Reduced Soil Disturbance Research Articles

Effects of different tillage practices on soil water-stable aggregation and organic carbon distribution in dryland farming in Northern China

Knowledge about the changes in soil aggregate stability and soil organic carbon (SOC) under different tillage treatments is necessary to assess the feasibility of adoption of conservation practices for sustaining productivity and protecting the environment in dryland farming in northern China. In this study, four treatments, no-till with straw mulching (NTSM), all straw return tillage (ASRT), shallow rotary treatment (SRT) and conventional tillage (CT) were set and a 5years field experiment was carried out to study the effects of different tillage practices on soil aggregates stability and organic carbon distribution. We found that macro-aggregate (>2mm and 0.25–2mm) proportion, mean weight diameter, total amount, content of SOC in macro-aggregate and proportion of SOC in macro-aggregate were significantly improved by NTSM, ASRT and SRT. In all treatments, soil ability to sequester carbon was improved more prominently in NTSM, and macro-aggregate proportion, mean weight diameter, total amount SOC in macro-aggregate and proportion of SOC in macro-aggregate were improve by 29.4%,30.9%,84.9% and 30.7% respectively by NTSM. In addition, improvement effects on soil aggregates stability and carbon sequestration ability in ASRT were all higher than in SRT, and compared to NTSM, macro-aggregate proportion was slightly higher (1.7%) in ASRT, but SOC content and amount in aggregates were remarkably lower. Our results revealed that reducing soil disturbance, increasing straw returning and especially their combined application (i.e. NTSM in this study) can effectively be used to reduce soil erosion and improve carbon sequestration in dryland farming in northern China.

Changes in soil quality after converting <i>Pinus</i> to <i>Eucalyptus</i> plantations in southern China

Abstract. Vegetation plays a key role in maintaining soil quality, but long-term changes in soil quality due to plant species change and successive planting are rarely reported. Using the space-for-time substitution method, adjacent plantations of Pinus and first, second, third and fourth generations of Eucalyptus in Guangxi, China were used to study changes in soil quality caused by converting Pinus to Eucalyptus and successive Eucalyptus planting. Soil chemical and biological properties were measured and a soil quality index was calculated using principal component analysis. Soil organic carbon, total nitrogen, alkaline hydrolytic nitrogen, microbial biomass carbon, microbial biomass nitrogen, cellobiosidase, phenol oxidase, peroxidase and acid phosphatase activities were significantly lower in the first and second generations of Eucalyptus plantations compared with Pinus plantation, but they were significantly higher in the third and fourth generations than in the first and second generations and significantly lower than in Pinus plantation. Soil total and available potassium were significantly lower in Eucalyptus plantations (1.8–2.5 g kg−1 and 26–66 mg kg−1) compared to the Pinus plantation (14.3 g kg−1 and 92 mg kg−1), but total phosphorus was significantly higher in Eucalyptus plantations (0.9–1.1 g kg−1) compared to the Pinus plantation (0.4 g kg−1). As an integrated indicator, soil quality index was highest in the Pinus plantation (0.92) and lowest in the first and second generations of Eucalyptus plantations (0.24 and 0.13). Soil quality index in the third and fourth generations (0.36 and 0.38) was between that in Pinus plantation and in first and second generations of Eucalyptus plantations. Changing tree species, reclamation and fertilization may have contributed to the change observed in soil quality during conversion of Pinus to Eucalyptus and successive Eucalyptus planting. Litter retention, keeping understorey coverage, and reducing soil disturbance during logging and subsequent establishment of the next rotation should be considered to help improving soil quality.

Heterogeneous Preferences and the Effects of Incentives in Promoting Conservation Agriculture in Malawi

Malawi faces significant challenges in meeting its future food security needs because there is little scope for increasing production by simply expanding the area under cultivation. One potential alternative for sustainably intensifying agricultural production is by means of conservation agriculture (CA), which improves soil quality through a suite of farming practices that reduce soil disturbance, increase soil cover via retained crop residues, and increase crop diversification. We use discrete choice experiments to study farmers’ preferences for these different CA practices and assess willingness to adopt CA. Our results indicate that, despite many benefits, some farmers are not willing to adopt CA without receiving subsidies, and current farm-level practices significantly influence willingness to adopt the full CA package. Providing subsidies, however, can create perverse incentives. Subsidies may increase the adoption of intercropping and residue mulching, but adoption of these practices may crowd out adoption of zero tillage, leading to partial compliance. Further, exposure to various risks such as flooding and insect infestations often constrains adoption. Rather than designing subsidies or voucher programs to increase CA adoption, it may be important to tailor insurance policies to address the new risks brought about by CA adoption.

Impact of organic no-till vegetables systems on soil organic matter in the Atlantic Forest biome

Soil organic matter is widely recognized as a strategy used to improve soil quality and reduce carbon emissions to the atmosphere. A field study was carried out to investigate the effects of cover crops in organic no-till vegetables systems on changes in soil organic matter and CO2C emissions, in dry and rainy seasons. We hypothesized that CO2C emissions are higher in conventional till as compared with no-till, and that no-till increases soil C sink. The crop rotation comprised a 3-year cropping sequence involving two crops per year—cabbage (Brassica oleracea L.) in winter and eggplant (Solanum melongena L.) in summer time. Treatments were no-till on dead mulch of grass (Avena strigosa Schreb. and Zea mays L.), leguminous (Lupinus albus L. and Crotalaria juncea L.), intercrop (grass and leguminous) and conventional till (no dead mulch) with rotary hoe arranged in a randomized block design on a clayey Oxisol (Typic Haplustox) at Domingos Martins-ES, Brazil. On 2012 and 2013, disturbed soil samples at three different layers (0–5, 5–15 and 15–30cm) and undisturbed samples at 0–10, 10–20 and 20–30cm, for chemical and organic matter characterization were taken. CO2C emissions and soil temperature were measured in situ on March, May, August and October 2012 and February 2013 (after 3 years of experiment). Conventional till site showed the lowest microporosity values and the highest macroporosity, followed by lower soil bulk density at 0–10cm layer. Total organic C ranged from 34.94 to 50.48gkg−1 in intercrop and 27.11 to 43.74gkg−1 in conventional till. Total N ranged from 2.81 to 5.34gkg−1 in grass and 2.54 to 4.51gkg−1 in conventional till. Highest C stock was recorded in intercrop. Conventional till showed lower labile C values while recalcitrant C was higher in the intercrop treatment. The annual average of CO2C emissions (μmolCO2m−2s−1) followed the order: grass (15.89)>intercrop (13.77)>leguminous (13.09)>conventional till (11.20). Highest annual average of soil temperature was recorded in conventional till (23.95°C). Lowest annual mean of soil water content, microbial biomass C, and highest metabolic quotient were recorded in conventional till. These results suggest that the use of cover crops and organic compost in pre-planting promote C increments. The contribution of organic residues increases the water holding capacity and reduces soil temperature. No-till reduces soil disturbance and promotes a positive balance of C. Organic no-till vegetable systems is a strategy to increase soil C and should be encouraged in order to increase soil quality in the Atlantic Forest Biome in Brazil.

Short-Term Stover, Tillage, and Nitrogen Management Affect Near-Surface Soil Organic Matter

Corn (Zea mays L.) stover removal for biofuel or forage has implications on soil organic C (SOC). The objective of this study was to evaluate short-term (3-yr) stover management (retained or removed [79% removed, across treatments and years]), tillage system (chisel tillage, strip-tillage, and no-till [CT, ST, and NT, respectively]), and fertilizer N (0 and 224 kg N ha⁻¹) effects on particulate and total soil C and N in continuous corn (CC) cropping systems on fine-textured soils in the Upper Midwest. Soil samples were collected at study initiation in 2008 and at its conclusion in 2011. Stover removal decreased SOC in the surface depth (D1) by 15% compared to when it was retained and 11% when compared with the baseline level. In the same depth, SOC with CT was 10 and 9% less than with ST and NT, respectively, and 10% less than the baseline. Particulate organic matter C (POM-C) decreased in D1 between sampling times with stover removal in all tillage systems. When stover was retained, POM-C in D1 increased 36 and 40% over the baseline with ST and NT, respectively, but decreased 18% with CT. Chisel tillage decreased POM-C in the sampled soil profile by 13 and 17% compared with ST and NT, respectively, and by 21% when compared with the baseline. These results demonstrate that annually harvesting the maximum quantities of stover in CC allowable by field-scale machinery can reduce near-surface particulate and total soil organic matter in the Upper Midwest after 3 yr, but losses can be reduced by tillage systems that reduce soil disturbance.

Grazing and no-till cropping impacts on nitrogen retention in dryland agroecosystems.

As the world's population increases, marginal lands such as drylands are likely to become more important for food production. One proven strategy for improving crop production in drylands involves shifting from conventional tillage to no-till to increase water use efficiency, especially when this shift is coupled with more intensive crop rotations. Practices such as no-till that reduce soil disturbance and increase crop residues may promote C and N storage in soil organic matter, thus promoting N retention and reducing N losses. By sampling soils 15 yr after a N tracer addition, this study compared long-term soil N retention across several agricultural management strategies in current and converted shortgrass steppe ecosystems: grazed and ungrazed native grassland, occasionally mowed planted perennial grassland, and three cropping intensities of no-till dryland cropping. We also examined effects of the environmental variables site location and topography on N retention. Overall, the long-term soil N retention of >18% in these managed semiarid ecosystems was high compared with published values for other cropped or grassland ecosystems. Cropping practices strongly influenced long-term N retention, with planted perennial grass systems retaining >90% of N in soil compared with 30% for croplands. Grazing management, topography, and site location had smaller effects on long-term N retention. Estimated 15-yr N losses were low for intact and cropped systems. This work suggests that semiarid perennial grass ecosystems are highly N retentive and that increased intensity of semiarid land management can increase the amount of protein harvested without increasing N losses.

13C abundance shows effective soil carbon sequestration in Miscanthus and giant reed compared to arable crops under Mediterranean climate

Many studies on soil organic carbon (SOC) sequestration in perennial biomass crops are available for Atlantic and continental environments of North Central Europe, while there is insufficient information for Southern Europe. Therefore, we assessed SOC turnover under Mediterranean climate, after a 9-year-old conversion from two annual crop systems, continuous wheat and maize/wheat rotation, to Miscanthus (Miscanthus sinensis × giganteus) and giant reed (Arundo donax), respectively. The naturally occurring 13C signature down to 0.60 m was used to evaluate the total amount of SOC in annual vs perennial species and to determine the portion of SOC derived from perennial species. Soil organic C was significantly higher under perennial (average, 91 Mg C ha−1) than annual species (average, 56 Mg C ha−1), with a stronger accumulation in the topsoil (0–0.15 m). This difference was consistent with reduced soil disturbance associated with perennial crop management. After 9 years of Miscanthus plantation, the amount of C4-derived C was 18.7 Mg ha−1, mostly stored at 0–0.15 m, whereas the amount of C3-derived C under giant reed was 34.7 Mg ha−1 and was more evenly distributed through soil depths, probably due to its deeper root apparatus. It is suggested that both Miscanthus and giant reed have a remarkable potential for SOC sequestration also under Mediterranean conditions, while supporting the growing bioenergy sector with biomass supply.

Shallow mixing of surface soil and liquid dairy manure conserves nitrogen while retaining surface residue

Incorporation of spring-applied manure is known to reduce N volatilization losses and hence increase the N value of the manure. However, traditional incorporation methods are not compatible with reduced-tillage systems requiring minimum residue coverage of 30 %. Here, eight New York dairy farms participated in 2008 in a 2-year on-farm trial. This trial was designed to test the hypothesis that shallow mixing of soil involving aerator incorporation of spring-applied manure is as effective as chisel incorporation of manure in conserving manure N for corn (Zea mays, L) uptake while retaining more surface residue. The eight fields selected for this trial varied from first to third year corn after hay and had varying manure histories. All fields were subjected to a randomized complete block design with four replicates comparing surface application of manure, as control, shallow incorporation of manure with an aerator, and chisel incorporation of manure. Starter N applications were 39 kg N/ha or less, and manure application rates ranged from 51 to 112 kL/ha. Results show that shallow incorporation of manure significantly reduced soil disturbance and retained, on average, 30 % more surface residue cover than obtained with chisel incorporation. Chisel and aerator-based incorporation resulted in similar soil nitrate levels at 13 of 16 site years, suggesting similar levels of N conservation. Across all sites and years, incorporation increased silage yield by 0.9–1.5 Mg DM/ha, independent of incorporation method. Based on these results, we show that shallow mixing of soil and spring-applied manure is a suitable option for conserving N and maintaining greater surface residue coverage without compromising on yield or silage quality.

保护性耕作对农田碳、氮效应的影响研究进展

PDF HTML阅读 XML下载 导出引用 引用提醒 保护性耕作对农田碳、氮效应的影响研究进展 DOI: 10.5846/stxb201305121021 作者: 作者单位: 中国农业大学农学与生物技术学院,中国农业大学农学与生物技术学院,中国农业大学农学与生物技术学院,中国农业大学农学与生物技术学院,中国农业大学农学与生物技术学院 作者简介: 通讯作者: 中图分类号: 基金项目: 公益性行业(农业)科研专项(201103001) Advances in effects of conservation tillage on soil organic carbon and nitrogen Author: Affiliation: Key Laboratory of Farming System,Ministry of Agriculture of the People’s Republic of China;College of Agronomy and Biotechnology,China Agricultural University,Key Laboratory of Farming System,Ministry of Agriculture of the People’s Republic of China;College of Agronomy and Biotechnology,China Agricultural University,Key Laboratory of Farming System,Ministry of Agriculture of the People’s Republic of China;College of Agronomy and Biotechnology,China Agricultural University,Key Laboratory of Farming System,Ministry of Agriculture of the People’s Republic of China;College of Agronomy and Biotechnology,China Agricultural University,Key Laboratory of Farming System,Ministry of Agriculture of the People’s Republic of China;College of Agronomy and Biotechnology,China Agricultural University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:作物产量的高低主要取决于土壤肥力,如何保持并提高土壤肥力是确保我国粮食安全和农业可持续发展的重要任务,也是众多学者关注的焦点。土壤有机碳和氮素是评价土壤质量的重要指标,其动态平衡直接影响土壤肥力和作物产量。随着全球气候变化及环境污染问题的愈加突出,农田土壤固碳及提高氮效率成为各界科学家研究的热点。目前,保护性耕作已成为发展可持续农业的重要技术之一,对土壤固碳及氮素的利用具有很大的影响。深入了解保护性耕作对土壤有机碳固持与氮素利用效率提高的影响机制,对于正确评价土壤肥力有着重要意义。但由于气候、土壤及种植制度等条件不一致,关于保护性耕作对农田碳、氮效应结论不一。阐述了国际上保护性耕作对农田系统土壤有机碳含量变化及其分解排放(如CO2和CH4)、氮素变化及其矿化损失(如NH3挥发、N2O排放与氮淋失)和碳氮素相互关系(如C/N层化率)影响的研究进展,并分析了其影响因素和相关机理。尽管国内保护性耕作的研究已进行30 多年,但在土壤有机碳与氮素方面与国外相比依然有较大的差距。保护性耕作对土壤固碳与氮素利用的影响机制,碳素和氮素在土壤-植株-大气系统中的转移变化,及结合农事管理等综合评价其生态效应的研究很少。在此基础上,提出未来我国保护性耕作在土壤有机碳固定和氮素利用方面的重点研究方向:(1)在定位试验基础上进一步探讨保护性耕作对土壤有机碳及氮素利用的影响机制;(2)深入研究土壤有机碳和氮素的相互关系及其对土壤肥力的影响;(3)结合环境保护与土壤可持续管理对保护性耕作农田土壤固碳及氮素高效利用的系统评价研究;(4)加强保护性耕作对农田碳、氮效应的宏观研究,合理评价保护性耕措施下对农田碳、氮综合效应。 Abstract:Soil fertility is one of the most important factors determining crop production. Maintaining and improving soil fertility, which has become an increasing focus for agricultural scientists, is crucial for food security and sustainable agricultural development in China. Soil organic carbon (SOC) and nitrogen (N) directly affect soil fertility and ultimately crop yield, and thus are considered as important soil quality indicators. With the concerns on global warming and environmental pollution, more attention is being paid on enhancing SOC sequestration and improving N use efficiency (NUE) in cropland. Currently, conservation tillage is widely regarded as an important part of sustainable agriculture and has been adopted by many countries, due to its benefits in conserving soil, saving water, fuel and energy, and protecting the environment. Numerous studies have indicated that conservation tillage (i.e., no-till and minimum tillage) increases SOC and total N storages by reducing soil disturbance and increasing residue retention. Thus, a deep understanding of the mechanisms of conservation tillage on enhancing SOC sequestration and NUE is of fundamental significance for soil fertility assessment. However, there are still controversies about the effects of conservation tillage on SOC sequestration and NUE, mainly due to the diverse climates, soil types, cropping systems, and experimental durations. This paper provides a review about the research progresses of conservation tillage effects on SOC content and decomposition (e.g., CO2 and CH4 emission), total N content and mineralization (e.g., NH3 volatilization, N2O emission, and NO3- leaching), and the relationships between SOC and N processes (e.g., C/N stratification) in farmland systems. Meanwhile, this article also assessed factors and mechanisms that influence SOC and N use. Although studies on conservation tillage have been conducted more than 30 years, there are some gaps between China and the other countries, especially on SOC and N processes under conservation tillage systems. Because of the large differences in experiment conditions, the mechanisms of tillage effects on SOC sequestration and N use are not well understood. Furthermore, systematic studies on carbon and N transformations in the soil-plant-atmosphere-continuum are rare under different tillage systems, which make it difficult to conduct in-depth studies of conservation tillage. Meanwhile, considering the emissions of agricultural practices, few papers have assessed the ecological effects of conservation tillage on the interactions between C and N processes. Therefore, it is necessary to study the underpinning mechanisms that govern tillage effects on SOC sequestration and N use. Our analysis showed that the potential researchable areas and priorities on the influences of conservation tillage on SOC and N processes in China were: (1) strengthen the on-site studies on the mechanisms of conservation tillage effects on SOC sequestration and N use; (2) enhance the study of relationships between SOC and N and their interaction effect on soil fertility under conservation tillage; (3) link environmental protection, sustainable soil management, SOC sequestration and N use; and (4) deepen the study of conservation tillage effects on SOC sequestration and N use in macro-scale. 参考文献 相似文献 引证文献

Evolution of Conservation Tillage Systems for Processing Tomato in California’s Central Valley

Traditional processing tomato (Solanum lycopersicum) production in California’s Central Valley relies heavily on tillage to produce high yields. However, recent research and farm innovation have produced a variety of conservation tillage (CT) management alternatives that cut costs, reduce soil disturbance, and produce fewer emissions. A 12-year study in Five Points, CA, demonstrated that CT methods reduced tractor passes by 40%, lowered tillage costs by ≈$80 per acre in 2011 dollars, and achieved comparable yields as standard tillage (ST) methods. As comparable yield performance and net profitability are further demonstrated, an array of CT systems will become increasingly attractive to producers and more common in Central Valley tomato growing areas.

Physical, chemical, and biochemical mechanisms of soil organic matter stabilization under conservation tillage systems: A central role for microbes and microbial by-products in C sequestration

Conservation tillage practices that entail no or reduced soil disturbance are known to help preserve or accumulate soil organic matter (OM). However, the underlying mechanisms especially at the molecular level are not well understood. In this study soil samples from 25-year-old experimental plots continuously cropped with barley (Hordeum vulgare L.) under no-tillage (NT) and chisel tillage (CT) were subjected to a new physical fractionation method to isolate dissolved OM, mineral-free particulate OM located outside aggregates (physically and chemically unprotected), OM occluded within both macroaggregates and microaggregates (weakly and strongly protected by physical mechanisms, respectively), and OM in intimate association with minerals (protected by chemical mechanisms). The whole soils and OM fractions were analyzed for organic C and N content and by modern nuclear magnetic resonance (NMR) techniques. The soil under NT stored 16% more organic C and 5% more N than the soil under CT. Compared to CT, NT increased free organic C content by 7%, intra-macroaggregate organic C content by 20%, intra-microaggregate organic C content by 63%, and mineral-associated organic C content by 16% and decreased dissolved organic C content by 11%. The mineral-associated OM pool accounted for 65% of the difference in total organic C content between NT and CT, whereas the intra-microaggregate OM only explained 18%, intra-macroaggregate OM 14%, and free OM 11%. The NMR experiments revealed that the free and intra-aggregate OM fractions were dominated by crop-derived materials at different stages of decomposition, whereas the mineral-associated OM pool was predominately of microbial origin. Overall, our results indicate that microbes and microbial by-products associated with mineral surfaces and likely physically protected by entrapment within very small microaggregates constitute the most important pool of OM stabilization and C sequestration in soils under NT. Most probably the slower macroaggregate turnover in NT relative to CT boosts not only the formation of microaggregates and thereby the physical protection of crop-derived particulate OM, but more importantly the interaction between mineral particles and microbial material that results in the formation of very stable organo-mineral complexes.

Variations of carbon stock with forest types in subalpine region of southwestern China

Subalpine forests in southwestern China were exploited extensively in the second half of the 20th century. Old growth forests (OGFs) dominated by firs had largely been replaced by spruce plantation forests (SPFs), spruce and birch mixed forests (SBMs), natural birch forests (NBFs), and fir and birch mixed forests (FBM). The main objectives of this study are to quantify the ecosystem carbon (C) stock in these five forest types and to estimate their C sequestration capacity. Sixty-nine stands were sampled across the Miyaluo forest region located in the subalpine zone of southwestern China. The C stocks in the tree-layer, understory, herbs, mosses, forest floor, coarse woody debris (CWD) and soil were estimated. The mean total biomass in SPF, SBM, NBF, FBM, and OGF was 125.9, 131.2, 135.7, 191.7, and 651.1t/ha, respectively. The OGF had the highest level of C stock. Total biomass and C density were significantly higher in FBM than those in SPF, SBM and NBF. FBM had a significantly higher mean annual increment (MAI) than all other types. Soil C accounted for a large proportion (68.4–76.5%) of the ecosystem C pools in SPF, SBM, NBF and FBM, but only 40.5% C was stored in the OGF’s soils relative to 51.5% in the biomass. Of the C stock in the upper 0–80cm soil, about 50% was stored in the upper 0–20cm, and more than 74% in the upper 0–40cm. Soil C stock in OGF, NBF and FBM was significantly higher than that in SPF and SBM. Soil disturbance during timber harvest, site preparation and tree planting explains less soil C stock in the SPF and SBM stands compared to other forest types. These results suggest natural mixed forest restoration can be a promising approach for increasing C sequestration capacity in the subalpine region. Also, reducing soil disturbance during forest management practices plays an important role in increasing the soil C stock.

Long-term farming systems research in the central High Plains

AbstractIn recent decades, there has been growing interest among farming and scientific communities toward integrated crop–range–livestock farming because of evidence of increased crop production, soil health, environmental services and resilience to increased climatic variability. This paper reviews studies on existing cropping systems and integrated crop–range–livestock systems across the USA which are relevant in the context of summarizing opportunities and challenges associated with implementing long-term crop–range–livestock systems research in the highly variable environment of the central High Plains. With precipitation ranging from 305 to 484mm and uncertain irrigation water supply, this region is especially vulnerable to changing moisture and temperature patterns. The results of our review indicate that diverse crop rotations, reduced soil disturbance and integrated crop–livestock systems could increase economic returns and agroecosystem resilience. Integrating agricultural system components to acquire unique benefits from small- to medium-sized operations, however, is a challenging task. This is because assessment and identification of suitable farming systems, selection of the most efficient integration scheme, and pinpointing the best management practices are crucial for successful integration of components. Effective integration requires development of evaluation criteria that incorporate the efficiency of approaches under consideration and their interactions. Therefore, establishing the basis for more sustainable farming systems in the central High Plains relies on both long-term agricultural systems research and evaluation of short-term dynamics of individual components.

Burning outcomes following aggregated retention harvesting in old-growth wet eucalypt forests

In Tasmania, Australia, aggregated retention (ARN1Abbreviations: ARN, aggregated retention; CBS, clearfell, burn and sow.1) is being implemented as an alternative to clearfelling in old-growth wet eucalypt forests. These forests have traditionally been regenerated using a high-intensity burn and aerial sowing, but the use of more complex harvesting designs makes conventional high-intensity burning difficult. In 2007, a new burning method (‘slow burning’) was developed specifically for ARN coupes. This paper compares site preparation, burning weather conditions and burning outcomes in ARN and conventional clearfell, burn and sow (CBS) coupes burnt from 2007 to 2010. ARN coupes had higher perimeter-to-area ratios than paired CBS coupes, and 8% more of the harvested area was affected by firebreaks. Although there was less burnt seedbed and more compacted seedbed in ARN coupes compared to clearfelled coupes, mean levels of receptive seedbed were adequate and are unlikely to limit regeneration success. Burn impact on unharvested forest was greater in ARN coupes, due largely to burning in the retained aggregates. Despite this, only 11% of aggregate area was burnt overall, and the current guidelines for aggregate size (most >1ha) appear sufficient to keep burn impact within acceptable thresholds. Firebreaks affected from 4–32% of the harvested area in the coupes measured in this study, and were 10m wide on average, twice the required width. To reduce soil disturbance and potential impacts on regeneration, firebreaks should be established only where absolutely necessary, and firebreak widths should be minimised wherever possible.

Soil carbon dynamics as influenced by tillage and crop residue management in loamy sand and sandy loam soils under smallholder farmers’ conditions in Malawi

Conservation agriculture (CA) characterised by minimal soil disturbance, permanent soil surface cover by dead or living plants and crop rotations is one way of achieving higher soil organic carbon (C) in agricultural fields. Sandy loam and loamy soil samples from zero tillage (ZT) and conventional tillage (CT) plots were taken from farmers’ fields during the dry season in August 2006. Soil organic carbon (SOC) and soil organic nitrogen (SON), microbial biomass carbon (MB-C) and microbial biomass nitrogen (MB-N), C mineralization and SOC distribution in particle size fractions in 0–20 cm layer were evaluated. Forty eight farmers’ fields were randomly sampled at four different locations in Central and Northern Malawi, representing ZT plots maintained for a different number of years, and ten fields under CT with similar soil type and crop grown were selected. SOC and SON in ZT fields were 44 and 41 % (4 years ZT) and 75 and 77 % (5 years ZT) higher, respectively, than CT plots. MB-C and MB-N in ZT fields were 16 and 44 % (4 years ZT) and 20 and 38 % (5 years ZT) higher, respectively, than CT plots. However, MB-C and MB-N in ZT fields were 27 and 25 % (2 years ZT) and 17 and 9 % (3 years ZT) lower than in CT plots. The proportion of the total organic C as microbial biomass C was relatively higher under CT than ZT treatments. The higher SOC and MB-C content in the ZT fields resulted in 10, 62, 57 % higher C mineralization rate in ZT plots of 3, 4 and 5 years of loamy sand soils and 35 % higher C mineralization rate in ZT plot of 2 years than CT of sandy loam soils in undisturbed soils in the laboratory. Simulating plough from the undisturbed soils that were used for C mineralization experiment resulted in linear curves indicating that all organic C was already depleted during the first incubation period. The relative distribution of soil organic matter (SOM) in silt and clay size fractions was strongly correlated (r = 0.907 and P ≤ 0.01) with silt percentages. Easily degradable carbon pool (CA,f) was correlated (r = 0.867 and P ≤ 0.05) with organic carbon in sand size fraction. In developing viable conservation agriculture practices to optimize SOC content and long-term sustainability of maize production systems, priority should be given to the maintenance of C inputs, crop rotations and associations and also to reduced soil disturbance by tillage.

Lawn soil carbon storage in abandoned residential properties: An examination of ecosystem structure and function following partial human-natural decoupling

Residential abandonment is on the rise in many urban areas, with unknown implications for ecosystem structure and function on land slated for partial or full restoration to native habitat. Partial decoupling of human and natural systems could reduce disturbance (e.g., trampling, recreational traffic) and modify vegetation structure in a way that alters soil carbon storage, an ecosystem function that many municipalities consider a management objective of growing importance. We quantified soil carbon percent and mass to 10 cm depth and examined vegetation structure in 50 vacant and 10 occupied residential lawns located in Richmond, VA, with the principal objective of determining whether occupancy status alters trajectories of soil carbon storage or its correspondence with household economic/demographic indicators and vegetation cover. Abandoned residential lawns supported significantly less grass cover, but these declines were largely offset by increases in emergent overstory (>1 m height) vegetation cover. Soil carbon percent and mass did not differ between lawns of occupied and abandoned residences, even though significant, but highly uncertain, increases in soil carbon mass occurred in the first decade following vacancy. Instead, all residential lawns exhibited similar significant increases in soil carbon percent and mass with increasing residence age and neighborhood affluence, the former indicating annual carbon accretion rates of 20 g m(-2). We conclude that in this early stage of vacancy, soil carbon storage is already subtly responding to declines in human intervention, with reduced soil disturbance and sustained vegetation cover in abandoned lawns playing likely roles in emerging soil carbon storage trajectories.

Organic matter distribution in aggregate sizes of a mollisol under contrasting management

Total and particulate organic matter content in different aggregate sizes can be used as an indicator of land use effect. We hypothesized that tillage reduction increases total (SOC) and particulate soil organic C (POC) contents and the stability of larger aggregates of high-SOC-content Mollisols. Three management systems (continuous pasture (Pp), and continuous cropping under conventional tillage (CT) and notillage (NT)) were evaluated. Oven dried soil samples (0-5 and 5-20 cm), were wet sieved through 2000, 250 and 50 µm sieves after immersion (IW) and capillary (CW) wetting. Particulate organic matter (>50 µm) was separated in both the whole soil and in each aggregate fraction, SOC and mineral associated organic C contents were determined, and POC was calculated by subtraction. Reduced soil disturbance (Pp and NT) yielded more SOC and POC in the whole soil and macroaggregates with higher stability (Pp>NT>CT). Under Pp, macroaggregates showed the highest SOC and POC. Under NT, macroaggregates showed higher SOC and POC and aggregate stability than CT though lower than Pp. Less tillage-induced disruption (Pp and NT) led to higher SOC and POC contents in more stable macroaggregates but continuous no-tillage appeared not to be enough to reverse the effects of long lasting conventional management practices on these Mollisols.

Does no‐till farming induce water repellency to soils?

AbstractSoil water repellency (SWR) is an intrinsic and dynamic soil property that can influence soil hydrology and crop production. Although several land use systems have been shown to induce water repellency in soil, the specific effects of no‐till cropping on SWR are poorly understood. This article reviews the impacts of no‐till on SWR and identifies research needs. No‐till cropping generally induces 1.5 to 40 times more SWR than conventional tillage, depending on soil type. This may result from near‐surface accumulation of hydrophobic organic C compounds derived from crop residues, microbial activity and reduced soil disturbance. While large SWR may have adverse impacts on soil hydrology and crop production, the level of SWR under no‐till relative to conventional tillage may contribute to aggregate stabilization and intra‐aggregate C sequestration. More research is needed to discern the extent and relevance of no‐till induced SWR. This includes: (1) further assessment of SWR under different tillage systems across a wide range of soil textures and climates, (2) comparison of the various methods for measuring SWR over a range of water contents, (3) inclusion of SWR in routine soil analysis and its use as a parameter to evaluate management impacts, (4) assessment of the temporal and spatial changes in SWR under field conditions, (5) further assessment of the impacts of the small differences in SWR between no‐till and conventionally tilled soils on crop production, soil hydrology and soil C sequestration, and (6) development of models to predict SWR for different tillage systems and soils.

Tillage effects on soil organic carbon storage and dynamics in Corn Belt of Ohio USA

Abstract No-till (NT) agriculture reduces soil disturbance, conserves soil and water, and lowers the cost of agricultural production. However, its role in soil organic carbon (SOC) sequestration can be soil and site specific. The applicability of the results from long-term tillage experiments (LTTEs) showing positive rate of carbon (C) sequestration is being questioned under large scale farmers’ field conditions. Therefore, this study assessed the soil C dynamics under conventional till (CT) and NT practices using three LTTEs and three farmer's field sites in Ohio, USA with diverse soil types, and environmental and management conditions. The hypothesis tested was that reduced soil disturbance in NT management system enhances soil C sequestration in comparison to CT management. Soils were sampled (0–40 cm) from adjacent CT, NT and woodlot (WL) plots at each site. Total C and nitrogen (N) pools were calculated based on equivalent soil mass basis. The SOC was fractioned into old C and new (corn C) using δ13C natural abundance. The CT soils had 26–55% lower SOC and 7–34% lower N pool compared to forest soils. Most of the historic SOC and N losses in cultivated soils occurred within the plow (0–25 cm) layer. The SOC pool in the top 40 cm was significantly greater under NT than CT at LTTEs and Coshocton farm. There were no significant differences in SOC pool of the top 40 cm among CT and NT at Delaware and Hoytville farms. Old C accounted for 69% and 66% of SOC under CT and NT, respectively at Northwestern Agricultural Research Station. However, at Western Agricultural Research Station, corn-derived C dominated CT and NT soils, accounting for 55% and 66% of SOC in the top 40 cm, respectively. At North Appalachian Experimental watersheds, corn-derived C dominated NT soils (64%), while old C dominated CT soils (64%). Result of this study indicated that a decrease in SOC and N pools occurs when forest soil is cultivated. Conversion of CT to NT restores some of the depleted SOC and N pools. This supports our hypothesis that the reduced soil disturbance in NT system slows the decomposition of SOC which increases soil C sequestration. The quantity and rate of loss or sequestration depends on several factors including soil type, texture and drainage, tillage intensity, and duration of NT practice.

Effects of tillage on microbial populations associated to soil aggregation in dryland spring wheat system

Tillage may influence the microbial populations involved in soil aggregation. We evaluated the effects of no till (NT) and conventional tillage (CT, tillage depth about 7 cm) continuous spring wheat system on culturable heterotrophic bacterial communities predominant in microaggregates (0.25–0.05 mm) and on soil-aggregating basidiomycete fungi in aggregate-size classes (4.75–2.00, 2.00–0.25, and 0.25–0.05 mm) at 0–20 cm depth of a Williams loam (fine-loamy, mixed, Typic Argiustolls) in dryland Montana, USA. Enzyme-linked immunosorbent assay used to quantify antigenic response to basidiomycete cell walls, was higher in NT than in CT in 4.75–2.00 mm size class in 2007 and higher in all classes and years at 0–5 cm depth, but was not different between tillage, years, and classes at 5–20 cm. The culturable bacteria from microaggregates were subjected to a soil sedimentation assay to determine their soil binding capability. The proportion of isolates which can function as soil aggregators was higher in NT than in CT at 0–5 cm but was not different at 5–20 cm. Our results provide a first insight into the beneficial effects of dryland NT compared to CT in reducing soil disturbance and residue incorporation and enriching the proportion of microorganisms responsible for aggregation, especially at the soil surface.