Soil degradative effects of slope length and tillage methods on alfisols in western Nigeria. III.Soil physical properties

Effects of six slope lengths, 60 m to 10 m with 10-m increments, on soil physical properties were evaluated for plough-based conventional till and no-till seedbed preparation on field runoff plots for three consecutive years from 1984 to 1987. Soil physical properties measured included texture, bulk density, infiltration capacity, and soil moisture retention characteristics. Conventional till treatment caused a rapid increase in soil bulk density and penetration resistance, and decrease in available water capacity and equilibrium infiltration rate. Gravel content increased with cultivation duration. Soil bulk density of 0–5 cm depth was 1·20 Mg m⁻³ for 1984, 1·39 Mg m⁻³ for 1985 and 1·46 Mg m⁻³ for 1986 for conventional till; and 1·13 Mg m⁻³ for 1984, 1·33 Mg m⁻³ for 1985, and 1·27 Mg m⁻³ for 1986 for the no-till treatment. The penetration resistance of the no-till treatment was relatively low and increased with cultivation duration. Mean penetration resistance for 0–5 cm depth was 2·2 kg cm⁻² in 1984, 2·71 kg cm⁻² in 1985, and 3·79 kg cm⁻² in 1986. The available water capacity decreased in both tillage methods without any consistent trends with regard to slope length. The equilibrium infiltration rate declined drastically for long slopes and conventional till methods. The data support the conclusion that these soils should be managed with short slope lengths and a no-till method of seedbed preparation. © 1997 John Wiley & Sons, Ltd.     

Interrelationship among slope steepness,tillage practice and rainfall properties with surface runoff and soil loss on Mollisols in Northeast China

ABSTRACT

Soil erosion and rainfall-induced runoff are well studied yet remain somewhat unpredictable from one natural rainfall to the next, due to interactions between erosion parameters. This study quantified the relationship between annual (2011–2016) and individual (2016) rain events with overland flow (runoff) and soil loss in China’s northern ‘corn-belt’. Two tillage practices and slopes were evaluated (no-till and conventional till, 5° and 7° slopes). Results showed 54 rainfall events for a total of 394 mm precipitation ranging between May and October 2016. Runoff occurred 13 times in the conventional till with 7° slope, accounting for 25.9% of the precipitation volume and caused 15.6 t ha^?1 erosion. It occurred twice in the no-till with 5° slope plot and caused 0.2 t ha^?1 erosion., Thus the no-till with 5° slope treatment is the best tillage system to protect soil in Mollisols in Northeast China. Broad analysis coupled with a detail review of three rainfall events demonstrates that water either runs off plots quickly or rapidly infiltrates while sediment moves in a pulsing manner.     

Soil degradation by Erosion of a typic hapludalf in central Ohio and its rehabilitation

Soil erosion and runoff were monitored from 1988 to 1990 on a Miamian soil (Typic Hapludalf) of 5-6 per cent slope using field runoff plots. Four treatments were studied: (i) disk-plough up and down the slope to 0.3 m depth (DP); (ii) disk-plough up and down the slope followed by a protective netting (PN); (iii) uncultivated fallow without any vegetation followed by surface soil removal (R); (iv) uncultivated fallow with natural vegetation followed by ploughing (F). Mean annual runoff losses were 6, 114 and 128 mm, or 4, 20 and 18 per cent of the rainfall, and mean annual soil losses were 1.2, 85.0 and 64.0 Mg ha⁻¹ in 1988, 1989 and 1990, respectively. Mean runoff amounts were 26, 69, 116 and 118mm and mean annual soil losses were 0.4, 23.2, 58.6 and 118 Mg ha⁻¹ for the F, PN, DP and R treatments, respectively. In comparison with DP, PN decreased annual runoff by 40.3 per cent and annual soil loss by 79.5 per cent. The high mean soil loss for the R treatment was due to erosion following soil removal. An additional 2920 Mg ha⁻¹ of surface soil was removed from the R treatment in May 1990. The F treatment reduced runoff by 78, 77 and 62 per cent and reduced soil loss by 99.7, 99.4 and 98.4 per cent compared with the R, DP and PN treatments, respectively. Mean losses of K, Ca, Mg and P were 1.3, 4, 1 and 01 kg ha⁻¹, respectively for F, 3, 16, 5 and 0.3kg ha⁻¹, respectively, for PN, 5, 31, 1 and 0.6kg ha⁻¹, respectively, for DP, and 3, 32, 12 and 0.4 kg ha⁻¹, respectively, for R. Soil and nutrient losses for each treatment were in the order R > DP > PN > F. The soil organic carbon (SOC) content was significantly affected by soil erosion and management treatments, and ranged from 0.98 per cent for the R treatment to 2.3 per cent for the F treatment. Soil surface removal for the R treatment in 1990 reduced water-stable aggregates (WSA) by 9.0 per cent, SOC by 0.6 per cent, and clay content of the uppermost 0-50 mm depth by about 7.0 per cent. Mean total porosity (f_t) ranged from 0.43 for the F to 0.52 for the DP treatment. Cumulative infiltration for 3h ranged from 13 cm for R to 34cm for PN, with corresponding infiltration rates of 4 cm h⁻¹ and 13 cm h⁻¹, respectively. Regardless of the treatment, there were also temporal changes in soil properties. In comparison with 1988, measurements made in 1990 showed a significant decrease in WSA of 21.3 per cent, an increase in clay content of 2.8 per cent, and a decrease in SOC of 0.39 per cent. Runoff and soil losses were significantly correlated with the mean weight diameter (MWD), SOC, bulk density (p_b) and available water capacity (AWC). Plant height measured 8 weeks after planting (WAP) for the R treatment was reduced by 33.3 per cent, 33.0 per cent and 29.0 per cent compared withh DP, PN and F, respectively. Nitrogen uptake by maize plants (Zea mays L.) 10 WAP for the R treatment was lower by 15 per cent, 8 per cent, and 6 per cent compared with the DP, PN and F treatments, respectively, while P uptake was lower by 33 per cent, 32 per cent and 29 per cent, respectively, compared with the same treatments. Grain yield was 9.78 Mg ha⁻¹ for PN, 9.76 Mg ha⁻¹ for DP, 8.64 Mg ha⁻¹ for F and 6.60 Mg ha⁻¹ for R during the 1990 crop season. Grain yield was reduced by about 32.4 per cent in the R treatment compared with the PN treatment, representing a maize grain yield reduction of 158 kg ha⁻¹ for each centimeter of soil lost.     

Surface runoff and soil erosion estimation using the SWAT model in the Keleta Watershed,Ethiopia

This study evaluates surface runoff generation and soil erosion rates for a small watershed (the Keleta Watershed) in the Awash River basin of Ethiopia by using the Soil and Water Assessment Tool (SWAT) model. Calibration and validation of the model was performed on monthly basis, and it could simulate surface runoff and soil erosion to a good level of accuracy. The simulated surface runoff closely matched with observed data (derived by hydrograph separation). Surface runoff generation was generally high in parts of the watershed characterized by heavy clay soils with low infiltration capacity, agricultural land use and slope gradients of over 25 per cent. The estimated soil loss rates were also realistic compared to what can be observed in the field and results from previous studies. The long‐term average soil loss was estimated at 4·3 t ha⁻¹ y⁻¹; most of the area of the watershed (∼80 per cent) was predicted to suffer from a low or moderate erosion risk (<8 t ha⁻¹ y⁻¹), and only in ∼1·2 per cent of the watershed was soil erosion estimated to exceed 12 t ha⁻¹ y⁻¹. Expectedly, estimated soil loss was significantly correlated with measured rainfall and simulated surface runoff. Based on the estimated soil loss rates, the watershed was divided into four priority categories for conservation intervention. The study demonstrates that the SWAT model provides a useful tool for soil erosion assessment from watersheds and facilitates planning for a sustainable land management in Ethiopia. Copyright © 2010 John Wiley & Sons, Ltd.     

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 loss and runoff on semiarid land as amended with urban solid refuse

Organic amendment is a proved method of improving soil physical properties thus affecting runoff and soil erosion. Urban wastes are a potential source of organic matter and their use would also be a convenient way of disposing of them. A field experiment was conducted from October 1988 to September 1993 in a semiarid Mediterranean site to determine the effect of applying several rates (65, 130, 195 and 260 Mg ha⁻¹) of organic urban solid refuse (USR) on total runoff and soil loss. At the lowest rate, total runoff decreased by 67 per cent compared to the control plot. The decrease was 98 per cent when the highest rate was used. The lowest rate reduced total sediment loss by 81 per cent and the highest rate of 99 per cent. The decrease in soil erodibility at the different USR rates varied from 76 to 95 per cent depending on the year for the lowest rate and between 90 and 99 per cent for the other rates. Clear differences in the hydrologic and erosion responses were found between the eight initial rainfall events (during the first 10 months of the experiment) and the remainder of the events. The causes of such differences were due to the initial tillage of the soil by rotovation and the growth of natural vegetation in the treated plots. The mechanical effect of tillage reduced runoff and increased soil erodibility, although the effect was short‐lived. The addition of USR reduced runoff but lasted longer. An applied rate of 90–100 Mg ha⁻¹ could be considered suitable for application in semiarid zones. Copyright © 2000 John Wiley & Sons, Ltd.     

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.     

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.     

Effects of Tillage Methods on Soil Carbon and Wind Erosion

Current interest in soil‐conserving tillage in China has developed from the concern that Chinese agricultural land loses 73·8 Mg C annually. Previous research has shown that changing from conventional tillage to conservation tillage field management increases soil C sequestration. The aim of this study is to determine if no tillage with stubble retention can reduce soil carbon loss and erosion compared with conventional tillage for a cornfield in northern China. We found that soil organic C storage (kg m⁻²) under conservation tillage in the form of no post‐harvest tillage with stubble retention increased from 28% to 62% in the soil depths of 0–30 cm (p < 0·01) compared with the conventional tillage. Retaining post‐harvest stubble with a height of 30 cm and incorporating the stubble into the soil before seeding the next spring increased soil organic carbon the most. Carbon storage (kg ha⁻¹) in aboveground and belowground biomass of the corn plants in seedling and harvest stages was significantly greater (p < 0·01) with stubble retention treatments than with conventional tillage. Carbon content in root biomass in all treatments with stubble retention was significantly greater than that with conventional tillage. Soil erosion estimates in the study area under conservation tillage with stubble retention was significantly lower than that under conventional tillage during the monitoring period. Given the complexities of agricultural systems, it is unlikely that one ideal farming practice is suitable to all soils or different climate conditions, but stubble retention during harvesting and incorporation of the stubble into soil in the next spring appears to be the best choice in the dry northern China where farmlands suffer serious wind erosion. Copyright © 2015 John Wiley & Sons, Ltd.     

Mechanized tillage systems effects on soil erosion from an alfisol in watersheds cropped to maize

The degradative effects of mechanized farming operations on soils in the tropics are not widely documented. This study was conducted to quantify the effects of mechanized no-till and conventional tillage systems on runoff, erosion and changes in soil properties. Experiments were conducted on twin watersheds of about 5 ha each. Only the conventionally plowed watershed was terraced to control erosion. Measurements made with a rate-measuring H-Flume indicated that runoff and erosion from the terraced and conventionally tilled watershed were several times greater, compared with the unter-raced no-till watershed. Cumulative runoff in 1979 was 10 times and erosion 42.2 times higher from the plowed watershed than from the no-till watershed. The infiltration capacity 5 years after land development was 3.8 cm h^?1 for the plowed and 10.4 for the no-till watershed. Surface soil from the no-till watershed retained more water at all soil water potentials than that from the plowed treatment. The gravel content in the surface layer of the plowed watershed was 25.1%, compared with 15.8% in the no-till watershed. The maize grain yield from the twelfth consecutive crop was 3 Mg ha^?1 for the no-till and 1 Mg ha^?1 for the plowed watershed.     

Effects of vertical hedge interval of vetiver grass on erosion on steep agricultural lands

Vetiver grass is widely used to reduce soil erosion and has been applied in many areas of the world. However, studies of the effect of vertical hedge intervals on runoff, soil loss and outflow sediment size distribution under a steep slope area are rare. The vetiver grass system (VGS) with three vertical hedge intervals (0·75, 1·5 and 3 m) and no hedgerow were tested at three land slopes (30, 40 and 50 per cent) under three simulated rainfall intensities (60, 85 and 110 mm h⁻¹). It has been observed that vetiver grass (Vetiveria nemoralis) has great potential for reducing runoff and soil loss by about 38·7–68·6 and 56·2–87·9 per cent, respectively. The vetiver strips delayed incipient runoff and reduced peak runoff rate and steady erosion rate. The land slope affected soil loss but did not have a significant effect on runoff. A narrow vetiver hedge interval slightly reduced runoff and soil loss more than a wider one. The soil loss equation obtained in this study revealed that runoff has a higher effect on soil loss. The median sediment size that passed through the vetiver strip increased with rainfall intensity and was mostly dominated by very fine sand, silt and clay. Copyright © 2009 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.     

Runoff and losses by erosion in soils amended with sewage sludge

In order to promote the transformation of a burnt Mediterranean forest area into a dehesa system, 10 t ha⁻¹ of dry matter of the same sewage sludge in three different forms: fresh, composted and thermally‐dried, were added superficially to field plots of loam and sandy soils located on a 16 per cent slope. This application is equivalent to 13ċ8 t ha⁻¹ of composted sludge, 50 t ha⁻¹ of fresh sludge and 11ċ3 t ha⁻¹ of thermally‐dried sludge. The surface addition of a single application of thermally‐dried sludge resulted in a decrease in runoff and erosion in both kinds of soil. Runoff in thermally‐dried sludge plots was lower than in the control treatment (32 per cent for the loam soil and 26 per cent for the sandy soil). The addition of any type of sludge to both soil types also reduces sediment production. Significant differences between the control and sludge treatments indicate that the rapid development of plant cover and the direct protective effect of sludge on the soil are the main agents that influence soil erosion rates. Results suggest that the surface application of thermally‐dried sludge is the most efficient way to enhance soil infiltration. Copyright © 2003 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.     

Assessment of soil erosion hazard in Kilie catchment,East Shoa,Ethiopia

This paper reports on a field study conducted in Kilie catchment, East Shoa Zone, Ethiopia to assess the rate of soil erosion by employing a soil loss prediction model (Universal Soil Loss Equation) integrated with in remote sensing and geographical information systems (RS/GIS), environment and gully measurement techniques. The final soil erosion risk map was produced after multiplication of the six factors involved in the USLE and RS/GIS. Gully measurement showed that the erosion rate is higher for the upland areas than the lowlands due to inappropriate soil and water conservation measures, free grazing by animals and conversion of hillside areas into farmlands. About 97·04 per cent of the study catchment falls within a range of 0–10 t ha⁻¹ yr⁻¹ sheet/rill erosion rate. We found that 2·17 per cent of the study area in the uplands has a soil erosion rate falling between 10 and 20 t ha⁻¹ yr⁻¹. About 0·8 per cent of the study area in the uplands is hit by severe sheet/rill erosion rate within the range of 20–60 t ha⁻¹ yr⁻¹. Gully erosion extent in the study area was evaluated through gully measurement and quantification methods. Gully density of 67 m ha⁻¹ was recorded in the catchment. The gully to plot area ratio was found to be 0·14 on average. Hence, in the upland areas, sustainable land management practices are required in order to reduce the rate of soil erosion. Copyright © 2011 John Wiley & Sons, Ltd.     

Modelling Post‐Tree‐Harvesting Soil Erosion and Sediment Deposition Potential in the Turano River Basin (Italian Central Apennine)

The overall aim of the paper is the assessment of human‐induced accelerated soil erosion processes due to forest harvesting in the Upper Turano River Basin. The spatio‐temporal pattern of soil erosion processes was investigated by means of a spatially distributed modelling approach. We used the Unit Stream Power Erosion and Deposition model. During the soil erosion‐modelling phase, the forest cover changes were mapped via remote sensing. According to this operation, the forest sectors exploited for timber production amounted to about 2781 ha or 9·9% of the wooded surface from March 2001 to August 2011. In this period, the average annual net soil erosion rate estimated by means of modelling operations totalled 0·83 Mg ha⁻¹ y⁻¹ for all the forest lands. The net soil erosion rate predicted for the disturbed forest lands is significantly higher than the average value for the entire forest (5·34 Mg ha⁻¹ y⁻¹). Estimates indicate a soil loss equal to 8521 Mg y⁻¹ (net soil erosion 0·34 Mg ha⁻¹ y⁻¹) in the undisturbed forest area (254 km²), whereas the 27·8 km² of disturbed forest area could potentially lose 14 846 Mg y⁻¹. The paper shows that a disturbed forest sector could produce about 74·2% more net erosion than a nine times larger, undisturbed forest sector. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of Land Management on Different Forms of Soil Carbon in Olive Groves in Mediterranean Areas

This study analyses soil organic carbon (SOC) and hot‐water extractable carbon, both measures of soil quality, under different land management—(i) conventional tillage (CT); (ii) CT plus the addition of oil mill waste alperujo (A); (iii) CT plus the addition of oil mill waste olive leaves (L); (iv) no tillage with chipped pruned branches (NT₁); and (v) no tillage with chipped pruned branches and weeds (NT₂)—in a typical Mediterranean agricultural area: the olive groves of Andalusia, southern Spain. SOC values in CT, A, NT₁ and NT₂ decreased with depth, but in NT₂, the surface horizon (0–5 cm) had higher values than the other treatments, 47% more than the average values in the other three soils. In L, SOC also decreased with depth, although there was an increase of 88·5% from the first (0–10 cm) to the second horizon (10–16 cm). Total SOC stock values were very similar under A (101·9 Mg ha⁻¹), CT (101·7 Mg ha⁻¹), NT₁ (105·8 Mg ha⁻¹) and NT₂ (111·3 Mg ha⁻¹, if we consider the same depth of the others). However, SOC under L was significantly higher (p < 0·05) at 250·2 Mg ha⁻¹. Hot‐water extractable carbon decreased with depth in A, CT and NT₁. NT₂ and L followed the same pattern as the other management types but with a higher value in the surface horizon (2·3 and 4·9 mg g⁻¹, respectively). Overall, our results indicate that application of oil mill waste olive leaves under CT (L) is a good management practice to improve SOC and reduce waste. Copyright © 2014 John Wiley & Sons, Ltd.     

Organic Farming Affects C and N in Soils Under Olive Groves in Mediterranean Areas

Under semiarid climatic conditions, intensive tillage increases soil organic matter losses, reduces soil quality, and contributes to climate change due to increased CO₂ emissions. There is a need for an agricultural management increasing soil organic matter. This paper presents the organic carbon (OC) and nitrogen (N) stocks, C:N ratio and stratification ratios (SRs) of these properties for olive groves soils under long‐term organic farming (OF), and conventional tillage (CT) in Los Pedroches valley, southern Spain. The results show that OF increased C and N stocks. The soil organic carbon (SOC) stock was 73·6 Mg ha⁻¹ in OF and 54·4 Mg ha⁻¹ in CT; and the total nitrogen (TN) stock was 7·1 Mg ha⁻¹ and 5·8 Mg ha⁻¹ for OF and CT, respectively. In the surface horizon (A: 0–16·9 cm in OF and Ap: 0–21·8 cm in CT) and Bw horizon (16·9–49·6 cm in OF and 21·8–56 cm in CT), SOC and TN concentrations and C:N ratios were higher in OF than in CT. Soil properties stratification in depth, expressed as a ratio, indicates the soil quality under different soil management systems. The SR of SOC ranged from 2·2 to 3·1 in OF and from 2·1 to 2·2 in CT. However, only SR2 (defined by Ap‐A/C) showed significant differences between CT and OF. The SR of TN showed similar trends to that of the SR of SOC. Organic farming contributes to a better soil quality and to increased carbon sequestration. Copyright © 2013 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.     

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.