Nitrogen and harvest management of Conservation Reserve Program (CRP) grassland for sustainable biomass feedstock production

The Biomass Regional Feedstock Partnership has identified grasslands planted under the Conservation Reserve Program (CRP) as a potential source for herbaceous bioenergy feedstock. The goal of this project is to assess the yield potential of CRP grasslands across diverse regions. Consistent with that goal, the objective of this project was to establish yield potential and quality parameters for several different CRP grasslands, representative of different growing environments. Standard field scale agricultural practices were used as management guidelines at each location. The test locations were identified and established based on known regions containing concentrated tracts of CRP grassland and represented variable climatic parameters and production histories. Biomass production potential for CRP land dominated by either warm‐ or cool‐season grass mixtures in each location was evaluated over the course of three growing seasons (2008, 2009, and 2010). Specifically, a mixture of warm‐season perennial grasses was evaluated in North Dakota, Kansas, and Oklahoma, while a cool‐season mixture was evaluated in Montana, Georgia, and Missouri. Maximum biomass yields for the three warm‐season CRP sites ranged from 4.0 to 7.2 Mg ha^?1 and for the three cool‐season CRP sites 3.4–6.0 Mg ha^?1. Our results demonstrate that CRP grassland has potential as a bioenergy feedstock resource if the appropriate management practices are followed.     

Impacts of management practices on bioenergy feedstock yield and economic feasibility on Conservation Reserve Program grasslands

Perennial grass mixtures planted on Conservation Reserve Program (CRP) land are a potential source of dedicated bioenergy feedstock. Long‐term nitrogen (N) and harvest management are critical factors for maximizing biomass yield while maintaining the longevity of grass stands. A six‐year farm‐scale study was conducted to understand the impact of weather variability on biomass yield, determine optimal N fertilization and harvest timing management practices for sustainable biomass production, and estimate economic viability at six CRP sites in the United States. Precipitation during the growing season was a critical factor for annual biomass production across all regions, and annual biomass production was severely reduced when growing season precipitation was below 50% of average. The N rate of 112 kg ha^?1 produced the highest biomass yield at each location. Harvest timing resulting in the highest biomass yield was site‐specific and was a factor of predominant grass type, seasonal precipitation, and the number of harvests taken per year. The use of N fertilizer for yield enhancement unambiguously increased the cost of biomass regardless of the harvest timing for all six sites. The breakeven price of biomass at the farmgate ranged from $37 to $311 Mg^?1 depending on the rate of N application, timing of harvesting, and location when foregone opportunity costs were not considered. Breakeven prices ranged from $69 to $526 Mg^?1 when the loss of CRP land rental payments was included as an opportunity cost. Annual cost of the CRP to the federal government could be reduced by over 8% in the states included in this study; however, this would require the biomass price to be much higher than in the case where the landowner receives the CRP land rent. This field research demonstrated the importance of long‐term, farm‐scale research for accurate estimation of biomass feedstock production and economic viability from perennial grasslands.     

Cellulosic feedstock production on Conservation Reserve Program land: potential yields and environmental effects

Producing biofuel feedstocks on current agricultural land raises questions of a ‘food‐vs.‐fuel’ trade‐off. The use of current or former Conservation Reserve Program (CRP) land offers an alternative; yet the volumes of ethanol that could be produced and the potential environmental impacts of such a policy are unclear. Here, we applied the Environmental Policy Integrated Climate model to a US Department of Agriculture database of over 200 000 CRP polygons in Iowa, USA, as a case study. We simulated yields and environmental impacts of growing three cellulosic biofuel feedstocks on CRP land: (i) an Alamo‐variety switchgrass (Panicum virgatum L.); (ii) a generalized mixture of C4 and C3 grasses; (iii) and no‐till corn (Zea mays L.) with residue removal. We simulated yields, soil erosion, and soil carbon (C) and nitrogen (N) stocks and fluxes. We found that although no‐till corn with residue removal produced approximately 2.6–4.4 times more ethanol per area compared to switchgrass and the grass mixture, it also led to 3.9–4.5 times more erosion, 4.4–5.2 times more cumulative N loss, and a 10% reduction in total soil carbon as opposed to a 6–11% increase. Switchgrass resulted in the best environmental outcomes even when expressed on a per liter ethanol basis. Our results suggest planting no‐till corn with residue removal should only be done on low slope soils to minimize environmental concerns. Overall, this analysis provides additional information to policy makers on the potential outcome and effects of producing biofuel feedstocks on current or former conservation lands.     

Stunning pigs with nitrogen and carbon dioxide mixtures: effects on animal welfare and meat quality

The aim of this study was to assess the effect of exposure to the gas mixtures of 70% nitrogen (N₂) and 30% carbon dioxide (CO₂; 70N30C), 80% N₂ and 20% CO₂ (80N20C) and 85% N₂ and 15% CO₂ (85N15C) on aversion, stunning effectiveness and carcass, as well as meat quality in pigs, and to compare them with the commercial stunning of 90% CO₂ (90C). A total of 68 female pigs were divided into four groups and stunned with one of the gas mixtures. During the exposure to the gas, behavioural variables (retreat attempts, escape attempts, gasping, loss of balance, muscular excitation and vocalizations) were recorded, and at the end of the stunning, corneal reflex and rhythmic breathing were assessed. After slaughter, meat quality parameters such as pH at 45 min post mortem (pH45) and at 24 h post mortem (pHu), electrical conductivity, drip loss and colour, in the Longissimus thoracis (LT) and Semimembranosus (SM) muscles were measured, and the presence of ecchymosis on the hams was noted. The PROC MIXED and the PROC GENMOD of SAS® were used to analyse the parametric and binomial variables, respectively. The ‘gas mixture’ was always considered a fixed effect and the ‘live weight’ as a covariate. To assess the correlation between meat quality and behaviour measures, PROC CORR was used. Pigs exposed to 90C showed a higher percentage of escape attempts and gasping, a lower percentage of vocalization and shorter muscular excitation phase than pigs exposed to the other N₂ and CO₂ mixtures (P < 0.05). After stunning, no pig exposed to 90C showed corneal reflex or rhythmic breathing, whereas 85% and 92% of the animals exposed to N₂ and CO₂ mixtures showed corneal reflex and rhythmic breathing, respectively. Animals stunned with 80N20C and 85N15C had a lower pH45 (P < 0.01) than animals exposed to 90C. Electrical conductivity in the SM muscle was lower (P < 0.001) in 90C and 70N30C pigs than in 80N20C and 85N15C pigs, whereas in LT, it was lower (P < 0.05) in 90C pigs than in 85N15C. As the CO₂ concentration of the gas mixture was decreased, the prevalence of exudative pork increased. Twenty-five percent of animals exposed to N₂ and CO₂ mixtures (n = 68) had ecchymosis in their carcasses, whereas no animal stunned with 90C had ecchymosis. In conclusion, although N₂ and CO₂ stunning exhibit fewer signs of aversion than 90C, their induction time to unconsciousness is longer, and this may negatively affect meat and carcass quality.     

Effects of harvest frequency and biosolids application on switchgrass yield,feedstock quality,and theoretical ethanol yield

Sustainable development of a bioenergy industry will require low‐cost, high‐yielding biomass feedstock of desirable quality. Switchgrass (Panicum virgatum L.) is one of the primary feedstock candidates in North America, but the potential to grow this biomass crop using fertility from biosolids has not been fully explored. The objective of this study was to examine the effects of harvest frequency and biosolids application on switchgrass in Virginia, USA. ‘Cave‐in‐Rock’ switchgrass from well‐established plots was cut once (November) or twice (July and November) per year between 2010 and 2012. Class A biosolids were applied once at rates of 0, 153, 306, and 459 kg N ha^?1 in May 2010. Biomass yield, neutral and acid detergent fiber, cellulose, hemicellulose, lignin, and ash were determined. Theoretical ethanol potential (TEP, l ethanol Mg^?1 biomass) and yield (TEY, l ethanol ha^?1) were calculated based on cellulose and hemicellulose concentrations. Cutting twice per season produced greater biomass yields than one cutting (11.7 vs. 9.8 Mg ha^?1) in 2011, but no differences were observed in other years. Cutting once produced feedstock with greater TEP (478 vs. 438 l Mg^?1), but no differences in TEY between cutting frequencies. Biosolids applied at 153, 306, and 459 kg N ha^?1 increased biomass yields by 25%, 37%, and 46%, and TEY by 25%, 34%, and 42%, respectively. Biosolids had inconsistent effects on feedstock quality and TEP. A single, end‐of‐season harvest likely will be preferred based on apparent advantages in feedstock quality. Biosolids can serve as an effective alternative to N fertilizer in switchgrass‐to‐energy systems.     

Direct and indirect effects of nitrogen deposition on species composition change in calcareous grasslands

Atmospheric nitrogen (N) deposition has been identified as a major threat to biodiversity, but field surveys of its effects have rarely focussed on sites which are actively managed to maintain characteristic species. We analysed permanent quadrat data from 106 plots in nature reserves on calcareous grassland sites in the United Kingdom collected during a survey between 1990 and 1993 and compared the data with the results from resurvey of 48 of these plots between 2006 and 2009. N deposition showed no significant spatial association with species richness, species diversity, or the frequency of species adapted to low nutrient conditions in the 1990–1993 dataset. However, temporal analysis showed that N deposition was significantly associated with changes in Shannon diversity and evenness. In plots with high rates of N deposition, there was a decrease in species diversity and evenness, a decline in the frequency of characteristic calcareous grassland species, and a lower number of rare and scarce species. As all sites had active management to maintain a high diversity and characteristic species, our results imply that even focussed management on nature conservation objectives cannot prevent adverse effects of high rates of N deposition. Structural equation modelling was used to compare different causal mechanisms to explain the observed effects. For change in Shannon diversity, direct effects of N deposition were the dominant mechanism and there was an independent effect of change in grazing intensity. In contrast, for change in herb species number, indirect effects on soil acidity, linked to both N and S deposition, were more important than direct effects of N deposition.     

氮肥运筹对砂田西瓜产量、品质及氮素积累与转运的影响

通过田间试验研究了不同氮肥运筹方式对砂田西瓜产量、品质及氮素和干物质积累与转运的影响.结果表明： 基肥氮过低或过高均不利于砂田西瓜苗期生长,伸蔓期或膨果期不施氮肥则限制了西瓜“源”或“库”的形成,在相同的施氮量水平下,T₄(30%基肥+30%伸蔓肥+40%膨瓜肥)和T₆\[100%基肥+长效复合肥添加剂(NAM)\]处理较传统施肥模式T1(30%基肥+70%伸蔓肥)西瓜坐果后茎叶干物质和氮素积累量显著降低,而果实干物质和氮素积累量显著增加.其中,T₄处理的氮素运转率和氮素贡献率分别达到33.6%和12.0%,T₄和T₆处理的氮素收获指数、氮肥偏生产力和氮肥利用率较传统施肥模式T₁分别显著提高14.1%和12.7%、11.6%和12.5%、5.3%和8.7%.T₄和T₆处理较T₁西瓜分别增产11.6%和12.5%,可溶性糖含量分别显著提高16.5%和11.7%,有效酸度分别提高4.5%和2.8%,糖酸比分别提高19.4%和13.4%,Vc含量分别提高35.6%和19.0%.因此,T₄和T₆处理为砂田西瓜高产优质的较优氮肥运筹模式,若减轻砂田施肥难度,延长砂田使用年限,可采用100%基肥+NAM(T₆)的施肥方式.     

保护性耕作对农田碳、氮效应的影响研究进展

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。     

农田施氮对水质和氮素流失的影响

基于ISI Web of Science数据库,利用文献计量学方法分析了自1957年以来各国在农田氮流失领域的研究发展态势,综述了农田氮流失特征及氮流失防控措施。结果表明,目前各国对农田氮流失的研究主要集中在施氮对水体水质的污染和监测方法上,涉及的关键词主要有Groundwater、Water quality、Surface water、Nitrate pollution、Eutrophication、Contamination、Nonpoint source pollution、Lysimeter、Runoff、Subsurface drainage等。中国、美国和加拿大等农业大国的研究机构在这一领域的研究成果最多发文量最多的期刊主要分布在荷兰、美国和中国。文献分析表明,受降水、地形、土壤、施肥等诸多管理措施的影响,不同区域的农田氮流失量差别很大,中国各类农田的氮流失量(13.7—347 kg/hm~2)明显高于欧美国家(4—107 kg/hm~2)。我国单位面积化肥(357.3 kg/hm~2)和氮肥(165.1 kg/hm~2)施用量均远高于世界平均用量(87.5 kg/hm~2和52.9 kg/hm~2),当季氮肥利用率(17%)却明显低于世界平均水平(58%),表明氮肥施用过量且利用率过低是造成氮流失的关键因素。综合分析农田氮流失防控措施发现,从源头控制氮流失是最有效的措施,优化农艺管理措施和氮迁移过程拦截等分别可减少15%—92%、46%—77%的氮素流失,其中针对农田适宜施氮量的研究最多。然而,面对粮食生产需求与资源短缺、水体水质持续恶化的现状,未来的研究重点应从简单的表观平衡向整个农田生态系统的氮素循环过程转变,更为迫切的是加快探索以水质保护为目标的化肥氮施用阈值(造成环境污染的临界施氮量),并推广示范这些有效的氮流失防控措施。     

减量施氮对大棚黄瓜产量和品质的影响

利用在东部沿海丘陵区玻璃大棚中的长期定位试验,设置农民习惯施氮(N₁, 800 kg·hm^-2)、氮减量25%(N₂, 600 kg·hm^-2)、氮减量50%(N₃, 400 kg ·hm^-2)、不施肥(CK)4种不同化肥施氮水平和施有机肥(ON, 400 kg N·hm^-2)处理,研究了不同施氮量对黄瓜产量及品质的影响.结果表明: 与农民习惯施氮相比,施氮量减少50%能保证黄瓜的果实产量,并大幅提高经济效益.不同处理黄瓜果实硝酸盐含量范围在94.2～136.1 mg·kg^-1,均未超过我国蔬菜卫生安全标准,不同施肥处理比CK增加了18.1%～44.5%,其中N₃处理下增加幅度最小.施用化肥降低了黄瓜果实中Vc、可溶性糖和可溶性蛋白含量,在施氮量600 kg·hm^-2处理中最低.不同施氮处理在短期内改变土壤pH等理化性质,然而在过量施肥条件下黄瓜产量、经济效益与土壤性质无显著相关性.因此,在东部沿海丘陵区的大棚生产条件下,氮肥施用量减少50%可以保证黄瓜产量和果实品质.     

采伐剩余物管理措施对二代杉木人工林土壤全碳、全氮含量的长期效应

根据福建省南平市峡阳国有林场二代杉木(Cunninghamia lanceolata(Lamb.) Hook)人工林5种采伐剩余物管理措施(收获采伐剩余物和地被层、全树收获、仅收获树干和树皮以及加倍采伐剩余物、炼山)下0-40 cm深度土壤全碳、全氮含量15a的监测数据,研究了采伐剩余物管理措施对杉木林土壤碳氮含量的影响.结果显示,加倍采伐剩余物处理样地5次取样年份(造林第3年、第6年、第9年、第12年和第15年)0-10 cm土层土壤全碳、全氮含量均高于其他处理样地,但单因素方差分析显示,采伐剩余物管理措施在5次取样年份对0-10 cm、10-20 cm和20-40 cm土层全碳、全氮含量均没有显著影响(P＞0.05).重复测量方差分析显示,杉木造林15a期间土壤全碳、全氮含量随年份显著变化(P＜0.01),但处理措施以及处理措施与取样年份的交互作用对3个土层土壤全碳、全氮含量影响不显著(P＞0.05).杉木林15年生时,不同处理样地3个土层碳储量差异不显著(P＞0.05),0-40 cm土层平均值为88.71 Mg/hm2.表明采伐剩余物管理措施对亚热带杉木人工林土壤全碳、全氮含量的长期效应并不显著.     

不同氮肥基追比例对高温胁迫下小麦籽粒产量和品质的影响

选用强筋小麦品种济麦20、烟农19、藁麦8901做试验材料,设置不同氮肥基追比例和籽粒灌浆中后期高温胁迫处理,研究了不同氮肥基追比例对高温胁迫条件下小麦籽粒产量和品质的影响.研究结果表明,追氮比例由50%增加到70%,3个品种的千粒重、籽粒产量、粗蛋白含量、湿面筋含量、醇溶蛋白含量、谷蛋白含量、HMW-GS含量、LMW-GS含量、HMW-GS/LMW-GS比值显著提高.济麦20和烟农19的谷蛋白大聚合体含量、谷蛋白大聚合体体积加权平均粒径和表面积加权平均粒径因追氮比例提高而升高, 藁麦8901则无显著变化.济麦20和烟农19的面团形成时间、面团稳定时间因追氮比例提高而延长, 藁麦8901基本不受影响.追氮比例由50%增加到70%,3个品种的籽粒支链淀粉/直链淀粉比值显著降低,淀粉糊化高峰黏度、低谷黏度、稀懈值、最终黏度和反弹值相应降低.总之,提高氮肥追施比例可在一定程度上缓解灌浆期高温胁迫对小麦粒重和蛋白质质量的不利影响,但对淀粉质量产生负面效应,且品种间存在差异.