Optimized N-mineralization parameters of loess soils from incubation experiments

Summary Nitrogen mineralization from long term incubation experiments with dried loess soils from southern Lower Saxony has been split by an optimization procedure into three contributing fractions: one from the resistant organic material (index rpm), another from decomposable plant residues (index dpm), and a third one from autolyzing microbial biomass (index bom). The nitrogen contents at the end of February averages 650 kg nitrogen per hectare and the 30 cm arable layer for the rpm, 30 to 50 kg N/ha for the dpm and about 65 kg N/ha for microbial biomass. The corresponding mean reaction coefficients at 35°C are .0058, .16 and about .35 per day, respectively. A rough approximation of the temperature dependence of the reaction coefficients has also been estimated.This paper was presented in part at the 1981 Congress of the German Soil Science Society held in Berlin, and at a colloquium at the Institute of Soil Chemistry, Pisa, Italy, Oct. 19th, 1981; nothing of it has been published before, however.     

Effects of management practices on annual net N-mineralization in a restored prairie and maize agroecosystems

Nitrogen (N) mineralization is a spatially variable and difficult component of the N cycle to quantify accurately under field conditions. Net N-mineralization was compared by direct measurement, indirect estimate, and laboratory incubation for a restored tallgrass prairie and for deficiently and optimally N-fertilized, no-tillage (NT) and chisel-plowed (CP) maize (Zea mays L.) agroecosystems on Plano silt loam soil (fine-silty, mixed, superactive, mesic Typic Argiudoll) in Wisconsin, USA. Four years of in-situ field measurements using an incubated-soil-core/ion-exchange-resin-bag technique showed that land use significantly affected net N-mineralization. Net N-mineralization was consistently smaller in the restored prairie than in the maize agroecosystems and typically larger in the CP than in the NT maize agroecosystems. Three independent methods for indirectly estimating annual net N-mineralization (i.e., N budget residual, deficiently N-fertilized plant N uptake, and profile-scaled in-situ field measurements) were relatively consistent at capturing land-use and tillage effects on net N-mineralization. Laboratory incubation and periodic leaching of Fall-sampled soils demonstrated that both mineralized N and labile C were co-limiting factors influencing N-mineralization in agricultural soils and generally supported field measurements by showing a significant difference in net N-mineralization with and without added fertilizer-N.     

温度、水分和森林演替对中亚热带丘陵红壤氮素矿化影响的模拟实验

研究了温度、水分和演替阶段及其交互作用对中亚热带丘陵红壤区森林土壤氮素矿化过程及其矿化速率的影响.结果表明：温度和演替阶段对土壤氨化速率影响显著,其中12 ℃<24℃<36 ℃,灌丛林和马尾松(Pinus massoniana)林低于常绿阔叶林(P＜0.05);而水分的影响不显著.水分和演替阶段对土壤硝化速率有显著影响,土壤半饱和含水量高于自然含水量及饱和含水量,且马尾松林高于灌丛林(P＜0.05);而温度的影响不显著.温度、水分和演替阶段对土壤氮净矿化速率的影响均显著,其中12 ℃<24 ℃<36 ℃,土壤半饱和含水量高于自然含水量和饱和含水量,灌丛林<马尾松林<常绿阔叶林(P＜0.05).温度升高有利于提高土壤氨化速率和净矿化速率,温度过高则抑制土壤硝化速率;土壤含水量适中有利于土壤氮素矿化过程;顺行演替将提高土壤供氮能力,且抑制过强的硝化作用.     

Incubation studies on mineralization of organic sulphur and organic nitrogen

Summary Incubation studies were carried out to investigate the release of sulphur and nitrogen in West Indian soils. Sulphur and nitrogen released or fixed were estimated at 10 days intervals up to 60 days incubation period.All the soils released sulphate when incubated at 30°C. A rapid initial flush of mineralization of both sulphur and nitrogen took place in Cocal fine sand and Montreal sandy loam. In Piarco sandy clay loam and Mayaro sandy loam sulphur mineralization was not accompanied by a concomitant mineralization of nitrogen. An inconsistent pattern of release of sulphur and nitrogen was noticed in Montserrat clay, Akers sandy clay loam, Bellevue sandy clay loam and Soufriere cindery gravelly loamy sand.The release of sulphur does not appear to be related to the total amount of carbon, nitrogen or sulphur. Nitrogen mineralized was significantly correlated with total nitrogen and total sulphur. The correlation between organic matter and nitrogen mineralized was highly significant (r=0.87^**) whereas with sulphur mineralized it did not reach significance. This suggests that nitrogen and sulphur are not mineralized at the same rate in these soils.     

Rates of net nitrogen mineralization in disturbed and undisturbed soils

Quantification of net nitrogen mineralization (NNM) in soils is indispensable in order to optimize N fertilization of crops. Two long-term laboratory incubation methods were applied to determine rates of net nitrogen mineralization (r_NNM) of soils from two sites of arable land (sandy loam soil, silty loam soil) at four temperature levels (2°C, 8°C, 14°C, 21°C). Since variability within replicates was small, the modified 12-week incubation method of Stanford and Smith (1972) using disturbed soils allowed to establish reliable Arrhenius functions with reasonable expenditure. The fit of the functions derived from the 5-month incubation of 23 undisturbed soil columns (4420 cm³) was worse. This was caused by greater variability and less differentiation between temperature levels. Results of both experiments could be described best by zero-order kinetics. Mean mineralization rates of disturbed samples were approximately twice as high than those of undisturbed samples. The suitability of both methods for the prediction of NNM at site conditions is discussed. Actual respiration (AR) at incubation temperatures and substrate induced respiration (SIR) were measured at the end of the incubation of undisturbed soil columns. The results presented reveal that soil microbial communities develop in a different manner during long-term incubation at different temperatures. This behavior offends the underlying assumption that soil microbes remain in steady-state during incubation and that rising rates are physiological reactions to temperature enhancement. Therefore soil microbial biomass (SMB) dynamics during the experiment has to be accounted for when rates of NNM and Arrhenius functions are established. R Merck Section editor     

N-mineralization in Löss-Parabrownearthes: Incubation experiments

Summary Nitrogen mineralization in Löss-Parabrownearthes was studied in long-term incubation experiments at different temperatures. Results obtained were used to optimize the parameters of a first-order kinetic model for N-mineralization of these soils: average reaction coefficients obtained by incubationat 35°C are 0.00737±0.00081 per day for the old organic material, and 0.25±0.07 per day for the fresh organic material.The mineralizable nitrogen of the fresh organic material at the beginning of march amounts to about 90±20 kg N/(ha*30 cm), independent of the kind of preceding crop. Temperature dependence of mineralization was estimated roughly. Attempts to simplify the procedure of evaluation of these parameters are described.Aqualfs and Udalfs according to the 7th approximation.     

温度对不同粘粒含量稻田土壤有机碳矿化的影响

模拟了亚热带地区3种不同粘粒含量的水稻土(砂壤土、壤粘土、粉粘土)在5种温度(10、15、20、25和30℃)下的有机碳(SOC)矿化特征,分析SOC矿化对温度变化的响应.结果表明:在160d的培养期内,温度对3种水稻土SOC矿化量的影响有一定差异,30℃时砂壤土、壤粘土和粉粘土SOC矿化量分别是10℃时的3.5、5.2和4.7倍.在较低温度(≤20℃)下,SOC矿化速度较低且相对稳定;在较高温度(≥25℃)下,前期SOC矿化速度较高,随着培养时间的延长逐渐降低,并趋于稳定.3种水稻土SOC矿化的温度系数(Q10)随培养时间出现波动,砂壤土的Q10平均值最低,为1.92,壤粘土和粉粘土的Q10平均值较接近,分别为2.37和2.32;3种土壤矿化速率常数(k)与温度呈极显著的指数相关(P<0.01).3种水稻土有机碳矿化对温度变化的响应敏感度依次为壤粘土>粉粘土>砂壤土.     

Soil drying and organic matter decomposition

Summary A study was made of the effects of drying the soil at various temperatures on the subsequent mineralization of carbon, nitrogen and phosphorus of native and added organic matter in the soil.Heating the soil, especially at 100°C was shown to increase the solubility of soil nitrogen, phosphorus and organic matter. On moistening dried soil and incubating, the mineralization of native soil organic matter (humus) increased with the drying temperature and with the length of drying period. Drying, especially at 100°C, reduced the decomposition of fresh organic matter added to the soil. In contrast it increased the mineralization of soil organic nitrogen, but while the bulk of the inorganic nitrogen so produced was converted to nitrate at the lower drying temperature, nitrification did not occur in the soil dried at 100°C.Addition of decomposable organic materials caused nitrate immobilization and retarded the nitrification of the ammonia produced.Drying the soil also caused an immobilization of soil phosphorus, but while this was short-lived at the lower temperatures, it persisted up to twelve weeks in the soil dried at 100°C. Addition of decomposable organic materials increased phosphorus immobilization.     

Total soil nitrogen and nitrogen mineralization

Summary The mineralization capacity of 24 different soils was determined from incubation experiments. Relatively rapid mineralization and nitrification was found with soils from cultivated land, and pastures, but soils under natural vegetative covers of conifers and hardwoods were mostly ammonifying. A close relationship could be established between the total nitrogen content of the soil and the amount of mineral nitrogen formed during incubation. Important connections could also be shown between the available nitrogen contents at different times during the incubation period; these suggest that the incubation period can be considerably shortened.     

Nitrogen balance studies for different Egyptian soils cropped with corn

Summary The nitrogen balance for four different Egyptian soils cropped with corn and fertilized with increasing amounts of ammonium sulphate was studied in pot experiments. The tested soils were clay loam, calcareous sandy loam, sandy loam and sand. Nitrogen added as seeds, fertilizers, irrigation water and insecticides, nitrogen removed by the plants including thinned plants and fallen leaves and the nitrogen content of the soils before sowing and after the harvest were determined and used to draw the balance sheet.The obtained results showed that nitrogen loss ranged between 6.8 and 51.5 per cent depending mainly on soil type and to some extent on the rate of applied ammonium sulphate. Nitrogen uptake by the corn plants was lowest from the clay loam soil and highest from the sandy soil. In all cases it increased slightly with the addition of nitrogen fertilizer. re]19720918     

Short-term mineralization of maize residues in soils as determined by carbon-13 natural abundance

Studies of soil organic matter equilibria must include estimates of C turnover. The objective of this study was to provide data on how the natural ¹³C abundance method can be used to determine the flow of C from C₄ residues and soil organic matter (C₃-source) in a short-term incubation. Corn residue was added at a rate of 5.7 mg C g⁻¹ soil to two soils, a clay and a sandy clay loam. During the course of a 35-day incubation in a CO₂-free system, CO₂-C and ¹³C natural abundance of the respired CO₂ were measured. About 20% of the corn residue-C added was mineralized in both soils as determined from the CO₂ respired and the ¹³C natural abundance of the respired CO₂. Mineralization of the added residues was also calculated as the difference of the total amount of the respired CO₂-C between the control and the corn residue-treated soils divided by the total amount of corn residue-C. Values were 35% for the clay soil, and 30% for the sandy clay loam soil. The difference in values calculated from the ¹³ C natural abundance and the difference method was due to mineralization of the indigenous soil organic C resulting from the addition of corn residues. Use of the natural ¹³C abundance method could determine the degree of ‘priming effect’ in soils amended with C₄-C residues. This revised version was published online in June 2006 with corrections to the Cover Date.     

不同退化沙地土壤碳的矿化潜力

通过实验室土壤培养试验 ,研究了科尔沁退化沙质草地不同生境 (流动沙地 ,半固定沙地 ,固定沙地和丘间低地 )下土壤碳的矿化潜力及不同凋落物在沙地土壤中的分解。经 33d的室内培养 ,不同生境土壤 CO2 - C的释放有极显著的差异 ,与生境植被盖度 ,凋落物积累 ,土壤沙化程度 ,土壤有机碳和全氮含量的分布有显著相关。流动沙地土壤有极低的土壤有机碳和氮的含量及其微弱的土壤微生物呼吸 ,表明土地沙漠化不仅导致土壤有机碳库衰竭 ,也使土壤微生物活性丧失。在有机质含量很低的流动沙地和半固定沙地土壤中 ,含氮量高的小叶锦鸡儿 (Caragana microphylla)凋落物比含氮量低、C/N比高的差巴嘎蒿(Artemisia halodendron)和 1年生植物凋落物有较快的分解。在沙漠化的演变中 ,土壤的粗粒化 ,有机物质和养分及微生物活性的丧失制约着凋落物在土壤中的矿化潜力。灌木的存在使更多的有机物质和养分积聚在灌丛下 ,形成灌丛肥岛 ,因而显著贡献于碳的固存。     

Fertilization influences nitrogen dynamics in soils under Dalbergia sissoo

The influence of added ammonium, phosphorus, potassium, and gypsum on net nitrogen mineralization was studied in soil beneath a six-year-old plantation of the N₂-fixing tree Dalbergia sissoo in Pakistan. Soil with and without amendments was placed in polyethylene bags and incubated, buried in the soil, for 30 days. After that time the soil was analyzed and net ammonium and nitrate production and net nitrogen mineralization were calculated. The addition of ammonium stimulated nitrification indicating that the process was substrate limited. The inhibition of nitrification by Nitrapyrin showed that the process is autotrophic in these soils. Gypsum addition lowered soil pH from 8.0 to 7.2 and significantly stimulated ammonification, nitrification and net nitrogen mineralization. The addition of potassium more than tripled the soil K:Na ratio. Net ammonium and nitrate production and net nitrogen mineralization all increased in this treatment. The addition of phosphorus had no significant effect on soil nitrogen dynamics.     

Immobilization,mineralization and the availability of the fertilizer nitrogen during the decomposition of the organic matters applied to the soil

Summary Immobilization and mineralization of the tracer nitrogen (K¹⁵NO₃) applied to the soil together with several organic matters during their decomposition was investigated in incubation experiments.After incubation for three months at 30°C, the decomposition rates of rice straw, hardwood bark, sawdust, softwood bark and peat moss were 41, 15, 7, 5, and 5%, respectively. After incubation for three months at 30°C, 100 and 80% of the fertilizer nitrogen were immobilized in the treatment with 2.0% of rice straw and sawdust carbon, respectively. These resulted in the lowered uptake of the fertilizer nitrogen by plants. In case of peat moss and barks, the amount of fertilizer nitrogen which transformed to the organic nitrogen fractions was quite small and the plant uptake of the nitrogen was hardly affected. Remineralization of the immobilized nitrogen was clearly observed after 2 months' incubation in case where rice straw carbon was added to the extent of 0.5 and 1.0%, but it was not observed in case where other organic matter carbon was added.The data showed that peat moss and barks were highly resistant to the action of microorganisms. As a results the immobilization process of the fertilizer nitrogen incubated with these organic matter was quite slow.     

玉米和大豆秸秆还田初期对黑土CO2排放的影响

通过恒温培养试验,研究了不同类型秸秆还田后的土壤CO₂排放特征及其与秸秆C、N含量的关系,以明晰黑土区不同类型秸秆还田后的分解特征,探明还田秸秆的C、N含量对固碳效果的影响.结果表明： 在61 d的培养试验中,土壤CO₂排放速率随时间呈现出“下降 稳定 增大(出现‘较高值’) 下降”的过程.不同类型秸秆还田后土壤CO2排放速率随时间变化的特征存在明显差异,主要体现在“较高值”出现和持续的时间不同.秸秆类型对土壤CO₂累积排放量具有显著影响,前21 d和前61 d的土壤CO2累积排放量对秸秆添加的响应不同.在前21 d,玉米根、玉米茎下部、玉米叶、大豆叶的CO₂累积排放量(约160 μmol·g^-1)显著大于其他秸秆;而除大豆叶外,大豆秸秆61 d的CO₂累积排放量均比玉米秸秆大.前21 d CO₂累积排放量与秸秆含碳量的比值(CR)和秸秆的C/N、含氮量之间均呈显著的线性相关;而61 d的CO₂累积排放量与秸秆的C、N含量之间不存在线性关系.综上,在还田条件下,秸秆类型对土壤CO₂的排放有明显影响;大豆秸秆比玉米秸秆容易分解,但与长时间分解不同,大豆秸秆还田最初阶段的分解速率小于玉米秸秆;秸秆的C/N、含氮量只对还田最初阶段的土壤CO₂排放有较大影响.     

玉米和大豆秸秆还田初期对黑土CO2排放的影响

通过恒温培养试验,研究了不同类型秸秆还田后的土壤CO₂排放特征及其与秸秆C、N含量的关系,以明晰黑土区不同类型秸秆还田后的分解特征,探明还田秸秆的C、N含量对固碳效果的影响.结果表明： 在61 d的培养试验中,土壤CO₂排放速率随时间呈现出“下降 稳定 增大(出现‘较高值’) 下降”的过程.不同类型秸秆还田后土壤CO2排放速率随时间变化的特征存在明显差异,主要体现在“较高值”出现和持续的时间不同.秸秆类型对土壤CO₂累积排放量具有显著影响,前21 d和前61 d的土壤CO2累积排放量对秸秆添加的响应不同.在前21 d,玉米根、玉米茎下部、玉米叶、大豆叶的CO₂累积排放量(约160 μmol·g^-1)显著大于其他秸秆;而除大豆叶外,大豆秸秆61 d的CO₂累积排放量均比玉米秸秆大.前21 d CO₂累积排放量与秸秆含碳量的比值(CR)和秸秆的C/N、含氮量之间均呈显著的线性相关;而61 d的CO₂累积排放量与秸秆的C、N含量之间不存在线性关系.综上,在还田条件下,秸秆类型对土壤CO₂的排放有明显影响;大豆秸秆比玉米秸秆容易分解,但与长时间分解不同,大豆秸秆还田最初阶段的分解速率小于玉米秸秆;秸秆的C/N、含氮量只对还田最初阶段的土壤CO₂排放有较大影响.     

季节性冻融期间川西亚高山/高山森林土壤净氮矿化特征

气候变暖情景下季节性冻融格局的改变可能显著影响高寒森林土壤氮素矿化过程.本文采用原状土壤移位培养的方法,以海拔梯度形成的温度差异模拟气候变暖,研究了川西亚高山/高山森林在生长季节和季节性冻融期间土壤的净氮矿化量和净氮矿化速率.结果表明： 在川西亚高山/高山森林,土壤铵态氮和硝态氮含量均表现为从生长季节至冻结初期明显下降,完全冻结期明显增加,而在融化初期明显降低的变化过程.季节性冻融期土壤的净氮矿化量和净氮矿化速率显著低于生长季节,并且出现明显的氮素固持现象.与低海拔相比,中海拔森林土壤的氮素固持作用相对较大,高海拔相对较小,可能与不同海拔梯度土壤温度变化及引起的冻融循环密切相关.在生长季节,土壤净氮矿化量和矿化速率均随海拔的降低呈明显增加趋势,尤其在低海拔处土壤的氮素矿化作用最为强烈.在气候变暖背景下,温度的增加明显促进了生长季节土壤氮素矿化,并且通过提高冻融循环频次、缩短冻结时间来影响土壤氮素矿化速率.这一过程可能受到微环境的影响.     

黄土高原土壤有机碳矿化及其与土壤理化性质的关系

土壤有机碳矿化与陆地生态系统碳循环和全球气候变化密切相关。采集98个共7类黄土高原土样,通过密闭培养法对有机碳矿化动态进行分析,探讨了土壤理化性质对有机碳矿化的影响。结果表明,黄土高原地区主要土壤有机碳在培养初期日均矿化量较高,之后逐渐降低。土壤类型对黄土高原土壤有机碳矿化影响较大,不同土壤有机碳的日均矿化量、累积矿化量和矿化率具有显著或极显著的差异。褐土有机碳总矿化量最高,CO2-C达到0.252g.kg-1,风沙土最低,CO2-C仅为0.095g.kg-1。下层土壤的有机碳矿化量较上层的有所下降,但土层深度对有机碳矿化大体上无明显影响。一级动力学方程能很好模拟黄土高原土壤有机碳矿化特征。供试土壤有机碳矿化潜力(Cp)和矿化速率常数(k)值均较低,分别为0.329-0.116g.kg-1和4.55-8.57×10-5d-1。不同土壤的Cp值变异较大,而k和Cp/SOC值无明显的变异。土壤Cp与土壤总有机碳、全氮、全磷、速效钾、粘粒和粉粒含量均呈极显著的正相关,而与k、pH值和砂粒含量呈显著的负相关。研究结果对黄土高原土壤有机碳循环和土壤碳库研究具有重要的科学价值。     

Failure of an iterative curve-fitting procedure to successfully estimate two organic N pools

Fitting a double negative exponential function to N mineralization data can be used to characterize two organic nitrogen pools; an easily decomposable (N_dpm) and a resistant one (N_rpm). The relevance of those two calculated N mineralization pools was investigated by adding easily decomposable organic material to soils. Soil amended with crop residues of sugar-beet or bean was mixed with an equal amount of coarse sand, incubated at 35 °C and leached at specific time-intervals. Upon leaching, NH₄ ⁺ and NO₃ ^- were measured in the extracts. A double negative exponential function was fitted to the data and two organic N pools were defined. Fitting a double negative exponential function to N mineralization data to characterize an active and resistant organic N pool was sometimes impossible; the N mineralization data did not always resemble a negative exponential function. Additionally, the size of the two pools calculated were not constant with time and were often meaningless; the N_rpm pool was greater than the soil organic N content, the size of the N_rpm pool was smaller than the N_dpm pool or one of the N pools was negative. Relevant values for both N_rpm and N_dpm which were consistent with incubation time were only obtained when excessive amounts of organic material, normally not dealt with in the field, were applied.     

Herbivore trampling as an alternative pathway for explaining differences in nitrogen mineralization in moist grasslands

Studies addressing the role of large herbivores on nitrogen cycling in grasslands have suggested that the direction of effects depends on soil fertility. Via selection for high quality plant species and input of dung and urine, large herbivores have been shown to speed up nitrogen cycling in fertile grassland soils while slowing down nitrogen cycling in unfertile soils. However, recent studies show that large herbivores can reduce nitrogen mineralization in some temperate fertile soils, but not in others. To explain this, we hypothesize that large herbivores can reduce nitrogen mineralization in loamy or clay soils through soil compaction, but not in sandy soils. Especially under wet conditions, strong compaction in clay soils can lead to periods of soil anoxia, which reduces decomposition of soil organic matter and, hence, N mineralization. In this study, we use a long-term (37-year) field experiment on a salt marsh to investigate the hypothesis that the effect of large herbivores on nitrogen mineralization depends on soil texture. Our results confirm that the presence of large herbivores decreased nitrogen mineralization rate in a clay soil, but not in a sandy soil. By comparing a hand-mown treatment with a herbivore-grazed treatment, we show that these differences can be attributed to herbivore-induced changes in soil physical properties rather than to above-ground biomass removal. On clay soil, we find that large herbivores increase the soil water-filled porosity, induce more negative soil redox potentials, reduce soil macrofauna abundance, and reduce decomposition activity. On sandy soil, we observe no changes in these variables in response to grazing. We conclude that effects of large herbivores on nitrogen mineralization cannot be understood without taking soil texture, soil moisture, and feedbacks through soil macrofauna into account.