Shallow Ploughing Research Articles

Response of sugar beet to some mechanical management practices, irrigation and plant densities

The aim of this study was to see the effect of four mechanical practices (shallow ploughing, laser deep ploughing and laser leveled soil + deep ploughing), three irrigation intervals (every 4 weeks, every 6 weeks and every 8 weeks) and three plant densities (35 cm (20000), 25 cm (28000) and 15 cm (46000) plants/fed.) on growth of sugar beet plants of Farida cultivar. Sowing of sugar beet at a laser leveled soil + deep ploughing, among lower plant densities 20.000 plants/fed (1 feddan = 0.42 ha) and irrigation intervals every 8 weeks gave a significant increase in root length, root perimeter, crop growth rate(CGR) and relative growth rate(RGR) in comparison to other treatments.

Effect of reduced tillage systems on earthworm communities in a 6-year organic rotation

Chisel plough or no-till practises are clearly attributed to sustainable farming for the support of soil organisms and soil biological functioning. However, in organic farming these techniques are only applied to a very small extent since there is a need for cultivation to control weeds. In organic farming it is important to develop and establish less destructive soil tillage practises to benefit from the support of soil organisms, especially from ecosystem engineers like earthworms. In this study three tillage systems were compared on a silty, loess' derived soil in a 6 crop rotation. The tillage systems established were: (1) “ecomat” shallow (10 cm) inversive ploughing; (2) a ridge culture system; and (3) conventional tillage (inversion tillage) down to 30 cm. In fall 2005, three years after establishment of the field plots earthworm communities were investigated using formalin extraction. In total 6 species were detected. The earthworm abundance was low, ranging from 0 to 84 individuals m −2. Shallow ploughing using the “ecomat” technique was not different than conventional ploughing in its effects on earthworm populations, while the ridge culture system was significantly reduced in earthworm numbers and biomass compared to conventional ploughing. We conclude that both “ecomat” and “ridge culture” do not support earthworms and significantly reduce earthworm densities. The reductions in tillage depth alone are not effective for improving the habitat quality for earthworms in soil.

Reducing ploughing depth and nitrogen fertilisation in hilly environment of the centre of italy (marche)

For the purpose to provide a contribution about ploughing subject three ways were compared in a quadriennal rotation from Experimental Industrial Crops Institute in Osimo. During the years 1986-1999, in a factorial experiment with 4 replications, traditional (50 cm), shallow ploughing (25 cm) and chiseling (50 cm) plus reduced ploughing (25 cm) were compared with two crop rotations (sugar beet- wheat; shelling peas-wheat) and three nitrogen levels (0, 92, 184 kg ha-1) in a split block experiment. The conventional and chiseling plus reduced ploughing did not influenced sugar-beet or peas yield or qualitative and quantitative crop traits; like it was emphasized in the previous seven years. Wheat seed yield was positively influenced by reduced ploughing done to the previous crop but not by rotation. Straw yield was higher after sugar beet than after peas. Nitrogen fertilisation allowed the best technical yield of wheat at the intermediate level of 90 kg ha-1, whereas more nitrogen (180 kg ha-1) improved only the biomass and heads per squared meter at harvesting, lowering the test weight of wheat. In conclusion we could affirm that, in this experience, the best ploughing for sugar-beet and shelling peas is at 25 cm. Moreover it was not possible to reduce fertilisation of wheat following shelling peas (leguminous crop).

Water infiltration and clod size distribution as influenced by ploughshare type, soil water content and ploughing depth

Soil management techniques, especially tillage, have been linked to the creation of low-permeability pans that reduce soil infiltrability and increase runoff and soil erosion on agricultural soils. In Iran, the mouldboard plough is the standard tillage implement used for primary tillage and that could create a compacted plough pan, especially under wet conditions. It was hypothesised that serrations on the ploughshare would increase water infiltration into the soil. A field experiment was conducted in Isfahan (central Iran) on a silty clay loam soil (Typic Haplargids). The infiltration rate and cumulative infiltration of water into furrow bottoms after ploughing with a mouldboard plough were measured using a double-ring infiltrometer. The plough was equipped with five share types (deep-suck share (control), trapezoidal share with/without sharepoint and serrated share with/without sharepoint) and ploughing performed under two soil water contents (0.55 and 0.85 plastic limit, PL), and two ploughing depths (15 and 20 cm). The clod mean weight diameter (MWD) was determined as an index of soil pulverisation, using dry sieving. The average 90 min cumulative water infiltration for the serrated share with sharepoint was significantly greater than for the other share types due to the furrow-bottom soil cracking resulting from an increase in the thickness of cutting edge of the plough. Ploughing at 0.85 PL significantly improved cumulative water infiltration compared with ploughing at 0.55 PL. The final infiltration rate for the serrated share with/without sharepoint was statistically similar to that of deep-suck share (control). For shallow ploughing at 0.85 PL, the clod MWD for the trapezoidal share without sharepoint was significantly greater than that of the control. For the serrated share with sharepoint, the proportion of coarse clods (⩾40 mm) was significantly higher under dry condition (0.55 PL), when compared with the moist condition (0.85 PL), whereas for the rest of ploughshare types, those proportions were statistically similar. These results indicate that for improving water infiltration and still having similar soil pulverisation, the deep-suck share could be replaced by the serrated share with sharepoint in heavy soil (i.e., silty clay loam) with low water infiltration while ploughing at a moisture content of 0.85 PL.

Tillage reduction in Central East Italy

SUMMARY The effect of several soil tillage methods (plowing at a depth of 20-25 cm, chiseling at 30 cm and plowing at 20 cm plus sub-soiling at 50 cm factorially combined with three biennial rotations (wheat-sugarbeet; wheat-sorghum; wheat-sunflower) were studied between 2000 and 2005. Sugarbeet confirmed the supposed increased need for deep tillage, whereas sorghum and sunflower were less sensitive. With dry soil chiseling was enough to prepare a seed bed compared with plowing plus sub-soiling, whereas with moist soil, shallow plowing gave the best results in sorghum but not in sugarbeet. Plowing plus sub-soiling requires more energy and it could be justified only in sugarbeet. Wheat yielded better after sugarbeet and sunflower than after sorghum. Minimum tillage was as efficient as shallow plowing for wheat seed bed preparation.

Effect of impingement angle on slurry erosion behaviour and mechanisms of 1017 steel and high-chromium white cast iron

In the present work a series of systematic erosion tests were carried out to investigate the influence of impingement angle on erosion mechanisms of 1017 steel and high-Cr white cast iron using a slurry whirling-arm test rig. Scanning electron microscopy (SEM), image analysis system, optical microscopy as well as gravimetric and microhardness measurements were utilized to identify the slurry erosion process. Test results showed that, the effect of impingement angle on erosion mechanisms of 1017 steel has three regions. In the first region ( θ ≤ 15°) shallow ploughing and particle rolling were the dominant erosion mechanisms, microcutting and deep ploughing in the second region (15° < θ < 75°), while indentations and material extrusion prevailed in the third region ( θ ≥ 75°). For high-Cr white cast iron the test results showed that, the erosion mechanisms involved both plastic deformation of the ductile matrix and brittle fracture of the carbides. At low impingement angles (up to 45°) observations of microphotographs of the impacted surfaces revealed that, plastic deformation of the ductile matrix was the dominant erosion mechanism and the carbides fracture was negligible which lead to small erosion rate. Whereas, at high impingement angles (greater than 45°) gross fracture and cracking of the carbides were the main erosion mechanisms in addition to indentation with extruded lips of the ductile matrix.

Nitrogen and phosphorous in a loam soil of central Italy as affected by 6 years of different tillage systems

Tillage practices can influence content and dynamics of soil N and P. A field study was conducted on a loam soil (Typic Udifluvent) in Italy, to determine mineral and organic N and P concentrations at the end of 6 years of different tillage systems. Maize ( Zea mays L.) was cropped since 1970, and managed since 1994 with deep ploughing (DP) to 40 cm, ripper subsoiling (RS) to 40 cm, shallow ploughing (SP) to 20 cm and minimum tillage with harrow disk (MT) to 10 cm. At the end of the sixth year, soil was collected in 10 cm increments to a total depth of 40 cm. Surface concentration of total N was higher with MT than with RS, SP and DP, but differences disappeared at lower depths. Soil water content was lower under DP and SP treatments than under MT and RS. Residual NO 3-N in the soil profile was not different among tillage treatments. During 6 years, MT increased soil quality, by enrichment of organic N and improvement of soil water content at the surface. Moldboard ploughing was a less sustainable tillage system in this environment.

Interactive effect of tillage depth and mulch on soil temperature, productivity and water use pattern of rainfed barley ( Hordium vulgare L.)

Soil porosity and organic matter content influence the hydrology, thermal status and productivity of agricultural soils. Shape, size and continuity of soil pores are determined by tillage practices. Thus appropriate tillage and mulch management can conserve residual soil moisture during the post rainy season. This can play a key role in enhancing productivity under the rainfed ecosystem of subhumid region in eastern India. A field study was carried out on a fine loamy soil from 1993–1994 to 1995–1996. Two tillage treatments were conventional ploughing (150 mm depth) and shallow ploughing (90 mm) depth. Each tillage practice was tested with three mulch management viz., no mulch, soil dust mulch and rice ( Oryza sativa L.) straw mulch. Soil organic carbon, bulk density, moisture retentivity, soil temperature with productivity and water use pattern of barley ( Hordium vulgare L.) were measured. Reduction in ploughing depth resulted in nominal increase in profile (0.0–1.2 m) moisture status, yield, and soil thermal status at 14:00 and water use efficiency (WUE). However, it decreased the magnitude of soil temperature in the morning (07:00). Straw mulch conserved 19–21 mm of moisture in the profile (1.2 m) over the unmulched condition. Both soil dust and rice straw mulching elevated soil thermal status at 07:00 as compared to unmulched condition, but this trend was reversed at 14:00. Straw mulching significantly increased grain yield and WUE over soil dust mulch and unmulched condition. Impact of straw mulch was more pronounced under shallow ploughing depth. Shallow tillage with rice straw mulching is recommended to the farmers to obtain higher level of yield and water use efficiency.

Influences of soil tillage and fertilization on maize yield and weed infestation

The field experiment was conducted after wheat harvesting (July 1997) on Zemun Polje chernozem. Maize was grown under dry farming system (without irrigation) for three growing seasons (the factor A: 1998, 1999 and 2000). Soil tillage systems (the factor B) included three treatments as follows: B1) zero tillage (direct sowing in non-cultivated soil), B2) minimum tillage (tillage with a soil miller only and sowing) and B3) conventional tillage (stubble field shallow ploughing, ploughing in autumn, presowing soil preparing and sowing). In each soil tillage treatment three levels of fertilization were used as follows: C1) unfertilized (control), C2) the first level of fertilization (kg ha −1 : 150 N + 105 P 2 O 5 + 75 K 2 O) and C3) the second level of fertilization (kg ha −1 : 300 N + 211 P 2 O 5 + 150 K 2 O). The field experiment was conducted in four replicates. Area of base plot was 25 m 2 . Under drought stress of the 2000 growing season it was only 6.08 t ha −1 or 35% lower compared to 1999. The conventional tillage (yield 9.86 t ha −1 ) resulted by 24% and 84% yield increases compared to reduced tillage and zero-tillage, respectively. Using the second rate of fertilizer (yield 8.86 t ha −1 ) increased yields by 17% and 32% compared to the first rate and non-fertilized treatments, respectively. Weeds infestations (weeds m −2 ) under conventional tillage was considerably lower (7) compared to reduced (39) and zero-tillage (46).

The fate of cadmium in field soils of the Danubian lowland

The susceptibility of soils to deep penetration of cadmium was assessed by measuring cadmium adsorption on soil particles <0.01 mm, easily mobile in soil macropores, and bypassing ratio. The latter is defined as a ratio of the rate of macropore flow to the rate of total (macropore and matrix) flow. Measurements were made on soils from the Danubian lowland, which is a large (1260 km 2) agriculturally managed area situated in the south-west of Slovakia, with a shallow (0.5–3.8 m deep) underlying aquifer containing about 10 km 3 of freshwater. In this study, the susceptibility of soils to deep penetration of cadmium was assessed on light, loamy-sand soil in Kalinkovo, medium heavy, loamy soil in Macov, and heavy, clay soil in Jurova. It was found that when the interaction between soil and cadmium lasted 1 min, more than 35, 32, and 48% of cadmium was adsorbed on the particles <0.01 mm in soils from Kalinkovo, Macov, and Jurova, respectively. In the case of ponding infiltration, more than 50% of water can flow via topsoil macropores in Kalinkovo, about 70% in Macov, and 96% in Jurova. This value of bypassing ratio can be met during an irrigation/rain with higher intensity then the infiltration rate into the soil matrix of studied soils. As the rains resulting in the macropore flow can occur 24 times on average in south-western Slovakia during the vegetation season, the probability of deep penetration of cadmium is very high, mainly during an initial stage of rainfall. For this reason, some mitigative agricultural practices (e.g. subsurface fertilizer banding or shallow ploughing) should be used in this region to prevent soils from the deep penetration of cadmium.

Effect of Tillage Methods on Termite Damage to Maize in South Africa

Fungus growing termites, Microtermes sp. and Odontotermes sp. are important pests of maize in southern Africa. They damage roots and stems of maize plants and cause lodging of plants after senescence. Termite nests are difficult to locate and destroy and no effective method of control has yet been developed. Different tillage methods that could destroy nests were evaluated in the field over two seasons. Tillage methods included deep chisel plough, shallow chisel plough, deep mouldboard plough, rip and rip-on-row. Significant differences were observed in the effect of different tillage methods on lodging of maize plants. The deep mouldboard plough treatment that disturbed and overturned soil to a depth of 0.30 m resulted in significant reduction in incidence of lodged plants. The deep chisel treatment disturbed the upper 0.25 m soil layer and also resulted in a significant reduction in the incidence of lodging. The shallow chisel and rip-on-row treatments had the highest incidence of lodging. Deep tillage methods are, however, not considered to be a long-term solution for termite damage in maize.

Chaetomium globosum for reducing primary inoculum of Diaporthe phaseolorum f. sp. meridionalis in soil-surface soybean stubble in field conditions

Abstract The potential of an antibiotic-producing isolate of Chaetomium globosum (CgA-1) to suppress Diaporthe phaseolorum f. sp. meridionalis (Dpm) in soybean stubble was studied in field microplots of no-tillage, minimum-tillage, and shallow plowing. Mature soybean stems colonized in vitro with Dpm were spread on the soil surface and C. globosum ascospore suspension, without nutrient supply, was sprayed over the entire plot prior to any tillage operation. Perithecial formation and survival of Dpm in soybean stems, concomitantly with colonization by C. globosum, were monitored for a 180-day period (mid-autumn through winter and mid-spring), which is the normal interval between soybean harvest and sowing. The proportion of soybean stem segments occupied by Dpm and number of perithecia formed decreased linearly with time and showed a strong negative correlation with increase in the occupation by C. globosum. At the end of the study, which coincided with the soybean sowing season, the soybean stubble was free from viable Dpm and was colonized by C. globosum. The effectiveness of C. globosum in eliminating the pathogen from surface-borne residue or harrowed-in residue was similar but much slower than in the shallow-plowed microplots. C. globosum successfully competed with major interfering fungi such as, Trichoderma, Nigrospora, and Fusarium in colonizing the soybean stems above and under the soil surface. The data provide strong evidence for use of the antibiotic-producing isolate of C. globosum to control soybean stem canker disease.

The Study on Dynamics Succession of Community in Degenerated Ssteppe of Leymus chinensis After Shallow Ploughing

The Study on Dynamics Succession of Community in Degenerated Ssteppe of Leymus chinensis After Shallow Ploughing

Tillage erosion intensity in the South Canterbury Downlands, New Zealand

Growing awareness of the pressure on land resources emphasises the need to understand the full range of processes operating in human-impacted agroecosystems. In such systems one of the greatest threats to long-term sustainability is the erosion and depauperation of soil, which, until recently, was attributed almost entirely to water erosion. This study builds on recent awareness of the significance of tillage erosion and presents the results of an experimental investigation of tillage erosion due to mouldboard ploughing. Aluminium cubes were used to trace soil translocation as a result of a single pass of the plough perpendicular to the contour in downslope and upslope directions. In common with others studies, translocation was found to be directly proportional to slope tangent for downslope tillage and unrelated to slope for upslope tillage. The influence of non-topographic variables on the relationship between translocation distance and slope was partially filtered out by using the ratio of translocation distances in the tillage direction and perpendicular to tillage. Shallow plough depths of 0.17 m produced tillage detachment of only 230 kg/m2; however, a high tillage translocation coefficient of 1.16 m/pass resulted in a soil flux coefficient of 265 kg/m.pass. The high tillage translocation coefficient is probably partly due to the loose nature of the regularly cultivated loessic soil, however, on the basis of comparison with other published studies, it is suggested that the high tillage speed of 7 km/h is the principal control on the magnitude of the coefficient. Analysis of the available data suggests that a 30% reduction in tillage erosion intensity could be obtained by reduction of the tillage speed to 4 km/h; nevertheless, more experimental work is needed to test this suggestion. On the transect studied, a pair of opposing passes of the mouldboard plough would produce erosion rates as high as 5.1 kg/m2.year (51 t/ha.year) from shoulder slope elements and as high as 1.9 kg/m2.year (19 t/ha.year) over half of the slope length. This pattern matched closely the distribution of 137Cs-derived erosion rates documented previously for a nearby field, suggesting that for this environment, as for many mechanised agricultural systems, tillage erosion is the dominant soil redistribution process and the greatest threat to long-term sustained on-site productivity. Reduction of tillage erosion should, therefore, be seen as a priority in the development of sustainable land management strategies.

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 g kg −1<2 μm) in the IJsselmeer polders and on Luvisols (120–160 g kg −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.

Impact of ecological and conventional arable management systems on chemical and biological soil quality indices in Nicaragua

We measured the activity and soil microbial biomass in volcanic ash soils from 10 sites under ecological farming (no pesticides, shallow ploughing, mulching, organic fertilizers, crop rotation) and 15 sites under conventional farming (pesticides, mineral fertilizers, deep ploughing). Our aim was to determine the effects of management system on soil quality and soil fertility in tropical Nicaragua in relation to soil type. None of these sites were irrigated. Conventional management led to significantly increased amounts of total soil P and a significantly larger biomass C-to-P ratio compared to ecological management. Almost all of the other microbial properties, i.e. soil basal respiration, ergosterol and biomass C were significantly improved by ecological management. Also the biomass C-to-soil C ratio was significantly increased, but not the metabolic quotient qCO 2 or the ergosterol-to-biomass C ratios, indicating that the positive effects of ecological management were mainly due to increased C input rates. Biomass C, ergosterol, and basal respiration rate were significantly larger at the loamy sites than at the sandy sites. The same was true for the biomass C-to-soil C ratio, but the ergosterol-to-biomass C ratio and the metabolic quotient qCO 2 were larger at the sandy sites. Our results demonstrate that ecological management is an important tool for soil conservation and sustainable management of arable land in Nicaragua. However, the decline in total P and the low P availability to soil microorganisms need attention as a precaution against P deficiency. The improvement was greatest at the loamy sites, although the effects of management system were in most cases independent of the soil type. For this reason, ecological management should be preferably promoted on loamy soils.

Mechanical and chemical control of red rice ( Oryza sativa L. var. sylvatica) in rice ( Oryza sativa L.) pre-planting

Two field experiments were set up to assess the effectiveness of different herbicides and mechanical means for the pre-planting control of red rice seedlings. In the first experiment, carried out in the 1995–1996 period, dalapon–sodium (at 12.75 kg a.i. ha -1) was compared to mechanical control using a blade harrow and light mouldboard plough, both working at 8–10 cm depth. In this experiment, the weed control obtained with mechanical treatments ranged between 69 and 91%, while with dalapon it always exceeded 92%. Harrowing and shallow ploughing gave similar or lower yields to those obtained with dalapon. The effective working time of the chemical treatment was only between 12 to 20% of that achieved with harrowing and shallow ploughing, respectively. In the second experiment, carried out in the 1995–1997 period, several herbicides were compared. In this experiment, the best results were obtained with cycloxydim, clethodim and dalapon–sodium, which resulted in red rice control that was always over 95%.

Winter wheat pests and their natural enemies under organic farming system in Slovakia: Effect of ploughing and previous crop

Organic farming system of winter wheat was investigated in Solvakia over three years, 1995–1997. The system was carried out on a small scale (four plots of 50 m2). Neither pesticides nor inorganic fertilisers were applied. Effect of two treatments, ploughing and previous crop, on the community of pests and natural enemies was surveyed. There were two types of ploughing (shallow and deep) made in autumn before sowing. As previous crops, silage-maize and alfalfa were used each season. The effect of all factors was analysed by multivariate method, redundancy analysis (RDA) and Monte Carlo permutation to assess statistical significance. During three years, 37 taxons of pests and 27 taxons of natural enemies were recorded. The results of RDA showed that the community of insects (pests and natural enemies) was mainly influenced by temporal variation. The highest abundance of all insects was observed in 1996. The effect of the two treatments on the community of pests and natural enemies was less obvious. Pests were found to be significantly more influenced by ploughingthan by previous crop. Most of pests occurred more abundantly on plots with shallow ploughing and on plots after maize. Abundance of natural enemies were, however, significantly affected by previous crop. Majority of them were more abundant on plots after maize than after alfalfa. Ploughing had only marginally significant effect on natural enemies that were more abundant on shallow ploughed plots. Both ploughing and previous crop had only negligible effect on species diversity of natural enemies.

Long-term experiments with different depths of mouldboard ploughing in Sweden

With the main objective to produce a basis for advice to farmers concerning optimal ploughing depth under various conditions, a series of field experiments were initiated throughout Sweden. At 19 sites on various soils (clay content 72–521 g kg −1, organic matter content 21–89 g kg −1) mouldboard ploughing to about 15, 22 and 28 cm depth was repeated annually for up to 17 years. The total number of location-years was 241. Traditional farming had previously been practised at the sites, including annual mouldboard ploughing to 20–25 cm depth. Spring-sown barley ( Hordeum vulgare L.) and oats ( Avena sativa L.) were the most frequent crops but many other crops were grown less frequently. Crop residues were generally returned to the soil; straw was chopped at harvest. Post-emergence herbicides were regularly used, generally resulting in an adequate control of annual weeds. However, the control of perennial weeds, particularly couch grass ( Elymus repens L. Gould) was often inadequate. At ploughing depths of 22 and 28 cm, the mean crop yields were 2% and 3%, respectively, higher than at 15 cm. However, the results varied considerably between sites. In soils with a high silt content, the shallowest ploughing resulted in up to 10% higher yield than deeper ploughing, provided the control of perennial weeds was adequate. The main reason seemed to be improved structural stability in the surface soil because the concentration of organic matter in this layer became higher the shallower the ploughing. In clay soils with relatively stable structure, as well as in sandy soils, the deepest ploughing resulted in the highest yields, probably because of the deeper loosening. At sites where perennial weeds imposed problems, the weed control was better the deeper the ploughing, sometimes increasing the relative yield after deeper ploughing by several percent as compared with shallow ploughing. Most of this effect was obtained already at the intermediate ploughing depth. The results led to the following conclusions for Swedish agriculture. It may be profitable to plough sandy soils annually as deep as 30 cm, coarse sandy soils perhaps even deeper. In clay and clay loam soils, ploughing deeper than 20–25 cm generally cannot be recommended. In silty soils with an unstable structure, mouldboard ploughing, if any, should be shallow (≤15 cm), and perennial weeds should be controlled by other methods.

Effects of conventional tillage on biochemical properties of soils

Modification of soil environment by different farming practices can significantly affect crop growth. Tillage causes soil disturbance, altering the vertical distribution of soil organic matter and plant nutrient supplies in the soil surface, and it may affect the enzyme activity and microbial biomass which are responsible for transformation and cycling of organic matter and plant nutrients. In this study, the influence of three conventional tillage systems (shallow plowing, deep plowing and scarification) at different depths on the distribution and activity of enzymes, microbial biomass and nucleic acids in a cropped soil was investigated. Analysis of variance for depth and tillage showed the influence of the different tillage practices on the activity of some enzymes and on the nucleic acids. Glucosidase, galactosidase, nitrate reductase and dehydrogenase activity were significantly affected by the three tillage modalities. Activity in the upper layer (0–20 cm) was higher in the plots tilled by shallow plowing and scarification than in those tilled by deep plowing. Positive relationships were observed between the soil enzymes themselves, with the exception of urease and pyrophosphatase activity. Moreover, significant correlations were found between DNA and β-galactosidase, and between RNA and β-glucosidase, β-galactosidase, alkaline phosphatase and phosphodiesterase. α-Glucosidase, β-galactosidase, alkaline phosphatase and phosphodiesterase were highly correlated with biomass C determined by the fumigation-extraction method.