Land-use effects on organic matter and physical properties of soil in a southern Mediterranean highland of Turkey

Forest and grassland soils in highlands of southern Mediterranean Turkey are being seriously degraded and destructed due to extensive agricultural activities. This study investigated the effects of changes in land-use type on some soil properties in a Mediterranean plateau. Three adjacent land-use types included the cultivated lands, which have been converted from pastures for 12 years, fragmented forests, and unaltered pastures lands. Disturbed and undisturbed soil samples were collected from four sites at each of the three different land-use types from depths of 0–10 cm and 10–20 cm in Typic Haploxeroll soils with an elevation of about 1400 m. When the pasture was converted into cultivation, soil organic matter (SOM) pool of cultivated lands for a depth of 0–20 cm were significantly reduced by, on average 49% relative to SOM content of the pasture lands. There was no significant difference in SOM between the depths in each land-use type, and SOM values of the forest and pasture lands were almost similar. There was also a significant change in soil bulk density (BD) among cultivation (1.33 Mg m⁻³), pasture (1.19 Mg m⁻³), and forest (1.25 Mg m⁻³) soils at depth of 0–20 cm. Only for the pasture, BD of the depth of 0–10 cm was significantly different from that of 10–20 cm. Depending upon the increases in BD and disruption of pores by cultivation, total porosity decreased accordingly. Cultivation of the unaltered pasture obviously increased the soil erodibility measured by USLE-K factor for each soil depth, and USLE-K factor was approximately two times greater in the cultivated land than in the pasture indicating the vulnerability of the cultivated land to water erosion. The mean weight diameter (MWD) and water-stable aggregation (WSA) were greater in the pasture and forest soils compared to the cultivated soils, and didn’t change with the depth for each land-use type. Aggregates of >4.0 mm size were dominant in the pasture and forest soils, whereas the cultivated soils comprised aggregates of the size ≤0.5 mm. I found that samples collected from cultivated land gave the lowest saturated hydraulic conductivity values regardless of soil depths, whereas the highest values were measured on samples from forest soils. In conclusion, the results showed that the cultivation of the pastures degraded the soil physical properties, leaving soils more susceptible to the erosion. This suggests that land disturbances should be strictly avoided in the pastures with the limited soil depth in the southern Mediterranean highlands.     

Soil Property Changes After Conversion from FOrest to Pasture in Mount Sacinka,Artvin, Turkey

Turkey's forests have been continuously facing conversion into both agriculture and pasturelands, causing not only degradation and fragmentation of forested lands but also negative changes in soil properties that have not been thoroughly investigated. In order to determine possible changes in some physical and hydrophysical soil parameters along with the dispersion ratio between natural coppice forests and the neighbouring forest‐to‐grassland converted areas, a foothill of Mount Sacinka in Artvin was chosen as a research area. Besides land use, possible effects of elevation change on soil properties due to the mountainous and moderately steep landscape of the region were also taken into consideration. The soil samples were analysed for soil texture, permeability, field capacity, bulk density, organic matter, pH and dispersion ratio. The results indicated that whereas permeability (43·05 mm h⁻¹ in forest and 18·82 mm h⁻¹ in pasture), field capacity (43·45% in forest and 38·08% in pasture) and organic matter (6·36% in forest and 5·34% in pasture) values turned out to be higher in forest soils, bulk density (0·91 g cm⁻³ in forest and 1·06 g cm⁻³ in pasture) and pH (5·89 in forest and 6·55 in pasture) values were low in grassland soils, meaning that conversion has negative effects on soil properties. Additionally, the mean dispersion ratios of 27·55% and 33·58% for forest and pastureland soils, respectively, indicated soil erosion problems in both land uses. In addition, as for elevation effect, forest soils especially showed better characteristics at higher elevations with high permeability, field capacity and organic matter and low pH and dispersion ratio. Copyright © 2015 John Wiley & Sons, Ltd.     

Changes in Physical Properties of Soils with Land Use Time in the Brazilian Savanna Environment

Soils from central Brazil have been intensively used over the last decades because of the rapid conversion of savannas ( Cerrado ) into corn/soybean fields. The objective of this work is to study modifications in the physical properties of soils in the Rio Verde watershed, as a function of the land use time for agriculture, determined from classification of Landsat satellite images between 1980 and 2010. Soil samples were collected at surface (0–20 cm) and subsurface (20–40 cm) horizons for the different classes of land use time (<10, 10–20, 20–30, and >30 years). The following physical properties were measured: bulk density (BD), air permeability (K_a), penetration resistance (PR), microporosity (MI), macroporosity (MA), and total porosity (TP). Results showed a strong expansion with time of agriculture that occupied 35·3% (1980), 37·4% (1990), 51·3% (2000), and 60·9% (2010) of the watershed area. When properties were compared with those from the reference areas (preserved soils under native vegetation), significant differences were observed for all the physical attributes of soils for a land use time higher than 20 years. Overall, BD and PR increased with land use time, and the opposite was verified for K_a, MA, and TP. Some physical properties presented values (e.g., 1·54 g cm⁻³ for BD and 0.06 cm³ cm⁻³ for MA) close to the critical ones reported to affect crop development, but they were not still impacting on local soybean yield. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of organic versus conventional arable farming on soil structure and organic matter dynamics in a marine loam in the Netherlands

Abstract. We compared the effects of conventional and organic arable farming on soil organic matter (SOM) content, soil structure, aggregate stability and C and N mineralization, which are considered important factors in defining sustainable land management. Within one soil series, three different farming systems were selected, including a conventional and an organic arable system and permanent pasture without tillage. The old pasture represents optimal conditions in terms of soil structure and organic matter inputs and is characterized by high earthworm activity. More than 70 years of different management has caused significant differences in soil properties. SOM content, mineralization, earthworm activity and water-stable aggregation decreased as a result of tillage and arable cropping when compared with pasture, but were significantly greater under organic farming than under conventional farming. Total SOM contents between 0 and 20 cm depth amounted to 15, 24 and 46 g kg⁻¹ for the conventional arable, organic arable and permanent pasture fields, respectively. Although less sensitive to slaking than the conventionally managed field, the soil under organic farming was susceptible to compaction when high pressures were exerted on the soil under wet conditions. The beneficial effects of organic farming are generally associated with soil biochemical properties, but soil physical aspects should also be considered. Depending on soil type and climate, organic farmers need to be careful not to destroy the soil structure, so that they can enjoy maximum advantage from their organic farming systems.     

中国农耕区土壤有机质含量及其与酸碱度和容重关系

对我国农耕区土壤有机质区域变化及其与酸碱度和容重关系进行系统分析,为耕地地力提升和改善土壤结构提供支撑。基于国家级耕地长期定位监测点913个,统计分析全国及7大区域（东北NE、华北NC、西北NW、长江中游MYR、长三角YRD、华南SC、西南SW）耕层土壤有机质含量、酸碱度及容重变化特征。结果表明,全国农耕区耕层土壤有机质含量平均值为22.4~24.8 g/kg。其中有机质含量中等偏低的监测点位占比达72.5%。不同区域耕层土壤有机质含量差异显著（p<0.05）,MYR耕层土壤有机质含量显著高于其他6个区域。全国农耕区耕层土壤pH和容重平均分别为（6.90±1.20）,（1.30±0.15） g/cm³。不同土壤利用方式对土壤有机质、酸碱度及容重产生影响。水田耕层土壤有机质含量显著高于旱地,旱地耕层土壤pH和容重则显著高于水田。亚当斯方程和指数函数分别推荐拟合土壤容重对有机质含量响应关系（R²=0.09,RMSE=0.17,n=759）,以及土壤pH对土壤有机质含量响应（R²=0.16,RMSE=1.24,n=886）。全国农耕区耕层土壤有机质含量总体中等偏低,呈现出东南向西北依次降低趋势。土壤pH及容重与土壤有机质呈现显著的负相关关系。亚当斯模型及指数方程能较好地拟合土壤容重及pH对有机质的响应关系,可用于非线性插值法补充土壤容重及pH缺失值。     

Temporal variation of soil compaction and deterioration of soil quality in pasture areas of Colombian Amazonia

In the Amazon basin, tropical rainforest is being slashed and burned at accelerated rates for annual crops over a couple of years, followed by forage grasses. Because of poor management, the productivity of established pastures declines in a few years so that grazing plots are abandoned and new areas are deforested. Previous studies in the region report higher bulk density in soils under pasture than in similar soils under forest. The objective of this study was to detect changes in the physical quality of the topsoil of nutrient-poor Typic Paleudults in the colonisation area of Guaviare, Colombian Amazonia, and analyse the effect of soil deterioration on pasture performance. Temporal variation of soil compaction under pasture was analysed by comparing natural forest taken as control and pasture plots of Brachiaria decumbens (Stapf) grouped into three age ranges (<3, 3–9, >9 years). Evidence of soil compaction through cattle trampling, after clearing the primary forest, included the formation of an Ap horizon with platy structure and dominant greyish or olive colours, reflecting impaired surface drainage, the increase of bulk density and penetration resistance, and the decrease of porosity and infiltration rate. From primary forest to pastures older than 9 years, bulk density of the 5–10 cm layer increase was 42% in fine-textured soils and 30% in coarse-textured soils. Penetration resistance ranged from 0.45 MPa under forest to 4.25 MPa in old pastures, with maximum values occurring at 3–12 cm depth in pastures older than 9 years. Average total soil porosity was 58–62% under forest and 46–49% under pasture. Basic infiltration dropped from 15 cm h⁻¹ in the original forest conditions to less than 1 cm h⁻¹ in old pastures. Crude protein content and dry matter yield of the forage grass steadily decreased over time. No clear relationship between declining protein content as a function of pasture age and changes in chemical soil properties was found, but there was a high negative correlation (r=−0.81) between protein content and bulk density, reflecting the effect of soil compaction on pasture performance. After about 9–10 years of use, established grass did no longer compete successfully with invading weeds and grazing plots were abandoned. As land is not yet a scarcity in this colonisation area, degraded pastures are seldom rehabilitated.     

Soil structure changes due to different land-use practices in the central Zagruos region,Iran

In this study, the effect of land-use treatments and the feasibility of fractal dimension to quantify soil aggregate stability were investigated in the central Zagrous, Iran. For this purpose, the non-linear fractal dimension (D_nl), linear fractal dimension (D_l) and the mean weight diameter (MWD) of aggregates were compared. Soil samples from three sites with four adjacent land-use types, namely: forest area (F), cultivated lands adjacent to forest (CAF), pasture (P) and cultivated lands adjacent to pasture (CAP) were collected. Results showed that soils under cultivated lands had higher bulk density (BD) (1.30–1.38 Mg m^?3) compared to the adjacent soils under forest (1.19 Mg m^?3) and pasture (1.21 Mg m^?3). In the 0–15 cm layer, soil organic matter (SOM) content in the cultivated plots were respectively 30% and 31% lower compared to the forest and pasture soils. The lowest CVs belonged to D_nl (5–8%) demonstrating that D_nl was more accurate than D_l (8–14%) and MWD (30–53%) methods. CAP had the largest value of D_nl, while P had the smallest value of D_nl. Difference of D_nl between forest and pasture was not significant, whereas both of them significantly differed from CAF and CAP. D_l did not differ significantly between forest and CAF. There were significant differences between forest and pasture for the measured MWD. Both fractal dimensions had negative correlation with MWD, SOM, hydraulic conductivity (HC) and macroaggregates (>0.25 mm) and positive correlation with BD and total porosity (TP).     

Short-Term Impacts of Gray Water Irrigation on Soil Characteristics in Land-Treatment Vegetation Filters

This study on soil quality parameters was conducted from December 2008 to July 2010 to see the short-term impacts of gray water irrigation on physical and chemical properties of soil. The results envisaged slight positive impacts of wastewater irrigation on upper soil layers (0–30 cm) with an increase in soil organic matter (SOM) from 1.45% to 1.89% and nutrient content increases from 199 to 267 kg ha^?1 nitrogen (N), from 12.4 to 27.1 kg ha^?1 phosphorus (P), and from 131 to 136 kg ha^?1 potassium (K). Slight changes were also recorded in the soil pH and electrical conductivity (EC), which increased from 6.39 to 6.81 and 145 to 229 μS cm^?1 respectively, in the upper soil layers. The soil bulk density (BD) slightly decreased to 1.34 g cm³ in the treatment plot from 1.45 g cm³ at the commencement of the trial, which indicates good soil conditioning under the gray water irrigation trial.     

曲靖市耕地土壤有机质状况

2006—2011年,采集曲靖市耕地12个土类13 171个土壤样品,进行有机质测定,了解曲靖市耕地土壤有机质状况。结果表明,与第二次土壤普查结果相比,曲靖市耕地不同土类土壤有机质有升有降。其中,赤红壤、水稻土、紫色土、冲积土和燥红土有机质平均含量分别升高13.0%、16.8%、19.5%、52.5%和222.4%;而草甸土、黄壤、红壤、石灰(岩)土、黄棕壤、棕壤和沼泽土平均含量则分别降低了6.2%、17.7%、19.6%、32.3%、36.0%、42.9%和74.1%。从面积上来看,80.8%的旱作耕地土壤有机质平均含量低于第二次土壤普查结果,这意味着曲靖市旱作耕地土壤质量有所退化。耕地土壤管理中需加强绿肥生产利用、秸秆还田,提升土壤有机质。     

赣南地区稀土矿采矿迹地枯落物层和土壤层贮水功能研究

为探究赣南废弃稀土矿区土壤水源涵养功能,对其采矿迹地枯落物层和土壤层贮水功能采用环刀法进行研究。结果表明,不同采矿迹地0—30cm土层土壤含水量平均值表现为天然林地(180.37g/kg)>堆积地(170.67g/kg)>挖矿地(86.36g/kg);土壤容重平均值表现为堆积地(1.54g/cm^3)>挖矿地(1.31g/cm^3)>天然林地(1.20g/cm^3);土壤毛管孔隙度平均值表现为天然林地(44.08%)>堆积地(37.89%)>挖矿地(35.82%);土壤毛管蓄水量平均值表现为天然林地(440.77t/hm^2)>堆积地(378.94t/hm^2)>挖矿地(358.20t/hm^2)。土壤最大蓄水量的表现与土壤毛管蓄水量相似。不同采矿迹地涵养水源能力天然林地最强,其单位面积蓄水量为(561.34±44.32)t/hm^2,挖矿地最差,其值为(431.65±53.66)t/hm^2。由此可见,天然林地土壤水源涵养功能强于各采矿迹地,稀土矿区采矿作业对枯落物层和土壤层贮水功能影响较大。     

Effects of eucalyptus and coniferous plantations on soil properties in Gambo District,southern Ethiopia

Abstract

Plantation establishment using exotic species on disturbed cultivated and undisturbed primary forest soils is common in Gambo district, southern Ethiopia, but their effects on soil properties are not fully known. This study investigated the effects of plantation species on major soil physical and chemical properties and further evaluated the soil quality under different land uses. Soil samples in triplicates, collected under different plantations, were analysed for their physical and chemical properties. Based on these soil properties, an integrated soil quality index was determined. The soil bulk density (BD) varied from 0.72 to 0.80 cm^?3 in plantations established on primary forest land and natural forest and from 0.86 to 1.14 g cm^?3 in those plantations established on cultivated soils. Also significantly lower pore volume and infiltration rate were observed under plantations established on cultivated lands than those on primary forest soils. Higher water volume (% at ?1500 kPa matric potential) was obtained in soils under Juniperus procera and natural forest compared with that under the rest of the plantations investigated. The concentration of soil organic carbon (SOC) varied from 3.4 to 10.2%, N from 0.3 to 1.0% and Av.P from 1.5 to 7.0% in soils under plantations and natural forest. Exchangeable cations generally showed a decreasing trend with depth in all land use types with minor exceptions. The concentrations of exchangeable Ca⁺² varied from 6.5 to 22.7 cmol kg^?1 and were significantly higher under Juniperus procera than under Eucalyptus species. The soil under plantations on previously cultivated lands showed soil quality index below 0.5 (the baseline value), while those established on undisturbed forest soil were generally above that value. The study results suggest that selecting species such as Juniperus procera and prolonging the harvesting period would improve and maintain the quality of soil properties.     

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     

Lignin and carbohydrates in soils under secondary forest,alley-cropping,and continuous farming,Thailand

This study was designed to investigate the impact of three land-use practices in Thailand on soil organic matter (SOM) composition. The land uses were continuous farming (till), alley-cropping, and secondary forest. Samples, taken from the top 10 cm soil surface, were fractionated into clay- (< 2 μm), silt- (2–20 μm), and sand-sized particles (20–2000 μm) prior to analyses of C, N, lignin-derived phenols and individual carbohydrates. As particle size increased, the C/N ratio and the concentration of lignin-derived phenols increased, whereas the degree of lignin oxidation as well as ratios of microbially derived hexoses to plant-derived pentoses decreased. Thus, the coarser the particle size, the less the SOM was altered by microbes. Seven years of alley-cropping increased SOM levels only little but considerably affected SOM composition by affecting the SOM of the sand fraction. The SOM concentration in the sand fraction increased in the order continuous farming < alley-cropping < secondary forest. In the same order, microbial alteration of lignin and carbohydrates of sand-sized SOM decreased. Both the different concentrations of SOM in the sand fractions as well as its different composition contributed, therefore, to different SOM among the sites. Increasing lignin-to-carbohydrate ratios for bulk soils and fractions in the order continuous farming < alley-cropping < secondary forest reflected such changes in SOM composition sensitively.     

Soil Sample Depth in Pasture Soils for Environmental Soil Phosphorus Testing

Phosphorus (P) in runoff from agricultural land is a major contributor to eutrophication of surface waters. This study investigated the relationship between dissolved P in surface runoff and soil-test P measured at different sample depths (0–2 and 0–10 cm). Soil at these depths was collected from 136 sites in southeast New South Wales, Australia, under pastoral agriculture, covering a wide range of soil types and land-use intensity, from native pasture to intensive dairying. Bicarbonate-extractable soil P concentrations at these two depths were curvilinearly related over a very wide range of P (r² = 0.91). Small-plot rainfall simulations were conducted at 14 of these locations, for which the relationship between the sampling depths was even closer (r² = 0.95). After dividing the soils into two groups based on parent material (basalt and nonbasalt), linear relationships were found between extractable soil P and runoff dissolved reactive P, with more of the variance being accounted for with the sedimentary soils (r² = 0.89, 0–10 cm; 0.91, 0–2 cm) compared with basalt soils (r² = 0.63; 0–10 cm; 0.57, 0–2 cm). The results suggest that agronomic soil P testing in pastoral soils (typically 0–10 cm depth) is sufficient for estimating the potential for losses of P in runoff and that there is no need to collect shallow soil samples especially for this purpose.     

Soil properties and soil water conditions in the yangjuangou catchment of the chinese loess plateau

Soil properties and soil water conditions were assessed for different land use (forest, arable land, grassland) on a silty Calcaric Regosol in the Yangjuangou Catchment of the Chinese Loess Plateau. The loess here is unimodal, poorly sorted with abundant coarse silt, has very low dry bulk density (1.11?–?1.38?g cm^???3) and little organic carbon content (1.6?–?3.7?g kg^???1). The soils are hydrophilic, have high porosity (0.5?–?0.55 cm^3?cm^???3), unsaturated hydraulic conductivity, and plant available water content (0.34?–?0.4 cm^3?cm^???3). Soil properties are quite uniform in space. Land use had no significant effects on soil properties and soil water conditions.     

Are horticulture-based land uses benign for fertility and health of soils in mid to high hills of the north-western Himalayan region?

ABSTRACT

Soil fertility in many parts of the north?western Himalayan region (NWHR) has declined owing to accelerated nutrient mining under existing crop regime. Therefore, this study aimed to assess effect of the predominant horticulture?based land uses on soil fertility and health in mid and high hills of NWHR. Soil samples (0?20 cm) were collected, analyzed for different soil chemical attributes (pH, electrical conductivity, organic C, available primary-, secondary-, and micro-nutrients), and compared across five key land uses: perennial grass (PG), peach orchard (PO), apple orchard (AO), field vegetable farming (VF), and protected vegetable farming (PV). Soils of the investigated land uses were neutral to near neutral in soil reaction (6.3?6.8) except field vegetable and protected vegetable farming. Amount of soil organic C and labile organic C was significantly higher (p ≤ 0.05) in soils of apple orchards (18.6 g kg^?1 and 687.3 mg kg^?1, respectively) and peach orchards (20.4 g kg^?1 and 731.3 mg kg^?1, respectively) over others. An abrupt and significant increase in Olsen-P was recorded in soils of field vegetable farming (17.1 mg kg^?1) and protected vegetable farming (13.0 mg kg^?1), which shifted their nutrient index (NI) of P in to high category (≥ 2.33). The concentration of mineralizable-N in soil was statistically at par in soils under perennial grass and fruit orchards, while protected vegetable farming showed maximum soil mineralizable-N content (115.5 mg kg^?1) and NI of nitrogen (1.83). The NI was in high category (≥ 2.33) for copper, iron, and manganese in majority of the land uses. In view of the results, temperate fruit?tree based land uses are benign in up?keeping soil fertility and soil health, and needs promotion on large scale. Additionally, policies to create incentives for the build-up of soil organic matter and replenishment of the depleted soil macro and micro nutrients in vegetable-farmed lands are warranted.     

Soil microstructure alterations induced by land use change for sugarcane expansion in Brazil

Land use change (LUC) alters soil structure and, consequently, the functions and services provided by these soils. Conversion from extensive pasture to sugarcane is one of the largest land transitions in Brazil as a result of the growth of the domestic and global demands of bioenergy. However, the impacts of sugarcane expansion on the soil structure under extensive pasture remains unclear, especially when considering changes at the microscale. We investigated whether LUC for sugarcane cultivation impacted soil microstructure quality. Undisturbed soil samples were taken from two soil layers (0–10 and 10–20 cm) under three contrasting land uses (native vegetation—NV, pasture—PA and sugarcane—SC) in three different locations in the central-southern Brazil. Oriented thin sections (30 μm) were used for micromorphological analysis. The total area of pores decreased following the LUC in the following order: NV > PA > SC in both soil layers. The area of large complex packing pores (>0.01 mm²) also decreased with the LUC sequence: NV>PA>SC. Qualitative and semi-quantitative micromorphological analysis confirmed porosity reduction was driven by the decrease in complex packing pores and that biological features decreased in the same LUC sequence as the quantitative parameters. Therefore, LUC for sugarcane expansion reduced microscale soil porosity, irrespectively of soil type and site-specific conditions, indicating that the adoption of more sustainable management practices is imperative to preserve soil structure and sustain soil functions in Brazilian sugarcane fields.     

Limitations of farm management data in analyses of decadal changes in SOC stocks in the Danish soil-monitoring network

Changes in soil organic carbon (SOC) storage in agricultural land are an important part of the Land Use, Land-Use Change and Forestry component of national greenhouse gas emission inventories. Furthermore, as climate mitigation strategies and incentives for carbon farming are being developed, accurate estimates of SOC stocks are essential to verify any management-induced changes in SOC. Based on agricultural mineral soils in the Danish soil-monitoring network, we analysed management effects on SOC stocks using data from the two most recent surveys (2009 and 2019). Between 2009 and 2019, the average increase in SOC stock was 1.2 Mg C ha⁻¹ for 0–50 cm despite a loss of 1.2 Mg C ha⁻¹ from the topsoil (0–25 cm), stressing the importance of including deeper soil layers in soil-monitoring networks. Comparing all four national surveys (1986, 1997, 2009, 2019), the mean SOC stock of mineral soils in Denmark appears stable. The change in SOC stock between 2009 and 2019 was analysed in detail in relation to management practices as reported by farmers. We found that the effects of single management factors were difficult to isolate from co-varying factors including soil parameters and that the use of farm management data to explain changes in SOC stocks observed in soil-monitoring networks appears limited. Uncertainty in SOC stock estimates also arises from low sampling frequency and statistical challenges related to regression to the mean. However, repeated stock measurements at decadal intervals still represent a benchmark for the overall development in regional and national SOC storage, as affected by actual farm management.     

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.     

Effects of lime and sewage sludge on soil,pasture production,and tree growth in a six‐year‐old Populus canadensis Moench silvopastoral system

In many regions worldwide, silvopastoral systems are implemented to enable sustainable land use allowing short, medium, and long‐term economic returns. However, the short‐term production in silvopastoral systems is often limited due to nonappropriate soil‐fertility management. This study evaluated the effects of two doses of lime (0 and 2.5 t CaCO₃ ha^–1) and three sewage‐sludge treatments (0, 200, and 400 kg total N ha^–1 y^–1 applied in 2 consecutive years) on soil characteristics (soil pH, soil organic matter [SOM], soil nitrogen, cation‐exchange capacity [CEC]), pasture production, and tree growth in a silvopastoral system of Populus × canadensis Moench in Galicia, northern Spain during 6 years after establishment. Soil pH increased during the experimental period for all treatments, although this effect was more pronounced after lime application. Changes in SOM and soil nitrogen content were not consistent over time, but sewage‐sludge application seemed to result in higher values. Higher CEC was found for treatments with lime and sewage‐sludge application. Following incorporation of lime and sewage sludge, pasture production was significantly enhanced (cumulative pasture production 51.9 t DM ha^–1 for Lime/N400 compared to 39.0 t DM ha^–1 for No lime/N0). This higher pasture production also affected tree growth due to more severe competition between pasture and tree resulting in slower tree growth. Liming and application of sewage sludge are relevant measures to improve soil fertility and thereby optimizing the overall production of silvopastoral systems. However, it is important not to overintensify pasture production to ensure adequate tree growth.