Sárdi Katalin (2011)
Debreceni Egyetem, Nyugat-Magyarországi Egyetem, Pannon Egyetem
Table of Contents
The mode, depth and quality of primary tillage are dominant factors of a tillage system because they not only affect the circumstances of seedbed preparation but they also determine the costs of all of the other interventions. Ploughing is the mode of primary tillage in a tillage system based on ploughing, whose most important action is turning the soil over. The agronomical benefits of ploughing come from inverting the soil, but concerns of importance are also related to inverting (Table 7.1).
Table 7.1 Advantages and considerations of conventional ploughing
From an agronomical perspective ploughing entails risks where it aggravates erosion, if it produces a soil surface with clods or even with large smeared clods necessitating several rounds of secondary tillage (which will inevitably entail recompacting the soil and turning soil into dust). Clodding, pulverising, the aggravation of water and wind erosion as well as compaction itself are ploughing’s environmental risk factors. Knowledge of further risks entailed by inverting – including increased carbon-dioxide flux, loss of organic material, disturbing earthworms habitats – enables not only taking an objective view of ploughing but it may also prompt the farmer to prevent greater damage. The value and the risks of ploughing vary by its timing. Ploughing is regularly carried out in the regional circumstances in the summer, in the autumn and in the spring (Figure 7.1). The conclusion that can be drawn from Figure 7.1 the benefits of ploughing carried out in different seasons should be exploited and the risks – since they are known and can be taken into account – should be alleviated.
Figure 7.1 Possible time of ploughing, advantages and considerations in Pannonian region
The quality of the result of ploughing is, in general, affected by certain parameters of the soil (clay content, heaviness of texture), moisture content and workability, which is determined by these parameters. The physical condition – compact or loose – also has a substantial impact. Factors of relevance from the aspect of operation include the plough implement design, setting and the mode of ploughing (using conventional or reversible plough). The following factors are taken into account in evaluating the result of ploughing.
Frequently encountered defects after ploughing, in the summer:
stubble stripping is not carried out or it is carried out late as a consequence of which the soil dries out and it becomes much less ploughable.
stubble stripping is not followed by pressing, the soil is left cloddy, with a large surface through which soil moisture is lost; disturbing the soil makes it dry out to a greater depth and becomes a lot harder to plough later on.
deep stubble stripping is carried out (by disking) and the surface is left without pressing; though the tilled layer provides some isolation, the chance for high quality ploughing diminishes.
It is clear from the above that stubble treatment defects contribute more to poor ploughing quality than had been usually assumed. Defects encountered in the course of ploughing, during and at the end of summer, in dry weather are as follows.
Ploughing in the summer, without levelling and pressing the surface. Farmers applying this practice disregard the soil moisture loss and the risks to which crops sown in late summer or spring will be exposed. Indeed, the soil moisture reserves may drop to such a low level where even the very survival of crops will be at risk, if the next one is a dry season.
Damaging the soil structure. Owing to the substantial moisture loss caused by a wrongly chosen or a badly performed stubble stripping intervention ploughing results in a heavily cloddy surface, as a consequence of which surface forming or pressing has to be postponed until the first rain. The soil keeps losing water during until surface forming and pressing, and since it is cloddy, it goes unevenly soaked. An additional intervention inevitably entails additional costs and traffic induced soil damage.
Loss of organic materials. The excessive aeration and large surface of ploughed soil boosts aerobic microbial activity, whose end product – carbon-dioxide – is emitted in the atmosphere. Soil disturbance, moving the soil about, that is entailed by ploughing, i.e. tillage leaving large soil surface exposed to the air and resulting in increased aeration, has contributed – over centuries – to the degradation of organic materials and to the upsetting of the carbon balance.
Unfavourable biological effects. Between large clods torn up from the desiccated top layer of the soil, even useful biological activity (earthworms) gets suspended for quite a while.
The benefits of summer ploughing come from turning the top layer over while its disadvantages stem from the loss of soil moisture and from the difficulties of the subsequent tillage operations. Where ploughing in the summer is opted for, account must be taken of the possibility of disadvantages outweighing the benefits that may come from inverting.
Defects in the course of ploughing, in the autumn (winter) or in a wet soil:
Puddling the soil underneath the ploughed layer, producing large smeared clods on the surface. The farmer may hope for the crumbling effects of the alternating processes of freezing and thawing out in the summer, but this should not be over-estimated. For frost has no loosening effect on soil pressed by the plough share and compacted by tractor tyres in the furrow. Any impact that is detrimental to the soil – including smearing and puddling – leaves its mark on the structure, making the soil more and more prone to pulverising and clodding.
Uneven ploughing depth which is linked to variations in the soil features or to higher resistance of a compacted layer formed earlier. Ploughing the same depth as a routine, particularly when the soil has soaked over, leads to increasing risk of plough pan appearing or thickening in the soil. The increased resistance of compressed soil – if the traction power is suitable only for average soil conditions – makes it impossible to reach the required depth. It takes increased draught power, higher quality ploughs or some other technique (ripping) to break and work the compacted layer.
Unless improved ploughing techniques are adopted, an earlier created plough pan develops into a permanent feature at a depth between 25 and 30 cm.
Furrows and ridges created by ploughing in lands (that is by conventional mode) are not eliminated or they even grow more and more marked. Rainwater accumulates in puddles in a field that is growing increasingly ‘undulating’ and the quality and the feasibility of other production procedures decline.
The greatest benefit of ploughing in the autumn is that the soil is rendered suitable for taking in and storing autumn and winter precipitation. After poorly performed ploughing, however, this expectation is hardly met at all. Instead of seeping down into deeper layers rainwater landing on the surface accumulates above the compact plough pan layer and it runs off the field down the furrows. Additional losses occur when freezing is followed by thawing.
Levelling the surface and seedbed preparation after poorly finished ploughing:
Uneven surface features created by ploughing remain visible even when the crop has emerged. If the degree of cloddiness and the soil moisture content varies within a field even the best efforts will not be enough to create an even quality of soil during the crumbling interventions or in seedbed preparation. An uneven seedbed results in defects in the crop emergence and in differences in the crop growth later on.
Soil that has soaked through to different depths in the winter will dry out unevenly in the spring. In one part of the field the soil is not trafficable yet while in other parts it has dried out excessively. Consequently, the first interventions in the spring may just as easily result in compaction by traffic or in smearing as in dust forming.
Water transport between soil layers smeared by ploughing or by seedbed preparation become upset, which may entail particularly serious risks in a dry growing season. For the soil susceptibility to drought is aggravated primarily by physical state defects obstructing the vertical movement of soil moisture, while insufficient precipitation is only the second most important cause of water shortage problems.
The quality of the seedbed is a sum of all of the outputs (and the quality of the outputs) of all of the tillage interventions from stubble treatment to seedbed preparation. Although it is not impossible to create a seedbed that looks good, even in a poorly ploughed field (though it takes a larger amount of more expensive work), it is hardly possible to produce a seedbed that meets the crop requirements.
Ploughing, if not properly, is characterised by the following, regardless of the site:
it is hardly possible to lay down the required groundwork for cropping if ploughing is carried out on soil of unsuitable moisture content,
inverting and surface forming are highly energy-intensive operations both separately and in combination, if they are carried out on desiccated soil (e.g. if no stubble stripping was carried out first),
surface that has not been levelled or pressed results in increased loss of water after ploughing in the summer or in the spring,
the structure is damaged if ploughing is carried out on too wet soil (through compaction and puddling) or on too dry soil (through clodding),
in the case of ploughing in lands the soil in the headland area where the tractor turns is subject to increased traffic induced soil damage,
plough pan compaction develops when wet soil is ploughed many times over several years. If the edge of the ploughshare is not sharp enough it is prone to smear the soil and in this case the mode of ploughing makes not much difference.
In summary, a poorly performed ploughing does much damage to the soil, instead of economic benefit. This, of course, does not apply to ploughing in general. Problems are caused by poorly timed or finished ploughing, not by the plough itself. Partly to mitigate damage caused by the climate change the plough is probably going to be used less frequently in this region in the future.
Ploughing is good when the soil has been worked to the planned depth, inverting is perfect, the slices of soil cut off by the plough crumble adequately or well, depending on the soil current condition, the ploughing passes are not clearly separated, there are no patches of soil left intact (dead furrows) and the bottom of the furrows is not compacted. High quality ploughing can be achieved through proper operation of the machinery. It is difficult to get close to what qualifies as ‘good’ with the aid of the conventional plough (there being more idle running without actual ploughing, along with inevitable traffic-induced damage), while a reversible plough helps producing better output. The type of the plough itself and the mode of ploughing only offer the possibility but no guarantee for achieving high quality ploughed land. Good ploughing helps economical utilisation of the agronomical benefits offered by inverting the soil, including:
reliable groundwork for cropping,
turning over manure and soil improving materials, crop residues and weeds (that hinder seedbed preparation) and weed seeds into the desired depth in the soil,
improving the effectiveness of crop protection,
conserving or preserving the soil structure (this is most effective in humid soils).
The above benefits can be attained most easily if the soil is suitable for ploughing (i.e. when it is humid), and if reaching the planned ploughing depth and quality is not hindered by physical soil defects. The goal of rationalising ploughing-based tillage systems is to retain this technique that is so highly popular among farmers, to prevent typical defects and to alleviate cropping and environmental risks.
The following are mitigated or reduced in the wake of rationalising tillage systems based on ploughing:
damage linked to the frequency of ploughing,
damage linked to inverting the soil,
the risks linked to the timing of ploughing,
the number of tillage operations between ploughing and seeding without loss of quality, and
the total number of tillage passes.
Ploughing can even have an improving effect, if by inverting the pulverised top soil layer over a more friable layer can be brought to the surface (a spade test needs to be carried out beforehand). Ploughing may be necessitated for crop protection through deteriorating the chances of survival of pests, pathogens and weeds and through disturbing their activity. Nevertheless, instead of ploughing whether or not it is really necessary, this technique should be applied at carefully planned intervals.
The risk of inverting the soil can be mitigated by improving the quality of the inverting action and by eliminating unfavourable changes (e.g. large surface through which moisture is lost, loss of organic material). Turning the soil over should be resorted to when the state of the soil is favourable – when it is moist, its surface has not been compacted – and surface forming can be carried out with the aid of an implement combined with the plough. Instead of conventional ploughing it is more rational (saving on costs and preserving the soil) to carry out this task with the aid of reversible plough combined with surface forming element, when the soil is not damaged by traffic resulting from idle running (with ploughs raised) and a separate surface forming intervention. Even if the farmer insists on using the conventional plough it is possible to apply a surface forming tool (with a rotary element) preserving the soil structure. Table 7.3 shows the levels of environmental risks entailed by inverting, from which conclusions can be drawn with regard to the possible ways of preventing damage. Carbon-dioxide flux and organic material loss can be alleviated by reducing the large surface area and the volume of air pockets in the soil. In a humid soil the expected quality can be attained, while in a dry soil clods can be sliced up and the surface can be evened with the aid of suitable tillage implements.
Earthworms’ habitat is disrupted by inverting. A soil after proper surface forming, which has not lost much of its moisture content quickly becomes habitable for earthworms, while the process takes more time in a soil damaged by clodding and overly loosened in the summer. Earthworms disappear from soils that have been smeared and then dried out. Ploughing with a reversible plough combined with a surface forming implement in the same pass entails a smaller environmental risk whatever the soil moisture content, than does conventional ploughing without surface forming. Conventional ploughing does the better job on larger fields. Using some surface forming element does no damage in this case either: its use should depend on the current soil moisture content.
The risk relating to the timing of ploughing can be reduced by enhancing agronomical benefits, such as effective inverting, avoiding the production of clods to be broken down later on etc. Risks differ from season to season (autumn, spring, summer, see: Table 7.1). High quality ploughed soil can be produced in any of the seasons if the soil falls in the range of favourable moisture content levels but moisture loss is more difficult to control in the summer and in the spring. Whichever season ploughing is carried out in, it must not deteriorate the soil physical and biological condition. Risks are increased by compacting and smearing the soil in the case of ploughing in the autumn, by compacting and moisture loss in case of ploughing in the spring and by extreme moisture loss in the case of ploughing in the summer. Accordingly, there is a need for mitigating the risks entailed by inverting the top soil from the aspect of agronomy (preventing defects) and from that of the environment (preventing damage). Combining the plough with some surface forming element – if ploughing is carried out within the moisture range in which the soil type concerned is suitable for ploughing – should provide the best results, irrespective of the time of the year in which ploughing is carried out.
Quality may be improved and the number of tillage processes to be carried out between ploughing and seeding may be reduced only following high quality ploughing that does not necessitate an increased number of supplementary interventions for agronomical purposes.
In the conventional tillage system based on ploughing the farmer has to face the possibility of deteriorating quality and growing risks throughout the period between the completion of harvesting and sowing the next crop. The greatest risks lie in loss of soil moisture (increasing the damage caused by the climate), traffic induced soil damage (conventional ploughing) and secondary tillage in separate passes. Accumulation of agronomical defects (moisture loss, inadequate crumbling of clods, increased dust forming and recompacting by traffic) points to the potential of expanding environmental damage. Rationalising the tillage system based on ploughing – with ploughing carried out in the soil optimum moisture range for this kind of intervention – offers a chance for preventing damage and cutting costs.
The quality of the operations before ploughing (stubble stripping), and of inverting affect the total number of tillage passes. The solution lies in reducing the soil moisture loss, for instance through carrying out stubble stripping with the aid of cultivator combined with crumbling and pressing elements, ploughing with reversible plough combined by a surface forming element, seedbed preparation using some implement that does not turn the soil into dust.