Buried Bags Research Articles

Biodegradable plastic film mulch increases the mineralisation of organic amendments and prevents nitrate leaching during the growing season in organic vegetable production

AbstractIntroductionOrganic vegetable production relies on inputs of organic forms of nitrogen (N). This presents a challenge as it needs to be mineralised by the soil microbial community. Difficulties matching the timing and rate of organic N amendments to crop demand could potentially lead to high rates of nitrate leaching. The use of plastic film mulch (PFM) has the potential to increase crop yield, accelerate N mineralisation, reduce rainfall infiltration and therefore N leaching. Biodegradable PFM reduces the risk of contaminating soil with plastics. Although these positive effects have been proven in major conventionally grown commodity crops, the effects of PFMs are poorly understood in organic vegetable crops, particularly in moist temperate climates prone to N losses via winter leaching.Materials & MethodsOur plot‐scale field experiment attempted to quantify the effect of biodegradable PFM on N leaching and N mineralisation in organic lettuce production in the presence and absence of biodegradable PFM. It took place in one season within a longer‐term experimental organic vegetable rotation.ResultsWe used two methods to measure the rate of carbon and N mineralisation: the buried bag method showed biodegradable PFM resulted in no additional N mineralisation; however, the ion exchange membrane method indicated an increase in N mineralisation of 30%. During heavy rainfall at the end of the growing season, nitrate leaching was observed only in the non‐PFM plots, leading to N losses equivalent to 6.3 g N m−2. This led to surplus mineral N at harvest of 18.1 g N m−2 in the PFM treatment and 8.6 g N m−2 in the corresponding unmulched plots. This did not lead to more leaching in the mulched plots in the following 6 months.ConclusionIn conclusion, our evidence supports the use of biodegradable PFMs to enhance the sustainability of organic vegetable production systems in temperate climates.

Overcoming ecological feedbacks in seagrass restoration

Overcoming ecological feedbacks is a major limiting factor reducing the success of many seagrass restoration projects. Negative feedbacks occur when biotic or abiotic conditions of a site are changed sufficiently after the loss of seagrass to prevent its recovery, even after the original stressors are remediated. While negative feedbacks in seagrass restoration are common, there remain limited studies of ways to reduce them and kick‐start the necessary positive feedbacks to promote recovery. We used field and laboratory experiments to investigate key ecological feedbacks in seagrass (Zostera marina) restoration by testing the role of hessian bags and seed burial in reducing seed predation and promoting plant development. We used a double‐hurdle model approach to predict “seagrass emergence success” and “seagrass growth success” across planted field plots. We found that planting seeds in hessian bags and burying them in the sediment improved the likelihood of seeds developing into mature plants. We recorded an average 13‐fold increase in shoot density for seeds planted in buried bags relative to raked furrows. This could be the combined result of reduced predation as well as bags mimicking emergent traits of mature seagrass to withstand physical impacts. We supplement these findings with laboratory evidence that hessian bags provide protection from predation by green shore crabs. Overall, we found a low and variable success rate for seed‐based restoration and indicate other feedbacks in the system beyond those we controlled. However, we show that small methodological changes can help overcome some key feedbacks and improve restoration success.

Predicting nitrogen mineralization from dairy manure and broadleaf residue in a semiarid cropping system

AbstractApproximately 37% of US milk production occurs in semiarid regions, providing an opportunity to recycle manure nutrients through a variety of cropping systems. Accurate prediction of nitrogen (N) mineralization is critical to determine manure application suitability in intensive irrigated agriculture as many crops in the region have quality parameters that are sensitive to N. Research was conducted in southcentral Idaho to evaluate N mineralization via a buried bag methodology to develop a predictive N‐mineralization model. The study was arranged in a randomized complete block design with manure application rates of 18, 36, and 52 Mg·ha−1 (dry weight basis) both annually and biennially with synthetic fertilizer and untreated check treatments. The crop rotation included small‐grain and broadleaf crops. In the final year of the study, preplant soil organic carbon, total nitrogen, and NO3–N concentrations were positively linearly correlated with manure application rate. Nearly five times as much N was mineralized annually in the 0‐ to 30‐cm depth as compared to the 30‐ to 60‐cm depth. Increased rates of N mineralization for each kilogram of added N occurred in years when residue from broadleaf crops (slope = 0.17) was applied as compared to years with manure only application (slope = 0.07). Stepwise modeling determined that the most predictive model for seasonal N mineralization (R2 = 0.79) included manure N, residue N, soil organic matter, and electrical conductivity. These results allow preplant N mineralization estimation and will prove critical for managing manure in semiarid regions for agronomic, economic, and environmentally sound crop production.

Nitrogen mineralization following fall‐applied compost to subsurface drip‐irrigated processing tomatoes in California

AbstractOrganic wastes diverted from landfills can reduce greenhouse gas emissions and are used as supplemental nutrient sources for agricultural crops after they are composted. In California, compost should be applied in the fall to processing tomatoes (Solanum lycopersicum L.) to avoid delaying field preparation and transplanting in the spring. The objective of this study was to determine soil nitrogen (N) mineralization following fall application of greenwaste compost (GWC) based on the change of mineral N during a 4 month in‐field buried bag soil incubation in 2 prospective subsurface drip‐irrigated processing tomato fields (PTF1 and PTF2). GWC rates of 0, 11, 22, and 34 Mg ha−1 were evaluated in PTF1 and PTF2 in October 2019. Very dry surface soil conditions in fall 2019 and the disruptive procedure used to prepare soil for in‐field incubation using the buried bag method led us to calculate net N mineralization after adjusting for the initial mineral N concentration of the unamended (0 Mg ha−1) control. The adjusted net N mineralization was significantly less in PTF1 (8.6 mg N kg−1) than PTF2 (16.4 mg N kg−1) and the estimated net N mineralization rate of the surface 0–15 cm soil depth following GWC application to PTF1 was less than PTF2 (1.6–1.9 vs. 2.3–3.1 kg N ha−1 week−1). In‐field incubation requires soil disturbance that likely affected N mineralization and additional research should consider the feasibility of using pretreatments or pre‐incubations to account for disruption to antecedent soil conditions.

Nitrogen and Carbon Mineralization from Green and Senesced Leaf Litter Differ between Cycad and Angiosperm Trees.

Plant leaf litter decomposition is directly influenced by the identity of the source plants and the leaf age. Defoliation of forests by tropical cyclones (TC) transfers copious amounts of high-quality green leaf litter to soils. We used a soil amendment approach with the incubated buried bag method to compare carbon (C) and nitrogen (N) mineralization dynamics of green and senesced leaf litter from cycad Cycas micronesica and angiosperm Morinda citrifolia trees on the island of Guam. Soil priming increased the decomposition of pre-existing organic C, and were greater for green leaf litter additions than senesced leaf litter additions. Available N content increased by day 14 and remained elevated for the entire 117-d incubation for soils amended with green M. citrifolia litter. In contrast, available N content increased above those in control soils by day 90 and above those in soils amended with senesced litter by day 117 for green C. micronesica litter. The net N mineralization rate was higher than control soils by 120% for the senesced litter treatments and 420% for the green litter treatments. The results reveal a complex but predictable interplay between TC defoliation and litter quality as defined by tree identity. We have illuminated one means by which increased frequency of intense TCs due to climate change may alter the global C and N cycles.

Mid-term effects of wildfire and salvage logging on gross and net soil nitrogen transformation rates in a Swedish boreal forest

Wildfires are natural and important disturbances of boreal forest ecosystems, and they are expected to increase in parts of the boreal zone through climate warming. There is a broad understanding of the immediate effects of fire on soil nitrogen (N) transformation rates, but less is known about these effects several years after fire. In July 2014, a large wildfire in the boreal forest zone of Central Sweden took place. Four years after the wildfire, we measured processes linked to the soil N cycle using the 15N pool dilution method (for gross N mineralization, consumption and nitrification) and the buried bags method (for net N mineralization), in soils from stands of different fire severity that had or had not been subjected to salvage logging. Gross N mineralization and consumption rates per unit carbon (C) increased by 81 % and 85 % respectively, in response to high fire severity, and nitrification rates per unit C basis decreased by 69 % in response to high fire severity, while net N mineralization was unresponsive. There was no difference in the effect of salvage logging across stands of differing fire severity on N transformation rates, although concentrations of resin adsorbed nitrate (NO3–) were overall 50 % lower in logged compared to unlogged stands. We also found that irrespective of burn severity, N immobilization rates exceeded N nitrification rates, and immobilization was therefore the dominant pathway of gross N consumption. Gross N consumption rates were higher in burned than unburned stands, despite there being a higher active microbial biomass in unburned soil, which suggests an even higher immobilization of N over time as the microbial biomass recovers following fire. Our study shows that soil N transformation rates were more affected by changes in fire severity than by salvage logging, and that four years after the fire many aspects of the N cycle did not differ between burned and unburned stands, suggesting substantial resilience of the N cycle to fire and salvage logging. However, we note that long term impact and many additional ecosystem properties or processes should be evaluated before concluding that salvage logging has no ecosystem impact. Furthermore, shortened fire regimes following climate warming accompanied with shorter intervals between salvage logging practices, could still impact the capability for the N cycle to recover after an intense fire. While wildfire in the boreal region results in a shift from nutrient conserving to nutrient demanding plant species, our results suggest this shift is dependent on a relatively short-lived pulse of higher N cycling processes that would have likely dissipated within a few years after the fire.

The advancing mycelial frontier of ectomycorrhizal fungi.

This article is a Commentary on Hagenbo et al. (2021), 230: 1609–1622.

Proximity to charred logs in burned forests likely affects decomposition processes in the soil

We studied the spatial decomposition rates of standardised organic substrates in soils (burned boreal pine-dominated sub-xeric forests in eastern Finland), with respect to charred and non-charred coarse woody debris (CWD). Decomposition rates of rooibos plant litter inside teabags (C:N = 42.870 ± 1.841) and pressed-sheet Nordic hardwood pulp (consisting of mainly alpha-cellulose) were measured at 0.2 m distance from 20 charred (LC0.2) and 40 non-charred logs (LNC0.2). We also measured decomposition at 60 plots located 3–10 m away from downed logs (L3,10). The rooibos decomposition rate constant ‘k’ was 8.4% greater at the LNC0.2 logs than at the L3,10 or LC0.2 logs. Cellulose decomposed more completely in 1 micron mesh bags at LNC0.2 (44% of buried bags had leftover material) than at LC0.2 (76%) or L3,10 (70%). Decomposition of cellulose material was rapid but varied greatly between sampling plots. Our results indicate that decomposition of the standardised organic matter was more rapid close to CWD pieces than further away. However, only the plots located near non-charred logs (LNC0.2) exhibited high decomposition rates, with no corresponding increase observed at the charred logs (LC0.2). This suggests a possible noteworthy indirect effect of forest burning on soil organic matter (SOM) decomposition rates close to charred CWD after forest fires. We urge for more studies on this tentative observation as it may affect the estimates on how fires affect carbon cycling in forests.

Blunt olfaction in sexually sluggish male rats.

Among the intact male rats, a subpopulation has been found to show little or no sexual behavior, even after experiencing several mating sessions. This study investigated whether sexually sluggish (SS) males show behavioral differences from normal copulatory (NC) males, other than those concerning sexual behavior. The olfactory preference of males was measured through the time spent displaying nose-poking behavior directed at sexually active males and estrous females for odor exploration in a three-chamber apparatus. Both the NC and SS males showed a significant preference for the odor of estrous females compared with that of male odors. However, SS males spent significantly less time nose-poking estrous females than NC males. The food-finding test was performed after overnight fasting. Our findings showed that all the NC males found the buried pellet within 5 min, whereas over 60% of the SS males failed to find it. The males were also tested for their ability to find a buried bag containing soiled bedding from estrous female cages. The bag was found by 80% of NC males, but only by 20% of SS males. Our results suggest that SS and NC male rats differ not only in sexual behavior but also in other functions such as olfaction.

The impact of cover crop shoot decomposition on soil microorganisms in an apple orchard in northeast China

Mowing can facilitate the incorporation of cover crop shoots into soil and improve the properties of soils in apple orchards. This article evaluated how apple orchard soil responds to the decomposition of the shoot residues of three cover crops[native mixed herbs (NMS), red clover (RCS), and ryegrass (RES)] in terms of microbial metabolism and biomass, and discussed the relationships between microbial responses and shoot chemistry. The chemical composition of shoots was analysed and a buried bag experiment was carried out to simulate shoot decomposition in an apple orchard. The results revealed significant differences in the chemical compositions and shoot C:N ratios (NMS: 10.9, RCS: 19.1, and RES: 12.9) of the three cover crops. The decomposition of the cover crop shoots promoted microbial metabolism and boosted soil bacterial reproduction (increase in the biomass indicator muramic acid: 19.44, 124.15, and 14.83 mg kg−1, respectively. But there are different types of effects on soil fungal reproduction (change in the biomass indicator glucosamine: 712.51, 887.45, and 103.97 mg kg−1), and they are obviously negative, significantly positive, and non-significant respectively. Thus, the native mixed herbs and red clover are preferable swards for better shoot enhancement in apple orchard.

宁南山区典型植物根系分解特征及其对土壤养分的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 宁南山区典型植物根系分解特征及其对土壤养分的影响 DOI: 10.5846/stxb201710101807 作者: 作者单位: 西北农林科技大学,西北农林科技大学,中国科学院水利部水土保持研究所,西北农林科技大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然基金面上项目（41671280）；国家十二五科技支撑（2015BAC01B01） Effects of typical plant root decomposition on soil nutrients in southern Ningxia Author: Affiliation: North West Agriculture and Forestry University,North West Agriculture and Forestry University,Institute of Soil and Water Conservation, Chinese Academy of Sciences,North West Agriculture and Forestry University Fund Project: The National Natural Science Foundation of China (General Program, Key Program, Major Research Plan) 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:根系分解是陆地生态系统碳和养分循环的重要地下生态过程，研究宁南山区典型植物根系分解特征及其对土壤养分的影响，能够丰富和完善陆地生态系统的物质和能量循环机制，为我国黄土高原植被恢复过程中植物与土壤之间的养分循环提供依据。连续2年研究了宁南山区3种典型植物（长芒草、铁杆蒿和百里香）根系的分解特征及其对土壤养分的影响。结果表明，长芒草、铁杆蒿和百里香根系年分解指数（K）分别0.00891、0.01128、0.01408，分解速率依次表现为百里香 > 铁杆蒿 > 长芒草。分解16个月后3种典型植物根系释放大量养分，其中碳的释放量在57.05-124.39 g/kg；氮的释放量在0.12-0.47 g/kg。3种典型植物根系对土壤养分的影响主要表现为：试验结束时，0-5 cm表层土壤有机碳含量提高了0.17-0.35 g/kg，5-20 cm土层土壤有机碳含量提高了0.26-0.35 g/kg。相关性分析可知，植物根系养分释放量与土壤养分含量之间存在一定的负相关关系，当土壤养分含量较低时，根系会增加养分释放量进行补充。由此可知，根系分解提高了土壤养分含量，有效的促进了养分在根系-土壤中的循环。 Abstract:Root decomposition is an important underground ecological process of carbon and nutrient cycling in terrestrial ecosystems. Studying the root decomposition characteristics of typical plants and their effects on soil nutrients in the mountainous area of southern Ningxia can provide a basis for nutrient cycling between plants and soil in vegetation restoration in Loess Plateau of China. The decomposition characteristics of three typical plant roots and the trend for soil nutrient change in the South Ningxia Loess Hilly Region of Northwest China, were studied for 2 years using the buried bag method. The results showed that the annual decomposition indices (K) of Stipa bungeana, Artemisia sacrorum, and Thymus mongolicus roots were 0.00891, 0.01128, and 0.01408, respectively, and the decomposition rate in turn showed as Thymus mongolicus > Artemisia sacrorum > Stipa bungeana. After 16 months, a substantial amount of root nutrients had been released. The release amount of carbon was 57.05-124.39 g/kg while for nitrogen it was 0.12-0.47 g/kg. The effects of three typical plant roots on soil nutrients were as follows: the contents of soil organic carbon increased by 0.17-0.35 g/kg in a 0-5 cm soil layer, and by 0.26-0.35 g/kg in a 5-20 cm soil layer. Correlation analysis showed that some negative correlation exists between the release amount of root nutrients and soil nutrient content. When the soil nutrient content is low, roots will increase nutrient release to supplement soil nutrients. This indicates that root decomposition increases soil nutrient content and effectively promotes nutrient cycling in the root-soil system. 参考文献 相似文献 引证文献

Evaluation of Controlled Release Urea on the Dynamics of Nitrate, Ammonium, and Its Nitrogen Release in Black Soils of Northeast China.

Controlled release urea (CRU) is considered to enhance crop yields while alleviating negative environmental problems caused by the hazardous gas emissions that are associated with high concentrations of ammonium (NH4+) and nitrate (NO3−) in black soils. Short-term effects of sulfur-coated urea (SCU) and polyurethane-coated urea (PCU), compared with conventional urea, on NO3− and NH4+ in black soils were studied through the buried bag experiment conducted in an artificial climate chamber. We also investigated nitrogen (N) release kinetics of CRU and correlations between the cumulative N release rate and concentrations of NO3− and NH4+. CRU can reduce concentrations of NO3− and NH4+, and PCU was more effective in maintaining lower soil NO3−/NH4+ ratios than SCU and U. Parabolic equation could describe the kinetics of NO3− and NH4+ treated with PCU. The Elovich equation could describe the kinetics of NO3− and NH4+ treated with SCU. The binary linear regression model was established to predict N release from PCU because of significant correlations between the cumulative N release rate and concentrations of NO3− and NH4+. These results provided a methodology and data support for characterizing and predicting the N release from PCU in black soils.

Optimizing Weight Method to Evaluate Nitrogen Release Characters of Polymer-Coated Urea in Paddy Soil under Field Conditions

ABSTRACTPolymer-coated urea can improve nitrogen (N) use efficiency of rice. But, the nitrogen release characters from flooded paddy soil are lacking. Traditional weight methods use a vacuum oven to dry. Depending on the coating, some polymer-coated urea still retain water after drying. A new weight method was proposed: washing fertilizer granules in the buried bags with distilled water, and transferring to a plastic bag, then placing it at −80°C for 2 h, and then transferring to the lyophilizer to dry for 24 h. The method was compared with chemical analyses. This result indicated that the weight method can be used for determining N release characteristics in paddy soil. In the whole growing season, over 75% of N was released. Different amounts of granules in the bag can influence the result. The release rate of 10.0 g in bags was higher than 3.0 g. Surface applied polymer-coated urea has a higher rate than deep application.

Efficacy of fumigant treatments and inoculum placement on control of Macrophomina phaseolina in strawberry beds

Soil disinfestation is one of the main concerns of strawberry growers. The phased-out of methyl bromide (MeBr) and the lack of equally effective fumigants has increased the difficulty in controlling soilborne pathogens such as Macrophomina phaseolina, causal agent of charcoal rot. Soil fumigant treatments were tested in Dover, Florida during the 2012–13, 2013–14 and 2014–15 seasons. The treatments included MeBr as a standard and common alternatives such as chloropicrin (PIC), 1,3-dichloropropene (1,3D), dimethyl disulfide (DMDS), potassium N-methyldithiocarbamate (Kpam) and sodium methyldithiocarbamate (Vapam). The efficacy of different fumigation rates and application methods was also investigated. Treatment effects were evaluated using sclerotia of M. phaseolina buried in bags 7.6 and 20.3 cm deep in the center of the bed, or 7.6 cm deep on the side of the bed (7.6 s). Additionally, strawberry crowns infected with M. phaseolina were buried 7.6 cm deep in the center of the bed during the 2012–13 and 2013–14 growing seasons. At the end of the 2013–14 and 2014–15 growing seasons, plant mortality and charcoal rot incidence (%) were also determined. Except for 1,3-dichloropropene:chloropicrin 39/60, most treatments were effective in reducing the colony forming units (CFUs) of M. phaseolina in buried bags or crowns buried at the center of the bed and reduced percent of charcoal rot incidence each season. Most treatments applied by shank produced similar reductions in inoculum levels at the center and sides of the bed, whereas drip treatments effectively reduced inoculum in bags buried at both depths in the center of the bed, but not at the side of the bed. Thus, one of the main problems of the current fumigants is poor distribution in the soil beds and strawberry growers should consider application methods that will achieve a more uniform distribution of the fumigants.

Development of a buried bag technique to study biochars incorporated in a compost or composting medium

The purpose was to develop a netbag technique suitable for burying biochar in a compost or composting medium, followed by its collection in a clean state (i.e., free of compost debris) without loss or damage, for physicochemical analyses. Collection in a clean state is required to ensure that the analytical data of various biochars are representative and comparable. Five criteria were identified to evaluate the suitability of netbag. A small netbag (3.5 × 3.5 cm) was developed using nylon fabric (30-μm mesh) to contain ∼1 g of biochar. A production system was developed to make 15 netbags per batch. Unlike commonly used litterbags, polypropylene was used to seal netbags. Two experiments were conducted in which three biochars, made from macadamia nutshell, hardwood shaving, and chicken litter, were co-composted with chicken manure and sawdust and also incubated with a chicken litter-based commercial compost. Biochars were added at the rates of 5 or 10 % in the co-composting and 10 or 20 % in the incubation experiments. The biochar-containing netbags were buried in the co-composting and incubation mediums for 133 days. Various physicochemical analyses were conducted with netbag-biochars and their compost mediums. The netbags collected after both experiments showed no visible sign of degradation. The weight of netbag-biochars from co-composting and incubation systems did not reduce significantly over the experimental period, thereby indicating no loss of biochar. No visible evidence of entry of solid particles from compost medium was found on the netbag-biochars. Pretests indicated that the netbag and biochars absorbed pore solution from the medium. Findings showed that elements translocated between the netbag-biochar and compost medium. A colony of coccus bacteria was found on the surface of composted chicken litter biochar, denoting probable entry of bacteria from compost medium. Unlike conventional litterbags, the netbags were suitable for burying and extracting biochar in compost/composting mediums due to smaller size, smaller mesh, and strong sealing with polypropylene. The netbags addressed all the five criteria. Therefore, it was concluded that, in the co-compost or incubated-compost medium, the biochar retained in the netbag and the biochar mixed with the medium were exposed to a similar bio-oxidative environment, and netbag-biochar represents the biochar in the medium. This means that these netbags can be used as a convenient means to examine the effects of the composting process or incubation in compost on biochar.

Soil N2O fluxes along an elevation gradient of tropical montane forests under experimental nitrogen and phosphorus addition

Nutrient deposition to tropical forests is increasing, which could affect soil fluxes of nitrous oxide (N2O), a powerful greenhouse gas. We assessed the effects of 35-56 months of moderate nitrogen (N) and phosphorus (P) additions on soil N2O fluxes and net soil N-cycling rates, and quantified the relative contributions of nitrification and denitrification to N2O fluxes. In 2008, a nutrient manipulation experiment was established along an elevation gradient (1000, 2000 and 3000 m) of montane forests in southern Ecuador. Treatments included control, N, P and N+P addition (with additions of 50 kg N ha−1 yr-1 and 10 kg P ha−1 yr-1). Nitrous oxide fluxes were measured using static, vented chambers and N cycling was determined using the buried bag method. Measurements showed that denitrification was the main N2O source at all elevations, but that annual N2O emissions from control plots were low, and decreased along the elevation gradient (0.57 ± 0.26 to 0.05 ± 0.04 kg N2O-N ha-1 yr-1). We attributed the low fluxes to our sites’ conservative soil N cycling as well as gaseous N losses possibly being dominated by N2. Contrary to the first 21 months of the experiment, N addition did not affect N2O fluxes during the 35-56 month period, possibly due to low soil moisture contents during this time. With P addition, N2O fluxes and mineral N concentrations decreased during Months 35-56, presumably because plant P limitations were alleviated, increasing plant N uptake. Nitrogen plus phosphorus addition showed similar trends to N addition, but less pronounced given the counteracting effects of P addition. The combined results from this study (Months 1-21 and 35-56) showed that effects of N and P addition on soil N2O fluxes were not linear with time of exposure, highlighting the importance of long-term studies.

Evaluating Winter/Spring Seeding of a Native Perennial Bunchgrass in the Sagebrush Steppe

Sagebrush (Artemisia tridentata Nutt.) plant communities in the Great Basin region are being severely impacted by increasingly frequent wildfires in association with the expansion of exotic annual grasses. Maintaining native perennial bunchgrasses is key to controlling annual grass expansion, but postfire restoration of these species has proven difficult with traditional fall drill-seeding. We investigated the potential for winter/spring seeding bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love) in southeast Oregon. In 2011–2013, 500 seeds were planted in fall, or weekly from March through early May in 1·m-2 plots using a randomized block design with 5 replications. Germination was estimated using buried bags, and emergent seedlings were counted weekly from March to June. Germination and emergence varied strongly between years and by within-year timing of planting. With adequate precipitation, percent germination was high (up to 100%) regardless of timing of planting and emergence density decreased (P ≤ 0.05) with advancing winter/spring planting date in drier years. Emergence density was high (approaching 300 plants/m-2) with adequate precipitation but varied strongly across planting weeks for winter/spring plantings. Percent survival of emergent seedlings to harvest (July) was approximately 25–50% lower (P ≤ 0.05) for fall-planted seeds in all years; survival of winter/spring seedlings was 80–100% with no discernable pattern between planting weeks. Our results indicate that winter/spring seeding of perennial bunchgrasses is biologically feasible in years with adequate precipitation but fall seeding was more consistently successful. Additional research is needed to determine environmental factors driving within-year variation in demographics for winter/spring planted seeds.

Germination characteristics and seedbank of the alien species Leucaena leucocephala (Fabaceae) in Brazilian forest: ecological implications

SummaryPlant species invasiveness is frequently associated with rapid proliferation and production of seeds that can persist in the soil for long periods of time. Leucaena leucocephala (Fabaceae) is an alien and invasive species, for example in Brazilian forest and savannah ecosystems. This study quantified the invasive potential of this species by analysing its seed rain (using seed collectors), seed longevity in the soil (stored in buried bags) and the germination capacity of the soil seedbank (by collecting soil samples in the study area). Our results showed that seed rain occurred throughout the year, although more intensely from July to September, with about 5500 seeds m−2 year−1 being released. The numbers of seeds in the buried bags diminished over time and intact seeds showed low germinability (approximately 15%), although their viability remained >80% of the recovered seeds after two years of in situ storage. The germinability of seeds collected directly from the soil was approximately 40%, indicating that more than half of the seeds of soil seedbank were dormant (physical dormancy). Leucaena leucocephala produces large numbers of seeds and is able to form a persistent short‐lived seedbank (viability 1–5 years). These factors may contribute significantly to its invasive potential, which makes it difficult to control this species once it becomes established. As control costs become higher over time, immediate public efforts are needed to counter this threat.

Biochar and Manure Effects on Net Nitrogen Mineralization and Greenhouse Gas Emissions from Calcareous Soil under Corn

Few multiyear field studies have examined the impacts of a one‐time biochar application on net N mineralization and greenhouse gas emissions in an irrigated, calcareous soil; yet this use of biochar is hypothesized as a means of sequestering atmospheric CO2 and improving soil quality. We fall‐applied four treatments: stockpiled dairy manure (42 Mg ha−1 dry wt.), hardwood‐derived biochar (22.4 Mg ha−1), combined biochar and manure, and no amendments (control). Nitrogen fertilizer was applied in all plots and years based on treatment's preseason soil test N and crop requirements and accounting for estimated N mineralized from added manure. From 2009 to 2011, we measured greenhouse gas fluxes using vented chambers, net N mineralization using buried bags, corn (Zea mays L.) yield, and N uptake, and in a succeeding year, root and shoot biomass and biomass C and N concentrations. Both amendments produced persistent soil effects. Manure increased seasonal and 3‐yr cumulative net N mineralization, root biomass, and root/shoot ratio 1.6‐fold, CO2–C gas flux 1.2‐fold, and reduced the soil NH4/NO3 ratio 58% relative to no‐manure treatments. When compared with a class comprising all other treatments, biochar‐only produced 33% less cumulative net N mineralization, 20% less CO2–C, and 50% less N2O‐N gas emissions, and increased the soil NH4/NO3 ratio 1.8‐fold, indicating that biochar impaired nitrification and N immobilization processes. The multi‐year nature of biochar's influence implies that a long‐term driver is involved, possibly related to biochar's enduring porosity and surface chemistry characteristics. While the biochar‐only treatment demonstrated a potential to increase corn yields and minimize CO2–C and N2O‐N gas emissions in these calcareous soils, biochar also caused decreased corn yields under conditions in which NH4–N dominated the soil inorganic N pool. Combining biochar with manure more effectively utilized the two soil amendments, as it eliminated potential yield reductions caused by biochar and maximized manure net N mineralization potential.

Nitrogen cycling in canopy soils of tropical montane forests responds rapidly to indirect N and P fertilization.

Although the canopy can play an important role in forest nutrient cycles, canopy-based processes are often overlooked in studies on nutrient deposition. In areas of nitrogen (N) and phosphorus (P) deposition, canopy soils may retain a significant proportion of atmospheric inputs, and also receive indirect enrichment through root uptake followed by throughfall or recycling of plant litter in the canopy. We measured net and gross rates of N cycling in canopy soils of tropical montane forests along an elevation gradient and assessed indirect effects of elevated nutrient inputs to the forest floor. Net N cycling rates were measured using the buried bag method. Gross N cycling rates were measured using (15) N pool dilution techniques. Measurements took place in the field, in the wet and dry season, using intact cores of canopy soil from three elevations (1000, 2000 and 3000m). The forest floor had been fertilized biannually with moderate amounts of N and P for 4years; treatments included control, N, P, and N+P. In control plots, gross rates of NH4 (+) transformations decreased with increasing elevation; gross rates of NO3 (-) transformations did not exhibit a clear elevation trend, but were significantly affected by season. Nutrient-addition effects were different at each elevation, but combined N+P generally increased N cycling rates at all elevations. Results showed that canopy soils could be a significant N source for epiphytes as well as contributing up to 23% of total (canopy+forest floor) mineral N production in our forests. In contrast to theories that canopy soils are decoupled from nutrient cycling in forest floor soil, N cycling in our canopy soils was sensitive to slight changes in forest floor nutrient availability. Long-term atmospheric N and P deposition may lead to increased N cycling, but also increased mineral N losses from the canopy soil system.