Gaseous emissions of nitrogen and carbon from urban vegetable gardens in Bobo‐Dioulasso,Burkina Faso

Urban and peri‐urban agriculture (UPA) is an important livelihood strategy for the urban poor in sub‐Saharan Africa and contributes to meeting increasing food demands in the rapidly growing cities. Although in recent years many research activities have been geared towards enhancing the productivity of this land‐use system, little is known about turnover processes and nutrient efficiency of UPA. The aim of our study therefore was to determine horizontal fluxes of N, P, K, and C as well as gaseous N and C emissions in urban vegetable gardens of Bobo‐Dioulasso, Burkina Faso. Two gardens referred to as “Kodéni” and “Kuinima” were selected as representative for urban and peri‐urban systems classified as: (1) “commercial gardening + field crops and livestock system” and (2) “commercial gardening and semicommercial field crop system”, respectively. A nutrient‐balance approach was used to monitor matter fluxes from March 2008 to March 2009 in both gardens. Ammonia (NH₃), nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions from the respective soils were measured during the coolest and the hottest period of the day using a closed‐chamber system. Annual partial balances amounted to 2056 kg N ha^–1, 615 kg P ha^–1, 1864 kg K ha^–1, and 33 893 kg C ha^–1 at Kodéni and to 1752 kg N ha^–1, 446 kg P ha^–1, 1643 kg K ha^–1, and 21 021 kg C ha^–1 at Kuinima. Emission rates were highest during the hot midday hours with peaks after fertilizer applications when fluxes of up to 1140 g NH₃‐N ha^–1 h^–1, 154 g N₂O‐N ha^–1 h^–1, 12 993 g CO₂‐C ha^–1 h^–1 were recorded for Kodéni and Kuinima. Estimated annual gaseous N (NH₃‐N + N₂O‐N) and C (CO₂‐C + CH₄‐C) losses reached 419 kg N ha^–1 and 35 862 kg C ha^–1 at Kodéni and 347 kg N ha^–1 and 22 364 kg C ha^–1 at Kuinima. For both gardens, this represented 20% and 106% of the N and C surpluses, respectively. Emissions of NH₃, largely emitted after surface application of manure and mineral fertilizers, accounted for 73% and 77% of total estimated N losses for Kodéni and Kuinima. To mitigate N losses nutrient‐management practices in UPA vegetable production of Bobo‐Dioulasso would greatly benefit from better synchronizing nutrient‐input rates with crop demands.     

Horizontal matter fluxes and leaching losses in urban and peri‐urban agriculture of Kabul,Afghanistan

Little is known about nutrient fluxes and nutrient‐use efficiencies in urban and peri‐urban agriculture (UPA) of rapidly expanding cities in developing countries. Therefore, horizontal flows of carbon (C), nitrogen (N), phosphorus (P), and potassium (K) as well as leaching losses of mineral N and P were measured over 2 years in three representative agricultural production systems of Kabul. These comprised 21 gardens and 18 fields dedicated to vegetable farming, cereal farming, and table‐grape production (vineyards). Across sites (fields and gardens) biennial inputs averaged 375 kg N ha^–1, 155 kg P ha^–1, 145 kg K ha^–1, and 15 kg C ha^–1 while with harvests 305 kg N ha^–1, 40 kg P ha^–1, 330 kg K ha^–1, and 7 kg C ha^–1 were removed. In vegetable gardens, biennial net balances were 80 kg N ha^–1, 75 kg P ha^–1, –205 kg K ha^–1, and 4 kg C ha^–1, whereas in cereal farming biennial horizontal balances amounted to –155 kg N ha^–1, 20 kg P ha^–1, –355 kg K ha^–1, and 5 kg C ha^–1. In vineyards, corresponding values were 295 kg N ha^–1, 235 kg P ha^–1, 5 kg K ha^–1, and 3 kg C ha^–1. Annual leaching losses in two selected vegetable gardens varied from 70 to 205 kg N ha^–1 and from 5 to 10 kg P ha^–1. Night soil and irrigation water were the major sources among the applied nutrient inputs in all studied farming systems, contributing on average 12% and 25% to total N, 22% and 12% to total P, 41% and 53% to total K, and 79% and 10% to total C, respectively. The results suggest that soils in extensive cereal fields are at risk of N and K depletion and in vegetable gardens of K depletion, while vineyards may be oversupplied with nutrients possibly contributing to groundwater contamination. This merits verification.     

中国北方农田氮磷淋溶损失污染与防控机制

突破厚包气带农田根层氮磷淋溶与地下水污染复杂定量关系和阻控机理是国际研究难点。本文系统梳理了重点研发专项"农田氮磷淋溶损失污染与防控机制"项目取得的主要进展,项目包括以下4方面研究内容:1)北方主要农区农田根层氮磷淋溶时空规律;2)根层—深层包气带氮磷淋溶机制和主控因子;3)黑土、潮土和褐土氮磷淋溶阻控机制及其效果; 4)典型农区氮磷淋溶风险与区域消减途径。主要科学发现包括:1)受土地利用类型、地下水埋深、包气带岩性、水文地质条件等综合因素的影响,黑土区、潮土区和褐土区根层氮磷淋溶规律与地下水硝酸盐超标率体现出空间不一致和较大差异性。黑土区虽然根层淋溶较小,然而受地形地貌影响,地下水水质对淋溶响应更强烈,应该进一步研究黑土区地下水水质对淋溶的响应机制。华北潮土区和褐土区厚包气带具有明显氮阻控能力,应该进一步加强厚包气带对氮磷淋溶减排机理与途径研究。2)基于长期施肥定位试验和12 m深观测井对包气带农田土壤氮盈余累积特征和淋失规律的研究发现,华北平原区的环境安全施氮量约为200kg(N)·hm~(-2)·a~(-1),超过环境安全阈值的多投入氮肥中有51%淋失到1m根层以下,不合理灌溉、强降水、大孔隙和裂隙是造成土壤硝酸盐淋溶的主要因素,对包气带累积硝态氮的淋失作用可影响至6m以下土层。3)利用深层取样和生物学方法结合,对厚包气带0～10.5m原位土壤微生物的反硝化活性和微生物区系组成的研究结果表明,表层土壤是微生物进行反硝化的主要场所,深层土壤中反硝化作用显著减弱,"碳饥饿"是限制底层土壤反硝化微生物丰度与活性的关键因素;室内培养试验证实添加碳源可有效激活土壤微生物的反硝化活性,为"根层截氮包气带脱氮"的淋溶阻控机理找到了突破口。4)利用黑土、潮土和褐土区氮磷淋溶阻控试验、全国农业面源污染国控监测网、北方农区地下水硝酸盐监测网和NUFER (NUtrient flows in Food chains, Environment and Resourcesuse)模型,提出了养分损失脆弱区区划和区域氮磷污染削减草案,可为农业绿色发展和面源污染阻控提供科学依据。     

设施菜地土壤氮素运移及淋溶损失模拟评价

设施菜地因大水大肥管理方式导致的氮素淋失已成为当前关注焦点。探寻氮素淋失阻控技术需要首先探明土壤中NO_3~--N的运移和淋失过程,找到淋失阻控的关键点,从而实现蔬菜栽培高产量低环境成本。本研究以京郊设施菜地黄瓜-番茄轮作系统为研究对象,通过田间试验获取土壤温度、湿度、NO_3~--N含量等数据,对反硝化-分解(DNDC)模型进行参数校验,并以农民常规种植模式为基线情景,设置改变土壤基础性质、灌溉量、施氮量等不同情景,运用DNDC模型对设施菜地系统土壤氮素运移及淋溶损失进行定量评价。结果表明:经验证后的DNDC模型能够较好地模拟蔬菜产量、5 cm土壤温度和0～20 cm土壤孔隙含水率变化以及NO_3~--N的迁移过程,是模拟和评价氮素运移和损失的有效工具。模拟不同情景表明,设施菜地0～60 cm土壤NO_3~--N累积主要受灌溉水量和氮肥施入量的影响,此外土壤pH和土壤有机碳的变化也是影响NO_3~--N运移的重要因子。节水节肥是设施菜地氮素淋失减量的最有效方法,相比常规措施,同时减少20%灌溉量和20%施氮量可明显降低59.04%的NO_3~--N淋失量。同时,在节水节肥的基础上改变灌溉方式并提高20%土壤有机碳含量,在保证蔬菜产量的前提下,能够进一步降低69.04%的NO_3~--N淋失量。可见, DNDC模型为设施菜地NO_3~--N淋失评价和阻控提供了一个较好的解决方案。在当前重点关注减氮节水等管理措施的同时,提高土壤本身的质量,不失为一种更有效的减少设施菜地氮素淋失的途径。     

Potential nitrogen and phosphorus leaching from soils fertilized with meat and bone meal

Abstract

The nitrogen and phosphorus contents of meat and bone meal (MBM) make it a potentially valuable nutrient source in agriculture. Its narrow N:P ratio, however, makes it a potential environmental risk if it is not utilized with caution. A column-leaching experiment was conducted to assess potential nitrogen and phosphorus leaching from bare soils fertilized with MBM. This should give an idea of the efficacy of autumn or early spring MBM application on land devoid of vegetation cover. Earlier greenhouse and field experiments have indicated that nitrogen mineralization after MBM application takes place relatively rapidly. The column experiment conducted here has indicated that spring application of MBM prior to planting can result in the loss of mineral nitrogen, reducing the total amount of N available to the crop. A higher initial loss (up to 47 mg l^?1) of ammonium was found for the MBM treated soils, but this declined to less than 0.1 mg l^?1 by the end of the experiment, 11 weeks later. Nitrate loss was highest at the onset of the experiment for the soils that received mineral N fertilizer. With time, however, the largest nitrate losses were associated with the MBM-treated soils. Nitrate leaching continued to well beyond the end of the experiment. The effect will most certainly be exacerbated when the crop N (rather than crop P) requirement forms the basis for MBM application. The amount of P leached as ortho-P is probably small but may also represent an environmental risk if N remains to be the basis of MBM application. Based on the results presented here and considering the dangers of elevated nutrient losses, autumn and early spring MBM application may not be recommended.     

降雨对吉林省黑土区雨养春玉米农田氮磷淋溶的影响

吉林省黑土区是我国玉米生产的重要基地,农业集约化程度较高,农业面源污染风险较大。因此,掌握吉林省黑土区降雨与农田氮磷淋溶的关系,对区域生态农业可持续发展意义重大。本研究基于吉林省4个面源污染监测点,于2016-2019年春玉米季对降雨情况、淋溶量、淋溶液氮磷浓度及淋溶强度等进行了动态监测,系统分析了吉林省黑土区自然降雨与农田氮磷淋溶的关系。结果表明:1)吉林省黑土区降雨年际间和监测点间差异较大,年际间波动在424～554mm,春玉米全生育期平均降雨量为475mm;不同监测点降雨量大小依次为通化(593～785 mm)公主岭(512～699 mm)梨树(305～434 mm)农安(197～342 mm)。2)淋溶量和降雨强度呈极显著正相关关系,降雨强度每增加10 mm·(24h)-1,淋溶量增加1.81mm。全生育期(4-10月)降雨量与淋溶次数、淋溶概率分别呈极显著和显著正相关,降雨量每增加100mm,淋溶次数约增加3次,淋溶概率上升6%。当全生育期降雨量超过74mm时,淋溶概率增加,可能引起淋溶;而当全生育期降雨量达到217mm时,淋溶次数增加,可以发生淋溶。产生淋溶的降雨等级一般以中雨(10～24.9 mm)和大雨(25～49.9 mm)为主。3)淋溶量和淋溶液总氮浓度呈极显著正相关,与总磷浓度无明显相关关系。4)总氮淋溶强度与降雨强度呈极显著正相关,降雨强度每增加10 mm·(24h)-1,总氮淋溶强度增加0.73kg·hm~(-2),而总磷淋溶强度与降雨强度无明显相关性。由此可见,吉林省黑土区农田在春玉米雨养条件下以氮素淋溶为主,且与降雨密切相关,应因地制宜采取农艺措施在源头上阻控农业面源污染的发生,为农业生态可持续发展提供有效途径。     

Carbon dioxide and gaseous nitrogen emissions from biochar‐amended soils under wastewater irrigated urban vegetable production of Burkina Faso and Ghana

To quantify carbon (C) and nitrogen (N) losses in soils of West African urban and peri‐urban agriculture (UPA) we measured fluxes of CO₂‐C, N₂O‐N, and NH₃‐N from irrigated fields in Ouagadougou, Burkina Faso, and Tamale, Ghana, under different fertilization and (waste‐)water regimes. Compared with the unamended control, application of fertilizers increased average cumulative CO₂‐C emissions during eight cropping cycles in Ouagadougou by 103% and during seven cropping cycles in Tamale by 42%. Calculated total emissions measured across all cropping cycles reached 14 t C ha^?1 in Ouagadougou, accounting for 73% of the C applied as organic fertilizer over a period of two years at this site, and 9 t C ha^?1 in Tamale. Compared with unamended control plots, fertilizer application increased N₂O‐N emissions in Ouagadougou during different cropping cycles, ranging from 37 to 360%, while average NH₃‐N losses increased by 670%. Fertilizer application had no significant effects on N₂O‐N losses in Tamale. While wastewater irrigation did not significantly enhance CO₂‐C emissions in Ouagadougou, average CO₂‐C emissions in Tamale were 71% (1.6 t C ha^?1) higher on wastewater plots compared with those of the control (0.9 t C ha^?1). However, no significant effects of wastewater on N₂O‐N and NH₃‐N emissions were observed at either location. Although biochar did not affect N₂O‐N and NH₃‐N losses, the addition of biochar could contribute to reducing CO₂‐C emissions from urban garden soils. When related to crop production, CO₂‐C emissions were higher on control than on fertilized plots, but this was not the case for absolute CO₂‐C emissions.     

Soil phosphorus dynamics in a Vertisol as affected by cattle manure and nitrogen fertilization in soybean‐wheat system

Repeated application of phosphorus (P) as superphosphate either alone or in conjunction with cattle manure and fertilizer N may affect the P balance and the forms and distribution of P in soil. During 7 years, we monitored 0.5 M NaHCO₃ extractable P (Olsen‐P) and determined the changes in soil inorganic P (P_i) and organic P (P_o) caused by a yearly dose of 52 kg P ha^—1 as superphosphate and different levels of cattle manure and fertilizer N application in a soybean‐wheat system on Vertisol. In general, the contents of Olsen‐P increased with conjunctive use of cattle manure. However, increasing rate of fertilizer nitrogen (N) reduced the Olsen‐P due to larger P exploitation by crops. The average amount of fertilizer P required to increase Olsen‐P by 1 mg kg^—1 was 10.5 kg ha^—1 without manure and application of 8 t manure reduced it to 8.3 kg ha^—1. Fertilizer P in excess of crop removal accumulated in labile (NaHCO₃‐P_i and P_o) and moderately labile (NaOH‐P_i and P_o) fractions linearly and manure application enhanced accumulation of P_o. The P recovered as sum of different fractions varied from 91.5 to 98.7% of total P (acid digested, P_t). Excess fertilizer P application in presence of manure led to increased levels of Olsen‐P in both topsoil and subsoil. In accordance, the recovery of P_t from the 0—15 cm layer was slightly less than the theoretical P (P added + change in soil P — P removed by crops) confirming that some of the topsoil P may have migrated to the subsoil. The P fractions were significantly correlated with apparent P balance and acted as sink for fertilizer P.     

基于养分损失脆弱区的氮磷淋溶分区消减策略

农业面源污染研究多聚焦于田块尺度,缺少对区域尺度氮磷损失风险和消减途径的探索。因此,本研究提出在区域尺度依据养分损失风险制定管理策略,以期在现有技术条件下充分发挥减排措施潜力、全面提升面源污染区域阻控效力。本文利用水质监测数据、文献数据、地理要素空间数据和基于NUFER（NUtrient flows in Food chains,Environment and Resources use）模型模拟的养分损失结果,划定了我国养分损失脆弱区;在此基础上,按照我国农业生态区划和养分损失脆弱区级别确定了各区养分管控程度,并结合各区自然和社会经济条件选取可行、高效的养分管理技术,形成了我国氮磷淋溶区域消减策略和技术列单;最后通过模型再次评估了分区氮磷消减策略的效果。结果表明：养分损失脆弱区和潜在脆弱区覆盖了全国耕地面积的52%,广泛分布于主要农产品产区,呈现显著的空间聚集特征;分区养分管理可以消减51%的潜在脆弱区面积,消减潜力较大的区域集中在东北、长江中下游和西南地区;氮淋溶强度超过22.6 kg·hm^-2的区域覆盖耕地面积3.1×10⁷ hm²,通过实施基于养分损失脆弱区的分区氮磷消减措施,氮淋溶超标区内耕地面积减少至1.9×10⁷ hm²,消减比例约为40%。上述养分损失脆弱性区划和区域氮磷消减草案可为农业绿色发展和面源污染控制提供科学依据。     

不同蔬菜种植模式对土壤淋溶水总氮、总磷和COD的影响

以中国农业大学曲周实验站始于2002年的日光温室有机蔬菜长期定位试验为基础,采用渗漏计装置收集地下1 m深淋溶水,通过测定2014年春茬茄子与秋茬芹菜土壤淋溶水总氮、总磷和化学需氧量(COD),研究不同蔬菜种植模式(有机、综合、常规)下土壤养分淋失情况。结果表明:有机模式总氮淋失量两茬蔬菜之和为137.02 kg·hm~(-2),分别比综合和常规模式减少12.0%和25.9%;总磷淋失量两茬蔬菜之和为18.23 kg·hm~(-2),分别比综合和常规模式高51.2%和119.9%;淋溶水COD两茬蔬菜之和为856.99 kg·hm~(-2),分别比综合和常规模式高32.4%和3.1%。3种模式下不同时期淋溶水总氮、总磷与COD变化趋势差异显著。春茬茄子总氮淋失量前期维持在较高水平,追肥后出现峰值,之后迅速降低,进入6月份后一直在较低水平波动;总磷淋失量变化相对平缓,呈先增加后减小的变化趋势,6—7月间达到峰值;淋溶水COD前期稍有降低,追肥前达到最低值,进入5月份后到茄子季结束呈现逐渐上升的趋势。综上,有机种植模式在减少氮素淋失方面较综合和常规模式表现出优势,但会显著增加磷素淋失风险,并在一定程度上提高淋溶水COD。     

不同水肥措施下华北露地菜地氮淋溶特征

华北地区典型一年两季露地蔬菜种植系统,蔬菜生长季水热同季、种植管理中水氮供应充足且往往过量,造成大量氮素淋溶到深层土壤,不仅造成水肥资源利用率低,对地下水质也造成威胁。本文以华北潮褐土黄瓜-白菜一年两季典型露地蔬菜为研究对象,利用田间试验研究不同氮肥用量及优化措施(包括抑制剂、生物炭、秸秆还田)以及控制灌溉量对蔬菜产量、土壤氮淋溶及氮平衡的影响。研究结果表明:1)华北典型露地菜地氮肥主要损失去向为深层土壤中积累及氮淋溶。2)农民常规施肥处理[黄瓜季和白菜季各施550 kg(N)·hm~(-2)]淋洗出80cm土壤剖面的总氮占当季氮肥施用量的10.0%,减氮20%和50%分别使总氮淋溶量降低23.8%和45.6%;减氮20%对蔬菜产量没有显著影响,减氮50%对水肥需求量较高的黄瓜产量有显著影响(减产19.6%)。3)减氮20%配合脲酶抑制剂和硝化抑制剂、施用生物炭和添加秸秆还田分别使全年总氮淋溶量比常规水肥处理降低40.7%、43.0%和34.3%,而对蔬菜产量没有显著影响。4)减少灌溉量15%和30%分别使总氮淋溶比常规水肥处理降低43.1%和50.5%,水氮协同调控对降低氮淋溶效果显著;对需水量较高的黄瓜季,灌溉量降低30%黄瓜产量显著降低13.9%。5)高量水肥投入条件下连续种植蔬菜3年6季后,0～80cm土壤剖面硝态氮积累量占0～200 cm土壤剖面积累量的38.2%～50.7%,土壤剖面积累了大量硝态氮而且向深层土壤中移动。因此,合理控制水肥管理,特别是减氮结合脲酶抑制剂和硝化抑制剂配合水分管理,是经济可行的有效阻控土壤氮淋溶的措施。     

黑土区农田氮磷淋溶消减措施

黑土是我国重要的土壤资源,承载了全国50%以上的玉米产量。但过量的化肥施入和不合理的农业管理造成黑土土壤氮磷大量残留,氮磷淋溶风险增强。相关研究表明,尽管黑土区旱地农田氮磷淋溶损失相对较低,肥料残留效应仍致使其潜在淋溶风险增强。因此,本研究综合分析了环境因子和农业管理措施对黑土区农田氮磷淋溶特征的影响规律,明确了黑土氮磷淋溶消减措施,并针对玉米农田和蔬菜地提出消减策略。具体结果如下:施肥和降水是影响黑土农田氮磷淋溶的重要因素,灌溉是影响蔬菜地氮磷淋溶的关键农田管理措施;按需施肥、有机无机配施、避免雨热同期追肥、节水灌溉、免耕秸秆覆盖、不同作物轮作和添加生物炭等均是适合于当地气候和土壤条件的氮磷淋溶阻控措施。建议玉米农田采用一次性基肥施入,有机肥占比50%～70%,采用免耕秸秆覆盖技术;蔬菜地在常规施肥和灌溉频次下分别降低20%的施肥量和灌溉量,推荐蔬菜秋季收获后秸秆粉碎深埋等管理措施。本研究明确了黑土区农田氮磷淋溶消减策略,有助于实现黑土区农业绿色可持续发展和绿色生态环境的构建。     

Long‐term development of nitrogen fluxes in a coniferous ecosystem: Does soil freezing trigger nitrate leaching?

In many forest ecosystems chronically large atmospheric deposition of N has caused considerable losses of inorganic N by seepage. Freezing and thawing of soil may alter the N turnover in soils and thereby the interannual variation of N seepage fluxes, which in turn makes it difficult to evaluate the N status of forest ecosystems. Here, we analyzed long‐term monitoring data of concentrations and fluxes of dissolved inorganic N (DIN) in throughfall and seepage from a Norway spruce stand at the Fichtelgebirge (SE Germany) between 1993 and 2004. Despite constant or even slightly increasing N inputs in throughfall, N losses with seepage at 90 cm declined from 15–32 kg N ha^–1 y^–1 in the first years of the study period (1993–1999) to 3–10 kg N ha^–1 y^–1 in 2000 to 2004. The large N losses in the first years coincided with extreme soil frost in the winter of 1995/96, ranging from –3.3°C to –1.0°C at 35 cm soil depth. Over the entire observation period, maximum fluxes of nitrate and ammonium were observed in the mineral soil following thawing of the soil. The elevated ammonium and nitrate fluxes resulted apparently from increased net ammonification and nitrification rates in the mineral soil, whereas mineral‐N fluxes in the O horizon were less affected by frost. Our data suggest that (1) extreme soil frost may cause substantial annual variations of nitrate losses with seepage and that (2) the assessment of the N status of forest ecosystems requires long periods of monitoring. Time series of biogeochemical data collected over the last 20–30 y include years with extreme cold winters and warm summers as well as unusual precipitation patterns. Analysis of such long‐term monitoring data should address climate extremes as a cause of variation in N outputs via leaching. The mean loss of 14.7 kg N with seepage water during 12 y of observation suggests that the forest ecosystem was saturated with N.     

Changes in soil nitrogen availability due to stand development and management practices on semi‐arid sandy lands,in northern China

Soil nitrogen (N) availability is one of the limiting factors for plant growth on sandy lands. Little is known about impacts of afforestation on soil N availability and its components in southeastern Keerqin sandy lands, China. In this study, we measured N transformation under sandy Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations of different ages (grassland, young, middle‐aged, close‐to‐mature) and management practices (non‐grazing and free‐grazing) during the growing seasons using the ion exchange resin bag method. Results showed that, for all plots and growing season, soil NH‐N, NO‐N, mineral N, and relative nitrification index, varied from 0·18 to 1·54, 0·96 to 22·05, 1·23 to 23·58 µg d⁻¹ g⁻¹ dry resin, and 0·76 to 0·97, respectively, and NO‐N dominated the available N amount due to intense nitrification in these ecosystems. In general, the four indices significantly increased in the oldest plantation, with corresponding values in non‐grazing sites lower than those in free‐grazing sites (p < 0·05). Our studies indicated that it is a slow, extended process to achieve improvement in soil quality after afforestation of Mongolian pine in the study area. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of extensive land use and re‐wetting on diffuse phosphorus pollution in fen areas—results from a case study in the Drömling catchment,Germany

Fen‐soil cultivation in NE Germany resulted in severe peat degradation; therefore present and future management is aimed to restore degraded sites by re‐wetting. Evidence in the literature indicates that decreasing redox potentials in re‐wetted fens may result in an increased risk of diffuse water pollution with P. However, little is known about the impact of different fen‐preserving land‐management schemes on the redox potential in soil and on the P dynamics in adjacent surface water. We investigated effects of peat degradation and re‐wetting on redox potential and P mobilization on extensive grassland, re‐wetted intensive grassland, and alder swamp forest in the Drömling (Saxony‐Anhalt, Germany). The results showed that the redox potentials of peat lands were almost below the theoretical stability fields of Fe(III)‐containing minerals. The re‐wetted site was characterized by the highest concentrations of soluble reactive P (SRP) in surface water. Average SRP concentrations up to 0.36 mg l^–1 indicated an increased P load. The concentration of SRP in the Ohre river, which is the central drainage channel of the Drömling catchment, significantly increased since 1996. The P concentrations of surface water were found to be indirectly correlated with the redox potentials.     

Effects of short‐term nitrogen supply from livestock manures and cover crops on silage maize production and nitrate leaching

Resource use efficiency requires a correct appreciation of the nitrogen (N) fertilizer replacement value (NFRV, percentage of total N applied) of manures. We assessed the NFRVs of the liquid fraction originating from separated pig slurry (MC), untreated pig slurry (PS), untreated cattle slurry (CS), the solid fraction from separated pig slurry (SF) and solid farmyard manure from cattle (FYM) in two consecutive years in silage maize grown on a sandy soil. Maize yields responded positively to each of these N sources applied at rates up to 150 kg of mineral fertilizer equivalents per ha per year (i.e. NFRV × total N rate). The observed NFRVs, relative to calcium ammonium nitrate fertilizer, amounted to 78% for MC, 82% for PS, 79% for CS, 56% for SF and 34% for FYM when averaged over both years. NFRVs were positively related to the ammonium‐N share in the total N content. Rye cover crop establishment after the harvest of maize reduced nitrate concentrations of the upper groundwater by, on average, 7.5 mg nitrate‐N/L in the first year and 10.9 mg/L in the second year, relative to a bare soil. Regardless of the presence of a cover crop, nitrate concentrations responded positively to the applied rate of effective N (total N × NFRV) but less to postharvest residual soil mineral N.     

The effect of nitrogen fertilization and no‐till duration on soil nitrogen supply power and post–spring thaw greenhouse‐gas emissions

With a world population now > 7 billion, it is imperative to conserve the arable land base, which is increasingly being leveraged by global demands for producing food, feed, fiber, fuel, and facilities (i.e., infra‐structure needs). The objective of this study was to determine the effect of varying fertilizer‐N rates on soil N availability, mineralization, and CO₂ and N₂O emissions of soils collected at adjacent locations with contrasting management histories: native prairie, short‐term (10 y), and long‐term (32 y) no‐till continuous‐cropping systems receiving five fertilizer‐N rates (0, 30, 60, 90, and 120 kg N ha^–1) for the previous 9 y on the same plots. Intact soil cores were collected from each site after snowmelt, maintained at field capacity, and incubated at 20°C for 6 weeks. Weekly assessments of soil nutrient availability along with CO₂ and N₂O emissions were completed. There was no difference in cumulative soil N supply between the unfertilized long‐term no‐till and native prairie soils, while annual fertilizer‐N additions of 120 kg N ha^–1 were required to restore the N‐supplying power of the short‐term no‐till soil to that of the undisturbed native prairie soil. The estimated cumulative CO₂‐C and N₂O‐N emissions among soils ranged from 231.8–474.7 g m^–2 to 183.9–862.5 mg m^–2, respectively. Highest CO₂ fluxes from the native prairie soil are consistent with its high organic matter content, elevated microbial activity, and contributions from root respiration. Repeated applications of ≥ 60 kg N ha^–1 resulted in greater residual inorganic‐N levels in the long‐term no‐till soil, which supported larger N₂O fluxes compared to the unfertilized control. The native prairie soil N₂O emissions were equal to those from both short‐ and long‐term no‐till soils receiving repeated fertilizer‐N applications at typical agronomic rates (e.g., 90 kg N ha^–1). Eighty‐eight percent of the native soil N₂O flux was emitted during the first 2 weeks and is probably characteristic of rapid denitrification rates during the dormant vegetative period after snowmelt within temperate native grasslands. There was a strong correlation (R² 0.64; p < 0.03) between measured soil Fe‐supply rate and N₂O flux, presumably due to anoxic microsites within soil aggregates resulting from increased microbial activity. The use of modern no‐till continuous diversified cropping systems, along with application of fertilizer N, enhances the soil N‐supplying power over the long‐term through the build‐up of mineralizable N and appears to be an effective management strategy for improving degraded soils, thus enhancing the productive capacity of agricultural ecosystems. However, accounting for N₂O emissions concomitant with repeated fertilizer‐N applications is imperative for properly assessing the net global warming potential of any land‐management system.     

The fate of nitrogen,phosphorus and potassium in long‐term experiments in Skierniewice

On the basis of long‐term fertilization experiments in Skierniewice, being conducted since 1923 at the Experimental Field of Warsaw Agricultural University, the fate (or balance) of nitrogen for a period of 35 years and that of phosphorus and potassium for 20 years, was studied. The balance includes N, P and K rates applied in mineral fertilizers and farmyard manure (FYM), uptake of these nutrients by the crop plants and the changes in the content of total N and total P and of slow release K in the soil during that time. The nitrogen balance shows a loss of this nutrient of 11—14 kg N ha^—1 y^—1, which corresponds to 15% of the applied ammonium nitrate on fields without FYM but to 23% on fields with FYM, in spite of crop yields being considerably greater on fields treated with FYM. The phosphorus balance indicated that in the 0—70 cm soil layer less than 4% of P from superphosphate was not found. In the treatment not fertilized with potassium for many years, the plants took up 49 kg K ha^—1 y^—1 from slow release forms because the fraction of available K did not change during that period. When calculating the potassium balance only 1.6% of K from potash salt were not found in plots without FYM but 12.3% of the applied KCl were not recovered in treatments with FYM. The comparison of the P‐ and K‐uptake from organic and mineral fertilizer in the two crop rotations indicates a higher P‐ and K‐efficiency from FYM than from inorganic fertilizer.     

Residual effect and nitrate leaching in grass‐arable rotations: effect of grassland proportion,sward type and fertilizer history

A key point in designing grass‐arable rotations is to find the right balance between the number of cultivations and the length of the grass phase. In a field experiment, we investigated the effect of cropping history (grazed unfertilized grass–clover and fertilized [300 kg N per hectare] ryegrass, proportion of grassland and previous fertilizer use) on crop growth and nitrate leaching for 2 years following grassland cultivation. In the final year, the effect of perennial ryegrass as a catch crop was investigated. The nitrogen fertilizer replacement value (NFRV) of grassland cultivation was higher at 132 kg N per hectare in the rotation with 75% grassland compared with on average 111 kg N per hectare in rotations with 25 and 38% grassland and the NFRV of ryegrass in the rotation was higher than that of grass–clover. Nitrate leaching following cultivation was not affected by the proportion of grassland in the crop rotation or sward type. However, there was a considerable effect of having a ryegrass catch crop following the final barley crop as nitrate leaching was reduced from 60 to 9 kg N per hectare. When summarizing results from the crop rotations over a longer period (1997–2005), management strategy adopted in both the grassland and arable phases appeared to be the primary instrument in avoiding nutrient losses from mixed crop rotations, irrespective of grass proportion. In the arable phase, the huge potential of catch crops has been demonstrated, but it is also important to realize that all parts of the grass‐arable crop rotations must be considered potentially leaky.