Water Management

Prevention of surface run-off

The risk of surface run-off already occurs with a barely noticeable slope of 2%. The risk of run-off is particularly high on soils that are difficult to absorb rainwater, i.e. poorly drained, sodden, without plant cover, with low humus content and with shallow subsoil compaction. It is also greater in fields with a shape that favours the formation of concentrated streams of water after heavy rainfall, so-called runoff valleys.

Soil degradation by water erosion mainly leads to a reduction in the thickness of the soil profile and a decrease in soil fertility. Annual soil loss in Poland as a result of water erosion is estimated at about 76 t/km2, or an average of about 0.8 t/ha, and for land in erosion areas about 3 t/ha.

The destructive effects of water erosion also include: deformation of landforms, disruption of water relations, destruction of vegetation and damage to technical facilities. The effects of surface run-off can be reduced through appropriate agrotechnical measures and the creation of structures that stop the movement of water on fields. Anti-erosion drainage is not only the protection of soils and land from erosive degradation and devastation, but at the same time the cheapest way to combat drought, steppe and flooding. Anti-erosion treatments or structures can be divided in terms of their duration of action into permanent (multi-annual) and temporary (seasonal). Permanent measures mainly include management measures such as the layout of land, fields and roads, development of gullies, technical facilities (terracing, strengthening of roads, permanent watercourses, construction of dykes, etc.), while periodic measures include anti-erosion agrotechnology, ditches draining periodic surface run-off and others. The inputs for the implementation of the various measures vary. The treatments that require the development of technical designs and considerable mechanisation of the execution works, e.g. gully development, have high inputs and high unit costs. In addition, they also require expenditure on ongoing maintenance. On the other hand, measures such as the introduction of an anti-erosion layout of land, fields and roads cost practically little, especially when combined with land consolidation. Expenditure on periodic measures – agrotechnical measures – is included in the costs of agricultural production every year.

Determining land use structure involves determining the relative proportions and location of forest, agricultural and water uses in the relief. It is generally considered that the more land is saturated with permanent vegetation, the greater its resistance to erosion. Forest land and phytomeliorative plantings have the greatest anti-erosion effect.

Permanent grasslands are, after forests and wooded areas, another vegetation formation with high anti-erosion values. The protective function of grassland is due to the ability of the strongly developed root system to bind the soil and cover its surface with a dense mass of stems and leaves. In addition, grassland vegetation plays a huge role in the soil-forming process. Field vegetation counteracts erosion to a much lesser extent than forest and meadow vegetation.

Forming the shape of fields and the agricultural road network is another set of anti-erosion measures, and its basis is the appropriate layout of these elements. On slopes with a gradient of more than 10° (18%), anti-erosion agrotechnology is no longer sufficient and a cross-country (contour) field layout is needed. The aim of such an arrangement is not only anti-erosion considerations, but also to achieve the most homogeneous habitat conditions possible. The width of the contour plots should decrease as the slope increases, so that the slopes become steeper and erosion is controlled, but fields that are too narrow make it difficult to mechanise cultivation (bagna.pl/images/artykuly_gfx/erozja.pdf). Anti-erosion agrotechnology can be a stand-alone treatment on moderately eroded land or a complementary treatment on more eroded land. Among the agrotechnical treatments, transverse-step tillage is of primary importance. Transverse-step autumn ploughing on slopes with up to 10 per cent slopes reduces the severity of erosion several times and at the same time increases, by several to several tens of millimetres, the water reserve in a one-metre layer of soil after snowmelt and increases yields by several per cent. In addition to ploughing, the transverse direction of sowing and planting is important, which significantly reduces the extent of erosion during the growing season. The sowing date, especially for winter crops, should be as early as possible, as this then ensures good rooting and tillering of the plants and thus better soil protection against erosion.

Also, the fertilisation of soils in eroded areas should be adapted to the elements of its relief: most abundant on the slopes, on average on the tops, and least abundant at the foot of the slopes and in the valleys.

The correct selection and succession of plants in the crop rotation is another fundamental link in the system of anti-erosion agrotechnics. Grasses and their mixtures with broad bean plants have the greatest anti-erosion properties, followed by perennial broad bean plants.

Annual species have less protective capacity, with rye and oilseed rape or wheat and barley protecting the soil from erosion better than spring row crops. Crop rotation in areas subject to erosion should take into account the longest possible soil cover with plants, growing perennial or heavily tillering crops.