Chemical fractionation of phosphorus in calcareous soils of Hamedan,western Iran under different land use

We investigated the effects of land uses on P distribution and availability in selected calcareous soils under different management practices. KCl‐P (labile P), NaOH‐P (Fe‐Al‐bound P), HCl‐P (Ca‐bound P), and residual P (Res‐P) fractions at 0–30 cm depth were determined for soils planted to garlic, orchard, pasture, potato, leafy vegetables, and wheat. Trends in P distribution between chemical fractions were similar between land uses. Ca‐bound P was the most abundant P fraction in the soils, constituting between 61% and 78% of the total P, whereas P associated with labile was less abundant (< 2%). Soils under leafy vegetables and wheat along with pasture presented the highest and lowest values in all fractions of P, respectively. Labile P generally was highest for leafy vegetables and potato. Labile P and Fe‐Al‐bound P comprised < 1.4% and 8% of total P, respectively. Residual P ranged from ≈ 14% (potato and garlic) to 31% (pasture). Long‐term fertilization increased P allocation to inorganic fractions, as Ca‐bound P contained 78% of total P for potato and garlic and 74% for leafy vegetables but 61% for pasture. A strong positive correlation between labile P and Fe‐Al‐bound P (r = 0.534, p < 0.01), labile P and Ca‐bound P (r = 0.574, p < 0.01), Ca‐bound P and Fe‐Al‐bound P (r = 0.504, p < 0.01), Olsen‐P and CaCl₂‐P (r = 0.821, p < 0.01) was found. Principal‐component analysis showed that the first four components accounted for most of the variation, 32.5%, 16.9%, 12.9%, and 7.9% of total variation, respectively.     

The long‐term soil phosphorus balance across Chinese arable land

Quantifying temporal and spatial variation of soil phosphorus (P) input, output and balance across Chinese arable land is necessary for better P management strategies. Here, we address this challenge using a soil P budget to analyse the soil P balance in arable land across the whole of China, for the period 1980–2012. Results indicated that the total P input to soil increased from 22.5 kg P/ha in 1980 to 79.1 kg P/ha in 2012. However, the total P output from soil only increased from 17.9 kg P/ha in 1980 to 36.9 kg P/ha in 2012. Therefore, the average net soil P surplus in China increased from 4.6 kg P/ha in 1980 to 42.1 kg P/ha in 2012. Our research found great variation in soil P balances across different regions. Soil P balance varied between regions with the order of southeast (SE) > north central (NC) and the middle and lower reaches of Yangtze River (MLYR) > southwest (SW) > northwest (NW) > northeast (NE). Phosphorus that has accumulated in agricultural soil across China could theoretically meet crop P demands for approximately 4.8–12.0 yrs, depending on the bioavailability of P stored in soils. Increasing the return rates of manure and straw could substantially reduce the demand for fertilizer‐P. This paper represents a basis for more targeted, regionally informed P fertilizer recommendations in Chinese soils.     

Land use change and land degradation in China from 1991 to 2001

China has long been experiencing intense land use/cover changes (LUCC). Undesirable land use/cover changes have resulted in widespread land degradation. This study examines the temporal and spatial dynamics of land use change and land degradation as evident from land use survey datasets (1991–2001). Six prominent land degradation processes were identified, namely: desertification, secondary salinisation, loss of agricultural use, deforestation, grassland degradation and loss of wetland. Rates of conversion were calculated and distribution patterns were mapped with the aid of GIS. The results showed that these land use changes have affected the wider environment and accelerated land degradation. It provided a more complete and up‐to‐date picture of China's land degradation which helps to develop improved conservation policies that combat land degradation and promote sustainable land management. Copyright © 2006 John Wiley & Sons, Ltd.     

Soil organic matter dynamics after the conversion of arable land to pasture

 Conversion of arable land (maize) to pasture will affect the soil organic matter (SOM) content. Changes in the SOM content were studied using a size- and density-fractionation method and ¹³C analysis. Twenty-six years of maize cropping had resulted in a depletion of carbon stored in the macro-organic fractions (>150 μm) and an increase in the <20 μm fraction. Maize-derived carbon in the upper 20 cm increased from 10% in the finest fraction (<20 μm) to 91% in the coarse (>250 μm), light (b.d. <1.13 g cm^–3) fractions. Pasture installation resulted in a rapid recovery of the total SOM content. Up to 90% of the pasture-derived carbon that was mineralized during maize cropping was replaced within 9 years. Especially the medium and coarse size (>150 μm) and light (b.d. <1.13 g cm^–3) fractions were almost completely regenerated by input of root-derived SOM. The amount of medium-weight and heavy macro-organic fractions (>150 μm; b.d. >1.13 g cm^–3) in the 0- to 20-cm layer was still 40–50% lower than in the continuous pasture plots. Average half-life times calculated from ¹³C analyses ranged from 7 years in the light fractions to 56 years in heavy fractions. Fractionation results and ¹³C data indicated that mechanical disturbance (plowing) during maize cropping had resulted in vertical displacement of dispersed soil carbon from the 0- to 20-cm layer down to 60–80 cm. Conversion of arable land to pasture, therefore, not only causes a regeneration of the soil carbon content, it also reduces the risk of contaminant transport by dispersed soil carbon. Received: 10 March 1998     

适宜超高压处理条件脱除大蒜臭味保持抗氧化和抑菌能力

为了提升大蒜头产品的品质,该研究将超高压技术应用于大蒜头产品处理中,探究了在200、300、400、500 MPa压力条件下处理10 min,大蒜风味物质,尤其是含硫挥发性化合物的变化,同时考察超高压对大蒜主要活性成分大蒜素含量、抗氧化和抑菌能力的影响.试验结果表明,超高压处理较于在95℃下60 s的蒸汽漂烫处理,不仅具有良好的杀菌作用,同时还可以去除大蒜中的刺激性风味,起到脱臭作用.大蒜经500 MPa处理后,主要蒜臭味嗅感物质二烯丙基二硫化物含量降低至30.69%,经过热处理的大蒜,二烯丙基二硫醚化合物则降低至54.68%,与超高压处理后的大蒜具有显著性差异(P<0.05).500 MPa处理后的大蒜中大蒜素浓度上升至0.079 mmol/L,高出热处理组具有显著性差异(P<0.05);铁离子还原能力较热处理组高出64.24%,具有显著性差异(P<0.05),1,1-二苯基-2-三硝基苯肼清除率高出热处理组28.68%,具有显著性差异(P<0.05);经热处理后的大蒜均丧失全部抑菌能力,而超高压处理后的大蒜对不同种的细菌仍具有一定的抑菌能力,对黑曲霉的抑菌能力与无处理组无显著差异.相关性分析结果显示,大蒜的抑菌能力与硫醚类化合物显著相关(r>0.884),与二烯丙基二硫醚、总酚含量未呈现显著相关,抗氧化能力未与硫醚类化合物含量、二烯丙基二硫醚、总酚呈显著相关趋势.研究结果为大蒜头产品的品质改良提供参考.     

The role of soil chemical properties,land use and plant diversity for microbial phosphorus in forest and grassland soils

Management intensity modifies soil properties, e.g., organic carbon (C_org) concentrations and soil pH with potential feedbacks on plant diversity. These changes might influence microbial P concentrations (P_mic) in soil representing an important component of the P cycle. Our objectives were to elucidate whether abiotic and biotic variables controlling P_mic concentrations in soil are the same for forests and grasslands, and to assess the effect of region and management on P_mic concentrations in forest and grassland soils as mediated by the controlling variables. In three regions of Germany, Schwäbische Alb, Hanich‐Dün, and Schorfheide‐Chorin, we studied forest and grassland plots (each n = 150) differing in plant diversity and land‐use intensity. In contrast to controls of microbial biomass carbon (C_mic), P_mic was strongly influenced by soil pH, which in turn affected phosphorus (P) availability and thus microbial P uptake in forest and grassland soils. Furthermore, P_mic concentrations in forest and grassland soils increased with increasing plant diversity. Using structural equation models, we could show that soil C_org is the profound driver of plant diversity effects on P_mic in grasslands. For both forest and grassland, we found regional differences in P_mic attributable to differing environmental conditions (pH, soil moisture). Forest management and tree species showed no effect on P_mic due to a lack of effects on controlling variables (e.g., C_org). We also did not find management effects in grassland soils which might be caused by either compensation of differently directed effects across sites or by legacy effects of former fertilization constraining the relevance of actual practices. We conclude that variables controlling P_mic or C_mic in soil differ in part and that regional differences in controlling variables are more important for P_mic in soil than those induced by management.     

黄土高原典型流域土壤侵蚀对退耕还林土地利用变化的响应

黄土高原土壤侵蚀严重,为此中国从1999年起实施了大规模的退耕还林工程。为了分析退耕还林土地利用变化对土壤侵蚀的影响,该研究以黄土高原清水河流域为研究区域,将2000—2020年流域退耕还林工程的实施依据主要措施的不同划分为4个阶段,应用RUSLE（revised universal soil loss equation）模型分析土壤侵蚀强度的变化特征,采用情景模拟方法提出一个区分土地利用变化和降雨变化对土壤侵蚀影响程度的算法,判别土地利用变化对土壤侵蚀的影响程度,将土地利用变化分解为土地利用转换和改造2种形式,在剔除降雨变化影响的基础上分析土地利用变化对土壤侵蚀的影响过程。结果表明：1）2000、2005、2011、2014和2020年流域平均侵蚀模数分别为36.21、41.02、24.93、23.72和8.24 t/(hm²·a),土壤侵蚀强度明显下降;土地利用变化和降雨变化对土壤侵蚀的阶段平均影响程度分别为75.23%和24.77%,土地利用变化在流域土壤侵蚀的变化中起了主导作用。2）流域土地利用转换区侵蚀强度的变化直接受转换过程中地类类别变更及所实施主要相关措施差异的影响,改造区侵蚀强度的变化直接受改造过程中所实施主要相关措施的影响。剔除降雨变化的影响后：改造区的阶段平均起始侵蚀模数较转换区高43.47%,其水土流失综合治理的难度总体上大于转换区;转换区侵蚀模数的阶段平均下降量较改造区高50.80%,改造区侵蚀量的阶段合计减少量占流域阶段合计减少量的71.16%,土地利用转换在降低其实施地区土壤侵蚀强度方面发挥了重要作用,而土地利用改造因实施面积较大在减少流域土壤侵蚀总量方面发挥了重要作用。3）剔除降雨变化的影响后,草地侵蚀量的阶段合计变化量占流域阶段合计变化量的70.51%,且草地阶段合计变化量中改造区占67.41%,其变化特别是其改造对流域土壤侵蚀的影响最大。该研究在分析土地利用变化对土壤侵蚀的影响程度和过程方面作了一些尝试,研究结果可为黄土高原退耕还林成果巩固及高质量发展有效措施的制定提供科学依据。     

Phosphorus sequestration in soil aggregates after long-term tillage and cropping

Cultivated soils in the Everglades are being converted to their historic use as pastures or seasonally flooded prairies as parts of restoration efforts, but long-term cultivation may have altered soil P distribution and availability which may pose eutrophication hazards upon change in land use. The objectives of this study were to determine the distribution of P in soil chemical and physical fractions for contrasting long-term land management practices. The distribution of P in labile, Fe–Al bound, Ca bound, humic–fulvic acid, and residual pools in five aggregate-size fractions were measured for fields under sugarcane (Saccharum sp.) cropping for 50 years and perennial pasture for 100 years. Both land uses were characterized by a high degree of macroaggregation, as aggregates >0.25 mm contained 76 and 83% of the total soil under cultivation and pasture, respectively. Soils under sugarcane sequestered a total of 77 kg ha⁻¹ more P than pasture at 0–15 cm. The distribution of P in chemical fractions significantly varied between land uses as cultivation increased P sequestration in Ca-bound fractions more for sugarcane (244 kg P ha⁻¹) than pasture (65 kg P ha⁻¹). Pasture sequestered more P in organic pools, as storage in humic–fulvic acid and residual fractions were 26 and 25%, respectively, higher than sugarcane. Labile P was 100% higher for pasture than sugarcane, but Fe–Al bound P storage did not differ between land uses. Aggregation increased P sequestration in humic–fulvic acid and residual fractions, and P storage in organic pools increased with increasing aggregate size. In contrast, cultivation decreased aggregation and increased P accumulation in inorganic fractions. Long-term cultivation altered the distribution of soil P from organic to inorganic pools. The P stored in inorganic pools is stable under current land use, but may be unstable and pose eutrophication hazards upon onset of future land use change to the seasonally flooded prairie ecosystem.     

基于GIS的土壤有机碳储量核算及其对土地利用变化的响应

土地利用变化是影响土壤有机碳储量变化的重要驱动因素,为了进一步探讨土地利用变化对土壤碳储量的影响,该文根据土壤样点数据、土壤类型图、土地利用类型图,分析了江苏省1985年和2005年表层土壤有机碳密度的变化以及土地利用变化对表层土壤有机碳密度的影响,主要结论如下：1）江苏省表层土壤有机密度的空间变化趋势为：黄淮平原生态区南北差异明显,北部的沂沭泗平原丘岗以增加为主,南部的淮河下游平原以减少为主;沿海滩涂与海洋生态区持平为主;而长江三角洲平原生态区表现不一：沿江平原丘岗生态亚区以增加为主,而茅山宜溧低山丘陵生态亚区和太湖水网生态亚区均表现为有机碳密度的减少;2）各地类表层土壤有机碳密度均有所增加;耕地-林地、草地;草地-林地、建设用地;建设用地-耕地、草地、林地;水域的转出以及未利用地的转出等转换类型有利于土壤碳储量的增加、其他地类间的转换会造成一定的碳排放。     

广西农民自主型细碎化耕地归并整治模式及效果评价

随着社会经济的发展,耕地细碎化越来越成为制约农业发展的瓶颈,该文根据广西龙州县弄农屯实地调研,探究破解耕地细碎化的路径——农民自主型"小块并大块"土地整治模式,以期对创新土地整治实践和乡村振兴战略实施提供借鉴。该文主要采用半结构化访谈法,模型定量法和案例研究法。研究结果:1)农民自主型"小块并大块"土地整治模式是农民"自下而上"开展权属调整并主导实施,政府"自上而下"按照相关农田建设标准进行经济补偿相结合的土地整治模式创新;2)该模式机理是,细碎化通过直接或间接影响土地、资本、技术、劳动等耕地利用系统要素,进而影响产量、成本和效率;通过"小块并大块",改进的细碎化与高水平经济发展下耕地利用系统要素重新协调与适应,即"小块并大块"通过调整地块空间位置而调整生产关系,促进了生产关系与生产力的重新协调适应;3)弄农屯农民自主型"小块并大块"土地整治模式,通过填平土沟和归并田埂增加耕地面积,通过地块归并显著减少地块数量,完善田间道路和农田水利设施,从而显著提高耕地利用效率和增加单位面积产量,促进农业结构调整以显著增加收益。研究结论:农民自主型"小块并大块"土地整治模式是农民"自下而上"与政府"自上而下"相结合的典型模式,能够显著降低耕地细碎化程度,促进细碎化与耕地利用系统要素优化与协调,是实现小农户和现代农业发展有机衔接的有效路径。     

东北黑土区不同土地利用方式下农田土壤微生物多样性

为探究黑龙江省黑土区不同土地利用方式下土壤微生物多样性,该研究主要采用Biolog Eco微平板法,以荒地为对照,研究了黑龙江省中部和西南部黑土区玉米、水稻、大豆及土豆4种不同土地利用方式下土壤微生物多样性的变化。结果表明：1）可培养细菌的数量从大到小依次为土豆、水稻、大豆、玉米、荒地,但群落Shannon-Wiener多样性指数从高到低依次为：荒地（2.18）、玉米（2.11）、土豆（2.00）、水稻（1.73）、大豆（1.49）;2）不同利用方式下黑土区微生物碳源利用程度大致随培养时间的延长而升高,并且氨基酸、糖类以及聚合物类是黑土微生物代谢的最主要碳源;玉米地土壤微生物的Shannon-Wiener指数（3.18）、McIntosh指数（5.96）、丰富度指数（24.89）、及Simpson指数（0.95）比其他土地利用方式土壤微生物的多样性指数高,而水稻田土壤微生物的多样性指数最低,土豆、大豆与荒地土壤微生物的多样性指数间无显著差别;3）不同土地利用方式显著影响了土壤微生物群落碳源代谢多样性,并且对土壤微生物群落代谢特征起分异作用的主要碳源类型为糖类、氨基酸类和羧酸类,其中糖类尤为突出。该研究将有助于了解黑土区土壤微生物多样性与土地利用方式之间的关系,为黑土区农业的可持续发展提供一定的科学依据。     

抛荒土地不同处理及利用方式对喀斯特地区土壤微生物的影响

土壤微生物特性是土壤养分的储存库,土壤养分也影响土壤微生物活性,了解两者的相互作用机制对土地利用与管理提供理论依据,而喀斯特地区不同土地利用方式相关研究较少。基于喀斯特峰丛洼地火烧、刈割、刈割除根、封育、种植玉米、种植桂牧1号杂交象草6种坡面典型的土地利用方式的动态监测样地建设与调查,该文分析了不同土地利用方式下土壤微生物特性,揭示其与土壤养分相互作用机制。结果表明,不同土地利用方式对土壤养分的影响不同,土壤有机质（soil organic matter,SOM）、全氮（total nitrogen,TN）、全磷（total phosphorus,TP）、碱解氮（available nitrogen,AN）等沿封育、火烧、刈割、刈割除根、种植桂牧1号、种植玉米等土地利用方式的转变而减少;不同土地利用方式土壤微生物生物量各不同,土壤微生物量碳（microbial biomass carbon, MBC）：244.98～1 246.89 mg/kg、土壤微生物量氮（microbial biomass nitrogen,MBN）：35.44～274.69 mg/kg、土壤微生物量磷（microbial biomass phosphorus,MBP）：30.88～64.72 mg/kg,其中,种植玉米土壤微生物生物量均最低,其土壤质量退化现象严重;不同土地利用方式土壤微生物种群数量及组成影响不同,种植玉米和桂牧1号杂交象草细菌占绝对优势,而火烧、刈割、刈割除根及封育均以放线菌占绝对优势,真菌的比例很少;不同土地利用方式土壤微生物特性与土壤养分之间相互作用关系不同：火烧的土壤TP和MBP、全钾（total potassium,TK）与MBC、TN与放线菌作用最强且均呈正相关,刈割的土壤TN与MBC呈正相关,刈割除根的速效磷（available phosphorus,AP）与MBN正相关,封育的pH值与MBC、真菌负相关,种植玉米的TN、TK与MBP负相关,种植桂牧1号杂交象草的pH值与真菌负相关、与放线菌正相关;聚类分析可以将喀斯特峰丛洼地6种土地利用方式划分为4类,其中封育和火烧最好。     

Short‐term and residual availability of nitrogen after long‐term application of organic fertilizers on arable land

Knowledge on short‐term and long‐term availability of nitrogen (N) after application of organic fertilizers (e.g., farmyard manure, slurry, sewage sludge, composts) provides an important basis to optimize fertilizer use with benefits for the farmer and the environment. Nitrogen from many organic fertilizers often shows little effect on crop growth in the year of application, because of the slow‐release characteristics of organically bound N. Furthermore, N immobilization after application can occur, leading to an enrichment of the soil N pool. However, this process finally increases the long‐term efficiency of organic fertilizers. Short‐term N release from organic fertilizers, measured as mineral‐fertilizer equivalents (MFE), varies greatly from 0% (some composts) to nearly 100% (urine). The most important indicators to be used for predicting the short‐term availability of N are total and NH ‐N contents, C : N ratio (especially of the decomposable organic fraction), and stability of the organic substances. Processing steps before organic fertilizers are applied in the field particularly can influence N availability. Composting reduces mineral‐N content and increases the stability of the organic matter, whereas anaerobic fermentation increases NH ‐N content as well as the stability of organic matter, but decreases the C : N ratio remarkably, resulting in a product with a high content of directly available N. Nevertheless, long‐term effects of organic fertilizers rather slowly releasing N have to be considered to enable optimization of fertilizer use. After long‐term application of organic fertilizers, the overall N‐use efficiency is adequate to a MFE in the range of 40%–70%.     

Changes in copper content and distribution in young,old and abandoned vineyard acid soils due to land use changes

We studied total Cu content and its distribution in 33 surface soil samples cultivated with vines for variable lengths of time in the Monterrei designation of origin (DO), located in Galicia (NW Spain). The study was focused on the influence of land use changes on soil degradation by effect of Cu accumulation and availability. Total copper concentration in soils ranged from 25 to 272 mg kg⁻¹. The time during which each soil was cultivated with vines was found to affect both the total concentration of copper and its distribution. The average concentration of copper in young vineyards was 64 mg kg⁻¹, whereas those in old and abandoned vineyards were 100 and 132 mg kg⁻¹, respectively. Copper bound to organic matter and to amorphous inorganic colloids were greater in old and abandoned vineyards, where they accounted for 51 and 52 per cent, respectively, of total copper, than in young vineyards (39 per cent). Copper bound to crystalline Al and Fe colloids accounted for 21, 22 and 12 per cent of total Cu in old, abandoned and young vineyards respectively. The prevalence of Cu bound to the organic fraction reduces the adverse environmental effects of this metal on soil organisms and plants. However, some management practices such as organic matter addition or liming should be implemented in order to delay or avoid soil degradation in young vineyards. For abandoned vineyards, the influence of new land uses on potential Cu mobilisation necessitates careful examination. Copyright © 2007 John Wiley & Sons, Ltd.     

Role of soil organic matter in stabilization of water-stable aggregates in Soils under different types of land use

Three Andosols (used as grassland, upland field, and paddy field) and two Gray Lowland soils (used as upland field and paddy field) were examined to study the role of organic matter in the stabilization of soil aggregates. It was found that prolonged use of Andosols as grassland or as upland field enabled to maintain a higher level of soil organic carbon than use as paddy field. However, paddy soil exhibited a greater aggregate stability (determined by wet-sieving procedure) than soil under upland field or grassland management. Comparison between two Gray Lowland soils also showed that aggregates in the paddy soil were more stable than in the upland field soil. Among organic constituents examined (such as sodium pyrophosphate (SPP)-extractable organic matter and carbohydrates), only the contents of hot water (HW)-extractable carbohydrates of the soils were significantly correlated with aggregate stability. Paddy soils which showed a greater aggregate stability contained a larger amount of HW -extractable carbohydrates in the soils, and a larger amount of HW -extractable carbohydrates regardless of the size of their aggregates compared with other soils. These findings suggest that HW -extractable carbohydrates which represents easily decomposable organic materials may be of special importance for the stabilization of aggregates in the soils.     

紫色土小流域土壤流失对不同土地利用类型的响应

 小流域土壤流失特征不仅反映了流域的土地利用和管理状况,而且对其下游水体环境和水利设施安全具有深刻的影响。1999—2000年间以紫色土区3个具有不同集水面积、物理特征和土地利用类型的典型小流域为研究对象,探讨不同雨型下土壤流失对不同土地利用类型的响应特征。中大型降雨和间歇型降雨侵蚀下,以林地为主要土地利用类型的流域输沙模数最小,平均为866kg·hm-2,谷地农田利用类型最高,平均为5 550kg·hm-2。次降雨侵蚀力和次降雨峰值径流流量,分别是紫色土区非林地和林地利用为主小流域输沙模数变异的主要影响因子。     

Influence of different land uses on soil nitrogen transformations after conversion from an Indian dry tropical forest

The effects of alternate land uses, such as grassland, cropland and mine spoil on mineral nitrogen (N), N-transformation rate and microbial biomass N (MBN) in dry tropical forest soils of India were studied. The mean annual mineral N in the forest, grassland, cropland and mine spoil ecosystems, respectively ranged from 15.24 to 19.58, 17.8 to 18.56, 16.49 to 19.85 and 10.52 to 13.44 µg g^− 1, net nitrification rate from 14.15 to 23.4, 10.11 to 11.38, 8.07 to 9.16, 10.52 to 13.44 µg g^− 1mo^− 1; net N-mineralization rate from 17.38 to 26.36, 13.99 to 15.41, 10.99 to 12.5, 5.43 to 7.68 µg g^− 1mo^− 1and and microbial biomass N from 41.25 to 58.87, 34.47 to 47.95, 27.88 to 30.43 and 22.95 to 25.26 µg g^− 1, respectively. The values were within the range reported by previous studies in different tropical environments. The mean annual net nitrification rates declined after conversion into grassland, cropland and mine spoil by 43, 54 and 78%, respectively, net N mineralization by 33, 46 and 70%, and microbial biomass N by 29%, 42% and 52%, respectively.The MBN was positively related to root biomass and total plant biomass, while microbial-N and inorganic N are reciprocally, while nitrification and N-mineralization are directly related to seasonal soil moisture and temperature. The microbial biomass N, nitrification and N-mineralization are negatively related to smaller fraction (< 0.1 mm) of the soil. Above- and below-ground biomass also have had their impact on microbial biomass N, and thereby N-mineralization. Thus, in dry tropical forests, land-use change affects remarkably the nitrogen transformation process in soil.     

Effects of parent material and land use on soil erodibility

The objective of the present investigation was to find out the effect of different parent materials and land use on soil erodibility. Four types of parent materials such as andesite, basalt, alluvial, and gypsum, and three land use types such as grass, clover, and maize, all wide spread in Erzurum Province in Turkey, were tested. Aggregate stability and soil erodibility factors were determined. The susceptibility of soils against erosion decreased in the order of parent materials basalt > andesite > alluvial > gypsum. Likewise, the susceptibility of land use can be sorted as follows: grass > clover > maize.     

中国粮食主产区耕地生产能力空间分布特征

核算区域耕地资源生产能力,揭示耕地生产能力层次差异,分析耕地资源生产潜力的空间分布特征,对于科学确定区域耕地利用与保护对策,特别是支撑区域土地整治以及高标准农田建设,保障国家耕地资源安全战略具有重要意义。该文以中国粮食主产区(黑龙江省、吉林省、辽宁省、河北省、山东省、江苏省6省)乡镇尺度的耕地资源生产能力核算数据为基础,核算了粮食主产区理论生产能力、可实现生产能力和实际生产能力差值以及生产能力特征,并分析了耕地生产能力在省级及二级区尺度上的分布特征,揭示了耕地区县级利用强度与利用潜力。研究结果表明:中国粮食主产区(6省)的耕地理论生产能力、可实现生产能力和实际生产能力分别为5.12、4.03和3.28亿t。江苏省的江淮平原区理论单产、可实现单产和实际单产均最高,黑龙江省的大小兴安岭山地区理论单产最低,河北省的后山坝上高原区可实现单产、实际单产最低。河北平原区及山东省理论利用潜力明显高于其他地区。耕地资源理论生产能力较高表明通过实施高标准农田建设,粮食主产区增产潜力巨大;而6省区可实现利用潜力普遍较低,表明通过政策提升耕地生产能力的空间有限。该文为粮食主产区耕地资源数量、生产能力并重管理提供了决策依据。