Soil Microbial Community Composition and Diversity in the Rhizosphere of a Chinese Medicinal Plant

Rehmannia glutinosa is an important medicinal plant, but there is a serious problem of decreasing productivity with its continuous cropping on the same land. We hypothesize some relationships between this problem and the disturbed soil ecosystem. In this work, two community‐based microbiological measurements, community‐level physiological profiling (CLPP) using Biolog sole carbon (C) source utilization tests and phospholipid ester–linked fatty acid (PLFA) profiles, were used to evaluate soil microbial community function and composition of different R. glutinosa cropping soils. Field investigation showed that the problems with continuous cropping occurred not only in 2‐year continuous fields but also in 5‐year rotation fields. Soil basal respiration and metabolic quotient were significantly greater in R. glutinosa cropping soils than in the noncropping controls. In contrast, the Shannon index from the Biolog data set was lower in R. glutinosa cropping soils. Both CLPP‐ and PLFA‐based principal component analyses (PCA) showed distinct groupings of soil microbial communities in R. glutinosa rhizosphere, and 11 PLFAs representing different microbes were identified from the principal component scores of PLFAs. Among these, an abundance of PLFA 18:2ω6,9, which is a biomarker of soil fungi, was significantly higher in R. glutinosa cropping soils than control soils. These results suggest an alteration of soil microbial community following R. glutinosa cropping, and this might be an important reason for the constraints associated with continuous cropping.     

Assessing Farmers' Knowledge of Weed Species,Crop Type and Soil Management Practices in Relation to Soil Quality Status in Mai‐Negus Catchment,Northern Ethiopia

Soil quality (SQ) assessment from farmers' point of view can be used as a primary indicator for planning sustainable agriculture. Despite this fact, limited information is documented with regard to SQ indicators, for example weed species, crop types and management practices from farmers' knowledge perspectives. The aims of this study are to analyse factors that determine farmers' knowledge of SQ, identify SQ indicators of weed species and crop types across different SQ status and assess soil‐and‐crop management practices that maintain SQ in the Mai‐Negus catchment, northern Ethiopia. Fifty‐two farmer household heads were chosen randomly for questionnaire interview. The results showed significant (p ≤ 0·05) differences in the proportion of respondents who used different crop‐and‐soil management practices. The success of overall prediction by the logistic regression model (model χ² = 0·84, p < 0·01) and level of model correct predictions (86%) indicated that the explanatory variables have sufficiently explained farmers' knowledge of SQ indicators. Provided that other conditions remained constant, the odds ratio of variables such as farmer experience, access to information, farm location, education, field slope and land tenure have significantly increased the likelihood of farmers for being knowledgeable of SQ indicators. This study also demonstrated that most farmers are knowledgeable in identifying weed species, crop types and management practices across various SQ status, which suggests that such SQ indicators should be used to assess SQ status (degradation severity) while locating fields to be intervened using appropriate management strategies. © 2013 The Authors. Land Degradation & Development published by John Wiley & Sons, Ltd.     

基于主成分-聚类分析评价不同轮作模式对土壤肥力的影响

为探明我国西北半干旱区"粮经饲"不同轮作模式的土壤肥力效应,于2017年在宁夏自治区固原市原州区设置玉米-豌豆(C-Pe)、玉米-玉米(C-C)、2龄苜蓿(2A)、高粱-马铃薯(B-Po)、燕麦-玉米(O-C)、马铃薯-燕麦(Po-O)、豌豆-高粱(Pe-B)7种轮作处理模式,研究了不同粮草轮作模式土壤养分、酶活性及可培养微生物群落特征,并进行土壤肥力综合评价。结果表明:(1)不同轮作处理模式对土壤养分影响显著,与其他轮作模式相比,2A模式更有利于土壤养分的累积,而C-C模式增加了对养分的消耗,C-Pe和Po-O模式的有机质、全氮、速效氮、速效磷和速效钾含量高于B-Po和O-C模式,轮作处理对全钾含量影响较小。(2)不同轮作处理模式对土壤酶活性影响显著,2A模式较其他轮作模式显著增加了土壤脲酶和蔗糖酶活性(P<0.05),C-C模式土壤酶活性最低。O-C和Pe-B模式的蔗糖酶、脲酶和碱性磷酸酶活性高于B-Po模式。(3)不同轮作处理模式对土壤可培养微生物数量影响显著,且各轮作模式下土壤微生物数量以细菌占绝对优势,放线菌次之,真菌数量最少,并有明显的土层垂直分布规律,与其他轮作模式相比,2A、C-C和B-Po模式的细菌数量和微生物总数量显著下降(P<0.05),真菌数量显著增加(P<0.05),O-C模式的细菌数量和微生物总数量明显增加,真菌数量降低。(4)运用主成分分析-数值聚类方法对不同轮作模式下土壤养分、土壤酶活性、土壤微生物数量的15个指标进行土壤肥力综合评价,主成分分析提取的2个主成分累计贡献率达89.38%,第1主成分以土壤有机质、全氮、速效氮、全磷、速效磷、速效钾、蔗糖酶、脲酶和碱性磷酸酶贡献最大,达63.56%,第2主成分以细菌数量、真菌数量和微生物总数贡献最大,达25.82%,且各轮作模式在2个主成分上的综合得分排名为2A>Pe-B>C-Pe>O-C>Po-O>B-Po>C-C。再以2个主成分得分进行聚类,将7个模式共分为3类,第1类(2A)土壤综合肥力最好;第2类(Pe-B、O-C、C-Pe、Po-O、B-Po)土壤综合肥力较好;第3类(C-C)土壤综合肥力较差。研究结果为当地耕作方式改良提供理论依据和实践指导。     

Soil‐quality‐index model for assessing the impact of groundwater on soil in an intensively farmed coastal area of E China

Soil quality is important in measuring sustainable land‐use and soil‐management practices. It is usually assessed by evaluating important physical, chemical, and biological soil properties. For this study, a site‐specific 22 variables representing pertinent soil (0–10 cm) and groundwater properties were selected as potential soil‐quality indicators in a coastal salt‐affected farmland of E China. To investigate the role of groundwater in soil‐quality assessment, we designed two sets of minimum data sets (MDSs). Minimum data set 1 (MDS1) had inputs of the 19 soil chemical and physical properties whereas MDS2 was based on the 22 soil and groundwater properties. Using principal‐component analysis, discriminant analysis, and soil‐quality‐index (SQI) model, we demonstrated the procedures of MDS selection, indicator normalization, and integration of MDS into SQI value for soils used for the two cropping systems. Results indicated selection of SOCD, AK, and ρ_b as MDS1 indicators but MDS2 indicators included SOM, SOCD, Cl, Na, WT_g, and EC_g. These were found to be the most effective discriminators between the two cropping systems. Available K (AK) made greatest contribution to SQI using MDS1 indicators, however, WT_g, EC_g, and Cl were the greatest contributors to the SQI for MDS2. Contribution of SOCD to SQI was severely inhibited in cotton–barley rotation system while EC_g and WT_g contributions to SQI were inhibited in rice–rape rotation system. In general, cotton–barley rotation system had a better soil quality over rice–rape rotation system as the former had higher SQI values than the latter for both MDSs. Crop parameters did also exhibit significant relationship with the SQI values using MDS2 but it was not significant for MDS1. Our results suggest that in addition to soil chemical, physical, and biological indicators, groundwater properties particularly the WT_g and EC_g are also important for assessing soil quality in an intensively farmed coastal area.     

Conservation Tillage,Rotations, and Cover Crop Affecting Soil Quality in the Tennessee Valley: Particulate Organic Matter,Organic Matter,and Microbial Biomass

Abstract

The impact of conservation tillage, crop rotation, and cover cropping on soil‐quality indicators was evaluated in a long‐term experiment for cotton. Compared to conventional‐tillage cotton, other treatments had 3.4 to 7.7 Mg ha^?1 more carbon (C) over all soil depths. The particulate organic matter C (POMc) accounts for 29 to 48 and 16 to 22% of soil organic C (SOC) for the 0‐ to 3‐and 3‐ to 6‐cm depths, respectively. Tillage had a strongth influence on POMc within the 0‐ to 3‐cm depth, but cropping intensity and cover crop did not affect POMc. A large stratification for microbial biomass was observed varing from 221 to 434 and 63 to 110 mg kg^?1 within depth of 0–3 and 12–24 cm respectively. The microbial biomass is a more sensitive indicator (compared to SOC) of management impacts, showing clear effect of tillage, rotation, and cropping intensity. The no‐tillage cotton double‐cropped wheat/soybean system that combined high cropping intensity and crop rotation provided the best soil quality.     

Soil organic carbon,nitrogen, and phosphorus distribution in stable aggregates of an Ultisol under contrasting land use and management history

Different land‐use affects the organization of mineral soil particles and soil organic components into aggregates and the consequent arrangement of the aggregates will influence essential ecosystem functions. We investigated a continuous rubber plantation (forested), land fallowed for 10 y (fallow), 10‐y continuous arable cropping land and cropped land with top soil removed (TSR) for concentrations of C, N, and P in bulk soil and dry aggregates. Results showed that a high level of soil disturbance decreased the proportion of surface (0–15 cm) soil aggregate stability (low mean weight diameter) in TSR by 149% and arable cropping by 125% compared with the forested. Aggregate associated SOC was higher in aggregate‐size fractions of forested land‐use when compared with that in 10‐y fallow, continuous arable cropping, and TSR. For aggregate associated N, fallow and forested land‐use types concentrated higher proportion across aggregate sizes than the arable cropping and TSR. Macro aggregate fractions generally contained higher concentrations of C, N, and P compared with the micro‐aggregates. Water transmission indicators like total porosity and saturated hydraulic conductivity recorded higher values with forested and fallow land‐use than the others. We can thus conclude that long‐term soil disturbance due to cultivation and removal of top soil reduces the accumulation of soil C, N, and P in bulk soil and decreases water transmission properties. On the other hand, aggregate‐associated C, N and P accumulations are dependent on the level of soil surface disturbance and aggregate sizes.     

Assessment of Horizantal and Vertical Variabilities of Soil Quality using Multivariate Statistics and Geostatistical Methods

The aim of this study is to examine the horizantal and vertical spatial changes of soil quality (SQ) in rice-cultivated soils located on the Bafra Deltaic Plain—one of the most important alluvial deltaic plains and production centers of Turkey. The study examines these spacial changes by calculating the soil quality index (SQI) for soils 0–30 cm and 30–60 cm deep. For SQI calculations, seventeen potential physicochemical SQ indicators of eighty-three soil samples were assessed. Quality indicators to be used in these calculations were selected by considering the clay content, correlation relationship, and principal components analysis (PCA) of potential quality indicators. Clay, silt, sand, electrical conductivity (EC), exchangeable calcium (Ca_exc), and exchangeable magnesium (Mg_exc) were selected as quality indicators, and silt was found to be the most important quality indicator for both soil depths. The SQ of researched soils changed from low to high for both soil depths.     

Long‐Term Durum Wheat‐Based Cropping Systems Result in the Rapid Saturation of Soil Carbon in the Mediterranean Semi‐arid Environment

Climate, soil physical–chemical characteristics, land management, and carbon (C) input from crop residues greatly affect soil organic carbon (SOC) sequestration. According to the concept of SOC saturation, the ability of SOC to increase with C input decreases as SOC increases and approaches a SOC saturation level. In a 12‐year experiment, six semi‐arid cropping systems characterized by different rates of C input to soil were compared for ability to sequester SOC, SOC saturation level, and the time necessary to reach the SOC saturation level. SOC stocks, soil aggregate sizes, and C inputs were measured in durum wheat monocropping with (Ws) and without (W) return of aboveground residue to the soil and in the following cropping systems without return of aboveground residue to soil: durum wheat/fallow (Wfall), durum wheat/berseem clover, durum wheat/barley/faba bean, and durum wheat/Hedysarum coronarium. The C sequestration rate and SOC content were lowest in Wfall plots but did not differ among the other cropping systems. The C sequestration rate ranged from 0.47 Mg C ha⁻¹ y⁻¹ in Ws plots to 0.66 Mg C ha⁻¹ y⁻¹ in W plots but was negative (−0.06 Mg C ha⁻¹ y⁻¹) in Wfall plots. Increases in SOC were related to C input up to a SOC saturation value; over this value, further C inputs did not lead to SOC increase. Across all cropping systems, the C saturation value for the experimental soil was 57.7 Mg ha⁻¹, which was reached with a cumulative C input of 15 Mg ha⁻¹. Copyright © 2015 John Wiley & Sons, Ltd.     

Short-term effect of cultivation and crop rotation systems on soil quality indicators in a coastal newly reclaimed farming area

Purpose

Soil quality (SQ), a measure of the sustainability of land use and soil management practices, can be assessed by indicators including soil physical, chemical, and biological properties. Our primary objectives were to investigate the influence of consecutive cultivation and different crop rotation systems on individual SQ indicators and to examine the impact of rotation systems on SQ using soil quality index (SQI) model.

Materials and methods

A site-specific selection of 17 potential SQ indicators representing soil chemical and physical attributes (0–10 cm) and groundwater features on 60 sampling locations and 10 representative soil profiles was chosen in a typical coastal newly reclaimed farmland of north Jiangsu Province, China. Using ANOVA analysis, the crop rotation effect was analyzed by comparing SQ indicators between rice/rape rotation soil and cotton/barley rotation soil. An overall SQI was calculated to examine whether plant biomass indices exactly responded to the SQI value.

Results and discussion

Results indicated that cultivation had significant effect on some soil profile characteristics, including SOM, SOCD, AP, CEC, AK, EC_e, and I _f. Crop rotation systems also had significant influence on some SQ indicators. Compared with cotton/barley rotation soil, rice/rape rotation soil was characterized by higher organic matter, undifferentiated nutrient storage and salinity/alkalinity, lower water accommodation and infiltration, and adverse groundwater conditions. Cotton/barley rotation had higher SQI values over rice/rape rotation (0.523 vs. 0.422). SQ indicators of SAR_e, EC_e, and WT_g contributed the most to the overall SQI value for each rotation system. Plant biomass indices significantly correlated with the SQI values for both rotation systems, suggesting that the SQI values essentially reflected the status of SQ.

Conclusions

Such results allowed us to conclude that cotton/barley rotation system contributed more to the improvement of SQ than rice/rape rotation system in coastal farming area. Also, we suggested SOCD, AK, ρ _b, WT_g, and EC_g as the minimum data set for SQ assessment, as they had potential in discriminating the effect of rotation systems on SQ between the rotation systems used here.     

Effect of Cropping System on Physical Properties of Clay Soil Under Intensive Rice Cultivation

Cropping systems are thought to alter soil quality in paddy rice fields. This study was conducted to quantify the long‐term effects of continuous crop production under different cropping systems with different crop rotations on physical properties of alluvial clay soil in the Mekong Delta, Vietnam. Soil samples were collected from four treatments: (i) traditional intensive rice monoculture with three rice crops per year (R–R–R); (ii) rotation with two rice crops and maize (R–M–R); (iii) rotation with two rice crops and mung bean (R–Mb–R); and (iv) rotation with one rice and two upland crops, mung bean and maize (R–Mb–M). We hypothesized that cropping systems with rotations of upland crops and their temporary beds improve the physical quality of paddy rice soil; hence, they are better options towards sustainable agriculture. Results show an improvement of soil physical quality for systems with two rice crops and one upland crop (R–M–R and R–Mb–R) and those with one rice crop with two upland crops (R–Mb–M) compared with intensive rice monoculture (R–R–R). This was translated in decreased bulk density and soil strength, increased soil organic carbon and total porosity, and higher aggregate stability index, plant‐available water capacity, and Dexter's S index, especially at depths of 10–20 and 20–30 cm. The systems with different upland crops (maize or mung bean) showed similar high physical quality improvement. To maintain soil quality in future seasons, introducing a cropping system with at least one upland crop in rotation with rice is recommended. Copyright © 2014 John Wiley & Sons, Ltd.     

Soil Quality Indicators in Relation to Land Use and Topography in a Small Catchment on the Loess Plateau of China

Better understanding of how the loess soils respond to topography and land use under catchment‐scale vegetation restoration is needed to enable science‐based land management interventions for the policy‐driven “Grain‐for‐Green” eco‐restoration program in the Loess Plateau of China. The objective of this study was to characterize the relationships of four selected soil quality indicators to land use under vegetation restoration and topography for a small catchment (0·58 km²) in the Loess Plateau. The major land uses established in the catchment are cropland, fallow (i.e., natural revegetation), grassland, and jujube orchard. The four soil quality indicators were soil organic carbon (SOC), soil total nitrogen (STN), soil total phosphorus (STP), and mean root zone soil water content during the wet season (MRZSWwet). SOC, STN, and MRZSWwet were significantly different (p < 0·05) for different land uses. Grassland showed the highest values for these three properties, whereas cropland had relatively low values for SOC and STN. Land use had no effect on STP, although the lowest value was observed in grassland. Spatial analysis showed that various relations between soil quality indicators and topography (slope and elevation) were observed. These relations were generally weak for most of them, and they varied with land uses. Further analyses indicated that land uses, slope, and elevation had significant effects on the relations between different soil quality indicators. The results here should provide useful information for the further development of “Grain‐for‐Green” program. Copyright © 2012 John Wiley & Sons, Ltd.     

山药连作对土壤微生物群落及土壤酶活性的影响

以山药连作（0 a,1 a,2 a）和轮作（山药—小麦）土壤为研究对象,探讨耕作模式对山药种植地耕层土壤（0—30 cm）微生物数量和酶活性的影响。结果表明:土壤耕层的有机质、全氮、有效磷和速效钾含量随山药连作年限的延长而逐渐降低,而山药—小麦轮作模式则有助于恢复地力。山药连作、轮作的土壤均以细菌所占比例最大,放线菌次之,真菌最少;与对照（0 a）相比,细菌、放线菌数量均随着山药连作年限增加呈递减趋势;但放线菌的降幅明显大于细菌,表现出对连作年限更强的敏感性;真菌数量随连作年限呈先升后降的趋势。山药连作可以明显降低土壤脲酶、碱性磷酸酶和蔗糖酶的活性,轮作模式则可以激发该三种酶的活性,其中轮作较连作2 a的处理可以明显提高脲酶和蔗糖酶活性,差异分别达显著水平（p < 0.05）和极显著水平（p < 0.01）。说明山药连作会破坏土壤耕层微生物种群结构,并抑制土壤酶活性,轮作可以在一定程度上改善土壤微生物群落结构及酶活性质量。     

Temporal Variation of Hydro‐Physical Properties of Paddy Clay Soil under Different Rice‐Based Cropping Systems

Spatial variability of hydro‐physical properties has long been observed, whereas temporal variation is much less documented and considered in studies and applications, particularly of paddy clay soils under different cropping systems. The objective of this study was therefore to assess the seasonal‐ and inter‐seasonal variation of selected hydro‐physical properties of a paddy clay soil under different rice‐based cropping systems with contrasting tillage. In a long‐term experiment, plots were arranged in a randomized complete block design with four treatments and four replications: (i) rice–rice–rice; (ii) rice–maize–rice; (iii) rice–mung bean–rice; and (iv) rice–mung bean–maize. Soil samples were collected at three depths (0–10, 10–20 and 20–30 cm) at three times during two cropping seasons, i.e., 15 days after soil preparation (DASP), 45 DASP and 90 DASP during the winter–spring and spring–summer seasons. Results show that temporal variability of soil bulk density, macro‐porosity (MacP) and matrix‐porosity within both seasons and between seasons was limited for cropping systems with upland crop rotations, whereas within season variation was significant for rice monoculture system. Observed variation in bulk density, matrix‐porosity and MacP was mainly associated with cropping system and soil depth. Field saturated hydraulic conductivity of topsoil showed great temporal variability, both seasonal and inter‐seasonal, in correspondence with MacP (r  = 0·58). These results highlight the need of depth differentiated soil sampling and time consideration when evaluating management practices on soil physical properties and modeling the hydrological behavior of paddy soil. Copyright © 2017 John Wiley & Sons, Ltd.     

Soil quality assessment based on soil organic matter pools under long-term tillage systems and following tillage conversion in a semi-humid region

A field study was conducted to assess the long-term effects of no-tillage (NT) and conventional tillage (CT), and the short-term effects following tillage conversion from CT to NT (NT_n) and from NT to CT (CT_n) on soil quality (SQ) indicators in a semi-humid climate. First, plots of a long-term tillage experiment on a Luvic Phaeozem initiated in 1986 were split into two subplots in 2012, yielding four treatments: NT, CT, NT_n and CT_n. In 2015, composite soil samples were collected from each treatment and from a natural site (Ref) at depths 0–5, 5–10, 10–20 and 0–20 cm. Several indicators were determined: soil organic carbon (SOC) and nitrogen (SON); particulate organic C (POM-C) and N (POM-N); potential N mineralization (PMN) and soil respiration (R_s). Moreover, bulk density was determined in long-term tillage systems. Different ratios between indicators were calculated, with emphasis on its function in the agroecosystem, that is functional indicators. Significant differences in SOC, SON and PMN were found between CT and NT at most depths. In contrast, 3 years after tillage conversion, only a part of the SQ indicators studied were modified mainly at the 0–10 cm depth. The functional indicators showed differences between tillage systems in the long-term and after short-term tillage conversion depending on the depth; however, the PMN/SON ratio demonstrated differences at all depths. Under these conditions, this ratio-related to easily mineralizable N fraction proved to be a promising indicator for assessing SQ under contrasting tillage systems regardless of the sampling depth.     

科尔沁沙地南缘樟子松人工林对土壤水盐的影响

为掌握科尔沁沙地南缘樟子松造林40多年对土壤水分、盐度的影响。以科尔沁沙地樟子松林地、草地2020年3月至2021年11月土壤、气象数据为基础，采用双累积曲线法(DCM)验证样地选取的合理性，利用空间代替时间法(STM)研究樟子松林地、草地土壤含水量、盐度的变化规律，以及与气象因子关系的差异。樟子松林地改变了土壤纵向剖面水分、盐度分布规律，二者均趋于正“S”形分布；林地有效提高土壤储水量(p<0.05),降低土壤盐度，缩减水分次活跃层范围；林地土壤水分变异性更高(p<0.05),盐度变异性更低(p>0.05);林地的气象因子与土壤水分、盐度指标各分项之间关联程度与草地不同，减弱与降雨的相关性，增加与水汽压亏缺的相关系数。樟子松林生态系统具有较强的涵养水源、抑制土壤盐渍化的功能。     

Soil Organic Carbon and Nitrogen Fractions in Temperate Alley Cropping Systems

Abstract

Alley cropping may promote greater sequestration of soil organic carbon. The objective of this study was to examine spatial variability of soil organic carbon (C) and nitrogen (N) fractions relative to tree rows in established alley cropping systems in north central Missouri. Soils were collected to a depth of 30 cm from two alley cropped sites, a 19‐yr‐old pecan (Carya illinoinensis)/bluegrass (Poa trivialis) intercrop (pecan site) and an 11‐yr‐old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (maple site). Particulate organic matter (POM) C constituted 15–65% and 14–41% of total organic C (TOC) at the pecan and maple sites respectively, whereas POM N comprised 3 to 24% of total N (TKN). TOC and TKN were on average 13% and 18% higher at the tree row than at the middle of the alley for surface soils (0–10 cm) at the pecan site, respectively. Similarly, POM C was two to three times higher at the tree row than the alley for subsurface soils at the maple site. No differences in microbial biomass C and N between positions were observed. Observed results suggest the existence of spatially dependent patterns for POM C, TOC, and TKN, relative to tree rows in alley cropping.     

Soil carbon as affected by cover crops under no‐till under tropical climate

In tropical, low‐fertility soils, crop yields are dependent on soil carbon, and cropping systems under no‐till can increase soil C stocks. Plant residues supplied by cover crops in no‐till systems may improve aggregate stability and soil carbon, which may be further increased with the introduction of a legume in the cropping system. This research studied the effects of cover crops in rotation with soybean under no‐till on soil carbon and nitrogen, in Botucatu, Brazil, for 3 yr. The cover crops were millet (Penninsetum americanum Leek), cober crop (Sorghum bicolor × Sorghum sudanense) and sunn hemp (Crotalaria juncea L.), grown in the spring. Fallow without cover crops was used as a control. Grain sorghum (Sorghum bicolor L. Moench) and soybean (Glycine max (L.) Merril) were grown in fall–winter and summer, respectively. Generally, cover crops increased soil carbon contents, but soil N was only increased by sunn hemp in the particulate organic C fraction. An increase in the labile carbon fraction in the topsoil layers was closely related to cover crop root development. Fallow in spring should not be recommended in degraded soils with lowcarbon stock. Labile‐fractioned soil organic carbon and total carbon levels are more efficiently increased by grasses than by legumes in the short term, and grasses cropped in spring increase soil C/N ratio. Conversely, the introduction of a legume (sunn hemp) maintained a more stable C/N ratio, that is around 10, which would be more effective in increasing soil C in the long term.     

Bare Soil Reflectance to Characterize Variability in Soil Properties

Remote sensing allows for the rapid and inexpensive acquisition of soil reflectance data. Knowing what soil parameters have the greatest influence on bare soil imagery will facilitate better use of remote sensing for precision crop management. The objectives of this study were (i) to determine measured soil properties that are most influential on remotely sensed bare soil reflectance and (ii) to select which spectral band or combination of spectral bands is best for describing individual soil properties. This study was conducted on three study sites located in northeastern Colorado. All sites were in irrigated continuous corn (Zea mays L.) cropping systems. Remotely sensed imagery was acquired by aircraft prior to planting. Soil samples were collected and analyzed for bulk density, soil color (moist and dry), organic matter, organic carbon, soil texture, and cone index. Principal component analysis (PCA) was performed for the green, red, and near-infrared (NIR) bands of the imagery. Least-squares regression analysis was used for analyzing relationships between remote sensing data and soil data. Across study sites, the first principal components of the green, red, and NIR bands were found to have significant statistical relationships with organic carbon and sand, silt, and clay fractions. Individual spectral bands explained a significant portion of the variability in soil moisture, moist soil color, dry soil color, organic carbon, sand, silt, and clay. Results from this study support the use of remote sensing for assessment of soil variability.     

Degradation and abandonment of mechanized rain‐fed agricultural land in the Southern Gadarif region,Sudan: the local farmers' perception

In the Gadarif Region of Sudan, destruction of the natural vegetation for agricultural expansion is one of the major causes of the degradation of renewable resources and the environment. This study identifies and analyses the farmers' attitudes and perceptions towards agricultural land degradation and abandonment. The cross‐sectional data collected from ten key informants and 41 large‐scale farmers focussed on the degradation and abandonment of mechanized agricultural land. The results of the study show that the respondents are well aware that soil degradation is in various forms are taking place on their cultivated agricultural land. This is based on their perception and interpretation of indicators such as weed infestation, poor soil fertility and soil compaction. Continuous cropping, mono‐cropping, rainfall shortage and the use of inferior seeds are the main reasons of land degradation as indicated by farmers. The main measures acknowledged to maintain and improve land productivity are repeated soil ploughing, abandonment/fallow periods and crop rotation. The study adduces evidence of widespread land degradation. The mitigation measures followed by the farmers may though not be sufficient to restore the soil fertility. The application of appropriate chemical fertilizers, sound crop rotation and long fallow periods can be recommended. Any management and research intervention regarding the problem of land degradation should; however, be concerted with the farmers' knowledge. Copyright © 2009 John Wiley & Sons, Ltd.     

Deforestation and land-use effects on soil degradation and rehabilitation in western Nigeria. II. Soil chemical properties

Temporal changes in soil chemical and nutritional properties were evaluated in a long-term experiment conducted on Alfisols in West Africa. Effects of land use and cropping duration on soil chemical properties at 0–5 cm and 5–10 cm depths were evaluated for five treatments: (1) alley cropping with Leucaena leucocephala established on the contour at 4-m intervals; (2) mucuna (Mucuna utilis) fallowing for 1 year followed by maize (Zea mays)-cowpea (Vigna unguiculata) cultivation for 2 years on severely degraded land; (3) fallowing with mucuna on moderately degraded soils; (4) ley farming involving growing improved pastures for 1 year, grazing for the second year, and growing maize-cowpea for the third year on severely degraded land; (5) ley farming on moderately degraded soils. Soil chemical properties were measured once every year from 1982 through 1986 during the dry season, and included pH, soil organic carbon (SOC), total soil nitrogen (TSN), Bray-P, exchangeable cations, and effective cation exchange capacity (CEC). Regardless of the cropping system treatments, soil chemical quality decreased with cultivation time. The rate of decrease at 0–5 cm depth was 0·23 units year⁻¹ for pH, 0·05 per cent year⁻¹ for SOC, 0·012 per cent year⁻¹ for TSN, 0·49 cmol kg⁻¹ year⁻¹ for Ca²⁺, 0·03 cmol kg⁻¹ year⁻¹ for Mg²⁺, 0·018 cmol kg⁻¹ year⁻¹ for K⁺, and 0·48 cmol kg⁻¹ year⁻¹ for CEC. Although there was also a general decrease in soil chemical quality at 5–10 cm depth, the trends were not clearly defined. In contrast to the decrease in soil properties given above, there was an increase in concentration at 0–5 cm depth of total acidity with cultivation time at the rate of 0·62 cmol kg⁻¹ year⁻¹, and of Mn³⁺ concentration at the rate of 0·081 cmol kg⁻¹ year⁻¹. Continuous cropping also increased the concentration of Bray-P at 0–5 cm depth due to application of phosphatic fertilizer. Trends in soil chemical properties were not clearly defined with regards to cropping system treatments. In general, however, soil chemical properties were relatively favorable in ley farming and mucuna fallowing treatments imposed on moderately degraded soils. Results are discussed in terms of recommended rates of fertilizer use, in view of soil test values, expected yields, and critical limits of soil properties.