Soil and fertiliser
Soil and fertiliser
We talk about different types of soil such as sand, clay and loess. This is the upper part of the soil where the roots grow and attach themselves to the earth. This prevents them from blowing over and allows them to draw up water and nutrients.
To be able to do this, air is also needed in the soil. Almost all soil types are suitable for growing fruit trees, but the soil conditions do affect how much fruit you get and how well the trees grow, so here is some explanation.
Sandy soil cannot hold water and nutrients by itself; it needs humus to do so. Depending on how good the sandy soil is (the darker the better), it contains more or less humus.
You can add humus by adding organic material to the soil. This can be potting soil, compost or old farmyard manure.
Clay soil and loess soil can retain nutrients by themselves, so they do not need soil improvement. If it is heavy clay, then it is good to add humus, so that the soil can hold air better and is easier to work.
Humus also darkens the soil, so it will warm up faster in spring and the plants will grow better.
Be careful with undigested organic materials, such as a lot of straw and bark, as they need a lot of nitrogen fertiliser for digestion and extract it from the soil. This leaves nothing for the plants, they will grow poorly and have yellow leaves.
Potting soil, old farmyard manure and compost are fine.
The development of the root system depends strongly on the soil structure. A soil with a good structure (crumb structure) contains a lot of air and water. In such soils, the roots will develop well and result in healthy, vigorous trees.
Sometimes it is necessary to break through impenetrable layers. After building a house, the soil is sometimes so compacted and entrenched that it has to be opened up to a depth of 80 cm.
The capillary action of the soil is also important: when there is too much water, it sinks into the ground and when it is dry, the water rises again through the soil. This is not possible with a disturbing layer.
If the soil is often too wet and the water cannot drain away properly, it is important to install a drainage system. It is also possible to plant on mounds, which can be raised by about 50 cm. Make sure that the raised soil is well mixed with the subsoil and put the plants in it.
The clay-humus complex
Clay and humus create a fertile soil. Both substances are rich in nutrients and have the ability to retain nutrients and keep the soil from leaching out. The stored nutrients are then gradually released to the plant.
Clay and humus are also the binding agents par excellence to make sand grains stick together and thus enable an airy crumb structure. They also improve water capacity.
Nature does not fertilise, and yet we see impressive trees in forests and parks. This is because the soil naturally contains nutrients. But not as much is needed as people think. Water (H2O) and carbon dioxide (CO2) are in fact the most important building elements for every plant (approx. 95%) and are usually present in abundance. All other nutrients are only needed in limited quantities as building materials or for metabolism. Because of the closed cycle in nature (leaves and fruit fall off and decompose on site), most minerals return to the soil and the growth process can continue from year to year. In our gardens, the situation is different. There, we practice overexploitation. We harvest fruit to eat. The closed cycle is broken here and the soil is impoverished. The law of restitution says that the nutrients removed by the harvest must be returned by means of compost or fertiliser.
We also want to stimulate growth and increase yields in our gardens and this can be achieved to some extent by proper fertilisation.
Fertilising is sometimes an absolute necessity because through selection we have created greedy plants that need extra nutrition. We can divide the nutrients that make up about 5% of the plant into three groups:
Nitrogen(N) Phosphorus(P) Potassium(K)
Very little of these is needed. Iron (Fe), Manganese (Mn), Boron (B), Zinc (Zn), Molybdenum (Mo) and Copper (Cu) are the most important ones. They are usually present in sufficient amounts in organic fertilizers and composts. This is also the case with sulphur from the previous group.
All these nutrients are found in small quantities in compost, potting soil and old farmyard manure. For this reason, it is not easy to go overboard with these fertilisers and relatively large quantities may be used. To meet the needs of the plant with concentrated products, one uses many small quantities of a compound NPK fertiliser with the addition of magnesium and lime.
The acidity or PH
Acid rain and the disappearance of lime from the soil through leaching and absorption by the plant are the causes of soil acidification. Acidic soils are detrimental to plant growth. Sand and peat soils are particularly affected.
In acid soils, many nutrients are blocked and thus cannot be absorbed by the plant.
A good lime treatment can remedy this. Preferably use soft and slow-acting carbonated lime, such as seaweed lime or magnesium lime. Soil sampling can advise on the amount of lime needed. Otherwise, stick to the amount stated on the packaging.
The degree of acidity is indicated by the letters pH (potential hydrogenium), followed by the number that indicates the correct acidity. PH7 is called a neutral soil. The lower the number, the more acidic the soil. The higher the figure above pH 7, the more alkaline or calcareous the soil. The most suitable acidity for apples and pears on weak rootstock is a slightly acidic to neutral soil, i.e. pH 5.5 to 7. Pears on weedy rootstock require a slightly more acidic soil than apples.
Commercially available pH testers allow you to determine the approximate acidity of the soil yourself. However, if you want a complete picture of the nutritional state of the soil, you can consider a soil analysis. In addition to a correct statement of the acidity and humus content, you will also receive an overview of the content of the main nutrients, namely nitrogen, phosphoric acid, potassium (potash) and an accompanying fertilisation recommendation. As an enthusiast, you should preferably always use organic fertilisers.