Sensitivity of Nitrogen Mineralization Indicators to Crop and Soil Management

Abstract

Soil nitrogen (N) mineralization indicators are useful only if they are sensitive to management practices. The precision of measurement and the sensitivity of the following indicators to crop sequence, tillage, and liming effects were compared: (i) mineral N production during a 24‐day incubation under aerobic conditions, (ii) ammonium (NH₄)‐N production under waterlogged conditions, (iii and iv) hot potassium chloride (KCl)–extractable and hydrolyzable NH₄‐N (the latter obtained by subtracting initial NH₄‐N from extracted NH₄‐N), and (v) protease activity. The coefficients of variation decreased in this order: protease activity>KCl‐hydrolyzable NH₄‐N>aerobic incubation>KCl‐extractable NH₄‐N=anaerobic incubation. Most of the test results obtained using the indicators were correlated with each other. Mineralizable N measured by aerobic and anaerobic incubation was sensitive to tillage, liming, and crop sequences, especially when using soil 5‐cm deep. Hot KCl‐extractable NH₄‐N was influenced by tillage but not liming, and less sensitive than the incubation procedures to crop sequence. The protease assay produced no significant test. It was concluded that anaerobic incubation can provide a relatively sensitive assessment of management effects on soil mineralizable N.     

Nutrient Partitioning and Carbon and Nitrogen Mineralization of Switchgrass Plant Parts

Switchgrass (Panicum virgatum L.) is a native warm-season (C₄) grass that has the potential to be used as a bioenergy crop and reduce increases in atmospheric carbon dioxide (CO₂). Continuous production and removal of switchgrass, however, may deplete soil fertility. A strategy of returning plant components higher in nutrients to the field during harvest may help maintain soil fertility. In this study, nutrient partitioning in switchgrass parts over time and their C and N mineralization patterns in soil were determined. Switchgrass (cv. Alamo) was harvested on a biweekly schedule from June to October, with plants from each harvest separated into six parts (top, middle, and bottom leaves and stems) for mineral and fiber analysis. Plant materials from three harvests were used in an incubation study to determine effects of plant component, age, and composition on carbon (C) and nitrogen (N) mineralization. Results indicated that a strategy of returning specific plant parts to the field would not substantially conserve soil nutrients without proportionally decreasing materials available for bioenergy production. Structural components (cell wall and cellulose) were dominant factors affecting the quantity of C mineralized. Approximately 50% of C added as switchgrass was mineralized after 100 days of incubation. Soil N immobilization was observed in all switchgrass plant part treatments.     

Carbon Mineralization and Water-Extractable Organic Carbon and Nitrogen as Predictors of Soil Health and Nitrogen Mineralization Potential

ABSTRACT

The United States Department of Agriculture Natural Resources Conservation Service (NRCS) launched a national “Soil health initiative” in 2012; as a part of that effort, a soil health index (SHI) has been developed. The SHI is calculated using results of three soil tests: 24-h carbon mineralization following rewetting of air-dried soil (C_min, by the “Solvita” proprietary method) and water-extractable organic carbon (C) and nitrogen (N). These tests are being promoted both as the inputs into the SHI calculation and as predictors of soil N mineralization potential. Soil was collected from 35 California fields in annual crop rotations; 20 fields were under certified organic management and the other 15 under conventional management, to provide a range of soil properties and management effects. Carbon mineralization was determined by the Solvita method, and by a comparison method utilizing head space carbon dioxide (CO₂) monitoring by infrared gas analyzer (IRGA); additionally, two soil wetting protocols were compared, capillary wetting (the Solvita method) and wetting to 50% water-filled pore space (WFPS). Both water-extractable C (WEOC) and N (WEON) were determined using NRCS-recommended protocols. Net N mineralization (N_min) was also determined after a 28-day aerobic incubation at 25°C. Solvita C_min was highly correlated with the IRGA method using capillary wetting (R² = 0.81). However, capillary soil wetting resulted in high gravimetric water content that significantly suppressed C_min compared to the 50% WFPS method. N_min was correlated with Solvita C_min (r = 0.54) and with WEOC and WEON (r = 0.62 for each comparison); combining these three measurements into the SHI slightly improved the correlation with N_min. The organically managed soils scored higher than the conventional soils on the SHI, with a minority of organic soils and the majority of conventional soils scoring below the NRCS target threshold. SHI and soil organic matter were correlated, suggesting an inherent bias that would complicate the application of a national SHI standard.     

残落物混合分解对杨树-农作物复合系统土壤碳氮矿化的影响

采用室内培养的方法研究杨-麦、杨-花生等不同复合经营模式下,杨树叶与农作物秸秆混合后对土壤碳、氮矿化及土壤微生物量的影响。结果表明:(1)单一模式中,花生叶处理的有机碳矿化累积量最大,花生茎秆、杨树叶处理次之,小麦秸秆处理最低。混合处理有机碳矿化累积量依次为杨树叶-花生叶>杨树叶-花生茎秆>杨树叶-小麦秸秆,且培养结束时,混合物表现出明显的促进作用;(2)土壤微生物量碳、氮与各残落物氮含量、C/N比存在显著的相关性;(3)杨树叶、小麦秸秆及其混合物处理的土壤矿质态氮含量均低于对照,而添加花生叶、花生茎秆以及它们与杨树叶的混合物使矿质态氮含量高于对照。试验说明杨-麦、杨-花生复合模式均能有效提高土壤微生物的生物量,调节碳的动态及氮的供应,而选择种植含氮量高的农作物更有利于促进残落物分解和养分归还,这对深入研究林-农复合系统的模式筛选、结构优化及可持续经营具有一定的现实意义。     

石灰岩山地侧柏纯林非生长季土壤氮矿化研究

为探明石灰岩山地侧柏纯林非生长季土壤氮矿化能力,采用PVC管原位培养法对济南南部山区石灰岩山地人工恢复不同年限(5,10,25年)的侧柏纯林土壤的氮矿化能力进行研究。结果表明:3种不同恢复年限侧柏纯林NO3--N含量先升高后降低然后再有所升高,NH4+-N含量变化没有明显的规律性。其净硝化速率和净氮矿化速率均在11月份达到最大值,分别为(0.07±0.04)mg/(kg.d),(0.11±0.01)mg/(kg.d),(0.15±0.02)mg/(kg.d)和(0.15±0.04)mg/(kg.d),(0.29±0.02)mg/(kg.d),(0.33±0.03)mg/(kg.d)。石灰岩山地侧柏纯林土壤的净氮矿化速率与土壤湿度表现为二次函数关系,但随湿度增加,土壤净氮矿化能力降低。土壤净氮矿化与土壤pH值呈显著负相关(r=-0.452,p=0.018),与土壤有机碳含量、微生物量碳含量和C/N比均呈正相关关系,但相关性不显著(r=0.076,p=0.707;r=0.374,p=0.055;r=0.337,p=0.086)。非生长季石灰岩山地侧柏纯林土壤有较强的氮转化能力,气温变化所导致的土壤环境因素对氮矿化有显著影响。     

Nitrogen Mineralization Characteristics of Disturbed and Undisturbed Soil Samples for Four Main Soil Types on the Loess Plateau

Long-term alternate leaching aerobic incubation was conducted to study nitrogen (N) mineralization in four main soil types under disturbed (D) and undisturbed (UD) conditions from the Loess Plateau (China). Results showed that N mineralization of the UD and D samples decreased from southern to northern Shaanxi Province. Nitrate was the main component of N mineralization during the aerobic incubation for both the D and UD samples. However, net inorganic N in the D samples was less than in UD samples. The average total mineralized N levels were 30% larger for the set of D samples than for the UD samples, and the mineralization potential of the D samples was larger than that of UD samples. Further studies are required to develop predictive methods for quantifying N availability.     

Impact of Distillery Effluent on Soil Carbon and Nitrogen Dynamics in a Vertisol of Central India

Distilleries produce a huge quantity of effluents, popularly known as spent wash (SW), which when bio-methanated produce post-methanation effluents (PME). A field experiment on soybean–wheat system was conducted for five consecutive years in a Vertisol of central India to evaluate the effect of distillery effluent (DE) on soil carbon and nitrogen dynamics. Ten treatment combinations consisting of control, 100% NPK + Farmyard Manure (FYM), and graded level of SW and PME were applied. Total carbon content of soil increased significantly with applications of FYM and DE. SW was found superior in enhancing carbon content of soil in comparison to PME. Farmyard Manure contributed more carbon toward the recalcitrant pool, whereas DE contributed more carbon toward the active and slow pool. Nitrogen (N) availability was significantly improved with the application of DE. Balanced application of DE may act as amendment for increasing C and N stocks in Vertisol.     

Nitrogen Mineralization and Nitrification in Two Soils with Different pH Levels

ABSTRACT

Soil pH is one of the properties that mostly influences nitrification rates, and can be used as a tool for controlling this process, seen that depending on its extent it may lead to nitrogen (N) losses and subsequent contaminations. The aims of this study were to evaluate mineralization and nitrification of two soils at different pH levels. The experimental design was factorial with two factors and three replicates, with the first factor referring to two samples of red latosols, one eutrophic (LV1) and the other dystrophic (LV2), and the second factor was soil’s pH, at six levels: 4.0, 4.5, 5.0, 5.5, 6.0, and 6.5. Samples were incubated for 70 days in laboratory conditions. Both nitrate (N-NO₃) and mineral N contents were determined and adjusted to growth models. The eutrophic soil presented higher mineral N and N-NO₃, and the increase of pH levels led to increases of both inorganic N and N-NO₃contents. Increases in pH levels caused N-NO₃levels to increase in both soils, however this occurrence happened because it increased the amount of mineralized N in the soil, seen that in all pH ranges in both soils practically all mineral N was in the form of N-NO₃.     

Container and Installation Time Effects on Soil Moisture,Temperature, and Inorganic Nitrogen Retention for an in situ Nitrogen Mineralization Method

Mineralization contributes significantly to agronomic nitrogen (N) budgets and is difficult to accurately predict. Models for predicting N‐mineralization contributions are needed, and development of these models will require field‐based data. In situ mineralization methods are intended to quantify N mineralization under ambient environmental conditions. This study was conducted to compare soil moisture and temperature in intact soil cores contained in cylinders to those in adjacent bulk soil, compare the effect of two resin‐bag techniques on water content of soil within cylinders, and assess the effect of installation duration on inorganic N retention by resins. The study was conducted at a dryland conventionally tilled corn (Zea mays L.) site and an irrigated no‐tillage corn site in eastern Nebraska. Soil in cylinders was slightly wetter (<0.05 g g^?1) and warmer (<1 °C) than adjacent soil. Soil water content was <80% water‐filled pore space (WFPS) at all sampling times and differed little between the two resin‐bag techniques. Greater soil water content and temperature conditions (though small) observed during most of the study period likely enhanced N mineralization within the cylinder compared to N mineralization in adjacent bulk soil, but the magnitude is likely much less than core‐to‐core variation normally observed in a field. Installing cylinders for more than 60 days resulted in loss of inorganic N from resins. Care is needed during installation to ensure that compaction of soil below the cylinder does not impede water movement through the intact soil core. The in situ method utilizing intact soil cores and resin bags replaced at 28‐ to 40‐day intervals is a viable method for measuring N mineralization.     

Mineralization of Organic-Amendment-Derived Nitrogen in Two Mediterranean Soils with Different Organic-Matter Contents

The use of organic fertilizers in lands with low organic-matter content, such as those found in the Mediterranean region, is an attractive option for enhancing soil quality and fertility status. However, it is difficult to assess the nitrogen (N) mineralization rate and the quantity of the organic amendment to be added. Thus we conducted a 300-day incubation trial, where four commonly found organic amendments (three different animal manures and one sewage sludge) were mixed with two soils. Our aim was to assess the potentially mineralizable N with the use of the first-order exponential model. Our findings indicated that the N-mineralization data fitted well to the model we used and that the active N fraction (eluted available N per total N added) ranged from 28.4% to 50.3%, depending on indigenous organic carbon (C) content, as well as on the organic amendment C/N ratio and total N content.     

Contributions of Organic Nitrogen Forms to Mineralized Nitrogen during Incubation Experiments of the Soils on the Loess Plateau

Interval leaching long‐term water‐logged incubation and interval leaching long‐term aerobic incubation were carried out to study the changes of different soil organic nitrogen (N) forms and their contributions to mineralized N during N‐mineralization process on 10 kinds of farmland soils with markedly different physical and chemical properties on the Loess Plateau. The results showed that the N‐mineralization capability and capacity using the two incubation methods were evidently different. After 217 days, cumulative mineralized N, the decreased amounts of total acid‐hydrolyzable N, acid‐hydrolyzable ammonia N, and acid‐hydrolyzable amino acid N in the water‐logged incubation were about twice those in the aerobic incubation. Soluble organic N leached in the aerobic incubation was four times that in the water‐logged incubation, which implied that organic N in the aerobic incubation mineralized more thoroughly than that in the water‐logged incubation. The correlation analysis of the changes of soil organic N forms with crop N uptake showed that the reduced amount of total acid‐hydrolyzable N in the water‐logged incubation was closely associated with total N uptake by two successive‐season crops (winter wheat and summer maize), and the decreased amounts of total acid‐hydrolyzable N and amino acid N in the aerobic incubation were highly significantly related to the N uptake of both the first season crop (winter wheat) and successive‐season maize. Multiple regression analysis, path analysis, and partial correlation analysis of the changes of soil organic N forms with mineralized N indicated that ammonia N was a main contribution to mineralized N in the water‐logged incubation, whereas both acid‐hydrolyzable amino acid and ammonia N were main contributions to mineralized N in the aerobic incubation. These results suggested that acid‐hydrolyzable ammonia was the primary contribution to mineralized N during N mineralization process with the two incubation methods.     

Mineralization of Three Organic Manures Used as Nitrogen Source in a Soil Incubated under Laboratory Conditions

Abstract

The rate and timing of manure application when used as nitrogen (N) fertilizer depend on N‐releasing capacity (mineralization) of manures. A soil incubation study was undertaken to establish relative potential rates of mineralization of three organic manures to estimate the value of manure as N fertilizer. Surface soil samples of 0–15 cm were collected and amended with cattle manure (CM), sheep manure (SM), and poultry manure (PM) at a rate equivalent to 200 mg N kg^?1 soil. Soil without any amendment was used as a check (control). Nitrogen‐release potential of organic manures was determined by measuring changes in total mineral N [ammonium‐N+nitrate‐N (NH₄ ⁺–N+NO₃ ^?–N)], NH₄ ⁺–N, and accumulation of NO₃ ^?–N periodically over 120 days. Results indicated that the control soil (without any amendment) released a maximum of 33 mg N kg^?1soil at day 90, a fourfold increase (significant) over initial concentration, indicating that soil had substantial potential for mineralization. Soil with CM, SM, and PM released a maximum of 50, 40, and 52 mg N kg^?1 soil, respectively. Addition of organic manures (i.e., CM, SM, and PM) increased net N released by 42, 25, and 43% over the control (average). No significant differences were observed among manures. Net mineralization of organic N was observed for all manures, and the net rates varied between 0.01 and 0.74 mg N kg^?1 soil day^?1. Net N released, as percent of organic N added, was 9, 10, and 8% for CM, SM, and PM. Four phases of mineralization were observed; initial rapid release phase in 10–20 days followed by slow phase in 30–40 days, a maximum mineralization in 55–90 days, and finally a declined phase in 120 days. Accumulation of NO₃ ^?–N was 13.2, 10.6, and 14.6 mg kg^?1 soil relative to 7.4 mg NO₃ ^?–N kg^?1 in the control soil, indicating that manures accumulated NO₃ ^?–N almost double than the control. The proportion of total mineral N to NO₃ ^?–N revealed that a total of 44–61% of mineral N is converted into NO₃ ^?–N, indicating that nitrifiers were unable to completely oxidize the available NH₄ ⁺. The net rates of mineralization were highest during the initial 10–20 days, showing that application of manures 1–2 months before sowing generally practiced in the field may cause a substantial loss of mineralized N. The rates of mineralization and nitrification in the present study indicated that release of inorganic N from the organic pool of manures was very low; therefore, manures have a low N fertilizer effect in our conditions.     

Mineralization of Nitrogen in Soils Amended with Dairy Manure as Affected by Wetting/Drying Cycles

Abstract

Interest in manure management and its effects on nitrogen (N) mineralization has increased in recent years. The focus of this research was to investigate the N‐mineralization rates of different soil types in Coastal Plain soils and compare them to a soil from Illinois. Soils with and without dairy composted manure addition were subjected to different wetting/drying cycles [constant moisture at 60% water‐filled pore space (WFPS) and cycling moisture from 60 to 30% WFPS] under laboratory conditions at three different temperatures (11°C, 18°C, and 25°C). Samples were collected from three different soil types: Catlin (Mollisols), Bama (Ultisols), and Goldsboro (Utilsols). Soil chemical and physical properties were determined to help assess variations in N-mineralization rates. Addition of composted manure greatly impacted the amount of N mineralized. The amount of manure‐derived organic N mineralized to inorganic forms was mainly attributed to the soil series, with the Catlin (silt loam) producing the most inorganic N followed by the Goldsboro (loam) and then Bama (sandy loam). This was probably due to soil texture and the native climatic conditions of the soil. No significant differences were observed between the constant and cycling moisture regimens, suggesting that the imposed drying cycle may not have been sufficient to desiccate microbial cells and cause a flush in N mineralization upon rewetting. Nitrogen mineralization responded greatly to the influence of temperature, with the greatest N mineralization occurring at 25°C. The information acquired from this study may aid in predicting the impact of manure application to help increase N‐use efficiency when applied under different conditions (e.g., climate season) and soil types.     

侵蚀红壤区植被恢复对表层与深层土壤有机碳矿化的影响

试验研究了典型红壤侵蚀区不同植被恢复年限(0,11,31a)的表层(0—10cm)和深层(60—80cm)土壤有机碳矿化特征。结果表明:深层土壤有机碳84d累积矿化量或潜在矿化量显著低于表层土壤,植被恢复则显著增加了表层和深层土壤累积矿化量或潜在矿化量(P0.05),相关分析显示土壤有机碳累积矿化量或潜在矿化量与WSOC、MBC和SOC显著(P0.05)或极显著(P0.01)相关,表明碳矿化底物数量是决定土壤碳累积矿化量或潜在矿化量的主导因子;对照表层土壤的矿化速率常数(k)高于深层土壤的,植被恢复降低了表层土壤的k值(P0.05),对深层土壤的k值却没有显著影响;而深层土壤矿化率显著高于表层土壤,且植被恢复后均显著降低(P0.05),相关分析显示土壤有机碳矿化率与微生物代谢熵呈极显著的正相关(P0.01),表明微生物碳利用效率是影响土壤碳矿化率的重要因素,而深层土壤微生物碳利用效率显著低于表层土壤,但植被恢复可以改善侵蚀红壤的环境条件,提高土壤微生物的碳利用效率,从而增强土壤固碳能力。     

Predicting Nitrogen and Carbon Mineralization of Composted Manure and Sewage Sludge in Soil

The capability of organic wastes to release available N in soil varies largely, depending on their source and form of production, or rather on their composition and biodegradability. Our purpose was to predict mineralization rates of different materials using their analyses joined with a simulation model, and to evaluate the influence of soil type and application rate of the organic materials on N and C transformations in soil. Four organic materials, sewage sludge (SS), sewage sludge compost (SSC), cattle manure compost (CMC), hen and cattle manure compost (HCMC), were applied to two soils at rates of 2 and/or 4%. The soils were incubated aerobically for 168 days at 30°C, during which CO₂ evolution rates and mineral-N concentrations were measured periodically. Hot water extractable C and N of all organic amendments correlated well with short term C and N mineralization, except HCMC that immobilized N although its soluble N content was large. NCSOIL, a computer model that simulates C and N cycling in soil with organic amendments, predicted well C and N mineralization of SS, SSC and CMC when considered as three-pool materials that decomposed at specific rates of 0.4, 0.024 and 10^?4 d^?1, using hot water soluble C and N as the labile pool. N immobilization by HCMC could be simulated only if the distribution of N between the labile and resistant pools was derived by optimization of NCSOIL, while hot water soluble C was labile. Laboratory methods to determine an intermediate pool or components that contribute to immobilization are required for improving the predictions of C and N mineralization from organic amendments.     

Protocols for Nationally Coordinated Laboratory and Field Research on Manure Nitrogen Mineralization

Abstract

The National Program structure of USDA‐ARS provides an opportunity to coordinate research on problems of national and global significance. A team of USDA‐ARS scientists is conducting nationally coordinated research to develop predictions of manure N availability to protect water quality and improve farm solvency. Experimental design and research protocols were developed and used in common across all participating locations. Laboratory incubations are conducted at each location with a minimum of three soils, three temperatures, two wetting/drying regimes, and two manure treatments. A soil from the central United States (Catlin silt loam, fine‐silty, mixed, superactive, mesic Oxyaquic Argiudoll) is used as an internal reference across all locations. Incubation data are compiled across locations to develop generalized predictions of manure nitrogen mineralization (Nmin). Field validation data are then obtained by monitoring nitrogen (N) transformations in manure‐amended soil cores equipped with anion exchange resin to capture leached nitrate. This field data will be used to compare laboratory‐based predictions with field observations of Nmin in each soil, climatic zone, and manure type represented. A Decision Support System will then be developed for predicting manure N mineralization across ranges in soil, climate, and manure composition. Protocols used by this research team are provided to 1) document the procedures used and 2) offer others detailed information for conducting research on nutrient transformation processes involving collaboration across locations or complementary research between laboratory and field environments.     

模拟氮沉降对温带不同森林类型土壤氮矿化速率的影响

通过室内模拟不同氮形态(NH4+-N、NO3--N、NH4+-N+NO3--N)沉降实验,研究不同氮形态沉降对温带不同森林类型(椴树红松混交林、白桦天然次生林、红松人工林和落叶松人工林)土壤氮矿化速率的影响。结果表明:在整个培养期间,与对照相比,经过氮沉降土壤净氨化速率、净硝化速率及净矿化速率都呈现出增长趋势,而其增加的程度又取决于森林类型、土层、氮处理类型和处理时间。不同林型土壤净氨化速率、净硝化速率及净矿化速率受氮沉降影响不同,混交林对氮沉降的响应要弱于阔叶林,高于针叶人工纯林;土壤A层比土壤B层对氮沉降敏感;以铵态氮形态沉降时对铵态氮含量、净氨化速率影响较大,以硝态氮形态沉降时对硝态氮含量、净硝化速率影响较大,混合形态的氮沉降要比单种形态的氮沉降使土壤净氨化速率、净硝化速率及净矿化速率增加幅度更高;氮沉降时间越长,土壤净氨化速率、净硝化速率及净矿化速率与对照差距越大,说明氮沉降对土壤的影响存在累加效应。     

Nationally Coordinated Evaluation of Soil Nitrogen Mineralization Rate using a Standardized Aerobic Incubation Protocol

Abstract

Aerobic incubation methods have been widely used to assess soil nitrogen (N) mineralization, but standardized protocols are lacking. A single silt loam soil (Catlin silt loam; fine‐silty, mixed, superactive, mesic, Oxyaquic Arguidoll) was subjected to aerobic incubation at six USDA‐ARS locations using a standardized protocol. Incubations were conducted at multiple temperatures, which were combined based on degree days (DD). Soil water was maintained at 60% water‐filled pore space (WFPS; constant) or allowed to fluctuate between 60 and 30% WFPS (cycle). Soil subsamples were removed periodically and extracted in 2 M potassium chloride (KCl); nitrate (NO₃) and ammonium (NH₄) concentrations in extracts were determined colorimetrically. For each location, the rate of soil organic‐matter N (SOMN) mineralization was estimated by regressing soil inorganic N (N_i) concentration on DD, using a linear (zero‐order) model. When all data were included, the mineralization rate from four datasets was not statistically different, with a rate equivalent to 0.5 mg N kg^?1 soil day^?1. Soil incubated at two locations exhibited significantly higher SOMN mineralization rates. To assess whether this may have been due to pre‐incubation conditions, time‐zero data were excluded and regression analysis was conducted again. Using this data subset, SOMN mineralization from five (of six) datasets was not significantly different. Fluctuating soil water reduced N‐mineralization rate at two (of four) locations by an average of 50%; fluctuating soil water content also substantially increased variability. This composite dataset demonstrates that standardization of aerobic incubation methodology is possible.     

草甸沼泽土壤硝化-反硝化作用和有机碳矿化对氮输入的响应

通过室内培养实验.研究了草甸沼泽土壤N2O排放和反硝化损失对氮输入的响应特征,结果表明,在培养期(23 d)内N2O平均排放速率为0.32(NO).0.87(N1).17.69(N2),28.07(N3)μgN2O-N/(kg±·h),反硝化平均损失速率为0.25(NO),0.81(NI),22.29(N2),30.28(N3)μgN2O--N/(kg±·h).两者都随氮输入量增高而升高.其中,N3处理N2O平均排放速率和反硝化平均损失速率与对照差异显著(p<0.05),N1和N2与对照差异不显著.N2O排放总量占氮输入的比例为0.03%(N1),1.04%(N2).1.76%(N3),反硝化损失总量占氮输入的比例为0.04%(N1),1.29%(N2),1.93%(N3).均表现为随氮输入量的增大而增高.N1处理下有机碳矿化速率低于对照,而N2和N3有机碳矿化速率高于对照,说明低氮输入对有机碳矿化有一定抑制作用,.高氮输入促进有机碳矿化.     

外源碳氮输入对元阳梯田土壤有机氮厌氧矿化的影响

采用室内培养法研究了元阳梯田3个海拔梯度(高海拔为1626~1672 m、中海拔为1532~1537 m和低海拔为1445~1459 m)表层(0~30 cm)土壤和同一海拔3个土壤层次(0~30 cm、30~60 cm和60~90 cm)氮素在厌氧条件下的矿化特征。结果表明:4种矿化处理(对照、加碳、加氮和加碳氮)20天的培养,净矿化量均随海拔高度的降低而降低,随土层深度的增加而降低。矿化速率随培养时间呈现出下降的趋势,后期矿化量变幅缓慢。四种处理净矿化量与土壤有机碳(TOC)、全氮(TN)、溶解性有机碳氮(DOC和DON)、微生物量碳(MBC)、易氧化碳(ROC)及轻组碳氮(LFC和LFN)均呈显著性正相关(P0.05)。20天的培养期内的净矿化量总体表现为:对照和加氮处理大于加碳和加碳氮处理。表明有机碳的投入降低了净矿化,可减少氮的损失,元阳梯田土壤中的碳可能对土壤中有限氮素资源具有良好的保蓄作用。