Effect of Polyacrylamide integrated with other soil amendments on runoff and soil loss: Case study from northwest Ethiopia

Anionic polyacrylamide (PAM) has the potential to reduce soil erosion through soil conditioning. However, a comprehensive study about its effectiveness especially when applied combined with other amendments have rarely been conducted in the tropical highland climatic conditions, such as in Ethiopia. The study assessed the effectiveness of PAM (P = 40 kg ha^?1) alone or integrated with other soil amendments such as gypsum (G = 5 t ha^?1), lime (L = 4 t ha^?1) and biochar (B = 8 t ha^?1) on runoff and soil loss at Aba Gerima watershed in the Upper Blue Nile basin, northwest of Ethiopia, where there is high erosion-caused soil degradation. A total of 79 daily runoff and sediment data were collected from eight runoff plots (1.3m × 4m) with three replications planted with teff (Eragrostis tef) crop for two years (2018 & 2019) rainy seasons. Associated changes in soil physicochemical properties and crop growth parameters were investigated. Treatments reduced seasonal runoff by 12–39% and soil loss by 13–53%. The highest reduction in runoff was observed from P + B and PAM treatments while the highest reduction in soil loss was observed from that of P + L and PAM treatments. Integrating PAM with other amendments improved soil structural stability, moisture content, soil pH (P + L) and organic matter (P + B), leading to favorable environment for crop growth (biomass yield) and reduced runoff and soil erosion. Unlike PAM, biochar and lime amendments may need more time after application to be more effective. Hence continuing the field experiment and studying physico-chemical mechanisms for extended period will better elucidate their single or combined effectiveness over time.     

Erosion rates and nutrient losses affected by composted cattle manure application in vineyard soils of NE Spain

Land preparation for mechanisation in vineyards of the Anoia–Alt Penedès region, NE Spain, has required major soil movements, which has enormous environmental implications not only due to changes in the landscape morphology but also due to soil degradation. The resulting cultivated soils are very poor in organic matter and highly susceptible to erosion, which reduces the possibilities of water intake as most of the rain is lost as runoff. In order to improve soil conditions, the application of organic wastes has been generalised in the area, not only before plantation but also every 3–4 years at rates of 30–50 Mg ha^− 1 mixed in the upper 30 cm.These organic materials are important sources of nutrients (N and P) and other elements, which could reduce further fertilisation cost. However, due to the high susceptibility to sealing of these soils, erosion rates are relatively high, so a higher nutrient concentration on the soil surface increases non-point pollution sources due to runoff.The aim of this study is to analyse the influence of applied composted cattle manure on infiltration, runoff and soil losses and on nutrients transported by runoff in vineyards of the Alt Penedès–Anoia region, NE Spain. In the two plots selected for the analysis, composted cattle manure had been applied in alternate rows 1 year previous to the study. In each plot soil surface samples (0–25 cm) were taken and compared to those of plots without manure application. The study was carried out at laboratory scale using simulated rainfall. Infiltration rates were calculated from the difference between rainfall intensity and runoff rates, and the sediment and total nitrogen and phosphorus were measured for each simulation. In addition, the influence of compost was investigated in the field under natural rainfall conditions by analysing the nutrient concentration in runoff samples collected in the field (in the same plots) after seven rainfall events, which amount different total precipitation and had different erosive character.Compost application increases infiltration rates by up to 26% and also increases the time when runoff starts. Sediment concentration in runoff was lower in treated (13.4 on average mg L^− 1) than in untreated soils (ranging from 16.8 to 23.4 mg L^− 1). However, the higher nutrient concentration in soils produces a higher mobilisation of N (7–17 mg L^− 1 in untreated soils and 20–26 mg L^− 1 in treated soils) and P (6–7 mg L^− 1 in untreated soils and 13–19 mg L^− 1 in treated soils). A major part of the P mobilised was attached to soil particles (about 90% on average) and only 10% was dissolved. Under natural conditions, higher nutrient concentrations were always recorded in treated vs. untreated soils in both plots, and the total amount of N and P mobilised by runoff was higher in treated soils, although without significant differences. Nutrient concentrations in runoff depend on rainfall erosivity but the average value in treated soils was twice that in untreated soils for both plots.     

典型黑土区陡坡植草水土流失防治效果研究

[目的]研究陡坡生物防治与影响因素的变化关系,为侵蚀沟治理、水土保持植被措施配置等决策提供科学依据。[方法]设置2个坡度,7种草本植被配置模式,于2018年6—9月开展了自然小区水土流失监测。[结果] 1∶1.5和1∶1.2坡比边坡草本建植当年分别较裸地平均减流27%和26%,减沙52%和21%,坡度由34°增加到40°,地表径流虽未增加,但土壤侵蚀量明显增加;影响产流产沙的降雨因子主要有雨量,I_(30),E,EI_(30),坡度变陡,相关性增强;建植草无芒雀麦和紫花苜蓿混播减流减沙效果最好,紫花苜蓿、无芒雀麦、早熟禾3种草种混播减流效果优于单播;1∶1.2坡比边坡随着植被盖度的增加减沙效果逐渐增强,且在植被盖度大于50%时减沙效果接近1∶1.5坡比边坡。[结论]在无芒雀麦和紫花苜蓿混播草本配置下,1∶1.2坡比削坡在侵蚀沟治理时可采用,能减少20%的削坡占地面积。     

Harvest intensity of aromatic shrubs vs. soil erosion: An equilibrium for sustainable agriculture (SE Spain)

In the Mediterranean Europe, where rainfall is scarce and irregular but often of high intensity, wild shrubs protect the soil against erosivity of raindrops. Moreover, some of these plants are the economic income for local farmers. Particularly in SE Spain, soil erosion is a core factor in environmental degradation attributed primarily to the cultivation practices and human pressure on the land. Over a four-year period, soil erosion and runoff were monitored in erosion plots on a mountainside, comparing four harvest intensities of four aromatic shrubs (Lavandula lanata L., Santolina rosmarinifolia L. Origanum bastetanum, and Salvia lavandulifolia V.): 0% (HI-0), 25% (HI-25), 50% (HI-50), and 75% (HI-75). Also, the fresh biomass and essential-oil content were quantified in each treatment. The erosion plots were located in Lanjarón (Granada, SE Spain) on the southern flank of the Sierra Nevada Mountains, on a 20% slope, and of 96 m² in area. The average soil loss for HI-0, HI-25, HI-50, and HI-75 during the study period was 144.6, 187.2, 256.0, and 356.0 kg ha^− 1, respectively, and runoff 2.6, 3.2, 3.4, and 4.7 mm, respectively. The lowest average soil erosion and runoff rates for the study period were recorded with plant cover of S. lavandulifolia V. 67.6 kg ha^− 1 and 1.3 mm, respectively. Since no significant differences were found between HI-25 and HI-50 for soil erosion and runoff, and harvest and distillation of wild-aromatic plants currently persists as an important economic activity in mountainous areas of the study zone, we recommend a rational harvest (HI-50), leaving the 50% of the plant biomass in the field (especially for sage and lavender) to avoid the soil degradation. In this sense, the harvest of 50% of fresh herb of sage, santolina, lavender, and oregano produced reasonable essential-oil yield of 12.7, 14.0, 19.7, and 18.3 L ha^− 1, respectively. The inappropriate harvest of aromatic plants and the intensity farming systems of mountain areas endanger land conservation, and there is an urgent need to implement appropriate land management which has a large-scale perspective but acts at the local level.     

Soil mineral nitrogen concentration within cycles of flood irrigation: Effect of rice stubble and fertilization management

Two field experiments using macro (3.5 × 12m) plots and ¹⁵N-labelled fertilizer on micro (155 mm internal diameter) plots were undertaken to measure the effects of rice (Oryza sativa L.) stubble management and nitrogen fertilizer strategies on N transformations within a series of intermittent flood irrigations. Nitrate concentration fell by 90% during each flooding, and analysis of ¹⁵N micro plots showed the loss was due to denitrification rather than leaching. Over 52% of the ¹⁵N was lost. Apparent loss over four irrigations from macro plots receiving 60 kg urea-N ha⁻¹ was 37 kg N ha⁻¹ while unfertilized plots lost 19 kg N ha⁻. Stubble incorporation reduced nitrate accumulation rate and increased immobilization, thereby reducing denitrification losses by 23%. Nitrate concentration in the 0–100 mm soil layer increased after the soil water content fell below field capacity during the drying portion of each cycle, but the net nitrification rate fell with increasing number of cycles.Ammonium content in the top 100mm of soil fell from 35kgNha⁻¹ to 3kgNha⁻¹ over four irrigations. This fall was ascribed to the combined effects of nitrification and immobilization. Immobilization was greatest on plots where large quantities of rice stubble had been incorporated, and over 50% of the applied ¹⁵N was retained in the soil on these plots compared with 40% (SED = 3.5%) on plots where stubble had been burnt. We conclude that the poor response of rice to fertilization at sowing is due to a combination of denitrification and immobilization of applied nitrogen during cycles of wetting and drying prior to permanent flood.     

Surface runoff and soil erosion in a natural regeneration area of the Brazilian Cerrado

The Brazilian Cerrado has been converted to farmland, and there is little evidence that this expansion will decrease, mainly because agriculture is the country’s main economic sector. However, the impacts of intense modification of land use and land cover on surface runoff and soil erosion are still poorly understood in this region. Here, we assessed surface runoff and soil loss in a woodland Cerrado area under a former pasture area, which was abandoned and has undergone a natural regeneration process for 7 years (RC). Its results were compared with that found in an undisturbed area of woodland Cerrado (CE), 40-month-old eucalyptus (3.0 × 1.8 m) (EU), and pasture under rotational grazing (PA). The study was conducted on Red Acrisol located in the Brazilian Cerrado. We performed rainfall simulations on a plot of 0.7 m² and using three constant rainfall intensities of 60, 90, and 120 mm h⁻¹ for 1 h. For each rainfall intensity, we carried out four repetitions using different plots in each treatment, i.e. 12 plots per treatment studied and 48 plots in total. We noted that the soil physical properties were improved in RC and, consequently, water infiltration and soil erosion control; RC presented surface runoff and soil loss different from EU and PA (α = 0.05). The macroporosity and soil bulk density affected surface runoff in RC and PA because the RC was used as pasture and is currently regenerating back to the cerrado vegetation. As the rainfall intensity increased, EU became more similar to PA, which showed the highest surface runoff and soil loss. Our findings indicate that natural regeneration processes (pasture to the cerrado vegetation) tend to improve the soil ecosystem services, improving infiltration and reducing surface runoff and soil erosion.     

Residue impacts on runoff and soil erosion for different corn plant populations

The year to year carry-over effects of biomass additions under different plant populations on runoff and erosion are unclear. The objective of this study was to quantify the impact of different plant populations on residue cover to elucidate the effects of residue cover on runoff and erosion. The residue management system involved shredding of corn (maize) biomass after harvest, incorporating the residue in the spring, and leaving the land fallow until it was no-till planted the following spring. Runoff and soil losses were measured on 18 runoff plots with plots arranged in two areas with each having three randomized treatments (0%, 50%, and 100% plant population) with three replications. The two areas were managed as a fallow/no-till corn rotation in two cycles of alternating years. Surface residue cover was highly dynamic with significant changes between cycles and seasons in response to the management practices. The annual soil losses were reduced by 47% and 54% for the 50% and 100% plant populations, respectively compared to the control. However, the annual soil loss even for the 100% plant population was still nearly seven times the tolerable soil loss limit of 7 ton ha⁻¹. The normal erosion protection afforded by no-till practices was lost by the incorporation of residue the previous year.     

The critical role of human activities in land degradation in Rwanda

Agriculture on steep land is widespread in Rwanda. Conservation strategies, such as grass strips and terracing, were introduced by the government and international agencies to lower soil losses due to fluvial processes in this fragile setting. Minimal attention has been given to assessing soil losses due to farming activities or to developing conservation strategies to control soil erosion resulting from these human activities. This study evaluates soil losses resulting from both runoff and human activities in a densely populated region of northwestern Rwanda. During a 4-year period, 11 Wischmeier-type plots were cultivated with the typical local crops. Grass strips and grass/shrub strips were planted at 5-m intervals on eight of these plots. Five meters is the common spacing of this government-encouraged conservation practice. These strips were found to be useful for reducing soil loss from runoff, but they were relatively ineffective in curtailing soil losses resulting from human activities associated with the local farming system. The soil loss on the cultivated plots, resulting from activities such as hoeing, averaged over 68·2 t ha⁻¹ year⁻¹. Unless conservation strategies curtail human induced soil losses as well as those due to fluvial processes, the land resource will continue to degrade and farmland will cease to be productive in the study area.     

Soil losses due to cassava and sweet potato harvesting: A case study from low input traditional agriculture

Soil loss due to crop harvesting (SLCH) has been established as an important soil erosion process that has significantly contributed to soil degradation in highly mechanised agriculture. This has stimulated the need to investigate the importance of this process of erosion under low input agriculture where, until now, only water and tillage erosion are known as important phenomena causing soil degradation. This study was conducted in Eastern Uganda with the following objectives: (1) to assess the amount of soil lost due to the harvesting of cassava roots and sweet potato tubers under low input agriculture, (2) to look into the factors that influence variations in these soil losses, and (3) to estimate the amount of plant nutrients lost due to SLCH for cassava and sweet potato. Soil sticking to roots and tubers was washed and the soil suspension oven dried to estimate the amount of soil lost after harvesting. Mean annual soil loss for cassava was 3.4 tonnes ha⁻¹ and for sweet potato was 0.2 tonnes ha⁻¹. Ammonium acetate lactate extractable soil nutrient losses for cassava were N = 1.71 kg ha⁻¹ harvest⁻¹, P = 0.16 kg ha⁻¹ harvest⁻¹, K = 1.08 kg ha⁻¹ harvest⁻¹ and for sweet potato were N = 0.14, P = 0.01 kg ha⁻¹ harvest⁻¹, K = 0.15 kg ha⁻¹ harvest⁻¹. Difference in soil loss due to crop harvesting for cassava and sweet potato could be due to: (1) smaller yields of sweet potato leading to smaller soil losses on an area basis, (2) smoother skin and less kinked morphology of sweet potato that allowed less soil to adhere, and (3) the fact that sweet potato is planted in mounds which dry out faster compared to the soil under cassava. Soil moisture content at harvesting time and crop age were significant factors that explained the variations in the soil lost at cassava harvesting. Soil loss under cassava justifies the need to conduct further investigations on this process of soil erosion under low input agriculture.     

Nitrogen addition stimulates different components of soil respiration in a subtropical bamboo ecosystem

Soil respiration is an important carbon (C) flux of global C cycle, and greatly affected by nitrogen (N) addition in the form of deposition or fertilization. However, the effects of N addition on the different components of soil respiration are poorly understood. The aim of this study is to investigate how the components of soil respiration response to N addition and the potential mechanisms in a subtropical bamboo ecosystem. Four N treatment levels (0, 50, 150, 300 kg N ha⁻¹ year⁻¹) were applied monthly in a Pleioblastus amarus bamboo plantation since November 2007. Total soil respiration (RS_T) and soil respiration derived from litter layer (RS_L), root-free soil (RS_S), and plant roots (RS_R) were measured for one year (February 2010 to January 2011). The results showed that the mean rate of RS_T was 428 ± 11 g C m⁻² year⁻¹, and RS_L, RS_S, RS_R contributed (30.2 ± 0.7)%, (20.7 ± 0.9)%, and (49.1 ± 0.7)%, respectively. The temperature coefficients (Q₁₀) of RS_T, RS_L, RS_S, and RS_R were 2.87, 2.28, 3.09, and 3.19, respectively, in control plots. Nitrogen additions significantly increased RS_T and its three components. RS_R was stimulated by N additions through increasing fine root biomass and root metabolic rate. The positive effects of N additions on soil fertility, microbial activity, and the quality and amount of aboveground litterfall also stimulated other CO₂ production processes. In the background of increased N input, response of RS_T and components of RS_T are primarily due to the positive response of plant growth in this bamboo ecosystem.     

Residue cover and rainfall intensity effects on runoff soil organic carbon losses

Soil cover and rainfall intensity (RI) are recognized to have severe impacts on soil erosion and an interaction exists between them. This study investigates the effect of rainfall intensity (RI) and soil surface cover on losses of sediment and the selective enrichment of soil organic carbon (SOC) in the sediment by surface runoff. A field rainfall simulator was used in the laboratory to produce 90 min rainfall events of three rainfall intensities (65, 85 and 105 mm h^− 1) and four cover percentages (0%, 25%, 50% and 75%) on soil material at 9% slope. A strong negative exponential relation was observed between cover percentage and RI on sediment loss under 85 and 105 mm h^− 1 of rain, while under RI of 65 mm h^− 1, the highest sediment loss was observed under 25% cover. Overall, higher RI and lower cover produced higher sediment and consequently higher nutrient loss, but resulted in a lower SOC enrichment ratio (ER_SOC) in the sediment. The amount of runoff sediment rather than the ER_SOC in the sediment was the determinant factor for the amount of nutrients lost. The values of ER_SOC were high and positively correlated with the ER values of particles smaller than 20 µm (p < 0.01). Although the sediment contained substantially more fine fractions (fine silt and clay, < 20 µm), the original soil and runoff sediment were still of the same texture class, i.e. silt clay loam.     

The phosphorus source determines the arbuscular mycorrhizal potential and the native mycorrhizal colonization of tall fescue and wheatgrass

The study assesses the effect of two phosphate (P) sources (soluble superphosphate (SP) and rock phosphate (RP)) on the arbuscular mycorrhizal potential (AMP), the root arbuscular mycorrhizal colonization (AMC) and the growth of tall fescue and wheatgrass of a grassland soil from Argentina. Mycorrhizal potential was assessed with soil samples collected from 2 years for tall fescue and wheatgrass swards before and after field plots were fertilized with 0 and 60 kg P ha⁻¹ as SP or RP. Mycorrhizal potential both at unfertilized and at RP fertilized plots was high (12–14 AM propagules g⁻¹), however fertilization with SP caused a decrease in AMP (0.70–0.95 AM propagules g⁻¹). A range of soil P between 4 and 46 mg P kg⁻¹ and a range of root AMC between 6% and 50% were obtained after fertilization with four rates of SP and RP (0, 15, 30, and 60 kg P ha⁻¹) in plots where tall fescue and wheatgrass were grown during 2 years. Soil P and root mass were higher in the top 10-cm depth than in the 20-cm of the soil profile, but AMC did not change with depth. Shoot dry matter (SDM) production of both grasses did not differ after fertilization with SP or RP, particularly at second year. The AMP positively correlated with the indigenous AMC, and they were not different between tall fescue or wheatgrass. Lineal-plateau relationships between soil P, relative SDM and AMC were established. Highest relative SDM was attained at 6.5 mg P kg⁻¹ in plots fertilized with RP, and at 15.2 mg P kg⁻¹ with SP. Variability in colonization was well accounted by the soil P (at 0–10 cm depth) fertilized with SP (r² = 0.48, P 0.01), but any relationship was found with RP. The AMC decreased with increasing available soil P from plots with SP until 18.3 mg kg⁻¹ (a decrease of 2.2% per mg P kg), after that AMC was stabilized at about 6.9%. Our study clearly showed that fertilization with SP or RP produced similar available soil P content and grasses SDM production. Mycorrhiza root colonization and propagules decreased after fertilization with SP, but fertilization with RP did not decrease mycorrhizal propagules nor colonization. It can be concluded that RP fertilization instead SP could allow obtaining acceptable tall fescue and wheatgrass yield enhancing mycorrhizal potential of soils and indigenous colonization of plants and thus maximizing the use of fertilizer.     

Effectiveness of geotextiles in reducing runoff and soil loss: A synthesis

Despite geotextiles having potential for soil conservation, limited scientific data are available to assess the effects of geotextiles in reducing runoff and water erosion. Hence, the objective of this review is to analyse the effects of plot length (L) and other possible affecting factors [cover percentage (C, %), slope gradient (S), rainfall duration (D), rainfall intensity (I), sand, silt and clay contents, soil organic matter (SOM) content and geotextile type (natural or synthetic)] on the effectiveness of geotextiles in reducing soil and water loss, based on reported experimental data. From linear regressions, C (%) and soil sand, silt and clay contents are found to be the most important variables in reducing SLR (ratio of soil loss in bare plots to that in geotextile treated plots) for splash, C (%) for interrill and D (min) for rill and interrill erosion processes, respectively. Soil clay and silt contents and D are key variables in decreasing RR (ratio of runoff from bare plots to that from geotextile treated plots) for interrill, and clay content for rill and interrill erosion processes, respectively. The linear relationship between mean b-value (geotextile effectiveness factor in reducing soil loss) and L of all studies was not significant (P > 0.05). The same is true for the relationship between L and SLR, and L and RR. However, when L is added to an equation as an interaction term with C (%), geotextile cover is significantly (P < 0.05) more effective in reducing SLR on shorter plots than longer ones for both interrill and rill and interrill erosion processes. Buffer strip plots (area coverage ∼ 10%) with Borassus and Buriti mats have the highest b-values.     

The effect of soil phosphorus on particulate phosphorus in land runoff

Accumulation of surplus phosphorus (P) in the soil and the resulting increased transport of P in land runoff contribute to freshwater eutrophication. The effects of increasing soil P (19–194 mg Olsen‐P (OP) kg⁻¹) on the concentrations of particulate P (PP), and sorption properties (Q_max, k and EPCo) of suspended solids (SS) in overland flow from 15 unreplicated field plots established on a dispersive arable soil were measured over three monitoring periods under natural rainfall. Concentrations of PP in plot runoff increased linearly at a rate of 2.6 μg litre⁻¹ per mg OP kg⁻¹ of soil, but this rate was approximately 50% of the rate of increase in dissolved P (< 0.45 μm). Concentrations of SS in runoff were similar across all plots and contained a greater P sorption capacity (mean + 57%) than the soil because of enrichment with fine silt and clay (0.45–20 μm). As soil P increased, the P enrichment ratio of the SS declined exponentially, and the values of P saturation (P_sat; 15–42%) and equilibrium P concentration (EPCo; 0.7–5.5 mg litre⁻¹) in the SS fell within narrower ranges compared with the soils (6–74% and 0.1–10 mg litre⁻¹, respectively). When OP was < 100 mg kg⁻¹, P_sat and EPCo values in the SS were smaller than those in the soil and vice‐versa, suggesting that eroding particles from soils with both average and high P fertility would release P on entering the local (Rosemaund) stream. Increasing soil OP from average to high P fertility increased the P content of the SS by approximately 10%, but had no significant (P > 0.05) effect on the P_sat, or EPCo, of the SS. Management options to reduce soil P status as a means of reducing P losses in land runoff and minimizing eutrophication risk may therefore have more limited effect than is currently assumed in catchment management.     

Risk assessment of the cultivation of a stacked Bt-maize variety (MON89034 × MON88017) for nematode communities

Genetically modified Bt-maize MON89034 × MON88017 contains three different genes derived from Bacillus thuringiensis (Bt) which enable protection against insect pests, due to expression of three different insecticidal crystal proteins (Cry proteins), i.e., Cry1A.105 and Cry2Ab2 against the European corn borer and Cry3Bb1 against the Western corn root worm. Nematodes are important organisms in agricultural soil ecosystems, and on fields with Bt-maize cultivation they will be exposed to Cry proteins released into the soil from roots or plant residues. The objective of this study was to analyze in a field experiment the effect of Bt-maize MON89034 × MON88017 on nematodes as non-target organisms. Nematode communities from soil planted with the Bt-maize were compared to those from soil planted with the near-isogenic cultivar (with and without chemical insecticide treatment) and two conventional maize cultivars. The experimental field consisted of 40 plots in a completely randomized block design (eight plots for each treatment), which were monitored over two growing seasons (2008 and 2009) at six sampling dates for nematode diversity at the genus level in the rhizosphere soil. Physicochemical soil properties and Cry protein concentrations were also analyzed. Nematodes showed very high abundances, as well as a high diversity of taxa and functional guilds, indicating the relevance of maize fields as their habitat. Neither Bt-maize cultivation, nor insecticide treatment adversely affected abundance or community structure of nematode assemblages in field plots compared to several non-Bt cultivars including a near-isogenic cultivar. This confirmed the risk estimations based on the analyzed soil concentrations of extractable Cry protein, not exceeding 4.8 ng g⁻¹ soil dry weight and thus revealing a safe toxicity-exposure ratio of >20.     

Evaluating the applicability of the water erosion prediction project (WEPP) model to runoff and soil loss of sandstone reliefs in the Loess Plateau,China

Soil erosion is one of the most serious environmental issues, especially in vulnerable areas such as the Pisha sandstone regions located in the Loess Plateau (China). In these types of reliefs, long-term studies monitoring runoff and soil loss are scarce, and even more considering the efficiency of different soil management techniques applied to reduce land degradation. In this study, seven years (2014–2020) of in-situ measurements of surface runoff and soil loss for different land uses (forestland, shrubland, grassland, farmland, and bare land) in a Pisha Sandstone environment at the Loess Plateau were conducted. We applied the Water Erosion Prediction Project (WEPP) model combining the large database with the precipitation regimes. Our results showed that runoff volume coming from observed and simulated data exhibited significant differences among them depending on the different vegetation types. Runoff and soil loss were different among diverse land use types as follows: farmland > grassland > shrubland > forestland. After conducting a calibration, we found satisfactorily simulated surface runoff and sediment yield based on precipitation regimes and land uses at sandstone reliefs. Simulation performance of surface runoff was better than sediment yield. The range of standard error of the model simulation for event and annual values of runoff were 4.71 mm and 12.19 mm, respectively. The standard error for event and annual values of soil loss were 4.19 t/hm² and 21.86 t/hm². In the calibration group, R² of runoff and soil loss were 0.92 and 0.86 respectively, while Nash-Sutcliffe coefficient (E) reached 0.90 and 0.85, respectively. In the validation group, the R² for both runoff and soil loss were 0.82 and 0.56, respectively. Nash-Sutcliffe coefficient (E) were 0.77 and 0.54 for the runoff and sediment yield. We concluded that using a detailed monitoring dataset, the WEPP model could accurately simulate and predict water erosion in the hillslopes of Pisha sandstone area.     

Tillage and crop management impacts on soil loss and crop yields in northwestern Ethiopia

Lack of appropriate agronomic practices is one of the major causes for soil erosion and low yields in teff (Eragrostis tef [Zucc.]) production in Ethiopia. A 3-yr study was conducted at the Aba Gerima watershed in northwestern Ethiopia, to investigate the effects of two tillage practices (reduced tillage [RT] and conventional tillage [CT]), two planting methods (row planting [RP] and broadcast planting [BP]), and two compaction options (with [+T] and without [–T] trampling) on soil loss and teff yields in a split-split plot arrangement. Sediment concentration ranged from 0.01 to 5.37 g L^?1 (mean, 0.25 g L^?1) in our study. Accordingly, the estimated total (August–October) soil loss ranged from 0.2 to 0.5 t ha^–1 (mean, 0.3 t ha^–1). The sediment concentration and total soil loss were significantly influenced (P < 0.05) by tillage, planting methods, and trampling only in the third monitoring year. RT reduced soil loss by 19% relative to that of CT, whereas RP resulted in a 13% reduction in soil loss over BP. The ?T plots showed a 15% reduction in soil loss as compared to + T plots. Results revealed significant increase in soil total carbon and nitrogen in RT and –T. Less soil loss and greater teff grain yield were obtained in plots with improved agronomic practices (RT and RP) compared to conventional ones (CT and BP). Based on our findings we conclude that the use of RT, RP, and –T practices can effectively minimize soil loss without any crop yield penalty.     

Assessing the tolerance to heavy metals of arbuscular mycorrhizal fungi isolated from sewage sludge-contaminated soils

Different fungal ecotypes were isolated from soils which had received long-term applications of metal-contaminated sewage sludge with the aim of studying the degree of tolerance and adaptation to heavy metals of arbuscular mycorrhizal (AM) fungi. The development and structural aspects of AM colonization produced by the different fungal isolates were studied using two host plants, Allium porrum and Sorghum bicolor, which were grown in either contaminated or non-contaminated soils. Four different AM fungi were successfully isolated from the experimental field plots: (i) Glomus claroideum, isolated from plots receiving only inorganic fertilizer; (ii) another apparently similar ecotype of Glomus claroideum, but isolated from plots with 300 m³ ha⁻¹ year⁻¹ of contaminated sludge added, (iii) an unidentified Glomus sp., present only in the less contaminated plots (100 m³ ha⁻¹ year⁻¹ of unamended sludge) and (iv) Glomus mosseae, isolated from plots receiving 100 or 300 m³ ha⁻¹ year⁻¹ of amended or unamended sludge (intermediate rates of contamination). There were consistent differences in behaviour among the four AM fungi tested with regard to the colonization levels they produced in non-contaminated and contaminated soils. Both total and arbuscular colonization were affected by heavy metal contamination. The main conclusions of this study are that Glomus sp. and G. mosseae isolates are strongly inhibited by heavy metals, which acted mainly by interfering with the growth of the external mycelium, and also by limiting the production of arbuscules. Our results suggest that G. claroideum isolates, particularly the ecotype which was isolated from the plots receiving the highest dose of metal-contaminated sludge, shows a potential adaptation to increased metal concentration in soil.     

Arbuscular mycorrhizal abundance in contaminated soils around a zinc and lead deposit

In order to study the variations in spore abundance and root colonization parameters of arbuscular mycorrhizal (AM) fungi in a naturally heavy metals polluted site and their relationships with soil properties, 35 plots in the Anguran Zn and Pb mining region were selected along a transect from the mine to 4500 m away. Within each plot, a composite sample of root and rhizospheric soil from a dominant indigenous plant was collected. The soil samples were analyzed for their physico-chemical characteristics. Spores were extracted, counted and identified at genus level. The roots were examined for colonization, arbuscular abundance, mycorrhizal frequency and intensity. Along the transect, the total and available (DTPA-extractable) concentration of Zn decreased from 6472 to 45 mg kg⁻¹ and 75 to 5 mg kg⁻¹, respectively. For Pb the values varied from 5203 to 0 mg kg⁻¹ and 32 to 0 mg kg⁻¹, respectively. In parallel, root colonization rate in the dominant native plants (except Alyssum sp.) varied from 35% to 85% and the spore numbers from 80 to 1306 per 200 g dry soil along the transect. Spores of Glomus were abundantly found in all plots as dominant, while Acaulospora spores were observed only in some moderately polluted and in control plots. AM fungal propagules never disappeared completely even in soils with the highest rates of both heavy metals. Spore numbers were more affected by Zn and Pb concentrations than root colonization. The variations of AM fungi propagules were better related to available than to total concentration of both metals. Spore numbers were positively correlated with mycorrhizal colonization parameters, particularly with arbuscular abundance.     

Factors affecting runoff and erosion under simulated rainfall in Mediterranean vineyards

Data on surface runoff and soil loss on gentle slopes with vineyards are analysed. Using a rainfall simulator, 22 rainstorms with varied intensities from 30 to 117.5 mm h⁻¹ and return periods from 2 to 127 years were reproduced. The experimental plots were installed on vineyards planted in straight rows and oriented with the slope direction having a mean gradient of 3.8°. The texture of soils was loamy, with a very heterogeneous surface gravel cover. Values of measured surface runoff varied from 7.2 mm h⁻¹ for low rainfall intensities (30 mm h⁻¹) and short return periods (2 years) to 41.9 mm h⁻¹ with simulation experiments of higher rainfall intensity (104 mm h⁻¹) and long return periods (68 years). Runoff increased linearly with rainfall intensity resulting in soil losses that also increased with rainfall intensity (18.2 g m⁻² h⁻¹ with storms of 30 mm h⁻¹, and 93.2 g m⁻² h⁻¹ with storms of 104 mm h⁻¹); however, r² explains only 36% of the variance. It was necessary to add other factors to improve the coefficient of determination (0.74; p = 0.001) and the predictive function of the equation. These variables were rainfall intensity, kinetic energy of the storm, runoff, soil resistance to drop detachment, surface gravel cover, and gradient. The equation obtained was validated with the USLE-M. In comparison with similar experiments in other regions, the results obtained for soil loss were very moderate, especially those caused by rainstorms of intermediate and low intensity.