvest was decreased by 58.5% and thus nitrogen use efficiency was increased significantly by 26.7%. The nitrogen balance calculation further demonstrated that the INTEGRATED approach performed better than CON with lower apparent nitrogen loss (decreased by 48.9%) which evidenced by the ammonium volatilization of top-dressing fertilizer was decreased by 31.1%, the Nmin movement to the deeper soil layers was reduced, and the apparent nitrogen leaching loss nearly equal to 0 under the INTEGRATED treatment. Therefore, in northern China, integrated application of green manure and chemical fertilizers is an efficient management approach for improving maize yields and NUE simultaneously.