Responses of vegetation and soils to three grazing management regimes in a semi‐arid highland mixed crop‐livestock system

Three grazing regimes [Cut‐and‐carry (CC), seasonal grazing (SG) and continuous grazing (CG)] currently applied in Tigrai region of northern Ethiopia were compared to identify the best grazing management in key native vegetation and soil attributes. More than 50% of the desirable species such as Andropogon, Cynodon and Phalaris spp were located in the CC and SG regimes. During the rainy season, the CC regime produced 1.7 and 2.7 more biomass than the SG and CG regimes, respectively. Herbaceous basal cover was 6.8 times more in the CC than in the CG regime. During the rainy season, herbaceous species diversity and richness were the least in the CG regime but similar in the CC and SG regimes. This similarity, however, changed during the dry season when the SG regime is grazed by livestock that led to a reduction in diversity. These results suggest that CC is superior to the traditional CG, but not always necessarily superior to the SG. The SG regime improved soil P status while the CG regime affected soil bulk density and total N negatively. The predominantly native vegetation grazing systems in Tigrai region can be improved cost effectively through cut‐and‐carry and seasonal grazing.     

Response of soil carbon dioxide fluxes,soil organic carbon and microbial biomass carbon to biochar amendment: a meta‐analysis

Biochar as a carbon‐rich coproduct of pyrolyzing biomass, its amendment has been advocated as a potential strategy to soil carbon (C) sequestration. Updated data derived from 50 papers with 395 paired observations were reviewed using meta‐analysis procedures to examine responses of soil carbon dioxide (CO₂) fluxes, soil organic C (SOC), and soil microbial biomass C (MBC) contents to biochar amendment. When averaged across all studies, biochar amendment had no significant effect on soil CO₂ fluxes, but it significantly enhanced SOC content by 40% and MBC content by 18%. A positive response of soil CO₂ fluxes to biochar amendment was found in rice paddies, laboratory incubation studies, soils without vegetation, and unfertilized soils. Biochar amendment significantly increased soil MBC content in field studies, N‐fertilized soils, and soils with vegetation. Enhancement of SOC content following biochar amendment was the greatest in rice paddies among different land‐use types. Responses of soil CO₂ fluxes and MBC to biochar amendment varied with soil texture and pH. The use of biochar in combination with synthetic N fertilizer and waste compost fertilizer led to the greatest increases in soil CO₂ fluxes and MBC content, respectively. Both soil CO₂ fluxes and MBC responses to biochar amendment decreased with biochar application rate, pyrolysis temperature, or C/N ratio of biochar, while each increased SOC content enhancement. Among different biochar feedstock sources, positive responses of soil CO₂ fluxes and MBC were the highest for manure and crop residue feedstock sources, respectively. Soil CO₂ flux responses to biochar amendment decreased with pH of biochar, while biochars with pH of 8.1–9.0 had the greatest enhancement of SOC and MBC contents. Therefore, soil properties, land‐use type, agricultural practice, and biochar characteristics should be taken into account to assess the practical potential of biochar for mitigating climate change.     

Biomass production and energy balance of Miscanthus over a period of 11 years: A case study in a large‐scale farm in Poland

Giant miscanthus (Miscanthus × giganteus Greef and Deuter) and Amur silver grass (Miscanthus sacchariflorus Maxim./Hack) are rhizomatous grasses with a C4 photosynthetic pathway that are widely cultivated as energy crops. For those species to be successfully used in bioenergy generation, their yields have to be maintained at a high level in the long term. The biomass yield (fresh and dry matter [DM] yield) and energy efficiency (energy inputs, energy output, energy gain, and energy efficiency ratio) of giant miscanthus and Amur silver grass were compared in a field experiment conducted in 2007–2017 in North‐Eastern Poland. Both species were characterized by high above‐ground biomass yields, and the productive performance of M. × giganteus was higher in comparison with M. sacchariflorus (15.5 vs. 9.3 Mg DM ha^?1 year^?1 averaged for 1–11 years of growth). In the first year of the experiment, the energy inputs associated with the production of M. × giganteus and M. sacchariflorus were determined at 70.5 and 71.5 GJ/ha, respectively, and rhizomes accounted for around 78%–79% of total energy inputs. In the remaining years of cultivation, the total energy inputs associated with the production of both perennial rhizomatous grasses reached 13.6–15.7 (M. × giganteus) and 16.9–17.5 GJ ha^?1 year^?1 (M. sacchariflorus). Beginning from the second year of cultivation, mineral fertilizers were the predominant energy inputs in the production of M. × giganteus (78%–86%) and M. sacchariflorus (80%–82%). In years 2–11, the energy gain of M. × giganteus reached 50 (year 2) and 264–350 GJ ha^?1 year^?1 (years 3–11), and its energy efficiency ratio was determined at 4.7 (year 2) and 18.6–23.3 (years 3–11). The energy gain and the energy efficiency ratio of M. sacchariflorus biomass in the corresponding periods were determined at 87–234 GJ ha^?1 year^?1 and 6.1–14.3, respectively. Both grasses are significant and environmentally compatible sources of bioenergy, and they can be regarded as potential energy crops for Central‐Eastern Europe.     

Effect of long‐term mineral fertilisation on soil microbial abundance,community structure and diversity in a Typic Hapludoll under intensive farming systems

Fertiliser application can not only influence plant communities, but also the soil microbial community dynamics, and consequently soil quality. Specifically, mineral fertilisation can directly or indirectly affect soil chemical properties, microbial abundance and, the structure and diversity of soil microbial communities. We investigated the impact of six different mineral fertiliser regimes in a maize/soybean rotation system: control (CK, without fertilisation), PS (application of phosphorus plus sulphur), NS (application of nitrogen plus S), NP (application of N plus P), NPS (application of N, P plus S) and NPSm (application of N, P, S plus micronutrients). Soil samples were collected at the physiological maturity stage of maize and soybean in March of 2013 and 2014, respectively. Overall, mineral fertilisation resulted in significantly decreased soil pH and increased total organic carbon compared with the control (CK). The analysis of terminal restriction fragment length polymorphism (T‐RFLP) revealed that mineral fertilisers caused a shift in the composition of both bacterial and fungal communities. In 2013, the highest value of Shannon diversity of bacterial terminal restriction fragments (TRFs) was found in control soils. In 2014, NPSm treated soils showed the lowest values of diversity for both bacterial and fungal TRFs. In both crop growing seasons, the analysis of phospholipid fatty acid (PLFA) detected the lowest value of total microbial biomass under CK. As PLFA analysis can be used to evaluate total microbial community, this result suggests that fertilisation increased total microbial biomass. When the bacterial and fungal abundance were examined using real time polymerase chain reaction, the results revealed that mineral fertilisation led to decreased bacterial abundance (16S rRNA), while fungal abundance (18S rRNA) was found to be increased in both crop growing seasons. Our results show that mineral fertiliser application has a significant impact on soil properties, bacterial and fungal abundance and microbial diversity. However, further studies are needed to better understand the mechanisms involved in the changes to microbial communities as a consequence of mineral fertilisation.     

The effects of organic and inorganic fertilizer applications to Miscanthus×giganteus,Arundo donax and Phalaris arundinacea,when grown as energy crops in Wales,UK

Two pot trials and one field trial were established to investigate the effects of organic and inorganic fertilizer applications to energy crops grown in mid‐Wales. Chicken litter and sewage cake applied at a high level in excess of MAFF recommendations produced an increased yield response in Miscanthus and Arundo plants. Miscanthus plants exhibited an increased growth response to all fertilizers applied in its second year. Fertilizer applications in accordance with MAFF recommendations produced no significant differences in yields for Miscanthus or Arundo potted plants. In the field there was an increased yield response of Miscanthus to inorganic nitrogen applications compared with organic manures, but not with control plots. Analysis of the Miscanthus plant material at harvest showed significant differences in the nitrogen, potassium and copper content between treatments. No mineral content differences were shown for Miscanthus rhizome material or Arundo plant material. The Phalaris plants did not exhibit significant differences in growth or yield parameters, but their plant matter showed differences in nitrogen, phosphorus, potassium, calcium, sulphur and boron content between treatments.     

Effects of slope aspect and vegetation types on selected soil properties in a dryland Hirmi watershed and adjacent agro‐ecosystem,northern highlands of Ethiopia

This study aimed to determine the spatial variation of topsoil properties as influenced by slope aspects and vegetation types. Three vegetation types and two slope aspects were considered. Disturbed and undisturbed samples were taken from the top soils. A two‐way analysis of variance was used to test significant mean differences (α = 0.05). Results showed that contents of bulk density, total porosity, organic matter and exchangeable magnesium were significantly different with changes in slope aspect (P < 0.05). Textural classes, organic matter, available phosphorus, carbon‐to‐nitrogen ratio, cation‐exchange capacity, per cent base saturation and exchangeable bases demonstrated significant variation among vegetation types (P < 0.05). The south‐facing aspect and the grass vegetation showed higher bulk density but lower organic matter and total porosity. As a remedy for the identified problems, there is a need to undertake plantation of indigenous trees.     

Effects of plant diversity,N fertilization,and elevated carbon dioxide on grassland soil N cycling in a long‐term experiment

The effects of global environmental changes on soil nitrogen (N) pools and fluxes have consequences for ecosystem functions such as plant productivity and N retention. In a 13‐year grassland experiment, we evaluated how elevated atmospheric carbon dioxide (CO₂), N fertilization, and plant species richness alter soil N cycling. We focused on soil inorganic N pools, including ammonium and nitrate, and two N fluxes, net N mineralization and net nitrification. In contrast with existing hypotheses, such as progressive N limitation, and with observations from other, often shorter, studies, elevated CO₂ had relatively static and small, or insignificant, effects on soil inorganic N pools and fluxes. Nitrogen fertilization had inconsistent effects on soil N transformations, but increased soil nitrate and ammonium concentrations. Plant species richness had increasingly positive effects on soil N transformations over time, likely because in diverse subplots the concentrations of N in roots increased over time. Species richness also had increasingly positive effects on concentrations of ammonium in soil, perhaps because more carbon accumulated in soils of diverse subplots, providing exchange sites for ammonium. By contrast, subplots planted with 16 species had lower soil nitrate concentrations than less diverse subplots, especially when fertilized, probably due to greater N uptake capacity of subplots with 16 species. Monocultures of different plant functional types had distinct effects on N transformations and nitrate concentrations, such that not all monocultures differed from diverse subplots in the same manner. The first few years of data would not have adequately forecast the effects of N fertilization and diversity on soil N cycling in later years; therefore, the dearth of long‐term manipulations of plant species richness and N inputs is a hindrance to forecasting the state of the soil N cycle and ecosystem functions in extant plant communities.     

快速城市化地区住宅用地表层土壤有机碳的变异性及其影响因素——以福州南台岛为例

在高分辨率影像提取福州市南台岛(仓山区)住宅用地的基础上,从覆盖研究区的30m×30m网格中随机选择50个样方进行表层土壤取样,进而分析这一快速城市化地区住宅用地表层土壤有机碳密度(Soil organic carbon density,SOCD)的变异特征及其影响因素。结果表明:城市地区住宅用地在剧烈的人类活动干扰下,土壤呈现明显的空间变异特征,其SOCD平均值为33.814t/hm~2,变异系数达72.8%,其中郊区村镇住宅用地0—20cm土层的SOCD高于城市居住用地72%,预示着村镇就地城市化后将造成土壤碳储量的下降;然而,表层土壤有机碳含量与密度在建成时间为0—5年和5—10年的城市住宅小区间无显著差异,只有住宅建成时间达到10—15年才有显著提高。基于湿度、热度、绿化率与物业管理费等因子构建的城市住宅区绿化环境管理质量指标,与城市居住区表层土壤有机碳含量及密度存在显著正相关,与土壤容重呈显著负相关,成为快速城市化地区影响SOCD变异的另一主要因素。     

Impact of land‐use change to Jatropha bioenergy plantations on biomass and soil carbon stocks: a field study in Mali

Small‐scale Jatropha cultivation and biodiesel production have the potential of contributing to local development, energy security, and greenhouse gas (GHG) mitigation. In recent years however, the GHG mitigation potential of biofuel crops is heavily disputed due to the occurrence of a carbon debt, caused by CO₂ emissions from biomass and soil after land‐use change (LUC). Most published carbon footprint studies of Jatropha report modeled results based on a very limited database. In particular, little empirical data exist on the effects of Jatropha on biomass and soil C stocks. In this study, we used field data to quantify these C pools in three land uses in Mali, that is, Jatropha plantations, annual cropland, and fallow land, to estimate both the Jatropha C debt and its C sequestration potential. Four‐year‐old Jatropha plantations hold on average 2.3 Mg C ha^?1 in their above‐ and belowground woody biomass, which is considerably lower compared to results from other regions. This can be explained by the adverse growing conditions and poor local management. No significant soil organic carbon (SOC) sequestration could be demonstrated after 4 years of cultivation. While the conversion of cropland to Jatropha does not entail significant C losses, the replacement of fallow land results in an average C debt of 34.7 Mg C ha^?1, mainly caused by biomass removal (73%). Retaining native savannah woodland trees on the field during LUC and improved crop management focusing on SOC conservation can play an important role in reducing Jatropha's C debt. Although planting Jatropha on degraded, carbon‐poor cropland results in a limited C debt, the low biomass production, and seed yield attained on these lands reduce Jatropha's potential to sequester C and replace fossil fuels. Therefore, future research should mainly focus on increasing Jatropha's crop productivity in these degraded lands.     

A thorough study of a Paratylenchus sp. in glasshouse‐grown lettuce: Characterisation,population dynamics,host plants and damage threshold as keys to its integrated management

In glasshouses practising monoculture of butterhead lettuce in Belgium, high densities of pin nematodes (Paratylenchus spp.) are frequently associated with reduced plant growth. Growers currently apply chemical soil disinfestation measures to manage this problem, although stricter phytosanitary regulations are forcing a shift towards integrated management. Efficient implementation of such management requires knowledge about the factors influencing nematode population dynamics, and the damage threshold for lettuce. The nematode populations in five Belgian glasshouses were monitored for at least 1 year by frequently soil sampling at 0–30 cm and 30–60 cm depth. An undescribed species of Paratylenchus was identified in all glasshouses based on morphological and molecular features. High nematode densities (>20,000 (100 ml soil)^?1) occurred in winter and spring. Chemical soil disinfestation lowered these populations greatly, although up to 14% survived in the deeper soil layer. After soil steaming under negative pressure, no pin nematodes were found. After 2 months of black fallow pin nematode densities were reduced by 50%–76%. Lamb's lettuce, parsley and wild rocket were found to be poor hosts in a pot experiment, while reproduction factors (P_f/P_i) on lettuce cultivars varied between 1 and 3. In three experiments with butterhead lettuce ‘Cosmopolia’ in pots with a series of 9 or 10 densities of Paratylenchus sp. [up to 35,000 (100 ml soil)^?1], no damage to lettuce heads was observed. However, root weight and root quality were reduced, and the corresponding damage thresholds were rather low [1,754 and 362 Paratylenchus sp. (100 ml soil)^?1, respectively]. Management strategies such as crop rotation, soil disinfestation or fallow are recommended to avoid pin nematode population build‐up.