秸秆及其生物炭对土壤碳库管理指数及有机碳矿化的影响

以河南省粮食主产区壤质潮土和砂土为研究对象,通过盆栽试验和室内恒温培养试验,研究了生物炭与不同腐殖化程度的传统有机物料(秸秆和腐熟鸡粪)单施及配施对壤质潮土和砂土有机碳储量、活性及碳库管理指数的影响,并进一步比较了小麦秸秆直接还田和制炭还田对土壤有机碳矿化的影响,以及生物炭对土壤原有有机碳矿化的调控作用。结果表明:相同添加量下,生物炭对土壤有机碳含量的提升效果优于秸秆和腐熟鸡粪,在壤质潮土和砂土上分别较对照提升了63.15%和115.62%。另外,生物炭显著增加了土壤稳态碳含量和土壤碳库指数(CPI),但降低了土壤碳素有效率(SC)和碳库活度指数(AI),对土壤易氧化有机碳(POXC)和碳库管理指数(CMPI)无显著影响,添加秸秆显著增加了2种土壤POXC含量、基础呼吸和CPMI。进一步通过室内恒温培养试验发现,秸秆可在培养前期(0～37天)大幅度提升2种类型土壤有机碳矿化速率和累积矿化量,秸秆制炭还田对土壤有机碳矿化无显著影响。此外生物炭对土壤原有有机碳矿化的调控作用受其施用量、外源活性有机碳输入和土壤类型的影响,高量生物炭(2%)对非秸秆还田土壤有机碳矿化表现出较强的负激发效应,而低量生物炭(0.55%)对秸秆还田土壤有机碳矿化表现出较明显的负激发效应。因此,从固碳减排角度考虑,秸秆制炭还田是更合理的利用方式,且应根据土壤施肥管理措施和土壤类型考虑生物炭的施用量,添加质量比为2%的生物炭可显著抑制土壤原有有机碳矿化,降低CO_2排放,但应避开秸秆快速腐解期施用。     

氮肥减量配施生物炭对稻田有机碳矿化及酶活性影响

氮肥减量配施生物炭对于提升土地生产力、提高土壤碳汇能力以及缓解气候变暖具有重要意义.依托大田试验,设置5个氮肥用量梯度(T0～T4):100％化肥氮,90％化肥氮,80％化肥氮,70％化肥氮,60％化肥氮,采用等氮原则,氮肥减少量用等氮量生物炭替代,以不施肥为对照(CK),结合室内矿化培养,揭示稻田有机碳矿化及酶活性对...     

施用生物质炭对旱地红壤有机碳矿化及碳库的影响

为探究生物质炭施入旱地红壤后对该地区土壤有机碳矿化以及有机碳库的影响,采用田间定位试验,设置7种生物质炭施用量处理,分别为0(C0),2.5(C1),5(C2),10(C3),20(C4),30(C5),40t/hm2(C6),以三库一级动力学理论为基础,对这7种处理的土样进行了室内呼吸培养试验。结果表明:(1)与C0相比,C4、C5和C6处理的土壤有机碳含量呈上升趋势,C5处理土壤有机碳含量上升幅度最大为14.66%;C2、C3、C4、C5和C6处理土壤活性碳均显著增加,C6处理增幅最大为25.00%;土壤惰性碳在C3、C4、C5和C6处理中显著增加,增幅分别为18.92%,40.09%,53.60%和49.55%;除C5处理外,其他生物质炭施用量下土壤缓性碳相对于C0处理,分别降低了1.96%,6.54%,8.82%,9.31%和12.91%。(2)与C0处理相比,施加生物质炭后土壤有机碳累积矿化量均显著降低,C6处理降低幅度达25.93%。随着生物质炭施用量的增加,土壤有机碳累积矿化量逐渐降低。(3)土壤有机碳、活性碳和惰性碳与生物质炭施用量存在极显著(p0.01)的正相关,土壤缓性碳与其存在显著(p0.05)的负相关。研究结果可为提升典型旱地红壤肥力,减缓温室气体排放提供科学依据。     

土壤水分和植物残体对紫色水稻土有机碳矿化的影响

采用为期62.d的实验室恒温(281)℃培养方法,研究了土壤水分和植物残体对紫色水稻土有机碳矿化的影响。结果表明,紫色水稻土有机碳矿化速率在培养30.d后基本达到稳定,好气条件下土壤有机碳累积矿化量高于淹水条件,且差异达到极显著水平。用一级动力学方程对植物残体的矿化速率进行拟合表明,好气条件下,植物残体的分解速率常数(k值)大小顺序为蚕豆秸秆玉米秸秆水稻秸秆,而淹水条件则为水稻秸秆蚕豆秸秆玉米秸秆。水分状况和植物残体化学组分的差异影响紫色水稻土中有机碳的动态变化,最终导致碳累积矿化量差异。     

可溶性有机碳的含量动态及其与土壤有机碳矿化的关系

采用我国东部地区的黑土、潮土、黄泥土和红壤水稻土,通过室内分析和培育试验,研究了不同水分条件下可溶性有机碳含量及土壤有机碳矿化量的动态变化,分析了淹水导致可溶性有机碳含量的变化程度及其对土壤有机碳矿化量的可能影响.结果表明,可溶性有机碳含量与水土比呈直线相关关系,累计提取量随浸提时间增加,单次提取量随提取次数降低.在8周的培养期内,淹水处理的可溶性有机碳含量均显著高于好气处理,黄泥土一号高46%～117%(p＜0.05),黄泥土二号高112%～285%(p＜0.001),潴育黄泥田高21%～73%(p＜0.05).在培养的前3周(黄泥土一号)或前4周(黄泥土二号),不同水分处理的日均土壤有机碳矿化量有极显著差异(p＜0.01),其后,差异不显著;但在整个培养过程中,淹水处理的累计土壤有机碳矿化量均极显著高于好气处理(p＜0.01).培养过程中,土壤有机碳的矿化速率动态与可溶性有机碳含量的变化趋势相一致,特别是黄泥土二号,可溶性有机碳含量与土壤有机碳日均矿化量达到极显著的相关关系(好气相关系数0.942,淹水相关系数0.975).结果还表明,两种黄泥土有机碳矿化量(包括日均矿化量和累计矿化量)的差异并不与全土有机碳含量相关,而主要是其可溶性有机碳含量明显不同所致.因此,对于原土可溶性有机碳含量较高的土壤,淹水显著提高可溶性有机碳量是导致其土壤有机碳矿化量高于好气处理的主要原因.     

氮沉降背景下生物炭施用对土壤有机碳组分的影响

通过18个月的盆栽试验,以杉木幼苗为研究对象,研究不同水平氮(N)沉降背景下(N0(0)、低N(40 kg/(hm2·a))和高 N(80 kg/(hm2·a))生物炭(BC)施用(B0(0)、B1(12 t/hm2)和 B2(36 t/hm2))对土壤有机碳(SOC)组分的影响.结果表明:与对照相比,单独施用BC以及...     

炭基肥对老茶园土壤有机碳矿化温度敏感性的影响

采取室内恒温培养法,以施用炭基肥（BF）、不施炭基肥（CK）的40a茶园土壤为研究对象,设定15℃、25℃和35℃共3种不同温度场景,连续监测土壤有机碳（soil organic carbon,SOC）矿化特征并分析有机碳矿化温度敏感性,为评估老茶园固碳减排及障碍消减提供参考。结果表明：（1）炭基肥提升了温变场景下茶园土壤pH值和SOC含量。15℃、25℃和35℃培养温度下,BF处理的土壤pH值较CK处理分别增加0.45、0.07和0.28个单位;BF处理的SOC含量较CK处理分别提高22.19%、16.65%和25.50%。（2）炭基肥增加了温变场景下茶园SOC累计矿化量、潜在矿化势（CS）及土壤呼吸强度,对SOC矿化呈现正激发效应。15℃、25℃和35℃培养温度下,BF处理的SOC累计矿化量较CK处理分别提高15.61%、46.51%和36.89%。BF处理的CS值随温度升高呈现先增加后减少的变化趋势,25℃培养温度下BF处理的CS值较15℃和35℃培养温度下分别提高147.11%和29.21%。（3）炭基肥降低温度升高处理下茶园SOC矿化温度敏感性。25～35℃温度范围内,BF处...     

酸雨对土壤有机碳氮潜在矿化的影响

Acid rain is a serious environmental problem worldwide. In this study, a pot experiment using forest soils planted with the seedlings of four woody species was performed with weekly treatments of pH 4.40, 4.00, 3.52, and 3.05 simulated acid rain （SAR） for 42 months compared to a control ofpH 5.00 lake water. The cumulative amounts of C and N mineralization in the five treated soils were determined after incubation at 25 ℃ for 65 d to examine the effects of SAR treatments. For all five treatments, cumulative CO2-C production ranged from 20.24 to 27.81 mg kg^-1 dry soil, net production of available N from 17.37 to 48.95 mg kg^-1 dry soil, and net production of NO3-N from 9.09 to 46.23 mg kg^-1 dry soil. SAR treatments generally enhanced the emission of CO2-C from the soils; however, SAR with pH 3.05 inhibited the emission. SAR treatments decreased the net production of available N and NO3-N. The cumulative CH4 and N2O productions from the soils increased with increasing amount of simulated acid rain. The cumulative CO2-C production and the net production of available N of the soil under Acmena acuminatissima were significantly higher （P 〈 0.05） than those under Schima superba and Cryptocarya concinna. The mineralization of soil organic C was related to the contents of soil organic C and N, but was not related to soil pH. However, the overall effect of acid rain on the storage of soil organic matter and the cycling of important nutrients depended on the amount of acid deposition and the types of forests.     

茶渣生物质炭对茶园土壤有机碳及其活性组分的影响

为探究生物质炭对茶园土壤有机碳含量及其稳定性的影响,将茶渣在500℃下制成生物质炭,针对雅安名山区3种典型茶园土壤（紫色土、水稻土和黄壤）进行112天的室内培养试验,包括CK,0.5%,1%,2%和4% 5种炭土比,共计15个处理,在培养的第1,2,7,30,60,112天取样测定。结果表明：茶渣生物质炭输入能显著增加紫色土、水稻土和黄壤总有机碳（TOC）含量和稳定性,且随添加比例的增加而增加,培养结束时3种土壤TOC的增幅范围依次为15.97%~96.64%,13.01%~72.36%和15.29%~321.43%,其中对黄壤TOC含量的提升作用最大;生物质炭加入后3种茶园土壤的微生物量碳（MBC）、水溶性有机碳（WSOC）和易氧化有机碳（ROC）含量也得到显著提升,到培养结束时3种土壤MBC含量变化最大的是紫色土,增幅范围为12.97%~40.35%,WSOC和ROC含量变化最大的均为黄壤,增幅范围分别为12.50%~50.00%和5.66%~54.72%;茶渣生物质炭显著提升了3种土壤有机碳的氧化稳定性,且随添加比例的增加而增强,紫色土、水稻土和黄壤的氧化稳定系数提升范围分别为28.07%~146.66%,44.79%~225.66%和447.18%~1 941.19%。     

生物质炭对稻田土壤有机碳组分的持效影响

生物质炭的应用已经被认为是以碳封存形式减轻气候变化的有效手段。本研究以一次性施用生物质炭3年后水稻土为对象,分析土壤总有机碳(TOC)、可溶性有机碳(DOC)、颗粒态有机碳(POC)、易氧化态有机碳(ROC)和微生物量碳(MBC)含量的变化,研究施用生物质炭对土壤有机碳和组分的后续影响。结果表明,在10 t hm-2、20 t hm-2和40 t hm-2的生物质炭施用水平下,显著提高土壤有机碳储量,增幅达9.15¹5.49%。施用生物质炭可长期稳定提高土壤TOC、ROC、POC和MBC分别达12.75%15.49%。施用生物质炭可长期稳定提高土壤TOC、ROC、POC和MBC分别达12.75%²3.36%、12.60%23.36%、12.60%²8.00%、10.88%28.00%、10.88%³4.00%和7.97%34.00%和7.97%¹2.35%,且土壤TOC与ROC、MBC极显著正相关,ROC与POC、MBC也存在极显著正相关,这可能与生物质炭可改善土壤结构、促进作物生长有关。因此,施用生物质炭是长期提高水稻土土壤碳储量和活性有机碳含量的有效措施。。     

Influence of soil compaction on carbon and nitrogen mineralization of soil organic matter and crop residues

 We studied the influence of soil compaction in a loamy sand soil on C and N mineralization and nitrification of soil organic matter and added crop residues. Samples of unamended soil, and soil amended with leek residues, at six bulk densities ranging from 1.2 to 1.6 Mg m^–3 and 75% field capacity, were incubated. In the unamended soil, bulk density within the range studied did not influence any measure of microbial activity significantly. A small (but insignificant) decrease in nitrification rate at the highest bulk density was the only evidence for possible effects of compaction on microbial activity. In the amended soil the amounts of mineralized N at the end of the incubation were equal at all bulk densities, but first-order N mineralization rates tended to increase with increasing compaction, although the increase was not significant. Nitrification in the amended soils was more affected by compaction, and NO₃ ^–-N contents after 3 weeks of incubation at bulk densities of 1.5 and 1.6 Mg m^–3 were significantly lower (by about 8% and 16% of total added N, respectively), than those of the less compacted treatments. The C mineralization rate was strongly depressed at a bulk density of 1.6 Mg m^–3, compared with the other treatments. The depression of C mineralization in compacted soils can lead to higher organic matter accumulation. Since N mineralization was not affected by compaction (within the range used here) the accumulated organic matter would have had higher C : N ratios than in the uncompacted soils, and hence would have been of a lower quality. In general, increasing soil compaction in this soil, starting at a bulk density of 1.5 Mg m^–3, will affect some microbially driven processes. Received: 10 June 1999     

Frequent addition of wheat straw residues to soil enhances carbon mineralization rate

In many ecosystems, residues are added frequently to soil, in the form of root turnover and litter fall. However, in most studies on residue decomposition, residues are added once and there are few studies that have investigated the effect of frequent residue addition on C mineralization and N dynamics. To close this knowledge gap, we mixed mature wheat residue (C/N 122) into soil at a total rate of 2% w/w once at the start (R1×), every 16 days (R4×), every 8 days (R8×) or every 4 days (R16×). Un-amended soil served as control. All treatments were mixed every 4 days. Soil respiration was measured continuously over the 80-day incubation. Inorganic N, K₂SO₄-extractable C and N, chloroform-labile C and N (as an estimate of microbial biomass C and N), soil pH and microbial community composition were assessed every 16 days. Increasing frequency of residue addition increased C mineralization per g residue. Compared to R1×, cumulative respiration per g residue at the end of the incubation (day 80) was increased by 57, 82 and 92% in R4×, R8× and R16×, respectively. The largest differences in soil respiration per g residue occurred in the first 30 days. Despite large increases in cumulative respiration, frequent residue addition did not affect inorganic N or K₂SO₄-extractable N concentrations, chloroform-labile C and N or soil pH. Compared to the control, all residue treatments resulted in increases in chloroform-labile C and N and soil pH but decreased inorganic and K₂SO₄-extractable N. Microbial community composition was affected by residue addition, however there were no consistent differences among residue treatments. It is concluded that experiments with single residue additions may underestimate residue decomposition rates in the field. The increased C mineralization caused by frequent residue additions does not appear to be due to an increased microbial biomass or changes in microbial community composition, but rather to increased C mineralization per unit biomass.     

Quantifying soil water effects on nitrogen mineralization from soil organic matter and from fresh crop residues

A loamy sand was incubated with and without addition of carrot leaves at six different water contents ranging from 6% to 20% (g 100 g^-1 dry soil) and N mineralization was monitored during 98 days. We calculated zero- and first-order rates for mineralization in the unamended soil and first-order rates for N mineralization in the residue-amended soil. Although N mineralization was strongly affected by soil moisture, rates were still important at 6% water content (corresponding to permanent wilting point), particularly in the residue-amended soil. Soil water content was recalculated as soil water tension and as percent water-filled pore space (%WFPS) and a parabolic, a logistic and a Gaussian-type function were fitted to the relation between N mineralization rates and water content, %WFPS or pF. Water potential was a less suitable parameter than either %WFPS or water content to describe the soil water influence on N mineralization, because N mineralization rates were extremely sensitive to changes in the water potential in the range of pF values between 1.5 and 2.5. In the residue-amended soil the Gaussian model yielded an optimum %WFPS of 56% for N mineralization, which is slightly lower than optimum values cited in literature. N mineralization in the unamended soil was more influenced by soil water than N mineralization from fresh crop residues. This could be explained by less water limitation of the microbial population decomposing the residues, due to the water content of the residues. The effect of the water contained in the residues was most pronounced in the lowest water content treatments. The water retention curves of both undisturbed and repacked soil were determined and suggested that extrapolation of results obtained during laboratory incubations, using disturbed soil, to field conditions will be difficult unless soil bulk density effects are accounted for, as is the case with the use of %WFPS.     

温度和植物残体对紫色母岩发育的水稻土有机碳矿化的影响

培养试验研究了2种温度下紫色水稻土有机碳的矿化特征以及添加不同植物残体对其矿化的影响。结果表明, 62d的培养过程中,有机碳累积矿化量在28℃条件下为C 66.79 mg/g;40℃条件下为C 86.99 mg/g,差异达到极显著水平。用一级动力学方程对植物残体的矿化速率进行拟合表明,28℃条件下,植物残体的分解速率常数（k）为蚕豆秸秆玉米秸秆水稻秸秆,而40℃条件下则为水稻秸秆玉米秸秆蚕豆秸秆。温度状况和植物残体化学组分的差异影响了紫色水稻土中有机碳的动态变化,最终导致了碳累积矿化量的差异。     

黑碳添加对土壤有机碳矿化的影响

通过室内培养试验,向土壤中分别添加不同温度制备的黑碳,热解温度分别为350℃(T350)、600℃(T600)和850℃(T850),研究了黑碳添加对土壤有机碳矿化的影响。结果表明,不同温度条件制备的黑碳在15℃和25℃培养条件下,土壤CO2释放速率总的趋势是前期分解速率快,后期缓慢。在整个培养过程中(112天),随着培养时间的延长,土壤CO2释放速率下降趋势逐渐降低,CO2释放速率相对值的大小随着培养温度的的升高而增大。在不同温度培养条件下,添加黑碳后土壤CO2-C累计量均是T350>T600>T850,T350土壤CO2-C累计量最高分别为415.26 mg/kg和733.82 mg/kg。添加不同黑碳后,土壤有机碳矿化增加率存在极显著差异(p<0.01),表明不同温度制备的黑碳对土壤有机碳矿化的影响显著。     

Nitrogen mineralization and availability of mixed leguminous and non-leguminous cover crop residues in soil

Whereas non-leguminous cover crops such as cereal rye (Secale cereale) or annual ryegrass (Lolium multiflorium) are capable of reducing nitrogen (N) leaching during wet seasons, leguminous cover crops such as hairy vetch (Vicia villosa) improve soil N fertility for succeeding crops. With mixtures of grasses and legumes as cover crop, the goal of reducing N leaching while increasing soil N availability for crop production could be attainable. This study examined net N mineralization of soil treated with hairy vetch residues mixed with either cereal rye or annual ryegrass and the effect of these mixtures on growth and N uptake by cereal rye. Both cereal rye and annual ryegrass contained low total N, but high water-soluble carbon and carbohydrate, compared with hairy vetch. Decreasing the proportion of hairy vetch in the mixed residues decreased net N mineralization, rye plant growth and N uptake, but increased the crossover time (the time when the amount of net N mineralized in the residue-amended soil equalled that of the non-amended control) required for net N mineralization to occur. When the hairy vetch content was decreased to 40% or lower, net N immobilization in the first week of incubation increased markedly. Residue N was significantly correlated with rye biomass (r=0.81, P<0.01) and N uptake (r=0.83, P<0.001), although the correlation was much higher between residue N and the potential initial N mineralization rate for rye biomass (r=0.93, P<0.001) and N uptake (r=0.99, P<0.001). Judging from the effects of the mixed residues on rye N Concentration and N uptake, the proportion of rye or annual ryegrass when mixed with residues of hairy vetch should not exceed 60% if the residues are to increase N availability. Further study is needed to examine the influence of various mixtures of hairy vetch and rye or annual ryegrass on N leaching in soil. Received: 10 March 1997     

Manipulating N mineralization from high N crop residues using on- and off-farm organic materials

We have studied the possibilities of manipulating N mineralization from high N vegetable crop residues by the addition of organic materials, with the aim of initially immobilizing the mineralized residue N with a view to stimulating remineralization at a later stage. Residues of leek (Allium porrum) were incubated with soil, alone and in combination with straw, two types of green waste compost (with contrasting C:N ratios) and tannic acid. Evolution of mineral N was monitored by destructive sampling. After 15 weeks, molasses was added to part of the samples in each treatment, and incubation continued for another 12 weeks. All materials added during the first incubation stage, except the low C:N compost, resulted in significant immobilization of the residue N. The immobilization with the high C:N compost (41.4 mg N kg⁻¹ soil) was significantly larger than with tannic acid and straw (both immobilized about 26 mg N kg⁻¹ soil). In the straw treatment, remineralization started in the first stage of incubation from day 50 onwards. The addition of molasses caused a strong and significant remineralization in the second stage (equivalent to 73% of the N initially immobilized) in the treatment with the high C:N ratio compost. In the case of tannic acid, there was no consistent effect on mineralization from addition of molasses. This was attributed to the fact that the immobilization observed was due to chemical rather than biological fixation of the residue N. A number of non-toxic organic wastes could be considered for use in mediating release of immobilized N from high N crop residue materials in an attempt to synchronize residue N availability with crop N demand.     

Decomposition and nitrogen mineralization from legume and non-legume crop residues in a subarctic agricultural soil

An understanding of the C and N dynamics of crop residues is important for efficient nutrient management. The present experiment was conducted to determine the rate of mass and N loss from alfalfa, faba bean, barley, and rape crop residues in a subarctic agricultural soil. Mass, C, and N losses were measured from residues contained in mesh bags and placed on the soil surface or buried 15 cm below the surface. The mass loss from October, 1988, to May, 1989, was the same for surface and buried alfalfa, barley, and rape residues, averaging 40, 20, and 61%, respectively, while surface and buried faba bean residue sustained 30 and 40% mass loss, respectively. The mass loss of the buried residues continued over the summer but not of those placed on the soil surface, resulting in an average 23% greater mass loss of the buried materials after 1 year. The N loss from October to May was similar from the surface and from the buried placements for the alfalfa, faba bean, and rape residues, averaging 11.3, 10.3 and 38.4 g N kg^-1 residue, respectively, while the surface and buried barley lost 2.9 and 4.2 g N kg^-1, respectively. The C:N ratio of all of the residues increased during the winter. These data indicate that the rate of decomposition and N mineralization from crop residues in subarctic environments can equal that measured in temperate climates. Furthermore, the concurrent loss of mass and N combined with an increase in the C:N ratio of the residues suggests that physical rather than biological processes were functioning during the winter. Most of the mass and N loss from these residues occurred during the winter, out of phase with crop demand, thereby creating the potential for N loss from the system and inefficient use of crop residue N.     

Dynamics of dissolved and extractable organic nitrogen upon soil amendment with crop residues

Dissolved organic nitrogen (DON) is increasingly recognized as a pivotal pool in the soil nitrogen (N) cycle. Numerous devices and sampling procedures have been used to estimate its size, varying from in situ collection of soil solution to extraction of dried soil with salt solutions. Extractable organic N (EON) not only consists of DON but contains also compounds released from soil biomass and desorbed organic matter. There is no consensus whether DON or EON primarily regulates N mineralisation in soil, and their contribution to N mineralisation has not been quantified simultaneously. We evaluated three sampling procedures on their ability to determine the dynamic of dissolved organic N pools. The three procedures were the determination of DON in 1) soil solution collected by centrifugation, and the determination of EON in 2) a 0.01 M CaCl₂ extract of field moist or 3) dried soil. We added unlabeled leek and ¹⁵N-labeled ryegrass residues to a loamy sandy soil to create a temporarily increase in DON and EON, to stimulate microbial activity, and to test whether the source and dynamics of the three pools differ. We also tested whether the flow of N through DON or EON was associated with the production of inorganic N using ¹⁵N isotope tracing. Sampling procedures significantly affected the amount, but not the dynamics and origin of the three organic N pools. DON and EON (determined on field-moist and dried soils) showed all a significant increase upon crop amendment and returned to their background concentrations within 10 to 30 days. The fraction of DON and EON originating from the crop residue slightly decreased over 138 days and was not different for DON and EON. Field moist extraction of a loamy sandy soil with 0.01 M CaCl₂ gave a reliable estimate of the concentration of in situ dissolved organic N. In contrast, extraction of dried soil significantly increased EON compared to DON. The agreement in dynamics, ¹⁵N enrichment and C-to-N ratio’s indicate that dissolved and extracted organic N have a similar role in N mineralisation. Our results also suggest that they make a minor contribution to N mineralisation; changes in the turnover rate of EON were not associated with changes in the net N mineralisation rate.     

Separate effects of the biochemical quality and N content of crop residues on C and N dynamics in soil

This study assessed the respective roles of biochemical quality and N content of plant residues on C and N dynamics in a soil. Both ¹⁵N- and ¹³C-labeled oilseed rape residues (roots, seedpod walls) combining different biochemical characteristics and similar N content or the same biochemical characteristics and different N contents were used as amendments. These treatments were combined with two levels of soil inorganic N to ensure that decomposition was not limited by N availability. The soil was incubated under laboratory conditions for 134 days. Soil amended with residues of similar biochemical quality (i.e. the two pod walls) displayed similar C mineralization dynamics when the initial N availability (residue+soil N) ranged from 1.7 to 3.2% of residue dry matter. The roots showed poorer decomposition than the pod walls, lower cumulative C mineralization and greater accumulation of root-derived C in the >50 μm coarse fraction of the soil organic matter. The N content of the residues influenced mineral N accumulation in the soil with a lower net immobilization of residues with low C-to-N ratios. Adding an exogenous source of inorganic N had no effect on C dynamics but modified the remineralization kinetics of the previously immobilized N, suggesting changes in the microbial community involved.