土地退化/恢复中土壤可蚀性动态变化

利用EPIC公式计算了不同开垦和退耕年限的土壤可蚀性K值,对黄土高原典型自然恢复区子午岭林区土地退化/恢复过程中土壤可蚀性的动态变化进行了系统的研究。结果表明：土地开垦后,土壤颗粒向粗骨化方向发展,有机碳含量降低,土壤可蚀性逐渐增强;土地退耕过程中,土壤有机碳含量逐渐增加,肥力水平提高,可蚀性逐渐减小;土壤中有机碳含量、全氮含量、水稳性团聚体含量以及团聚度与土壤可蚀性K值相关最为密切;土壤可蚀性的强弱本质上取决于土壤有机碳含量,恢复植被以提高土壤有机质含量,促进土壤团聚体的形成,增强土壤团聚度,是降低土壤可蚀性能的重要途径。     

Leaching and reclamation of calcareous saline‐sodic soil by moderately saline and moderate‐SAR water using gypsum and calcium chloride

Lysimeter experiments were conducted with sandy‐clay‐loam soil to study the efficiency of two amendments in reclaiming saline‐sodic soil using moderately saline and SAR (sodium‐adsorption ratio) irrigation water. Gypsum obtained from industrial phosphate by‐products and reagent grade Ca chloride were applied to packed soil columns and irrigated with moderately saline (ECe = 2.16 dS m^–1), moderate‐SAR water (SAR = 4.8). Gypsum was mixed with soil prior to irrigation at application rates of 5, 10, 15, 20, 25, and 32 Mg ha^–1, and Ca chloride was dissolved directly in leaching water at application rates of 4.25, 8.5, 12.75, 17.0, and 21.25 Mg ha^–1, respectively. The highest application rate in both amendments resulted in 96% reduction of total Na in soil. The hydraulic conductivity (HC) of soils receiving gypsum increased in all treatments. The highest HC value of 6.8 mm h^–1 was obtained in the highest application rate (32 Mg ha^–1), whereas the lowest value of 5.2 mm h^–1 was observed with the control treatment. Both amendments were efficient in reducing soil salinity and sodicity (exchangeable‐sodium percentage, ESP); however, Ca chloride was more effective than gypsum as a reclaiming material. Exchangeable Na and soluble salts were reduced with gypsum application by 82% and 96%, and by 86% and 93% with Ca chloride application, respectively. Exchangeable Ca increased with increasing amendment rate. Results of this study revealed that sodium was removed during cation‐exchange reactions mostly when the SAR of effluent water was at maximum with subsequent passage of 3 to 4 pore volumes. Gypsum efficiently reduced soil ESP, soil EC, leaching water, and costs, therefore, an application rate of 20 Mg ha^–1 of gypsum with 3 to 4 pore volumes of leaching water is recommended for reclaiming the studied soil.     

Energetic eco‐physiology of the soil microbiota in two landscapes of southern and northern Germany

Interactions between microbial communities and organic matter were analyzed for soils from the project regions ’︁Ecosystem Research in the Agricultural Landscape/FAM, Munich’ in southern Germany and ’︁Ecosystem Research in the Bornhöved Lake district’ from northern Germany using ratios between microbial biomass content (C_mic), microbial metabolic quotient (qCO₂) and organic carbon content (C_org). In the agricultural soils in southern Germany, the qCO₂/C_org ratio differed significantly with respect to agricultural management in contrast to ecophysiological C_mic/C_org ratio. In addition, C_mic/C_org ratio decreased from 39 to 21 mg C_mic g^—1 C_org and qCO₂/C_org ratio increased from 72 to 180 mg CO₂‐C g^—1 C_mic h^—1 (g C_org g^—1 soil)^—1 with increasing soil depth. For the upper soil horizons from the landscape in northern Germany the two quotients differed significantly with reference to land use showing highest microbial colonization under grassland and lowest under beech forest. In contrast, C use efficiency was lowest in arable field under maize monoculture and highest in a wet grassland having a high organic C content.     

Long‐term effects of fertilization on some soil properties under rainfed soybean‐wheat cropping in the Indian Himalayas

This study aims to examine the effects of long‐term fertilization and cropping on some chemical and microbiological properties of the soil in a 32 y old long‐term fertility experiment at Almora (Himalayan region, India) under rainfed soybean‐wheat rotation. Continuous annual application of recommended doses of chemical fertilizer and 10 Mg ha^–1 FYM on fresh‐weight basis (NPK + FYM) to soybean (Glycine max L.) sustained not only higher productivity of soybean and residual wheat (Triticum aestivum L.) crop, but also resulted in build‐up of total soil organic C (SOC), total soil N, P, and K. Concentration of SOC increased by 40% and 70% in the NPK + FYM–treated plots as compared to NPK (43.1 Mg C ha^–1) and unfertilized control plots (35.5 Mg C ha^–1), respectively. Average annual contribution of C input from soybean was 29% and that from wheat was 24% of the harvestable aboveground biomass yield. Annual gross C input and annual rate of total SOC enrichment from initial soil in the 0–15 cm layer were 4362 and 333 kg C ha^–1, respectively, for the plots under NPK + FYM. It was observed that the soils under the unfertilized control, NK and N + FYM treatments, suffered a net annual loss of 5.1, 5.2, and 15.8 kg P ha^–1, respectively, whereas the soils under NP, NPK, and NPK + FYM had net annual gains of 25.3, 18.8, and 16.4 kg P ha^–1, respectively. There was net negative K balance in all the treatments ranging from 6.9 kg ha^–1 y^–1 in NK to 82.4 kg ha^–1 y^–1 in N + FYM–treated plots. The application of NPK + FYM also recorded the highest levels of soil microbial‐biomass C, soil microbial‐biomass N, populations of viable and culturable soil microbes.     

Long‐term changes of aggregate‐associated and labile soil organic carbon and nitrogen after conversion from forest to grassland and cropland in northern Turkey

Soil management systems can have great effect on soil chemical, physical and biological properties. Conversion of forest to grassland and cropland can alter C and N dynamics. The objective of this study was to evaluate the changes in aggregate‐associated and labile soil organic C and N fractions after conversion of a natural forest to grassland and cropland in northern Turkey. This experiment was conducted on plots subject to three different adjacent land uses (forest, grassland and cropland). Soil samples were taken from 0–5, 5–15 and 15–30 cm depths from each land use. Some soil physical (soil texture, bulk density), chemical (soil pH, soil organic matter, lime content, total organic C and N, inorganic N, free and protected organic C) and biological (microbial biomass C and N, mineralizable C and N) properties were measured. The highest and lowest bulk densities were observed in grassland (1.41 g cm⁻³) and cropland (1.14 g cm⁻³), respectively. Microbial biomass C and total organic C in forest were almost twice greater than grassland and four‐times greater than cropland. Cultivation of forest reduced total organic N, mineralizable N and microbial biomass N by half. The great portion of organic C was stored in macroaggregates (>250 µm) in all the three land uses. Free organic C comprised smaller portion of soil organic C in all the three land uses. Thus, this study indicated that long‐term conversion of forest to grassland and cropland significantly decreased microbial biomass C, mineralizable C and physically protected organic C and the decreases were the greatest in cropland. Copyright © 2011 John Wiley & Sons, Ltd.     

Reclamation of a coastal reclaimed tidal land soil by gypsum and rice straw

This study was to evaluate the application effect of gypsum and rice straw on the saline–sodic soils of coastal reclaimed tidal lands during newly reclamation process by leaching method. Soil used in the lysimeter experiment is classified as Greyic Hydragric Anthrosols (Sodic Arenic). The experiment was carried out over a period of 1 year from May 2014 to July 2015 inside a plastic film house. Saturated electrical conductivity (EC_e) and exchangeable sodium percentage (ESP) values of soils in gypsum treatment and gypsum with rice straw treatment then reached the desalinization criteria (EC_e = 4.0 dS m^?1, ESP = 15%) after the five or six pore volumes leaching cycles. However, in spite the 10 pore volumes leaching cycles in control and rice straw alone treatment, the values did not reach the desalinization criteria. The results showed that effectiveness of improvement of sodicity and salinity in coastal reclaimed tidal land soils was in the order of gypsum = gypsum + rice straw > rice straw = control. Our study has shown that gypsum alone treatment or gypsum with rice straw treatment in a coastal reclaimed tidal land soils improves their physicochemical characteristics.     

Effects of glucose,cellulose, and humic acids on soil microbial eco‐physiology

Microbial eco‐physiology in soils is regulated by substrate quality of the organic matter. This regulation was studied for a forest and an agricultural soil by the combination of activity and biomass techniques. Soil respiration was stimulated by the substrate quality in the order, humic acid < cellulose < glucose over 20 days. Concurrently, substrate addition increased the respiratory quotient (RQ), defined as the ratio of mol CO₂ evolution per mol O₂ uptake. Anabolic processes were mainly induced by glucose addition. Soil preconditioned with glucose showed a decrease in the RQ value during glucose‐induced microbial growth in comparison to non‐amended control. The decrease in the RQ value induced by preconditioning with cellulose and humic acid was lower. Glucose, cellulose, and humic acid addition modified the microbial biomass as estimated by fumigation‐extraction (FE), substrate‐induced respiration (SIR), and ATP content. Since each biomass estimate refers to specific microbial components, shifts in microbial eco‐physiology and community structure induced by substrate quality were reflected by SIR : FE and SIR : ATP ratios. The active and glucose‐responsive biomass in the forest soil which was earlier suggested as being dominated by K‐strategists was increased in the order, humic acid < cellulose < glucose.     

Identification and performance of stress‐tolerant phosphate‐solubilizing bacterial isolates on Tagetes minuta grown in sodic soil

Tagetes minuta is moderately adapted to a wide range of climate and due to its tolerance to larger salt, pH and exchangeable sodium percentage (ESP) in soil it is considered to be a potential crop for salt‐affected soil. Its tolerance to adverse condition and association with halophilic microbes can combine to play a greater role in crop production and improvement in soil health. After screening, the potential phosphate‐solubilizing bacteria (PSB) RS‐1, RS‐2 and RS‐3 were isolated from sodic soils and tested in pot experiment using a naturally occurring sodic soil of pH 9.3 and an ESP of about 45. Under optimum conditions in the laboratory, these bacteria showed phosphorus solubilization potential in liquid medium containing tricalcium phosphate (TCP). Inoculation of PSB significantly increased plant growth in terms of height, number of branches, dry matter accumulation and nutrient uptake. Significant changes were also found in content and quality of essential oil. It was observed that PSB also improved the physical, chemical and biological properties of soil. The bacterial strains tested in this study have the potential for use as a biofertilizer in sustaining the growth of Tagetes minuta in salt stress soil and mitigating soil stress problems.     

不同土壤类型和农业用地方式对土壤微生物量碳的影响

通过野外调查与室内分析,研究了山东桓台县3种土壤类型(潮土、褐土和砂姜黑土)与农业用地方式(林地、菜地和粮田)对土壤表层(0—10.cm)微生物量碳的影响。结果表明,不同农业用地方式对微生物量碳的影响较大,3种利用方式的微生物量碳含量差异显著,依次为:粮田>菜地>林地;土壤类型不同,土壤微生物量碳含量也不相同。任何一种土壤,菜地的N、P、K含量都高于粮田和林地;有机质含量粮田>菜地>林地;pH值林地>粮田>菜地。全N、有机质与土壤微生物量碳呈极显著正相关,有效P与微生物量碳呈弱负相关,速效K、pH值和微生物量碳不相关。不同用地方式下土壤养分与微生物量碳的相关程度不同。秸秆还田和施用有机肥有利于提高土壤中微生物量碳水平,施用化肥在一定程度上能够增加微生物量碳。     

Long‐term no‐tillage effects on particulate and mineral‐associated soil organic matter under rainfed Mediterranean conditions

Soil organic carbon (SOC) plays an essential role in the sustainability of natural and agricultural systems. The identification of sensitive SOC fractions can be crucial for an understanding of SOC dynamics and stabilization. The objective of this study was to assess the effect of long‐term no‐tillage (NT) on SOC content and its distribution between particulate organic matter (POM) and mineral‐associated organic matter (Min) fractions in five different cereal production areas of Aragon (north‐east Spain). The study was conducted under on‐farm conditions where pairs of adjacent fields under NT and conventional tillage (CT) were compared. An undisturbed soil nearby under native vegetation (NAT) was included. The results indicate that SOC was significantly affected by tillage in the first 5 cm with the greatest concentrations found in NT (1.5–43% more than in CT). Below 40 cm, SOC under NT decreased (20–40%) to values similar or less than those under CT. However, the stratification ratio (SR) never reached the threshold value of 2. The POM‐C fraction, disproportionate to its small contribution to total SOC (10–30%), was greatly affected by soil management. The pronounced stratification in this fraction (SR>2 in NT) and its usefulness for differentiating the study sites in terms of response to NT make POM‐C a good indicator of changes in soil management under the study conditions. Results from this on‐farm study indicate that NT can be recommended as an alternative strategy to increase organic carbon at the soil surface in the cereal production areas of Aragon and in other analogous areas.     

Effects of consecutive applications of gypsum in equal,increasing, and decreasing quantities on soil hydraulic conductivity of a saline‐sodic soil

The objective of this study was to determine the effects of consecutive application of gypsum dissolved in leaching water on hydraulic conductivity of a saline‐sodic soil. Drainage type plastic columns with a 10 cm diameter were used in this laboratory experiment. Soil depth within columns was 30 cm with an average bulk density of 1.38 g cm^–3. Leaching water was applied in six equal portions. Total gypsum was applied at 1, 3, and 5 portions after dissolving in leaching water. In dissolution, equal (1.273 + 1.273 + 1.273 Mg ha^–1), increasing (0.637 + 1.273 + 1.910 Mg ha^–1) and decreasing (1.910 + 1.273 + 0.637 Mg ha^–1) quantities of gypsum were used. Results were compared with the control treatment, in which total amount of gypsum were mixed with surface layer of soil column before leaching. Hydraulic conductivity of soil increased in all treatments. The maximum hydraulic conductivity value was obtained at consecutive application of gypsum at decreasing quantities.     

Long‐term effects of manure and fertilization on soil organic matter and quality parameters of a calcareous soil in NW China

Long‐term applications of inorganic fertilizers and farmyard manure influence organic matter as well as other soil‐quality parameters, but the magnitude of change depends on soil‐climatic conditions. Effects of 22 annual applications (1982–2003) of N, P, and K inorganic fertilizers and farmyard manure (M) on total organic carbon (TOC) and nitrogen (TON), light‐fraction organic C (LFOC) and N (LFON), microbial‐biomass C (MB‐C) and N (MB‐N), total and extractable P, total and exchangeable K, and pH in 0–20 cm soil, nitrate‐N (NO ‐N) in 0–210 cm soil, and N, P, and K balance sheets were determined using a field experiment established in 1982 on a calcareous desert soil (Orthic Anthrosol) at Zhangye, Gansu, China. A rotation of irrigated wheat (Triticum aestivum L.)‐wheat‐corn (Zea mays L.) was used to compare the control, N, NP, NPK, M, MN, MNP, and MNPK treatments. Annual additions of inorganic fertilizers for 22 y increased mass of LFON, MB‐N, total P, extractable P, and exchangeable K in topsoil. This effect was generally enhanced with manure application. Application of manure also increased mass of TOC and MB‐C in soil, and tended to increase LFOC, TON, and MB‐N. There was no noticeable effect of fertilizer and manure application on soil pH. There was a close relationship between some soil‐quality parameters and the amount of C or N in straw that was returned to the soil. The N fertilizer alone resulted in accumulation of large amounts of NO ‐N at the 0–210 cm soil depth, accounting for 6% of the total applied N, but had the lowest recovery of applied N in the crop (34%). Manure alone resulted in higher NO ‐N in the soil profile compared with the control, and the MN treatment had the highest amount of NO ‐N in the soil profile. Application of N in combination with P and/or K fertilizers in both manured and unmanured treatments usually reduced NO ‐N accumulation in the soil profile compared with N alone and increased the N recovery in the crop as much as 66%. The N that was unaccounted for, as a percentage of applied N, was highest in the N‐alone treatment (60%) and lowest in the NPK treatment (30%). In the manure + chemical fertilizer treatments, the unaccounted N ranged from 35% to 43%. Long‐term P fertilization resulted in accumulation of extractable P in the surface soil. Compared to the control, the amount of P in soil‐plant system was surplus in plots that received P as fertilizer and/or manure, and the unaccounted P as percentage of applied P ranged from 64% to 80%. In the no‐manure plots, the unaccounted P decreased from 72% in NP to 64% in NPK treatment from increased P uptake due to balanced fertilization. Compared to the control, the amount of K in soil‐plant system was deficit in NPK treatment, i.e., the recovery of K in soil + plant was more than the amount of applied K. In manure treatments, the recovery of applied K in crop increased from 26% in M to 61% in MNPK treatment, but the unaccounted K decreased from 72% in M to 37% in MNPK treatment. The findings indicated that integrated application of N, P, and K fertilizers and manure is an important strategy to maintain or increase soil organic C and N, improve soil fertility, maintain nutrients balance, and minimize damage to the environment, while also improving crop yield.     

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.     

Microbial dynamics and natural remediation patterns of Fusarium‐infested watermelon soil under 3‐yr of continuous fallow condition

Long‐term monoculture of watermelon results in inhibited growth and decreased crop yields, possibly because of imbalance in microbial ecology caused by accumulation of the pathogen in soil. This results in serious problems in the economics of watermelon production. We investigated the build‐up of Fusarium in soil under watermelon cultivation and changes over 3 yr of fallow in a microcosm. We focused on changes in the microbial community of Fusarium‐infected soil, including the diversity of the microfloral species composition, and species abundance. Long‐term monoculture of watermelon leads to changes in microbial diversity and community structure. The microbes most readily cultured from infested soil were suppressed by watermelon wilt pathogen Fusarium oxysporum f. sp. niveum (FON). Of 52 isolated and identified culturable microbes, 83.3% of bacteria, 85.7% of actinomycetes, 31.6% of fungi and 20.0% of Fusarium sp. were inhibited by FON on bioassay plates. Prior to fallowing, infested soil was a transformed ‘fungus‐type’ soil. After 3 yr of fallow, the infested soil had remediated naturally, and soil microbial diversity recovered considerably. Abundance of dominant bacterial populations was increased by 118–177%, actinomycetes, fungi and FON were decreased by 23–32, 33–37 and 50%, respectively. The ratio of bacteria: actnomycetes: fungus: Fusarium sp. in infested soil changed from 24 000:100:4:1 prior to fallow to 57 000:100:3.5:1 after fallowing, nearer to the 560 000:400:8:1 ratio of healthy soil not used for watermelon cultivation. This suggests the ‘fungus‐type’ soil was converting to ‘bacteria‐type’ soil and that disrupted microbial communities in infested soil were restored during fallow.     

不同复垦模式及复垦年限对土壤微生物的影响

为了研究不同复垦年限及复垦植被模式对复垦土壤生物肥力的影响,通过野外调查和采样分析,对平朔安太堡露天煤矿不同复垦年限及复垦植被模式下和原地貌（对照）土壤中细菌、放线菌和真菌3种微生物的数量及变化进行了研究。结果表明：1）从微生物总数来看,随着复垦年限的增加,微生物总数呈增加的趋势,复垦13a的土壤微生物总数达到了624.35×105～1 448.19×105 cfu/g,平均可达1 183.01×105 cfu/g（除自燃地外）,最高的和原地貌已相当。2）在不同复垦年限及复垦模式复垦地0～20 cm表层土壤微生物三大类区系组成中,细菌数量占绝对优势（95%以上）,放线菌数量次之,真菌数量最少。3）不同复垦植被配置方式对复垦土壤微生物数量的增加作用不同。在同一地点不同复垦模式复垦7 a的土壤中微生物数量的变化趋势是紫穗槐＞沙枣＞沙棘。不同复垦模式复垦13 a,从微生物角度评价它们的生态效益是：云杉×油松×落叶松＞刺槐×油松×榆树＞刺槐×柠条＞冰草×刺槐×柠条。4）从土壤微生物与复垦土壤养分的相关系数来看,细菌数量和微生物总数与土壤有机质、碱解氮含量呈显著正相关。     

Long‐term effects on soil microbial properties of heavy metals from industrial exhaust deposition

Soil samples were taken at 0—10 cm and 10—20 cm depth from 7 clay‐marsh sites used as grassland close to Nordenham in the north of Lower Saxony, Germany. The sites had been contaminated by deposition of heavy metals from industrial exhausts, the level of contamination varying according to their distances from a lead factory. The soils were analyzed to assess the depth‐specific effects of NH₄NO₃ extractable and total amounts of Zn, Pb, and Cu on basal respiration, adenylates, ergosterol, and biomass C estimated by fumigation extraction (FE) and substrate‐induced respiration (SIR). Most of the chemical and biological properties studied decreased with depth, but depth‐specific differences in the relationships between these properties rarely occurred. The biomass C/soil organic C ratio was at a relatively high level, but most consistently reflected pollution as a decrease with increasing heavy metal load, independently of the method used for biomass C estimation. However, the SIR estimates were on average 44 % lower than those of FE, mainly due to pH effects. The metabolic quotient SIR‐qCO₂ increased with increasing NH₄NO₃ extractable and total heavy metal contents, but also with decreasing pH, whereas the FE‐qCO₂ remained unaffected by heavy metals and pH. The ATP/FE‐biomass C ratio was on average 8.2 μmol g^—1 and negatively affected by soil pH, but also by total Zn, NH₄NO₃ extractable Zn and Cu. The ergosterol/FE‐biomass C ratio was on average 0.29 %, i.e. at a very low level, and increased with increasing heavy metal content. This indicates a change in the community structure towards fungi.     

Effects of short‐rotation Eucalyptus plantations on soil quality attributes in highly acidic soils of the central highlands of Ethiopia

In recent decades, conversion of agricultural land to short‐rotation (5–10 years) Eucalyptus plantations has become a common practice in the highlands of Ethiopia. Yet, we have a poor understanding of the effect of these land conversions on soil quality attributes under acidic soil conditions. Previous studies along the same line but based merely on physico‐chemical properties of soils were inconsistent and contradictory. We compared soil physical, chemical and biological properties under 5‐ and 10‐year‐old Eucalyptus plantations with adjacent grassland soils. Results revealed that soil bulk density of adjacent grassland was significantly smaller than in the two Eucalyptus plantations. Although land‐use change from grassland to short‐rotation Eucalyptus did not affect soil texture significantly, values of soil pH, organic carbon, total nitrogen, calcium and cation exchange capacity (CEC) values in adjacent grassland were greater at both 0–10 cm and 10–20 cm depths compared with 5‐ and 10‐year‐old Eucalyptus plantations. Available phosphorus, exchangeable potassium and magnesium were not significantly affected under the three land‐use systems. Generally, no differences were observed in available phosphorus, potassium, calcium and magnesium concentrations or in CEC between the two sampling depths (0–10 cm and 10–20 cm). The microbial biomass carbon and microbial biomass nitrogen recorded in 5‐ and 10‐year‐old Eucalyptus plantations were comparable but significantly smaller than in adjacent grasslands. Kinetics parameters calculated using a first‐order equation (C_t = C_o (1?e^?kt)) showed potentially mineralizable carbon (C_o) was significantly larger (P < 0.001) under grassland compared with 5‐ and 10‐year‐old Eucalyptus plantations. Conversion of grassland to 5‐year‐old and 10‐year‐old Eucalyptus reduced the values of C_o by 21 and 43%, respectively. However, soil physical and chemical properties were not adversely affected by age of Eucalyptus over a 5‐year period. It is concluded that Eucalyptus plantations degrade soil ecosystem functioning and environmental sustainability compared with grassland.     

Leguminous trees for the restoration of degraded sodic wasteland in eastern Uttar Pradesh,India

The study was carried out in sodic lands of Sultanpur District, Uttar Pradesh, India. The barren soils and the soils supporting 3‐, 6‐ and 9‐year‐old plantations of Prosopis juliflora (Swartz) D.C. and Dalbergia sissoo Roxb. Ex. D.C. plantations were examined to assess the rate and extent of changes undergone by physical and chemical properties of the soil. The study brought out that these species indicated the process of soil rehabilitation from the early stages of growth and the extent of rehabilitation increased with the age of the plantation. P. juliflora was found to be more efficient in reclaiming the soil in comparison to D. sissoo. The decline in soil pH and exchangeable sodium percentage (ESP) indicates the desodification and enrichment with organic C, N, P and K indicates improvement in nutrient status of the soil. After 9 years of planting the surface soil was completely desodified as indicated by pH (<8ċ5), ESP (<15) and sodium adsorption ration (<15). A significant increase in organic C, exchangeable Ca²⁺ and Mg²⁺ and decrease in exchangeable Na⁺ reveals that the nutrient status is attaining suitable balance. The physical attributes of the soil also underwent improvement in terms of increase in porosity, water‐holding capacity, field capacity and decline in bulk density. The flocculation of dispersed soil surface and improvement in soil structure was indicated by increased infiltration rate (cm h⁻¹) and soil permeability (cm²). Copyright © 2003 John Wiley & Sons, Ltd.     

Reclamation of saline‐sodic soil under a rice–wheat system by horizontal surface flushing

Saline sodic soil with a high content of soluble carbonates is one of the important agricultural soils on the Central Indo‐Gangetic plains and elsewhere. Conventional reclamation procedures using gypsum application followed by vertical leaching (GC) is uneconomic; high ECe and precipitation of applied gypsum, reacting with soluble carbonates, reduce the efficacy of gypsum in these soils. This paper reports results from a project designed to evaluate reclamation by irrigation of the ploughed soil and turning of soil with a power tiller followed by flushing of standing water after 24 h, a second flushing after 7 days and subsequent application of gypsum and vertical leaching (GF2). Average rice and wheat production after GF2 significantly increased (25 and 62%, respectively) over the conventional practice. Compared with conventional treatment, GF2 significantly reduced the ECe and SAR of the soil and improved physical properties such as ζ‐potential, dispersible clay content, water stable aggregates expressed as MWD, and saturated hydraulic conductivity. Split application of gypsum between flushing (GF1/2 and GF2/3) gave similar results to GF2 in terms of soil amelioration and crop production.     

Potential of mine land reclamation for soil organic carbon sequestration in Ohio

Soils are an effective sink for carbon storage and immobilization through biomass productivity and enhancement of soil organic carbon (SOC) pool. The SOC sink capacity depends on land use and management. Degraded lands lose large amounts of C through SOC decomposition, erosion, and leaching. Thus, restoration of disturbed and degraded mine lands can lead to increase in biomass productivity, improved soil quality and SOC enhancement and sequestration. Reclamation of mined lands is an aggrading process and offers significant potential to sequester C. A chronosequence study consisting of 0‐, 5‐, 10‐, 15‐, 20‐ and 25‐year‐old reclaimed mine soils in Ohio was initiated to assess the rate of C sequestration by pasture and forest establishment. Undisturbed pasture and forest were used as controls. The SOC pool of reclaimed pasture sites increased from 15·3 Mg ha⁻¹ to 44·4 Mg ha⁻¹ for 0–15 cm depth and from 10·8 Mg ha⁻¹ to 18·3 Mg ha⁻¹ for 15–30 cm depth over the period of 25 years. The SOC pool of reclaimed forest sites increased from 12·7 Mg ha⁻¹ to 45·3 Mg ha⁻¹ for 0–15 cm depth and from 9·1 Mg ha⁻¹ to 13·6 Mg ha⁻¹ for 15–30 cm depth over the same time period. The SOC pool of the pasture site stabilized earlier than that of the forest site which had not yet attained equilibrium. The SOC sequestered in 0–30 cm depth over 25 years was 36·7 Mg ha⁻¹ for pasture and 37·1 Mg ha⁻¹ for forest. Copyright © 2000 John Wiley & Sons, Ltd.