Increased Soil Nitrate Research Articles

Black Plastic Tarps Advance Organic Reduced Tillage I: Impact on Soils, Weed Seed Survival, and Crop Residue

Intensive tillage degrades soil structure, decreases soil organic matter, and can cause soil compaction and erosion over time. Organic vegetable farmers are often dependent on tillage to incorporate crop residue, control weeds, and prepare seedbeds. Black, impermeable, polyethylene tarps applied on the soil surface and removed at planting can help suppress weeds before planting and reduce farmers’ reliance on tillage. However, little is known about how black tarps affect planting conditions and how they can be used to advance reduced tillage production systems. This study investigated the effects of tarp use and tarp duration on the soil environment, surface cover crop residue, and weed suppression to assess the efficacy of using tarps to improve reduced- and no-till practices for organic vegetable production. Experiments were conducted at three sites in the northeastern United States (Freeville, NY; Riverhead, NY; and Monmouth, ME) for 2 years. Following the termination of an oat cover crop, tarps were applied over untilled soils and left in place for four time periods: untarped (control), 3 to 5 weeks (short), 6 to 8 weeks (mid), and 10 or more weeks (long) before two removal dates. Soil moisture and temperature, cover crop residue, soil inorganic nitrogen, weed seed survival, and weed percent cover were measured after tarp removal. Soil moisture and temperature were generally higher under tarps at the time of removal compared with untarped areas at 10% to 55% and 1 to 3 °C, respectively, but the effects were inconsistent. Tarps significantly increased soil nitrate concentrations by 2-times to 21-times with longer tarp durations, resulting in higher concentrations compared with untarped controls. Tarps did not affect the amount of soil covered by cover crop residue and had no consistent effects on weed seed survival of Amaranthus powellii S. Wats. or Chenopodium album L., two common annual weed species in the Northeast. Tarping for at least 3 weeks reduced the weed percent cover by 95% to 100% at the time of removal. Increasing tarp duration beyond 3 weeks did not affect any measures except soil nitrate concentrations. These results indicate that tarps can facilitate the use of reduced-till and no-till practices for organic vegetables by creating a nutrient-rich and moist soil environment free of emerged weeds before planting without soil disturbance.

Field-scale management and environmental drivers of N2O emissions from pasture-based dairy systems

Emissions of N2O from two dairy farms with different grazing intensity responded non-linearly to increasing soil nitrate availability and total rainfall. Higher N2O emissions were observed immediately after grazing, due to the possible increased incidence of N deposition from animal excreta, increased soil compaction and low plant N uptake. The spatial distribution of N2O fluxes and soil nitrate contents reflected the effect of animal treading and excreta N deposition with N2O fluxes in the proximity of field gateways 11 times higher than the field average. Three years average annual N2O emissions were 6 times higher (9.3 ± 2.6 kg N2O-N ha−1 y−1) in the high grazing intensity farm than in the low grazing intensity farm (1.6 ± 0.2 kg N2O-N ha−1 y−1). This corresponded to 2% and 0.9% of the fertiliser N inputs lost as N2O for the high and low intensity farm, respectively. The GHG intensity (N2O emitted per kg of fat and protein corrected milk FPCM) for the intensive system was only almost two times higher than the non-intensive system (0.12 vs 0.08 kg CO2-eq per kg FPCM y−1 for the high and low intensity system, respectively). The high occurrence of N load hotspots near animal gateways in this study underlines the necessity to account for the spatial N variation in dairy grazing systems. Integrating the spatial management of N loads into improved farming practice has therefore significant scope to reduce N2O emissions and N losses from dairy grazing systems.

Comparing the impacts of an invasive grass on nitrogen cycling and ammonia-oxidizing prokaryotes in high-nitrogen forests, open fields, and wetlands

Numerous invasive plant species can increase soil nitrate (NO3−) by altering the nitrification process through plant-soil microbe interactions with ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). We evaluated how the invasive species Microstegium vimineum influenced physico-chemical soil properties, inorganic nitrogen (N) cycling, and AOA and AOB abundances under various environmental conditions. We paired 75 M. vimineum-invaded plots with 75 neighboring reference plots across forests, open fields, and forested wetlands within a state park in the Mid-Atlantic United States that has received high levels of N deposition. Soils were sampled for physico-chemical properties, NO3− and ammonium (NH4+) pools and availability, and AOA and AOB abundances. There were multiple soil impacts associated with M. vimineum across all ecosystems, most consistent were increased soil pH and increased NO3− pools. For other impacts, the directionality and effect sizes varied among ecosystems (e.g. NH4+ pools were 34% lower in forests, 35% lower in open fields, and 90% higher in wetlands relative to reference plots). Finally, forests had nearly all of impacts predicted by a pH-mediated nitrification plant-soil feedback. This study highlights the ability of an invasive grass to alter N cycling and soil properties in forests, open fields, and wetlands that have received high N deposition. We also show how invader-mediated impacts to N cycling may be dependent on the context of the ecosystem being invaded, including its hydrology, ambient soil conditions, and substrate-availability.

Soil nitrification increases with elevated phosphorus or soil pH in an acidic mixed mesophytic deciduous forest

The role of phosphorus (P) mediating nitrogen (N) transformation processes is poorly understood which raises an important question: Does P, like soil pH, have a strong control in altering the cycling of soil N? From 2010 to 2018, pH and/or P availability was elevated with lime and P fertilizer in three mixed mesophytic deciduous forests on the unglaciated portion of the Allegheny Plateau, southeast Ohio, USA. We hypothesized that in addition to soil pH, P addition can influence the cycling of soil N because both can change N dynamics, which can alter nitrification rates. Increasing soil pH increased nitrification and nitrate pools by 30 and 4 times, respectively during the growing season. Furthermore, elevating P also stimulated nitrification and increased soil nitrate pools by 10 and 2 times, respectively. However, the influence of raising soil pH on nitrification was diminished when combined with P addition. Results suggest that N biogeochemical processes are sensitive to P availability, but the mechanistic nature of this relationship appears complex with unclear feedback systems regulating nitrification rates from these deciduous forests.

Growth of comammox Nitrospira is inhibited by nitrification inhibitors in agricultural soils

The discovery of comammox Nitrospira being capable of complete oxidising ammonia to nitrate radically challenged the conventional concept of two-step nitrification. However, the response of comammox Nitrospira to nitrification inhibitors (NIs) and their role in soil nitrification remain largely unknown, which has hindered our ability to predict the efficiency of NIs in agroecosystems. We evaluated the effect of four NIs, 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin), 3,4-dimethylpyrazole phosphate (DMPP), allylthiourea (ATU) and dicyandiamide (DCD) on the growth of comammox Nitrospira, ammonia-oxidising archaea (AOA) and ammonia-oxidising bacteria (AOB) in two pasture and arable soils. The amendment of nitrogen fertiliser significantly increased soil nitrate concentrations over time, indicating a sustaining nitrification activity in both soils. The addition of all the four NIs effectively reduced the production of nitrate in both soils, but to varying degrees during incubation. The abundances of comammox Nitrospira clade A were significantly increased by addition of nitrogen fertilisers and significantly impeded by the four NIs in the pasture soil, but their abundances were only remarkably hindered by nitrapyrin in the arable soil. All the four NIs obviously inhibited the AOB abundances in both soils. Except for DMPP, the other three NIs effectively suppressed the AOA abundances in both soils. We provided new evidence that growth of comammox Nitrospira clade A can be stimulated by nitrogen fertilisers and inhibited by various nitrification inhibitors, suggesting their potential role in nitrification of agricultural soils.

Leaf leachates have the potential to influence soil nitrification via changes in ammonia‐oxidizing archaea and bacteria populations

AbstractSoil nitrogen (N) transformation is mainly controlled by microorganisms. Different plant species have specific effects on soil ammonia‐oxidizing archaea (AOA) and bacteria (AOB). Furthermore, plant secondary metabolites have dramatic influences on soil N transformation and soil ammonia‐oxidizers. However, no study has directly linked the changes in soil AOA and AOB communities to N transformation due to different plant species' leaf leachates, including comparing invasive versus native plants. We selected three invasive species, Wedelia trilobata, Ipomoea cairica and Mikania micrantha, and two native species, Wedelia chinensis and Merremia hederacea, and incubated soil with high and low concentrations of leaf leachates from the five species. Soil N transformation and ammonia oxidizer communities (based on quantitative PCR and 16S rRNA high‐throughput sequencing) were determined. Leaf leachates significantly affected soil N transformation and soil AOA and AOB abundance, and the effects were dependent on the plant species and leachate concentration. The leachate of W. chinensis increased soil net nitrification rates (NNR), whereas that of M. micrantha increased soil nitrate (NO3−) and NNR. The leachate of M. micrantha increased AOB amoA genes, whereas that of M. hederacea decreased AOA amoA genes. At the higher concentration, all leachates showed inhibitory effects on the relative abundance of all AOA taxonomic groups. Phenolics, flavonoids and organic carbon in leaf leachates had a negative correlation with soil NO3−, NNR and the amoA genes of AOA and AOB, whereas NH4+ and NO3− in leachates showed a positive correlation. Among the five species, the invasive species M. micrantha had the strongest positive effect on soil N transformation and AOB abundance. The altered soil ammonia oxidizer communities and modified N process rates induced by leaf leachates provide an explanatory mechanism for the differential effects of plant species on N cycling.Highlights Link changes in soil AOA and AOB to N cycling due to leaf leachates. Specific plants can dramatically alter soil ammonia‐oxidizer presence and abundance. Effects of invasive plants on soil N and AOB are mainly driven by M. micrantha. High concentrations of plant leachates reduced the relative abundance of AOA groups.

秸秆还田配施有机无机肥料对冬小麦土壤水氮变化及其微生物群落和活性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 秸秆还田配施有机无机肥料对冬小麦土壤水氮变化及其微生物群落和活性的影响 DOI: 10.5846/stxb201803190537 作者: 作者单位: 中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划课题（2016YFD0300808，2017YFD0801404）；中国科学院青年创新促进会会员（2017073） Effects of straw incorporation combined with inorganic-organic fertilization on soil water and nitrogen changes and microbial community structure in winter wheat Author: Affiliation: Institute of Geographic Sciences and Natural Resources Research,Institute of Geographic Sciences and Natural Resources Research,Institute of Geographic Sciences and Natural Resources Research,Institute of Geographic Sciences and Natural Resources Research,Institute of Geographic Sciences and Natural Resources Research 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:通过田间试验，研究秸秆还田配施不同肥料对冬小麦土壤的培肥效果以及对土壤水氮环境、酶活性及微生物群落结构的影响，为合理的秸秆还田方式与土壤可持续利用提供决策依据。试验于中国科学院禹城综合试验站进行，以冬小麦为研究对象，玉米秸秆全量还田为基础，设置五个处理，分别为（1）单施化肥（TF），（2）70%化肥+普通有机肥（TM），（3）70%化肥+微生物有机肥（TE），（4）70%化肥+微生物促腐菌剂（TJ），（5）70%化肥+微生物有机肥+微生物促腐菌剂（TEJ）。观测冬小麦生长中的水氮条件，分析小麦收获后土壤环境因子、酶活性以及磷脂脂肪酸（PLFA）变化特征；采用RDA冗余分析，识别环境因子、酶活性与土壤微生物群落结构之间的相关关系，研究秸秆还田与不同施肥方式组合对土壤的培肥效果。结果表明，相较施用化肥（TF），秸秆还田配施微生物有机肥（TE）显著提高了小麦生育后期的土壤含水率（13.3%-20.5%）；施用普通有机肥（TM）能够提高小麦生育后期土壤硝态氮（NO3--N）与铵态氮（NH4+-N）含量；且两者均能提高土壤微生物氮（MBN）与可溶性氮（DON）含量以及β-1，4-葡萄糖苷酶（βG）、纤维二糖水解酶（CBH）活性；但对土壤中酸性磷酸酶（AP）、亮氨酸氨基肽酶（LAP）活性无显著影响。各施肥组合中，TE处理PLFA总量最高（4733.1 ng/g），且微生物群落多样性指数均显著高于TF处理。βG、CBH活性与土壤微生物群落多样性存在正相关关系，MBN与DON与土壤微生物群落多样性关系最为密切，环境因子对微生物群落多样性影响的重要性排序为Moisture > NH4+-N > Avail-P > Temp > NO3--N > pH > EC。秸秆还田配施有机肥与微生物有机肥能合理调节土壤水氮环境，显著提高土壤微生物的数量与活性，有利于土壤生态环境的改善，其中秸秆还田配施微生物有机肥（TE）效果最为显著。 Abstract:Straw incorporation is one of the most important ways of utilizing straw resources. Owing to the differences in soil microenvironments, there are significant differences in the effect of straw incorporation combined with agronomic measures on soil fertility improvement. A field experiment was conducted to determine the effects of straw incorporation combined with inorganic-organic fertilizers on soil fertility improvement, water and nitrogen changes, enzyme activities, and microbial community structures in winter wheat, which provided the theoretical and technical foundation to formulate methods for straw incorporation and sustainable utilization of soil. The experimental field was located in the Yucheng Comprehensive Experiment Station of the China Academy of Sciences, Shandong Province, which has a summer maize-winter wheat rotation system. With winter wheat as the research object and maize straw returning to field as the basis, five treatments were carried out in the field experiment:(1) chemical fertilizer (TF), (2) 70% chemical fertilizer plus organic fertilizer (TM), (3) 70% chemical fertilizer plus microbial organic fertilizer (TE), (4) 70% chemical fertilizer plus microbial decomposition agent (TJ), and (5) 70% chemical fertilizer plus microbial organic fertilizer and microbial decomposition agent (TEJ). Soil water and nitrogen conditions during wheat growth were observed. After the winter wheat harvest, soil environmental factors, soil enzyme activity, and microbial phospholipid fatty acids (PLFA) of the topsoil in the different treatments were measured to understand their variation characteristics. Usingadopted canonical correlation analysis, the correlation of soil environmental factors and soil enzyme activities with soil microbial community structure was analyzed to determine soil fertility improvement by straw incorporation combined with inorganic-organic fertilizations. The results of the field experiment showed that more than the application of chemical fertilizers (TF), the application of microbial organic fertilizers (TE) significantly increased soil moisture (13.3%-20.5%) at later developing stages. The application of organic fertilizers (TM) increased soil nitrate nitrogen (NO3--N) and ammonium nitrogen (NH4+-N) contents at later developing stages. TM and TE also improved the concentration of microbial nitrogen (MBN) and dissolved nitrogen (DON), as well as the activities of soil β-glucosidase (βG) and cellobiohydrolase (CBH), whereas the activities of soil acid phosphatase (AP) and leucine aminopeptidase (LAP) in the treatments were not significantly different. The TE treatment showed the highest total amount of PLFA (4733.1 ng/g), and the microbial community diversity indexes of the TE treatment were significantly higher than those of the TF treatment. The results of the statistical analysis revealed that the activities of soil βG and CBH were positively correlated with soil microbial community and that the concentrations of MBN and DON were most closely related to soil microbial community. The canonical variables ordering result showed that the effect of soil physicochemical property on soil microbial community was Moisture > NH4+-N > Avail-P > Temp > NO3--N > pH > EC. These findings showed that straw incorporation combined with the application of organic fertilizer and microbial organic fertilizer reasonably regulated soil water and nitrogen conditions, increased the population and activity of soil microbes and the activity of soil enzymes, as well as helped improve the soil eco-environment. Among the treatments, TE (straw incorporation combined with the application of microbial organic fertilizer) showed the most significant effect. 参考文献 相似文献 引证文献

Effects of mulching measures on soil moisture and N leaching potential in a spring maize planting system in the southern Loess Plateau

A field experiment was conducted in the southern gully region of the Loess Plateau to study the effects of mulching measures on spring maize yield and nitrate accumulation in dryland areas under traditional tillage conditions. The study was performed to provide a scientific basis for spring maize planting and environmental protection in this area. The four treatments were non–mulching (CK), plastic film–mulching during the growth period (PM1), plastic film–mulching during the fallow period (PM2), and straw–mulching (JM). After 13 years of continuous application, the yield of spring maize, the nitrogen uptake by plants, and the nitrate nitrogen content at the harvest stage were measured. The results revealed that soil moisture content and water storage capacity of the three soil–mulching treatments were all higher than those of the non–mulching treatment. Soil water storage at a depth of 0–300 cm in the JM, PM1 and PM2 treatments was increased by 11.8%, 10.6% and 8.8%, respectively, compared with the CK treatment. Compared with the CK treatment, the mulching treatments significantly increased the aboveground biomass and grain yield of spring maize. The yield enhancement effect of the PM1 treatment was the most significant, with a yield of 1.1 Mg ha-1 and an increase of 26.72%. In addition to the JM treatment, the accumulation of soil nitrate at a depth of 0–300 cm in the PM1 and PM2 treatments was less than that of the CK treatment, but the largest increase in soil nitrate (80.20% in the JM treatment) was observed at a depth of 0–100 cm. The results suggest that in the rainfed agriculture in the southern Loess Plateau, mulching cultivation can effectively increase the soil moisture content and water storage capacity. PM1, and PM2 treatments could significantly reduce the content and accumulation of nitrate nitrogen in the deeper soil profile, and the three mulching measures could slow down the deep accumulation of soil nitrate nitrogen to a certain extent.

Variation in Soil Properties Regulate Greenhouse Gas Fluxes and Global Warming Potential in Three Land Use Types on Tropical Peat

This study investigated spatial factors controlling CO2, CH4, and N2O fluxes and compared global warming potential (GWP) among undrained forest (UDF), drained forest (DF), and drained burned land (DBL) on tropical peatland in Central Kalimantan, Indonesia. Sampling was performed once within two weeks in the beginning of dry season. CO2 flux was significantly promoted by lowering soil moisture and pH. The result suggests that oxidative peat decomposition was enhanced in drier position, and the decomposition acidify the peat soils. CH4 flux was significantly promoted by a rise in groundwater level, suggesting that methanogenesis was enhanced under anaerobic condition. N2O flux was promoted by increasing soil nitrate content in DF, suggesting that denitrification was promoted by substrate availability. On the other hand, N2O flux was promoted by lower soil C:N ratio and higher soil pH in DBL and UDF. CO2 flux was the highest in DF (241 mg C m−2 h−1) and was the lowest in DBL (94 mg C m−2 h−1), whereas CH4 flux was the highest in DBL (0.91 mg C m−2 h−1) and was the lowest in DF (0.01 mg C m−2 h−1), respectively. N2O flux was not significantly different among land uses. CO2 flux relatively contributed to 91–100% of GWP. In conclusion, it is necessary to decrease CO2 flux to mitigate GWP through a rise in groundwater level and soil moisture in the region.

Control of soil N cycle processes by Pteridium aquilinum and Erica cinerea in heathlands along a pH gradient

AbstractNitrate is a limiting resource in heathland acid soils. Nitrate levels increase in heathland soils after Pteridium aquilinum invasions, and this species is assumed to biologically control nitrogen cycle processes, thus increasing nitrate availability. We compared how P. aquilinum (bracken) and Erica cinerea (bell heather) modify processes driving nitrate availability along a soil pH gradient in a Natura 2000 reserve facing bracken invasion. Soil nitrate and ammonium concentrations, substrate‐induced respiration (SIR), denitrification and nitrification enzyme activities (DEA and NEA, respectively), root procyanidin concentrations, and denitrification inhibition by procyanidins were measured on five sites under P. aquilinum and E. cinerea stands. NEA and nitrate levels were higher, and ammonium levels and SIR lower, for P. aquilinum in the most acid soils. Procyanidins from both species induced the same level of denitrification inhibition, soil nitrate being correlated with root procyanidin concentration for both species. Soil nitrate correlated with NEA only for P. aquilinum. Our results show that both species increased procyanidin production in the most acid soils, thereby reducing denitrification and decreasing nitrate loss, this process being more efficient for E. cinerea. However, P. aquilinum additionally increased nitrification, and this double control on nitrification and denitrification was very efficient to increase soil nitrate availability in the most acid soils. This may participate to the success of P. aquilinum invasions in heathlands. This shows that approaches for bracken control in heathlands should better account for belowground processes and, more generally, that biological denitrification inhibition by plants may be a widespread phenomenon influencing soil N dynamics in N‐poor environments.

Circular economy fertilization: Testing micro and macro algal species as soil improvers and nutrient sources for crop production in greenhouse and field conditions

Nutrient losses from agricultural land to freshwater and marine environments contribute to eutrophication and often to the growth of algal blooms. However, the potential benefits of recycling this algal biomass back to agricultural land for soil quality and crop nutrition in a “circular-economy” has received little attention. We tested the effects of algal additions to arable soil in greenhouse-grown garden peas, and field plots of spring wheat, on plant growth and nutrition and physical and chemical properties of the soil. Representatives of five algal species, which contrasted in elemental composition, were applied at 0.2, 2 and 4 g kg−1 in the greenhouse and at 24 g m2 in the field. These included the cyanobacteria Arthrospira platensis (Spirulina), the unicellular green algae Chlorella sp., the red seaweed Palmaria palmata, and the brown seaweeds Laminaria digitata and Ascophyllum nodosum. In the greenhouse at the highest application rates (4 g kg−1), Chlorella sp., and Spirulina increased soil total nitrogen and available phosphorus, and Spirulina also increased soil nitrate concentrations. P. palmata and L. digitata significantly increased soil inorganic (NH4+ and NO3−) concentrations under all three application rates. Chlorella sp. significantly increased soil total P, N and C, available P, NH4+-N, and pea yield. Soil water-stable aggregates were unchanged by the algal additions in both the greenhouse and field study. In the field, 4 species (Chlorella sp. Spirulina, P. palmata and L. digitata) increased soil inorganic nitrogen concentrations, confirming their potential to recycle mineralizable nitrogen to agricultural soils, but no significant effects were found on wheat yields under the application rates tested.

Black Plastic Mulch or Herbicide to Accelerate Bur Oak, Black Walnut, and White Pine Growth in Agricultural Riparian Buffers?

This study was conducted in a riparian buffer bordering a 1 km segment of a headwater stream crossing a pasture site located in southern Québec (Canada). Three species were planted (black walnut (Juglans nigra L.), bur oak (Quercus macrocarpa Michx.), and eastern white pine (Pinus strobus L.)) with three vegetation treatments (control, herbicide (one application/year for 3 years), and black plastic mulch)). The main objective was to determine to which extent herbicide and plastic mulch, used with species having different ecological characteristics, affect tree growth and soil nutrient status in riparian buffers. Survival was high (>93%) for all species in all treatments. In the control (no vegetation treatment), growth was similar among species. Black walnut had the strongest growth response to herbicide and plastic mulch, and white pine had the weakest. For all species, growth was similar in the herbicide and the plastic mulch treatments. During the fifth growing season, plastic mulch increased soil nitrate and phosphorus compared to the herbicide treatment. In the plastic mulch treatment, higher soil nitrate supply was observed for species that preferentially uptake ammonium (black walnut and white pine). Soil nutrient supplies were similar between the control and herbicide treatments. Despite the more favorable nutritional conditions it provides, permanent black plastic mulching does not provide higher growth benefits after 5 years than a 3-year herbicide treatment. The high soil nitrate supply observed in mulched black walnut and mulched white pine may indicate a limited capacity for nitrate phytoremediation by these species.

Effect of Nitrate Leaching Caused by Swine Manure Application in Fields of the Yellow River Irrigation Zone of Ningxia, China

A five-year swine manure application trial and a study of nitrate leaching losses have been conducted. There were three treatments: traditional without manure (CK), traditional matched manure 4500 kg ha−2 (T1) and traditional matched manure 9000 kg ha−2 (T2). Nitrate nitrogen leaching losses at the 30-, 60-, and 90-cm soil layers were measured using the resin core method. The results indicate that the swine manure application did not noticeably increase soil nitrate leaching losses in the 30-cm layer. T1 (16.85 ± 0.40 kg ha−2) and T2 (17.01 °C0.46 kg ha−2) were not significantly different than CK (15.96 ± 0.41 kg ha−2) (P < 0.05), which was also the case at the 60-cm layer. However, there are significant differences between the treatments and CK at the 90-cm layer, although there were no significant differences between T1 and T2 in that layer. The application of manure can increase soil organic matter (SOM) and total nitrogen (TN). The SOM of T1 and T2 were increased to 0.95 g kg−1 and 1.41 g kg−1, respectively. The TN values of CK, T1 and T2 were 0.72, 0.78 and 0.88 g kg−1, respectively, in the 0 to 30 cm layer, and were improved by 7.72% and 22.04%.

Areas of residential development in the southern Appalachian Mountains are characterized by low riparian zone nitrogen cycling and no increase in soil greenhouse gas emissions

The critical role streamside riparian zones play in mitigating the movement of nitrogen (N) and other elements from terrestrial to aquatic ecosystems could be threatened by residential development in the southern Appalachian Mountains. Many studies have investigated the influence of agriculture on N loading to streams but less is known about the impacts of residential development. Here we consider the dynamics of changing riparian land use in the southern Appalachians that includes increased residential development at the expense of both forests and agriculture. We hypothesized that increased inputs of inorganic N from residential development will increase nitrogen cycling rates relative to forests, thereby preventing terrestrial N retention and increasing soil nitrate losses through leaching. In addition, we hypothesized that such development will increase emissions of N2O, CO2, and CH4, all potent greenhouse gases. We found riparian soil potential N cycling rates as well as N2O and CO2 efflux to be much greater with agricultural land use compared to either forested or residential land use. Our data suggest that residential development of forested riparian ecosystems does not increase N cycling or removal and, thus, might allow for greater potential N leaching into streams. Both agricultural and residential land use exhibited CH4 efflux while forested ecosystems were responsible for CH4 uptake. Overall, regional greenhouse gas emissions are projected to decline as high N2O and CO2 emitting agricultural land is converted to residential use.

A Forest Tent Caterpillar Outbreak Increased Resource Levels and Seedling Growth in a Northern Hardwood Forest.

In closed-canopy forests, gap formation and closure are thought to be major drivers of forest dynamics. Crown defoliation by insects, however, may also influence understory resource levels and thus forest dynamics. We evaluate the effect of a forest tent caterpillar outbreak on understory light availability, soil nutrient levels and tree seedling height growth in six sites with contrasting levels of canopy defoliation in a hardwood forest in northern lower Michigan. We compared resource levels and seedling growth of six hardwood species before, during and in the three years after the outbreak (2008–2012). Canopy openness increased strongly during the forest tent caterpillar outbreak in the four moderately and severely defoliated sites, but not in lightly defoliated sites. Total inorganic soil nitrogen concentrations increased in response to the outbreak in moderately and severely defoliated sites. The increase in total inorganic soil nitrogen was driven by a strong increase in soil nitrate, and tended to become stronger with increasing site defoliation. Seedling height growth increased for all species in the moderately and severely defoliated sites, but not in lightly defoliated sites, either during the outbreak year or in the year after the outbreak. Growth increases did not become stronger with increasing site defoliation, but were strongest in a moderately defoliated site with high soil nutrient levels. Growth increases tended to be strongest for the shade intolerant species Fraxinus americana and Prunus serotina, and the shade tolerant species Ostrya virginiana. The strong growth response of F. americana and P. serotina suggests that recurring forest tent caterpillar outbreaks may facilitate the persistence of shade intolerant species in the understory in the absence of canopy gaps. Overall, our results suggest that recurrent canopy defoliation resulting from cyclical forest insect outbreaks may be an additional driver of dynamics in temperate closed-canopy forests.

Precipitation overrides warming in mediating soil nitrogen pools in an alpine grassland ecosystem on the Tibetan Plateau.

Soils in the alpine grassland store a large amount of nitrogen (N) due to slow decomposition. However, the decomposition could be affected by climate change, which has profound impacts on soil N cycling. We investigated the changes of soil total N and five labile N stocks in the topsoil, the subsoil and the entire soil profile in response to three years of experimental warming and altered precipitation in a Tibetan alpine grassland. We found that warming significantly increased soil nitrate N stock and decreased microbial biomass N (MBN) stock. Increased precipitation reduced nitrate N, dissolved organic N and amino acid N stocks, but increased MBN stock in the topsoil. No change in soil total N was detected under warming and altered precipitation regimes. Redundancy analysis further revealed that soil moisture (26.3%) overrode soil temperature (10.4%) in explaining the variations of soil N stocks across the treatments. Our results suggest that precipitation exerted stronger influence than warming on soil N pools in this mesic and high-elevation grassland ecosystem. This indicates that the projected rise in future precipitation may lead to a significant loss of dissolved soil N pools by stimulating the biogeochemical processes in this alpine grassland.

Exotic invasive plants increase productivity, abundance of ammonia‐oxidizing bacteria and nitrogen availability in intermountain grasslands

Summary Exotic plant invasion is often associated with dramatic increases in above‐ground net primary productivity and soil nitrogen. However, most evidence for these increases comes from correlative studies of single species, leaving open the question of whether invasive plants drive these processes and whether they are consistent among invaders. We combined field surveys and measurements within experimental plantings to examine how plant productivity, soil nitrogen and the abundance of ammonia‐oxidizing bacteria (AOB) change in response to invasions by four exotic species. The relationship between plant productivity and soil nitrate differed among native and invasive species, suggesting a fundamental disparity in the effects of natives and invaders on ecosystem processes. In field surveys, dense patches of all invasive species had higher abundances of AOB than native‐dominated sites. Three of the four invasive species had higher productivity, soil nitrate concentrations and rates of potential nitrification as compared to nearby native‐dominated communities. In our experimental plantings, we found that two invasive species drove increases in soil nitrate and one invader caused increased productivity after a single season. Synthesis. Our results highlight the importance of the N cycling soil microbial community in how exotic invasive plants alter ecosystem function and show that shifts in function can occur rapidly.

A Combination of Biochar-Mineral Complexes and Compost Improves Soil Bacterial Processes, Soil Quality, and Plant Properties.

Organic farming avoids the use of synthetic fertilizers and promises food production with minimal environmental impact, however this farming practice does not often result in the same productivity as conventional farming. In recent years, biochar has received increasing attention as an agricultural amendment and by coating it with minerals to form biochar–mineral complex (BMC) carbon retention and nutrient availability can be improved. However, little is known about the potential of BMC in improving organic farming. We therefore investigated here how soil, bacterial and plant properties respond to a combined treatment of BMC and an organic fertilizer, i.e., a compost based on poultry manure. In a pakchoi pot trial, BMC and compost showed synergistic effects on soil properties, and specifically by increasing nitrate content. Soil nitrate has been previously observed to increase leaf size and we correspondingly saw an increase in the surface area of pakchoi leaves under the combined treatment of BMC and composted chicken manure. The increase in soil nitrate was also correlated with an enrichment of bacterial nitrifiers due to BMC. Additionally, we observed that the bacteria present in the compost treatment had a high turnover, which likely facilitated organic matter degradation and a reduction of potential pathogens derived from the manure. Overall our results demonstrate that a combination of BMC and compost can stimulate microbial process in organic farming that result in better vegetable production and improved soil properties for sustainable farming.

Wood base biochar alters inorganic N

Sustainable nut production and supply depend on soil nutrient availability, but current land management practices in macadamia farms, including soil erosion and minimal inter row groundcover in established orchards can reduce soil carbon (C) and impair soil fertility. Therefore, nut production in macadamia orchards relies heavily on inorganic and organic fertiliser application which brings an economic burden for farmers. Biochar, a C rich product from the pyrolysis of organic residues, has been shown to improve soil fertility and fertiliser use efficiency. In the current study, we aimed to explore the effects of a wood-based biochar at two application rates of 10 t ha-1 (B10) and 30 t ha-1 (B30) on soil C and nitrogen (N) cycling at months 0, 6, 12, 18 and 24 following its application to a macadamia orchard. No significant effects of biochar on soil soluble organic C and N were observed at months 0, 6 and 12 following biochar application. At months 12, 18 and 24, biochar significantly increased soil nitrate concentration with B30 compared to the control and B10 but differences were significant only at month 12.; ;

Effect of greenhouse soil bio-disinfection on soil nitrate content and tomato fruit yield and quality

Intensive horticultural practices in the greenhouse can cause proliferation of soil phytopathogenic organisms and pollution of groundwater from nitrate leaching. Among the different soil disinfection techniques, bio-disinfection through the addition of organic amendments (OA), with subsequent solarisation (biosolarisation) or without (biofumigation), is an efficient and economically viable alternative for the control of soil pathogens. This greenhouse experiment was conducted to initiate the process of conversion of a conventional tomato culture to organic farming. The effects of OA applied through biofumigation and biosolarisation in the first season on soil nitrate concentration and tomato fruit yield and quality were evaluated with the following treatments: control, no OA; T1, 0.3 kg m–2 of dehydrated pellets of Brassica carinata seed meal; T2, 0.8 kg m–2 of packaged and dehydrated B. oleracea var. italica; T3, T2 + 0.15 kg m–2 of dehydrated poultry manure; T4, T1 + 0.16 L m–2 of microbial cocktail. The experiment was carried out over the autumn crop cycle of two seasons (2011–12, 2012–13). Addition of OA increased soil nitrate concentration, more so with biosolarisation. Total and marketable yield of tomato and number of marketable fruits were higher in the biosolarised plots in the first crop after treatments. No effects were observed in the second crop after treatments. Except for tomato fruit firmness, quality attributes (size, soluble solids, acidity and colour) improved with some OA treatments. The supply of OA through biosolarisation is a soil disinfection technique with potential to minimise the impact of nitrate leaching and to provide improved yield and quality of tomatoes.