退耕还草对土壤水分养分演变的影响

研究了高原沟壑区1984～1998年种植小麦和退耕种植苜蓿期间,土壤水分、土壤有机碳氮含量的演变。结果表明,种植小麦在不施肥的条件下从1984年到1998年,0～300cm土层水分和耕层有机碳氮含量都保持相对稳定,增施氮磷肥或在氮磷肥基础上配施有机肥土壤80～200cm土层水分有降低趋势,而耕层有机碳氮含量分别提高14％～60％和12％～55％。地表植被在1984年由作物改种苜蓿后到1998年,0～300cm土层土壤水分由1984年的20％逐渐降低至10％,耕层有机碳氮含量分别增加23％～77％和20％～68％。无论种植小麦还是退耕种植苜蓿耕层以下土层的有机碳氮含量从1984年到1998年变化不大。在雨养农业区,水分利用效率是制约土壤水分和养分呈现相反变化的重要因素。     

Impacts of monoculture cropland to alley cropping agroforestry conversion on soil N2O emissions

Monoculture croplands are a major source of global anthropogenic emissions of nitrous oxide (N₂O), a potent greenhouse gas that contributes to ozone depletion. Agroforestry has the potential to reduce N₂O emissions. Presently, there is no systematic comparison of soil N₂O emissions between cropland agroforestry and monoculture systems in Central Europe. We investigated the effects of converting the monoculture cropland system into the alley cropping agroforestry system on soil N₂O fluxes at three sites (each site has paired agroforestry and monoculture) in Germany, where agroforestry combined crop rows and poplar short-rotation coppice (SRC). We measured soil N₂O fluxes monthly over 2 years (March 2018–January 2020) using static vented chambers. Annual soil N₂O emissions from agroforestry ranged from 0.21 to 2.73 kg N ha⁻¹ year⁻¹, whereas monoculture N₂O emissions ranged from 0.34 to 3.00 kg N ha⁻¹ year⁻¹. During the rotation of corn crop, with high fertilization rates, agroforestry reduced soil N₂O emissions by 9% to 56% compared to monocultures. This was mainly caused by low soil N₂O emissions from the unfertilized agroforestry tree rows. Soil N₂O fluxes were predominantly controlled by soil mineral N in both agroforestry and monoculture systems. Our findings suggest that optimized fertilizer input will further enhance the potential of agroforestry for mitigating N₂O emissions.     

Uncertainty analysis of soil organic carbon stock change in Canadian cropland from 1991 to 2001

National estimates of changes in the amount of soil organic carbon (SOC) in cropland requires an assessment of uncertainty for accounting and reporting under the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol. Canada has data sets on SOC stocks in croplands, historical changes in SOC levels due to management practices, and historical changes in the area of land devoted to certain soil management practices. We conducted an analysis of uncertainty of the change in SOC levels due to management practices in Canada from 1991 to 2001 using Monte Carlo analysis and a simple model. Probability distribution functions were determined for each of the inputs of the model, enabling us to assess the uncertainty for the output. The storage rate of SOC in cropland soils of Canada for the 10‐year period ranged from 3.2 to 8.3 Mt C yr^?1 at 95% confidence, with a mean of 5.7 Mt C yr^?1. Approximately 67% (about 3.8 Mt C yr^?1) of the increase in SOC storage in Canada occurred in Saskatchewan where the cropland area under no‐till increased from 10% to 35%, and the area of summer‐fallow declined from 43% to 20% during the study period. The large uncertainty in the effect of no‐till on SOC stock changes in the Gray‐Brown Luvisols of Ontario contributed most to the variance in the model output. If trends in agricultural management continue for the next 10‐year census period, the estimated SOC storage would comprise between 7% and 19% of the gap required to achieve the 6% reduction in 1990 greenhouse gas emission levels for Canada under the Kyoto Protocol.     

农田向农林复合系统转变过程中土壤物理性质的变化

以渭北黄土区农林实践中被广泛采用的核桃-小麦间作复合模式为研究对象,以两物种的单作系统为对照,研究单作农田向农林复合系统转变对土壤物理性质的影响,为农林复合系统经营管理和模型的建立提供理论依据.结果表明: 核桃-小麦间作对土壤物理性质的改善作用主要发生在0～40 cm土层.核桃-小麦间作可以避免表层(0～20 cm)土壤容重升高,同时在20～40 cm土层对单作农田形成的犁底层也有显著的改善作用.核桃-小麦间作对各土层田间持水量均表现出持续的改善作用,除在20～40 cm土层略低于核桃单作外,其他从第5年开始均高于两单作系统.核桃-小麦间作对各土层土壤孔隙度均存在持续的改善作用,在0～20 和20～40 cm土层与两单作系统相比存在显著差异,同时也能提高毛管空隙度的比例.农田向农林复合系统转变过程中对土壤容重、田间持水量、土壤孔隙度均有持续的改善作用,且对浅层土壤的改善作用强于深层土壤.     

退耕植茶地土壤团聚体及其无机磷组分分布特征

为了揭示土壤团聚体及其无机磷组分对退耕植茶的响应特征,以雅安市名山区中峰乡退耕植茶地(2～3年、9～10年、16～17年)为研究对象,选取邻近耕地为对照,采用野外调查与室内分析相结合的方法开展退耕植茶地土壤团聚体及其无机磷组分分布特征的研究.结果表明: 耕地及退耕植茶地土壤团聚体均以粒径>2 mm团聚体为主.随着退耕植茶年限的延长,各退耕植茶地粒径>5 mm的团聚体含量逐渐增加,粒径<5 mm的团聚体含量却逐渐降低.退耕植茶初期,退耕植茶地土壤团聚体平均质量直径(MWD)和几何平均直径(GMD)值与对照差异不明显,退耕植茶9～10年和退耕植茶16～17年显著高于对照,且随着退耕植茶年限的延长逐渐增大.退耕植茶地与耕地相比,其有效性较高的Al-P、Fe-P含量增加,有效性较低的O-P含量降低,随着退耕植茶年限的延长,各粒径团聚体中有效性较低的O-P逐渐降低,有效性较高的Al-P、Fe-P逐渐增加.耕地及退耕植茶地中Al-P、Ca-P含量随粒径的减小而增加,在<0.25 mm粒径中的含量最高;Fe-P在<0.25 mm粒径团聚体中的含量最多,其次是2～5 mm和0.25～0.5 mm粒径团聚体;退耕植茶后,O-P逐渐向较小粒径中富集,在<2 mm粒径中含量较高.     

黄土高原地区不同草地退耕模式水分利用效率的比较

研究了半干旱黄土高原区不同退耕模式下植被恢复的比较,对3种不同人工豆科牧草多年生紫花苜蓿alfalfa(Medicago sativa)、多年生沙打旺erect milkvetch(Astragalus adsurgens)、2年生草木樨sweetclover(Melilotus officinalis))和一种自然撂荒(fallow)进行了实地种植比较。通过3a研究发现:紫花苜蓿是耗水最严重的牧草,水分利用效率仅高于撂荒;沙打旺具有最高的地上总生物量和水分利用效率。紫花苜蓿和沙打旺地块中杂草生物量逐年降低,物种数量最低且没有增加。2年生草木樨地物种数和地上生物量逐年增高,草木樨对暴雨的入渗贮存能力最大,显著高于自然撂荒。草木樨结束生活史后第1年地上总生物量(和撂荒一样全为杂草)是撂荒地的两倍,且略高于紫花苜蓿的地上总生物量,同时物种数量也和物种数目最多的撂荒地没有显著差异(p<0.05)。草木樨显著降低了10～40cm土壤剖面的容重,草木樨结束生活史后残留根系有助于深层土壤水分恢复,水分状况恢复良好且优于紫花苜蓿和沙打旺。可见短期的人工干扰下两年生草木樨的种植有利于促进自然植被的恢复,优于自然撂荒和其他牧草种植的方式,容易推广且实际可行。     

土壤纤毛虫群落对退耕还林生态恢复的响应——以侧柏林为例

为了了解土壤纤毛虫群落对退耕还林区生态恢复下土壤环境变化的响应及尝试利用土壤纤毛虫群落特征评价退耕还林生态恢复的效果,于2010年3月至9月采用"非淹没培养皿法"、活体观察法、蛋白银染色法和Foissner计数法对甘肃陇南武都退耕还林区5个不同恢复阶段的样点和1个荒草坡对照样点的土壤纤毛虫群落特征进行了研究,同时测定了p H值、温度、含水量及速效磷、有效钾、铵态氮、有机质和有机碳含量等土壤环境因子并分析了生态恢复条件下土壤纤毛虫群落特征与土壤环境因子的相关性。研究中共鉴定到71种纤毛虫,隶属于3纲、10目、22科、29属。研究发现,不同恢复年限的土样中土壤纤毛虫的物种分布存在明显差异,并随恢复时间的延长,样点间物种相似性减小,群落组成复杂化,物种数、种群密度和物种多样性指数总体均呈增长趋势。优势类群也发生了演替,由恢复初期的肾形目演替到后期的下毛目。相关性分析结果表明,在生态恢复条件下,土壤有机质和铵态氮含量是影响土壤纤毛虫群落结构稳定性的主要因素,不同纤毛虫类群对生态恢复的响应存在差异。冗余分析显示,土壤纤毛虫群落很好地响应了生态恢复过程中土壤环境条件的变化。     

Comparison of maize,permanent cup plant and a perennial grass mixture with regard to soil and water protection

Agricultural production of biogas maize (Zea mays L.) causes hazards to aquatic ecosystems through high levels of nitrogen (N) inputs. Newly introduced and already established perennial crops such as the cup plant (Silphium perfoliatum L.) and perennial grass mixtures offer the possibility of more environmentally friendly agricultural bioenergy production. The objectives of this field study were to quantify and compare soil mineral N, water infiltration, water runoff, soil erosion and N leaching under maize, permanent cup plant, and a perennial grass mixture. The study was conducted from October 2016 to March 2019 in Braunschweig, Germany. Plots with cup plant and grass mixture exhibited lower mineral N contents than maize, especially between 30 and 90 cm soil depth. Soil water infiltration was significantly different between the three crops. The grass mixture had the highest infiltration rates (6.2 mm/min averaged across 3 years), followed by cup plant (3.6 mm/min) and maize (0.9 mm/min). During wet periods, higher N leaching was found for maize (up to 42 kg N ha^?1 year^?1) than for cup plant (up to 5 kg N ha^?1 year^?1) or the grass mixture (up to 11 kg N ha^?1 year^?1). While runoff and erosion for cup plant and the grass mixture were negligible during the study period, considerable amounts of runoff water and eroded sediment of up to 1.5 Mg ha^?1 year^?1 were collected from the maize plots despite the near flat terrain of the experimental field. Overall, permanent cup plant proved suitable as a component for energy cropping systems to reduce the risk of N leaching and soil erosion, which is particularly important for the preventive flood protection in view of the more frequent occurrence of high intensity rainfall under climate change conditions.     

长期施肥下农田土壤-有机质-微生物的碳氮磷化学计量学特征

探讨外源养分的输入对土壤系统内碳、氮、磷化学计量特征的影响,对于深刻认识农田土壤有机碳(C)和养分循环及其相互作用过程具有重要意义。以26年的农田长期定位施肥试验为平台,分析长期不同施肥条件下土壤、有机态及微生物生物量碳、氮、磷含量及其化学计量学特征,并根据内稳性模型y=c x~(1/H)计算其化学计量内稳性指数H。结果表明:与长期撂荒处理(CK_0)相比,种植作物条件下26年化肥配施有机肥处理(MNPK和1.5MNPK)显著降低微生物生物量氮含量,但显著提高了微生物生物量磷的含量。相对于撂荒处理,即使长期配施化肥磷处理(NP、PK、NPK),其土壤有机磷降低显著。对于C∶N比而言,化肥配施有机物料处理(秸秆或有机肥)的土壤C∶N比、有机质C∶N及微生物生物量C∶N比均显著低于化肥处理(N、NP、PK和NPK)。对于C∶P比而言,相对于撂荒处理,26年施用磷肥(化肥磷或有机磷)显著降低了土壤C∶P比和微生物生物量C∶P比,而CK和偏施化肥处理(N、NP和PK)显著降低了土壤有机质C∶P比。对于土壤N∶P比而言,撂荒处理土壤N∶P比显著高于其他处理,而撂荒处理土壤有机质N∶P比显著高于CK和化肥处理,表明不施肥或化肥条件下作物种植加剧了土壤有机质中氮素的消耗。微生物生物量C∶N、C∶P、N∶P比的内稳性指数H分别为0.24、0.75、0.64,不具有内稳性特征。微生物生物量C∶N、C∶P、N∶P比分别与土壤C∶N、C∶P、N∶P比呈显著正相关关系,但与土壤有机质碳氮磷化学计量比之间无显著相关性。表明土壤碳、氮、磷元素的改变会直接导致微生物生物量碳、氮、磷化学计量比的改变,但微生物生物量碳氮磷化学计量比对土壤有机质碳氮磷化学计量比无显著影响,土壤有机质的碳氮磷计量比可能更多是受到作物和施肥等养分管理措施的影响。     

Evaluation of the ECOSSE model for simulating soil organic carbon under Miscanthus and short rotation coppice‐willow crops in Britain

In this paper, we focus on the impact on soil organic carbon (SOC) of two dedicated energy crops: perennial grass Miscanthus x Giganteus (Miscanthus) and short rotation coppice (SRC)‐willow. The amount of SOC sequestered in the soil is a function of site‐specific factors including soil texture, management practices, initial SOC levels and climate; for these reasons, both losses and gains in SOC were observed in previous Miscanthus and SRC‐willow studies. The ECOSSE model was developed to simulate soil C dynamics and greenhouse gas emissions in mineral and organic soils. The performance of ECOSSE has already been tested at site level to simulate the impacts of land‐use change to short rotation forestry (SRF) on SOC. However, it has not been extensively evaluated under other bioenergy plantations, such as Miscanthus and SRC‐willow. Twenty‐nine locations in the United Kingdom, comprising 19 paired transitions to SRC‐willow and 20 paired transitions to Miscanthus, were selected to evaluate the performance of ECOSSE in predicting SOC and SOC change from conventional systems (arable and grassland) to these selected bioenergy crops. The results of the present work revealed a strong correlation between modelled and measured SOC and SOC change after transition to Miscanthus and SRC‐willow plantations, at two soil depths (0–30 and 0–100 cm), as well as the absence of significant bias in the model. Moreover, model error was within (i.e. not significantly larger than) the measurement error. The high degrees of association and coincidence with measured SOC under Miscanthus and SRC‐willow plantations in the United Kingdom, provide confidence in using this process‐based model for quantitatively predicting the impacts of future land use on SOC, at site level as well as at national level.     

Resistance and resilience of the forest soil microbiome to logging-associated compaction

Soil compaction is a major disturbance associated with logging, but we lack a fundamental understanding of how this affects the soil microbiome. We assessed the structural resistance and resilience of the microbiome using a high-throughput pyrosequencing approach in differently compacted soils at two forest sites and correlated these findings with changes in soil physical properties and functions. Alterations in soil porosity after compaction strongly limited the air and water conductivity. Compaction significantly reduced abundance, increased diversity, and persistently altered the structure of the microbiota. Fungi were less resistant and resilient than bacteria; clayey soils were less resistant and resilient than sandy soils. The strongest effects were observed in soils with unfavorable moisture conditions, where air and water conductivities dropped well below 10% of their initial value. Maximum impact was observed around 6–12 months after compaction, and microbial communities showed resilience in lightly but not in severely compacted soils 4 years post disturbance. Bacteria capable of anaerobic respiration, including sulfate, sulfur, and metal reducers of the Proteobacteria and Firmicutes, were significantly associated with compacted soils. Compaction detrimentally affected ectomycorrhizal species, whereas saprobic and parasitic fungi proportionally increased in compacted soils. Structural shifts in the microbiota were accompanied by significant changes in soil processes, resulting in reduced carbon dioxide, and increased methane and nitrous oxide emissions from compacted soils. This study demonstrates that physical soil disturbance during logging induces profound and long-lasting changes in the soil microbiome and associated soil functions, raising awareness regarding sustainable management of economically driven logging operations.     

Soil hydrological properties as influenced by long‐term nitrogen application and landscape positions under switchgrass seeded to a marginal cropland

Switchgrass (Panicum virgatum L.) has the potential to recover the soil hydrological properties of marginal lands. Nitrogen (N) and landscape position are the key factors in impacting these soil properties under switchgrass. The specific objective of this study was to investigate the responses of N rate (low, 0 kg N/ha and high, 112 kg N/ha) and landscape positions (shoulder and footslope) on near‐surface soil hydrological properties that included: infiltration rate (q_s), saturated hydraulic conductivity (K_sat), bulk density (ρ_b), penetration resistance (SPR), water retention (SWR), pore‐size distribution (PSD), and carbon (C) and nitrogen (N) fractions under switchgrass production. Data showed that, in general, the N and landscape position significantly influenced soil hydrological properties. Higher N rate decreased ρ_b (1.23 and 1.36 g/cm³ at 0–5 and 5–15 cm, respectively) and SPR (1.06 and 1.53 MPa at 0–5 and 5–15 cm, respectively) at both depths and increased the q_s, K_sat and Green–Ampt estimated sorptivity (S) and hydraulic conductivity (K_s) parameters, and SWR (0–5 cm depth) at 0 and ?0.4 kPa matric potentials (ψ_m). Furthermore, footslope position significantly decreased ρ_b, SPR at 0–5 and 5–15 cm depths, and increased the q_s, K_sat, S, K_s, and SWR (0–5 cm depth) at every ψ_m ranged from 0 to ?30.0 kPa. The higher N rate increased the coarse mesopores (60–1,000 μm) and total pores, whereas, footslope position increased the coarse mesopores, micropores (<60 μm), and total pores. Data from this study showed that planting switchgrass with 112 kg N/ha under footslope position helped in improving the soil hydrological properties, those can be beneficial in enhancing the biomass yield under marginal lands.     

Accumulation of soil organic carbon after cropland conversion to short‐rotation willow and poplar

The demand for bioenergy has increased the interest in short‐rotation woody crops (SRWCs) in temperate zones. With increased litter input and ceased annual soil cultivation, SRWC plantations may become soil carbon sinks for climate change mitigation. A chronosequence of 26 paired plots was used to study the potential for increasing soil organic carbon (SOC) under SRWC willow and poplar after conversion from cropland (CR) on well‐drained soils. We estimated SOC stocks in SRWC stands and adjacent CR and related the difference to time since conversion, energy crop species, SOC stock of the adjacent CR (proxy for initial SOC of SRWC) and the fine soil percentage (<63 μm) (FS). Soil cores to 40 cm depth were sampled and separated by layers of fixed depths (0–5, 5–10, 10–15, 15–25 and 25–40 cm). Additionally, soils were sampled from soil pits by genetic horizons to 100 cm depth. Comparisons of SOC stocks by equivalent soil masses showed that mean SOC stocks in SRWC were 1.7 times higher than those of CR in the top 5 cm of the soil (P < 0.001). The differences between SRWC and CR remained significant for the plough layer (0–25 cm) by a factor of 1.2 (P = 0.003), while no changes were detectable for the 0–40 cm (P = 0.32), or for the entire 0–100 cm soil layer (P = 0.29). The SOC stock ratio, that is the ratio of SOC stock in SRWC relative to CR, did not change significantly with time since conversion, although there was a tendency to an increase over time for the top 40 cm (P = 0.09). The SOC stock ratio was negatively correlated to SOC in CR and FS percentage, but there was no significant difference between willow and poplar at any depth. Our results suggest that SOC stocks in the plough layer increase after conversion to SRWC.     

Environmental costs and benefits of growing Miscanthus for bioenergy in the UK

Planting the perennial biomass crop Miscanthus in the UK could offset 2–13 Mt oil eq. yr^?1, contributing up to 10% of current energy use. Policymakers need assurance that upscaling Miscanthus production can be performed sustainably without negatively impacting essential food production or the wider environment. This study reviews a large body of Miscanthus relevant literature into concise summary statements. Perennial Miscanthus has energy output/input ratios 10 times higher (47.3 ± 2.2) than annual crops used for energy (4.7 ± 0.2 to 5.5 ± 0.2), and the total carbon cost of energy production (1.12 g CO₂‐C eq. MJ^?1) is 20–30 times lower than fossil fuels. Planting on former arable land generally increases soil organic carbon (SOC) with Miscanthus sequestering 0.7–2.2 Mg C4‐C ha^?1 yr^?1. Cultivation on grassland can cause a disturbance loss of SOC which is likely to be recovered during the lifetime of the crop and is potentially mitigated by fossil fuel offset. N₂O emissions can be five times lower under unfertilized Miscanthus than annual crops and up to 100 times lower than intensive pasture. Nitrogen fertilizer is generally unnecessary except in low fertility soils. Herbicide is essential during the establishment years after which natural weed suppression by shading is sufficient. Pesticides are unnecessary. Water‐use efficiency is high (e.g. 5.5–9.2 g aerial DM (kg H₂O)^?1, but high biomass productivity means increased water demand compared to cereal crops. The perennial nature and belowground biomass improves soil structure, increases water‐holding capacity (up by 100–150 mm), and reduces run‐off and erosion. Overwinter ripening increases landscape structural resources for wildlife. Reduced management intensity promotes earthworm diversity and abundance although poor litter palatability may reduce individual biomass. Chemical leaching into field boundaries is lower than comparable agriculture, improving soil and water habitat quality.     

晋西黄土区退耕还林22年后林地土壤物理性质的变化

退耕还林林地土壤物理性质的变化,是评价退耕还林措施及其生态效益的重要内容之一。选取晋西黄土区退耕22年后形成的3种典型乔木林分,包括自然恢复的辽东栎林、油松刺槐人工混交林和刺槐人工纯林,并以耕地作为对照,通过外业调查和采样分析,从深度和程度两方面研究了退耕还林对土壤容重、土壤总孔隙度和毛管孔隙度等物理性质的影响,结果表明:(1)就土壤容重而言,自然恢复林80 cm以上土层较耕地有显著变化(P0.05),平均降低了28.78%,变化程度最大的在10—20 cm土层;人工林较耕地显著变化发生在60 cm以上土层,混交林和纯林分别降低了10.58%和8.34%,变化程度最大的土层为20—40 cm;(2)3种退耕林地土壤总孔隙度在80 cm以上较耕地发生显著增加(P0.05),增加程度表现为自然恢复林(35.53%)混交林(15.04%)纯林(13.68%),20—40 cm土层变化程度最大;(3)土壤毛管孔隙度自然恢复林、混交林和纯林分别达到耕地的1.36,1.13和1.12倍,自然恢复林和人工林显著变化土层分别为80 cm和60 cm以上,变化程度最大的均为40—60 cm处;(4)土壤有机质和粘粒含量对土壤理化性质影响显著。对于土壤容重、总孔隙度和毛管孔隙度的变化,有机质的增加可解释31%以上,而粘粒含量的解释度则达到44%—51%,均为极显著水平(P0.01)。自然恢复林对于土壤物理性质影响程度和影响土层深度都大于人工林。     

Economic and greenhouse gas costs of Miscanthus supply chains in the United Kingdom

Miscanthus has been identified as one of the most promising perennial grasses for renewable energy generation in Europe and the United States [Mitigation and Adaptation Strategies for Global Change 9 (2004) 433]. However, the decision to use Miscanthus depends to a considerable degree on its economic and environmental performance [Soil Use and Management 24 (2008) 235; Renewable and Sustainable Energy Reviews 13 (2009) 1230]. This article assessed the spatial distribution of the economic and greenhouse gas (GHG) costs of producing and supplying Miscanthus in the UK. The average farm‐gate production cost of Miscanthus in the UK is estimated to be 40 £ per oven‐dried tonne (£ odt^?1), and the average GHG emissions from the production of Miscanthus are 1.72 kg carbon equivalent per oven‐dried tonnes per year (kg CE odt^?1 yr^?1). The production cost of Miscanthus varies from 35 to 55 £ odt^?1 with the lowest production costs in England, Wales and Northern Ireland, and the highest costs in Scotland. Sensitivity analysis shows that yield of Miscanthus is the most influential factor in its production cost, with precipitation the most crucial input in determining yield. GHG emissions from the production of Miscanthus range from 1.24 to 2.11 kg CE odt^?1 yr^?1. To maximize the GHG benefit, Miscanthus should be established preferentially on croplands, though other considerations obviously arise concerning suitability and value of the land for food production.     

半干旱区旱地不同覆盖种植方式玉米田的土壤水分和产量效应

为探讨半干旱区旱地不同种植方式玉米(Zea mays)田的土壤水分动态特征, 测定了全膜双垄沟播(PMF)、全沙覆盖(SM)和裸地(CK) 3种不同处理0-200 cm土壤水分季节变化、垂直变化及年际变化。结果表明: PMF明显改善玉米拔节前0-200 cm土壤的水分条件, 有利于玉米前期生长; 随着玉米生育进程的推进, 3种处理的耗水量依次为: PMF﹥SM﹥CK, 而土壤贮水量表现为CK﹥SM﹥PMF; 在相同降雨条件下, PMF处理0-200 cm土壤水分降雨入渗补给深度最大, SM次之, CK最小。随着种植年限增加, PMF的耗水量和耗水深度增加, 两年种植期间耗水深度从20-120 cm向120-200 cm推移; 连续种植两年后, 3种处理40-120 cm土壤含水量下降至9.0%以下, 其中PMF下降最快(7.9%), 土壤含水量接近萎蔫系数7.2%, 玉米只能靠当年降水生长, 如种植年限继续增加, 土壤极有可能形成干层。3种处理之间耗水量、产量、水分利用效率都存在显著差异, PMF最高, SM次之, CK最低。因此, 在半干旱区采用全膜双垄沟播种植玉米可显著提高产量, 但连续种植可导致土壤贮水量显著降低, 对农田可持续生产能力造成不利影响。     

Uptake and leaching of nitrogen from artificial urine applied to grassland on different dates during the growing season

Artificial urine, equivalent to 30 g N m^-2, was applied to replicated plots in a perennial ryegrass (Lolium perenne L.) sward, each plot receiving a single application on one of six dates between July and November 1990. Recoveries of urine-N in herbage up to the end of the growing season in November decreased linearly for consecutive application dates, ranging from 40% of the urine-N applied in July to a negligible proportion of the final application. In contrast, contents of urine-derived N remaining in the soil (to 1-m depth) in November increased from 3% of the N applied in July to 66% for the final application. Almost all of this was present as nitrate + nitrite-N. Only soils that had received urine in September or later contained significantly greater quatities of mineral-N than the control plots. The mineral-N content of soils collected the following April indicated that most of this urine-derived N had been lost from the soil over the winter. Estimates of the quantities of N leached ranged from 0.7 g N m^-2 from untreated plots to 18.6 g N m^-2 from plots treated with urine in November. Although grass yields and N uptakes in March and April provided evidence of a residual effect from the previous year's urine applications, contents of mineral-N and of potentially mineralisable N in urine-treated soils in April were not significantly different from those in untreated soils.     

Carbon sequestration and turnover in soil under the energy crop Miscanthus: repeated 13C natural abundance approach and literature synthesis

The stability and turnover of soil organic matter (SOM) are a very important but poorly understood part of carbon (C) cycling. Conversion of C₃ grassland to the C₄ energy crop Miscanthus provides an ideal opportunity to quantify medium‐term SOM dynamics without disturbance (e.g., plowing), due to the natural shift in the δ¹³C signature of soil C. For the first time, we used a repeated ¹³C natural abundance approach to measure C turnover in a loamy Gleyic Cambisol after 9 and 21 years of Miscanthus cultivation. This is the longest C₃–C₄ vegetation change study on C turnover in soil under energy crops. SOM stocks under Miscanthus and reference grassland were similar down to 1 m depth. However, both increased between 9 and 21 years from 105 to 140 mg C ha^?1 (P < 0.05), indicating nonsteady state of SOM. This calls for caution when estimating SOM turnover based on a single sampling. The mean residence time (MRT) of old C (>9 years) increased with depth from 19 years (0–10 cm) to 30–152 years (10–50 cm), and remained stable below 50 cm. From 41 literature observations, the average SOM increase after conversion from cropland or grassland to Miscanthus was 6.4 and 0.4 mg C ha^?1, respectively. The MRT of total C in topsoil under Miscanthus remained stable at ~60 years, independent of plantation age, corroborating the idea that C dynamics are dominated by recycling processes rather than by C stabilization. In conclusion, growing Miscanthus on C‐poor arable soils caused immediate C sequestration because of higher C input and decreased SOM decomposition. However, after replacing grasslands with Miscanthus, SOM stocks remained stable and the MRT of old C₃‐C increased strongly with depth.