Deforestation and land-use effects on soil degradation and rehabilitation in western Nigeria. I. Soil physical and hydrological properties

Assessments of the effects of deforestation, post-clearance tillage methods and farming systems treatments on soil properties were made from 1978 through 1987 on agricultural watersheds near Ibadan, southwestern Nigeria. These experiments were conducted in two phases: Phase I from 1978 through 1981 and Phase II from 1983 to 1987, with 1 year (1982) as a transition phase when all plots were sown with mucuna (Mucuna utilis). There were six treatments in Phase I involving combinations of land clearing and tillage methods: (1) manual clearing with no-till (MC-NT); (2) manual clearing with plough-till (MC-PT); (3) shear-blade clearing with no-till (SB-NT); (4) tree-pusher/root rake clearing with no-till (TP-NT); (5) tree-pusher/root-rake clearing with plough-till (TP-PT); (6) traditional farming (TF). The six treatments were replicated twice in a completely randomized design. The traditional treatment of Phase I was discontinued during Phase II. The five farming systems studied during Phase II with a no-till system in all treatments were: (1) alley cropping with Leucaena leucocephala established on the contour at 4-m intervals; (2) and (3) fallowing with Mucuna utilis on severely degraded and moderately degraded watersheds, respectively, for 1 year followed by maize-cowpea rotation for another; (4) and (5) ley farming involving establishment of pasture in the first year on severely and moderately degraded plots, respectively, controlled grazing in the second year, and growing maize (Zea mays)-cowpea (Vigna unguiculata) in the third year. All treatments, imposed on watersheds of 2–4 ha each, were replicated twice. The soil properties analyzed were particle size distribution, total aggregation and mean weight diameter of aggregates, soil bulk density, penetrometer resistance, water retention characteristics, infiltration capacity and saturated hydraulic conductivity. These properties were measured under the forest cover in 1978, and once every year during the dry season thereafter during Phases I and II. Prior to deforestation, mean soil bulk density was 0·72 Mg m⁻³ and 1·30 Mg m⁻³, soil penetration resistance was 32·4 KPa and 90·7 KPa, and mean weight diameter of aggregates was 3·7 mm and 3·2 mm for 0–5 cm and 5–10 cm depths, respectively. The infiltration rate was excessive (54–334 cm hr⁻¹) and saturated hydraulic conductivity was rapid (166–499 cm hr⁻¹) under the forest cover. Furthermore, water transmission properties varied significantly even over short distances of about 1 m. Deforestation and cultivation increased soil bulk density and penetration resistance but decreased mean weight diameter of aggregates. One year after deforestation in 1980, mean soil bulk density was 1·41 Mg m⁻³ for 0–5 cm depth and 1·58 Mg m⁻³ for 5–10 cm depth. Soil bulk density and penetration resistance were generally higher for NT than for PT methods, and the penetration resistance was extremely high in all treatments by 1985. During Phase II, soil bulk density was high during the grazing cycle of the ley farming treatment. Sand content at 0–5 cm depth increased and clay content decreased with cultivation duration. Soon after deforestation, saturated hydraulic conductivity and equilibrium infiltration rate in cleared and cultivated land declined to only 20–30 per cent of that under forest. Mean saturated hydraulic conductivity following deforestation was 46·0 cm hr⁻¹ for 0–5 cm depth and 53·7 cm hr⁻¹ for 5–10 cm depth. Further, infiltration rate declined with deforestation and cultivation duration in all cropping systems treatments. During Phase I, mean infiltration rate was 115·8 cm hr⁻¹ under forest cover in 1978, 20·9 cm hr⁻¹ in 1979, 17·4 cm hr⁻¹ in 1980 and 20·9 cm hr⁻¹ in 1981. During Phase II, mean infiltration rate was 8·5 cm hr⁻¹ in 1982, 11·9 cm hr⁻¹ in 1983, 11·0 cm hr⁻¹ in 1984, 11·3 cm hr⁻¹ in 1985 and 5·3 cm hr⁻¹ in 1986. Infiltration rate was generally high in ley farming and mucuna fallowing treatments. Natural fallowing drastically improved the infiltration rate from 19·2 cm hr⁻¹ in 1982 to 193·2 cm hr⁻¹ in 1986, a ten-fold increase within 5 years of fallowing. High-energy soil water retention characteristics in Phase I were affected by those treatments that caused soil compaction by mechanized clearing and no-till systems. Soil water retention at 0·01 MPa potential in 1979 was 19·2 per cent (gravimetrics) for SB, 17·9 per cent for TP, 15·9 per cent for MC and 17·8 per cent for TF methods. With regards to tillage, soil water retention was 17·8 per cent for NT compared with 16·8 per cent for PT. During Phase II, water retention characteristics were not affected by the farming system treatments. Mean soil water retention (average of 4 years' data from 1982 to 1986) at 0·01 MPa for 0–5 cm depth was 16·6 per cent for alley cropping, 16·7 per cent for mucuna fallowing and 16·8 per cent for ley farming. Mean soil water retention for 1·5 MPa suction was 9·3 per cent for alley cropping, 8·7 per cent for mucuna fallowing, and 9·3 per cent for ley farming. Water retention at 1·5 MPa suction correlated with the clay and soil organic carbon content.     

Soil degradative effects of slope length and tillage methods on alfisols in Western Nigeria. I. Runoff,erosion and crop response

Field runoff plots were established in 1984 to evaluate the effects of slope length on runoff, soil erosion and crop yields on newly cleared land for four consecutive years (1984–1987) on an Alfisol at Ibadan, Nigeria. The experimental treatments involved six slope lengths (60 m to 10 m at 10-m increments) and two tillage methods (plough-based conventional tillage and a herbicide-based no-till method) of seedbed preparation. A uniform crop rotation of maize (Zea mays)/cowpeas (Vigna unguiculata) was adopted for all four years. An uncropped and ploughed plot of 25 m length was used as a control. The water runoff from the conventional tillage treatment was not significantly affected by slope length, but runoff from the no-till treatment significantly increased with a decrease in slope length. The average runoff from the no-till treatment was 1·85 per cent of rainfall for 60 m, 2·25 per cent for 40 m, 2·95 per cent for 30 m, 4·7 per cent for 20 m and 5·15 per cent for 10 m slope length. In contrast to runoff, soil erosion in the conventional tillage treatment decreased significantly with a decrease in slope length. For conventional tillage, the average soil erosion was 9·59 Mg ha⁻¹ for 60 m, 9·88 Mg ha⁻¹ for 50 m, 6·84 Mg ha⁻¹ for 40 m, 5·69 Mg ha⁻¹ for 30 m, 1·27 Mg ha⁻¹ for 20 m and 2·19 Mg ha⁻¹ for 10 m slope length. Because the no-till method was extremely effective in reducing soil erosion, there were no definite trends in erosion with regard to slope length. The average sediment load (erosion:runoff ratio) also decreased with a decrease in slope length from 66·3 kg ha⁻¹ mm⁻¹ for 60 m to 36·3 kg ha⁻¹ mm⁻¹ for 10 m slope length. The mean C factor (ratio of soil erosion from cropped land to uncropped control) also decreased with a decrease in slope length. Similarly, the erosion:crop yield ratio decreased with a decrease in slope length, and the relative decrease was more drastic in conventional tillage than in the no-till treatment. The slope length (L) and erosion relationship fits a polynomial function (Y=c+aL+bL²). Formulae are proposed for computing the optimum terrace spacing in relation to slope gradient and tillage method. © 1997 John Wiley & Sons, Ltd.     

Soil quality changes under continuous cropping for seventeen seasons of an alfisol in western Nigeria

Tillage and soil management effects on soil physical and chemical qualities were monitored for eight years from 1979 through 1987 in a long-term experiment involving 17 consecutive crops of maize. Effects of no-till and plow-till methods of seedbed preparation were compared at two levels of residue management (residue removed versus residue returned) and two levels of fertilizer application (without fertilizer versus recommended fertilizer). Soil chemical quality was better for no-till compared with plow-till methods. Mean soil chemical properties of 0–5 cm depth for no-till and plow-till treatments respectively were 18·6 g kg⁻¹ versus 12·2 g kg⁻¹ for soil organic carbon content, 1·9 g kg⁻¹ versus 1·1 g kg⁻¹ for total soil nitrogen, 0·14 units yr⁻¹ versus 0·18 units yr⁻¹ rate of decline in soil pH, 63·1 mg kg⁻¹ versus 31·8 mg kg⁻¹ for Bray-P, and 6·0 cmol kg⁻¹ versus 2·3 cmol kg⁻¹ for Ca⁺². Soil chemical quality consistently declined, although the rate of decline differed among tillage and fertilizer treatments. There were also differences in soil physical quality. Soil bulk density increased with cultivation duration in both tillage methods, and use of furadan in no-till plots drastically increased soil bulk density. Infiltration rate and soil moisture retention at all suctions was consistently more for no-till than plow-till treatments. Decline in soil quality with cultivation was reflected in decrease in crop yields. © 1998 John Wiley & Sons, Ltd.     

Mulching effects on soil physical quality of an alfisol in western Nigeria

Degradation of soil physical quality, following deforestation and cultivation, is a major soil‐related constraint to an intensive use of soil for crop production in subhumid regions of subSaharan Africa. Use of crop residue mulch is an important strategy to minimize the risks of soil degradation. Therefore, a three‐year experiment was conducted to study the effects of five rates of mulch application (0, 2, 4, 6 and 8 Mg ha⁻¹ season⁻¹) on soil physical properties and growth and yield of maize (Zea mays). Mulch rate of rice straw significantly increased maize grain and stover yields during the first season, and the stover yield during the second season. In comparison with the control, the grain yield increased by 20 per cent at 2 Mg ha⁻¹ of mulch rate and by 33 per cent at 8 Mg ha⁻¹ of mulch rate. The rate of increase was 0·16 Mg ha⁻¹ for grain yield and 0·38 Mg ha⁻¹ for stover yield for every Mg of mulch applied. The increase in stover yield during the second season was 67 per cent for 8 Mg ha⁻¹ mulch rate compared with the unmulched control. Effects of mulch rate on soil physical properties were confined mostly to the surface 0–5 cm depth. For this depth, mulching decreased bulk density from 1·17 Mg m⁻³ for control to 0·98 Mg m⁻³, and penetration resistance from 1·54 kg cm⁻² to 1·07 kg cm⁻² for 8 Mg ha⁻¹ of mulch rate. Application of mulch up to 16 Mg ha⁻¹ yr⁻¹ for three consecutive years had no effect on soil physical properties below 5 cm depth. Experiments were probably not conducted for a long enough period. For mulch farming to be adopted by farmers of West Africa, it must be an integral part of the improved farming system. Copyright © 2000 John Wiley & Sons, Ltd.     

Soil carbon sequestration in sub‐Saharan Africa: a review

Restoration of degraded soils is a development strategy to reduce desertification, soil erosion and environmental degradation, and alleviate chronic food shortages with great potential in sub‐Saharan Africa (SSA). Further, it has the potential to provide terrestrial sinks of carbon (C) and reduce the rate of enrichment of atmospheric CO₂. Soil organic carbon (SOC) contents decrease by 0 to 63 per cent following deforestation. There exists a high potential for increasing SOC through establishment of natural or improved fallow systems (agroforestry) with attainable rates of C sequestration in the range of 0·1 to 5·3 Mg C ha⁻¹ yr⁻¹. Biomass burning significantly reduces SOC in the upper few centimeters of soil, but has little impact below 10 to 20 cm depth. The timing of burning is also important, and periods with large amounts of biomass available generally have the largest losses of SOC. In cultivated areas, the addition of manure in combination with crop residues and no‐till show similar rates of attainable C sequestration (0 to 0·36 Mg C ha⁻¹ yr⁻¹). Attainable rates of SOC sequestration on permanent cropland in SSA under improved cultivation systems (e.g. no‐till) range from 0·2 to 1·5 Tg C yr⁻¹, while attainable rates under fallow systems are 0·4 to 18·5 Tg C yr⁻¹. Fallow systems generally have the highest potential for SOC sequestration in SSA with rates up to 28·5 Tg C yr⁻¹. Copyright © 2005 John Wiley & Sons, Ltd.     

Soil organic carbon stock for reclaimed minesoils in northeastern Ohio

Reclamation of disturbed soils is done with the primary objective of restoring the land for agronomic or forestry land use. Reclamation followed by sustainable management can restore the depleted soil organic carbon (SOC) stock over time. This study was designed to assess SOC stocks of reclaimed and undisturbed minesoils under different cropping systems in Dover Township, Tuscarawas County, Ohio (40°32·33′ N and 81°33·86′ W). Prior to reclamation, the soil was classified as Bethesda Soil Series (loamy‐skeletal, mixed, acid, mesic Typic Udorthent). The reclaimed and unmined sites were located side by side and were under forage (fescue—Festuca arundinacea Schreb. and alfa grass—Stipa tenacissima L.), and corn (Zea mays L.)—soybean (Glycine max (L.) Merr.) rotation. All fields were chisel plowed annually except unmined forage, and fertilized only when planted to corn. The manure was mostly applied on unmined fields planted to corn, and reclaimed fields planted to forage and corn. The variability in soil properties (i.e., soil bulk density, pH and soil organic carbon stock) ranged from moderate to low across all land uses in both reclaimed and unmined fields for 0–10 and 10–20 cm depths. The soil nitrogen stock ranged from low to moderate for unmined fields and moderate to high in some reclaimed fields. Soil pH was always less than 6·7 in both reclaimed and unmined fields. The mean soil bulk density was consistently lower in unmined (1·27 mg m⁻³ and 1·22 mg m⁻³) than reclaimed fields (1·39 mg m⁻³ and 1·34 mg m⁻³) planted to forage and corn, respectively. The SOC and total nitrogen (TN) concentrations were higher for reclaimed forage (33·30 g kg⁻¹; 3·23 g kg⁻¹) and cornfields (21·22 g kg⁻¹; 3·66 g kg⁻¹) than unmined forage (17·47 g kg⁻¹; 1·98 g kg⁻¹) and cornfield (17·70 g kg⁻¹; 2·76 g kg⁻¹). The SOC stocks in unmined soils did not differ among forage, corn or soybean fields but did so in reclaimed soils for 0–10 cm depth. The SOC stock for reclaimed forage (39·6 mg ha⁻¹ for 0–10 cm and 28·6 mg ha⁻¹ for 10–20 cm depths) and cornfields (28·3 mg ha⁻¹; 32·2 mg ha⁻¹) were higher than that for the unmined forage (22·7 mg ha⁻¹; 17·6 mg ha⁻¹) and corn (21·5 mg ha⁻¹; 26·8 mg ha⁻¹) fields for both depths. These results showed that the manure application increased SOC stocks in soil. Overall this study showed that if the reclamation is done properly, there is a large potential for SOC sequestration in reclaimed soils. Copyright © 2005 John Wiley & Sons, Ltd.     

Modelling Soil Detachment of Different Management Practices in the Red Soil Region of China

Soil erosion from cropland is a primary cause of soil degradation in the hilly red soil region of China. Soil characteristics and the resistance of soil to erosion agents can be improved with appropriate management practices. In this study, hydraulic flume experiments were conducted to investigate the effects of five management practices [manure fertilizer (PM), straw mulch cover (PC), peanut–orange intercropping (PO), peanut–radish rotation (PR) and traditional farrow peanut (PF)] on soil detachment. Based on the results, three conservation management practices (PC, PM and PO) increased the resistance of soil to concentrated flow erosion. The rill erodibility of different treatments was ranked as follows: PC (0·001 s m⁻¹) < PM (0·004 s m⁻¹) < PO (0·007 s m⁻¹) < PF (0·01 s m⁻¹) < PR (0·027 s m⁻¹). The rill erodibility was affected by soil organic content, aggregate stability and bulk density. The soil detachment rate was closely correlated with the flow discharge and slope gradient, and power functions for these two factors were developed to evaluate soil detachment rates. Additionally, the shear stress, stream power and unit stream power were compared when estimating the soil detachment rate. The power functions of stream power and shear stress were equivalent, and both are recommended to predict detachment rates. Local soil conservation can benefit from the results of this study with improved predictions of erosion on croplands in the red soil region of China. Copyright © 2016 John Wiley & Sons, Ltd.     

Infiltration and Runoff Generation Under Various Cropping Patterns in the Red Soil Region of China

Soil and surface water runoff are the major causes of cropland degradation in the hilly red soil region of China. Appropriate tillage practices are urgently needed to reduce erosion and protect the soil surface. In this study, five tillage systems [manure fertiliser (PM), straw mulch cover (PC), peanut–orange intercropping (PO), peanut–radish rotation (PR) and traditional farrow peanut (PF)] were compared in terms of soil infiltration and the capacity to generate runoff. Based on field‐plot monitoring and simulated experiments, this study revealed that the organic content of the soil in the PO (19.43 g kg⁻¹), PC (18·63 g kg⁻¹) and PM (18·18 g kg⁻¹) treatments increased compared with those of the PF (15·64 g kg⁻¹) and PR (17.17 g kg⁻¹) treatments. Moreover, the three tillage practices also enhanced the soil's aggregate stability and infiltration capacity. The average annual runoff generation rates of the treatments were as follows: PR (3,141 m³ ha⁻¹ a⁻¹) > PF (2,189 m³ ha⁻¹ a⁻¹) > PC (755 m³ ha⁻¹ a⁻¹) > PM (514 m³ ha⁻¹ a⁻¹) > PO (388 m³ ha⁻¹ a⁻¹). The PO treatment reduced the runoff generation rate by approximately 82·3% compared with that of the PF treatment. Among the treatments, the PO treatment had the highest threshold rainfall depth (22 mm) for runoff generation. Regression analysis revealed that the threshold rainfall depths linearly increased with the infiltration rates. The results of this study could benefit local soil management and cropland conservation. Copyright © 2015 John Wiley & Sons, Ltd.     

Reclamation and salt leaching efficiency for tile drained saline‐sodic soil using marginal quality water for irrigating rice and wheat crops

Due to increased population and urbanization, freshwater demand for domestic purposes has increased resulting in a smaller proportion for irrigation of crops. We carried out a 3‐year field experiment in the Indus Plains of Pakistan on salt‐affected soil (EC_e 15·67–23·96 dS m⁻¹, pH_s 8·35–8·93, SAR 70–120, infiltration rate 0·72–0·78 cm h⁻¹, ρ _b 1·70–1·80 Mg m⁻³) having tile drainage in place. The 3‐year cropping sequence consisted of rice (Oryza sativa L.) and wheat (Triticum aestivum L.) crops in rotation. These crops were irrigated with groundwater having electrical conductivity (EC) 2·7 dS m⁻¹, sodium adsorption ratio (SAR) 8·0 (mmol L⁻¹)^1/2 and residual sodium carbonate (RSC) 1·3 mmol_c L⁻¹. Treatments were: (1) irrigation with brackish water without amendment (control); (2) Sesbania (Sesbania aculeata) green manure each year before rice (SM); (3) applied gypsum at 100 per cent soil gypsum requirement (SGR) and (4) applied gypsum as in treatment 3 plus sesbania green manure each year (GSM). A decrease in soil salinity and sodicity and favourable infiltration rate and bulk density over pre‐experiment levels are recorded. GSM resulted in the largest decrease in soil salinity and sodicity. There was a positive relationship between crop yield and economic benefits and improvement in soil physical and chemical properties. On the basis of six crops, the greatest net benefit was obtained from GSM. Based on this long‐term study, combined use of gypsum at 100 per cent soil gypsum requirement along with sesbania each year is recommended for soil amelioration and crop production. Copyright © 2010 John Wiley & Sons, Ltd.     

Environmental Factors Controlling Soil Organic Carbon Stocks in Two Contrasting Mediterranean Climatic Areas of Southern Spain

Managing soil carbon requires accurate estimates of soil organic carbon (SOC) stocks and its dynamics, at scales able to capture the influence of local factors on the carbon pool. This paper develops a spatially explicit methodology to quantify SOC stocks in two contrasting regions of Southern Spain: Sierra Norte de Sevilla (SN) and Cabo de Gata (CG). Also, it examines the relationship between SOC stocks and local environmental factors. Results showed that mean SOC stocks were 4·3 kg m⁻² in SN and 3·0 kg m⁻² in CG. Differences in SOC in both sites were not significant, suggesting that factors other than climate have a greater influence on SOC stocks. A correlation matrix revealed that SOC has the highest positive correlation with clay content and soil depth. Based on the land use, the largest SOC stocks were found in grassland soils (4·4 kg m⁻² in CG and 5·0 kg m⁻² in SN) and extensive crops (3·0 kg m⁻² in CG and 5·0 kg m⁻² in SN), and the smallest under shrubs (2·8 kg m⁻² in CG and 3·2 kg m⁻² in SN) and forests soils (4·2 kg m⁻² in SN). This SOC distribution is explained by the greatest soil depth under agricultural land uses, a common situation across the Mediterranean, where the deepest soils have been cultivated and natural vegetation mostly remains along the marginal sites. Accordingly, strategies to manage SOC stocks in southern Spain will have to acknowledge its high pedodiversity and long history of land use, refusing the adoption of standard global strategies. Copyright © 2015 John Wiley & Sons, Ltd.     

Sediment Yield Deduction from Check–dams Deposition in the Weathered Sandstone Watershed on the North Loess Plateau,China

As the basic unit of erosion and sediment yield, it was critical to determine the amount of soil erosion and sediment yield in the small watersheds for sustaining a reasonable water resource and sediment regulation system. In this study, we determined the sediment yield from the dams‐controlled watershed on the North Loess Plateau. Three check dams in the watershed were investigated by drilling ten‐hole sedimentation cores. The corresponding flood couplets were dated according to thickness of deposition layers, distribution of sediment particle size and historical erosive rainfall events. On the basis of the check dams capacity curve, the soil bulk density and the thickness of couplets, the deposit mass of check dams, and then the sediment yield of watershed at different temporal and spatial scale were deducted. In total of the 33, 60 and 55 couplets were corresponded to individual flood events in the dam MH1# from 1976 to 1984, the dam MH2# from 1985 to 2007, and the dam MH4# from 1981 to 2009, respectively. The specific sediment yield for flood events was 1,188.5–11,527.9 Mg km⁻², 1,278.6–17,136.7 Mg km⁻², and 3,395.9–33,698.5 Mg km⁻², and the annual average sediment yield was 10,728.6 Mg (km² · a)⁻¹, 12,662.9 Mg (km² · a)⁻¹, and 16,753.3 Mg (km² · a)⁻¹ in dam MH1#, MH2# and MH4# controlled watershed, respectively. The sediment yields were inversely proportional to the dams – controlled areas. For the whole watershed, the annual average sediment yield was 14,011.1 Mg (km² · a)⁻¹ from 1976 to 2009. There were large amounts of sediments (42.3–50.5%) were intercepted gradually along the way from small watersheds to the river channel. And the minimum rainfall for sediment deposited in the dams was greater than 20 mm in this watershed. The results of this study suggested that the sediments retained behind check dams were helpful to quantifying the amount of erosion sediment yield and understanding the soil erosion evolution in the small and ungauged watersheds. Copyright © 2016 John Wiley & Sons, Ltd.     

Assessing and Managing Soil Quality for Urban Agriculture in a Degraded Vacant Lot Soil

Following the decline of industrial manufacturing, many US cities have experienced severe population reductions that have resulted in large areas of vacant land. Urban agriculture has emerged as a desirable land use for these spaces, but degraded soils are common. Therefore, we measured soil and plant responses to amendments and management in urban lots where vacant houses had recently been demolished in Youngstown, OH, USA. Soil degradation was observed following demolition activities in the form of compaction (bulk density of 1·5–1·8 Mg m⁻³) and low soil microbial biomass C (21 mg C kg⁻¹ soil). Our split‐plot experiment measured the effects of organic matter (OM) amendments produced from yard wastes and the use of raised beds on soil properties and vegetable crop yields. Two years after their application, OM amendments resulted in significant improvement to a number of soil physical, chemical, and biological properties. Vegetable crop yields were improved by OM amendments in 2011 and by both OM amendments and the use of raised beds in 2012. A soil quality index, developed using factor analysis and the Soil Management Assessment Framework, produced values ranging from 0·60 to 0·85, which are comparable to those reported for rural agricultural soils. All results indicate that urban agriculture can be productive in vacant urban land and that amendments produced from urban yard wastes can improve soil quality at previously degraded sites and increase crop yields for urban agriculture. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

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

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

渭北台塬区新增坡耕地土壤侵蚀产沙模拟试验研究

[目的]研究不同放水流量条件下坡面土壤的侵蚀产沙规律,揭示渭北台塬区新增坡耕地坡度及土壤容重对侵蚀程度的影响,为该区坡耕地开发利用提供理论支持和实践指导。[方法]通过室内模拟试验开展研究。[结果]土壤入渗率随放水流量的增大呈现先增大后减小的趋势,且存在明显的转折点,并随容重的增大而减小,径流量随容重和放水量的增大而增大;土壤容重越大,产沙量也越大,容重1.6g/cm3较1.2g/cm3,1.4g/cm3的坡耕地产沙量明显增大;坡度越大,土壤侵蚀越剧烈,在5°坡时,产沙量存在临界值;放水流量越大,产沙量越大,当放水量超过6L/min时,增加趋势更加明显。[结论]渭北台塬区新增坡耕地的易侵蚀程度与土壤容重和坡度密切相关,为减少侵蚀,应控制容重在1.4g/cm3左右,坡度不宜超过15°。     

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.     

Spatiotemporal Heterogeneity of Soil Available Nitrogen During Crop Growth Stages on Mollisol Slopes of Northeast China

Spatiotemporal heterogeneity of soil available nitrogen (AN) (sum of NO₃⁻–N and NH₄⁺–N) is the essential basis for soil management and highly correlates to crop yield. Both geostatistical and traditional analyses were used to describe the spatiotemporal distribution of AN in the 0–20‐cm soil depth on typical Mollisol slopes (S1 and S2) in Northeast China. The concentration of NO₃⁻–N dynamics at slope positions was typically opposite to NH₄⁺–N. The peak values of AN typically moved from the summit of the slope to the bottom from spring to autumn and were mainly influenced by the content of NO₃⁻–N (S1, 7·9–18·9 mg kg⁻¹; S2, 1·2–103·6 mg kg⁻¹), both of NO₃⁻–N (S1, 3·9–8·3 mg kg⁻¹; S2, 2·2–28·0 mg kg⁻¹) and NH₄⁺–N (S1, 21·4–30·5 mg kg⁻¹; S2, 2·1–23·3 mg kg⁻¹), and NH₄⁺–N (S1, 10·5–28·9 mg kg⁻¹; S2, 5·0–39·0 mg kg⁻¹) in the seedling stage, vegetative growth stage, and reproductive growth stage, respectively. The spatial autocorrelation of AN was strong and was mainly influenced by structural factors during crop growth stages. This was mainly determined by soil erosion–deposition (SED) and soil temperature–moisture (STM) in the seedling stage; this was also mainly influenced by SED, STM, crop type, and crop growth in the vegetative growth stage and by early STM and early SED in the reproductive growth stage. Generally, the content of AN, NO₃⁻–N, and NH₄⁺–N on the whole slope was mainly determined by the early SED and local fertilizer application, while their spatiotemporal heterogeneity, especially the evenness, was mainly changed by SED, STM, crop growth, and crop types on the slope scale. In order to increase more crop yields, additional N fertilizer application on both the summit and the bottom during the vegetative growth stage and conservation tillage systems or additional soil amendments on the back slopes was necessary. Copyright © 2016 John Wiley & Sons, Ltd.     

Salt-tolerant forage cultivation on a saline-sodic field for biomass production and soil reclamation

Chemical reclamation of sodic and saline-sodic soils has become cost-intensive. Cultivation of plants tolerant of salinity and sodicity may mobilize the CaCO₃ present in saline-sodic soils instead of using a chemical approach. Four forage plant species, sesbania (Sesbania aculeata), kallar grass (Leptochloa fusca), millet rice (Echinochloa colona) and finger millet (Eleusine coracana), were planted in a calcareous saline-sodic field (EC_e = 9·6–11·0 dS m⁻¹, SAR = 59·4–72·4). Other treatments included gypsum (equivalent to 100 per cent of the gypsum requirement of the 15 cm soil layer) and a control (no gypsum or crop). The crops were grown for 5 months. The performance of the treatments in terms of soil amelioration was in the order: Sesbania aculeata ≅ gypsum > Leptochloa fusca > Echinochloa colona > Elusine coracana > control. Biomass production by the plant species was found to be directly proportional to their reclamation efficiency. Sesbania aculeata produced 32·3 Mg forage ha⁻¹, followed by Leptochloa fusca (24·6 Mg ha⁻¹), Echinochloa colona (22·6 Mg ha⁻¹) and Eleusine coracana (5·4 Mg ha⁻¹). Sesbania aculeata emerged as the most suitable biotic material for cultivation on salt-affected soils to produce good-quality forage, and to reduce soil salination and sodication processes.     

Tillage erosion,water erosion and soil quality on cultivated terraces near Xifeng in the Loess Plateau,China

This study sought to contribute to the understanding of soil redistribution by tillage on terraces and the extent and causes of within-field variation in soil properties by examining the spatial distributions of soil redistribution rates, derived using caesium-137, and of total nitrogen and total phosphorus concentrations, within a ribbon and a shoulder terrace in a yuan area of the Loess Plateau of China. Additional water erosion rate data were obtained for nine other terraces. Water erosion rates on the ribbon terraces were low (<1 kg m⁻² yr⁻¹), unless slope tangents exceeded 0·1. However, despite the use of animal traction, high rates of tillage erosion were observed (mean 5·5 kg m⁻² yr⁻¹). Soil nitrogen concentrations were related to rates of soil redistribution by tillage on the ribbon terrace examined in detail. In general, higher rates of water erosion (0·5–2·9 kg m⁻² yr⁻¹) and lower rates of tillage erosion (mean 1·4 kg m⁻² yr⁻¹) were evident on the longer shoulder terraces. On the shoulder terrace examined in detail, soil phosphorus concentrations were related to net rates of soil redistribution. A statistically significant regression relationship between water erosion rates and the USLE length and slope factor was used in conjunction with the simulation of tillage erosion rates to evaluate a range of terrace designs. It is suggested that off-site impacts of erosion could be further reduced by ensuring that the slope tangents are kept below 0·06 and lengths below 30 m, especially on the shoulder terraces. Tillage erosion and the systematic redistribution of soil nutrients could be reduced by modification of the contour-cultivation technique to turn soil in opposing directions in alternate years. Copyright © 1999 John Wiley & Sons, Ltd.     

Effects of no-till and disc plowing with and without residue mulch on tropical root crops in southeastern Nigeria

Fields experiments were conducted on an Ultisol in southeastern Nigeria to study the effects of no-tillage and disc plowing, with and without residue mulching, on soil properties and the growth and yield of cassava and yam. Plowing to a depth of 10 cm and then applying mulch decreased soil bulk density. Of the no-till plots, those with mulch had the greatest soil moisture retention at low suctions; those without mulch had low moisture retention for suctions exceeding 0.1 bar. Cassava plants in plowed plots were more vigorous than those in no-till plots, and mulching decreased plant height of cassava in the initial stages and increased plant height at about 38 weeks after planting. In the first 10 cm, yam root length density was 0.31 cm cm⁻³ for no-till plots vs. 0.27 cm cm⁻³ for plowed plots. Mulch application increased root length density of yam. The root length density of cassava was 0.32 cm cm⁻³ for no-till plots versus 0.16 cm cm⁻³ for plowed plots. Mulch application, however, significantly increased root length density of cassava in no-till plots only. Yield of yam tubers was more for plowed plots than no-till plots — 12.4 vs. 10.9 t ha⁻¹. The increase in yam tuber yield due to mulching was 21% for no-till and 28% for plowed treatments. The cassava tuber yield was more in no-till than in plowed plots, and application of mulch increased cassava tuber yield.