Changes in Soil Iron Fractions and Availability in the Loess Belt of Northern China After 28 Years of Continuous Cultivation and Fertilization

Iron(Fe) deficiency in calcareous soils of the Loess Plateau of China is a wide spread issue and primarily affects agricultural production due to the relatively higher soil pH and carbonate content. Understanding the relationships between Fe distribution in soil fractions, Fe availability, and their responses to cropping and fertilization could provide essential information for assessing Fe availability in soils and managing soils to improve Fe availability. A long-term field experiment was established in 1984 in a split-plot design using cropping systems as main plots and fertilizer treatments as subplots on a farmland in the Loess Plateau. The cropping systems included fallow, continuous wheat cropping, continuous alfalfa cropping, continuous maize cropping, and a rotation system that included a legume. Various fertilization treatments using chemical and/or manure fertilizers were included in each cropping system. Soil samples were collected from 0–10 and 20–40 cm depths in 2012. Long-term planting of crops significantly increased the concentrations of available Fe in the soils. The largest increase was observed in the continuous alfalfa cropping system. Long-term cropping significantly increased the concentrations of Fe associated with carbonates and organic matter, but decreased the concentration of Fe associated with minerals in the soils. The effect of fertilization on the distribution of Fe in the soil fractions varied with cropping system and soil depth. The fertilization treatment with manure generally increased the concentrations of Fe associated with the soil fractions.Long-term cropping and fertilization in the highland farmland significantly affected the availability of Fe and the distribution of Fe fractions in the soil.     

种植制度和施肥对半干旱区土壤中锰形态及有效性的影响

Manganese(Mn) deficiencies are common in soils on the Loess Plateau of China. This research provided essential information on improving Mn availability in semiarid soils through agricultural practices. Twelve cropping system and fertilization treatments were designed in a 28-year experiment. The cropping systems included long-term fallow, continuous winter wheat cropping, pea(1 year)-winter wheat(2 years)-millet(1 year) rotation(crop-legume rotation) cropping, and continuous alfalfa cropping. The fertilizer treatments under the cropping systems included no-fertilizer control(CK), application of P fertilizer(P), application of N and P fertilizers(NP), and application of N and P fertilizers and manure(NPM), but the NP treatment was excluded in the continuous alfalfa cropping system. Available Mn and Mn fractions of soil samples(0–20 and 20–40 cm depths) were measured and further analyzed quantitatively using path analyses. Results showed that the crop-legume rotation and continuous alfalfa cropping systems significantly increased available Mn compared with the fallow soil. Compared with the no-fertilizer control, manure application increased available Mn in soil of the continuous wheat cropping system. Across all treatments, the averaged content of mineral-, oxide-, carbonateand organic matter-bound and exchangeable Mn accounted for 42.08%, 38.59%, 10.05%, 4.59%, and 0.09% of the total Mn in soil,respectively. Cropping significantly increased exchangeable Mn in soil and the highest increase was 185.7% in the continuous wheat cropping system at 0–20 cm depth, compared with the fallow soil. Fertilization generally increased exchangeable and carbonate-bound Mn in soil. Carbonate-bound Mn was the main and direct source of available Mn in soil, followed by exchangeable and organic matterbound Mn. These results indicated that crop-legume rotation cropping, continuous alfalfa cropping and application of manure, have the potential to promote Mn availability in soils of rainfed farmlands.     

黄土高原区草粮（油）翻耕轮作的土壤水分及作物产量效应

为了评价苜蓿翻耕后进行不同轮作模式的水分适应性和经济效益,提出黄土高原区生态效益和经济效应较好的草田轮作模式。该文测定了6a生苜蓿草地翻耕后轮作农田和休闲地的土壤水分及作物产量,并进行经济效益分析。结果表明,不同草田轮作模式的土壤水分恢复作用存在差异。苜蓿地轮作第2年收获后,以苜蓿-休闲-休闲模式土壤水分状况最好,0～300cm土层土壤水分已接近连作农田水平,且100～340cm土层土壤水分较耕前出现了恢复现象;而苜蓿-冬小麦-冬小麦模式最差,土壤水分恢复层出现在120～320cm土层;6a生苜蓿地翻耕后经过2a轮作,0～500cm土层土壤水分仍未达到连作农田水平。轮作2a冬油菜平均籽粒产量和平均籽粒水分利用效率较连作冬油菜分别增加了34.9%、44.4%(P<0.05),轮作2a冬小麦平均籽粒产量和平均籽粒水分利用效率较连作冬小麦分别提高了45.0%、42.9%(P<0.05);效益分析表明,轮作2a冬小麦的平均产投比是连作2a冬小麦的近1.5倍,是轮作2a冬油菜的2.5倍,是连作2a冬油菜的3.4倍,6a生苜蓿地翻耕后轮作冬小麦比轮作冬油菜具有更高经济效益。该研究结果为黄土高原苜蓿草地可持续利用,建立稳定的旱地农业生态系统提供了理论依据。     

土区长期施肥对小麦-玉米轮作体系钾素平衡与钾库容量的影响

本文研究了土区小麦-玉米轮作体系长期氮磷钾化肥不同配合施用方式及氮磷钾化肥与秸秆或有机肥配合施用对钾素平衡以及土壤钾库的影响。试验包括9个处理,分别为不施肥（CK）、单施氮（N）、氮钾（NK）、磷钾（PK）、氮磷（NP）、氮磷钾（NPK）、氮磷钾配合一季秸秆还田（SNPK）、氮磷钾配合低量有机肥（M1NPK）和高量有机肥（M2NPK）。结果表明,除NK、PK和M2NPK处理外,其它处理小麦和玉米钾的携出量均大于钾的投入量,导致土壤钾素处于亏缺状态,20年累计亏缺量为6174333 kg/hm2。与试验前相比,长期施肥种植没有显著影响土壤全钾含量; 长期施用钾肥显著提高土壤速效钾含量,但长期不施钾肥处理的土壤速效钾含量也未显著降低; 无论施钾与否土壤非交换性钾（Mactotal K）以及非交换性钾中更容易被HNO3溶解提取的钾（Step K）均明显低于试验前水平。表明土壤非交换性钾可以作为该土壤钾素消耗的指标。考虑到施钾肥的经济投入和现有资源高效利用（如秸秆、有机肥）,从长远的角度出发,维持土壤钾素肥力以及土地可持续生产力,土区小麦-玉米轮作体系采用秸秆全部还田或施有机肥是必要的。     

长期轮作和连作对白浆土中氮素的影响

对轮作及大豆、玉米、小麦长期连作白浆土中氮含量及有机态氮组分变化进行研究。结果表明，在不施肥情况下，小麦连作区土壤由全氮、碱解氮降幅最大，酸解总氮、氨基酸态氮和氨基糖态氮降幅最小。在施有机肥情况下，土壤全氮、碱解氮及酸解总氮则以小麦连作区增幅最小，玉米连作区增幅最大；氨基酸态氮和氨基糖态氮在轮作区增幅最大。其他组分氮在轮作与连作小区间变化无规律。     

Nitrogen compounds in soil solutions of agricultural land

Plants are capable of taking up nitrogen (N) in both organic and inorganic forms, so the concentrations and relative proportions of different N forms in soils are likely to be important determinants of their N nutrition. Therefore, there is a need for greater knowledge of the N profiles of soils. In the study presented here we examined the potential plant-available N in soils from four sites with various agricultural histories (one recently fertilized), using small tension lysimeters to collect free and bound amino acids and inorganic N forms in solution, with minimal soil disturbance and with intact plants present. Subsequent analysis showed that concentrations of free amino acids ranged from 0.1 to 12.7 μM, whereas concentrations of bound amino acids were on average 50 times higher, and higher than ammonium and nitrate concentrations in all three unfertilized soils. In contrast, nitrate strongly dominated in the fertilized soil. Bound amino acids are likely to represent a potential replenishment pool for free amino acids, so the abundance and rate at which amino acid-containing substances are depolymerized might be important determinants of the availability of free amino acids. Our results highlight the need for further research on the liberation of free amino acids from polymers in agricultural soil, and the importance of bound amino acids as N sources for plants.     

Effect of cover crop management on soil organic matter

Characterization of soil organic matter (SOM) is important for determining the overall quality of soils, and cover crop system may change SOM characteristics. The purpose of this study was to examine the effect of cover crops on the chemical and structural composition of SOM. We isolated humic substances (HS) from soils with the following cover crop treatments: (a) vetch (Vicia Villosa Roth.)/rye (Sesale cereale L.), (b) rye alone, and (c) check (no cover crops) that were treated with various nitrogen (N) fertilizer rates. CPMAS-TOSS (cross-polarization magic-angle-spinning and total sideband suppression) ¹³C NMR results indicated that humic acids (HA) from soils under rye only were more aromatic and less aliphatic in character than the other two cover crop systems without fertilizer N treatment. Based on the DRIFT (diffuse reflectance Fourier transform infrared) spectra peak O/R ratios, the intensities of oxygen-containing functional groups to aliphatic and aromatic (referred to as recalcitrant) groups, the highest ratio was found in the HA from the vetch/rye system with fertilizer N. The lowest ratio occurred at the vetch/rye system without fertilizer N treatment. The O/R ratio of fulvic acids (FA) can be ranked as: vetch/rye without fertilizer>vetch/rye with fertilizer>no cover crop without fertilizer>rye alone (with or without fertilizer) soils. Both organic carbon (OC) and light fraction (LF) contents were higher in soils under cover crop treatments with and without fertilizer N than soils with no cover crop. These chemical and spectroscopic data show that cover crops had a profound influence on the SOM and LF characteristics.     

秸秆生物反应堆与菌肥对温室番茄土壤微环境的影响

为研究秸秆生物反应堆、微生物菌肥及两者配套措施对土壤理化性质和微生物功能多样性,以及作物生长的长期影响,试验以传统种植方式为对照(CK,常规栽培),研究了菌肥(T1,微生物菌肥4 kg/667 m2)、内置式秸秆生物反应堆(T2,秸秆(4 t/667 m2)+发酵沟菌剂(8 kg/667 m2)+腐熟猪粪(600 kg/667 m2))及2种措施配套处理(T3,秸秆(4 t/667 m2)+发酵沟菌剂(8 kg/667 m2)+微生物菌肥(4 kg/667 m2)+腐熟猪粪(600 kg/667 m2))对土壤理化性质和微生物功能多样性的影响。结果表明:1)与CK相比,秸秆生物反应堆能够在一定时期内提高土壤含水率;而菌肥能够在一定时期内降低土壤含水率,秸秆生物反应堆能够显著降低土壤酸性和电导率(EC,electrical conductivity)值,缓冲土壤酸化和次生盐渍化;而单施菌肥对土壤酸碱性和EC值没有显著影响。2)秸秆生物反应堆(T2)增加了土壤中有机质的含量和土壤微生物量,降低土壤中速效磷、钾的含量;微生物菌肥(T1)降低了土壤中有机质含量和微生物量,而显著提升了土壤的速效磷、速效钾含量,两种措施配套处理效果则更明显。3)菌肥能够改善土壤微生物对多聚物、碳水化合物和氨基酸的利用效率,而秸秆生物反应堆能够促进土壤微生物对于一部分氨基酸、羧酸类、酚酸类和胺类物质的利用。而2种措施同时使用时,其促进和改善微生物碳代谢能力的作用则更加显著。4)各处理均能够在一定程度上增加各年度番茄产量。综合考虑,认为内置式秸秆生物反应堆和菌肥配套处理(T3)能够更好的改善和修复日光温室连作土壤,增加作物产量,是一种较为有效的农艺措施。     

长期施肥对高原农业生态系统土壤有机碳和氮的影响

The effects of fertilization on the distributions of organic carbon (OC) and nitrogen (N) in soil aggregates and whether these effects vary with cropping system have not been well addressed.Such information is important for understanding the sequestration of OC and N in agricultural soils.In this study,the distributions of OC and N associated with soil aggregates were analyzed in different fertilization treatments in a continuous winter wheat cropping system and a legume-grain rotation system in a 27-year field experiment,to understand the effects of long-term fertilization on the distributions of OC and N in aggregates and to examine the recovery of soil OC and N in a highland agroecosystem.Manure fertilizer significantly decreased soil bulk density but increased the amount of coarse fractions and their associated OC and N stocks in the soils of both systems.Fertilizers N + phosphorus (P) and manure had similar effects on total soil OC and N stocks in both systems,but had larger effects on the OC and N stocks in ＞ 2 mm aggregates in the legume-grain rotation system than in the continuous winter wheat system.The application of P increased the OC and N stocks in ＞ 2 mm aggregates and decreased the loss of N from chemical fertilizers in the legume-grain rotation system.The results from this study suggested that P fertilizer should be applied for legume-included cropping systems and that manure with or without chemical fertilizers should be applied for semiarid cropping systems in order to enhance OC and N accumulation in soils.     

Amino acid composition of soil organic matter

This study investigated the amino acid composition of soil organic matter extracted from ten surface soils in addition to surface soils from two long-term cropping systems [continuous corn (CCCC), corn-soybean-corn-soybean (CSCS), and corn-oats-meadow-meadow (COMM)] at two sites in Iowa: the Clarion-Webster Research Center (CWRC) and the Galva-Primghar Research Center (GPRC). Results showed that, with the exception of asparagine pluse aspartic acid and glutamine plus glutamic acid, the other 13 amino acids studied, expressed as perecentages of total amino acids extracted, were generally very uniform among the soils. The total amino acids extracted from the ten soils were significantly correlated with organic carbon (C) ( and clay content (, but not with total nitrogen (N), pH, or sand content. Expressed as percentages or organic C and N in soils, the amounts extracted ranged from 10.9% to 32.4% and from 12.0% to 27.4%, respectively. The amino acid N identified, expressed as percentages of organic N extracted, ranged from 32% to 50% and the C/N ratios of the extracted organic matter ranged from 10.1 to 14.9. The type of rotation did not significantly affect the total amino acid content of the soils from the same N treatment, but it did affect the total amino acid content of soils from the control plots. The total amino acids measured under the different crop rotations at the CWRC site were in the order: COMM>CCCC>CSCS. The order for the GPRC site was: CSCS>COMM>CCCC. The amino acid N identified, expressed as percentages of organic N extracted from soils at the CWRC site, ranged from 33.1% to 50% and for the GPRC site ranged from 26.5% to 51.4%. The C/N ratios of the organic matter extracted ranged from 10.4 to 14.1 and from 6.5 to 14.3 for the soils from CWRC and GPRC sites, respectively. Received: 26 May 1997     

江苏省里下河地区“沤改旱”种绿肥的经验

“沤改旱”变一熟为二熟是耕作制度的重大改革,生产上如果安排不当,就会带来很大损失.例如,1958年兴化县林湖公社姚家大队改旱800亩,使三麦面积一下由1164亩扩大到1936亩,由于劳畜力和肥料跟不上,三麦单产平均只有50斤.1959年以后,该队逐年在沤改旱地区扩种绿肥,使绿肥面积由200亩扩大到800亩,粮盒单位面积产量由1959年的260斤上升为1963年的428斤,说明沤改旱后种植绿肥是沤田改良利用的一项有力措施.但一熟沤田地区群众尚缺乏种植绿肥的经验.为此,1963年秋我们在兴化县林湖公社姚家大队和严家公社严家大队沤改旱田上进行种植绿肥和施用磷肥的试验.1964年除继续在上述二点进行试验外,又协助宝应县芦村公社芦南生产队在沤改早的田上进行种绿肥的试验.本文除对沤改旱田上种好绿肥的几项重要措施分别叙述以外,还讨论几个问题.     

我国典型农田长期施肥的氮肥真实利用率及其演变特征

【目的】传统氮肥利用率是指当季作物吸收肥料氮占施用的肥料氮的比例,没有反映肥料氮在土壤中的残留及其利用情况。利用长期定位试验能反映土壤氮库变化的优势,分析不同施肥条件下作物的传统氮肥利用率(氮肥表观利用率)和真实利用率,揭示我国典型区域氮肥的真实利用和损失状况。【方法】本研究选用了两种旱地土壤(北京褐潮土和郑州轻壤质潮土)和两种水旱轮作土壤(重庆紫色土和武汉黄棕壤)上的长期定位试验(15~31年)在4种施肥处理,即不施肥(CK)、单施化肥氮(N)、化肥氮磷钾配施(NPK)和化肥氮磷钾与有机肥配施(NPKM)处理取样分析比较作物吸氮量、土壤全氮演变、年均氮肥表观利用率与真实利用率,并计算了不同施肥条件下的氮肥表观损失率与真实损失率。【结果】3个施肥处理,褐潮土、轻壤质潮土、紫色土和黄棕壤上的平均氮肥真实利用率为47.6%、56.6%、57.0%和56.3%,显著高于氮肥表观利用率(33.6%、42.1%、37.8%和25.8%)。这是因为NPK和NPKM处理的肥料氮在土壤氮库中的每年速率积累为N 6.26~37.3 mg/kg的。氮肥真实利用率在褐潮土和轻壤质潮土上比表观利用率高10.9%~17.5%在紫色土和黄棕壤上高18.6%~32.9%,说明传统氮肥利用率更为低估水田轮作下作物的真实利用率。NPK和NPKM处理,褐潮土和轻壤质潮土的氮肥表观利用率以每年1.76~2.49个百分点的速率显著上升,氮肥真实利用率以每年1.50~2.29个百分点的速率显著上升,说明华北旱地上化肥均衡施用和化肥与有机肥配施可增加氮肥的利用率,减少氮肥的损失。黄棕壤上的氮肥真实利用率在显著增加而表观利用率没有显著增加,是由于NPK和NPKM处理的黄棕壤全氮含量以每年N17.5~37.3 mg/kg的速率在显著增加说明化肥均衡施用和化肥与有机肥配施可增加黄壤的氮库库容。【结论】目前我国农田氮肥利用率普遍被低估约20%尤其是在土壤全氮含量变化较大的水旱轮作农田。     

施入~(15)N标记氮肥在长期不同培肥土壤的残留及其利用

采用盆栽试验和短期矿化培养相结合的方法,研究了施入15N标记氮肥(+N)及其与秸秆配施(+1/2N+1/2S)在3种长期(19年)不同培肥土壤(即:No-F,长期不施肥土壤;NPK,长期施用NPK化肥土壤;MNPK,长期有机无机肥配施土壤)中的残留及其矿化和作物吸收特性。结果表明,第一季小麦收获后,+1/2N+1/2S处理下三供试土壤和+N处理下的NPK和MNPK土壤残留肥料氮(残留15N)中有82.6%~95.1%以有机态存,而+N处理下No-F土壤残留15N有47.7%以矿质态存在。经过28 d矿化培养后,与NPK土壤相比,MNPK土壤氮素净矿化量显著增加,增幅为39%~49%;NPK和MNPK土壤残留肥料氮(残留15N)矿化量为1.23~1.90 mg kg-1,占总残留15N的2.78%~5.53%,均显著高于No-F土壤。与+N处理相比,+1/2N+1/2S处理显著提高了3供试土壤氮素净矿化量,但两施肥处理对NPK和MNPK土壤残留15N矿化量无显著影响。+N处理下No-F土壤残留15N的利用率为20%,显著高于NPK(9%)和MNPK(12%)土壤。两种施肥处理下,MNPK土壤残留15N的利用率均显著高于NPK土壤。短期培养期间土壤氮素矿化量和第二季小麦生育期作物吸氮量呈显著性正相关,而残留15N矿化量和第二季小麦吸收残留15N量间无显著性相关关系。长期有机无机配施可以提高土壤残留肥料氮的矿化量及有效性。     

Green manure rotation and application increase rice yield and soil carbon in the Yangtze River valley of China

The addition of organic matter via green manure rotation with rice is considered a smart agricultural practice to maintain soil productivity and support environmental sustainability. However, few studies have quantitatively assessed the impact of green manure rotation and application on the interactions between agronomic management practice, soil fertility, and crop production. In this study, 800 pairs of data from 108 studies conducted in the agricultural region of the Yangtze River, China were...     

小麦-玉米-大豆轮作下黑土农田土壤呼吸与碳平衡

农田生态系统是陆地生态系统的重要组成部分,探讨农田生态系统的土壤呼吸与碳平衡对于科学评价陆地生态系统在全球变化下的源汇效应具有重要意义。基于中国科学院海伦农业生态实验站的长期定位试验,对不同施肥处理下黑土小麦-玉米-大豆轮作体系2005—2007年的作物固碳量与土壤CO2排放通量进行了观测,并对该轮作体系下黑土农田生态系统的碳平衡状况进行了估算。结果表明:在小麦-玉米-大豆轮作体系中,作物固碳量的高低表现为:玉米>大豆>小麦,平均值分别为6 513 kg(C).hm-2、4 025 kg(C).hm-2和3 655kg(C).hm-2。从作物生长季土壤CO2排放总量来看,3种作物以大豆农田生态系统的土壤CO2排放总量最高,平均值达4 062 kg(C).hm-2;其次为玉米,为3 813 kg(C).hm-2;而小麦最低,为2 326 kg(C).hm-2。3种作物轮作下NEP(净生态系统生产力)均为正值,表明黑土农田土壤-作物系统为大气CO2的"汇",不同作物系统的碳汇强度表现为玉米>小麦>大豆,三者的平均值分别为3 215 kg(C).hm-2、1 643 kg(C).hm-2和512 kg(C).hm-2。长期均衡施用氮、磷、钾化肥或氮、磷、钾化肥配施有机肥后,小麦、玉米和大豆农田生态系统的固碳量和土壤CO2排放总量均明显增加,并在氮、磷、钾配施有机肥处理下达到最高。不同的施肥管理措施将改变土壤-植物系统作为大气CO2"汇"的程度,总体表现为化肥均衡施用下NEP值较高,而化肥与有机肥配施下农田生态系统的NEP值较低。     

Effect of Integrated Nutrient Management on Soil Physical Properties and Crop Productivity under a Maize (Zea mays)–Mustard (Brassica campestris) Cropping Sequence in Acidic Soils of Northeast India

A five-year (2001/02–2006/07) field experiment was carried out on acidic clay loam soil classified as Typic Hapludalf with a maize–mustard crop sequence to study the effect of continuous application of nitrogen, phosphorus, and potassium (NPK) fertilizers alone and in combination with lime, farmyard manure (FYM), and biofertilizers on soil physical properties, soil organic carbon (SOC), soil microbial biomass carbon (SMBC), and crop yields on the hilly ecosystem of Meghalaya. Significant improvement in the soil physical conditions of the soil was observed under integrated application of organic manure and inorganic fertilizers. Addition of NPK fertilizers along with organic manure, lime, and biofertilizers increased soil organic carbon (SOC) content, aggregate stability, moisture-retention capacity, and infiltration rate of the soil while reducing bulk density. The SOC content under the treatment of 100% NPK + lime + biofertilizer + FYM was significantly greater (68.58%) than in control plots. Maize and mustard crop yields also significantly increased (4.73- and 21.09-folds, respectively) with continuous application of balanced inorganic (100% NPK) + lime + biofertilizer + FYM as compared to the control plots. However, crop yields drastically reduced under application of integrated nutrients without FYM as compared to the treatment with FYM application. Thus, the results suggest that integrated use of a balanced inorganic fertilizer in combination with lime and organic manure sustains a soil physical environment that is better for achieving higher crop productivity under intensive cropping systems in the hilly ecosystem of northeastern India.     

Nitrogen dynamics in tropical soils of Mali,West Africa

Soil samples were collected from a loamy sand and a clayey soil near Cinzana, Mali, for the purpose of documenting the seasonal dynamics of soil inorganic N after 9 years under five crop-management systems. The cropping systems were: continuous grain sorghum (Sorghum bicolor) or millet (Pennisetum glaucum) without residue return, continuous grain with stalk residue returned to the field every second year, grain in rotation with cowpea (Vigna unguiculata), and grain in rotation with the green manure crops, sesbania (Sesbania rostrata) and dolichos (Dolichos lablab). A sharp increase in soil N was observed early in the rainy season in both soils. Extractable N concentration in loamy sand and clayey soils, respectively, peaked between 15–22 kg and 33–51 kg N ha^–1 in the upper 10 cm of soil. In the clayey soil, the higher soil N concentrations associated with the early season flush lasted 8 weeks after the onset of rain. Nitrogen addition through rotational crops and crop residue was low. Significant improvement of cereal grain yield may not be possible solely by rotation with sesbania and dolichos green manure or cowpea without additional nutrient input. Earlier cereal planting, where feasible, is recommended to improve synchrony of soil N mineralization and crop demand.     

Studies on the formation of soil aggregate (preliminary report) influence of water content and sucrose

It was emphasized by Russel (1934) that cation and polar-medium played the active part in the aggregation of preliminary particles. Jesse Elson pointed out that even the field which had raised crops for consecutive 32 years might yield a greater number of aggregates when fertilizers, especially manure and corn were given, than the field which had been given no fertilizers. It was confirmed by Mazurak that six year rotation, i. e. three year rotation of potato, oats or barkley and sugar beats preceeded by three year succession cropping of alfalfa, was more advantageous for the formation of water-stable aggregates than the succession cropping of potato. The effect of bactinal polysaccharide was pointed out by Geoghegan, and it was confirmed by Browing that the effect of sucrose would be two to four times greater than that of alfalfa, rye, vetch and wheat straw.     

连作植烟土壤酚酸类物质变化特征及其与主要环境因子的Mantel Test分析

为明确酚酸类物质在连作植烟土壤中的变化特征,探讨土壤主要环境因子对酚酸类物质的影响,以不同连作年限（4 a,6 a,8 a,14 a和16 a）植烟土壤为对象,研究了不同连作年限植烟土壤酚酸类物质、理化性状、酶活性和细菌多样性的变化特征,并利用Mantel Test分析了酚酸类物质与土壤主要环境因子的相关性。结果表明,随连作年限增加,土壤酚酸类物质和速效钾含量升高,pH、有机质含量、细菌菌群丰度和多样性降低,水解性氮和有效磷含量呈先降低后升高趋势,酶活性呈先升高后降低趋势。Mantel Test分析表明,土壤酚酸类物质含量与理化性状、酶活性和细菌丰度显著相关,且与理化性状相关性最高;不同酚酸类物质含量与土壤主要环境因子相关性存在差异,其中,对羟基苯甲酸和阔马酸与植烟土壤理化性状、酶活性以及细菌丰度的相关性最高。因此,在本试验条件下,连作植烟土壤酚酸类物质具有明显积累特征,植烟土壤环境恶化;酚酸类物质积累受理化性状、酶活性和细菌多样性影响,且理化性状影响最大;不同酚酸类物质受主要土壤环境因子的影响存在差异,其中对羟基苯甲酸和阔马酸积累所受影响最大。     

The influence of different land management practices on the transformation of humic acids in heavy loamy soddy-podzolic soils of the Cis-Urals region

The elemental composition and structure of humic acids were studied in heavy loamy soddy-podzolic soils of the Cis-Urals region under different land management practices. The humic acids in the soil of the long-term clean fallow, overgrown fallow (abandoned plot), and crop rotation plots differed in their composition and properties. The humic acids in the soils of the crop rotation with the regular application of manure and of the overgrown fallow were enriched in the components of both their central (nuclear) and peripheral parts. Such a structure ensured the active participation of humic acids in the carbon cycle with the simultaneous preservation of the soil’s fertility.