The range of plants grown and their sequence have indirect impacts – through tillage and cropping processes in general – on the appearance and aggravation of defects in soil condition. The following should be carefully considered in this regard:
Owing to the necessity of growing a small number of different cash crops plants that have favourable preceding crop effects may be dropped out of the cropping sequence.
Plants that can be grown profitably in a given site tend to have the same – usually long – growing seasons, their sowing and harvest may have to be carried out during the same time from year to year. Sowing plants of long growing seasons year after year may lead to depleting the soil moisture reserves in drier years and to deteriorating soil workability. The frequency of dry tillage periods result in alternating processes of crumbling and pulverising, while repeated harvesting and tillage periods with abundant precipitation lead to other types of damage (e.g. traffic induced soil damage, compaction, puddling, smearing).
A simple and unvaried cropping sequence may lead to weed infestation. Negative processes may be aggravated by failure to apply means of mechanical weed control – in particular, stubble stripping and treatment – and by random application of chemical weed control.
1. Tillage focusing on preserving the soil structure, organic material and moisture contents.
2. Alternating the time periods within the year of soil loading and recovery, i.e. different growing seasons, different periods sowing and harvesting during the year.
3. Reasonable plant nutrition.
4. Proper treatment of crop residues.
The influence of biological factors
5. Integrating soil loosening and soil structure improving plants in cash or forage crop growing (as primary or secondary crops during a given season)).
6. Dual cropping – e.g. undersowing, oversowing, mixed sowing, growing a second crop – with the aim of soil protection (catch crops) or for the purposes of soil nutrient management, producing animal feed or sowing seeds.
7. Reasonable application of the practice of setting aside land to let it rest and recover.
Tillage focusing on conserving soil structure, organic material and moisture is a fundamental pre-requisite for favourable biological effects to materialise (this applies to cropping after growing papilionaceous crops as well).
Differences in tillage depth, seed bed quality, nutrient and moisture requirements may help the farmer avoid unvaried cropping patterns. Different crop requirements are usually accompanied by different preceding crop effects and different types and quality of crop residue masses that require different treatments. Varying the tillage depth contributes to utilising the root zone potentials and to preventing the creation of a compacted tillage pan. Varying the time period of soil stress and recovery during the year provides benefits in terms of protecting the soil structure as well. Adapting to different requirements has favourable effects on crop protection as well, contributing to effective weed, pest and pathogen control and restricting their reproduction.
The preceding crop effect is made up of a variety of factors, including:
• site (exposure, soil, precipitation),
• effects on the soil:
• nutrient contents (favourable, neutral, unfavourable),
• moisture content (favourable, neutral, unfavourable),
• organic material content (favourable, neutral, unfavourable),
• structure (favourable, neutral, unfavourable),
• state: the depth of tillage required for the next crop.
• yield (main and by-product),
• pests, pathogens, weeds (restricting, neutral, aggravating),
• harvest time (the length of time available from harvest to the time of sowing the next crop), in view of the quantity and distribution of rainfall during the given season,
• the impacts of the procedures of its production technology (tillage, application of manure/fertilisers, crop protection, irrigation),
• crop residues, since their quantity and choppability determine whether there is a need for ploughing before the next crop, whether the residues should be inverted or left on the soil surface, whether there is a need for chopping the stalks to make tillage easier.
Accordingly, the state of the soil after the preceding crop is a highly important factor, determining – among other things – whether it is possible to reduce or eliminate tillage defects and to cut tillage costs.
The preceding crop is considered to be „favourable‟, if:
1. It is harvested early (e.g. in the middle of summer), offering the benefit of stubble stripping in reducing soil moisture loss.
2. It has a good biological after-effect (legumes, perennial papilionaceous crops, soil loosening crops).
3. It takes up small or moderate amounts of water.
4. It leaves a small quantity of crop residues or it leaves residues that can be easily and well chopped by the stubble stripping implement and can be left on the soil surface or part of which can be mixed into the soil.
5. The crop residues need to be chopped, there is no time constraint.
6. Its sowing had to be preceded by deeper primary tillage, as a consequence of which the next crop needs a less deep or no primary tillage at all.
7. The soil is dry there is a choice of several tillage techniques for primary tillage before the next crop, indeed there may even be no need for primary tillage at all.
8. The soil is compacted, the available length of time is sufficient for loosening the root zone.
9. There is a low occurrence of pests, pathogens and weeds, and they do not necessitate deeper and more costly primary tillage (ploughing).
10. Harvesting does not result in any soil damage that would necessitate deeper and more expensive primary tillage.
The preceding crop is considered to be „modestly favourable‟, if:
1. There is a shorter period of time between the date of harvest and that of sowing the next crop.
2. If the crop residues need to be chopped before tillage.
3. If it was preceded by deep primary tillage or ploughing yet the quantity of crop residues (maize, perennial papilionaceous plants) necessitate inverting.
4. If it has a positive biological after-effect (papilionaceous, loosening plant) only after soil conserving tillage.
5. If it takes up a medium amount or large amount of water, having a negative impact on the next crop and its tillage costs in a dry year.
6. In certain cases (e.g. after sunflower) ploughless tillage should be opted for.
7. If the soil is compacted, the shortage of time makes it difficult to carry out the required loosening.
8. In the case of extreme weather conditions there is a narrow range of applicable tillage techniques.
9. The state of the soil may deteriorate during the harvest period and this may necessitate deeper and more costly primary tillage.
10. The presence of pests, pathogens and weeds drives up the costs of primary tillage.
The preceding crop is „unfavourable‟, if:
1. It is harvested when the next crop is to be sown. Good organisation and a rationalised tillage regime is required for effectively managing and completing all of the operations required for harvest and sowing in a short period of time.
2. Crop residues need to be chopped to make tillage easier.
3. It has no favourable biological after-effect.
4. It takes up plenty of water, having a negative impact in a dry year both on the productivity of the next crop and on the tillage costs. The soil will not grow „mellowed‟ by the time of seeding in drier years.
5. In a wet season the time of both tillage and sowing may be delayed, the soil may be damaged and in some cases it may not be improved before the next season.
6. Defects in soil condition that had been created earlier cannot be remedied and new defects may appear.
7. It was sown after shallow primary tillage, its harvest resulted in traffic induced soil damage and the next crop is rather exacting with regard to the condition of the root zone.
The influence of biological factors
8. The shortage of time calls for minimum tillage, while the mass of crop residues necessitates primary tillage involving inverting.
9. Cropping in monoculture increases the costs of weed and pest control and this necessitates deeper and more expensive tillage.
10. Weather extremes reduce the range of suitable tillage techniques and particular care is required if causing damage is to be efficiently prevented.
In summary: „Preceding crop value‟ is the sum of the effects on the performance of the next crop and the required production techniques, which may be improved by conserving tillage, or may be deteriorated by wrongly chosen or performed tillage operations. The preceding crop requirement is a sum of the biological and agronomical requirements assisting the production of the next crop, some of which are met by soil conserving tillage.