Effect of tillage intensity on weed infestation in organic farming

Conservation tillage is not yet widely accepted by organic farmers because inversion tillage is considered to be necessary for weed control. Three long-term experiments were established with combinations of reduced and conventional plough tillage and stubble tillage to determine weed infestation levels in organic farming, i.e. herbicide application being excluded. Experiment 1 (with very low stocking density of perennial weeds) showed that in presence of primary tillage by mouldboard ploughing the number of annual weeds was nearly unaffected by the mode of stubble tillage. In experiment 2, however, with Canada thistle (Cirsium arvense) being artificially established, thistle density was significantly affected by stubble tillage and by a perennial grass–clover forage crop. Experiment 3 combined two levels of stubble tillage (skimmer plough, no stubble tillage = control) with four implements of primary tillage in the order of decreasing operation depth (deep mouldboard plough, double-layer plough, shallow mouldboard plough or chisel plough). Primary tillage by chisel plough resulted in significantly highest annual weed density compared to all other treatments. The natural C. arvense infestation in experiment 3 showed highest shoot density in the “skimmer plough/chisel plough” treatment compared to the lowest infestation in the “skimmer plough/double-layer plough” treatment. The poor capacity of the chisel plough for weed control was also reflected by the soil seed bank (5500 m⁻² C. arvense seeds for chisel plough, <300 seeds for all other primary tillage). A reduced operation depth of the mouldboard plough (“shallow mouldboard plough”) seemed to have an insufficient effect in controlling C. arvense infestation as well. Stubble tillage by the skimmer plough in addition to nearly any primary tillage operation largely reduced both annual weeds and thistle shoots. Most effective in controlling C. arvense was also a biennial grass–clover mixture as part of the crop rotation.Double-layer ploughing is a compromise between soil inversion and soil loosening/cutting and can be regarded as a step towards conservation tillage. In terms of controlling annual weeds and C. arvense, the double-layer plough was not inferior to a deep mouldboard plough and seems to be suitable for weed control in organic farming. Tilling the stubble shallowly after harvest can support weed control in organic farming remarkably, particularly in reducing C. arvense. If no noxious, perennial weeds occur and primary tillage is done by soil inversion, an omission of stubble tillage can be taken into consideration.     

Ergebnisse zur bodenverlagerung durch bearbeitungserosion in der jungmoränenlandschaft Nordostdeutschlands: Investigations of soil movement by tillage as a type of soil erosion in the young moraine soil landscape of Northeast Germany

Soil translocation by soil tillage can have a considerable importance on arable land. These results were published in the international literature. The aim of the experiments is to quantify the translocation of soil due to tillage with different typical tools. A mouldboard plough and a disc harrow were tested in field experiments on a slope (4° inclination) with sandy soil. The average movement of soil particles of the top soil was determined about the changed tracer concentration. The tracer coloured gravels were most suitable of all tested tracer. The comparison of the tools showed more soil translocation caused by mouldboard plough (145?kg) than by disc harrow (12?kg). The transport was also different: plough 0.50?m and disc harrow 0.11?m average distance.     

Tillage translocation and tillage erosion in the complex upland landscapes of southwestern Ontario, Canada

Tillage translocation and tillage erosion were measured throughout the topographically complex landscapes of two fields in the upland region of southwestern Ontario. Translocation of soil by tillage was measured by labelling plots of soil with chloride and measuring the tracer's forward displacement in response to single passes by four tillage implements (mouldboard plough, chisel plough, tandem disc and field cultivator). The change in translocation within the landscape was used to measure tillage erosion. All four implements were erosive. A relationship between tillage translocation and slope gradient was observed; however, the variability in translocation could not be explained by slope gradient alone. Slope curvature was responsible for some translocation through the planning action of tillage implements. Tillage depth and speed were subject to considerable discontinuous and inconsistent manipulation by the operator in response to changing topographic and soil conditions. Tillage speed decreased by as much as 60% during upslope tillage and increased by as much as 30% during downslope tillage, relative to that on level ground. Tillage depth decreased by as much as 20% and increased by as much as 30%, relative to that on level ground. This manipulation is typical for tillage in complex landscapes and was presumed largely responsible for the variability in the results. The manipulation of tillage depth and speed are affected by the tractor-implement match and the responsiveness of the tillage operator.     

Tillage and crop straw methods affect energy use efficiency,economics and greenhouse gas emissions in rainfed winter wheat field of Loess Plateau in China

Data from a field experiment conducted in China's Loess Plateau (2013–2015) were used to determine the energy balance of winter wheat (Triticum aestivum L.) as affected by tillage and straw treatments. Tillage treatments included chisel plow, no tillage, and mouldboard plow. Crop straw levels included straw returning and straw removed. The energy balance was evaluated by comparing the following parameters: net energy, energy profitability, energy use efficiency, and energy intensity. The yield parameters were significantly influenced by the tillage treatments and revealed that the chisel plow entailed fewer field operations and lower energy requirements with a higher yield than mouldboard plowing tillage. The highest proportion of energy input came from a nitrogen fertiliser, followed by diesel fuel. The total energy input applied per hectare increased with an increase in the tillage intensity, and the lowest energy input was required for the no tillage case with the straw returning treatment, and the highest for the case of mouldboard plow with the straw returning treatment. The lowest average energy intensity was recorded for the no tillage case, followed by the case of chisel plow tillage in both cropping seasons. Moreover, in the case of mouldboard plough tillage, the maximum energy intensity was recorded in both cropping seasons. In the cases of the chisel plow tillage and the no tillage, we observed the maximum energy gain, while in the no tillage case, we observed the maximum energy use efficiency. The net return and the benefit/cost ratio were higher in the case of straw returning than those in the case of no straw treatment. We concluded that no tillage and chisel plow tillage with straw returning could improve the energy use efficiency and the benefit/cost ratio of winter wheat production systems.     

Implement and soil condition effects on tillage-induced erosion

Water, wind, or tillage-induced soil erosion can significantly degrade soil quality. Therefore, understanding soil displacement through tillage translocation is an important step toward developing tillage practices that do not degrade soil resources. Our primary objective was to determine the effects of soil condition (i.e. grassland stubble versus previously tilled soil), opening angle, and harrow speed on soil translocation. A second field study also conducted on a Lixisol but only in the stubble field, quantified displacement effects of mouldboard ploughing. The field studies were located 12 km South of Évora, Portugal. Soil displacement or translocation after each tillage operation in both studies was measured using aluminium cubes with a side length of 15 mm as ‘tracers’. Offset angles for the harrow disk were 20°, 44° and 59°; tractor velocities ranged from 1.9 to 7.0 km h⁻¹ and tillage depth ranged from 4 to 11 cm. The depth of mouldboard ploughing was approximately 40 cm with a wheel speed of 3.7 km h⁻¹. The translocation coefficients for the two implements were very different averaging 770 kg m⁻¹ for the mouldboard plough and ranging from 9 to 333 kg m⁻¹ for the harrow disk. This shows that the mouldboard plough was more erosive than the harrow disk in these studies. All three variables (soil condition, opening angle, and tillage velocity) were critical factors affecting the translocation coefficient for the harrow disk. Displacement distances were the largest for compacted soils (stubble field), with higher opening or offset angles, and at higher velocities. The results also showed significant correlation for (a) mean soil displacement in the direction of tillage and the slope gradient and (b) soil transport coefficient and the opening angle. Our results can be used to predict the transport coefficient (a potential soil quality indicator for tillage erosion) for the harrow disk, provided tillage depth, opening angle, and tool operating speed are known.     

Tillage effects on soil properties and maize productivity in western Turkey

Information regarding the evaluation of long-term tillage effects on soil properties and summer maize growth after winter vetch in western Turkey is not available. Therefore, this study was conducted for 5 years with three types of tillage including conventional (mouldboard plough) and conservation (rototiller and chisel). Results indicated that tillage had no significant effect on penetration resistance, except at the bottom of 20 cm soil depth where it was higher in mouldboard plough than in rototiller and chisel. Bulk density in the topsoil of 10 cm decreased with the degree of soil manipulation during tillage practices. Rototiller caused significantly higher root, leaf and stems biomass and plant height than the other systems. The root dry weight was higher in the topsoil of 10 cm than at the bottom of this soil depth for all systems. The highest root dry weight was found in fourth year of chisel, but the lowest was recorded in the same year of plough, especially at the bottom of 20 cm due to higher penetration. Rototiller improved soil properties and maize growth compared to other systems in 2 of 5 years. We concluded that using rototiller for maize after winter vetch will be more effective compared with other systems.     

Reaction forces of lightweight mouldboard ploughs at slow speeds of tillage in Nitosol, Vertisol and Ferralsol soils under two moisture conditions

The mouldboard plough is the standard tillage implement used with animal power in Kenya. Various designs are currently used indiscriminately in varied soil types and conditions of operation. Their draught characteristics and comparative ability to achieve or maintain desired depths of operation under inherent edaphic conditions are unknown. The significance of variation in working speeds, when different species of draught animals are used, is also unknown. This study was therefore aimed at rating the performance of some common ploughs in order to advise farmers on optimisation of their use. Draught and vertical reaction (suction) on a per-tool basis were measured for four ploughs commonly used in the region; the Victory^®, the Rumpstad winding-body^® and two types of Rumpstad cylindrical-body^® ploughs, using an instrumented rig. The experiments were in Pellic Vertisol, Ferralsol and Nitosol soils under two soil moisture conditions. Draught increased significantly with depth for all four ploughs, hence, regulation of tillage depth is paramount to avoidance of drastic fluctuations. Similarly, vertical reaction increased with depth of ploughing, which implies a more stable operation, hence, when draught can be sustained over an acceptable work duration, it is desirable to set the ploughs to work deeply. Significant speed–depth interactions were also recorded, and these imply that speed is important when operating depth is stochastic as is the case in the dynamics of these ploughs. Overall, the Victory plough had the lowest draught requirement (0.32–1.02 kN) under dry and moist soil conditions, hence, was the best option for use in areas represented by the three soil types in Kenya. Soil-type had a significant effect on mean draught and vertical reaction in the order (Draught, Vertical reaction); Vertisol (1.65 kN, 0.70 kN) > Ferralsol (0.66 kN, 0.44 kN) > Nitosol (0.64 kN, 0.01 kN), and Ferralsol (1.17 kN, 0.71) > Vertisol (1.09 kN, 0.23 kN) > Nitosol (0.49 kN, 0.11 kN) under moist and dry conditions, respectively. These results suggest that the duration of continuous work periods with draught animals should be based on soil-type.     

Comparing soil physical properties from continuous conventional tillage with long‐term reduced tillage affected by one‐time inversion

In addition to various positive aspects, long‐term reduced tillage may cause disadvantages such as increased weed pressure and soil compaction. Thus, single inversion tillage is customarily used for overcoming these drawbacks; however, the effects on the enhanced soil functions are unknown. The main objective of this study was therefore to assess whether improved soil physical properties following long‐term reduced tillage remain after one‐time inversion tillage by mouldboard plough. The study was undertaken on a silt loam field in Lower Saxony, Germany. Since 1996, this field has been subdivided into three treatments; one was managed conventionally using a mouldboard plough (CT), while on the others a chisel plough (RT1) and a disc harrow (RT2) were employed. In October 2014, the entire field was mouldboard ploughed. The following year, four field campaigns were conducted to compare the soil physical properties of the continuously conventional tilled plot with those affected by one‐time inversion tillage (RT1 and RT2). Dry bulk density (DBD), saturated hydraulic conductivity (Ks) and infiltration rate [K(h)] were analysed in untrafficked and trafficked areas in each plot. There were clear differences between CT and RT. At all sampling dates, both RT plots had higher Ks and K(h) compared with CT. These differences also occurred to some extent on the trafficked areas. This suggests that improved soil hydraulic properties remained after one‐time inversion tillage of a long‐term reduced tilled field. Thus, one‐time inversion tillage may offer a suitable measure for overcoming some of the main disadvantages associated with long‐term reduced tillage, while preserving the positive effects on soil physical properties.     

Characterization of soil physical properties and organic matter under long-term primary tillage in a humid climate

Chisel ploughing is considered to be a potential conservation tillage method to replace mouldboard ploughing for annual crops in the cool-humid climate of eastern Canada. To assess possible changes in some soil physical and biological properties due to differences in annual primary tillage, a study was conducted for 9 years in Prince Edward Island on a Tignish loam, a well-drained Podzoluvisol, to characterize several mouldboard and chisel ploughing systems (at 25 cm), under conditions of similar crop productivity. The influence of primary tillage on the degree of soil loosening, soil permeability, and both organic matter distribution throughout the soil profile and organic matter content in soil particle size fractions was determined. At the time of tillage, chisel ploughing provided a coarser soil macrostructure than mouldboard ploughing. Mouldboard ploughing increased soil loosening at the lower depth of the tillage zone compared to chisel ploughing. These transient differences between primary tillage treatments had little effect on overall soil profile permeability and hydraulic properties of the tilled/non-tilled interface at the 15–30 cm soil depth. Although soil microbial biomass, on a volume basis, was increased by 30% at the 0–10 cm soil depth under chisel ploughing, no differences were evident between tillage systems over the total tillage depth. Mouldboard ploughing increased total orgainc carbon by 43% at the 20–30 cm soil depth, and the carbon and nitrogen in the organic matter fraction ≤ 53 μm by 18–44% at the 10–30 cm soil depth, compared to chisel ploughing.     

Assessment of tillage erosion by mouldboard plough in Tuscany (Italy)

This study was designed to characterise the soil translocation effect induced by mouldboard ploughing with an implement traditionally used in the Tuscany region (Central Italy). We discuss the results of a set of field experiments performed to measure soil displacement along slopes of varying gradient in different directions and at several depths of tillage. Using the Soil Erosion by Tillage (SETi) model, soil translocation patterns for different tillage scenarios were analysed, with special attention paid to the effects of the direction and depth of tillage on the extent and spatial pattern of soil movement. The lateral slope gradient S_P and tillage depth D were found to be the dominant controlling factors for total soil displacement. The effect of the slope gradient in a direction parallel to tillage S_T was much less pronounced. These findings reveal the importance of the asymmetric nature of the soil movement produced by mouldboard ploughing and the predominant effect of the lateral displacement d_P on the actual trajectory of soil motion. Results demonstrate that spatial patterns of soil redistribution due to mouldboard ploughing are highly variable and depend on the particular characteristics of the implement used. This dependence is so strong that maximum downslope soil translocation can occur during both, contour tillage or up–down tillage. For this particular mouldboard plough, maximum downslope soil transport took place at a tillage direction ca. 70° and not when tillage was conducted along the steepest slope direction (0°). These findings highlight the potential of the combined approach applied. The physically based SETi model can be properly calibrated using a relatively limited dataset from field experiments. Once calibrating, the SETi model can then be used to generate synthetic tillage translocation relationships, which can predict the intensity and spatial pattern of soil translocation over a much wider range of tillage scenarios than the particular experimental conditions, in terms of topography complexity (slope gradients and morphology) and the direction and depth of tillage. These synthetic relationships are useful tools for evaluating strategies designed to reduce tillage erosion.     

Tillage erosion within potato production systems in Atlantic Canada: I. Measurement of tillage translocation by implements used in seedbed preparation

In Canada, there is growing acceptance that tillage erosion is a serious form of soil degradation and a threat to the sustainability of agriculture across the country. To date, the potential risk for tillage erosion within potato production systems has not been investigated. The objective of this study was to generate tillage translocation values for primary and secondary tillage implements common to seedbed preparation within conventionally and conservation tilled potato production systems in Atlantic Canada. Tillage translocation was measured for each implement by labelling a plot of soil with a tracer. The tracer redistribution along the path of tillage was used to generate a summation curve to calculate mean soil movement in the direction of tillage. The results show that each primary and secondary tillage operation moved vast quantities of soil and is potentially erosive. Maximum displacement distances were considerably larger in this project than those reported in previous studies looking at tillage erosion by primary and/or secondary tillage implements. All four tillage implements tested moved soil at least 3 m, with the greatest translocated distances (5.6 m) observed for the chisel plough (CP) and vibrashank (VS). The mass of translocated soil (T_M) was greatest for the CP, followed by the mouldboard plough (MP), VS and offset disc (OD). In addition, compared to travelling downslope, the upslope speed of tillage was reduced by 38%, 21%, 32% and 12% for the MP, CP, OD and VS, respectively, while the depth of tillage was reduced by 6%, 5%, 35% and 2%, respectively. It is apparent that conservation tillage implements (the CP is generally promoted to reduce water erosion in Atlantic Canada) and secondary tillage implements (OD and VS) can move as much soil as conventional tillage implements such as the mouldboard plough, and must be considered when developing plans to reduce soil erosion within potato fields in Atlantic Canada.     

Modelling tillage translocation using step, linear-plateau and exponential functions

The distance over which soil is displaced and mixed during tillage has important implications for the understanding the dynamics of soil variability within complex soil-landscapes. In two preceding studies of tillage translocation, tillage was observed to displace soil over a length of approximately 1 m following single passes of four tillage implements (chisel plough, mouldboard plough, tandem disc and field cultivator), and over a length of approximately 2 m per sequence of conventional tillage (one pass of mouldboard plough, two passes of tandem disc and one pass of field cultivator). Using data from these studies step, linear-plateau and exponential functions were assessed for their ability to estimate the magnitude of translocation and the redistribution pattern of soil within the till-layer, and to predict the redistribution pattern of soil within the till-layer. On average, step, linear-plateau and exponential models estimated 100.0%, 100.2% and 102.5% of the magnitude of translocation and 76%, 88% and 93% of the soil redistribution pattern, respectively. Based on these results, it was concluded that linear-plateau and exponential functions are suitable models of tillage translocation. The exponential model was superior to the step and linear-plateau models, and an improvement over the existing diffusion model.     

Soil management by shallow mouldboard ploughing in The Netherlands

The structure of the soil in the arable layer is controlled by tillage, soil biota activities and weathering, whereas the structure below this layer is mainly the result of the activities of soil biota. Organic farmers tend to minimise the depth of the main tillage operation to encourage soil biota to create a soil structure with continuous biopores and a well crumbled topsoil. The best main tillage operation for preventive weed control, especially important in organic farming, is mouldboard ploughing. The shallow ploughing experiments described in this paper were conducted to ascertain the minimum ploughing depth for an ecologically accountable, sustainable tillage system with good weed control, good land qualities (in terms of workable days, aeration and soil moisture conditions) and finally with good yields. The “ecoplough” used for shallow ploughing was developed by Rumptstad Industries to meet the requirements of relatively shallow ploughing with good soil inversion for weed control. The plough has seven or eight bottoms for ploughing depths of 0.12–0.20 m, a working width of 2.1 m and a working speed of 1.7 m s⁻¹. Its width is such that the tractor with wide low-pressure tyres runs on top of the land.

After using the plough for 6 years on Luvisols (>200 gkg⁻¹<2 μm) in the IJsselmeer polders and on Luvisols (120–160 gkg⁻¹<2 μm) in polders near the northern coast of The Netherlands, it was found that compared with conventional ploughing, shallow ploughing required less energy and labour and produced a relatively smooth surface. The latter facilitates the preparation of a seedbed consisting of relatively fine, strong, stable and moist aggregates. Organic matter, soil biota and nutrients were concentrated higher in the profile, influencing the workability of the soil, the growth of weeds and the growth of crops. Most of the yields were similar to yields after conventional ploughing, but weed populations increased when ploughing depth was <0.2 m. It was concluded that for organic farming on “active” soils (soils subject to shrink/swell with >200 g kg⁻¹<2 μm), shallow ploughing seems to be the best reduced tillage system. It has several advantages. The main factor determining the minimum ploughing depth is control of weeds, especially of perennials.     

Influence of mouldboard plough and rotary harrow tillage on microbial biomass and nutrient stocks in two long-term experiments on loess derived Luvisols

The nutrient-specific effects of tillage on microbial activity (basal respiration), microbial biomass (C, N, P, S) indices and the fungal cell-membrane component ergosterol were examined in two long-term experiments on loess derived Luvisols. A mouldboard plough (30 cm tillage depth) treatment was compared with a rotary harrow (8 cm tillage depth) treatment over a period of approximately 40 years. The rotary harrow treatment led to a significant 8% increase in the mean stocks of soil organic C, 6% of total N and 4% of total P at 0–30 cm depth compared with the plough treatment, but had no main effect on the stocks of total S. The tillage effects were identical at both sites, but the differences between the sites of the two experiments were usually stronger than those between the two tillage treatments. The rotary harrow treatment led to a significant increase in the mean stocks of microbial biomass C (+18%), N (+25%), and P (+32%) and to a significant decrease in the stocks of ergosterol (−26%) at 0–30 cm depth, but had no main effect on the stocks of microbial biomass S or on the mean basal respiration rate. The mean microbial biomass C/N (6.4) and C/P (25) ratios were not affected by the tillage treatments. In contrast, the microbial biomass C/S ratio was significantly increased from 34 to 43 and the ergosterol-to-microbial biomass C ratio significantly decreased from 0.20% to 0.13% in the rotary harrow in comparison with the plough treatment. The microbial biomass C-to-soil organic C ratio varied around 2.1% in the plough treatment and declined from 2.6% at 0–10 cm depth to 2.0 at 20–30 cm depth in the rotary harrow treatment. The metabolic quotient qCO₂ revealed exactly the inverse relationships with depth and treatment to the microbial biomass C-to-soil organic C ratio. Rotary harrow management caused a reduction in the microbial turnover in combination with an improved microbial substrate use efficiency and a lower contribution of saprotrophic fungi to the soil microbial community. This contrasts the view reported elsewhere and points to the need for more information on tillage-induced shifts within the fungal community in arable soils.     

Soil displacement and tillage erosion during secondary tillage operations: the case of rotary harrow and seeding equipment

This study reports the results of a series of experiments that were set up on agricultural land in central Belgium to investigate soil translocation and erosivity resulting from a secondary tillage operation using an implement sequence of a rotary harrow and seeder. Aluminium cubes were used as tracers of soil movement. Results show that soil displacement resulting from tillage with such an implement sequence is far from insignificant. This is mainly related to the relatively shallow tillage depth as well as to the loose initial soil condition of such secondary tillage operations. The calculated value for the tillage transport coefficient k (123 kg m⁻¹ per tillage operation) is comparable with k-values from implements that are considered to be more erosive, like mouldboard and chisel implements. In conclusion, this study shows that tillage erosion not only results from relatively aggressive tillage operations such as mouldboard and chisel passes, but that secondary operations contribute significantly to soil displacement and tillage erosion.     

Wheel traffic impact on soil conditions as influenced by tillage system in Central Anatolia

The increased limiting effects of soil compaction on Central Anatolian soils in the recent years demonstrate the need for a detailed analysis of tillage system impacts. This study was undertaken to ascertain the effects of seven different tillage systems and subsequent wheel traffic on the physical and mechanical properties of typical Central Anatolian medium textured clay loam soil (Cambisol), south of Ankara, Turkey. Both tillage and field traffic influenced soil bulk density, porosity, air voids and strength significantly except the insignificant effect of traffic on moisture content. Traffic affected the soil properties mostly down to 20 cm. However, no excessive compaction was detected in 0–20 cm soil depth. The increases of bulk density following wheel traffic varied between 10–20% at 0–5 cm and 6–12% at 10–15 cm depth. In additions, traffic increased the penetration resistance by 30–74% at 0–10 cm and 7–33% at 10–20 cm. Less wheel traffic-induced effects were found on chisel tilled plots, compared to ploughed plots. Soil stress during wheel passage was highly correlated with soil strength. Also, both tillage and traffic-induced differences were observed in mean soil aggregate sizes, especially for mouldboard ploughed plots. The obtained data imply that chisel+cultivator-tooth harrow combination provides more desirable soil conditions for resisting further soil compaction.     

Effects of tillage depth on organic carbon content and physical properties in five Swedish soils

The soil tillage system affects incorporation of crop residues and may influence organic matter dynamics. A study was carried out in five 15–20 year old tillage experiments on soils with a clay content ranging from 72 to 521 g kg⁻¹. The main objective was to quantify the influence of tillage depth on total content of soil organic carbon and its distribution by depth. Some soil physical properties were also determined. The experiments were part of a series of field experiments all over Sweden with the objective of producing a basis to advise farmers on optimal depths and methods of primary tillage under various conditions. Before the experimental period, all sites had been mouldboard ploughed annually for many years to a depth of 23–25 cm. Treatments included primary tillage to 24–29 cm depth by mouldboard plough (deep tillage) and to 12–15 cm by field cultivator or mouldboard plough (shallow tillage). Dry bulk density, degree of compactness and penetration resistance profiles clearly reflected the depth of primary tillage and substantially increased below that depth. Compared to deep tillage, shallow tillage increased the concentration of organic carbon in the surface layer but decreased it in deeper layers. Total quantity of soil organic carbon and carbon–nitrogen ratio were unaffected by the tillage depth. Thus, a reduction of the tillage depth from about 25 cm to half of that depth would appear to have no significant effect on the global carbon cycle.     

Performance of low-draft tillage implements on a hard setting Alfisol of the SAT in India

Abstract. Four bullock-drawn tillage implements (mouldboard plough, chisel plough, sweeps, and shovels) were evaluated on a hard-setting Alfisol. Measurements included draft requirement, bulk density, cone index, soil crust strength, water content of the plough-layer and crop yield. Changes in bulk density and cone index due to tillage decreased with time and were negligible by the end of the growing season. After tillage with a mouldboard plough the crust was stronger than after tillage with other implements. The shovel cultivator enabled the soil to store more water, and required least draft per unit effective area of cut.     

Fine-earth translocation by tillage in stony soils in the Guadalentin, south-east Spain: an investigation using caesium-134

Tillage erosion is increasingly recognised as an important soil erosion process on agricultural land. In view of its potential significance, there is a clear need to broaden the experimental database for the magnitude of tillage erosion to include a range of tillage implements and agricultural environments. The study discussed in this paper sought to address the need for such data by examining tillage erosion by a duckfoot chisel plough in stony soils on steep slopes in a semi-arid environment. Results of the investigation of coarse fraction (rock fragment) translocation by tillage in this environment have been presented elsewhere and the paper focuses on tillage translocation and erosion of the fine earth. Tillage translocation was measured at 10 sites, representing both upslope and downslope tillage by a duckfoot chisel plough on five different slopes, with tangents ranging from 0.02 to 0.41. A fine-earth tracer, comprising fine earth labelled with ¹³⁴Cs, was introduced into the plough layer before tillage. After a single pass of the plough, incremental samples of plough soil were excavated and sieved to separate the fine earth from the rock fragments. Translocation of the fine-earth tracer was established by analysing the ¹³⁴Cs content of the samples of fine earth. These data were used to establish translocation distances for each combination of slope and tillage direction. Translocation distances of the fine earth were not significantly different from translocation distances of the coarse fraction. For all sites, except uphill on the 0.41 slope, translocation distances were found to be linearly related to slope tangent. The soil flux due to tillage for each site was calculated using the translocation distance and the mass per unit area of the plough layer. For slopes with tangents <0.25, the relationship between soil flux and tangent was linear and the soil flux coefficient derived was 520–660 kg m⁻¹ per pass. This is much larger than the coefficients found in other studies and this high magnitude is attributed to the non-cohesive nature and high rock fragment content of the soil in this investigation. A second contrast with previous studies was found in non-linearity in the relationship between soil flux and tangent when steeper slopes were included. This was a product of variation in plough depth between the steepest slopes and the remainder of the study area. On the basis of the study it is suggested that an improved understanding of tillage erosion may be obtained by considering the dual processes of tillage detachment (mass per unit area of soil subject to tillage) and tillage displacement (equivalent to translocation distance per pass) in assessing, comparing and modelling tillage translocation. An improved model is proposed that recognises the complexity of soil redistribution by tillage, provides a framework for process-based investigation of the controls on tillage fluxes, and allows identification of potential self-limiting conditions for tillage erosion.     

Measurement and modelling of the effects of initial soil conditions and slope gradient on soil translocation by tillage

Tillage erosion studies have mainly focused on the effect of topography and cultivation practices on soil translocation during tillage. However, the possible effect of initial soil conditions on soil displacement and soil erosion during tillage have not been considered. This study aims at investigating the effect of the initial soil conditions on net soil displacement and the associated erosion rates by a given tillage operation of a stony loam soil. Tillage erosion experiments were carried out with a mouldboard plough on a freshly ploughed (pre-tilled) soil and a soil under grass fallow in the Alentejo region (Southern Portugal).

The experimental results show that both the downslope displacement of soil material and the rate of increase of the downslope displacement with slope gradient are greater when the soil is initially in a loose condition. This was attributed to: (i) a greater tillage depth on the pre-tilled soil and (ii) a reduced internal cohesion of the pre-tilled soil, allowing clods to roll and/or slide down the plough furrow after being overturned by the mouldboard plough.

An analysis of additional available data on soil translocation by mouldboard tillage showed that downslope displacement distances were only significantly related to the slope gradient when tillage is carried out in the downslope direction. When tillage is carried out in the upslope direction, the effect of slope gradient on upslope displacement distances was not significant. This has important implications for the estimation of the tillage transport coefficient, which is a measure for the intensity of tillage erosion, from experimental data. For our experiments, estimated values of the tillage transport coefficient were 70 and 254 kg m⁻¹ per tillage operation for grass fallow and pre-tilled conditions, respectively, corresponding to local maximum erosion rates of ca. 8 and 35 Mg ha⁻¹ per tillage operation and local maximum deposition rates of ca. 33 and 109 Mg ha⁻¹ per tillage operation.