Ridge tillage and contour natural grass barrier strips reduce tillage erosion

Large amounts of soil are eroded annually from tilled, hilly upland soils in the humid tropics. Awareness has been increasing that much of this erosion may be due to tillage operations rather than water-induced soil movement. This field study estimated soil translocation and tillage erosion for four tillage systems on Oxisols with slope gradients of 16–22% at Claveria, Misamis Oriental, Philippines. Soil movement was estimated using ‘soil movement tracers' (SMT) which consisted of painted 12-mm hexagonal steel nuts. The SMT were buried in three replicate plots of the following tillage treatments: (1) contour moldboard plowing in the open field (MP-open); (2) contour ridge tillage in the open field (RT-open); (3) contour moldboard plowing plus contour natural grass barrier strips (MP-strip); and (4) contour natural grass barrier strips plus ridge tillage (RT-strip). Two hundred SMT were placed at the 5-cm depth at 5-cm spacings on 10 rows and 20 columns in two microplots within each plot. The microplots were oriented with the boundaries running downslope and along the contour of each 8-m-wide × 38-m-long (downslope) tillage plot. After tilling the land for four successive corn (Zea mays L.) crops (20 tillage operations), the SMT were manually excavated and their positions recorded. Recovery of SMT ranged from 82% to 85%. Displacement of SMT was directly related to slope length, percent slope, and tillage method. Mean displacement distance of SMT during the four corn growing seasons was 3.3 m for MP-open, 1.8 m for RT-open, 1.5 m for the RT-strip, and 2.2 m for MP-strip. Based on tillage operations associated with two corn crops per year, mean annual soil flux was estimated to be 241, 131, 158 and 112 kg m⁻¹ for MP-open, RT-open MP-strip, and RT-strip, respectively. Compared to the mean annual soil loss for MP-open of 63 Mg ha⁻¹, soil loss was reduced by 30%, 45%, and 53% for the MP-strip, RT-open, and RT-strip systems, respectively. Both ridge tillage and natural grass barrier strips reduced soil displacement, soil translocation flux, and tillage erosion rates.     

Assessment of tillage translocation and tillage erosion by hoeing on the steep land in hilly areas of Sichuan, China

Most of the tillage erosion studies have focused on the effect of tractor-plough tillage on soil translocation and soil loss. Only recently, have a few studies contributed to the understanding of tillage erosion by manual tillage. Furthermore, little is known about the impact of tillage erosion in hilly areas of the humid sub-tropics. This study on tillage erosion by hoeing was conducted on a purple soil (Regosols) of the steep land, in Jianyang County, Sichuan Province, southwestern China (30°24′N and 104°35′E) using the physical tracer method.

The effects of hoeing tillage on soil translocation on hillslopes are quite evident. The tillage transport coefficients were 26–38 kg m⁻¹ per tillage pass and 121–175 kg m⁻¹ per tillage pass respectively for k₃- and k₄-values. Given that there was a typical downslope parcel length of 15 m and two times of tillage per year in this area, the tillage erosion rates on the 4–43% hillslopes reached 48–151 Mg ha⁻¹ per year. The downslope soil translocation is closely related to slope gradient. Lateral soil translocation by such tillage is also obvious though it is lower than downslope soil translocation. Strong downslope translocation accounts for thin soil layers and the exposure of parent materials/rocks at the ridge tops and on convexities in the hilly areas. Deterioration in soil quality and therefore reduction in plant productivity due to tillage-induced erosion would be evident at the ridge tops and convex shoulders.     

Tillage-induced CO2 loss across an eroded landscape

Soil carbon (C) losses and soil translocation from tillage operations have been identified as causes of soil degradation and soil erosion. The objective of this work was to quantify the variability in tillage-induced carbon dioxide (CO₂) loss by moldboard (MP) and chisel (CP) plowing across an eroded landscape and relate the C loss to soil properties. The study site was a 4 ha wheat (Triticum aestivum L. cv. Marshall) field with rolling topography and five soil types in the Svea-Barnes complex in west central Minnesota (N. Latitude = 45°41′W, Longitude = 95°43′). Soil properties were measured at several depths at a 10 m spacing along north–south (N–S) and west–east (W–E) transects through severely eroded, moderately eroded and non-eroded sites. Conventional MP (25 cm deep) and CP (15 cm deep) equipment were used along the pre-marked transects. Gas exchange measurements were obtained with a large, portable chamber within 2 m of each sample site following tillage. The measured CO₂ fluxes were largest with the MP > CP > not tilled (before tillage). The variation in 24 h cumulative CO₂ flux from MP was nearly 3-fold on the N–S transect and 4-fold on the W–E transect. The surface soil organic C on the transects was lowest on the eroded knolls at 5.1 g C kg⁻¹ and increased to 19.6 g C kg⁻¹ in the depositional areas. The lowest CO₂ fluxes were measured from severely eroded sites which indicated that the variation in CO₂ loss was partially reflected by the degradation of soil properties caused by historic tillage-induced soil translocation with some wind and water erosion.

The spatial variation across the rolling landscape complicates the determination of non-point sources of soil C loss and suggests the need for improved conservation tillage methods to maintain soil and air quality in agricultural production systems.     

Quantifying tillage translocation and deposition rates due to moldboard plowing in the Palouse region of the Pacific Northwest, USA

Most of the erosion research in the Palouse region of eastern Washington State, USA has focused on quantifying the rates and patterns of water erosion for purposes of conservation planing. Tillage translocation, however, has largely been overlooked as a significant geomorphic process on Palouse hillslopes. Tillage translocation and tillage deposition together have resulted in severe soil degradation in many steep croplands of the Palouse region. Few controlled experiments have heretofore been conducted to model these important geomorphic processes on Palouse hillslopes. The overarching purpose of this investigation, therefore, was to model tillage translocation and deposition due to moldboard plowing in the Palouse region. Soil movement by moldboard plowing was measured using 480-steel flat washers. Washers were buried in silt loam soils on convex–convex shoulder, linear-convex backslope, and linear-concave footslope landform components, and then displaced from their original burial locations by a moldboard plow pulled by a wheel tractor traveling parallel to the contour at ca. 1.0 m s⁻¹. Displaced washers were located using a metal detector, and the distance and azimuth of the resultant displacement of each washer from its original burial location was measured using compass and tape. Resultant displacement distances were then resolved into their component vectors of displacement parallel and perpendicular to the contour. A linear regression equation was developed expressing mean soil displacement distance as a function of slope gradient. Tillage translocation and deposition were modeled as diffusion-type geomorphic processes, and their rates were described in terms of the diffusion constant (k). A multivariate statistical model was developed expressing mean soil displacement distance as a function of gravimetric moisture content, soil bulk density, slope gradient, and direction of furrow slice displacement. Analysis of variance (ANOVA) revealed a weak correlation between soil displacement and both bulk density and moisture content. Soil displacement was, however, significantly correlated with direction of furrow slice displacement. Tillage translocation rates were expressed in terms of the diffusion constant (k) and ranged from 105 to 113 kg m⁻¹ per tillage operation. Tillage deposition rates ranged from 54 to 148 kg m⁻¹ per tillage operation. With respect to tillage deposition, the diffusion constant calculated from volumetric measurements of tillage deposits equals ca. 150 kg/m. The rates of tillage translocation and deposition are not completely in balance; however, these rates do suggest that soil tillage is a significant geomorphic process on Palouse hillslopes and could account for the some of the variations in soil physical properties and crop yield potential at the hillslope and farm-field scale in the Palouse region.     

Assessment of tillage erosion rates on steepland Oxisols in the humid tropics using granite rocks

Soil translocation by tillage may be an important factor in land degradation in the humid tropics. The objective of this study was to evaluate tillage-induced soil translocation on an Oxisol with 25% and 36% slopes in Claveria, Philippines for three tillage systems: contour moldboard plowing (CMP), moldboard plowing up and downslope (UMP), and contour ridge tillage (CRT). Small rocks 3–4 cm in “diameter” were used as soil movement detection units (SMDU). The SMDUs were placed at 10 cm intervals in a narrow 5-cm-deep trench near the upper boundary of each plot, the position of each rock recorded, and the trench backfilled. Five tillage operations used to produce one corn crop were performed during a one month period: two moldboard plowing operations for land preparation (except for CRT), one moldboard plowing for corn planting, and two inter-culture (inter-row cultivation) operations. After these operations, over 95% of the SMDU were recovered manually and their exact locations recorded. Mean annual soil flux for the 25% slope was 365 and 306 kg m⁻¹ y⁻¹ for UMP and CMP, respectively. For the 36% slope, comparable values were 481 and 478 kg m⁻¹ y⁻¹. Estimated tillage erosion rates for the 25% slope were 456 and 382 Mg ha⁻¹ y⁻¹ for UMP and CMP, respectively, and increased to 601 and 598 Mg ha⁻¹ y⁻¹, respectively, for the 36% slope. The mean displacement distance, mean annual soil flux, and mean annual tillage-induced soil loss for both slopes were reduced by approximately 70% using CRT compared to CMP and UMP.     

Short-term changes in nitrogen availability, gas fluxes (CO2, NO, N2O) and microbial biomass after tillage during pasture re-establishment in Rondônia, Brazil

Anthropogenic conversion of primary forest to pasture for cattle production is still frequent in the Amazon Basin. Practices adopted by ranchers to restore productivity to degraded pasture have the potential to alter soil N availability and N gas losses from soils. We examined short-term (35 days) effects of tillage prior to pasture re-establishment on soil N availability, CO₂, NO and N₂O fluxes and microbial biomass C and N under degraded pasture at Nova Vida ranch, Rondônia, Brazilian Amazon. We collected soil samples and measured gas fluxes in tilled and control (non tilled pasture) 12 times at equally spaced intervals during October 2001 to quantify the effect of tillage. Maximum soil NH₄⁺ and NO₃⁻ pools were 13.2 and 6.3 kg N ha⁻¹ respectively after tillage compared to 0.24 and 6.3 kg N ha⁻¹ in the control. Carbon dioxide flux ranged from 118 to 181 mg C–CO₂ m² h⁻¹ in the control (non-tilled) and from 110 to 235 mg C–CO₂ m² h⁻¹ when tilled. Microbial biomass C varied from 365 to 461 μg g⁻¹ in the control and from 248 to 535 μg g⁻¹ when tilled. The values for N₂O fluxes ranged from 1.22 to 96.9 μg N m⁻² h⁻¹ in the tilled plots with a maximum 3 days after the second tilling. Variability in NO flux in the control and when tilled was consistent with previous measures of NO emissions from pasture at Nova Vida. When tilled, the NO/N₂O ratio remained <1 after the first tilling suggesting that denitrification dominated N cycling. The effects of tilling on microbial parameters were less clear, except for a decrease in qCO₂ and an increase in microbial biomass C/N immediately after tilling. Our results suggest that restoration of degraded pastures with tillage will lead to less C matter, at least initially. Further long-term research is needed.     

Erosional effects on soil organic carbon stock in an on-farm study on Alfisols in west central Ohio

Soil erosion and depositional processes in relation to land use and soil management need to be quantified to better understand the soil organic carbon (SOC) dynamics. This study was undertaken on a Miamian soil (Oxyaquic Hapludalfs) under on-farm conditions in western Ohio with the objectives of evaluating the effects of degree of erosion on SOC stock under a range of tillage systems. Six farms selected for this study were under: no-till (NT) for 15, 10, 6 and 1.5 years; chisel till every alternate year with annual manure application (MCT); and annual chisel till (ACT). A nearby forest (F) site on the same soil was chosen as control. Using the depth of A horizon as an indicator of the degree of erosion, four erosion phases identified were: uneroded (flat fields under F, NT15, and on the summit of sloping fields under NT10, NT6, NT1.5 and MCT); deposition (NT10, NT6, NT1.5 and ACT); slight (NT10, MCT and ACT); and moderate erosion (NT10 and ACT). Core and bulk soil samples were collected in triplicate from four depths (i.e., 0–10, 10–20, 20–30 and 30–50 cm) for each erosional phase in each field for the determination of bulk density, and SOC concentrations and stocks. SOC concentration in NT fields increased at a rate of 5% year⁻¹ for 0–10 cm and 2.5% year⁻¹ for 10–20 cm layer with increasing duration under NT. High SOC concentration for NT15 is indicative of SOC-sequestration potential upon conversion from plow till to NT. SOC concentration declined by 19.0–14.5 g kg⁻¹ in MCT and 11.3–9.7 g kg⁻¹ in NT10 between uneroded and slight erosion, and 12.0–11.2 g kg⁻¹ between slight and moderate erosion in ACT. Overall SOC stock was greatest in the forest for each of the four depths. Total SOC stock for the 50 cm soil layer varied in the order F (71.99 Mg ha⁻¹) > NT15 (56.10 Mg ha⁻¹) > NT10 (37.89 Mg ha⁻¹) = NT6 (36.58 Mg ha⁻¹) for uneroded phase (P < 0.05). The lack of uneroded phase in ACT indicated high erosion risks of tillage, as also indicated by the high SOC stock for deposition phase from 0 to 50 cm soil layer (ACT (56.56 Mg ha⁻¹) > NT1.5 (42.70 Mg ha⁻¹) > NT10 (30.97 Mg ha⁻¹)). Tillage increased soil erosion and decreased SOC stock for top 10 cm layer for all erosional phases except deposition.     

Wind tunnel simulation of ridge-tillage effects on soil erosion from cropland

In the arid and semi-arid regions, ridge tillage was often used as an alternative practice for wind erosion control on the croplands without sufficient crop residues left during the fallow period. Through wind tunnel experiments, wind erosion rate and vertical mass flux profile of blown sand under the simulated conditions of ridge tillage and flat tillage were studied in 15, 10, 10, 5, 3 min exposures at the wind velocities of 8, 10, 15, 20, 24 m s⁻¹, respectively. The results for the soil tested indicate that the mean rate of wind erosion under flat tillage was 129.89 g m⁻² min⁻¹, while that under ridge tillage were 20–60% less. Under ridge tillage with different structures, average wind erosion rate had a positive correlation with the spacing between adjacent ridges. For the same ridge height, average wind erosion rate decreased with increasing ratio between the height of ridge and the width of furrow. For the same ratio between the height of ridge and the width of furrow, average wind erosion rate increased with increasing height of ridge. Power function relationships were found between wind erosion rate and wind velocity on all the simulated tillage conditions. A wind velocity of 15 m s⁻¹ was the critical velocity, above which wind erosion rate increased rapidly for the soil and simulated tillage conditions tested. Compared with flat tillage, ridge tillage remarkably decreased wind erosion rates when wind velocities were beyond 15 m s⁻¹. Under ridge tillage, the total mass of sand transported at a height of 0–20 cm above soil surface (Q_0–20), and the fraction of that travelling at a height of 0–4 cm (Q_0–4/Q_0–20), were less man mat under flat tillage. For the same ridge height, Q_0–4/Q_0–20 increased with increasing ratio between the height of ridge and the width of furrow. For the same ratio between the height of ridge and the width of furrow, Q_0–4/Q_0–20 decreased with increasing height of the ridge. Sand transport rate under flat tillage decreased with increasing height by a negative exponential function, while negative linear functions were found under ridge tillage. Thus ridge tillage decreased the rate of wind erosion and sand transportation near soil surface, reduced the loss of soil nutrient caused by wind erosion and plant damage caused by blown sand abrasion, which make it an effective agricultural technology for wind erosion control in the arid and semi-arid regions.     

Soil translocation by weeding on steep-slope swidden fields in northern Vietnam

This study investigated soil translocation associated with weeding on steeply sloped swidden fields attended by ethnic Da Bac Tay farmers in Hoa Binh Province in northern Vietnam. Annual soil loss rates of 4–6 Mg ha⁻¹ year⁻¹ were found on 20 m plots located on two separate hillslopes. Median soil flux rates were equivalent to 2.6–3.9 kg m⁻¹ pass⁻¹ for experiments conducted on slopes ranging from 0.54 to 0.84 m m⁻¹. The primary soil translocation process, the mechanical movement of soil via contact with a small hoe (ngheo), contributed approximately 60% of the weeding-related soil flux. Ravel, which is the rolling, bouncing, and sliding of soil clods downslope, was a secondary translocation process that accounted for almost 40% of the soil flux. Soil flux was most appropriately described with an exponential function that could predict the occurrence of ravel on steeper slopes. The observed soil fluxes were much smaller than those determined during weeding and hoeing at other tropical and subtropical sites, primarily because the tillage depth was very shallow (<1 cm) and weed density was low at the time of experimentation. The erosion rates associated with weeding were an order of magnitude lower than reported water erosion rates; therefore, the contribution to landscape change was believed to be small. Combined water and tillage erosion estimates indicated a possible unsustainable increase in soil loss on some steep-slope fields within the last few decades that has resulted from shorter fallow periods, longer periods of cultivation before fallowing, and greater weed pressure. Additional work is needed to verify these latter interpretations.     

Reassessment of tillage erosion rates by manual tillage on steep slopes in northern Thailand

Changing land-use practices in northern Thailand have increased tillage intensity. This study re-assesses the rate of tillage erosion by manual hoeing on steep slopes (17–82%) in northern Thailand. Previously collected soil translocation data during an on-farm tillage erosion experiment and additionally collected data during an on-farm tillage erosion survey have been analysed whereby a new calculation method (i.e. trapezoid tillage step) has been used. A comparison with previously collected data indicates that the trapezoid tillage step method and the tracer method are the most reliable methods to assess downslope translocation by manual tillage. Based on newly acquired understanding of the processes involved, soil fluxes by tillage erosion are quantified by linear functions for different slope gradient classes rather than one single diffusion-type equation for the whole slope range. For slope gradients smaller than 3%, soil fluxes are close to zero as farmers do not have a preferred tillage direction. For slope gradients between 3% and 70%, soil is tilled only in the downslope direction and soil fluxes range between 16 and 67 kg m⁻¹ tillage pass⁻¹. On slopes with gradients in excess of 70%, the angle of repose for soil clods is often exceeded resulting in a sliding down of the complete tilled top layer. These data are used to assess the soil flux for complete cropping cycles for the most dominant cropping systems in the highlands of northern Thailand: i.e. upland rice, maize, (soy) beans, cabbage and ginger. The on-site effects of tillage erosion will be very pronounced if parcels are short with respect to their slope length, cultivated for upland rice or cabbage, or when weed pressure is high. Tillage erosion results in a tillage step with low soil fertility and low infiltration capacity. Solutions to reduce tillage erosion intensity depend on the degree that tillage intensity can be reduced. This might happen by an improved weed management or by changing landuse to perrenial cropping. Other strategies are concentrating nutrients on the truncated hillslope sections and retaining soil on the field by vegetative buffers.     

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.     

Effect of cropland management and slope position on soil organic carbon pool at the North Appalachian Experimental Watersheds

Soil organic matter is strongly related to soil type, landscape morphology, and soil and crop management practices. Therefore, long-term (15–36-years) effects of six cropland management systems on soil organic carbon (SOC) pool in 0–30 cm depth were studied for the period of 1939–1999 at the North Appalachian Experimental Watersheds (<3 ha, Dystric Cambisol, Haplic Luvisol, and Haplic Alisol) near Coshocton, OH, USA. Six management treatments were: (1) no tillage continuous corn with NPK (NC); (2) no tillage continuous corn with NPK and manure (NTC-M); (3) no tillage corn–soybean rotation (NTR); (4) chisel tillage corn–soybean rotation (CTR); (5) moldboard tillage with corn–wheat–meadow–meadow rotation with improved practices (MTR-I); (6) moldboard tillage with corn–wheat–meadow–meadow rotation with prevalent practices (MTR-P). The SOC pool ranged from 24.5 Mg ha⁻¹ in the 32-years moldboard tillage corn (Zea mays L.)–wheat (Triticum aestivum L.)–meadow–meadow rotation with straight row farming and annual application of fertilizer (N:P:K=5:9:17) of 56–112 kg ha⁻¹ and cattle (Bos taurus) manure of 9 Mg ha⁻¹ as the prevalent system (MTR-P) to 65.5 Mg ha⁻¹ in the 36-years no tillage continuous corn with contour row farming and annual application of 170–225 kg N ha⁻¹ and appropriate amounts of P and K, and 6–11 Mg ha⁻¹ of cattle manure as the improved system (NTC-M). The difference in SOC pool among management systems ranged from 2.4 to 41 Mg ha⁻¹ and was greater than 25 Mg ha⁻¹ between NTC-M and the other five management systems. The difference in the SOC pool of NTC-M and that of no tillage continuous corn (NTC) were 16–21 Mg ha⁻¹ higher at the lower slope position than at the middle and upper slope positions. The effect of slope positions on SOC pools of the other management systems was significantly less (<5 Mg ha⁻¹). The effects of manure application, tillage, crop rotation, fertilizer rate, and soil and water conservation farming on SOC pool were accumulative. The NTC-M treatment with application of NPK fertilizer, lime, and cattle manure is an effective cropland management system for SOC sequestration.     

Tillage translocation and tillage erosivity by planting, hilling and harvesting operations common to potato production in Atlantic Canada

In Canada, the negative impacts of tillage erosion is a growing concern, especially in regions where highly erosive cropping and tillage systems are practiced on highly erodible, topographically complex landscapes. To date, tillage erosion studies have focused primarily on the movement of soil by primary and secondary tillage operations. However, in potato (Solanum tuberosum L.) production there is often considerable soil disturbance that occurs during “tertiary” field operations conducted during the growing season. Therefore, the objective of this project was to generate tillage translocation and erosivity values for implements common to planting, hilling and harvesting operations within intensive potato production systems in Atlantic Canada. Our results show that tertiary tillage operations result in significant soil displacement and can be equally as erosive as primary and secondary tillage operations. Both the planting, cultivating and hilling (PCH) sequence and the harvester moved soil extremely large distances (up to 23.6 and 6.0 m, respectively). In fact, the mean translocated distance of the tilled layer (T_L) and the mass of translocated soil (T_M) of the PCH sequence (0.42 m and 115.9 kg m⁻¹, respectively) and the harvester (0.55 m and 71.7 kg m⁻¹, respectively) are larger than those reported previously for primary and secondary tillage operations in New Brunswick. In addition, the net downslope movement of soil for the PCH sequence and the harvester was approximately 36 and 26 kg m⁻¹, respectively, suggesting that both tertiary tillage operations have the potential to be erosive. A direct relationship was observed between both T_L and T_M and slope gradient for the PCH sequence, but similar relationships were not found for the harvester, even though the harvester moved approximately 30 % more soil downslope than upslope. Linear regression functions were generally improved after including slope curvature in the model, but these results were not always significant. Soil movement by the PCH sequence and harvester were also largely influenced by tillage speed and tillage depth, and future research is needed under controlled conditions to determine whether it is changing topography or the variability in tillage speed and depth across the landscape in response to changing topography that is driving tillage erosion within mechanized agricultural systems. It is clear that tertiary tillage operations must be considered when developing best management practices to improve soil conservation strategies for potato production systems in Canada and worldwide.     

Soil translocation resulting from multiple passes of tillage under normal field operating conditions

Until now, most tillage erosion experiments were conducted under controlled soil and operating conditions. However, soil condition, tillage depth, speed and direction generally show substantial within-field variation. In this study, a series of tillage experiments were set up to investigate the erosivity of tillage under normal operating conditions. The effect of a typical tillage sequence, including multiple mouldboard, chisel and harrow passes, on soil translocation and tillage erosion was studied during a period of 3 years. Soil translocation in excess of 10 m was observed while the average net translocation rates ranged between 0 and 0.9 m. The results suggest that the annual tillage transport coefficient, associated with mechanized agriculture, is in the order of 781 kg m⁻¹ yr⁻¹. The experimental results also show that the tillage transport coefficient of a sequence of tillage operations can be reasonably well predicted from information provided by the farmer and by summing the transport coefficients obtained from controlled, single pass experiments. However, a Monte Carlo simulation showed that a relatively high number of tillage operations are required to obtain accurate estimates of the tillage transport coefficients in multiple pass experiments.     

Economics of tillage systems for spring wheat production in southwestern Saskatchewan (Canada)

The economic performance of continuous wheat (Triticum aestivum L.) and fallow-wheat rotations grown under conventional, minimum- and zero-tillage management practices on silt loam, sandy loam and heavy clay in southwestern Saskatchewan was determined during the relatively dry period of 1982–1988. The costs and returns for each rotation-tillage system were evaluated annually based on 1989–1990 price and cost conditions, and for various other plausible scenarios. Gross returns on silt loam were higher for continuous wheat (average 228 $ ha⁻¹) than for fallow-wheat systems (average 155 $ ha⁻¹). On the sandy loam, gross returns were similar for all cropping systems (average 112 $ ha⁻¹); on the heavy clay, they were higher for fallow-wheat than for continuous wheat (139 versus 119 $ ha⁻¹). Conservation tillage management increased gross returns over that obtained with conventional tillage only in years when growing season temperatures were high and precipitation was poorly distributed, or when the 21-month summerfallow period was droughty. On silt loam, gross returns were significantly lower with conservation tillage in as many as 3 of 7 years. On silt loam, net returns were highest for conventionally tilled continuous wheat when wheat prices were> 175 $ t⁻¹; at lower wheat prices, conventionally tilled fallow-wheat was the most profitable. On the other soils, minimum- and zero-tillage fallow-wheat provided the highest net returns at all wheat prices tested, with minimum tillage being slightly better at low wheat prices, but at these sites conventionally tilled fallow-wheat was not studied. The cost of production was highest for continuous wheat and for zero-tillage management. For fallow-wheat systems, conservation tillage required lower expenditures than conventional tillage for fuel, labor, machine repair and machine overheads; costs for minimum tillage averaged 9 $ ha⁻¹ and for zero tillage 15 $ ha⁻¹ lower on the silt loam. These savings were more than offset by increased herbicide costs which averaged 26 and 64 $ ha⁻¹ higher for minimum-tillage and zero-tillage systems, respectively. We concluded that producers in southwestern Saskatchean who are motivated primarily by short-term profit will find little incentive to adopt conservation tillage systems for spring wheat production, unless they are situated on soils that have already incurred severe soil loss or the soils are highly prone to further erosion losses.     

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.     

Depth distribution of soil organic C and N after long-term soybean cropping in Texas

Crop management practices have potential to enhance subsoil C and N sequestration in the southern U.S., but effects may vary with tillage regime and cropping sequence. The objective of this study was to determine the impacts of tillage and soybean cropping sequence on the depth distribution of soil organic C (SOC), dissolved organic C (DOC), and total N after 20 years of treatment imposition for a silty clay loam soil in central Texas. A continuous soybean monoculture, a wheat–soybean doublecrop, and a sorghum–wheat–soybean rotation were established under both conventional (CT) and no tillage (NT). Soil was sampled after soybean harvest and sectioned into 0–5, 5–15, 15–30, 30–55, 55–80, and 80–105 cm depth intervals. Both tillage and cropping intensity influenced C and N dynamics in surface and subsurface soils. No tillage increased SOC, DOC, and total N compared to CT to a 30 cm depth for continuous soybean, but to 55 cm depths for the more intensive sorghum–wheat–soybean rotation and wheat–soybean doublecrop. Averaged from 0 to 105 cm, NT increased SOC, DOC, and total N by 32, 22, and 34%, respectively, compared to CT. Intensive cropping increased SOC and total N at depths to 55 cm compared to continuous soybean, regardless of tillage regime. Continuous soybean had significantly lower SOC (5.3 g kg⁻¹) than sorghum–wheat–soybean (6.4 g kg⁻¹) and wheat–soybean (6.1 g kg⁻¹), and 19% lower total N than other cropping sequences. Dissolved organic C was also significantly higher for sorghum–wheat–soybean (139 mg C kg⁻¹) than wheat–soybean (92 mg C kg⁻¹) and continuous soybean (100 mg C kg⁻¹). The depth distribution of SOC, DOC, and total N indicated treatment effects below the maximum tillage depth (25 cm), suggesting that roots, or translocation of dissolved organic matter from surface soils, contributed to higher soil organic matter levels under NT than CT in subsurface soils. High-intensity cropping sequences, coupled with NT, resulted in the highest soil organic matter levels, demonstrating potential for C and N sequestration for subsurface soils in the southern U.S.     

Alternative tillage and crop residue management in wheat after rice in sandy loam soils of Indo-Gangetic plains

A 3-year field study was conducted to evaluate the effect of three tillage practices (conventional, zero and reduced/strip) with two nitrogen levels (120 and 150 kg N ha⁻¹) applied in primary strips and three crop residue management practices (removal, burning and incorporation) in secondary strips in wheat after rice. Reduced tillage resulted in significantly higher overall mean wheat yield (5.10 Mg ha⁻¹) compared to conventional (4.60 Mg ha⁻¹) and zero tillage (4.75 Mg ha⁻¹). Residue incorporation resulted in highest mean yield (5.86 Mg ha⁻¹) during third year. Maximum mean yield (6.1 Mg ha⁻¹) was obtained in reduced tillage followed by conventional tillage (5.8 Mg ha⁻¹) under residue incorporation in third year. The weed dry weight recorded at 30 days after sowing was highest (0.3 Mg ha⁻¹) under zero tillage and lowest under conventional tillage (0.16 Mg ha⁻¹). Among crop residue management practices, the highest dry weight of weeds (0.22 Mg ha⁻¹) was recorded under residue incorporation. The highest infiltration rate (1.50 cm h⁻¹) was recorded in residue incorporation followed by residue burning (1.44 cm h⁻¹) whereas; the lowest (0.75 cm h⁻¹) in zero tillage. Soil bulk density was the highest (1.69 Mg m⁻³) under zero tillage and the lowest in residue incorporation (1.59 Mg m⁻³). There were no changes in soil available P and K after each crop sequence in relation to tillage practices during first 2 years. Higher organic carbon (5.1–5.4 g kg⁻¹) was measured under zero tillage compared to other treatments. Residue incorporation increased soil organic carbon and available P while higher available K was monitored in burning treatment during the third year. These results suggest that reduced tillage and in situ incorporation of crop residues at 5 Mg ha⁻¹ along with 150 kg N ha⁻¹ were optimum to achieve higher yield of wheat after rice in sandy loam soils of Indo-Gangetic plains of India.     

Effects of agricultural management systems on soil organic carbon in aggregates of Ustolls and Usterts

Soil erosion contributes to the removal and redistribution of soil organic C from cultivated fields. The soil organic C content of wind erodible and water unstable aggregates is an important factor in determining the amount of carbon loss occurring in erosion processes. The relative distribution of organic carbon among aggregate size fractions may also affect the response of soils to erosion. Soil organic C distribution is dependent on the chosen management system. The effects of no-till, till, and grassland management systems on organic C content of erodible and non-erodible aggregates were examined in six Ustolls and two Usterts of central South Dakota. Organic C contents were related to dry- and wet-sieving to represent the potential influence of wind and water erosion on C loss in the absence of vegetative cover. Loss of aggregate stability in cultivated soils was associated with organic C loss. Most structural characteristics developed under tilled systems persisted after 6–16 years of no-till. Changes in distribution of organic C due to management systems were most evident in Ustolls where cultivation resulted in net soil C losses. Soil organic C was not significantly increased by the no-tillage practices applied in this on-farm study (in Ustolls 49 Mg ha⁻¹ in no-till versus 41 Mg ha⁻¹ in till, for 0–0.20 m depth). Soil properties of Usterts were less affected by land use and management practices due to the high shrink swell action and self-mixing. In both soil orders the greater concentration of organic C in the wind erodible (<1 mm) dry aggregate size fraction implies a high potential for organic C loss by erosion in addition to organic C loss from mineralization after tillage. Grassland when compared to cultivated topsoil showed the largest amounts of organic carbon stored and the minimal potential for erosion loss of soil organic C.