Soil and crop responses to controlled traffic farming in reduced tillage and no-till: some experiences from field experiments and on-farm studies in Sweden

ABSTRACT

The purpose of this study was to investigate the impact of controlled traffic farming (CTF) with respect to soil physical properties and crop yield for Swedish conditions. Three field trials were conducted for six growing seasons in central and southern Sweden. In two of the trials, we compared CTF with random traffic farming (RTF) in deep chiseling (DC, 15–20?cm), shallow cultivation (SC, 5–10?cm) and no-till. The third trial was on farm study by using the existing CTF module at the farm. In the tracks of CTF (traffic zone) dry bulk density was increased and water movement was decreased. Soil penetration resistance was greater in the traffic zone than in the crop zone in some of the trials but the difference was not statistically significant. On average, crop yield was similar between CTF and RTF for all trials. Yield in the traffic zone was significantly less than that in the crop zone in the on-farm trial, but the yield in both zones were similar in the field trial at Lönnstorp, south Sweden. On the contrary, in the field trial at Säby 1 in Uppsala, central Sweden, crop zone produced less yield than traffic zone probably because of too loose soil, which impaired the uptake of nutrients and water. We conclude that if vehicle weight is not very high and the soil is not vulnerable to compaction, dual wheels and CTF are equal options.     

Innovative methods in soil phosphorus research: A review

Phosphorus (P) is an indispensable element for all life on Earth and, during the past decade, concerns about the future of its global supply have stimulated much research on soil P and method development. This review provides an overview of advanced state‐of‐the‐art methods currently used in soil P research. These involve bulk and spatially resolved spectroscopic and spectrometric P speciation methods (1 and 2D NMR, IR, Raman, Q‐TOF MS/MS, high resolution‐MS, NanoSIMS, XRF, XPS, (µ)XAS) as well as methods for assessing soil P reactions (sorption isotherms, quantum‐chemical modeling, microbial biomass P, enzymes activity, DGT, ³³P isotopic exchange, ¹⁸O isotope ratios). Required experimental set‐ups and the potentials and limitations of individual methods present a guide for the selection of most suitable methods or combinations.     

Soil pore-water environment and CO2 emission in a Luvisol as influenced by contrasting tillage

Little is known how contrasting tillage (deep ploughing, top- and sub-soil loosening with straight or bent leg cultivator [BLC], direct drilling [DD]) affect important soil physical properties (total porosity [TP], pore size distribution [PSD], water release characteristics [WRC]) and CO₂ emissions from a Luvisol. The study was aimed to alleviate compaction on land that had been under reduced tillage for 4 successive years. Undisturbed core samples were collected from 5–10, 15–20 and 25–30 cm depths for soil WRCs, TP and pore-size distribution determination. A closed chamber method was used to quantify the CO₂ emissions from the soil. Soil loosening with straight or BLC produced the highest total soil porosity (on average 0.48 m³ m^?3) within 5–30 cm soil layer, while conventional tillage (CT) gave 6%, DD up to 25% reduction. Sub-surface loosening with a BLC was the most effective tool to increase the amount of macro- and mesopores in the top- and sub-soil layers. It produced 21% more macro- and mesopores within 25–30 cm soil layer as compared to the soil loosened with a straight leg cultivator. Plant available water content under CT and DD was lower as compared to that under deep loosening with straight or BLC (23% and 18%, respectively). DD produced 12% lower soil surface net carbon dioxide exchange rate than CT and by 25–28% lower than deep soil loosening with straight or BLC. The increase in micropores within 25–30 cm soil layer caused net carbon dioxide exchange rate reduction. The amount of mesopores within the whole 5–30 cm soil layer acted as a direct dominant factor influencing net CO₂ exchange rate (NCER) (Pxy = ?3.063; r = 0.86).     

Tobacco harvest phase is critical to runoff and soil loss in conventional tillage system

Soil erosion in tobacco (Nicotiana tabacum) cultivation has been reported in recent years around the world. Moreover, studies also demonstrated total soil loss during cultivation. In this study, we proposed an assessment of loss of water and soil during the phases of tobacco cultivation. The tobacco cultivation cycle is approximately 180 days in Southern Brazil. We divided this period into 6 phases from planting (September) to the end of the harvest. During the phases, there were variations in soil management, which may indicate different rates of water and soil loss. Gerlach gutters were used to mediate soil and water loss. At each phase of cultivation, we also measured the surface roughness of the soil, water retention, soil exposure, trampling, soil resistance and soil bulk. Our results show that during cultivation the water and soil loss were 10.2% and 62.7 Mg ha⁻¹, respectively. However, the variation of activities during tobacco cultivation indicates different rates of water and soil loss. In the first three phases (90 days after planting), the surface roughness remained high (~19.2%) due to the soil turning, thus reducing the loss of water and soil despite little ground surface coverage. The soil tillage is stopped when the harvest of tobacco begins 120 days after planting. During the harvest, there was an increase in daily activities in the tobacco field, as the leaves were harvested every week, thus reducing soil roughness (~6.8%) and increasing soil density and strength. These conditions increased the rate of soil erosion during harvest. Therefore, the harvest phase is critical to runoff and soil loss.     

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.     

Response of organic matter to reduced tillage and animal manure in a temperate loamy soil

The impacts of tillage and organic fertilization on soil organic matter (SOM) are highly variable and still unpredictable, and their interactions need to be investigated under various soil, climate and cropping system conditions. Our work examined the effect of reduced tillage and animal manure on SOM stocks and quality in the 0–40 cm layer of a loamy soil under mixed cropping system and humid temperate climate. The soil organic carbon (SOC) and N stocks, particulate organic matter (POM), and C and N mineralization potential (301 days at 15 °C) were measured in a 8‐yr‐old split‐plot field trial, including three tillage treatments [mouldboard ploughing (MP), shallow tillage (ST), no tillage (NT)] and two fertilization treatments [mineral (M), poultry manure 2.2 t/ha/yr C (O)]. No statistically significant interactive effects of tillage and fertilization were measured except on C mineralization. NT and ST showed greater SOC stocks (41.2 and 39.7 t/ha C) than MP (37.1 t/ha C) in the 0–15 cm increment, while no statistical differences were observed at a greater depth. N stocks exhibited similar distribution patterns with regard to tillage effect. Animal manure, applied at a rate representative of typical field application rates, had a smaller impact on SOC and N stocks than tillage. The mean SOC and N stocks were higher under O than M, but the differences were statistically significant only in the 0–5 cm increment. MP showed lower C‐POM stocks than NT and ST in the 0–5 cm increment, whereas greater C‐POM stocks were measured under MP than under NT or under ST in the 20–25 cm increment. Organic fertilization had no impact on C‐POM or N‐POM stocks. In the 0–25 cm increment, NT showed a lower C and N mineralization potential than MP. Our work shows that the sensitivity of SOM to reduced tillage for the whole soil profile can be relatively small in a loamy soil, under humid‐temperate climate. However, POM was particularly sensitive to the differential effects of tillage practices with depth, and indicative of differentiation in total SOM distribution in the soil profile.     

The role of tillage and crops on a soil loss of an arable Stagnic Luvisol

The poor physical, chemical and biological properties make Stagnic Luvisol highly susceptible to water erosion on sloping terrains. The objective of this paper is to estimate the effect of different tillage treatments and crops (maize, soybean, winter wheat, spring barley, oilseed rape) on water erosion. The highest erosion in investigation period (1995–2014) was recorded in the control treatment with fallow, followed by the treatment that involved ploughing and sowing up and down the slope. Significantly, lower soil losses were recorded in no-tillage and treatments with ploughing and sowing across the slope. Regarding the crops significantly higher soil losses were recorded in spring row crops (maize and soybean) compared to high-density winter crops (wheat and oilseed rape) and double crop (spring barley with soybean). In the studied period, an average loss of 46 mm of the plough layer was recorded in the control treatment, while in treatment with ploughing and sowing up and down the slope average annual soil loss was 10 mm. According to the results of this study no-tillage and tillage across the slope are recommended as tillage which preserves soil for the next generations in agro-ecological conditions of continental Croatia.     

The effects of cover crops and conventional tillage on soil and runoff loss in vineyards and olive groves in several Mediterranean countries

Cover crops (CC) in vineyards and olive groves provide an alternative to conventional tillage (CT) for land management. Runoff, sediment and nutrient loss from six sites in France, Spain and Portugal were compared over 3–4 yr. In general, runoff loss was not significantly reduced by the CC alternatives: average annual runoff coefficients ranged from 4.9 to 22.8% in CT compared with 1.9–25% in the CC alternatives. However, at two sites, reductions in average annual runoff coefficients were greater for CC: 17.2 and 10.4% in CT, 6.1 and 1.9% in CC. Nutrient loss in runoff followed a similar pattern to runoff, as did pesticide loss on the one site; reductions occurred when runoff losses were significantly reduced by CC. The lack of differences at the other sites is thought to be due to a combination of soil conditions at the surface (compaction and capping) and sub‐surface (low‐permeability horizons close to the surface). In contrast, CC always resulted in reductions in soil erosion loss, plus similar reductions in nutrients and organic matter (OM) associated with sediment. Soil erosion loss ranged from 1.4 to 90 t/ha/yr in CT compared with 0.04–42.7 t/ha/yr in CC. Overall, reductions in runoff and associated nutrient and pesticide loss from vineyards and olives occurred with the introduction of CCs only when soil permeability was sufficiently high to reduce runoff. In contrast, reduction in soil erosion and associated nutrients and OM occurred even when the amount of runoff was not reduced. In the most extreme encountered situations (highly erodible soils in vulnerable landscape positions and subject to highly erosive rainfall), additional conservation measures are needed to prevent unsustainable soil loss.     

Soil microbial response to tillage systems and fertilization in a sunflower rhizosphere

Tillage systems and fertilization have important effects on soil microorganism activity. Information regarding the simultaneous evaluation of long-term tillage and fertilization on soil microbial traits in sunflower fields is not available. Therefore, this study was conducted to determine the best tillage and fertilization system for soil microbial parameters. The experimental design was a split plot based on a randomized complete block design with three replications. Main plots consisted of the long-term tillage systems (1999–2011) including: no tillage (NT), minimum tillage (MT) and conventional tillage (CT). Six methods of fertilization, including farmyard manure (N1), compost (N2), chemical fertilizers (N3), farmyard manure + compost (N4); farmyard manure + compost + chemical fertilizers (N5), and control (N6) were arranged in subplots. Results showed that the highest amount of microbial biomass was observed in treatment NTN4. The highest and lowest values of enzyme activities (acid, alkaline phosphatase, urease, dehydrogenase and protease) were found in organic fertilizers + NT and chemical fertilizers + CT plots, respectively. Highest basal and induced respiration values were found for NTN4 treatment. Correlation coefficients between enzyme activity, respiration and microbial biomass carbon were significant.     

Soil loss estimation using rusle model to prioritize erosion control in KELANI river basin in Sri Lanka

Soil erosion contributes negatively to agricultural production, quality of source water for drinking, ecosystem health in land and aquatic environments, and aesthetic value of landscapes. Approaches to understand the spatial variability of erosion severity are important for improving landuse management. This study uses the Kelani river basin in Sri Lanka as the study area to assess erosion severity using the Revised Universal Soil Loss Equation (RUSLE) model supported by a GIS system. Erosion severity across the river basin was estimated using RUSLE, a Digital Elevation Model (15 × 15 m), twenty years rainfall data at 14 rain gauge stations across the basin, landuse and land cover, and soil maps and cropping factors. The estimated average annual soil loss in Kelani river basin varied from zero to 103.7 t ha-1 yr⁻¹, with a mean annual soil loss estimated at 10.9 t ha⁻¹ yr⁻¹. About 70% of the river basin area was identified with low to moderate erosion severity (<12 t ha−1 yr⁻¹) indicating that erosion control measures are urgently needed to ensure a sustainable ecosystem in the Kelani river basin, which in turn, is connected with the quality of life of over 5 million people. Use of this severity information developed with RUSLE along with its individual parameters can help to design landuse management practices. This effort can be further refined by analyzing RUSLE results along with Kelani river sub-basins level real time erosion estimations as a monitoring measure for conservation practices.     

黑土稻田连续深耕改善土壤理化性质提高水稻产量大田试验

为了明确深耕对水田土壤理化性质及水稻产量影响,该文在黑土型水稻土上开展深耕研究,应用自主研发的水田深翻犁,开展深翻、浅翻与旋耕大区对比研究。结果表明:浅翻和深翻可以降低土壤固相比率和容重,与旋耕相比,土壤固相比率降低幅度分别为0.74%~4.80%和1.86%~3.90%;10~20 cm土层土壤容重分别下降0.09 g/cm~3和0.08 g/cm~3,20~30 cm土层深翻处理土壤容重比旋耕下降0.03 g/cm~3;10~20 cm土层土壤的通气系数和饱和透水系数浅翻处理比旋耕分别提高4.04倍和2.71倍,深翻提高4.42倍和2.14倍;20~30 cm深翻比旋耕提高1.86倍和2.87倍,2年趋势一致;深翻可使土壤养分指标在各层趋于平均化;深耕可促进水稻根系生长,根系的生长量与根长增加幅度为6.53%~16.33%和10.81%~21.62%,深翻好于浅翻;深耕提高水稻产量,2015年浅翻和深翻处理水稻实测产量分别比旋耕增产6.91%和9.81%,2016年增产6.59%和7.84%,2年增产趋势一致。     

不同除草处理对经济林果园地水土保持作用的初步研究

丘陵、中低山区(海拔<1 500 m)是经济林果木发展的主要适生区域,亦是人类活动最频繁的区域,生态系统脆弱,一旦土壤地被物遭破坏,极易引起严重的水土流失.通过在四川盆地紫色土桃园地和盆边山地黄壤茶园地设置16个径流场,进行4种除草处理,应用不同除草方式调控水土流失试验1年,结果表明(1)除草试验处理的土壤侵蚀量和养分(N,P,K,OM)流失量排序是耕作除草＞草甘膦除草＞克无踪除草＞割草覆盖(CK).(2)除草试验处理的土壤侵蚀量与传统耕作除草相比较,坡度25°和坡度10°的桃园地应用草甘膦除草、克无踪除草和割草覆盖(CK)土壤侵蚀量分别减少61.7%,67.6%,85.7%和 12.6%,24.2%,50.4%;坡度18°和坡度8°的茶园地土壤侵蚀量分别减少71.2%,84.3%,89.3%和16.2%,52.3%,82.8%.(3)桃园地应用草甘膦除草,土壤养分N,P,K,OM流失量比克无踪除草分别高19.9%,9.2%,23.3%,15.4%(坡度25°)和16.2%,15.3%,17.0%,20.6%(坡度10°);茶园地应用草甘膦除草土壤养分N,P,K,OM流失量比克无踪除草分别高89.6%,90.7%,80.0%,106.6%(坡度18°)和85.1%,81.4%,76.2%,83.9%(坡度8°).(4)除草试验处理的杂草生物量和盖度 桃园地和茶园地应用草甘膦、克无踪和耕作除草的杂草生物量绝对干重分别是割草覆盖(CK)的16.0%,60.0%,75.0%和5.9%,43.9%,79.5%;桃园地应用草甘膦除草、克无踪除草、耕作除草和割草覆盖(CK)的杂草总盖度分别为40%,80%,65%和95%,茶园地应用草甘膦除草、克无踪除草、耕作除草和割草覆盖(CK)的杂草总盖度分别为25%,80%,95%和95%.     

Soil properties and yam yield under different tillage systems in a tropical Alfisol

In Nigeria, information is lacking regarding the most suitable tillage method in extensive yam production. Hence, five tillage methods were compared at two sites in 2008–2010 with reference to their effects on soil physical and chemical properties, leaf nutrient concentrations, growth and tuber yield of yam (Dioscorea rotundata Poir) on Alfisols at Owo (site A) and Akure (site B), south-west Nigeria. The tillage methods were: zero tillage (ZT), manual ridging (MR), manual mounding (MM), ploughing + harrowing (P + H) and ploughing + harrowing + ridging (P + H + R). P + H + R had lower soil bulk density than other tillage methods and resulted in higher leaf N, P, K, Ca and Mg and yam tuber yield. In ZT, bulk density, soil moisture content, soil organic C, N, P, K, Ca and Mg were significantly higher and temperature lower than other tillage methods. Results of multiple regressions revealed that bulk density significantly influenced the yield of yam rather than soil chemical properties. Compared with MR, MM, P + H and ZT, and averaged across years, P + H + R increased yam tuber yield by 12.3, 12.8, 34.9 and 50.7%, respectively, in site A and 12.9, 13.5, 25.2 and 44.5%, respectively, in site B. P + H + R was found to be most advantageous and is therefore recommended for yam cultivation.     

不同施肥和耕作制度下土壤微生物多样性研究进展

本文主要介绍了运用Biolog GN、磷脂脂肪酸(PLFA)、核酸分析法进行土壤微生物群落分析的优缺点,综述了施肥、耕作两种农业措施对土壤微生物多样性影响的研究进展。指出不同施肥处理对微生物影响效果不同,合理施用有机肥有利于维持土壤微生物的多样性及活性;由于受其他环境因素(如土壤类型、农作制度、残茬量等)的影响,不同耕作措施对土壤微生物多样性影响有差异,但是大多试验结果显示免耕、少耕能增加微生物多样性和生物量,保持系统的稳定性。文章还指出了目前研究中存在的问题,并对今后的研究方向做了展望。     

Management of a previously eroded tropical Alfisol with herbaceous legumes: Soil loss and physical properties under mound tillage

A study was carried out on a previously eroded Oxic Paleustalf in Ibadan, southwestern Nigeria to determine the extent of soil degradation under mound tillage with some herbaceous legumes and residue management methods. A series of factorial experiments was carried out on 12 existing runoff plots. The study commenced in 1996 after a 5-year natural fallow. Mound tillage was introduced in 1997 till 1999. The legumes – Vigna unguiculata (cowpea), Mucuna pruriens and Pueraria phaseoloides – were intercropped with maize in 1996 and 1998 while yam was planted alone in 1997 and 1999. This paper covers 1997–1999. At the end of each year, residues were either burned or mulched on respective plots. Soil loss, runoff, variations in mound height, bulk density, soil water retention and sorptivity were measured. Cumulative runoff was similar among interactions of legume and residue management in 1997 (57–151 mm) and 1999 (206–397 mm). However, in 1998, cumulative runoff of 95 mm observed for Mucuna-burned residue was significantly greater than the 46 mm observed for cowpea-burned residue and the 39–51 mm observed for mulched residues of cowpea, Mucuna and Pueraria. Cumulative soil loss of 7.6 Mg ha⁻¹ observed for Mucuna-burned residue in 1997 was significantly greater than those for Pueraria-mulched (0.9 Mg ha⁻¹) and Mucuna-mulched (1.4 Mg ha⁻¹) residues whereas in 1999 it was similar to soil loss from cowpea treatments and Pueraria-burned residue (2.3–5.3 Mg ha⁻¹). There were no significant differences in soil loss in 1998 (1–3.2 Mg ha⁻¹) whereas Mucuna-burned residue had a greater soil loss (28.6 Mg ha⁻¹) than mulched cowpea (6.9 Mg ha⁻¹) and Pueraria (5.4 Mg ha⁻¹). Mound heights (23 cm average) decreased non-linearly with cumulative rainfall. A cumulative rainfall of 500 mm removed 0.3–2.3 cm of soil from mounds in 1997, 3.5–6.9 cm in 1998 and 2.3–4.6 cm in 1999, indicating that (detached but less transported) soil from mounds was far higher than observed soil loss in each year. Soil water retention was improved at potentials ranging from −1 to −1500 kPa by Mucuna-mulched residue compared to the various burned-residue treatments. Also, mound sorptivity at −1 cm water head (14.3 cm h^−1/2) was higher than furrow sorptivity (8.5 cm h^−1/2), indicating differences in hydraulic characteristics between mound and furrow. Pueraria-mulched residues for mounds had the highest sorptivity of 17.24 cm h^−1/2, whereas the least value of 6.96 cm h^−1/2 was observed in furrow of Mucuna-burned residue. Pueraria phas eoloides was considered the best option for soil conservation on the previously eroded soil, cultivated with mound tillage.     

Predicting soil workability and fragmentation in tillage: a review

Soil workability and friability are required parameters to consider when creating suitable seedbeds for crop establishment and growth. Knowledge of soil workability is important for scheduling tillage operations and for reducing the risk of tillage‐induced structural degradation of soils. A reliable evaluation of soil workability implies a distinctive definition of the critical water content (wet and dry limits) for tillage. In this review, we provide a comprehensive assessment of the methods for determining soil workability, and the effects of soil properties and tillage systems on soil workability and fragmentation. The strengths and limitations of the different methods for evaluating the water content for soil workability, such as the plastic limit, soil water retention curve (SWRC), standard Proctor compaction test, field assessment, moisture‐pressure‐volume diagram, air permeability and drop‐shatter tests are discussed. Our review reveals that there is limited information on the dry limit and the range of water content for soil workability for different textured soils. We identify the need for further research to evaluate soil workability on undisturbed soils using a combination of SWRC and the drop‐shatter tests or tensile strength; (i) to quantify the effects of soil texture, organic matter and compaction on soil workability; and (ii) to compare soil water content for workability in the field with theoretical soil workability, thereby improving the prediction of soil workability as part of a decision support system for tillage operations.     

Soil alteration due to erosion, ploughing and levelling of vineyards in north east Spain

Since the 1970s and 1980s, the vineyard areas in the Mediterranean region of north east Spain have undergone profound transformation to allow greater mechanization. This has involved land levelling, deep ploughing and the elimination of traditional soil conservation measures. Recently the EU Common Agricultural Policy encourages this through the vineyard restructuring and conversion plans (Commission Regulation EC No 1227/2000 of 31 May 2000) by subsidizing up to 50% of the cost of soil preparation such as soil movement and land levelling. A clear example of the problems that this causes is in the Penedès vineyard region (Catalonia, north east Spain), and the present research analyses the changes in soil properties caused by erosion, deep ploughing and land levelling. The study was carried out in an area of 30 000 ha for which a Soil Information System at a scale of 1:50 000 was developed based on 394 field observations (89 soil profiles and 251 auger hole samples down to 120 cm). The results show that 74% of the described soil profiles are disturbed with evidence of soil mixing and/or profile truncation due to erosion, deep ploughing and/or land levelling. The evidence from the topsoils is mainly the presence of fragments of calcic or petrocalcic horizons, marls and sandstones. Other important properties for crops such as organic matter (OM) content and soil depth show statistically significant differences between disturbed soils and undisturbed soils (22.3–33.3% OM content depletion and 35.1% soil depth reduction). These results confirm that the soils of the region are significantly altered by mechanical operations which also influence soil erosion and contribute to global warming effect through depletion of soil OM.     

Soil tillage for crop production and for protection of soil and environmental quality: a Scandinavian viewpoint

Based on experience from 35 years of tillage research in Sweden, future development of soil tillage is discussed and some research problems are identified. Tillage and seeding methods must be more carefully adapted to conditions at individual sites and occasions. Low-pressure typres, better weed control and improved seed coulters favour the increased use of reduced tillage. In order to diminish the impact of agriculture on the environment, it is necessary to develop methods for establishment of crops in the early spring or immediately after harvest, even in soils with large amounts of crop residues or high moisture content. The roles of tillage methods, and of soil compaction and structure on environmental impact of agriculture must be investigated. World food production must increase, since the world population is rapidly increasing. Therefore, it is necessary to develop improved crop production systems, including crop establishment systems, which favour efficient use of basic crop growth factors, while protecting or increasing soil productivity. Compaction, decreased organic matter content, and erosion are important long-term threats to soil productivity.     

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 losses due to potato harvesting: a case study in western Turkey

Harvesting of potato (Solanum tuberosum L.) may cause soil losses, but the magnitude of such losses has not been widely documented. We quantified the amount of soil lost with the mechanical harvesting of potatoes in 39 fields in western Turkey in 2013. The amount of soil lost was 1.81 Mg/ha/harvest and increased with increased gravimetric water content and plant density. The cost to replace nutrients lost with soil was about US$3 per hectare. Overall, soil loss due to potato harvesting is an important component of total erosion in the study region.