Short‐ and medium‐term evolution of soil properties in Atlantic forest ecosystems affected by wildfires

The immediate effect of low and high severity wildfires on the main soil properties, as well as their short‐ and medium‐term evolution under field conditions, was examined. The study was performed with three pine forest soils (two Leptosols and one Humic Cambisol, developed over granite and basic schist, respectively), located in the Atlantic humid temperate zone (Galicia, NW Spain). Samples were collected from the A‐horizon (0–5 cm depth) of the burnt and the corresponding unburnt soils, immediately and 3, 6 and 12 months after the wildfires. Most properties analysed exhibit immediate fire‐induced changes and different evolution depending on fire severity and soil type. In general, immediately after the fire pH and soil properties related to nutrients availability increased and cation exchange capacity decreased, whereas properties related to soil organic matter content (C, N, Fe and Al oxides) had a variable effect depending mainly on the soil studied; all these modifications were accentuated by fire severity. These effects were attenuated in the short term in the soil affected by a low severity wildfire, but they lasted for at least 1 year in the soils affected by high severity wildfires, particularly in the Leptosols. The results showed the importance of the fire as a disturbance agent in the dynamic of nutrients and soil organic matter that is directly related with soil quality in the Galician forest ecosystems. Copyright © 2011 John Wiley & Sons, Ltd.     

Long‐term effects of tillage,nutrient application and crop rotation on soil organic matter quality assessed by NMR spectroscopy

Crop and land management practices affect both the quality and quantity of soil organic matter (SOM) and hence are driving forces for soil organic carbon (SOC) sequestration. The objective of this study was to assess the long‐term effects of tillage, fertilizer application and crop rotation on SOC in an agricultural area of southern Norway, where a soil fertility and crop rotation experiment was initiated in 1953 and a second experiment on tillage practices was initiated in 1983. The first experiment comprised 6‐yr crop rotations with cereals only and 2‐yr cereal and 4‐yr grass rotations with recommended (base) and more than the recommended (above base) fertilizer application rates; the second experiment dealt with autumn‐ploughed (conventional‐till) plots and direct‐drilled plots (no‐till). Soil samples at 0–10 and 10–30 cm depths were collected in autumn 2009 and analysed for their C and N contents. The quality of SOM in the top layer was determined by ¹³C solid‐state NMR spectroscopy. The SOC stock did not differ significantly because of rotation or fertilizer application types, even after 56 yr. However, the no‐till system showed a significantly higher SOC stock than the conventional‐till system at the 0–10 cm depth after the 26 yr of experiment, but it was not significantly different at the 10–30 cm depth. In terms of quality, SOM was found to differ by tillage type, rate of fertilizer application and crop rotation. The no‐till system showed an abundance of O‐alkyl C, while conventional‐till system indicated an apparently indirect enrichment in alkyl C, suggesting a more advanced stage of SOM decomposition. The long‐term quantitative and qualitative effects on SOM suggest that adopting a no‐tillage system and including grass in crop rotation and farmyard manure in fertilizer application may contribute to preserve soil fertility and mitigate climate change.     

Management Effects on Soil Organic Carbon Stock in Mediterranean Open Rangelands—Treeless Grasslands

Soil organic carbon (SOC) is subject to relatively rapid changes. In grasslands soils, the management system influences these changes. Therefore, these soils play a crucial role in climate change mitigation. Current research has developed strategies and methodologies to help us understand their role as a carbon sink. In this study, the SOC and total nitrogen contents and stocks (SOC‐S) and their variation with depth were evaluated in annual crop rotations (cereal–fallow). Fifty soil profiles were sampled in the Los Pedroches Valley (southern Spain). This area consists of Mediterranean open rangelands—treeless grasslands with cereal–fallow rotation, under two management systems: long‐term (20 years) organic farming (OF) and conventional tillage (CT). The studied soils were Cambisols (CM), Leptosols (LP) and Luvisols (LV). The objective of this research was to determine any management system effects (OF vs CT) on SOC and total nitrogen contents and stocks and their variation with profile depth. It was observed that SOC concentration decreased with depth (Ah–Ap > Bw > C). The SOC concentration was higher in the top soil for all studied soils in OF compared with CT. The highest totals of SOC‐S were found in LV‐OF (66·01 Mg ha⁻¹) and the lowest in LP‐CT (21·33 Mg ha⁻¹). Significant differences (p < 0·05) between soils types and management practices were found in carbon stocks, increasing the SOC‐S in OF compared with that in CT in all studied soils; this increase was 75·25%, 85·73% and 234·88% for CM, LV and LP, respectively. The results indicated that management practices significantly influence SOC‐S in the Los Pedroches Valley and, consequently, OF in annual crop rotations (cereal–fallow) is an excellent alternative to CT that increases the SOC content in Mediterranean open rangelands—treeless grasslands environments. Copyright © 2013 John Wiley & Sons, Ltd.     

Contribution of organic amendments to soil organic matter detected by thermogravimetry

Sustainable soil management requires reliable and accurate monitoring of changes in soil organic matter (SOM). However, despite the development of improved analytical techniques during the last decades, there are still limits in the detection of small changes in soil organic carbon content and SOM composition. This study focused on the detection of such changes under laboratory conditions by adding different organic amendments to soils. The model experiments consisted of artificially mixing soil samples from non‐fertilized plots of three German long‐term agricultural experiments in Bad Lauchstädt (silty loam), Grossbeeren (silty sand), and Müncheberg (loamy sand) with straw, farmyard manure, sheep faeces, and charcoal in quantities from 3 to 180 t ha^?1 each. In these mixtures we determined the organic carbon contents by elemental analysis and by thermal mass losses (TML) determined by thermogravimetry. The results confirmed the higher reliability of elemental analysis compared to TML for organic carbon content determination. The sensitivity of both methods was not sufficient to detect the changes in organic carbon content caused by small quantities of organic amendments (3 t ha^?1 or 0.1–0.4 g C kg^?1 soil). In the case of elemental analysis, the detectability of changes in carbon content increased with quantities of added amendments, but the method could not distinguish different types of organic amendments. On the contrary, the based on analysis of degradation temperatures, the TML allowed this discrimination together with their quantitative analysis. For example, added charcoal was not visible in TML from 320 to 330°C, which is used for carbon content determination. However, increasing quantities of charcoal were reflected in a higher TML around 520°C. Furthermore, differences between measured (with TML_110–550) and predicted mass loss on ignition using both organic carbon (with TML₃₃₀) and clay contents (with TML₁₄₀) were confirmed as a suitable indicator for detection of organic amendments in different types of soils. We conclude that thermogravimetry enables the sensitive detection of organic fertilizers and organic amendments in soils under arable land use.     

Ecological assessment of soils in high-mountain landscapes of northeastern part of the Greater Caucasus (Azerbaijan)

The current state of soils and bioproductivity of high-mountain pastures and hayfields in the northeastern part of Great Caucasus within Azerbaijan were studied, and the quality assessment of soils was performed. The ecological evaluation of soils was based on special assessment scales and soil bonitet scores. The soils suitable for the development of meadow vegetation were identified. The highest score (89 points) was given to mountainous meadow chernozemlike soils (Eutric Mollic Leptosols); these soils are most suitable for pasturing. Mountainous meadow soddy soils (Dystric Umbric Leptosols) ranked second (76 points). Mountainous meadow-steppe soils (Eutric Mollic Leptosols) were estimated at 72 points; these soils are suitable for plant communities of subalpine meadows. Mountainous meadow soddy–peaty soils (Brunic Umbric Leptosols) had the lowest score of 68 points mostly because of the excessive precipitation against the background of relatively low mean annual temperature limiting the biological productivity of alpine meadows.     

Amending a loamy sand with three compost types: impact on soil quality

The objective of this study was to investigate the effects of the long‐term addition of three compost types (vegetable, fruit and yard waste compost – VFYW, garden waste compost – GW and spent mushroom compost – SM) on the physical properties of a sandy soil and to quantify any such effects using indicators of soil physical quality. Soil samples were taken from a field with annual compost applications of 30 m³/ha for 10 yr and various physico‐chemical analyses were undertaken. Results show a significant increase in soil organic carbon (21%) with the VFYW and GW compost types. With SM, soil organic carbon increased by 16%. Increased soil macroporosity and water content at saturation with a corresponding decrease in bulk density were observed for all compost types. However, quantification of these improvements using existing soil physical quality indicators such as the ‘S‐index’, soil air capacity and matrix porosity gave mixed results showing that these indices perform poorly when applied to sandy soils. It is concluded that the long‐term application of compost does not significantly improve the physical properties of sandy soils, but the absence of adverse effects suggests that these soils are a viable disposal option for these composts, but new indices of quality are needed for the proper characterization of sandy soils.     

Effect of forest and soil type on microbial biomass carbon and respiration

The aim of study was to evaluate the variation of soil microbial biomass carbon (C_mic) and microbial respiration (M_R) in three types soil (Chromic Cambisols, Chromic Luvisols and Eutric Leptosols) of mixed beech forest (Beech- Hornbeam and Beech- Maple). Soil was randomly sampled from 0–10 cm layer (plant litter removed), 90 soil samples were taken. C_mic determined by the fumigation-extraction method and M_R by closed bottle method. Soil C_org, N_tot and pH were measured. There are significant differences between the soil types concerning the C_mic content and M_R. These parameters were highest in Chromic Cambisols following Chromic Luvisols, while the lowest were in Eutric Leptosols. A similar trend of C_org and N_tot was observed in studied soils. Two-way ANOVA indicated that soil type and forest type have significantly effect on the most soil characteristics. Chromic Cambisols shows a productive soil due to have the maximum C_mic, M_R, C_org and N_tot. In Cambisols under Beech- Maple forest the C_mic value and soil C/N ratio were higher compared to Beech-Hornbeam (19.5 and 4.1 mg C g^–1, and 16.3 and 3.3, respectively). This fact might be indicated that Maple litter had more easy decomposable organic compounds than Hornbeam. According to regression analysis, 89 and 68 percentage of C_mic variability could explain by soil C_org and N_tot respectively.     

Biological soil properties in a long‐term tillage trial in Germany

After 37 years of different soil‐tillage treatments in a long‐term field experiment in Germany, a number of biological soil characteristics was measured. The field trial comprised six major treatments with different implements and various depths. In this paper, results from a comparison of long‐term use of a plow (to 25 cm depth), a chisel plow (to 15 cm depth), and no‐tillage are presented. The biological soil characteristics measured include the soil‐organic‐carbon (SOC) content, microbial biomass, enzyme activities, and the abundance and biomass of earthworms. Long‐term use of a chisel plow and no‐tillage increased the organic‐C content in the uppermost soil layer (0–10 cm) compared with the plow treatment. The microbial biomass and the enzyme activities arginine‐ammonification, β‐glucosidase, and catalase decreased with depth in all treatments. Arginine‐ammonification and catalase were higher in the plow treatment in soil layers 10 to 30 cm. Additionally, the chisel plow caused an increase in number and biomass of earthworms compared to both other tillage treatments. Differences in earthworm numbers and biomass between plowing and no‐tillage were not statistically significant.     

Temperature sensitivity of anaerobic labile soil organic carbon decomposition in brackish marsh

The global warming has a potential for acceleration of labile soil organic carbon decomposition. Arrhenius equation is one of the useful equation for predicting temperature sensitivity of carbon decomposition, with the activation energy of rate constant being a key factor. The purpose of this study is the evaluation of temperature sensitivity of labile soil organic carbon decomposition under anaerobic condition in wetland soil using the activation energy of rate constant among different vegetation types. The soil samples were incubated at three different temperatures (10, 20, and 30°C) under anaerobic condition and carbon decomposition rates (sum of CO₂ and CH₄ production) were measured by gas chromatography. The first-order kinetic model with Arrhenius equation was used for approximate of anaerobic carbon decomposition. For determination of activation energy of rate constant, non-linear least-squares method was conducted between observed carbon decomposition rate and predicted carbon decomposition rate which calculated by Arrhenius equation. The activation energy of rate constant of anaerobic labile soil organic carbon decomposition was different among vegetation types. We successfully determined the activation energy of rate constant of CO2 or CH4 production from Phragites, Juncus, and Miscanthus+Cirsium-dominated vegetation soil with Arrhenius equation. Hence, this study suggests that Arrhenius equation was useful for evaluation of temperature sensitivity of labile soil organic carbon decomposition not only aerobic condition, but also anaerobic condition among several vegetation types in the wetland ecosystem. Moreover, gaseous carbon production from soil under Juncus yocoscensis dominated soil appeared higher activation energy and temperature sensitivity than that from soil under other vegetation types.     

Soil microbiological properties and its stratification ratios for soil quality assessment under different cover crop management systems in a semiarid vineyard

In vineyards in Spain, tillage and semiarid Mediterranean climatic conditions accelerate organic matter loss from the soil. Cover crops are a conservation management practice that can provoke changes in soil quality which requires evaluation. Stratification ratios of soil properties such as soil organic C and labile C fractions have been proposed for the assessment of soil quality under different soil management systems. Our objective was to study the effect of different cover crop management on various soil parameters and their stratification ratios. We evaluated three different soil managements in a Typic Haploxerept from NE Spain: conventional tillage (CT); 5‐y continuous cover crop of resident vegetation (RV); and 4‐y continuous cover crop of Festuca longifolia Thuill., followed by 1‐y Bromus catharticus L. after resowing (BV). We monitored soil organic C, particulate organic C, water soluble C, potentially mineralizable N, microbial biomass C, β‐glucosidase and urease enzymatic activities, and water stable aggregates at 0–2.5, 2.5–5, 5–15, 15–25, and 25–45 cm soil depths. We calculated soil depth stratification ratios of those soil properties. Resident cover crop increased microbiological properties, labile C fractions, and aggregation with respect to conventional tillage at 0–2.5 and 2.5–5 cm soil depths. However, for Bromus cover crop the same soil properties were lower than for the resident cover crop at 0–2.5 cm depth. Stratification ratios of β‐glucosidase and urease enzymatic activities, and particulate organic C showed a higher sensitivity than other soil properties; therefore, they would be the best indicators for soil quality assessment in semiarid Mediterranean vineyards.     

Effects of mineral surface iron on the CPMAS 13C-NMR spectroscopic detection of organic matter from soil fractions in an agricultural topsoil with different amendments

The decrease of NMR visibility of the C signal in soil samples due to the association between organic carbon (OC) and the topsoil mineral surface was investigated. CPMAS ¹³C‐NMR spectra were obtained for soil particle‐size fractions (< 2 μm, 2–20 μm, > 20 μm) and bulk soils from an agricultural topsoil (Chernozem) that had received three different amendments (no fertilization, mineral fertilization (NPK), mineral (NPK) and organic (cattle manure) fertilizations) at Bad Lauchstädt, Germany. The soil organic carbon content of the three soils depended on the degree of soil fertilization. There was no constant relationship between the total NMR signal intensity and the total amount of organic carbon (TOC) for all size fractions. Indeed, a key role played in the C signal intensity by the paramagnetic ferric ion from the clay content in soil fractions and bulk soils was confirmed. Thus, we describe the variations of C signal intensity by taking into account the distribution of clay‐associated OC and non‐associated OC pools. Depending on the amendment, the C signal visibility was weakened by a factor of 2–4 for the clay‐associated OC. This estimation was rendered possible by combining mineral specific surface area (SSA) measurements with the N₂ gas adsorption method (BET method) and determination of TOC and iron concentrations. This approach contributes to the quantitative evaluation of the CPMAS ¹³C‐NMR detection.     

Response of Soil Microbial Biomass and Enzyme Activity to Soil Fertilization in an Eroded Farmland of Chinese Mollisols

The aims of this study were to examine interrelationships between microbial biomass and enzyme activities of soil quality and to determine their suitability for differentiating areas. The study included five simulated erosion soil depths (0, 5, 10, 20, and 30 cm), which had received contrasting fertilizer treatments over a 5-year period in an eroded black soil of northeastern China. Our results indicated that soil microbial carbon, nitrogen, urease, phosphatase, and invertase activities declined as the erosion depth increased. On the five erosion depths, soil microbial carbon, phosphatase, and invertase variation ranged as follows: 35.4–53.3, 39.8–45.2, and 55.9–67.1%, respectively. In the fertilizer + manure treatment, soil microbial carbon, nitrogen, urease, phosphatase, and invertase activities were significantly greater (P < 0.05) than those of fertilizer treatment in all five different erosion depths. Overall, this study may be considered as the foundation for soil quality evaluation and fertility restoration in northeastern China and similar regions.     

Chemical fractionation to characterize changes in sulphur and carbon in soil caused by management

Classical chemical fractionation of soil sulphur (S) into HI‐reducible S and carbon‐bonded S does not separate S in soil into fractions that have differing mineralization potentials. Other techniques are needed to separate organic S into more labile and less labile fractions of biological significance, irrespective of their bonding relations. We have sequentially fractionated soil S and carbon (C) into their ionic forms released onto ion‐exchange resins and organic S and C extracted in alkali of increasing concentration. We evaluated the technique on pasture and arable soils that had received various fertilizer and cultivation treatments. Total S and C were greater in the soil of the fertilized pasture than in that of the unfertilized pastures. Continuous arable cropping decreased total soil S and C, whereas restoration to pasture caused an accumulation. Resin, 0.1 m NaOH, 1 m NaOH and residual fractions accounted for between 1–13%, 49–69%, 4–16% and 19–38% of total soil S and between 5–6%, 38–48%, 5–7% and 46–53% of total soil C, respectively. Among different S and C fractions, the size of the 0.1 m NaOH and residual fractions changed more with the change in land use and management. The 0.1 m NaOH fraction had a narrower C:S ratio (50–75:1) than did the residual fraction (96–141:1). The significant degree of change in these two fractions, caused by differences in land management, indicates that they may be useful indicators of change in ‘soil quality’.     

Metabolic characteristics of microbial communities of Aeolian sandy soils induced by saline water drip irrigation in shelter forests

The microbial metabolic activities of soils sampled at eight depths (0–5, 5–15, 15–30, 30–50, 50–70, 70–100, 100–150 and 150–200 cm) in shelter forests (comprising the tree species, Haloxylon sp.) along the Tarim Desert Highway under drip irrigation with different saline waters were investigated by using Biolog technology. Variance analysis and principal component analysis were conducted. The average well colour development (AWCD) values for single carbon source use by microorganisms increased with the incubation time. The microorganisms reached a lag phase within 24 hours of incubation and entered exponential and stationary phases after 48 and 216 hours of incubation, respectively; however, the death phase was not obvious. As the salinity of drip irrigation water increased, the AWCD values significantly decreased; the AWCD value in the land drip‐irrigated with lowest saline water (S8) was roughly 20% larger than that of the land drip‐irrigated with highest saline water (S1), which was mainly caused by the differences in the use of carboxylic acids, amino acids and phenolic compounds by soil microorganisms. The vertical differences in carbon source utilization by soil microbial communities were obvious: these may be caused by the vertical differences in soil organism abundance associated with distribution of roots in the shelter forest. The largest and smallest AWCD values were noted in the 70–100‐cm soil layer and 0–5‐cm topsoil layer, respectively. The correlation coefficients between the AWCD values and soil organic matter, total nitrogen, total phosphorus, total potassium, available potassium, available phosphorus, pH, cation exchange capacity and bulk density were > 0.85. Thus, the differences in carbon source metabolism activities of soil microorganisms were caused mainly by the soil chemical properties, with total nutrients being the main driving factor. Furthermore, the amounts of carboxylic acids, amino acids and polymers provided sensitive markers for distinguishing the ability of soil microorganisms to use carbon sources under drip irrigation with different saline waters. Saline water irrigation affected the soil microbial community in shelter forest and produced obvious differences among the shelter forests irrigated with different saline waters.     

Wavelet analysis of soil variation at nanometre‐ to micrometre‐scales: an example of organic carbon content in a micro‐aggregate

This paper demonstrates the potential of wavelet analysis to investigate fine‐scale spatial variation in soil without statistical assumptions that are generally implausible. We analysed the optical densities of different forms of carbon which were measured at intervals of 50 nm along a 16‐µm transect on a soil micro‐aggregate using near‐edge X‐ray fine‐structure spectroscopy (NEXAFS). We found different patterns of scale‐dependent variation between the carbon forms, which could be represented by pair‐wise wavelet correlations at the different scales, and by principal components analysis of all the correlations at each scale. These results represent only one small soil micro‐aggregate and are not presented as general findings about soil carbon, but they do indicate that fine‐scale variation of soil carbon can be complex in ways that the wavelet analysis can accommodate but alternative spatial statistics such as variograms cannot. Among the patterns of variation that the analysis could identify were scale‐dependent correlations of the different forms of carbon. In some cases, positive correlations were found at coarser scales and negative at the finest scales, suggesting a multi‐scale pattern in which contrasting forms of carbon are deposited in common clumps but at finer scales either one or the other form dominates. Aromatic and carboxylic carbon varied jointly in this way. Other forms of carbon, such as carboxylic and aliphatic carbon, were strongly correlated at the finest scales but not the coarser scales. We found evidence for changes in the variance and correlation of forms of carbon along the transect, indicating that the spatial distribution of carbon at these fine scales may be very complex in ways that are inconsistent with the assumptions of geostatistics. This quantitative analysis of the spatial patterns of different soil components at micro‐scales offers a basis for formulating and testing specific hypotheses on replicated samples.     

Use of different chemometric approaches for an estimation of soil properties at field scale with near infrared spectroscopy

Visible and near infrared spectroscopy (vis‐NIRS) may be useful for an estimation of soil properties in arable fields, but the quality of results are often variable depending on the applied chemometric approach. Partial least squares regression (PLSR) may be replaced by approaches which employ supervised learning methods or variable selection procedures in order to increase the proportion of informative wavelengths used in the estimation procedure, to reduce the noise of the spectra and to find the best fitting solution. Objectives were (1) to compare the usefulness of PLSR with either PLSR combined with a genetic algorithm (GA‐PLSR) or support vector machine regression (SVMR) for an estimation of soil organic carbon (SOC), total nitrogen (N), pH, cation exchange capacity (CEC) and soil texture for surface soils (0–5 cm, n = 144) of an arable field in Bangalore (India) and (2) to test and optimize different calibration strategies for GA‐PLSR for an improved estimation of soil properties. PLSR was useful for an estimation of SOC, N, sand and clay. In the cross‐validation (n = 96), accuracies of estimated soil properties generally decreased in the order GA‐PLSR > SVMR > PLSR. However, the order of estimation accuracies for the random validation sample (n = 48) changed to SVMR > GA‐PLSR > PLSR for SOC, N, pH, and CEC, whereas for clay the order changed to SVMR > PLSR > GA‐PLSR. A sequential procedure, which used the most frequently selected wavelengths of the GA‐PLSR runs, proved to be useful for an improved estimation of SOC and N. Overall, SVMR especially improved estimations of SOC and clay, whereas GA‐PLSR was particularly useful for SOC and N and it was the only approach which successfully estimated CEC in cross‐validation and validation.     

Effects of long-term waste water irrigation on soil organic matter, soil microbial biomass and its activities in central Mexico

 The effect of long-term waste water irrigation (up to 80 years) on soil organic matter, soil microbial biomass and its activities was studied in two agricultural soils (Vertisols and Leptosols) irrigated for 25, 65 and 80 years respectively at Irrigation District 03 in the Valley of Mezquital near Mexico City. In the Vertisols, where larger amounts of water have been applied than in the Leptosols, total organic C (TOC) contents increased 2.5-fold after 80 years of irrigation. In the Leptosols, however, the degradability of the organic matter tended to increase with irrigation time. It appears that soil organic matter accumulation was not due to pollutants nor did microbial biomass:TOC ratios and qCO₂ values indicate a pollutant effect. Increases in soil microbial biomass C and activities were presumably due to the larger application of organic matter. However, changes in soil microbial communities occurred, as denitrification capacities increased greatly and adenylate energy charge (AEC) ratios were reduced after long-term irrigation. These changes were supposed to be due to the addition of surfactants, especially alkylbenzene sulfonates (effect on denitrification capacity) and the addition of sodium and salts (effect on AEC) through waste water irrigation. Heavy metals contained in the sewage do not appear to be affecting soil processes yet, due to their low availability. Detrimental effects on soil microbial communities can be expected, however, from further increases in pollutant concentrations due to prolonged application of untreated waste water or an increase in mobility due to higher mineralization rates. Received: 28 April 1999     

Impacts of farmland conversion to apple (Malus domestica) orchard on soil organic carbon stocks and enzyme activities in a semiarid loess region

Land‐use change often affects the sizes of soil organic carbon (SOC) stocks and the activities of soil enzymes. Responses of relevant soil quality indices caused by farmland conversion to orchard are largely unknown in the semiarid loess regions. This study was conducted at orchard sites, which have been under very intensive cultivation, to evaluate the impacts of farmland conversion to apple (Malus domestica) orchard on SOC stocks and soil enzyme activities in the semiarid loess region of Weibei, Shaanxi province, China. The spatial and temporal changes in a variety of soil quality indices were measured for the 0–100 cm soil profile in apple orchards of three age groups (< 10 y, juvenile; 10–15 y, mature; > 15 y, over‐mature) and adjacent farmlands (control). After farmland conversion, total SOC (TOC) content and density and soil alkaline phosphatase activity significantly decreased, while soil catalase activity increased for the 0–100 cm soil profile. The labile SOC (LOC) content, its proportion to TOC content, and carbon management index (CMI, changes in the total content and lability of SOC) significantly increased in the 0–40 cm soil layer, whereas soil urease and invertase activities only increased in the 0–20 cm layer (P < 0.05). With increasing age of apple orchards, SOC stocks significantly increased after 10 y, being more than 10% larger in mature and over mature orchards than in adjacent farmlands. The LOC content and CMI value also had an increasing trend, while soil enzyme activities showed different response patterns. There were significant correlations between soil enzyme activities, SOC fractions, and CMI value (P < 0.05). We concluded that farmland conversion to apple orchard affected soil quality by reducing SOC stocks in the soil profile and changing SOC content as well as soil enzyme activities at various depth intervals. Long‐term apple cultivation was effective to restore SOC stocks, although it took over a decade to rebuild a new increasing trend after farmland conversion.     

土壤水解酶活性测定方法的研究进展

土壤水解酶直接参与有机物质的矿质化过程,对维持生态系统碳和养分的循环过程起重要作用。但不同研究者和实验室测定过程的差异,常给土壤酶测定方法的选定带来困难。针对这一问题,本文围绕土壤酶活性测定过程中样本贮存方式、酶底物选择以及培养条件等,对近二十多年来的研究成果进行了评述。土壤酶来源广泛,存在形式复杂,直接提取土壤酶还有很大的难度。目前土壤酶活性的测定主要是通过一定量底物在酶催化反应过程中的生成物或剩余物量来实现。基于对硝基酚衍生物为底物的分光比色法,因其成本低廉而被广泛使用。针对国际上未能建立统一的测定方法而导致研究数据之间难以进行比较的现状,作者认为现阶段土壤水解酶测定过程中应注意以下几点:1)尽量采用新鲜土样或短时间低温冷藏的土样;2)酶底物种类的选择应与国际接轨,采用饱和底物浓度使其反应速度接近最大值;3)缓冲液的pH值可与土壤pH值相近;4)4 h内培养的土壤酶,可忽略微生物抑制剂的使用。建议我国在近期内:1)应丰富土壤水解酶种类的研究;2)注重灵敏度高、需样量小以及培养时间短的荧光分析技术的应用;3)在强化典型土壤酶动力学特征研究基础上,尽快规范土壤酶活性的测定方法。     

Quantifying the interactions of land management practices and agricultural productivity using a soil quality index

It is desirable to develop an objective Soil Quality Index (SQI) to guide sustainable agronomic intensification, thereby promoting socio‐economic well‐being. This study pioneers the use of Ward's cluster and principal component regression methods to evaluate soil homogeneity and construct a SQI (expressed as %). Field data were acquired from five different sites within Ohio, USA, that were under no‐till (NT), conventional till (CT) management and natural vegetation (NV) land use. Soil pH, carbon/nitrogen (C/N) ratio, nitrate and soil organic carbon (SOC) concentrations were identified as primary drivers of soil quality. Based on Ward's cluster method, the soil properties of croplands were not significantly different from those under NV land use. However, SQI ranked surface soils under CT management as higher in quality than NV and NT managed soils, respectively. The coefficient of determination (R²) between SQI and corn (Zea mays L.) and soya bean [Glycine max (L.) Merr.] yields was 0.7 and 0.9, respectively, implying this SQI effectively relates soil properties, a function of anthropogenic land management practices, with crop yields. In future, time series analyses will be used to assess SQI versus crop yield dynamics, with key socio‐economic and climate variables.