轮牧高寒草甸温室气体排放的季节动态与羊粪的作用

用静态箱法测定了藏羊轮牧的高寒草甸温室气体的排放及其季节动态,分析了羊粪的作用。结果显示,高寒草甸土壤为CH4的汇,返青季CH4日吸收量最高,轻牧区为枯黄季最低,适度放牧增强高寒草甸吸收CH4的能力;高寒草甸土壤为CO2的源,牧草生长旺季日排放量最高,枯黄季最低,重牧促进高寒草甸CO2排放;放牧没有改变高寒草甸作为CH4汇／CO2源的功能。分析表明,羊粪具有抑制高寒草甸温室气体排放的趋势,季节对于温室气体排放的作用大于放牧。     

藏北紫花针茅高寒草原适宜放牧率研究

通过5年的放牧试验研究了藏北紫花针茅高寒草原地上现存量和草地净初级生产力以及藏系绵羊采食量和采食率,以期能够准确制定藏北高寒草原适宜放牧率。研究结果表明,试验初期放牧强度对藏北紫花针茅高寒草地现存量的影响并不显著;随着试验后期对放牧强度增倍,草地地上现存量随放牧强度增加而减少。放牧样地地上净初级生产力在试验初期高于对照样地,但随着放牧强度和时间的增加,到2010年时对照样地净初级生产力明显高于放牧处理(P<0.05)。绵羊采食量与放牧强度间存在显著负相关(P<0.05);绵羊采食率大小顺序为:重牧>轻牧>中牧。综合分析试验结果,轻度放牧条件下,不仅草地现存量和净初级生产力最大,并且绵羊采食量也为最大,因此建议在牧草生长季内藏北紫花针茅高寒草原放牧率应低于4只/1.67 hm²为宜。     

传统放牧模式下青藏高原高寒牧区藏系绵羊温室气体排放研究

通过LCA原理,建立一个由6只公羊和200母羊建群的适度放牧天然牧场,模拟一个世代周期(7年),估算传统放牧模式下青藏高原高寒牧区藏系绵羊温室气体碳密度,不同排放源及种群组分的贡献率。藏系绵羊温室气体碳密度为13.07kg CO2eq(kg活体重)-1或24.85kg CO2eq(kg胴体)-1。肠道发酵排放的CH4占温室气体总排放量的比例为79%,次之为从土壤氮输入和粪便中排放的N2O(20%)。建群繁殖种群和生产羔羊所排放的温室气体占整个系统的65%,35%由放牧期进行交易的羊产生。在整个系统构成成份中,母羊贡献最大(45%),生产期和交易期贡献率达46%。因此,在高寒牧区传统放牧模式下,可通过优化放牧方式(例如:提高母畜繁殖率减少母畜数量;缩短出栏周期),减少温室气体排放。     

不同放牧强度下祁连山东段草地生态系统氮磷计量特征

通过研究青藏高原祁连山东段高寒草甸牧区土草畜氮磷特征,以及高寒草甸放牧区家畜氮磷平衡现状,以期为高寒草地健康评价及家畜管理提供理论及技术支持。依饮水点为中心,由近及远设置3个相对放牧强度,研究地上植物群落特征、牧草及土壤营养成分及家畜氮磷平衡。结果表明:物种多样性和草地生物量轻牧和中牧强度均显著高于重牧强度(P0.05);土壤全磷含量在0~10cm和10~20cm土层中重牧强度显著高于轻牧强度和中牧强度(P0.05),而在20~30cm土层中中牧强度下显著高于轻牧强度和重牧强度(P0.01);土壤全氮含量0~10cm土层中重牧强度显著高于轻牧强度和中牧强度(P0.01),10~20cm土层中中牧强度显著高于轻牧强度(P=0.016),20~30cm土层中不同放牧强度下氮含量无显著性差异(P0.05);随着放牧强度的增加,牧草全磷含量线性下降(P0.001),N/P线性增加(P0.001),而全氮含量对放牧强度的响应不显著(P0.05);此外,高寒草甸泌乳牦牛体内氮沉积量为27.95g/d,呈正平衡,磷沉积量为-1.95g/d,呈负平衡。综上,合理放牧,维持高寒草甸土草畜氮磷流的平衡,对于家畜的健康生长以及草地的可持续利用具有重要作用。     

黄土高原雨养农业区不同种植模式土壤温室气体排放特征

研究陇中黄土高原旱作农田,设置了苜蓿-苜蓿(L-L)、苜蓿-休闲(L-F)、苜蓿-小麦(L-W)、苜蓿-玉米(L-C)、苜蓿-马铃薯(L-P)和苜蓿-谷子(L-M)6个处理,采用静态箱-气相色谱法和碳通量测量系统LI-8100对苜蓿后茬轮作不同作物土壤温室气体排放动态及其影响因素进行了测定与分析。研究结果表明,农田土壤表现为CO2源、N2O源和CH4吸收汇,且呈现夏秋高,春冬低的季节性变化特征。L-L处理的CO2累积排放量最高,L-W处理较之降低了42.43%;L-C处理的N2O累积排放量最高,L-P处理最低;CH4吸收量以L-M处理最高,较L-F和L-L分别增加了62.71%和31.87%,综合增温潜势表现为L-LL-ML-CL-PL-FL-W。相关分析结果表明,CO2、CH4、N2O排放量与脲酶、过氧化氢酶活性及土壤温度呈极显著相关(P0.01),与土壤水分在不同土层有显著相关性;逐步回归分析发现,土壤温度、过氧化氢酶是CO2和CH4排放的主导因素,土壤温度极显著影响气体排放,N2O排放主要受到环境因子的影响。综合来看,与长期苜蓿连作相比,黄土高原地区苜蓿种植一定年限之后轮作粮食作物能减少土壤温室气体排放量,减弱农田温室气体的增温效应,其中以小麦效果最佳。     

放牧强度对高寒草地土壤微生物胞外酶化学计量的影响

土壤微生物是土壤养分释放或固持的重要调节者。本实验以青藏高原高寒草原为研究对象，以藏羊放牧强度控制实验为平台(对照(CK,0),轻度放牧(LG,2 sheep·hm^-2),中度放牧(MG,4 sheep·hm^-2),重度放牧(HG,6 sheep·hm^-2)),开展不同放牧强度下高寒草地土壤和微生物养分变化特征及其对土壤微生物养分代谢的影响研究。结果显示：总体上，土壤碳氮磷含量在放牧干扰下呈减少趋势，而微生物碳氮磷含量及其化学计量的变化幅度较小；重牧的碳获取酶(β-葡萄糖苷酶)活性及化学计量显著高于其余处理。此外，中牧和重牧的C∶P不平衡和N∶P不平衡高于CK,而C∶N不平衡低于CK,这表示在中度或重度放牧下高寒草地主要受到碳、磷的限制。当面对自身与资源之间的养分不匹配时，高寒草地土壤微生物主要通过增加碳获取酶的分泌，来缓解在重牧下的养分限制。     

放牧和围封对藏北高寒草原紫花针茅群落生物量分配及碳、氮、磷储量的影响

草地围封工程是改善退化草原生态环境和促进牧区经济可持续发展的一项重大举措。以典型高寒草原紫花针茅(Stipa purpurea)群落为研究对象,选取自由放牧、围封4年和围封8年3块样地,比较分析不同草地管理方式下群落生物量分配和碳(C)、氮(N)、磷(P)储量差异。结果表明,自由放牧、围封4年和围封8年的群落地上生物量分别为46.12、146.40和256.44 g·m-2,0-15 cm土层根系生物量分别为274.74、214.87和764.59g·m-2,15-30 cm土层根系生物量分别为17.80、17.56和31.64 g·m-2;围封显著促进了植被群落的增长(P0.05),其中对围封4年的优势种紫花针茅和青藏苔草(Carex moorcroftii)总生物量影响最显著(P0.05)。围封显著提高了植物群落地上部分C、N、P储量,其中围封8年样地营养元素储量最高(P0.05)。研究结果有助于揭示草地围封工程对藏北高寒草原紫花针茅群落物质分配的影响,为评估该区域退牧还草的生态效应提供了基础数据。     

克氏针茅(Stipa krylovii)草原土壤与优势植物碳氮含量对放牧强度的响应

为探究不同放牧强度对土壤和植物的影响,本文以内蒙古阿巴嘎旗克氏针茅（Stipa krylovii）草原为研究区,通过野外采样和室内试验分析了禁牧（UG）、轻牧（LG）、中牧（MG）、重牧（HG）下土壤及优势植物克氏针茅、羊草（Leymus chinensis）和糙隐子草（Cleistogenes squarrosa）中有机碳、全氮含量和碳氮比及其相关性。结果表明：轻牧草场土壤有机碳和全氮含量显著高于其他放牧草场（P<0.05）,而各放牧强度对土壤碳氮比均无显著影响;与禁牧相比,放牧降低了克氏针茅和羊草有机碳含量,却增加了它们的全氮含量;糙隐子草的有机碳和全氮含量均显著增加（P<0.05）;土壤与植物的碳氮含量均无显著相关性。因此,从提高土壤与植物碳氮含量方面考虑,轻度放牧是克氏针茅草原适宜的放牧强度,禁牧并非合理的利用方式,但应避免重度放牧。     

贝加尔针茅草原主要植物地上生物量分配对放牧梯度的响应

通过对放牧梯度下贝加尔针茅草原主要植物不同器官(茎、叶、花或果)的生物量分配格局变化进行探索,结果表明:贝加尔针茅草原主要植物的繁殖分配随牧压梯度增加,表现出明显的规律性,中牧条件下,贝加尔针茅草原植物群落的繁殖分配与优势种羊草等较耐牧植物变化趋势一致,均较轻牧下显著增加,而优良禾草、豆科牧草等均显著减少;重牧条件下,植物群落的繁殖分配与优良禾草、豆科牧草等以及退化标志植物变化趋势一致,均较中牧下显著减少,而较耐牧植物羊草等均显著增加。     

施粪对典型草原温室气体排放的影响

研究以陇东典型草原为对象,采用静态箱–气象色谱分析法测定典型草原滩羊放牧生态系统在施粪7、14、21 d和不同温度下CO_2、CH_4和N_2O气体通量,分析了施粪后时间和温度对3种主要温室气体通量的影响。主要结果如下:1)施粪具有抑制典型草原3种主要温室气体通量趋势,温室气体通量随施粪后时间的延长而下降。施粪后草原CH_4吸收通量减少;CO_2和N_2O的排放通量先增加,但是21 d后低于对照组。2)除对照组CO_2排放通量与土壤温度呈正相关关系外,土壤温度与施粪组的对照组的CH_4吸收量、N_2O排放量,施粪组的CO_2排放量呈负相关关系。     

青藏高原高寒湿地温室气体释放对水位变化的响应

为了探究水位变化对青藏高原高寒湿地温室气体释放的影响,以高原东部若尔盖典型高寒湿地为研究对象,采用“中型实验生态系”的技术手段,研究了两种不同水位情形 [稳定水位(SW,0 cm)和波动水位(DW,从0 cm下降到45 cm,再复原到0 cm)] 对高寒湿地二氧化碳(CO₂)、甲烷(CH₄)和氧化亚氮(N₂O)三种温室气体释放的影响。结果表明,1)高寒湿地水位变化对土壤(0~10 cm)可溶性有机碳(DOC)没有显著影响;水位从0 cm下降到45 cm,再复原到0 cm,对铵态氮(NH4+-N)和硝态氮(NO3--N)的转化起到了促进作用;2)水位变化对高寒湿地CO₂释放影响不显著,SW和DW处理下CO₂累积释放量分别为235.2和209.7 g/m²;3)水位变化对CH₄释放有显著影响,CH₄累积释放量从SW处理的1.79 g/m²下降到DW处理的0.86 g/m²,下降了52.18%;4)水位波动处理抑制了N₂O的释放,其在SW和DW条件下的累积释放量分别是6.72和-7.36 mg/m²;5)高寒湿地土壤温度在10 ℃以上,CO₂和CH₄释放量与其呈显著正相关性,水位下降提高了CO₂和CH₄释放与温度的拟合度。     

Long-term trends in greenhouse gas emissions from the Canadian poultry industry

As people become more aware of the environmental footprint of different foods, consumers may modify their diets to reduce the impact of their diets on the environment. For this to occur, it is necessary to know the impact that individual food types have on the environment. This publication presents the greenhouse gas (GHG) emissions as well as the GHG emission intensity associated with various types of poultry production in Canada for the census years 1981 to 2006. Greenhouse gas emissions were calculated using the methodology from the Intergovernmental Panel on Climate Change adjusted for conditions in Canada. Direct emissions of CH₄, N₂ O, and CO₂ from birds, their facilities, and the avian crop complex, corresponding to the area used to grow the crops that feed Canadian poultry, were estimated using poultry diet surveys. Between 1981 and 2006, because of the strong growth of broiler production, GHG emissions from the poultry industry increased by 40%. The main GHG was N₂ O, representing approximately 57% of the total emissions. Fossil fuel CO₂ accounted for approximately 38%, whereas CH₄ accounted for 5%. In western Canada, GHG emission intensities decreased owing to a reduction in the consumption of fossil fuels associated with the adoption of reduced- and no-tillage cropping systems, whereas in eastern Canada, the reduction was due to lower N₂ O emissions. The emissions of all 3 GHG from turkeys decreased because of the more rapid turnover of a marketable product (shortened life span) in later census years. Compared with other Canadian meat protein commodities in 2001, poultry emitted only 47% as much GHG per unit of live weight as pork and only 10% as much GHG per unit of live weight as beef.     

翻压紫云英对稻田土壤还原物质变化特征及温室气体排放的影响

采用室内培养试验监测紫云英翻压后土壤还原物质和温室气体的动态变化,旨在为紫云英还田造成水稻僵苗及带来的环境效应提供理论依据。结果表明,翻压紫云英显著增加土壤还原性物质总量、活性还原性物质含量、Fe²⁺和Mn²⁺含量,显著降低土壤氧化还原电位(Eh)。与对照(CK)相比,翻压紫云英15000(M₁)、30000(M₂)、45000 kg·hm^-2(M₃)处理土壤还原性物质总量平均值分别增加0.34、0.80、1.16 cmol·kg^-1,土壤活性还原性物质含量平均值分别增加0.14、0.35、0.52 cmol·kg^-1,Fe²⁺含量平均值分别增加87.91、182.91、280.61 mg·kg^-1,Mn²⁺含量平均值分别增加10.12、12.77、15.73 mg·kg^-1,Eh平均值分别降低32.88、47.98、57.26 mV。还原性物质均在培养近15 d时达到高峰,M₃处理Fe²⁺含量最高超过400 mg·kg^-1,已达到水稻幼苗中毒浓度。翻压紫云英显著增加CO₂、CH₄排放,降低N₂O排放,增加了全球增温潜势(GWP)。与CK相比,M₁、M₂、M₃的CO₂排放速率平均值分别增加7.67、12.48、20.54 mg·kg^-1·d^-1,CO₂累计排放量分别增加171.63、293.42、498.45 mg·kg^-1,CH₄排放速率平均值分别增加0.04、0.09、0.21 mg·kg^-1·d^-1,CH₄累计排放量分别增加0.36、0.69、1.77 mg·kg^-1,N₂O排放速率平均值分别降低0.46、0.64、0.72 μg·kg^-1·d^-1,N₂O累计排放量分别降低10.00、13.02、14.36 μg·kg^-1,M₁、M₂、M₃的GWP平均值分别是CK的1.59、2.04、2.91倍。CO₂、N₂O排放主要集中在培养前期,CH₄排放主要集中在培养后期。还原性物质含量与CO₂、CH₄的排放呈显著正相关,与N₂O排放呈显著负相关。综上,翻压紫云英增加还原性物质含量,促使CO₂、CH₄排放,抑制N₂O排放,增加GWP。实践中翻压紫云英可增加水稻产量,探索适宜紫云英翻压量确保单位水稻产量下的GWP不增加实现增产和环境效应的双赢具有重要实践意义,但这需要通过盆栽和大田试验验证。     

不同降水格局下填闲种植对旱作冬小麦农田夏闲期土壤温室气体排放的影响

田间盆栽试验研究了不同降水格局下填闲种植对冬小麦农田夏闲期土壤温室气体排放的影响。试验采用控制降水格局(自然降水和减半降水)和填闲作物(黑麦草单播、长武怀豆单播、黑麦草和怀豆混播、裸地对照)双因素处理设计, 利用静态箱-气相色谱法对土壤CO₂、N₂O和CH₄排放通量进行观测。结果表明:1)各处理土壤是CO₂、N₂O的排放源, 是CH₄的弱吸收汇。2)降水格局和填闲种植对土壤温室气体排放均具有显著影响。与自然降水相比, 减半降水的土壤CO₂日均排放通量降低了33%, N₂O日均排放通量降低了17.9%, 但对CH₄通量影响不大。3)与裸地对照相比, 单播黑麦草、长武怀豆和二者混播日均CO₂排放通量提高了140.8%、135.6%和137.7%, 不同填闲处理间差异不显著。而日均N₂O排放通量分别降低了8.0%、21.8%和27.4%, 其中单播长武怀豆和混播处理与单播黑麦草处理差异显著。单播长武怀豆处理土壤日均CH₄吸收通量较裸地对照、单播黑麦草和混播处理分别降低了65.8%、63.7%和68.9%。4)与自然降水相比, 减半降水农田综合增温潜势平均下降了26.1%, 温室气体排放强度平均提高了47.2%。而与裸地对照相比, 单播黑麦草、单播长武怀豆和二者混播处理综合增温潜势平均分别提高了67.9%、65.5%和67.8%, 且各填闲作物处理间差异不显著。与单播黑麦草和混播处理相比, 在冬小麦夏闲期单播长武怀豆具有更高的地上生物量和更低的温室气体排放强度, 在自然降水条件下能够兼顾经济效益与生态效益, 适宜在本地区加以推广种植。     

内蒙古羊草草原温室气体交换通量的日变化特征研究

本文探讨了草的主要温室气体收支的现场观测的方法。     

基于高寒草地放牧系统次级生产力的优化放牧强度研究

依据小嵩草（Kobresia parva）高寒草甸和垂穗披碱草（Elymus nutans）/星星草（Puccinellia tenuflora）高寒混播人工草地牦牛放牧系统、紫花针茅（Stipa purpurea）高寒草原藏系绵羊放牧系统中草地次级生产力（家畜增重）的试验数据,构建了放牧家畜个体增重与放牧强度之间的模型：Y=a-bX（b>0）,以此为基础确定了单位面积草地次级生产力（家畜增重）与放牧强度之间的数学模型：Y=aX-bX²（b>0）;计算出各放牧系统最大生产力放牧强度：高寒草甸冷季和暖季草场分别是1.68头·hm^-2和2.52头·hm^-2,高寒人工草地牧草生长季为7.23头·hm^-2,高寒草原冷季、暖季和全年连续放牧草场分别是4.33,6.45,2.36只·hm^-2。     

Feeding distillers dried grains with solubles and organic trace mineral sources to swine and the resulting effect on gaseous emissions

The objective of the study was to evaluate the dietary effects of distillers dried grains with solubles (DDGS) with either inorganic or organic trace mineral sources on air emissions. Three diets were compared: a corn- and soybean meal-based control diet (Con), a diet containing 20% DDGS with inorganic trace mineral sources (20In), and a diet containing 20% DDGS with organic trace mineral sources (20Org). Groups of 6 pigs were allocated randomly to 1 of 12 environmentally controlled rooms for a 98-d experiment. A total of 72 pigs were blocked into 3 light and 3 heavy BW groups to minimize BW variation. Average initial BW for the light and heavy blocks were 22.6 kg and 27.0 kg, respectively. Concentrations and airflow of NH?, H?S, N?O, CH(4), CO?, and nonmethane total hydrocarbons (NMTHC) were measured in the exhaust air from each room. Body weight gain (94 kg per pig; P = 0.36) and G:F (0.39; P = 0.79) were not different as a result of diet, although a reduced feed intake was observed in pigs offered 20Org (P < 0.05). Total daily H?S emission mass was greater (P = 0.03) in rooms where the 20In diet was offered (462.26 mg) compared with rooms where the Con (354.62 mg) and 20Org (323.10 mg) diets were offered. No dietary effect (P = 0.47) was observed when H?S emissions were adjusted for S consumption (14.38 mg of H?S emitted daily per gram of S consumed). Compared with NH? emitted on the Con diet, the daily mass of NH? emitted decreased by 7.6% when pigs were fed 20In and increased by 11.0% in rooms where the 20Org was fed (P < 0.05). On a N consumption basis, feeding swine 20In significantly reduced NH? emissions compared with 20Org and Con, whereas NH? emissions from pigs fed 20Org were significantly greater than emissions from pigs fed the Con diet (P < 0.01). The NH? emission mass from rooms offered the Con, 20In, and 20Org diets was 120.1, 109.8, and 142.8 mg/g of N consumed/d, respectively (P < 0.01). Feeding DDGS with either inorganic or organic trace mineral sources increased the daily emission masses of CH? and NMTHC (P < 0.01), but not N?O emissions. Plasma urea N (P = 0.64), albumin (P = 0.39), globulin (P = 0.75), and total bilirubin concentrations (P = 0.82) were not different between diet groups. Results demonstrated that DDGS will increase H?S, CH?, NH?, and NMTHC emissions from pigs, but organic sources of trace minerals are a promising mitigation strategy to alleviate the adverse effect of DDGS on H?S emissions.     

放牧干扰对荒漠草原土壤性状的影响

在宁夏荒漠草原选取围封禁牧(NG)、轻度放牧(LG)、中度放牧(MG)和重度放牧(HG)4个放牧强度,研究不同放牧强度对土壤物理和化学性状的影响。结果表明,放牧干扰对荒漠草原土壤物理和化学性状影响显著。土壤含水量和孔隙度随着放牧强度的增加呈显著降低趋势,而土壤容重和pH值呈线性增加趋势。重度、中度、轻度放牧0～30 cm土壤含水量和孔隙度比围封禁牧分别降低了21.1%,12.0%,4.7% 和 3.2%,2.5%,2.1%。不同放牧强度土壤含水量随着土壤深度的增加均呈显著增加趋势。随着放牧强度的增加,土壤有机碳和C/N降低。重度放牧0～10和10～20 cm土壤有机碳比围封禁牧分别降低了20.6%和14.1%,土壤C/N分别降低了43.4% 和34.1%。土壤全磷、速效磷和全钾含量随着放牧强度增加呈增加趋势,而土壤电导率和全氮含量呈先增加后降低趋势。合理放牧可以改善荒漠草原土壤结构和养分性状,有利于遏制荒漠草原土壤的退化。     

Greenhouse gas emissions from pastoral based dairying systems: The effect of uncertainty and management change under two contrasting production systems

A previously developed model, the Pastoral Milk Emission Model (PME Model) was used to simulate both on-farm and off-farm greenhouse gas (GHG) e`missions (consisting of methane (CH₄), nitrous oxide (N₂O) and carbon dioxide (CO₂)) under two contrasting pastoral based milk production systems. There were two primary objectives to this study. Firstly within the production systems studied, to identify the effect simple management changes may have on GHG emissions and farm profitability so that financially viable whole farm GHG mitigation strategies could be developed. The potential effect these management changes could have on national GHG emissions was quantified. The second objective was to determine what effect the characteristics of the production system may have on the uncertainty surrounding the emission of GHGs.The two contrasting production systems were the standard production procedures recommended for Kilmaley, (County Clare, Ireland) and Moorepark (County Cork, Ireland), with grazing seasons of 149 and 250 days per year respectively. The management scenarios tested were changes in pasture quality, pasture utilisation, N application rates, silage quality, level of concentrate supplementation and calving date.Stochastic budgeting revealed that emissions of GHGs were greater at Kilmaley than Moorepark whatever the level of risk/uncertainty. Simple farming system changes, regardless of location, generally resulted in small changes in both on-farm and total GHG emissions (between—5.8 and + 5.1%). However silage quality demonstrated a site specific interaction. Tailor designed whole farm GHG mitigation strategies were developed by combining all identified management changes, which simultaneously reduced GHG emissions and increased farm profitability. Relative to the standard production systems at Moorepark and Kilmaley, on-farm and total GHG emissions were 6.65% and 8.42% and 11.40% and 11.64% respectively. Farm profitability increased at both sites. Projecting these potential reductions onto the national dairy herd revealed that significant reductions in GHG emissions are possible. Relative to 2005 national emissions the implementation of the standard systems would achieve a reduction of 3.46%, this would increase to 4.04% for the tailor designed strategies. Additional reductions in GHG emissions would be achieved through a lowering of inputs within the farm supply chain.Sensitivity analysis revealed differences between systems with regards to source strength, however regardless of the system, source strength was always greatest for enteric CH₄, confirmation that considerable efforts should be made to control this GHG source. However differences do exist between systems which suggests that national mitigation strategies must consider regional production systems if GHG reductions are to be maximised. This work has also highlighted the need for more data on indirect GHG emissions derived from leached N.