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 The conservation tillage technique chosen for a particular field was site-specific - the result of a combination of factors including the state of the soil, soil type, crop, weather conditions and machinery available on the farm.
The results presented in this section are from 25 fields of varying soil types on 18 farms across the 3 countries. Soil type has a strong influence on the inherent vulnerability of soil to erosion. In addition, soil type also affects the suitability of a particular soil for conservation tillage. In Belgium , the soil types were sands or sandy loams; sandy loams in Hungary ; and in the UK , the soils ranged from clays to sandy clay loams
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For more information on the problem of soil erosion, go to SOWAP and soil erosion |
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Conservation tillage: a practical method of reducing soil erosion |
- Practising conservation tillage reduced soil loss by up to 98% compared to mouldboard ploughing
- More soil was lost from fields with spring sown crops (maize, sugar beet, sunflower) compared to fields in winter crops (wheat and oilseed rape)
On mouldboard ploughed land in Hungary and at the Tivington site in the UK, the highest erosion rates were 6 and 3 t/ha respectively (in 2006). While these rates were up to 9 times lower than in Belgium (see below), losses of this magnitude are still unsustainable. Conservation tillage reduced the loss of soil at these sites to tolerable levels (considered by Young et al , 1998, to be about 1 t/ha); in the same year, erosion rates were 0.1 in Hungary and 0.7 t/ha at Tivington (see Figure 1 for Tivington information). |
| The greatest soil loss in one season - 28 t/ha - was seen from the mouldboard plough treatment at the Belgian demonstration site ( Huldenberg ) in 2004 - the result of a heavy thunderstorm on 7th August when over 60 mm of rain fell on a maize crop (Figure 1). The amount of soil lost from two conservation tillage parts of the same field were over 50% less at 7-14 t/ha. |
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Figure 1: Cumulative soil losses (t/ha) per crop per country on the conventional ploughed (MP) and conservation tilled areas (CT1 + CT2). Please note that conservation tillage treatments vary by crop, year and country so that CT1 at Tivington in 2003-2004 is different to that practised in 2004-2005 and also differs to that practised in Belgium. For more information about the soil management at the Tivington site go to Tivington soil management |
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| On the heavy clay soil at Loddington in the UK, almost no soil loss was recorded and although a rainfall event in October 2004 caused more erosion from one of the conservation tillage treatments compared to the ploughed treatment, the actual quantity of soil lost was very small - less than 0.1 t/ha. |
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| More soil was lost from fields with spring sown crops (maize, sugar beet, sunflower) in Belgium and Hungary, compared to fields in winter crops (wheat or oilseed rape) mostly grown in the UK . The reasons for this seem clear at first. For example, many operations are required to prepare the soil for planting sugar-beet, weakening the soil structure and leaving the soil surface vulnerable to spring rain. However, in the UK where wheat and oilseed rape were primarily grown, other factors e.g. less erodible soil types, two dry winters (in 2003 and 2004) and early drilling times will also have contributed to the lower erosion rates seen from fields established with these crops. |
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SOWAP's results therefore show that conservation tillage can significantly reduce soil erosion. They also demonstrate that erosion varies from field to field and from year to year, due to a combination of the weather, the health and management of the soil, cropping and the slope of the field and as already mentioned, soil type. These results are in line with other work. |
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Conservation tillage often reduces water run-off from fields |
- Conservation tillage can substantially reduce the amount of water running off fields but the impact was not as consistent as its effect in decreasing the amount of soil loss
- However, in situations where more runoff was produced from conservation tillage fields, soil erosion was still lower
 The variable response of runoff seems to be dependent on a combination of factors:
- The number of years in conservation tillage – in the first year of conversion in particular, fields were likely to produce greater run-off
- The surface of the soil - greater sealing of the soil surface or lower surface cover increased run-off volumes
- The amount of rainfall
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| In Hungary the advantage of conservation tillage was clear where run-off reduction of up to 95% was recorded (Figure 2). However, at one of the UK sites (Tivington), runoff was reduced by conservation tillage by about 60% in winter beans in 2005/6 but a year earlier in 2004/5 when the crop was winter wheat; more runoff was generated from the conservation tillage treatments. |
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| Figure 2: Cumulative run-off (mm) per crop per country on the conventional ploughed (MP) and conservation tilled areas (CT1 + CT2). Please note that conservation tillage treatments vary by crop, year and country so that CT1 at Tivington in 2003-2004 is different to that practised in 2004-2005 and also differs to that practised in Hungary. |
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| Although more run-off was generated from the conservation tillage treatments at Tivington in 2004-2005, there was no consequent increase in the amount of soil erosion. As already seen in Figure 1, conservation tillage reduced the amount of soil lost in this cropping season by 50% - 1.4 t/ha soil lost from the mouldboard plough treatment and only 0.6-0.7 t/ha from the conservation tillage treatments. |
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High runoff rates are related to high intensity rainfall events. For example, in Belgium three high intensity rainfall events in summer 2004 were responsible for almost all recorded runoff. At Loddington little run-off was recorded - a function of the soil type and the dry winters of 2003/04 and 2004/05. |
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| SOWAP's results therefore show that although conservation tillage can reduce run-off, its impact is not as consistent as its effect on soil erosion, but importantly, there was no increase in soil erosion when there was greater run-off. This means that water running off the conservation tillage sections of the fields carried less sediment with it. This has clear benefits downstream, with less sediment available to silt up ditches and streams. The results also demonstrate that run-off varies from field to field and from year to year, due to a combination of the weather, the health and management of the soil, cropping, the slope of the field and soil type. |
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| Conservation tillage can reduce nutrient loss from fields |
Total nitrogen (N) losses |
- Conservation tillage reduced the amount of nitrogen lost from fields
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This reflects the general trend of lower runoff and sediment loss from these treatments. Data from all sites showed that more N was lost with the eroded sediment, rather than in the runoff. |
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| Figure 3: Total N losses (runoff and sediment – kg/ha/season) from mouldboard ploughed (MP) and conservation tillage (CT) treatments in 3 SOWAP countries. Please note that conservation tillage treatments vary by crop, year and country. |
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Considerably greater nitrogen and other nutrients (see below) were lost from the demonstration site in Belgium compared to other countries. A slurry application on maize in 2004 followed by some heavy rainfall explains the much higher nutrient losses seen from this field.
No information from the Loddington site is shown as nutrient losses from all treatments were very small. |
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Total phosphorus (P) losses |
- Conservation tillage reduced the loss of phosphorus from fields
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Most phosphorus (P) loss is associated with eroded sediment, as P is strongly adsorbed onto sediment surfaces. Highest P losses were found at the Belgian site, with the ploughed treatment losing the greatest amount of total P (>14 kg/ha/season; Figure 4). This is explained by the high soil losses observed on the highly erodible, sandy loam soil at the Belgian field site.
P losses in other countries were much lower, but followed the same trend as overall sediment loss. |
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Figure 4: Total P losses (runoff and sediment – kg/ha/season) from mouldboard ploughed (MP) and conservation tillage (CT) treatments. Please note that conservation tillage treatments vary by crop, year and country. |
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Total potassium (K) losses |
- Conservation tillage reduced the loss of potassium from fields
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Potassium (K) mobility from arable soil is associated with soil erosion, as K is strongly adsorbed onto the surfaces of easily erodible soil particles. Indeed, total K losses follow the same trends as observed for P losses. Greatest losses were found at the Belgian site due to the higher soil losses recorded (Figure 5). |
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Figure 5: Total K losses (runoff and sediment – kg/ha/season) from mouldboard ploughed (MP) and conservation tillage (CT) treatments. Please note that conservation tillage treatments vary by crop, year and country. |
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| Total organic carbon losses |
- Conservation tillage did not consistently reduce carbon loss in sediment and run-off due to the higher organic carbon content of these soils
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In Belgium , the country with the highest losses of organic carbon, one of the conservation tillage treatments led to higher losses of carbon in sediment and runoff compared to the mouldboard plough treatment (Figure 6). This can be explained by a higher content of organic carbon on these particular soils, as further analysis showed that both conservation tillage treatments have higher organic carbon than the mouldboard ploughed soil. |
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In contrast, at Tivington greatest organic carbon losses came from the ploughed treatment. This trend was expected, as the latter represents the most disturbed and disrupted soil and where erosion losses were greatest. The lowest organic carbon losses came from the Loddington site with very little difference between the treatments. |
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Figure 6: Total Organic carbon losses in runoff and sediment kg/ha/season) from mouldboard ploughed (MP) and conservation tillage (CT) treatment. Please note that conservation tillage treatments vary by crop, year and country. |
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Conservation tillage maintains and improves soil quality |
- Conservation tillage led to an increase in soil organic carbon, especially in the top 0-5 cm of the soil profile .
- Conservation tillage soils had higher levels of total N than found in the ploughed treatments
- There was no impact of soil management on P and K levels
- There was no increase in the bulk density of conservation tillage soils and therefore no indication of an increase in compaction
- Conservation tillage soils had higher levels of soil moisture
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 A build up of organic carbon in the soil profile was expected under conservation tillage. This is because conventional tillage inverts the soil, mixing any organic matter present in the top layers ( e.g . from crop residues and roots) throughout the profile (to plough depth) (VIEW-MEDIAPLAYER or VIEW REALPLAYER). SOWAP's data shows that the accumulation of organic matter in the top 0-5 cm did not correspond to a reduction of organic carbon in the soil at depths to 30 cm. Higher levels of organic carbon in the soil represent a rich substrate for microbial populations, as well as a reduction in the susceptibility of the soil to erosion as already seen (soil erodibility). There was an indication of a small increase in organic matter over time in Belgium but this was not seen at other sites. |
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| Conservation tillage soil showed an increase in soil moisture content when compared to ploughed soil, especially on the clay soil at Loddington. Such improved water holding capacity would be important during times of drought both for the crop and for the biodiversity of the soil and could give farmers practising conservation tillage an advantage in such conditions. The ability of soil to hold water is also vital in helping to minimise peak runoff flows and reducing flooding risks. Conversely, it could be a disadvantage in spring, particularly on heavier land as such soils might stay colder and wetter for longer especially under a layer of crop residue, slowing down the germination of spring crops. |
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| An increase in compaction, especially in surface layers, is a concern for practitioners of conservation tillage. This is because of the lack of soil disturbance in a conservation tillage system can lead to the consolidation and compaction of the soil. However, no increase in compaction i.e no increase in soil bulk density, of conservation tillage soils was seen during SOWAP. |
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 There was some anecdotal evidence to suggest that conservation tillage soils were more resilient to trafficking than mouldboard ploughed soils. The picture on the left-hand side shows a tramline on the ploughed part of a field; the right-hand side is under no-till. The left-hand picture shows that the tramline has sunk about 8cm lower than the surface of the rest of the field, while under no-till, there was little compaction in the tramline.
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Conservation tillage benefits farmers and society |
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SOWAP has demonstrated that conservation tillage is an effective and practical solution to reducing soil erosion in parts of northern and central Europe . The practice improves the soil's resilience to erosion by reducing the number and intensity of soil management operations, by adding organic matter through crop residue (and cover crops) and by protecting the soil surface from raindrops using plant cover. On the farm, the farmer benefits from a healthy soil, which is kept in his fields along with the nutrients that he has applied. This provides the basis for a productive cropping system. The practice also benefits the local community by ensuring that eroded soil does not block streams and rivers increasing the risk of flooding and by contributing to a sustainable food supply.
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| This report is based on the work of Katleen Gillijns and Annemie Leys at K.U.Leuven in Belgium; Balazs Madarasz and Bela Czerpinsky of the Hungarian Academy of Sciences and Sophie Cooper and Rob Read at Cranfield University, UK |
