Soil type and their use
There are many different soil types. In this chapter, we highlight 3 different types of soil: peat soil, clay soil, sandy soil and mais and arable land.
Peat soil develops under the influence of water and is therefore often located in a wet and/or water-rich environment.
Good load-bearing capacity of the sod is an important condition for the intensive use of grassland. Poor drainage and a high organic matter content have a particularly bad influence on the use of grassland. This combination has always been very common in the original peat meadow area. At high ditch levels, the groundwater level will remain below ground level for longer periods. This means that there is a high risk of damage to the sod by trampling or driving over the sod, especially in spring and autumn. Since the early 1960s, research has therefore been conducted into the effect of better drainage capacity of peat grassland. The load-bearing capacity of the sod was an important parameter here. Many observations showed a clear improvement in the carrying capacity if there was better drainage. Based on these results, the drainage of tens of thousands of hectares of peat grassland has since been improved. An initial hesitation about desiccation or difficulties in watering livestock has given way to the deliberate provision for an optimal and sufficiently low ditch level. Much work has been carried out both in connection with land consolidation and in the context of land development projects and in combination with water board plans. Often ditches have been deepened through people's own initiative, and divers have been adapted and sewage systems installed through the use of their own resources. These measures, often in combination with drainage, have significantly improved the use of the peat pasture area in recent decades.
Typical of peat soil is the dropping ground levels over the years. This is the result of several processes.
One of the causes is the digestion (burning of oxidation) of the peat through contact with oxygen. Easily digestible material will disappear once it is no longer in the water or saturated with water. Better dewatering means that the groundwater level will decline faster. The thicker the peat that comes into contact with oxygen through dewatering, the greater the decline will be due to oxidation. The type of peat soil is also important. Due to the open structure, reed and forest peat will absorb more than the densely packed sphagnum peat. The decline is faster in the first years after better drainage. In the years that follow, the decline is much slower because the peat layer has already been digested. In addition, many peat soils have a clay cover. A change in the water level in this clay deck hardly results in an additional drop.
The soil dries up due to dewatering, this is also called shrinkage. This also causes the volume to decrease and a ground-level fall will occur.
The thicker the peat layer and the deeper the sand substrate, the greater the subsidence. The peat underwater has a lower weight. When the package which presses on the substrate becomes thicker due to better drainage, the substrate compresses more due to the increase in this weight this process is called settlement.
The total ground level drip is related to the processes above. Figure 2 shows the decline schematically. Peat soil will always decline the moment it rises above water. As it rises further above water, the decline due to the aforementioned processes initially increases. This mainly occurs in the first 5 years after better drainage and is therefore very dependent on the type of peat and the thickness of the clay cover. This decline must be taken into account when setting the level, building the pumping stations, culverts, and drainage.
Clay soil can be divided into sea clay and river clay. Both are being held back by water. Clay soil can be divided into a large number of classes and names. To determine which soil is suitable for agriculture, the weight of the soil is particularly important. This weight is determined by the content of lutum (= particles smaller than 0.002 millimeters). Another indication for the weight of clay soil is the percentage of siltable soil these indicate the particles smaller than 0.016 millimeters. Globally, in Dutch clay soil, the level of siltable soils is one and a half times higher than the clay content. If the soil contains more than 35% lutum (which is more than 50% siltable) we call it heavy clay soil. Heavy clay soil has limitations when it comes to using it for arable land. This is why most large areas of heavy clay soil are used as grassland.
For optimal use of grassland, the demands for workability are increasing. The machines are getting bigger and the working width is increasing every year. Narrow headlands are also undesirable for turning the machines. The sea clay area around the fields and more unpredictable parcels are also very obstructive during processing. To improve the machinability, leveling and plot enlargement are necessary. This has therefore been carried out on a large number of surfaces in the past decades. Many ditches have been replaced by drainage. The ditch level was set in such a way that the construction of drainage could be carried out at the desired depth. Puddles may form after leveling and drainage on very heavy clay soil. This is especially the case when heavy leveling has taken place. The top layer can also be compacted by processing. As a result, the water cannot penetrate the soil so quickly after a heavy rain shower. Some places where a lot of soil has been moved can subside after leveling. It is therefore advised to apply several ditches on very heavy clay soil after leveling. By giving the headlands the same width as the trench distance, it will cause little inconvenience during cultivation.
The largest area of sandy soil in the Netherlands is held back by the wind. Only a small area is being deposited by the sea or river water.
Due to soil-forming processes, there is a great diversity in sandy soil. Rinsing and washing in, accumulation of organic matter, oxidation, and reduction, etc. affect soil fertility, drought sensitivity, or flooding. By applying profile improvement, disruptive layers for dewatering and rooting can be removed. Also, the drought sensitivity can be reduced in this way and the bearing capacity can be improved.
The following matters are important for dewatering:
- If boulder clay occurs, there is a high risk of flooding. Especially when this occurs at a shallow level (less than 80 to 100 cm below ground level), high demands are placed on the drainage. Besides drainage, ditches are sometimes necessary.
- If there is a disturbing wash-in layer, it may be necessary to break it through with a profile improvement and/or to combine it with the entire profile. This improves the permeability of the soil and allows the drains to be further apart.
- A fine sandy and/or very flexible topsoil limits the smooth drainage of water through the soil. Newly sown plots in particular are sensitive to puddling due to liquefaction of the soil particles on the bare soil.
- The discharge of excess water through plot separations and lower-lying areas is not always possible. By widening ditches and optimizing divers, the period of temporary flooding can be shortened considerably.
Maize and arable land
The requirements for the cultivation of maize and arable farming are higher in comparison to the use of average grassland. Being able to sow in early spring and harvest in late autumn is very important for maize and arable crops. It is therefore not surprising that the requirements concerning drainage are higher than for grassland. Not every soil is suitable for maize or arable farming. Not too heavy clay soil and sandy soil are usually suitable. This also applies to peat soil, possibly mixed with sand soil (peat colonial soil). However, heavy clay and peat soils often have limitations. Higher requirements mean that the water must be drained smoothly and that the groundwater rises less quickly and is not allowed to rise quickly. This requires a closer drain distance and deeper drainage than for grassland. Before choosing an area, the possibility for maize and/or arable farming should be taken into account. Whether or not ditches can be replaced by drains can also play a role here. Although the processing capability is a high requirement, it should never be at the expense of good drainage. Poor drainage is almost always at the expense of the yield.