Alternativa bevattningsformer : 2. reglering av grundvattennivån
Subirrigation through regulation of groundwater levels is, in principle, a very favourable form of irrigation. There are, however, some requirements which must be met by the area to be irrigated. The area must have a level surface and little or no slope. The soil must have a relatively high permeability so that an artificial watertable can be created and maintained at a suitable depth below the soi1 surface. So that water consumption can be kept to a reasonable level, the soil must have a dense layer or a naturally high watertable to reduce downward flow of water in the profile. To achieve a maximum irrigation effect, variation in distance between soil surface and watertable should not be greater than 0.1 - 0.5 m (depending on soil type). This usually requires the installation of several weirs. On soils which are suitable for subirrigation, the drain spacing used in conventional drainage is usually satisfactory for subirrigation. Drainage pipes should be surrounded by a filter to reduce the risk of clogging and to promote water movement between soil and pipe. Water consumption is greater for subirrigation than for sprinkler irrigation, partly because some leakage into the surrounding area is unavoidable and partly because a certain quantity of water is required to elevate the watertable. The water used must be relatively free from suspended substances and salts. It must also be relatively free from organic material, which leads to bacteria1 growth in the pipe system and reduces its functioning. Because of this, waste water is less suitable for subirrigation. Subirrigation can be carried out in three ways: a) constant watertable during the growing season b) the watertable is allowed to fluctuate between certain pre-determined levels c) the watertable is elevated at the start of the growing season, after which the crop roots follow the sinking water level (requires deep rooting). Of these, the last method demands least labour and energy inputs but, if the site is suitable, all three methods are more effective than conventional methods.
Bevattningsformer; Underbevattning; Reglering av grundvattennivå
Report / Swedish University of Agricultural Sciences, Department of Soil Sciences, Division of Agricultural Hydrotechnics
Publisher: Institutionen för markvetenskap, Sveriges lantbruksuniversitet
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