Agriculture group symposium developments in soil cultivation technology

1. Sci. Food Agric. 1987,38, 125-139

Agriculture Group Symposium Developments in Soil Cultivation Technology

The following are summaries of papers presented at a meeting of the Agriculture Group of the Society of Chemical Industry, joint with the British Society of Soil Science, held on 18 February 1986 at the Society of Chemical Industry, I 4 1 5 Belgrave Square, London SWlX 8PS. The papers published here are entirely the responsibility of the authors and do not reflect the views of the Editorial Board of the Journal of the Science of Food and Agriculture.

Modern Cultivation Techniques for Cereals

W. C. T. Chamen, E. T. Chittey and J. V. Stafford

NIAE, Wrest Park, Silsoe, Bedford MK45 4HS, UK

There is concern about the build-up of compaction in the soils of Britain under arable crops. An experiment was designed with the aim of establishing a relation- ship between wheeling pressure and soil and crop responses, such that damaging levels of compaction caused by traffic could be identified.

An Evesham series soil with 60% clay content, typical of many arable soils in Britain, was selected for the experiment and three levels of wheel compaction (0,0.8 and 2.5 bar) were imposed in conjunction with direct drilling and shallow tine cultivation for winter wheat. The normal and low ground pressure (LGP) systems (2-5 and 0.8 bar, respectively) used conventional tractors and equipment which were fitted with additional tyres at low inflation pressure for LGP operation. The zero traffic system operated from permanent tramlines, leaving 1.8-m wide unwheeled beds on the plot area. In all three systems wheelings were built up progressively throughout the season and from one season to the next during normal cultural operations.

After three years of using these systems, soil cone penetration resistance above 100 mm tended to be greater after LGP, compared with normal traffic. Below 100 mm, resistance tended to increase with wheeling pressure, but this was less marked on the shallow cultivated plots. In all cases zero traffic resulted in

125

1. Sci. Food Agric. (38) (1987- Society of Chemical Industry, 1987. Printed in Great Britain

126 Agriculrural Group Symposium

significantly lower levels of soil resistance than either of the other traffic systems. Measurements of soil bulk density showed the same marked difference between zero wheelings and the other traffic systems. However, the correlation between wheeling pressure and density was more noticeable on the shallow cultivated plots than on the direct drilled plots. During soil preparation, the energy requirements for cultivation tended to reflect the measured soil strength properties, with the zero traffic system using only about 40% of the energy of that required on the normal traffic plots. The LGP system reflected the resistance measurements, requiring about 15% more input than the normal system. The most marked effect on soil tilth was also found to be between wheeled and unwheeled plots. Untrafficked soil was always friable, even in very dry periods, and was observed to retain more moisture close to the surface. Crop yield measurements reflected a manganese deficiency in the plants on the zero traffic plots, caused by loose soil conditions. Mean yields from three crop years were: normal, 7.47 t ha-'; LGP, 7.54 t ha-'; zero, 6.78 t ha-' (SED=O-15 t ha-'). Evidence from the 1985 harvest, however, suggested that a well-timed application of manganese sulphate can prevent a loss in yield from unwheeled soil.

From the results so far, the implications are that a LGP (0.8 bar) system offers only the advantage of increased access and reduced rutting. In contrast, the elimination of wheelings from the cropped area of soil seems to offer considerable scope for reducing cultivation energy inputs, reducing clodiness of seedbeds and providing more homogeneous soil conditions for crop establishment and growth. The machinery needed to achieve such a system is presently being investigated at NIAE.

ADAS Straw Incorporation Experiments

B. Davies," E. Lord" and J. Ruleb

a ADAS, Soil Science, Brooklands Avenue, Cambridge CB2 2DR, UK b Boxworth Experimental Husbandry Farm, Boxworth, Cambridge CB3 8NN, UK

Pressure on farmers to give up burning straw has prompted ADAS to examine the feasibility of incorporation in soil as an alternative. Farmers burn surface straw to save time and to improve the success rate of direct drilling and shallow cultivation. In addition, burning helps to control weeds, slugs and volunteer cereals, and may reduce the risk of some cereal diseases. In the autumn of 1982 ADAS started to examine problems of incorporation, with the objectives of being able to recom- mend the most economic method for any particular situation and to offer satisfactory practical guidelines for incorporation.

The method used has been to compare the yield of winter cereals after incorporation of straw with yields after burning in large plot replicated field experi-

Developments in soil cultivation technology 127

ments sited on the same land each year. The effect of autumn nitrogen has been tested in some of the trials.

Although the quantities of straw returned in the experiments reported are substantially greater than in previous incorporation trials, these results confirm the earlier conclusions that changing from ploughing down ash to ploughing down straw has little or no effect on yield or on crop husbandry (Tables 1 and 2). This suggests that where ploughing after burning is already practiced successfully there should be few problems in changing to ploughing down straw.

TABLE 1 Yield of Winter Cereal as Percentage of Bum and Shallow

Cultivation Soil type Straw incorporation method"

Discltine Plough

Very heavy Heavy Medium Light

101 (8 ) 100 (8) 97 (7) 101 (7) 97 (8 ) 97 (6)

101 (8) 102 (6)

a Figures in parentheses indicate number of sites.

TABLE 2 Yield of Winter Cereal as Percentage of Burn/Plough and Effect of Premixing

Before Ploughing Soil type Choplplough as Straw incorporation

by premixlplough as % of plough only"

% of burn/plough"

Very heavy 104 (3) 98 (6) 100 (6) Heavy 100 (3)

Medium 95 (4) 100 (6) f O O (13) Light 101 (14)

Figures in parentheses indicate number of sites.

On heavy soils ploughing carries extra expense and the risk of poorer seedbeds. The alternative is to incorporate straw by mixing without inversion. The advantages of this are speed, better seedbeds and lower machinery costs; the disadvan- tages are lower yield (see Tables 1 and 2), except on very heavy soils, and poorer weed control.

Average yield responses to autumn nitrogen on heavy and medium soils were not economic and were unaffected by the presence of straw. Less work has been done on light soils but the suggestion is that some may contain so little residual nitrogen that response to autumn application is economic.

This trial series will continue for several more years.

128 Agricultural Group Symposium

Low Draught Drainlaying Machines

D. R. P. Hettiaratchi and J. R. O’Callaghan

Department of Agricultural Engineering, University of Newcastle upon Tyne, Newcastle upon Tyne NE17RU, UK

Machines currently in use for the installation of deep drains for the improvement of agricultural land, whether they be of the trenching or trenchless type, are complex expensive machines which are best operated by specialist drainlaying organisations. The high draught requirements of these machines necessitate the use of crawler tractors and some trenchless systems even have to rely on additional ground anchors. If state subsidies were to be lifted, then drainage operations involving these expensive machines might cease to be viable. There is therefore a need to develop alternative lowdraught systems which can be carried on wheeled tractors and which, preferably, can be operated, during slack periods, by the farmer himself.

The key to the development of such systems lies in the reduction of the forces generated by the soil-working elements of the present machines. In a trenchless system this can be accomplished in two ways: first, by devolving the generation of the forces required to form the space occupied by the drain pipe away from the tractive elements of the machine directly to the tractor engine; secondly, by reducing the draught of the tine shank which normally extends down to the drain invert.

Research investigations at Newcastle on the mechanics of plant root penetration have demonstrated that the formation of a space within the soil by direct symmetric radial expansion of a cylindrical element is a more efficient technique when compared with the indirect punch-indentation mode induced by existing shaped expanders. The latter require high-draught forces which have to be provided by the tractor running gear.

The proposed technique is based on the location of a lay-flat hose element at drain invert level. The draught forces required for this operation are quite small. The space for accommodating the drain pipe is then formed either by pneumatic or hydraulic inflation of the hose. The forces developed in this operation are balanced and the energy required to deform the soil is supplied from the tractor engine and not its tractive elements. The pressure required to remould most subsoils by this means is around 30-40 kPa and is well within the capacity of a tractor-driven pump.

The drain-laying cycle consists of a series of stages in which the hose is first positioned in its flattened form at the correct gradient. It is then inflated, deflated and subsequently pulled ahead into the next section, and the cycle repeated. The drain pipe to be installed is towed behind the expanding hose into the space already formed by the previous inflation.

The cycle time for the operation depends mainly on the period occupied by the inflation and deflation of the hose. Emptying time has been found to take longer


than that required to pressurise the hose. Any convenient length of hose can be employed in this system, although a practical length of about 50 m is dictated by hose strength and volume. Corrugated drain pipes currently in use are not suitable for this system because of their inherent low tensile strength.

Under normal soil cutting conditions soil flows up along the tine shank towards the soil surface. The friction mobilised on the soil-metal boundary dictates the shape of the soil rupture surface. Cutting-blade theory, developed at Newcastle, has shown that if the mobilised friction is reversed, the size of the rupture zone is greatly reduced and there is a consequent decrease in the draught of the tine. Under favourable conditions a draught reduction of about half is possible. Mech- anical methods for achieving this reversal can be devised but at some cost in extra complication.

Problems concerned with the lack of soil shatter in the area above the drain invert and difficulties that can arise from unstable soils and rocks have not yet been fully resolved. A prototype machine which lays 100-mm diameter pipes at an invert of around 1.5 m has been built and tested. This machine is self-contained and is carried on a small farm tractor.

Cultivation Systems for Sugar Beet

M. Nuttall

Norfolk Agricultural Station, Morley, Wymondham, Norfolk NR18 9DB, UK

Work at the Norfolk Agricultural Station is currently investigating two problems encountered in sugar beet establishment: wind erosion on light soils, and compaction caused by tractor wheelings. On light soils, having to re-drill after a ‘blow’ not only reduces yield potential because of late drilling but is also expensive in terms of the cultivations carried out and the need to repeat herbicide applications. Mainly on medium and heavy soils, compaction from tractor wheelings during seedbed preparation can affect establishment but more particularly it will affect the subsequent growth of the crop. Results from two years (1984 and 1985) are presented.

On light soils prone to blowing, ploughing and conventional cultivations with a Dutch harrow were compared with systems using one-pass strip tillage or direct drilling into the stubble of the previous cereal crop. The intention was that the stubble would act as a windbreak and its roots would help bind the soil particles together and so prevent blowing. Other systems involved ploughing, and sugar beet was drilled into barley which had been established earlier in the spring. Finally, sugar beet was drilled directly into ploughed and pressed land. On medium soil at Morley (sandy loam) and on heavy soil (sandy clay loam) different methods of seedbed preparation and different cultivations systems were exam- ined. These systems were aimed at reducing o r eliminating compaction caused by


tractor wheelings where the sugar beet was going to grow. Several controlled wheeling systems compared different machines, and some one-pass drilling systems, including drilling into ploughed and pressed land, were also tested.

On the light soil in 1984 and 1985, plant establishment and sugar beet yield were generally better after ploughing, ploughing and pressing or drilling into a barley cover crop, when compared with strip tillage or direct drilling. However, during the conduct of these trials, the winds were not sufficiently strong to test the ability of the various systems to prevent wind erosion. On the sandy loam soil at Morley in 1984, there were no real differences between cultivation treatments. However, in 1985, plant establishment was generally low but was particularly poor after drilling on soil ploughed and pressed early or drilled by a strip tillage technique when compared with many other systems. As a result, yields were 50-51 t ha-' (adjusted to 16% sugar) compared with just over 60 t ha-' for some of the other cultivation systems. On the heavy land in 1985, rain interrupted drilling and the cultivation systems were unintentionally confounded with drilling date. Heavy rain immediately after drilling resulted in the loss of 30000 plants ha-' from the early drilled treatments, but this had little effect on yield.

In conclusion, it is felt that sugar beet can be drilled directly into ploughed and pressed land as a means of preventing wind erosion on light soils. Further work is currently in progress, but it would appear that a similar system could also be used on medium and heavy soils.

Autumn Cultivation to Improve the Establishment of Vegetables

H. R. Rowse

National Vegetable Research Station, Wellesbourne, Warwick CV35 9EF, UK

Crop establishment is a critical stage in any vegetable production system which involves sowing seed directly into the soil. It is becoming increasingly important as more crops are grown in tight production schedules to meet the demands of the supermarkets, and any delay or excessive unevenness in establishment can be very costly. The most usual cause of a delay in establishment is wet soil conditions which prevent cultivation and drilling. Work at NVRS has attempted to answer three questions:

1. Can autumn cultivation increase drilling opportunities in a wet spring? 2. To what extent can specialist vehicles reduce soil compaction in wet

3. What are the effects of autumn cultivation on crop establishment?

A simple model was developed that enabled weather data to be used to calculate the mean daily water content of a surface soil layer of specified thick- ness. Estimates of the number of work days in spring were made by calculating the

conditions?

Developmenrs in soil cultivation technology 131

number of days when the surface layer was drier than the plastic limit. For the years 1960-81 the model calculated that cultivation to 30 mm (representing the depth of spring cultivation required on autumn cultivated land) was possible on about two-thirds of the days in spring. The corresponding figure for cultivation to 120 mm (representing a more conventional spring cultivation) was one-third.

Soil compaction by tractor wheels was shown to be serious when a tractor was used on moist soils. However, a low ground pressure vehicle used for light cultivation and drilling produced less compaction in wet conditions than the tractor did in dry conditions.

The emergence of onion seedlings was studied on plots which had received one of three types of cultivation: autumn ploughing, followed by spring cultivation; autumn ploughing and soil levelling with no spring cultivation; and autumn ploughing and levelling with a very shallow (30 mm) spring cultivation. The extent and rate of seedling emergence was greater for the two treatments which involved autumn cultivation, particularly in dry conditions. This was probably due to the fact that zero o r very shallow spring cultivation did not disturb the capillary conductivity of the soil beneath the seed, which consequently had a better water

Weed growth in the spring on autumn-cultivated plots was much reduced when the autumn cultivation was done early enough to allow the weeds to grow and be sprayed. The three main advantages of autumn cultivation, however, were:

1. It provided more opportunities to establish a crop in a wet spring. 2. It enabled the use of much lighter equipment in the spring, which allows the

use of smaller vehicles and, hence, reduces soil compaction. 3. It produced better establishment, particularly in a dry season.

supply *

The Cultivation of Clay Soils-Effects of Soil Conditions for Root Growth

M. J . Goss ,~ D. G. Christian,O K. R. HowseO and P. Colbournb

., Rothamsted Experimental Station, Harpenden, Hertfordshire AL5 2JQ, UK *Welsh Plant Breeding Station, Aberystwyth, Dyfed SY23 3EB, UK

Satisfactory seedbeds can be difficult to create in clay soils in autumn following traditional mouldboard ploughing. In wet autumns the share can cause smearing and the loosened topsoil, which has reduced strength, may be too moist for immediate secondary tillage, whilst in dry autumns, ploughing can form harsh clods that are difficult to break down with several secondary cultivations. In contrast, cultivation systems using tined implements working at depths less than 10 cm or even direct drilling into untilled soil can reduce the number of passes required to prepare the land for drilling. What are the effects on soil conditions if such techniques are used over many seasons and what are the consequences if straw cannot be burned? Many clay soils are drained by mole and pipe systems but what are the benefits?


Several long-term field experiments started by the Letcombe Laboratory studied: (a) effects of tillage on a calcareous clay soil (Evesham series) and on two non-calcareous stagnogleys (Denchworth and Lawford series); (b) effects of drainage, also on Denchworth series soil; and (c) methods of straw disposal on a Lawford soil.

Simplified cultivation systems gave a more consolidated topsoil but the presence of macropores that were continuous into the subsoil allowed roots to penetrate more rapidly to depth than after ploughing. Drainage increased air- filled porosity in the topsoil and encouraged root development, which resulted in greater uptake of nutrients. Only drainage consistently improved the depth of root growth and activity and increased the water use of winter cereals. However, the weight of dry matter produced per millimetre of water used by the crop was the same in all treatments. Averaged over all years, grain yields were little affected by the method of cultivation but there was a benefit from drainage which averaged 10% over 8 years. Where straw remained on the surface, crop establishment was restricted, often by poor drill performance, but in addition tiller production was limited and plant weight was less than after burning. Effects on dry weight were similar if straw was only incorporated shallowly, a treatment which, in recent controlled laboratory studies, was shown to lower the shoot/root ratio. This could be overcome partly by adding nitrogen but toxic products of the aerobic decomposition of the straw also appeared to be important. Separating the developing seed from the straw by 2.5 cm of soil was beneficial. Grain yields were reduced when straw was shallowly incorporated, both because of the poorer vegetative growth, which reduced the number of fertile ears, and because of a high incidence of disease which reduced the weight of each grain and the number of grains per ear.

Simplified methods of cultivation were satisfactory for clay soils when autumn crops were grown and straw was burned; incorporating crop residues was associated with lower yields.

Ways of Extending the Moisture Content Limits for Satisfactory Tillage Operations

G. Spoor

Department of Agricultural Engineering, Silsoe College, Silsoe, Bedford MK45 4HS, UK

The timeliness of operations is frequently a critical factor in profitable crop production. Soil moisture content has a large influence on this through its effect on the quality of tillage, tractor efficiency and the risk of soil compaction damage. Operations may have to be delayed due to unsatisfactory moisture conditions for either the tillage operation itself or tractor usage.


Depending upon the type of soil manipulation required, the soil may have to be

(a) with an increase in bulk density--compressive failure; (b) with a decrease in density-brittle or loosening failure; (c) with no density change-ritical state failure.

The type of failure which occurs depends on the initial soil packing state and moisture content, the confining forces around the soil unit to be moved, and the direction in which it is loaded. Successful tillage is dependent upon manipulating the confining forces and the direction of loading through choice of implement or technique, to produce the required type of failure under the prevailing conditions. Low confining forces increase the chances of brittle failure over the widest possible range of moisture conditions. The reverse is required for compressive failure.

Soil must be moved towards, or be within, a space where it can expand for brittle failure. The closer the soil unit to the space, and the weaker the soil between the unit and the space, the lower the confining force. Deep compact soil layers can therefore be loosened very effectively at high moisture contents, by loosening progressively from the surface downwards. Similarly, power harrows and rotary cultivators, taking small cuts and throwing the soil towards a space, can loosen and break clods at high moisture contents, well within the plastic consis- tency range.

Downward loads moving soil towards the main soil mass, where confining forces are higher, will cause compressive failure. This is the situation under a tractor wheel. Successful soil working at high moisture contents therefore depends upon keeping the tractor wheel off the soil area to be cropped. This can be achieved by restricting traffic and wheels to firm, well-drained traffic lanes. The soil between the lanes can then be manipulated over the widest possible range of moisture conditions. The plastic limit is by no means the upper moisture limit for soil working, providing confining forces are kept low.

moved in one of three ways:

The Role of Climate and Soil Type for Straw Incorporation

A. J. Thomasson

Soil Survey of England and Wales, Rotharnsted Experimental Station, Harpenden, Hertfordshire AL5 210, UK

Climate affects the ease of incorporating straw, and the suitability of the resulting seedbed for autumn-sown crops. In moist climatic zones and particularly on heavy or slowly permeable land, the extra operations to incorporate straw cause a delay in drilling. This may lead to drilling under poor wet conditions, with additional risks of compaction as the soil strength becomes weak. In drier climatic zones the


additional tillage can lead to excessive evaporative loss of water, causing dry cloddy seedbeds and poor establishment of the following crop. These effects vary from year to year, and indeed some soils will display both problems in successive years. However, the general risks can be defined from average climatic data. Broadly, areas of eastern England with less than about 600 mm annual average rainfall, and an average date of return to field capacity later than 1 December, are most at risk from excessive drying during cultivation. Western, southern and northern areas with more than about 750 mm average annual rainfall, and an average date of return to field capacity before 1 November are most at risk from early onset of wet conditions with consequent compaction and smearing. An intermediate zone can be identified where moisture conditions in average years are acceptable for tillage and crop establishment, but the year to year variation in weather brings a more or less equal risk of excessive drying or wetness.

Soil suitability for straw incorporation is mainly dependent on topsoil texture, soil water regime (drainage status) and soil depth. Currently, the plough is the preferred method of incorporation. Hence, soils poorly suited to ploughing will give difficulty for straw incorporation. The suitability system has three classes:

sands, loams and peats, naturally well drained or effectively underdrained. shallow soils over chalk or limestone, loamy soils with impermeable subsoil. clay soils with impermeable subsoil, or close to groundwater.

Easy:

Intermediate/average:

Difficult:

Winter Barley Cultivation and Sowing Requirements for Southeast Scotland

B. C. Ball and M. F. O’Sullivan

Scottish Institute of Agricultural Engineering, Bush Estate, Penicuik, Midlothian EH26 OPH, UK

Scottish soils have been grouped according to cultivation requirement for winter barley. The cultivations required are: Group 1, direct drilling (no cultivation); Group 2, shallow ploughing or shallow cultivation to 5&150 mm depth; and Group 3, mouldboard ploughing to >150 mm depth. The grouping was derived by extrapolating the resultsof field experiments, mostly short term, to other soils and climatic areas, taking into account farming and advisory experience and local expertise on soils and crops. Our objectives were to present results in support of the allocation of minimum cultivation inputs to soil series, and to examine the extent to which broadcasting can replace drilling.

Soil physical conditions, winter barley yield and climate data were gathered from field experiments on soils in each group located in the southeast of Scotland. Soil physical measurements included: the maximum slope of the water release characteristic, which is related to the ease of soil drying; macroporosity; and water


content at cultivations or sowing. The extent of separation of the latter from the plastic limit gives a rough assessment of soil workability.

These measurements confirmed that conditions for direct drilling were more likely to be satisfactory in Group 1 than in Groups 2 and 3. Thus, a shorter rain- free period is required before direct drilling Group 1 soils than Group 2 or Group 3 soils. On experimental plots, correct timing of operations is easier and high inputs of sprays and machinery are more readily available than on farms. Hence, from our limited experimental data on some soils, long-term average yields were similar among cultivation-sowing systems irrespective of soil group, apparently contradicting the grouping. However, the cultivation input of each group takes into account the risks of yield reduction, assessed from soils and climatic data, which are smaller in experimental plots than on farms.

We conclude that the grouping is relevant to farming practice, since farm yields can be more dependent on cultivation than those in experiments where limitations to yields can be overcome by impractically high standards of management. Broadcasting is applicable to all groups: on soils of Groups 1 and 2 broadcasting is possible directly on to uncultivated stubble, whereas on Group 3 soils broadcasting is confined to cultivated soil. The rate of work with broadcasting is faster than with conventional drilling, allowing more crop to be sown in suitable conditions, no pre-sowing spraying is usually required and most compaction is restricted to tramlines which can be perennial.

Deep Tillage Studies with the Wye Double Digger

I. B. Warboys

Wye College, The University of London. Ashford, Kent TN25 5AH. UK

The Wye Double Digger was designed for deep tillage studies at Wye College.’ It is able to plough the topsoil and both loosen and mix amendments into the subsoil in one field operation to a depth of 0.5 m. Because of its very thorough loosening and mixing capability it has been widely used for deep tillage investigations, both in the UK and overseas, to evaluate the soil physical and chemical factors involved in crop growth. Other potential uses are for investigational work on textural improvement involving deep mixing of stratified soil layers and the provision of deeply loosened soil profiles for studies on compaction by traffic.

In the UK, work at Wye College, the Rothamsted Experimental Station and the National Vegetable Research Station, Wellesbourne has shown positive responses to double digging for a wide range of cereal and vegetable crops with, in some cases, additional benefits from fertiliser incorporation. For example, during the period 1978-80 increases in yield ranged from 11% to 16% for spring barley when additional P and K were incorporated on a heavy soil at Rothamsted. In the period 1981-83, although average yields on the same site were lower, nutrient


enrichment, with the Wye Double Digger, still gave a 23% increase.*These yield responses seemed to be best in dry years and other work at Wellesbourne supports the view that these responses are the result of greater root proliferation enhancing water extraction at depth.3 This is confirmed by further work at Wye College which has also shown the benefits of thorough subsoil loosening by double digging, which decreased compaction by 42.4% and increased the root extraction depths of the potato crop. In 1983 the increase in yield was 32.7% after double digging, and additional benefit was also found from irrigation.

Overseas in the Tropics where nutrient-deficient and acidic subsoils occur, a wide range of investigational work has been started. For example, deep incorporation of potash on impoverished subsoils in South Africa has resulted in higher yields of grain maize, arising from superior root development with less wilting. However, a large area of potential investigational work for the machine lies in its use for deep incorporation of lime, or gypsum, on acid subsoils which are widespread in Southern Africa and in South America and where aluminium toxicity prevents root penetration to depths below 22 cm. Comparisons with existing mechanical methods, such as deep ploughing or using tined subsoilers with lime blowers, shows that the Wye Double Digger can place and incorporate materials at depth more efficiently in terms of power and with a more even distribution.

References

1. Warboys, 1. B.; Wilkes, J. M.; Gooderham, P. T.; Wilkins, S. M. The development of a double-digging machine. Proc. 7th Conf. Int. Soil Tillage Res. Organisation, Sweden, 1976,46, 1-46.

2. Johnston, A. E.; McEwen, J. The special value for crop production of reserves of nutrients in the subsoil and the use of special methods of deep placement in raising yields. Proc. 18th Colloquium International Potash Institute, 1984, Italy.

3 . Rowse, H. R.; Stone, D. A. Deep cultivation of a sandy clay loam. 11. Effects on soil hydraulic properties and on root growth, water extraction and water stress in 1977 especially on broad beans. Soil Tillage Res. 1981, 1, 173-185.

The Effect of Subsoil Loosening and Deep Incorporation of P and K Fertilisers on the Yield of Arable Crops

M. J. Marks" and G. C. Soaneb

#ADAS Wye, Ashford, Kent "25 5AH, UK bSilsoe College, Silsoe, Bedford MK4S 4HS. UK

Substantial increases in crop yield from the thorough loosening of the subsoil with additional responses from incorporation of P and K fertiliser into the loosened subsoil have been reported elsewhere.'" This series of experiments was designed to investigate crop response to these treatments on a wide range of soil types.


The subsoil loosening was achieved with either the Wye Double Digger"' or a rigid tine winged sub~oiler;~ P and K fertiliser was applied at the rate of 350 kg ha-' P20, and K 2 0 . On the control treatments the fertiliser was spread on the soil surface and ploughed down. Although sites were obtained on a wide range of soil types the majority were located on well-drained, light and medium textured soils in intensive arable rotations. The degree of subsoil compaction varied consider- ably but at most sites a compacted subsoil layer was present before loosening.

Forty-two harvests were obtained from 16 experimental sites. No yield increases from subsoil loosening were recorded in 17 harvests of autumn-sown crops. At three sites on deep, silty soils loosening tended to reduce yields. At one site a response to subsoil incorporation of P and K fertiliser was found but this did not exceed the response to fertiliser applied to the topsoil. For spring-sown crops yield increases from subsoil loosening were obtained in 5 out of 25 harvests. These occurred with spring barley and sugar beet crops grown on sandy soils. The yield increases were associated with improved extraction of moisture from the loosened subsoils. Potatoes were unresponsive to subsoil loosening. In four harvests, mainly on silty soils, subsoil loosening reduced yields. The addition of P and K fertiliser tended to increase the yield of most spring-sown crops. In the majority an equal response was obtained from topsoil and subsoil placement but at two sites subsoil placement was more effective.

Monitoring of soil bulk density and penetration resistance indicated that most loosened subsoils recompacted to their original state within 3 years. Recompac- tion occurred more rapidly in subsoils with high sand or silt contents.

Yield increases from subsoil loosening were confined to the combination of spring-sown crops grown on light, sandy soils. The absence of response in autumn-sown crops may be related to their relative tolerance of subsoil compaction or may be influenced by the bias of autumn cropping towards the medium and heavy textured soils. Although it was demonstrated that yield responses were associated with improved extraction of subsoil water, it was not possible to demonstrate any correlation between response and weather.

The absence of yield increases in crops grown on silty soils is probably related to their large available water capacity but this does not adequately account for the trend towards yield reductions from subsoil loosening on these soils. The incorporation of P and K fertiliser into loosened subsoils resulted in small and infre- quent yield increases.

References

1 . El-Karouri, M. 0. H . ; Gooderham, P. T. The effect of soil physical conditions and nitrogen fertiliser on the yield of Italian ryegrass. J . Agric. Sci. Camb. 1977, 88, 743-75 1.

2. McEwen, J.; Johnston, A. E. The effect of subsoiling and deep incorporation of P and K fertilisers on the yield and nutrient uptake of barley, potatoes, wheat and sugar beet grown in rotation. J . Agric. Sci. Camb. 1979,92,695-702.

3. Stone, D. A. Subsoiling and deep incorporation of nutrients. NVRS Annual Report 1977, pp. 43-45.


4. Warboys, I. B.; Wilkes, J. M.; Gooderham, P. T.; Wilkins, S. M. The development of a double digging machine. Proc. 7th Conf. Int. Soil Tillage Res. Organisation, Sweden, 1976, 46, 1-46.

5. Godwin, R. J.; Spoor, G. The Design and Performance of Equipment for the Subsoil Placement of Fertiliser. Paper 81-1091. Am. SOC. Agric. Eng., St. Joseph, Michigan, USA.

Interactions Between Drainage and Cultivation on Soil Physical Conditions for Root Growth

M. J. GOSS," D. G. Christian,l K. R. Hawse," P. Colbournb and G. L. Harrisc

a Rothamsted Experimental Station, Harpenden, Hertfordshire AL5 2JQ. UK b Welsh Plant Breeding Station, Aberystwyth. Dyfed SY23 3EB, UK <MAFF Field Drainage Experimental Unit, Cambridge CB2 2LF, UK

Simplified tillage allows larger areas of clay soils to be sown in autumn. Such clay soils need draining but mole and pipe systems were designed for ploughed land and it is not known how effectively they would function with other tillage systems. The interactions between drainage and cultivation on soil physical conditions for crop growth, the discharge of water from drained land into water courses, and the losses of nitrogen from arable land are investigated in a long-term experiment started in 1978 at Brimstone Farm, Oxfordshire.

Twenty plots, each of 0.2 ha, are hydrologically isolated to 1.1 m; half the plots have mole and pipe drainage, the rest are undrained. Within each drainage treatment, half the plots are ploughed and half are direct-drilled.

The topsoil of direct-drilled plots was more consolidated and had fewer large pores compared to that on ploughed plots. Drainage increased the volume of air- filled pores, especially on direct-drilled plots. During winter in undrained land, the mean depth to the water table was about 18 cm; it was closer to the soil surface after ploughing than after direct-drilling. Drainage lowered the water table by about 20 cm and in direct-drilled plots the water table rose and fell more rapidly following rainfall than in ploughed plots. After rainfall, the peak rates of discharge from the drains developed quicker and were larger on direct-drilled land than from ploughed soil, but the total discharge through the drains was less. Over winter, losses of nitrate-nitrogen in drainage water were greater after ploughing. The application of autumn nitrogen increased losses in drainage water. In the spring, losses of nitrogen were very variable and depended on the rainfall in the 10 days after fertiliser application. Nitrogen losses by denitrification were relatively small and averaged 5 kg N ha-l after direct-drilling and 1.2 kg N ha-1 after ploughing. Dry matter accumulation and uptake of nutrients, including nitrogen, were generally unaffected by cultivation. Drainage increased shoot growth and the uptake of major nutrients was consequently greater. In the spring, root growth was much reduced in undrained plots; roots were deeper in direct-drilled plots than in ploughed land. By anthesis, roots were still deeper in drained plots


but effects of tillage had disappeared. There were more roots in the surface layers of undrained land and also more in direct-drilled soil. In two of the 5 years there was a significant interaction between cultivation and drainage on grain yield. In 1983. emergence of winter oats, sown late into wet surface soil, was severely limited on the undrained direct-drilled plots. In 1985, drainage did not increase yields of oilseed rape after direct-drilling, possibly because the mole drains had deteriorated and the water table was much shallower than on the ploughed plots. Drainage interacted with cultivation to modify soil physical conditions and affected the growth of roots over winter, but in spring effects of cultivation decreased. Drainage increased yield by nearly 10% on the average of 8 years.

Materials Approach to Soil Cultivation Problems

H. W. Chandler

Department of Metallurgy & Engineering Materials. University of Newcastle upon Tyne. Newcastle upon Tyne N E l 7 R U . UK

Agricultural soil mechanics has largely used the concepts developed in civil engineering. There has been a consequent lack of interest in the way that soils fracture. This basic fracture process involves breaking bonds between the soil crumbs. When the crumbs are bonded and the bonding between crumbs is weak, the soil behaves in a brittle manner. When the bonding between crumbs is strong, compared with its internal strength, the crumb will become distorted. This produces a ductile tear.

The way in which soil is broken up by an implement depends on the strength and ductility of the soil. For example, a plough, working in a hard brittle soil, produces cracks ahead of the share. Large clods are produced which are too strong to be broken up as they move across the mouldboard. In contrast, in a soft ductile soil little cracking occurs and a ribbon of soil is produced. When the soil is brittle enough for the share to crack it. but weak enough to break as it tumbles into the furrow, little further tillage is needed.

To test for these soil properties a clod of soil is placed between a ball and a steel cone and the maximum force and movement needed to split the clod are noted. The product there gives an indication of how cultivatable the soil is in its present condition.

Documents

Agriculture group symposium developments in soil cultivation technology