Effect of farm management on topsoil organic carbon and aggregate stability in water: A case study from Southwest England,UK

There are few reliable data sets to inspire confidence in policymakers that soil organic carbon (SOC) can be measured on farms. We worked with farmers in the Tamar Valley region of southwest England to select sampling sites under similar conditions (soil type, aspect and slope) and management types. Topsoils (2–15 cm) were sampled in autumn 2015, and percentage soil organic matter (%SOM) was determined by loss on ignition and used to calculate %SOC. We also used the stability of macroaggregates in cold water (WSA) (‘soil slaking’) as a measure of ‘soil health’ and investigated its relationship with SOC in the clay‐rich soils. %SOM was significantly different between management types in the order woodland (11.1%) = permanent pasture (9.5%) > ley‐arable rotation (7.7%) = arable (7.3%). This related directly to SOC stocks that were larger in fields under permanent pasture and woodland compared with those under arable or ley‐arable rotation whether corrected for clay content (F = 8.500, p < .0001) or not (F = 8.516, p < .0001). WSA scores were strongly correlated with SOC content whether corrected for clay content (SOC_adj R² = .571, p < .0001) or not (SOC_unadj R² = 0.490, p = .002). Time since tillage controlled SOC stocks and WSA scores, accounting for 75.5% and 51.3% of the total variation, respectively. We conclude that (1) SOC can be reliably measured in farmed soils using accepted protocols and related to land management and (2) WSA scores can be rapidly measured in clay soils and related to SOC stocks and soil management.     

Do tillage and conversion of grassland to cropland always deplete soil organic carbon?

ABSTRACT

Conversion of grassland to cropland is widely reported to deplete soil organic carbon (SOC) largely due to tillage effects on the decomposition of SOC. However, most studies report on long-term changes in SOC following the conversion and little is known about the changes in the short term. Net ecosystem carbon budget (NECB) measures the difference between total C input (i.e., manure, above- and below-ground plant residues) and C loss through heterotrophic respiration (RH). However, most studies that report temporal SOC do not report other components of the NECB like RH, total C inputs and often do not include the cumulative annualized change of these components. This review evaluated the change in C input, RH, NECB and SOC after conversion of permanent/continuous grassland to cropland within 5 years after the conversion. We also reviewed and compared no-tillage and conventional tillage on SOC storage and accumulation. Total C input was higher in grassland than cropland largely due to high root biomass, as opposed to aboveground residue, and therefore grassland tended to have higher NECB. Despite higher NECB in grassland, the SOC stocks in cropland (cornfield) converted from grassland were greater than that in continuous grassland within first 2–3 years of conversion. The combination of manure C addition and tillage in cropland showed potential to maintain NECB and increase SOC. Within the continuous grassland C addition alone increased NECB but did not result in a corresponding increase in SOC. Residue retention and manure addition are recognized as good practices for increasing SOC, this study however, shows that combining them with occasional tillage, especially in managed grasslands, could increase the rate of SOC storage in soils.     

油-棉连作棉田油菜秸秆覆盖对棉田杂草发生及土壤杂草种子库的动态影响

在安徽省沿江棉区开展了油菜秸秆覆盖对棉田杂草发生、棉花生长及土壤杂草种子库影响的研究。结果表明,随着油菜秸秆覆盖量的增加,对棉田杂草的抑制效果增强。与未覆盖秸秆且不除草处理相比较,7000Kg/hm²秸秆覆盖量处理棉花单株铃数和子棉产量显著提高。7000Kg/hm²秸秆覆盖量处理在覆盖后30d、60d和120d逐步减少0-20cm土层杂草种子库密度,与全程除草剂处理较一致；随着覆盖量减少,对0-20cm土层杂草种子库密度降低幅度减小。全程除草剂处理降低0-5cm土层杂草种子库多样性,而油菜秸秆覆盖则可能增加0-5cm土层的杂草种子库多样性。3500Kg/hm²覆盖量+秸秆覆盖30d后喷施除草剂处理的抑草效果和增产效果与全程除草剂处理一致。因此,在安徽省沿江棉区油-棉连作棉田推荐使用3500Kg/hm²油菜秸秆覆盖量+秸秆覆盖30d后喷施除草剂。     

Novel soil quality indicators for the evaluation of agricultural management practices: a biological perspective

Developments in soil biology and in methods to characterize soil organic carbon can potentially deliver novel soil quality indicators that can help identify management practices able to sustain soil productivity and environmental resilience. This work aimed at synthesizing results regarding the suitability of a range of soil biological and biochemical properties as novel soil quality indicators for agricultural management. The soil properties, selected through a published literature review, comprised different labile organic carbon fractions [hydrophilic dissolved organic carbon, dissolved organic carbon, permanganate oxidizable carbon (POXC), hot water extractable carbon and particulate organic matter carbon], soil disease suppressiveness measured using a Pythium-Lepidium bioassay, nematode communities characterized by amplicon sequencing and qPCR, and microbial community level physiological profiling measured with MicroResp^TM. Prior studies tested the sensitivity of each of the novel indicators to tillage and organic matter addition in ten European long-term field experiments (LTEs) and assessed their relationships with pre-existing soil quality indicators of soil functioning. Here, the results of these previous studies are brought together and interpreted relative to each other and to the broader body of literature on soil quality assessment. Reduced tillage increased carbon availability, disease suppressiveness, nematode richness and diversity, the stability and maturity of the food web, and microbial activity and functional diversity. Organic matter addition played a weaker role in enhancing soil quality, possibly due to the range of composition of the organic matter inputs used in the LTEs. POXC was the indicator that discriminated best between soil management practices, followed by nematode indices based on functional characteristics. Structural equation modeling shows that POXC has a central role in nutrient retention/supply, carbon sequestration, biodiversity conservation, erosion control and disease regulation/suppression. The novel indicators proposed here have great potential to improve existing soil quality assessment schemes. Their feasibility of application is discussed and needs for future research are outlined.     

青饲料收获机切碎辊刀具的优化设计及试验

青饲料收获机切碎辊刀具的设计直接影响秸秆的切割质量。刀具与秸秆接触时的受力分析表明，切割力与秸秆的压应力有关，而压应力不仅与秸秆物理特性有关，也与刀刃的倾斜角有关。利用Ansys-Workbench有限元软件进行仿真分析，结果表明,当刀具材料为65Mn、刀具厚度为8 mm、刀尖倾斜角度为30°时，刀具的等效应力最小。以秸秆层厚度、刀具倾斜角、秸秆含水率为试验因素，以切割装置切割秸秆时的扭矩值为试验指标，通过正交试验及交互作用分析，确定了因素对指标影响的主次关系为：A2>C2>B2>A>BC>AC>C>B，当秸秆层厚度7.5 cm、刀具倾斜角度35°、秸秆含水率35%时，刀辊扭矩值最小。验证试验结果表明选取的较优参数组合真实可行。该研究为新型刀具及防堵刀辊的机理研究提供了理论和试验借鉴。     

耕作方式及秸秆还田对土壤性质、微生物碳源代谢及小麦产量的影响

以小麦品种济麦22为试验材料,采用裂区试验设计,耕作方式为主区,分别设常规翻耕(C)、深松(S)、旋耕(R)处理,副区为秸秆还田量,分别设秸秆全还田(P)和秸秆不还田(A)处理,采用Biolog Eco技术测定土壤微生物碳源代谢功能,并分析土壤基本理化性质和作物产量。结果显示:深松与秸秆还田均有利于土壤含水量和有机碳含量的提高,0～15 cm土层分别提高了9.78%和24.00%,15～30 cm土层分别提高了7.08%和15.81%;深松提高了15～30 cm土层的pH值6.67%,秸秆还田提高了0～15 cm土层的pH值4.32%。深松和秸秆还田均有利于代谢多样性(丰富度指数、香浓多样性指数)、碳源代谢强度的提高,0～15 cm土层分别提高了26.84%、3.84%和38.02%,15～30 cm土层分别提高了11.87%、 3.63%和14.74%。主成分分析表明常规翻耕秸秆不还田和旋耕耕作秸秆不还田碳源代谢功能相近,15～30 cm层次内常规翻耕秸秆全还田碳源代谢功能和深松耕作秸秆全还田处理相近。深松和秸秆还田平均提高了小麦产量5.82%,微生物碳源代谢功能与小麦产量具有极显著的相关性。     

小麦-玉米轮作体系不同旋耕和深耕管理对潮土微生物量碳氮与酶活性的影响

【目的】通过研究黄淮平原潮土区两年不同轮耕模式下土壤微生物量碳氮、酶活性的差异和变化特征,为该地区选择适宜的耕作制度提供理论依据。【方法】2016-2018年采用裂区设计进行田间小麦–玉米轮作系统下的轮耕试验。主处理为小麦季旋耕(RT)和深耕(DT),3个副处理为玉米季免耕(NT)、行间深松(SBR)、行内深松(SIR),共6个处理。2017、2018年玉米收获后,每10 cm一个层次,测定了0-50 cm土层土壤有机质、全氮、速效养分、微生物量碳(SMBC)、微生物量氮(SMBN)和脲酶、蔗糖酶、中性磷酸酶活性。【结果】各处理土壤有机质、全氮、速效养分、SMBC、SMBN及酶活性均随土层深度的增加而降低,40-50cm土层不受耕作方式的影响。小麦季深耕和玉米季深松对表层土壤有机质和全氮影响不明显,但显著提高了深层土壤有机质和全氮含量。小麦季旋耕显著增加了玉米季0-10 cm土层中速效养分含量,而小麦季深耕条件下的DT-SBR和DT-SIR处理则显著增加了20-40 cm土层中的速效养分含量。在0-20 cm土层,小麦季旋耕条件下的RT-NT、RT-SBR和RT-SIR处理的SMBC明显高于小麦季深耕条件下的DT-NT、DT-SBR和DT-SIR处理,但在20-40 cm土层,SMBC和SMBN均表现为小麦季深耕处理显著高于旋耕处理,且以DT-SIR处理SMBC (67.99 mg/kg)和SMBN (45.96 mg/kg)最高。小麦季深耕处理提高了深层(30-40 cm)土壤微生物量氮/全氮值,但降低了表层(0-20 cm)土壤中的微生物熵。玉米季深松处理(RT-SBR、RT-SIR、DT-SBR和DT-SIR)较免耕处理(RT-NT和DT-NT)均提高了土壤酶活性,其中,在0-20 cm土层,RT-SBR和RT-SIR处理土壤脲酶活、蔗糖酶和中性磷酸酶活性较高;而DT-SBR和DT-SIR处理则提高了深层(20-40 cm)土壤中这三种酶的活性。【结论】在本试验期内,小麦季旋耕–玉米季深松处理(RT-SBR和RT-SIR)能明显提高0-10 cm土壤速效养分含量、0-20 cm土壤微生物量碳含量,而小麦季深耕–玉米季深松处理(DT-SBR和DT-SIR)则提升了20-40 cm土层土壤有机质、全氮、速效养分、微生物量碳和氮含量;小麦季深耕处理提高了深层(30-40 cm)微生物量氮/全氮比,但降低了表层(0-20 cm)土壤微生物熵。     

耕作措施对坡耕地红壤地表径流氮磷流失的影响

云南山地面积约占全省土地总面积的94%,特殊的地形特征,极易引发坡面土壤侵蚀和养分流失,严重影响了农业可持续生产。采取有效的农艺措施来减少坡耕地土壤养分流失是十分有必要的。为此,通过4年定位试验对顺坡(2组处理)、横坡(2组处理)2种耕作方向的复合农艺措施处理进行研究。结果表明:云南坡地红壤的径流时间主要集中在6—9月,且产流雨量占年降雨量的65.62%～75.82%。产流雨量与年降雨量呈现一致趋势。径流量和产流雨量呈线性关系(R_(NVF)~2=0.597 7,R_(OVF)~2=0.415 1,R_(OHF)~2=0.378 2,R_(OHFR)~2=0.335 5),其相关性大小顺序为顺坡处理横坡处理,不施肥处理施肥处理,覆膜处理揭膜处理(P0.01)。大雨(25～49.9 mm)和暴雨(≥50 mm)造成了年度大部分径流和养分的流失。横坡垄作组处理产生地表径流(177.13±28.87)～(182.28±33.75) mm,径流中总氮流失量(7.66±2.51)～(7.85±1.92) kg/hm~2,总磷流失量为(0.91±0.26)～(1.09±0.27) kg/hm~2,与顺坡垄作OVF(常规处理)相比径流和养分极显著减少了49.57%～52.13%,33.16%～53.88%(P0.01)。不同耕作措施下,复合耕作模式(优化施肥+横坡垄作+旺长期揭膜)拦截径流和养分流失的效果最好。RDA分析结果发现,与降雨量相比较,径流量是影响氮磷养分变化的主要环境因子(P0.01)。径流量与氮养分(NH_4~+-N除外)流失量的相关性高于与磷的相关性,表明氮比磷更容易随径流流失。顺坡处理NVF和OVF与环境因子径流量和氮磷养分流失量TN、TDN、NO_3~--N、NH_4~+-N、TP、TDP呈正相关,横坡处理OHF和OHFR与其呈负相关。     

Short-term spatiotemporal variation of soil CO2 emission,temperature, moisture and aeration in sugarcane field reform areas under the influence of precipitation events

Soil CO₂ emission (FCO₂) in agricultural areas results from the interaction of different factors such as climate and soil conditions. Our objective was to investigate the spatiotemporal variation of FCO₂, temperature (T_soil), moisture (M_soil) and air-filled pore space (AFPS), as well as their interactions, during the sugarcane field reform. The study was conducted on a 90 × 90 m sampling grid with 100 points at 10 m spacings. Ten assessments of FCO₂, T_soil and M_soil were carried out at each point over a 28-day period. The greatest mean values of FCO₂ (0.74 g m⁻² hr⁻¹) and M_soil (31.7%) were obtained on Julian day 276, 2013, being associated with precipitation events at the study site. Also, the smallest values of AFPS (19.17%) and T_soil (20.90°C) were observed on the same day. The spatial variability of FCO₂, T_soil, M_soil and AFPS was best described by an adjusted spherical model, although an exponential model better fitted some results. The spatial pattern of all soil attributes showed little temporal persistency, indicating a high complexity for FCO₂ during precipitation. Correlation maps assisted in identifying regions where M_soil and AFPS better controlled the emission process and where T_soil was important. A major challenge for world agriculture is to increase the efficiency of conventional soil management practices. We highlight the importance of the spatial pattern of soil properties that directly influence the CO₂ emission dynamics. Future mitigation actions should involve less intense tillage and ensure homogeneous applications of soil inputs, thereby reducing production costs and the contribution of these activities to CO₂ emissions during the sugarcane field reform.     

柔性机械式大豆精量排种器设计与试验

针对免耕播种作业时沙土和碎秸等飘浮物被气吸式排种器吸入充种室内，导致排种工作部件损坏、排种质量降低等问题，设计了一种柔性清护种机械式大豆精量排种器。对排种器工作过程进行理论分析，确定了影响工作性能的主要结构与工作参数；通过单因素对比试验确定了对排种性能影响最小的护种毛刷材料；采用三因素五水平二次正交旋转中心组合试验方法，以作业速度、充种倾角、护种距离为试验因素，以合格指数、漏播指数、重播指数和破损指数为评价指标，应用Design-Expert 8.0.6.1软件对试验结果进行方差分析。结果表明：各因素对合格指数的影响显著性由大到小依次为作业速度、护种距离、充种倾角，各因素对漏播指数的影响显著性由大到小依次为护种距离、作业速度、充种倾角，各因素对重播指数的影响显著性由大到小依次为作业速度、充种倾角，护种距离影响不显著，各因素对破损指数的影响显著性由大到小依次为护种距离、作业速度、充种倾角；当作业速度为8~12km/h、充种倾角70°、护种距离为-1.5mm时，排种合格指数大于94%、漏播指数小于3%、重播指数小于3%、破损指数小于0.2%，满足免耕大豆高速精量播种作业要求。