Direct-drilled Soil Research Articles

The effect of soil compaction and fumigation on poor early growth of wheat under direct drilling

Poor early growth of wheat was studied in a tillage experiment at Cowra, N.S.W., in the 1986 season to determine the involvement of soil physical and biological factors in this problem. A compaction treatment to achieve bulk density and shear strength comparable with those detected in the direct-drilled soils was imposed on the conventionally cultivated soil. Soil fumigation was used to investigate the significance of biological factors in causing poor early growth. In the absence of fumigation, the dry weight per plant 98 days after sowing for the direct-drill treatments was approximately a third of the conventional treatment. The fumigation treatment was effective in completely eliminating the poor early growth observed in the direct-drilled soils. No significant reduction in shoot growth was detected as a consequence of the compaction treatment, despite a reduction in root growth to the level detected in the nil fallow. The results suggest that poor early growth was caused by micro-organisms present in the direct-drilled soils.

Residual effects of a slant-legged subsoiler on shoot growth and grain yield of spring barley

SummaryIn a long-term cultivation experiment comparing mouldboard ploughing, shallow cultivation and direct drilling, soil compaction was identified as a problem. Root growth was restricted and this possibly caused a decline in grain yield of spring barley. The residual effects of a slant-legged subsoiler (Trade name, ‘Paraplow’) on the growth and yield of spring barley up to 34 months after its use were measured.In 1982, soil not loosened with the ‘Paraplow’ had a grain yield of 5·16 t/ha and cultivation with the ‘Paraplow’ either 22 or II months previously had a negligible effect. Although the implement improved mean plant establishment by up to 12 plants/m2, compensatory tillering occurred in the treatments that initially had fewer plants, thus reducing differences in dry-matter production and grain yield at harvest. The long-term system of cultivation had a larger effect on grain yield than the ‘Paraplow’ did. Grain production on direct-drilled and shallow cultivated soils exceeded that after mouldboard ploughing by up to 0·55 t/ha (P < 0·05). The ‘Paraplow’ used 22 months previously increased grain yield by 0·47 t/ha on a direct-drilled soil that had become compacted.In 1983, the emergence of seedlings was low (54%) due to waterlogging of the seed bed between germination and emergence. The ‘Paraplow’ used 8 months previously increased the mean number of plants that emerged by 20 plants/m2. More seedlings survived on the soil loosened by the ‘Paraplow’ because it drained more freely than the undisturbed soil. Cultivating with the ‘Paraplow’ 11, 23 and 34 months previously increased grain yield by 0·27, 0·29 and 0·13 t/ha respectively, but the mean grain yield was only 2·70 t/ha. This improvement was caused by a greater number of grains per m2 on the soils loosened with the ‘Paraplow’. Grain weight was unaffected by cultivation system or by ‘Paraplow’ treatment.

Residual effects of a slant-legged subsoiler on some soil physical conditions and the root growth of spring barley

SummarySoil disturbance caused by a slant-legged subsoiler (Trade name, ‘Paraplow’) and the duration of its effect was investigated in an experiment comparing long-term direct drilling with shallow tine cultivation and mouldboard ploughing. The ‘Paraplow’ significantly reduced soil strength, measured by cone resistance, to the depth of cultivation (33–35 cm) for up to 20 months, after which soil recompacted. The ‘Paraplow’ increased the volume of soil with cone resistance < 1·5 MPa by 52% within its working depth, compared with an equivalent depth of undisturbed soil. Contour diagrams of cone resistances clearly illustrate the patterns of soil loosening caused by the ‘Paraplow’.Measurements on soil cores (73 mm diameter × 50 mm) show that the ‘Paraplow’ did not appear to increase significantly the volume of macropores (> 60 μm) in direct-drilled soil, nor did it reduce the bulk density in the top 5 cm as effectively as the mouldboard plough.The root density of spring barley, measured at the beginning and end of tillering, was significantly increased within the horizon disturbed by the ‘Paraplow’ but below the depth of loosening there were no differences. This improvement of root growth probably resulted from an increase in the number of large pores (which could not be measured adequately in the soil cores), as well as the reduced soil strength. Better drainage of the soil loosened with the ‘Paraplow’ suggested that macroporosity was improved. The need to sample large volumes of soil to detect changes in bulk density and macroporosity is stressed.

Surface physical properties of a sandy loam soil under different tillage practices

The infiltration behaviour and physical properties of a hardsetting sandy loam soil at Cowra, N.S.W., following 2 years of different tillage treatments are reported. Soil that had not been cultivated for 25 years was also investigated at an adjacent pasture site. Infiltration of simulated rainfall at the end of the wheat-growing season gave moisture profiles that were quite different for cultivated, direct drilled and pasture soils. The moisture profile for the cultivated soil suggested the presence of an impeded layer which retarded the movement of infiltrated rain to the subsoil. Porosity measurements confirmed the presence of a layer with significantly fewer macropores (> 300 �m diameter) at the 50-100 mm depth in the cultivated soil, when compared with the direct drilled soil. The old pasture soil had significantly higher porosity (> 300 �m diameter) in the top 100 mm. Aggregate stabilities and organic carbon contents were measured in narrow increments to 150 mm depth for the three different soils, and revealed that a surface 25 mm layer of high organic carbon and highly stable macro-aggregates was present in the pasture and direct drilled soils but absent in the cultivated soil. The unstable surface layer in the conventionally cultivated soil was a consequence of the mixing and inverting action of cultivation and was not due to a net loss of organic carbon from the profile. The organic carbon content of the pasture soil was not significantly different from the direct drilled soil below 50 mm; however, it was significantly lower than the conventionally cultivated soil between 50 and 150 mm depth. These results indicate a need to adopt tillage practices that can preserve the top 25 mm layer of such fragile soils.

Soil nitrogen supply of wheat in relation to method of cultivation

The supply of soil nitrogen to successive wheat crops was compared for direct-drilled and conventional tillage systems on a red earth in south-eastern Australia. There was no significant effect of tillage on the total plant uptake of nitrogen, nor on the decline of soil nitrogen during a 5-year cropping cycle. During the growth of the last two crops in the cycle, the rates of net mineralization, nitrate leaching from the topsoil and crop-nitrogen uptake were measured, for both tillage systems, by an in situ sequential sampling method. For the first of these crops the rates of net mineralization were unaffected by tillage, but for the second crop the rates were greater on the direct-drilled soil. Variation in the rates of mineralization within both seasons could largely be explained by changes in temperature and soil water content. Leaching of nitrate from the topsoil was consistently greater for the direct-drilled soil, where seedlings initially accumulated less nitrogen than those growing on conventionally-cultivated soil. However, the differences in uptake did not persist, and at maturity similar amounts of nitrogen, representing less than 50% of the seasonal net mineralization, were accumulated in the above-ground parts of crops grown under the two systems.

A study of mole drainage with simplified cultivation for autumn-sown crops on a clay soil. 5. Losses of nitrate-N in surface run-off and drain water

Direct drilling of autumn-sown cereal crops reduced the loss of nitrate in drainage. Losses of nitrate nitrogen in water draining from arable land have been measured for 4 seasons, 1980–1984. The field experiment was on a mole-drained clay soil in southern England. Autumn-sown cereal crops were established by direct drilling or after ploughing and traditional seed-bed preparation. Losses ranged from 3 to 75 kg N ha −1 year −1, with an average of 34 kg N ha −1 year −1. Most of the loss (about 90%) was removed via the mole-drain system. Measured loss of nitrate from the direct-drilled soil was 76% (range 48–89%) of that lost from the ploughed soil. Mole drains apparently increased loss of nitrate directly to the river system. In the absence of mole drains, nitrate loss in surface drainage averaged 6 kg N ha −1, compared with 4 kg N ha −1 in the presence of drains. However, in one year, exceptionally high amounts of nitrate (80 kg N ha −1) were lost from undrained, direct-drilled land because of poor crop establishment; deep leaching of nitrate in the undrained soil was not measured. Approximate calculations show that up to half the autumn-applied fertiliser-N was lost by leaching and up to 15% of spring applications.

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.

Effects of season and management on the vane shear strength of a clay topsoil

SUMMARYVane shear strength, water status and bulk density were measured at various times in a growing season at two depths in a swelling clay topsoil. The site comprised experimental plots that had been ploughed annually, or direct‐drilled for 10 years; short‐term fallow areas, created on adjacent long‐term grassland, were compared with the arable plots. In the middle of the topsoil layer (nominally 120 mm depth) of all three treatments shear strength was linearly related to water content, and similarly to bulk density in the direct‐drilled and ploughed soils. Closer to the soil surface (nominally 40 mm), relationships between strength and wetness or density were less distinct, particularly in the spring, when drying was not accompanied by an increase in strength; possible reasons for this anomaly are considered. The shear strength of the untilled soils was greater, at both depths, than that of the ploughed soil. Other factors including density, water potential, soil structure and organic constituents, differed with time or between treatments, and their contribution to variations in shear strength are discussed.

Controlled seedbed traffic after ploughing or direct drilling under winter barley in Scotland, 1980–1984

In each of four seasons, zero, one, two, four and six passes of an unladen tractor were applied uniformly over the whole plot area both to ploughed and secondary cultivated and to direct-drilled winter barley seedbeds before sowing on a sandy clay loam. In addition, a one-pass treatment was applied in which tractor-type inflation pressures were reduced to around half the minimum recommended values. A mouldboard plough was used in the first season and a chisel plough replaced it in the final three seasons. After the traffic treatments, the chisel-ploughed soil, but not the mouldboard-ploughed or direct-drilled soils, were cultivated to sowing depth and the crop then sown, grown and harvested without further traffic on all seedbeds. Traffic substantially increased soil strength and bulk density and reduced air-filled porosity in the top 300 mm of soil and reduced permeability to air and gaseous relative diffusivity at seed depth. On direct-drilled soil, because of cumulative effects from season to season and because multiple wheel passes were more effective than on ploughed soil, compaction was, for all traffic treatments except the zero pass, greater than on ploughed soil. Plant populations were severely depressed, especially after more than two wheel passes, when transient waterlogging of ploughed or direct-drilled seedbeds occurred during establishment. Grain yield was markedly reduced by traffic when this resulted in inadequate plant populations or excessive soil strength below sowing depth. Annual variations in traffic effects on plant population and grain yield were related to variation in rainfall. Under-inflation of conventional tractor tyres, when soil conditions were generally critical, gave worthwhile improvements in soil strength and aeration and hence crop establishment and yield, especially on ploughed seedbeds. Although the soil has been classified an unsuitable for direct drilling with conventional traffic because it is readily compacted, direct drilling was satisfactory with zero traffic. During sequential direct drilling with other than zero traffic, yields improved progressively and, after three years, equalled or exceeded those after ploughing, due to improvement in soil structure.

Effect of conversion from ryegrass pasture to wheat cropping on aggregation and bacterial populations in a silt loam soil in New Zealand

Water-stable aggregates and soil bacteria were studied from May to January in a field trial comparing soil structure under three treatments: wheat sown in ploughed soil, direct-drilled wheat and long-term grass. During the trial, both the proportion and size of macroaggregates (> 250 �m) tended to increase. These increases were accompanied by decreases in the proportions of particles in all smaller size ranges, including <2 �m, in the early part of the growing season, but, over summer, larger macroaggregates (> 2000 �m) increased at the expense of particles between 2000 and 63 �m. The highest proportion of larger macroaggregates occurred under grass, in all except the spring sampling, while the lowest proportion occurred in the ploughed soils. Numbers of bacteria, obtained by direct microscopy, were higher in the ploughed soil soon after ploughing than in the direct-drilled soil, but no other treatment effect was detected. In all plots, numbers of bacteria were lowest in November when the soil was the driest. There were up to twice as many bacteria per g of < 20 �m diameter fraction soil compared with the rest of the soil. Seasonal changes in the bacterial population of the <20 �m diameter fraction did not follow the changes in the whole soil.

The effect of cultivation system and soil factors on the performance of herbicides against Alopecurus myosuroides

SUMMARYAspects of chemical and cultural control of Alopecurus myosuroides (blackgrass) in winter wheat were studied on a naturally‐occurring infestation over a 3‐yr period. In two experiments a comparison was made between ploughing and direct drilling, whilst in the third experiment direct drilling alone was used. Straw was spread and burnt in each year. Herbicide treatments were: chlortoluron and isoproturon in all three experiments; diclofop‐methyl and pendimethalin in two experiments; metoxuron, terbutryne, tri‐allate, carbetamide, propyzamide, chlorsulfuron + methabenthiazuron and trifluralin + linuron in one experiment. Herbicides were applied either pre‐emergence, early post‐emergence or late postemergence to separate sub‐plots. Surface soil (0–2.5 cm) samples were collected each year from unsprayed areas and used for soil analyses and for herbicide activity studies in pot experiments.Ploughing resulted in much lower populations of A. myosuroides than direct drilling. Most herbicides gave much better control of A. myosuroides in ploughed than in direct drilled soil in field and pot experiments, regardless of application time. Diclofop‐methyl, applied early post‐emergence at 1.13 kg a.i./ha, was the only herbicide treatment in field experiments to achieve over 90% weed control in direct drilled soil. Differences in adsorption between soils given different cultivations, determined as Kd values for chlortoluron and isoproturon, were much greater than differences in organic matter.The much greater adsorptive capacity of direct drilled soil, and consequently the poorer performance of all soil‐acting herbicides, was attributed to the concentration of burnt straw residues near the soil surface.

The effects of direct drilling, shallow cultivation and ploughing on some soil physical properties in a long-term experiment on spring barley

SummaryPhysical measurements were made on the soil of a long-term cultivation experiment comparing direct drilling, tine cultivation and mouldboard ploughing for spring barley to investigate possible reasons for differences in yield. The soil was a typical argillio brown earth, approximately 90 cm of sandy clay loam topsoil and clay loam subsoil overlying magnesian limestone. For the three periods 1971–4, 1975–7 and 1978–80 the mean grain yields were marginally lower after direct drilling than after shallow cultivation or ploughing. There was an average decline in yield of 1·33 t/ha from the first to the last period, the decline being greater for direct drilling than the other two tillage systems. Although the surface horizon (0–5 cm) of direct-drilled soil had a higher content of organic matter than the ploughed, this did not increase the stability of the aggregates. Slaking tests had shown the soil to be inherently unstable and likely to suffer from structural problems. After the first 3 years bulk density of direct-drilled soil (0–15 cm) increased markedly toca.l·5 g/cm8and then remained relatively stable. In the ploughed soil, density increased steadily over the period to an average value of co. 1·45 g/cm8. Tine cultivation to 7–8 cm reduced cone resistance values in the surface compared with direct-drilled soil but below 15 cm there were no significant differences. Ploughing gave significantly lower values than direct drilling to a depth of 30 cm. Measurements of pore sizes in direct-drilled and ploughed soil were highly variable with few significant differences. Mean air capacity values (1978–80) tended to be lower in direct-drilled than in ploughed topsoil particularly for plots direct drilled after 7 years of deep tine cultivation. A limited number of root measurements in 1978 and 1980 showed that the length of root per unit of ground area was much less after direct drilling than after ploughing. Shallow cultivation, surprisingly, gave most root with a greater proportion of the root system below 20 cm than in the other two treatments. The classification of this soil according to its suitability for direct drilling cereals is discussed.

Water redistribution and use by barley in two ploughed and direct drilled stagnogley soils

Soil water content and potential were measured in two ploughed and direct-drilled soils growing winter and spring barley, an imperfectly drained loam and a poorly drained sandy clay loam. Water extraction by spring barley was greater from the topsoil after ploughing than after direct drilling. Late in the season, water uptake from the subsoil by spring barley was greater after direct drilling than after ploughing. There was no detectable cultivation effect on water use by winter barley. Water infiltration was faster after direct drilling than after ploughing mainly because of the greater by-pass flow (i.e. flow through large pores, against the hydraulic gradient in the soil matrix) after direct drilling under both crops. The possible effects of these differences on the suitability of the two soils for direct drilling are discussed.

The effect of tillage on soil surface properties and the water balance of a xeralfic alfisol

Two long term tillage trials were established in 1977 on a xeralfic alfisolat a location receiving 210 mm of rain in the winter (growing) season. One trial was cropped continuously and the other one in alternate years, to spring wheat. Yields and soil physical conditions did not differ markedly in the first 3 years between tillage treatments although the ploughed soil had the lowest soil strengths and highest porosities. However, by the fifth and sixth years soil physical conditions were much poorer for crop growth on the ploughed treatments and those yields on both trials were only half that of the direct drilled crops. There was a 10-fold reduction in hydraulic conductivity and an increase in aggregate instability measured by the slaking and remould-dispersion test. These changes were paralleled by reductions in depth to wetting front and the amount of water stored in the top 120 cm of the profile. Because the site was nearly level no significant runoff occurred and the 40–70 mm less soil water stored in the ploughed treatments at seeding were ascribed to increased evaporation from wetter soil surfaces. In constant-flux infiltration measurements, time to ponding was found to be least on flattened, undisturbed surfaces and greatest on combine-drilled, direct-seeded soil. A relative reduction in organic matter in the 0–2.5 cm zone of the ploughed soil was found by the third year, and by the sixth year this had become a significant reduction compared with the direct drilled treatments. Concentration of organic matter in this layer of the direct drilled soils afforded protection against remould-dispersion of wet soil by traffic, stock or raindrop action. As alfisols have inherently weak structural stability, direct drilling is seen as providing a stable system for continuous cropping for this soil order in semi-arid regions. The increase in water use efficiency in areas where drought is a major constraint to yield is of paramount significance in this context.

The uptake of soil and fertilizer-nitrogen by barley growing under Scottish climatic conditions

Field experiments were carried out using 15N-labelled calcium nitrate, to investigate the relative uptake by barley of fertilizer-N and soil-N. On imperfectly drained till soils uptake of soil-N increased with increasing rate of fertilizer, but remained constant on a brown sand, possibly due to more efficient root exploration in the latter soil. In four out of five seasons, late uptake of soil-derived N was a major feature, and uptake from ploughed soil as compared with uptake from direct-drilled soil was correlated with seasonal rainfall patterns. Significantly higher quantities of both fertilizer- and soil-derived N were taken up by winter barley than by spring barley, reflecting the longer growth period and higher dry matter yield from the former crop.

Effect of under-inflation of tractor tyres on seedbed compaction and winter barley establishment and yield

Both ploughed and direct-drilled winter barley seedbeds on a sandy clay loam were compacted by an unladen tractor with all tyre pressures at either the minimum or rather less than half the minimum recommended values. These traffic treatments were applied uniformly across the width of the same plots in each of three seasons. In the first year, when the crop was drilled into the compacted seedbed on ploughed soil only, reduced tyre pressures were shown to result in similar soil cone resistances and vane shear strengths, but noticeably higher values of soil airfilled porosity, plant emergence and yield. In the second and third years, when the compacted seedbeds on ploughed soil were cultivated to 40 mm before sowing, treatment effects on establishment were negligible but compaction below the seedbed was rather less for the reduced pressure treatment and grain yield tended to be higher. Effects on direct-drilled soil were very much smaller or nonexistent. It was concluded that for maximum benefit to be gained from a reduction in tyre pressure the contribution of the carcass stiffness to the mean ground pressure should be low. Although the pressure reductions considered here cannot be recommended for commercial agriculture, the results should be of value to tyre designers, and also show the potential of any device which allows tyre pressure to be altered from the tractor cab.

Direct drilling and shallow cultivation compared with ploughing for spring barley on a clay loam in northern England

SummaryAn experiment was made on a clay loam soil to compare direct drilling, shallow cultivation and ploughing for spring barley over a period of 3 years (1975–7). At a uniform rate of fertilizer application (75 kg N, 40 kg P2O6, 40 K2O/ha) combined drilled with the seed, the mean grain yields over 3 years were 5·89, 6·07 and 6·13 t/ha, respectively, direct drilling producing significantly less grain than shallow cultivation or ploughing in 1975 only.For 1975 and 1976 the mean uptake of nitrogen by shoots of barley at anthesis was 25 kg N/ha less after direct drilling than after ploughing but in 1977 there was no difference. The smaller uptake of nitrogen by direct-drilled barley in 1976 was more likely caused by less available nitrogen in the soil than by smaller root systems. Soil strength (cone resistance) and soil bulk density of the direct-drilled treatments were greater than those of the ploughed and shallow cultivated. Although concentration gradients of extractable phosphorus and potassium formed in direct-drilled and shallow-cultivated soils, the quantities of these nutrients in the top soil differed little between the treatments. After 3 years there were more deep burrowing earthworms (particularly Lumbricus terrestris) in tilled than in untilled soil.

Factors influencing the variation of some properties of soils in relation to their suitability for direct drilling

Soils from fifteen field experiments in the United Kingdom and one in France that compared direct drilling with mouldboard ploughing were examined with respect to their composition and physical properties. Indices of the stability and shrinkage of soil aggregates were obtained by measurement and an index of compactability was derived from an established relationship. It was hypothesized that these properties were possible determinants of soil responses to zero-tillage. Aggregate stability and shrinkage were correlated with organic carbon and clay content, respectively. Organic matter contents were greater at the surface of direct-drilled soils than in the complete topsoil layer after direct drilling or ploughing. In some cases the increase in organic matter significantly improved the physical properties of the soils. The three indices, of stability, shrinkage and compactability, were each ranked in high intermediate or low groups, and the soils classified according to their ratings in these groups. The resulting classification broadly agreed with a previous one of soil suitability for sequential direct drilling mainly based on experimental agronomy.

N use by winter wheat established in cultivated and direct-drilled soils

SummarysLabelled fertilizer N (15N depleted ammonium sulphate) was used to investigate both soil and fertilizer N use by winter wheat established in contrasting seed beds, these being soil cultivated to 20 cm depth or left undisturbed. The crop's response to, and recovery of, a range of N levels from 0 to 280 kg/ha given as a divided application in spring, were measured over two seasons. It was found that during the first season the direct-drilled wheat took up, on average, more fertilizer N but less soil N than wheat in cultivated soil, probably through differences in organic-matter mineralization. The different cultivation systems produced similar grain yields at all rates of applied N; however, when no fertilizer N was given, dry-matter production and soil-N uptake by the crop in the undisturbed soil were substantially less than by the crop in the cultivated soil. Crop recovery of the fertilizer N at harvest was between 29 and 40% of that given. After harvest, an average of one third of the applied fertilizer N was found in the top 60 cm of the soil profile. In the following season on the same plots a second winter wheat crop, receiving no fertilizer N, was drilled. At harvest there was shown to be an increase in grain yield and soil- and fertilizer-N uptake at the higher srates of N given in the previous season. In spite of this the recovery of the labelled residues was small, no more than 6% of the original application, or 15% of the residues remaining in the soil, irrespective of cultivation system.

Tillage and growth of a wheat crop in a loamy sand

In the fourth consecutive year of a long-term tillage trial in a loamy sand in Western Australia above- and below-ground growth of a wheat crop (cv. Gamenya) was monitored. The grain yield was nearly 20% greater in the crop sown after ploughing than in those crops sown by direct drilling. A similar trend had been noted in each preceding year. Cumulative water use was 15 and 9 mm less with zero and minimum tillage than with ploughing. The ploughed treatment had lower soil strengths, not only in the seedbed but also to 50 cm in the subsoil, until 8 weeks after seeding. These lower soil strengths coincided with more-rapid wetting of the subsoil under ploughing, and faster root extension rates. Dry matter production was significantly greater in the ploughed crop from the initial sampling date, and direct-drilled crops were not able to compensate in the later part of the season, despite using slightly more water during that period. The slower wetting of the profile under direct drilling was a persistent feature over several seasons in this soil type. It was considered responsible for the increased soil strength and slower root extension rates. The implications of direct-drilled sandy soils for crop productivity, and drainage control of recharge soils in saline catchments, are discussed.