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.     

Humic substances in soil and crop sciences: P. MacCarthy, C.E. Clapp, R.L. Malcolm and P.R. Bloom (Editors), American Society of Agronomy and Soil Science Society of America, Madison, WI, 1990, 281 pp., price US$ 30.00, ISBN: 0-89118-104-0

Studies were conducted to determine changes in organic matter and microbial biomass carbon in comparison with structural stability at the surface soil (0–5 cm) of a Charlottetown fine sandy loam, an Orthic Podzol, at three tillage and grassland sites situated in Prince Edward Island. The tillage experiments, established for 3–5 years, included comparisons of mouldboard ploughing, direct drilling, shallow tillage, and chisel ploughing. Two indices of soil structural stability were used: mean weight diameter (MWD) and aggregation index (AI). The latter index assigns a weight factor to aggregate size ranges based on their value for plant germination and root growth.Direct drilling and reduced tillage increased the level of soil organic carbon by 10–17%, relative to mouldboard ploughing. Organic carbon was more enriched in 1–2 mm and 4.75–9.00 mm macroaggregates, especially the former, compared with whole soil. The MWD of aggregates after wet sieving was 33% and 55%, relative to the grassland sites, for mouldboard ploughing and direct drilling, respectively. On these soils of similar mineralogy and particle size, a close linear relationship (r=0.942) was observed between organic carbon (r=0.947) and nitrogen (r=0.923). The AI was significantly correlated to both organic carbon and microbial biomass carbon using power regression. In contrast to MWD, the AI under direct drilling and reduced tillage, associated with an organic carbon level of 2.5%, approximated the AI under grass. Overall, the study showed that minimum tillage systems in humid climates can improve structural stability at the soil surface of fine sandy loams over a relatively short time frame.     

A long-term comparison of ploughing, tine cultivation and direct drilling on the growth and yield of winter cereals and oilseed rape on clayey and silty soils

The effects of mouldboard ploughing, shallow tined cultivation and direct drilling on yields of winter wheat, barley, oats and oilseed rape were compared over 10 years. Three field experiments were conducted on two non-calcareous clays (stagnogleys) and a weakly structured silty soil (argillic brown earth). Two spring N levels were applied to the winter wheat plots on the clay soil in three years and to the winter barley plots on the silty soil in one year. This paper reports the soil bulk density and water content at sowing and the crop growth, yield components and yields obtained during the later years of the study: 1979–1984 on the clayey soils and 1981–1984 on the silty soil.

In the years when cereals were grown, differences in yield between cultivation treatments were small and inconsistent. Oilseed rape yielded significantly more after direct drilling than ploughing because of better establishment and uniformity of growth.

The success of continuous reduced tillage depended on both burning crop residues and good weed control.     

Direct drilling compared with ploughing for winter wheat grown continuously and the effects of subsoiling

Abstract. Direct drilling was compared with mouldboard ploughing on a sandy clay loam using winter wheat as the test crop for a period of four years (1978/79 to 1981/82). The effect of short- and long-term sequences of direct-drilling on grain yield from 1981/85 was also investigated and in 1983/84 and 1984/85 the effect of soil loosening by a slant-legged subsoiler, the'Paraplow'. The range in annual mean yields was 7.19 to 9.32 t ha^-1. There were no significant differences in grain yield between direct-drilling and ploughing except in 1979 when direct-drilled wheat yielded 0.60 t ha^-1 more than wheat after ploughing. The number of years the land had been direct-drilled had no effect on grain yield.
Using a slant-legged subsoiler on direct-drilled land significantly reduced cone resistance and increased root density, but these effects were variable across the working width of the implement. Subsoiling did not increase yield in 1983/84, and in 1984/85 it reduced yield by 0.45 t ha^-1.
Long-term direct drilling of winter wheat on the Tickenham soil series is unlikely to result in a loss of yield provided straw is burnt and grass weeds are controlled.     

Temporal variability of soil macroporosity in a fine sandy loam under mouldboard ploughing and direct drilling

The temporal variability of soil porosity, especially macropores (> 50 μm), and associated porosity factors such as pore continuity, percent water-filled pore space (%WFPS), and earthworm numbers and biomass were determined over 3 years under direct-drilling and mouldboard ploughing. The study was conducted on a Charlottetown fine sandy loam, an Orthic Podzol with a humid to perhumid soil-moisture regime.Differences in soil porosity between tillage systems were mainly confined to the surface 0–8-cm soil depth. Fissures (> 300 μm), or large pores, were reduced under direct drilling compared with mouldboard ploughing, but subject to regeneration over the winter period. The absence of soil loosening caused the volume of macropores to fall below 10% during the growing season. Tillage had a residual effect on soil porosity, maintaining the volume of macropores between 11 and 18%. Differences between tillage and ice-induced porosity influenced the degree of macropore regeneration. In general, water-storage pores were similar between tillage systems. A close relationship (r² = 0.832) was observed between dry bulk density and macroporosity under both tillage systems. The relationship between macroporosity and pore continuity (K_sat), which differed between tillage systems, indicated that a macroporosity of between 8 to 10% (v/v) would maintain adequate soil permeability. In contrast, the %WFPS, which was closely related (R² = 0.952) to macroporosity and soil water content, indicated that the volume of macropores should exceed 14% to provide an optimum level of air-filled pore space.Under humid soil-moisture regimes, the use of macroporosity as an index of critical soil structure or limiting density needs to be based both on adequate soil permeability and on water-filled pore space. Although direct drilling maintained adequate functional porosity, the need for an optimum aerobic environment may necessitate loosening of the surface soil on an annual basis.     

Cultivation and nitrogen requirements for drilled and broadcast winter barley on a surface water gley (Gleysol)

Direct drilling, seed broadcasting plus rotovation, rotovation plus drilling and shallow mouldboard ploughing plus drilling were examined as possible quick and cheap alternatives to conventional mouldboard ploughing. The experiment ran for four seasons during 1980–1984. In the first season nitrogen was top-dressed at a uniform rate slightly greater than recommended, but in the final three seasons, dressings were either at the recommended rate or at 40% greater than the recommended rate. The topsoil (0–300 mm depth) of the experimental site was a sandy clay loam containing 4% w/w easily oxidisable organic matter overlying a slowly permeable subsoil. The experimental site was situated in south-east Scotland.In the first season, the non-ploughing treatments yielded less than conventional ploughing treatments because wet weather prevented adequate chemical weed control. In the remaining three seasons direct-drilling and broadcasting plus rotovation yielded, on average, 6% more grain than the normal ploughed and rotovated plus drilled treatments. Total root lengths were least in the direct-drilled and broadcast treatments and plant populations were independent of treatment. In the broadcast and direct-drilled treatments, P and K and organic matter were concentrated in the surface layer as were most of the roots. Of the non-ploughing treatments, the direct-drilled soil was the most compact. The broadcast seedbed was the least compact because there was no traffic after the soil was cultivated to incorporate the seed. Direct-drilled soil was suspected to have the most stable structure because it contained most organic matter, particularly at the surface. Weed control, timing of operations and control of traffic were critical to the success of direct drilling. Since adverse weather conditions may prevent the attainment of such a high standard of management, the recommended minimum cultivation requirement is ploughing to > 150 mm depth. Increasing the nitrogen rate to 40% above that recommended gave an economically worthwhile 0.6 t ha⁻¹ increase in grain yield.     

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.     

Specific draught for mouldboard plough, chisel plough and disc harrow at different water contents

The objective of the present study was to measure the specific draught (force per cross-sectional area of worked soil) and energy use for soil fragmentation for different tillage implements and soil conditions. Draught was calculated from measurements of fuel consumption and speed during tillage with a mouldboard plough and a chisel plough set to working depths of 13, 17 and 21 cm, and a disc harrow. Tillage was carried out at three different water contents (“Wet”, “Moist” and “Dry”) on two sites. The average working depth was calculated from weighing the loose soil within a 0.25-m² frame. Specific area of the soil was determined by sieving. Soil strength was measured in situ using a shear vane and a penetrometer. Average working depth was much less than the set working depth for the chisel plough. Specific draught was generally the lowest for the mouldboard plough and the highest for the chisel plough, and increased with decreasing soil water content. The specific draught was strongly correlated to soil cohesion, but not to penetration resistance. The proportion of coarse aggregates after tillage was the highest for the mouldboard plough and the lowest for the moist soil. The energy use for soil fragmentation was in most cases the lowest for the disc harrow, while there were small differences between the chisel and the mouldboard ploughs. The results show that the mouldboard plough is energy efficient for loosening soil, while the disc harrow is energy efficient for soil fragmentation during primary tillage. Tillage at an intermediate water content, close to the plastic limit, gave the largest proportion of small aggregates and consequently the lowest energy use for soil fragmentation.     

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.     

Reduced tillage in north-west Europe—A review

The main features of the climate and soils of the main crop production areas of different countries in north-west Europe are outlined, and the main crops grown are summarised. The need for tillage is considered; provided that suitable conditions exist for germination, root growth is most likely to be influenced by mechanical impedance and aeration. Traditional tillage may not always be necessary and may hinder timely sowing of crops. Shallow tillage can facilitate planting a larger area of crops closer to the optimum dates in autumn and in spring, which also saves energy and labour.Research experience with reduced tillage over the last 20–25 years is reviewed. Shallow tillage has been as good as mouldboard ploughing at the traditional depth in most countries on a wide range of soil types, if weed control was satisfactory. Direct drilling has often proved satisfactory in the absence of crop residues for autumn sown crops (wheat, barley, oil-seed rape and beans) where drainage (and therefore soil aeration) was not limiting. Direct drilling has not generally been successful for spring sown crops. Direct drilling is inappropriate for root crops, but strip tillage for sugar beet may become practicable. Some research on soil conditions associated with these experiments is considered.Crop residues are a major constraint to shallow tillage or direct drilling of autumn sown crops. The limitations of reduced tillage due to inadequate weed control, wheel-traffic damage and unsatisfactory drainage are reviewed. The need for occasional deep loosening is also discussed. Where the amount of residues is small, much tillage may be unnecessary, except to relieve compaction by wheels; bed systems or wide-span gantries to avoid wheel damage could become practical developments for some crops.     

The influence of tillage on the proportion of organic carbon and nitrogen in the microbial biomass of medium-textured soils in a humid climate

Summary Microbial biomass C and N respond rapidly to changes in tillage and soil management. The ratio of biomass C to total organic C and the ratio of mineral N flush to total N were determined in the surface layer (0–5 cm) of low-clay (8–10%), fine sandy loam, Podzolic soils subjected to a range of reduced tillage (direct drilling, chisel ploughing, shallow tillage) experiments of 3–5 years' duration. Organic matter dynamics in the tillage experiments were compared to long-term conditions in several grassland sites established on the same soil type for 10–40 years. Microbial biomass C levels in the grassland soils, reduced tillage, and mouldboard ploughing treatments were 561, 250, and 155 g g^-1 soil, respectively. In all the systems, microbial biomass C was related to organic C (r=0.86), while the mineral N flush was related to total N (r=0.84). The average proportion of organic C in the biomass of the reduced tillage soils (1.2) was higher than in the ploughed soils (0.8) but similar to that in the grassland soils (1.3). Reduced tillage increased the average ratio of mineral N flush to total soil N to 1.9, compared to 1.3 in the ploughed soils. The same ratio was 1.8 in the grassland soils. Regression analysis of microbial biomass C and percent organic C in the microbial biomass showed a steeper slope for the tillage soils than the grassland sites, indicating that reduced tillage increased the microbial biomass level per unit soil organic C. The proportion of organic matter in the microbial biomass suggests a shift in organic matter equilibrium in the reduced tillage soils towards a rapid, tillage-induced, accumulation of organic matter in the surface layer.     

Preliminary investigation on the response of spring barley (Hordeum sativum) to soil cultivation with the ‘paraplow’

In a long-term cultivation experiment on a sandy clay loam overlying magnesian limestone and cropped with spring barley (Hordeum sativum) each year, mouldboard ploughing, shallow tine cultivation and direct drilling were compared. Compaction had become evident on the direct drilled treatment and to alleviate this the ‘Paraplow’, a slant-legged soil loosening implement, was used on all treatments to a depth of 35 cm in the autumn of 1980.A crop of spring barley (var. Athos) was grown in 1981, at a nitrogen fertiliser rate of 75 kg ha^?1 N. Root growth, shoot dry matter, nitrogen uptake, grain yield and components of yield were recorded. Soil strength (by cone resistance) and dry bulk density of the soil were also measured. As a mean of all cultivation systems the ‘Paraplow’ increased grain yield by 12%. The response of the crop to cultivation by the ‘Paraplow’ was greatest on the mouldboard ploughed and long-term direct-drilled systems. The latter out-yielded the former, with shallow tine cultivation intermediate.The decrease in soil strength caused by the ‘Paraplow’ resulted in more rapid penetration of root axes and greater proliferation of roots in each horizon of the profile. There was no significant effect on shoot dry matter up to anthesis but, at harvest, barley on land treated with the ‘Paraplow’ had more ears with more grains per ear. Thousand-grain weight was not affected.The poorer growth of barley on ploughed than direct drilled land in 1981 was explained by temporary waterlogging of the soil in May.     

Does shifting from conventional to zero tillage in combination with a cover crop offers opportunities for silage maize cultivation in Flanders?

Tillage is an important agricultural practice, influencing the physical, chemical and biological soil characteristics. In this paper the influence of various tillage systems combined with or without a cover crop under different nitrogen fertilization levels on silage maize yield and soil fertility was investigated. Based on a field trial in Bottelare (Belgium), during the period 2007–2015, it was concluded that for each tillage system higher nitrogen levels resulted in a higher yield. In addition, the highest yield was achieved for the conventional tillage system, the yield gain for mouldboard ploughing varied between 13% (2015) and 71% (2012) compared to zero tillage. In case reduced tillage was adopted, the yield loss compared to mouldboard ploughing varied between 6% (2013 and 2015) and 24% (2012). Furthermore, it seemed that the accumulated temperature during the growing season and rainfall around flowering were decisive in determining maize yield. Additionally, rainfall in the period 60 days post sowing was significantly negatively correlated with the yield from the zero tillage plots, whereas in case tillage was adopted no correlations with rainfall 60 days post sowing were detected. Concerning the soil organic carbon content and the amount of earthworms, no clear trends could be observed. Zero tillage resulted in high weed pressure and caused soil compaction. So, in this trial, under humid conditions, the less labor intensive zero tillage system did not result in competitive maize yields. In conclusion, reduced tillage methods offer opportunities for maize cultivation in Belgium. This method of farming resulted in a lower yield, however, the difference with mouldboard ploughing was not significant. Therefore, adopting a reduced tillage system can be seen as a valid alternative for ploughing as this tillage system ensures a sustainable environment.     

Changes in the weed communities as affected by different primary soil tillage and deep loosening

Long-term soil cultivation at the same depth affects soil characteristics and crop productivity. The aim of the study was to investigate the impact of a long-term different intensity soil tillage methods and deep loosening on weed number, weed agrobiological group and soil seed bank changes in till Bathygleyic Dystric Glossic Retisol soil under the climatic conditions of the Western Lithuania (geographical coordinates 55°43′38″N, 21°27′43″E). The study included different soil tillage methods (conventional ploughing, shallow ploughing and shallow ploughless tillage) and deep loosening. During investigational years, the greatest weed number in crops and the greatest weed seed number in the seed bank were determined in the soil reduced tillage (shallow ploughing and shallow ploughless tillage). The weed number in crops of conventional ploughing soil was 35.8% lover compared to reduced tillage soil. The weed seed number in the seed bank of conventional ploughing was 49.6% lover compared to reduced tillage Decreasing soil tillage intensity resulted in weed seeds concentration in the upper topsoil. A one-time deep loosening had a significant effect during the crop rotation: the weed number in crops and weed seed number in the seed bank were determined to have increased by 26.6% and 51.6% in conventional ploughing soil and by 11.9% and 23.2% shallow ploughless soil respectively. However, after deep loosening, the number of Poa annua in crops decreased 2.9 times in plots of conventional ploughing and 1.7 times – in plots of shallow ploughing soil.     

Effects of soil water content during primary tillage – laser measurements of soil surface changes

Soil water content during tillage can have a large impact on soil properties and tillage outcome. Measurement of soil relief in relation to fixed elevation points provides a non-destructive method of monitoring loosening/compacting processes during the year. The main objective of this study was to determine the effect of soil water content during primary tillage on soil physical properties.

The treatments included mouldboard and chisel ploughing of a clay soil on three occasions in the autumn, with gradually increasing water content (0.76, 0.91 and 1.01 × plastic limit). Soil surface height was measured by laser within a 0.64 m² area from fixed steel plates after each tillage occasion, and before and after seedbed preparation in the following spring. The measurements of surface height were compared with measurements of other soil physical properties, such as bulk density, saturated hydraulic conductivity and seedbed properties.

Tillage at the lowest water content (0.76 × plastic limit) produced the greatest proportion of small aggregates, and generally the most favourable soil conditions for crop growth. Soil loosening, as measured by increase in soil height during primary tillage, was highest for mouldboard ploughing and for tillage at the lowest water content. Differences between tillage treatments decreased with time, but were still significant after sowing in the spring. Natural consolidation during winter was smaller than the compaction during seedbed preparation in the spring. No significant differences in bulk density were found between treatments, and thus soil surface height was a more sensitive parameter than bulk density determined by core sampling to detect differences between treatments.

Late tillage under wet conditions caused a greater roughness of the soil surface and the seedbed base, which was also found in the traditional seedbed investigation. The effect of tillage time on seedbed properties also resulted in a lower number of emerged plants in later tillage treatments.

The laser measurements were effective for studying changes in soil structure over time. The results emphasize the need to determine changes in soil physical properties for different tillage systems over time in order to model soil processes.     

Influence of tillage on crop residue cover, soil properties and yield components of cowpea in derived savannah ectones of Nigeria

The effects of five tillage treatments: no tillage (NT), disc harrowing (DH), mouldboard ploughing followed by disc harrowing (MPH), disc ploughing followed by disc harrowing (DPH), and disc ploughing followed by two passes of disc harrowing (DPHH) on crop residue cover, soil properties and some yield parameters of cowpea were investigated for a derived savannah ectone soil. The residue left on the soil surface for NT, DH, and MPH is not significantly different. The NT left 32.1 and 44.3% more residue on the soil surface than the DPH and DPHH treatments, respectively. The NT treatment had least average value of soil bulk density of 1.01 g/cm³. The mean soil bulk densities for the DH, MPH, DPH and DPHH vary between 1.20 and 1.35 g/cm³. The soil moisture content decreased with increasing soil depth. At the soil depth of 10–30 cm, the cone penetration resistance at NT was 1.18 MPa compared with 0.92 MPa for the DH treatment, although these were not significant (p≤0.05). The tillage treatments had a significant effect on grain yield, mass of leaves and stems, root length density, and number of pods per plant of cowpea except on the germination count. DH and NT treatments gave different grain yield and number of pods per plant but these values were not statistically different and represent the highest grain yield and number of pods per plant among the other treatments were considered. The root zone exploration revealed highest root density at shallow depths with the DH and MPH treatments.     

Soil mineral-N and N-fertilizer requirements of spring cereals in two long-term tillage trials on loam soil in southeast Norway

Much uncertainty exists among growers concerning the need to adjust N-fertilizer application to cereals when reduced tillage is adopted. Studies in long-term trials are required to give an adequate answer to this question, which is of both economic and environmental interest. N-fertilizer requirements of spring cereals and of soil mineral nitrogen contents at different times of the year were measured over the period 1991–1996 in two long-term tillage trials established in 1980 at Kise (60°46′N, 10°49′E) on morainic loam soil. Tillage treatments comprised conventional tillage with autumn ploughing and reduced tillage without ploughing and with harrowing in spring kept to the minimum necessary for seeding. Four levels of N-fertilizer (0, 60, 90 and 120 kg N/ha) were compared in 1991–1995 in barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.), and their residual effect was measured in 1996. Levels of soil mineral nitrogen before fertilization in spring were on an average 8% lower with reduced tillage than with conventional tillage. Plant development was delayed with reduced tillage, but this was compensated for later in the season. A two-year incubation study under covered plots in the field did not reveal any effect of tillage on net nitrogen mineralisation. There was a tendency to higher straw yield with reduced tillage, but no overall effect on grain yield. Responses to N-fertilizer were almost identical with both the tillage systems, and yields increased up to the highest level of application. Crop nitrogen contents were monitored, but only minor differences were found between tillage systems in total uptakes and apparent N-fertilizer recoveries. On the basis of these results it is concluded that long-term reduced tillage does not affect the N-fertilizer requirements of spring cereals on loam soils under cool climatic conditions.     

Carbohydrate composition in relation to structural stability, compactibility and plasticity of two soils in a long-term experiment

The effects of tillage on soil organic carbon content, carbohydrate content, monosaccharide composition, aggregate stability, compactibility and plasticity were investigated in a field experiment on a gleysol and on a cambisol under winter barley in South-East Scotland. Two long-term treatments (direct drilling and conventional mouldboard ploughing for 22 years) were compared with short-term direct drilling and broadcast sowing plus rotavation for 5 years. Carbohydrate released sequentially to cold water, hot water, 1.0 M HCl and 0.5 M NaOH was determined after hydrolysis as reducing sugar equivalent to glucose in both fresh and air-dried samples. All other measurements were made on dry soils only. About 3% of the soluble carbohydrate was extracted by cold water, 10% by hot water, 12% by HCl and 75% by NaOH from both the dry and fresh soils. The total reducing sugars of the fractions were proportional to the total organic carbon determined by dichromate oxidation or C analysis. Organic carbon and carbohydrates were concentrated near the surface of the direct drilled soil, but were more uniformly distributed with depth in the ploughed soil. The surface soil under direct drilling was more stable, less compactible and had greater plasticity limits than under ploughing. However, particle size distributions were unaffected by tillage so that differences in soil properties were attributed to differences in the quantity and quality of organic matter. Differences in compactibility, structural stability and plasticity limits between depths and tillage treatments correlated with total carbon and with total carbohydrates. The hot water extractable carbohydrate fraction correlated best with aggregate stability and the NaOH fraction correlated best with compactibility and plastic limit. Both fractions were greatest in the long-term direct drilled soil. The hot water fraction had a galactose plus mannose over arabinose plus xylose ratio of 1.0–1.6 in comparison to 0.4–0.7 in the NaOH fraction indicating that the microbial contribution within the hot water-soluble fraction was the greater. The hot-water fraction was likely to contain more exocellular microbial polysaccharides involved in the stabilizing of soil aggregates. The hot-water and NaOH carbohydrate fractions may be good indicators of soil organic matter quality relevant to the preservation of good soil physical conditions.     

Effect of tillage on earthworms over short- and medium-term in conventional and organic farming

Earthworms play an important role in many soil functions and are affected by soil tillage in agricultural soils. However, effects of tillage on earthworms are often studied without considering species and their interactions with soil properties. Furthermore, many field studies are based on one-time samplings that do not allow for characterisation of temporal variation. The current study monitored the short (up to 53 days) and medium term (up to 4 years) effects of soil tillage on earthworms in conventional and organic farming. Earthworm abundances decreased one and three weeks after mouldboard ploughing in both conventional and organic farming, suggesting direct and indirect mechanisms. However, the medium-term study revealed that earthworm populations in mouldboard ploughing systems recovered by spring. The endogeic species Aporrectodea caliginosa strongly dominated the earthworm community (76%), whereas anecic species remained <1% of all earthworms in all tillage and farming systems over the entire study. In conventional farming, mean total earthworm abundance was not significantly different in reduced tillage (153 m⁻²) than mouldboard ploughing (MP; 130 m⁻²). However, reduced tillage in conventional farming significantly increased the epigeic species Lumbricus rubellus from 0.1 m⁻² in mouldboard ploughing to 9 m⁻² averaged over 4 years. Contrastingly, in organic farming mean total earthworm abundance was 45% lower in reduced tillage (297 m⁻²) than MP (430 m⁻²), across all sampling dates over the medium-term study (significant at 3 of 6 sampling dates). Reduced tillage in organic farming decreased A. caliginosa from 304 m⁻² in mouldboard ploughing to 169 m⁻² averaged over 4 years (significant at all sampling dates). Multivariate analysis revealed clear separation between farming and tillage systems. Earthworm species abundances, soil moisture, and soil organic matter were positively correlated, whereas earthworm abundances and penetration resistance where negatively correlated. Variability demonstrated between sampling dates highlights the importance of multiple samplings in time to ascertain management effects on earthworms. Findings indicate that a reduction in tillage intensity in conventional farming affects earthworms differently than in organic farming. Differing earthworm species or ecological group response to interactions between soil tillage, crop, and organic matter management in conventional and organic farming has implications for management to maximise soil ecosystem functions.