Promoting microbial immobilization of soil nitrogen during restoration of abandoned agricultural fields by organic additions

Application of organic materials to soils to enhance N immobilization into microbial biomass, thereby reducing inorganic N concentrations, was studied as a management option to accelerate the reestablishment of the native vegetation on abandoned arable fields on sandy soils the Kiskunság National Park, Hungary. Sucrose and sawdust were used at three different topographic sites over 4 years. N availability and extractable inorganic N concentrations were significantly reduced in all sites. Soil microbial biomass C and microbial biomass N increased significantly following C additions, but the microbial C to microbial N ratio remained unaffected. It is concluded that the combined application of the rapidly utilized C source (sucrose) promoted N immobilization, whereas the addition of the slowly utilized C source (sawdust) maintained the elevated microbial biomass C and microbial biomass N in the field.     

Microbial biomass and microbial C:N ratio in bulk soil and buried bags for evaluating in situ net N mineralization in agricultural soils

The in situ net nitrogen mineralization (N_net) was estimated in five agricultural soils under different durations of organic farming by incubating soil samples in buried bags. Simultaneously, soil microbial C and N was determined in buried bags and in bulk soil under winter wheat and after harvest. The aim was to check for variations in soil microbial biomass contents and microbial C:N ratios during the incubation period, and their importance for N_net rates. Microbial C and N contents were highest in soils that had been organically farmed for 41 years, whereas N_net rates were highest in a short‐term organically managed soil that had been under grassland use until 36 years ago. The mean coefficient of variation in the bulk soil for microbial C estimates ranged from 5 to 12 %. Microbial N contents were similar inside buried bags and in the bulk soil at the end of the incubation periods. Under winter wheat during the incubation period until harvest, microbial C contents and microbial C:N ratios (in 10—27 cm depth only) decreased more strongly inside buried bags than in the bulk soil. Following harvest of winter wheat and ploughing, microbial biomass increased while in situ N_net decreased, presumably due to N immobilization. The N_net rates were not correlated with microbial N contents or changes in microbial N contents inside buried bags. At the end of the vegetation period of winter wheat, N_net rates were negatively correlated with microbial C:N ratios. Because these ratios concurrently decreased more inside buried bags than in the bulk soil, the N_net estimates of the buried bag method may differ from the N_net rates in the bulk soil at that time.     

废弃农耕地自然演替过程中微生物群落与土壤特性间的关系

The changes of microbial biomass carbon (MBC) and nitrogen (MBN) and microbial community in the topsoil of the abandoned agricultural land on the semi-arid Loess Plateau in China during the natural succession were evaluated to understand the relationship between microbial community and soil properties. MBC and MBN were measured using fumigation extraction, and microbial community was analyzed by the method of fatty acid methyl ester (FAME). The contents of organic C, total N, MBC, MBN, total FAME, fungal FAME, bacterial FAME and Gram-negative bacterial FAME at the natural succession sites were higher than those of the agricultural land, but lower than those of the natural vegetation sites. The MBC, MBN and total FAME were closely correlated with organic C and total N. Furthermore, organic C and total N were found to be positively correlated with fungal FAME, bacterial FAME, fungal/bacterial and Gram-negative bacterial FAME. Natural succession would be useful for improving soil microbial properties and might be an important alternative for sustaining soil quality on the semi-arid Loess Plateau in China.     

有机物料输入稻田提高土壤微生物碳氮及可溶性有机碳氮

土壤微生物量碳、氮和可溶性有机碳、氮是土壤碳、氮库中最活跃的组分,是反应土壤被干扰程度的重要灵敏性指标,通过设置相同有机碳施用量下不同有机物料处理的田间试验,研究了有机物料添加下土壤微生物量碳（soil microbial biomass carbon,MBC）、氮（soil microbial biomass nitrogen,MBN）和可溶性有机碳（dissolved organic carbon,DOC）、氮（dissolved organic nitrogen,DON）的变化特征及相互关系。结果表明化肥和生物碳、玉米秸秆、鲜牛粪或松针配施下土壤微生物量碳、氮和可溶性有机碳、氮显著大于不施肥处理（no fertilization,CK）和单施化肥处理,分别比不施肥处理和单施化肥平均高23.52%和12.66%（MBC）、42.68%和24.02%（MBN）、14.70%和9.99%（DOC）、22.32%和21.79%（DON）。化肥和有机物料配施处理中,化肥+鲜牛粪处理的微生物量碳、氮和可溶性有机碳、氮最高,比CK高26.20%（MBC）、49.54%（MBN）、19.29%（DOC）和32.81%（DON）,其次是化肥+生物碳或化肥+玉米秸秆处理,而化肥+松针处理最低。土壤可溶性有机碳质量分数（308.87 mg/kg）小于微生物量碳（474.71 mg/kg）,而可溶性有机氮质量分数（53.07 mg/kg）要大于微生物量氮（34.79 mg/kg）。与不施肥处理相比,化肥和有机物料配施显著降低MBC/MBN和DOC/DON,降低率分别为24.57%和7.71%。MBC和DOC、MBN和DON随着土壤有机碳（soil organic carbon,SOC）、全氮（total nitrogen,TN）的增加呈显著线性增加。MBC、MBN、DOC、DON、DOC+MBC和DON+MBN之间呈极显著正相关（P<0.01）。从相关程度看,DOC+MBC和DON+MBN较MBC、DOC、MBN、DON更能反映土壤中活性有机碳和氮库的变化,成为评价土壤肥力及质量的更有效指标。结果可为提高洱海流域农田土壤肥力,增强土壤固氮效果,减少土壤中氮素流失,保护洱海水质安全提供科学依据。     

有机无机肥配施对盐渍化土壤微生物量和呼吸的影响

微生物可以通过摄入能量合成有机渗透压物质来实现对盐度的适应,然而,不同程度盐渍土微生物对能量的需求可能会发生改变。因此,该研究于2018－2019年开展田间定位试验,选取河套灌区轻度盐渍土S1（电导率为0.46 dS/m）及中度盐渍土S2（电导率为1.07 dS/m）为研究对象,设置了6个处理,包括不施氮（CK）,单施无机氮（U1）以及分别用有机氮（U3O1、U1O1、U1O3和O1）替代25%、50%、75%和100%的无机氮,监测了土壤微生物量碳氮及土壤呼吸在第二个生长季的动态状况。结果表明：土壤盐渍化程度增加会导致土壤微生物量及微生物活性下降,S1土壤较S2土壤微生物量碳高12.01%～68.81%,土壤微生物量氮高14.31%～58.58%,土壤呼吸速率高11.75%～54.71%。不同盐分条件下,适当的有机肥施入比例可以显著提高土壤微生物量及微生物活性,S1和S2盐渍土分别以U1O1及O1处理较优。相关性分析表明,土壤呼吸速率与土壤微生物量碳氮呈极显著正相关（P＜0.01）,土壤温度、土壤矿质氮与土壤微生物量碳氮、土壤呼吸速率呈显著正相关（P＜0.05）。从玉米产量及改善土壤微生物生存环境角度,得到该地区适宜的施肥模式为,轻度盐渍土：有机氮替代50%无机氮;中度盐渍土：有机氮替代100%无机氮。     

Effects of substituting chemical fertilizers with manure on rice yield and soil labile nitrogen in paddy fields of China: A meta-analysis

Substituting chemical fertilizers with manure is an important method for efficient nutrient management in rice cropping systems of China.Labile nitrogen(N) is the most active component of the soil N pool and plays an essential role in soil fertility.However,the effects of manure substitution on soil labile N in rice cropping systems and their relationships with soil properties,fertilization practices,and climatic conditions remain unclear and should be systematically quantified.Here,we investiga...     

Kinetics of C and N mineralization, N immobilization and N volatilization of organic inputs in soil

C and N mineralization data for 17 different added organic materials (AOM) in a sandy soil were collected from an incubation experiment conducted under controlled laboratory conditions. The AOM originated from plants, animal wastes, manures, composts, and organic fertilizers. The C-to-N_AOM ratios (η_AOM) ranged from 1.1 to 27.1. Sequential fibre analyses gave C-to-N ratios of soluble (η_Sol), holocellulosic (η_Hol) and ligneous compounds (η_Lig) ranging from 1.1 to 57.2, 0.8 to 65.2, and 3.5 to 25.3, respectively. Very different patterns of net AOM-N mineralization were observed: (i) immobilization for four plant AOM; (ii) moderate mineralization (4-15% AOM-N) for composts; (iii) marked mineralization (11-27% AOM-N) for 1 animal AOM, 1 manure and 2 organic fertilizers; and (iv) high rates of transformations with possible gaseous losses for some N-rich AOM.The Transformation of Added Organics (TAO) model proposed here, described AOM-C mineralization (28 °C, 75% WHC) from three labile (L′), resistant (R) and stable (S) compartments with the sole parameters P′_L and P_S=fractions of very labile and stable compounds of AOM, respectively. Dividing the C-compartments by their C-to-N estimates supplied the remaining N_AOM fraction (RAONF). A P_im parameter split the TAO nitrogen fraction (TAONF=added N-RAONF) into two compartments, immobilized (imN) and inorganic (inorgN) N. A P_im>0 value meant that all the TAONF plus a fraction (P_im−1) of native soil inorganic N was immobilized. Additional N mineralization was predicted when necessary from imN by first order kinetics (constant k_remin). The TAO version with two parameters P_im and k_remin allowed us to predict very different patterns of N mineralization and N immobilization. In a few cases, a further first order kinetic law (constant k_v) was added to predict N volatilization from inorgN. Two hypotheses were tested: (i) η_L′, η_R, η_S (C-to-N of L′, R and S)=η_Sol, η_Hol, η_Lig, respectively, (ii) η_L′=η_R=η_S=η_AOM. The first hypothesis was validated by these data, and the second was a good approximation of the former one. In all the cases, predictions were in good agreement with measured values.     

有机肥和化肥长期施用对土壤活性有机氮组分及酶活性的影响

本文以中国农业科学院山东禹城长期定位施肥试验为平台,研究了长期施用有机肥和化肥26年后对土壤活性氮库不同组分［颗粒有机氮（POM-N）、 可溶性有机氮（DON）、 微生物量氮（SMBN）及轻组有机氮（LFOM-N）］及土壤酶活性的影响。结果表明,与不施肥相比,长期施肥显著提高了土壤全氮、 颗粒有机氮、 可溶性有机氮、 微生物量氮以及轻组有机氮的含量,长期施有机肥效果好于化肥,施用高量有机肥效果好于施用常量有机肥。常量施用量下,50%有机肥和50%化肥配施处理其土壤全氮和活性有机氮库各组分含量与高量化肥处理的相当。长期施化肥处理土壤全氮及活性有机氮库各组分含量随施肥量的增加而显著增高。POM-N对土壤全氮的贡献率最高,且明显受施肥方式的影响,LFOM-N对土壤全氮的贡献率不随施肥方式的改变而变化。长期施肥处理土壤脲酶、 碱性磷酸酶和蔗糖酶活性显著增加,它们之间及与土壤全氮、 速效磷及有机碳含量间呈现显著或极显著相关性,脲酶活性与土壤各活性氮组分间也存在显著或极显著相关性; 但长期施肥后土壤过氧化氢酶的活性低于不施肥     

黄土高原某些耕作土壤中土壤微生物生物量C、N与矿化N的关系

The chloroform fumigation-incubation method was used to measure the soil microbial biomass C (SMBC) and N (SMBN) in 16 loessial soils sampled from Ansai, Yongshou and Yangling in Shaanxi Province. The SMBC contents in the soils ranged from 75.9 to 301.0 μg C g^-1 with an average of 206.1 μg C g^-1, accounting for 1.36%~6.24% of the total soil organic C with an average of 3.07%, and the SMBN contents from 0.51 to 68.40 μg N g^-1 with an average of 29.4 μg N g^-1, accounting for 0.20%~5.65% of the total N in the soils with an average of 3.36%. A close relationship was found between SMBC and SMBN, and they both were positively correlated with total organic C, total N, NaOH hydrolizable N and mineralizable N. These results confirmed that soil microbial biomass had a comparative role in nutrient cycles of soils.     

水稻-小麦轮作系统中土壤活性有机碳库对长期施用化肥，秸秆和粪便的敏感度

Labile soil organic carbon(SOC) pools, estimated through chemical fractionation techniques, are considered sensitive indicators of management-induced changes in quality and composition of soil organic matter. Although the impacts of organic manure and crop residue applications on C sequestration in rice-wheat system are fairly well documented, their influence on labile SOC pools is relatively less known. Impacts of organic manure, rice straw, and inorganic fertilizer nitrogen(N) applications on soil total organic carbon(TOC)and SOC pools including water-extractable organic C(WEOC), hot water-soluble organic C(HWOC), potassium permanganateoxidizable organic C(KMnO 4-C), microbial biomass C(MBC), mineralizable organic C(Cmin), and the oxidizable fractions of decreasing oxidizability(easily-oxidizable, oxidizable, and weakly-oxidizable) were investigated in an 11-year field experiment under rice-wheat system. The field experiment included treatments of different combinations of farmyard manure, rice straw, and fertilizer N application rates, with C inputs estimated to be in the range from 23 to 127 Mg ha-1. After 11 years of experiment, WEOC,HWOC, and KMnO 4-C were 0.32%–0.50%, 2.2%–3.3%, and 15.0%–20.6% of TOC, respectively. The easily-oxidizable, oxidizable,and weakly-oxidizable fractions were 43%–57%, 22%–27%, and 10%–19% of TOC, respectively. The applications of farmyard manure and rice straw improved WEOC, HWOC, KMnO 4-C, easily-oxidizable fraction, Cmin, and MBC, though the rates of change varied considerably from-14% to 145% and-11% to 83% of TOC, respectively. At the C input levels between 29 and 78 Mg C ha-1during the 11-year period, the greatest increase was observed in WEOC and the minimum in KMnO 4-C. Water-extractable organic C exhibited a relatively greater sensitivity to management than TOC, suggesting that it may be used as a sensitive indicator of management-induced changes in soil organic matter under rice-wheat system. All the other labile SOC pools exhibited almost the same sensitivity to management as TOC. Most of the SOC pools investigated were positively correlated to each other though their amounts differed considerably. Long-term applications of farmyard manure and rice straw resulted in build-up of not only the labile but also the recalcitrant pool of SOC, emphasizing the need for continued application of organic amendments for permanence of the accrued C under the experimental conditions.     

Gradients in N‐cycling attributes along forestry and agricultural land‐use systems are indicative of soil capacity for N supply

Indicators of soil quality associated with N‐cycling were assessed under different land‐use systems (native forest – NAT, reforestation with Araucaria angustifolia or Pinus taeda and agricultural use – AGR) to appraise the effects on the soil potential for N supply. The soil total N ranged from 2 to 4 g/kg (AGR and NAT, respectively), and the microbial biomass N ranged from 80 to 250 mg/kg, being higher in NAT and A. angustifolia, and lower in P. taeda and AGR sites. Activities of asparaginase (ca. 50–200 mg NH₄⁺‐N/kg per h), glutaminase (ca. 200–800 mg NH₄⁺‐N/kg per h) and urease (ca. 80–200 mg NH₄⁺‐N/kg/h) were also more intense in the NAT and A. angustifolia‐reforested soils, indicating greater capacity for N mineralization. The NAT and AGR soils showed the highest and the lowest ammonification rate, respectively (ca. 1 and 0.4 mg NH₄⁺‐N/kg per day), but the inverse for nitrification rate (ca. 12 and 26%), indicating a low capacity for N supply, in addition to higher risks of N losses in the AGR soil. A multivariate analysis indicated more similarity between NAT and A. angustifolia‐reforested sites, whilst the AGR soil was different and associated with a higher nitrification rate. In general, reforestation with the native species A. angustifolia had less impact than reforestation with the exogenous species P. taeda, considering the soil capacity for N supply. However, AGR use caused more changes, generally decrease in indicators of N‐cycling, showing a negative soil management effect on the sustainability of this agroecosystem.     

Effect of organic and inorganic sources of nutrients on soil microbial activity and soil organic carbon build-up under rice in west coast of India

The effect of medium-term (5 years) application of organic and inorganic sources of nutrients (as mineral or inorganic fertilizers) on soil organic carbon (SOC), SOC stock, carbon (C) build-up rate, microbial and enzyme activities in flooded rice soils was tested in west coast of India. Compared to the application of vermicompost, glyricidia (Glyricidia maculate) (fresh) and eupatorium (Chromolaena adenophorum) (fresh) and dhaincha (Sesbania rostrata) (fresh), the application of farmyard manure (FYM) and combined application of paddy straw (dry) and water hyacinth (PsWh) (fresh) improved the SOC content significantly (p < 0.05). The lowest (p < 0.05) SOC content (0.81%) was observed in untreated control. The highest (p < 0.05) SOC stock (23.7 Mg C ha^?1) was observed in FYM-treated plots followed by recommended dose of mineral fertilizer (RDF) (23.2 Mg C ha^?1) and it was lowest (16.5 Mg C ha^?1) in untreated control. Soil microbial biomass carbon (C_mb) (246 µg g^?1 soil) and C_mb/SOC (1.92%) were highest (p < 0.05) in FYM-treated plot. The highest (p < 0.05) value of metabolic quotient (qCO₂) was recorded under RDF (19.7 µg CO₂-C g^?1 C_mb h^?1) and untreated control (19.6 µg CO₂-C g^?1 C_mb h^?1). Application of organic and inorganic sources of nutrients impacted soil enzyme activities significantly (p < 0.05) with FYM causing highest dehydrogenase (20.5 µg TPF g^?1 day^?1), phosphatase (659 µg PNP g^?1 h^?1) and urease (0.29 µg urea g^?1 h^?1) activities. Application of organic source of nutrients especially FYM improved the microbial and enzyme activities in flooded and transplanted rice soils. Although the grain yield was higher with the application of RDF, but the use of FYM as an organic agricultural practice is more useful when efforts are intended to conserve more SOC and improved microbial activity.     

燕沟流域土壤微生物学性质对植被恢复过程的响应

以黄土高原丘陵区陕北延安燕沟流域为例,研究了退耕地土壤微生物生物量对植被恢复过程的响应。结果表明,随植被恢复年限的增加,植被盖度、多度和物种数均呈现先增加后减少然后又增加的趋势。同对照农地相比,表层(0—5 cm)土壤呼吸速率和土壤微生物生物量均明显增加。表层土壤呼吸速率和微生物量碳、氮、磷分别比对照农地增加31.61%3~60.75%和15.19%5~12.81%、122.91%6~97.15%、193.5%2~068.17%。表层土壤呼吸速率对植被恢复的响应是在植被恢复初期(02~9年),随植被恢复年限的增加而增加;植被恢复305~5年期间,随植被恢复年限的增加而减少;而植被恢复55年以后,又随植被恢复年限的增加而增加。植被恢复过程中,土壤微生物量碳、氮和磷的变化与土壤呼吸速率变化趋势类似。除植被恢复8和16年外,植被恢复年限间的土壤呼吸速率、呼吸熵和微生物量碳、氮、磷均有显著性差异。表层土壤呼吸速率与土壤微生物量氮、磷呈极显著相关,土壤微生物量碳与土壤微生物量氮呈显著相关;而土壤呼吸熵与呼吸速率和微生物量碳、氮、磷相关性不明显。     

不同有机物料还田对华北农田土壤固碳的影响及原因分析

中国农业面临着废弃物数量大、污染严重,农田土壤生产力低的现实问题。该研究以增加农田土壤固碳为目标对砂质农田进行有机物料还田,将秸秆、猪粪、沼渣和生物炭4种物料用尿素调节等氮还田,对农田土壤有机碳、颗粒有机碳、可溶性有机碳和微生物量碳的含量进行测定,并探究不同有机物料还田对土壤有机碳的影响原因。研究结果表明:物料还田3a后,生物炭、猪粪和沼渣处理土壤有机碳(SOC)比秸秆处理分别高262.4%、26.8%和20.7%;2014—2015年生物炭处理的土壤微生物量碳(MBC)较秸秆处理降低2.9%~35.5%,猪粪处理和沼渣处理的土壤可溶性有机碳(DOC)分别提高17.1%~60.1%和7.2%~64.8%;2014—2015年生物炭、猪粪和沼渣处理土壤颗粒有机碳(POC)较秸秆处理提高10.8%~148.2%、9.5%~58.3%和11.3%~57.6%;物料还田后,土壤总有机碳(TOC)和POC呈极显著的回归关系(R2=0.67,P0.001),土壤DOC与MBC有极显著相关性(R2=0.52,P0.001)。与秸秆还田相比,生物炭还田有利于土壤POC的累积进而促进土壤有机碳的提升,猪粪和沼渣则通过提高土壤MBC、DOC和POC的含量,促进土壤有机碳的周转和固定。从农田土壤固碳角度而言,生物炭,猪粪和沼渣还田优于秸秆还田。     

Changes in C and N fractions with composted manure plus chemical fertilizers applied in apple orchard soil: an in‐situ field incubation study on the Loess Plateau,China

We investigated the effects of compost (CM ), made from poultry and cattle manure with spent mushroom substrate, plus chemical fertilizers (CF s) on soil organic carbon (C) and nitrogen (N) fractions in silty loam soil of the Loess Plateau. Eight fertilizer practices were applied in a 7‐year‐old ‘Red Fuji’ apple (Malus domestica Borkh.) orchard for 360 days. Compared to CM alone, CM –CF s decreased slightly soil total organic C but increased total N by 4.3–11.6%. Notably, CM –CF s increased soil microbial biomass C (MBC ) by 2.7–26.5% and microbial biomass N (MBN ) by 7–13.7%. Soil water‐soluble carbon (WSC ) was increased by 20.7% and 19.2% when 2% CM plus N and phosphorus (P) (2%M–NP ) and 4% CM plus N and P (4%M–NP ) were applied, respectively. Whereas 0.5% CM plus N and P (0.5%M–NP ) increased WSC by 9.3% on day 30 but decreased it by 7.2% from 30–360 days. Hot water‐soluble C increased by 13.1–14.6% from 0–180 day, but thereafter, the effect disappeared. Compared to CF s, CM –CF s increased MBN by 35.1–115.6%, and increased alkali‐hydrolyzable‐N by 3.5–55.8% over 180–360 days of incubation. Additionally, CM –CF s promoted N mineralization, increasing NH ₄‐N and NO ₃‐N contents. Based on the changes in C and N fractions and available nutrients, 2%M–NP (45 t/ha of CM plus 450 kg/ha of N and 157.5 kg/ha of P) may be the optimal fertilizer strategy for stimulating soil microbial growth and activity, and enhancing nutrient cycling for apple growth.     

不同有机物料培肥对渭北旱塬土壤微生物学特性及土壤肥力的影响

通过田间试验,研究了施用不同有机物料对渭北旱塬耕地土壤微生物学特性及土壤肥力的影响。结果表明,化肥与不同有机物料配合施用,土壤微生物学特性［微生物量碳（MBC）、微生物量氮（MBN）、脲酶、碱性磷酸酶］以及部分土壤养分状况（全氮、速效磷、速效钾、阳离子交换量）比单施化肥处理均得到进一步改善。化肥配施秸秆堆肥处理效果最明显,其中微生物量碳增加了41.96%,微生物量氮增加了54.55%,脲酶活性增加了19.71%,碱性磷酸酶活性增加了7.35%,速效磷增加了63.12%;而且土壤微生物量碳、氮与速效磷、阳离子交换量呈显著正相关,微生物商（qMB）、脲酶活性、碱性磷酸酶活性与全氮、速效氮、速效钾含量呈显著相关;同时SMBC、SMBN、qMB等与作物产量密切相关（相关系数分别为0.85,0.74,0.82）。因此,化肥配施秸秆堆肥处理在渭北旱地雨热条件下对于全面提升土壤质量具有重要的意义;同时该区域土壤中微生物量碳氮与土壤养分状况、作物产量具有很好的一致性,可以表征土壤肥力状况及生产力水平。     

过量施氮对旱地土壤碳、氮及供氮能力的影响

【目的】过量施氮会影响土壤有机碳、氮的组成与数量,进而改变土壤供氮能力,但关于西北旱地长期过量施用氮肥后土壤有机碳、氮及土壤供氮能力变化的研究尚缺乏。本文在长期定位试验的基础上,通过分析不同氮肥水平特别是过量施氮条件下土壤硝态氮,有机碳、氮和微生物量碳、氮的变化,探讨长期过量施氮对土壤有机碳、氮及供氮能力的影响。【方法】长期定位试验位于陕西杨凌西北农林科技大学农作一站。在施磷(P2O5)100kg/hm2的基础上,设5个氮水平,施氮量分别为N 0、80、160、240、320 kg/hm2。重复4次,小区面积40 m2,完全随机区组排列。种植冬小麦品种为小堰22。本文选取其中3处理,以不施氮为对照(N0)、施氮量N 160 kg/hm2为正常施氮(N160),施氮量N 320 kg/hm2为过量施氮(N320),分别于2012年6月小麦收获后和10月下季小麦播前采集土壤样品,进行测定分析。【结果】过量施氮导致下季小麦播前0—300 cm各土层硝态氮含量显著增加,平均由对照的2.8 mg/kg增加到15.5 mg/kg;同时,0—60 cm和0—300 cm土层的硝态氮累积量分别由对照的47.2和108.9 kg/hm2增加到76.5和727.7 kg/hm2。过量施氮也增加了夏闲期间0—300 cm土层土壤有机氮矿化量,由对照的72.4 kg/hm2增加到130.7 kg/hm2。但过量施氮未显著增加土壤的有机碳含量,却显著增加了土壤有机氮含量,过量施氮0—20、20—40 cm土层土壤有机碳分别为9.24和5.39 g/kg,有机氮分别为1.05和0.71 g/kg,较对照增加52.2%和54.3%。同样,过量施氮未显著影响0—20、20—40 cm土层土壤微生物量碳含量,其平均含量分别为253和205 mg/kg,却显著提高了0—20、20—40 cm土层土壤微生物量氮含量,由对照的24.1和7.5 mg/kg提高到43.6和16.1 mg/kg。【结论】过量施氮可以显著增加旱地土壤剖面中的硝态氮累积量、夏闲期氮素矿化量、小麦播前土壤氮素供应量和土壤微生物量氮含量,但对土壤有机碳和微生物量碳没有显著性影响,同时过量施氮增加了土壤硝态氮淋溶风险,故在有机质含量低的黄土高原南部旱地冬小麦种植中不宜施用高量氮肥,以减少土壤氮素残留和农业投入,达到保护环境和培肥土壤的目的。     

The mineralization rate of black soil carbon in the deep layers of Japanese volcanic ash soil may be easily accelerated by labile carbon supply

ABSTRACT

The stability of black soil carbon in the deep layers of Japanese volcanic ash soil (i.e., buried A horizons) is often explained by its unique chemical (molecular structure) and physical (associated with short-range-order minerals) recalcitrance. However, the stability of black soil C in buried A horizons may be changed by labile C supply for soil microbes. Here, we hypothesized that the mineralization of black soil C in buried A horizons of Japanese volcanic ash soil could be easily accelerated by a supply of labile C (i.e., a priming effect; PE). To test our hypothesis, we investigated the direction and magnitude of the PE with a buried A horizon in Japan using ¹³C-labeled glucose (2.188 atom %) in a short-term (21 days) incubation study. We also investigated the effect of mineral nitrogen (N), which could contribute to microbial activity in this incubation study. We found that a positive PE occurred by glucose supply with (182%) or without (181%) mineral N input over the 21-day incubation, and its values were very similar to the PE ratios previously reported in other deep soils. The estimated mean residence time (MRT) of black soil C considering PE was clearly accelerated by glucose supply, regardless of mineral N input, compared with the initial soil MRT. These results strongly support our hypothesis that the mineralization rate of black soil C in buried A horizons is easily accelerated by a labile C supply, and it also demonstrates important implications for the effects of global warming on buried A horizons (e.g., increased root exudation, fine root biomass supply, and N deposition) in Japanese volcanic ash soils.