Optimal plant nutrition ensures healthy plants and economically successful plant cultivation with high yields and good harvest quality. However, the precondition for this is balanced and demand-based fertilization. It must be remembered that plant nutrition and plant health are mutually dependent! A sick plant cannot make efficient use of even the best nutrient supply and turn it into yield and quality. On the other hand, nutrient deficiencies – and also significant nutrient surpluses – lead to increased susceptibility to diseases and pests and/or plant stress.
Plant diseases do not necessarily cause complete failure of the plants. Often they only lead to a temporary loss of assimilation area (e.g. mildew in cereals). A good supply of nutrients to the plant is thus the basis of a high regeneration capacity. In addition, the supply of nutrients of a plant can also directly influence susceptibility to pathogens and pests and/or the formation of the plant’s own antibodies.
Sulphur and boron strengthen resistance
The supply of nutrients can also directly influence susceptibility to pathogens and pests and/or the formation of the plant’s own antibodies. A telling example is the plant’s supply of boron. In addition to its involvement in the development of cell walls and membranes, boron also plays an essential role in the formation of the plant’s own antibodies, known as phytoalexins. These make plants more resistant, for example to fungal pathogens. A good supply of boron thus not only protects sugar beet from the dreaded heart rot, it can also contribute to plant health in cereals.
Another interesting example is sulphur, an essential nutrient and as such involved in a number of metabolic processes in plants. An inadequate supply of sulphur has a direct effect on the yield, quality and health of plants. An example of this is sulphur induced resistance (SIR). This denotes the reinforcement of the natural resistance of plants to diseases through targeted sulphur fertilization.
The fungicidal effect of sulphur has been known for over 100 years and is one of the most efficient remedies for powdery mildew in vines. By comparison, in SIR research, sulphur is added to the soil as sulphate. The aim is to increase the influence of individual sulphur-containing metabolic products in the plant on the plant’s defence mechanisms against pathogens. If it is successful in effectively improving the plant’s defence mechanism through optimised sulphur fertilization (in combination with pesticides if necessary), sulphur fertilization may contribute to increasing vitality. SIR thus potentially represents an effective instrument for protecting plants against diseases, both in conventional and organic farming.
This is acknowledged for example for the boron supply of plants. In addition to its involvement in the development of cell walls and membranes, boron also plays an essential role in the formation of the plant’s own antibodies. These make plants more resistant to fungal pathogens. A good supply of boron protects for example sugar beet from the dreaded heart rot, and can also contribute to plant health in cereals.
Nitrogen surpluses can bring poor results
Not only nutrient deficits, but also nutrient surpluses can have negative consequences for plant health. Nitrate nitrogen for example, unlike ammonium nitrogen, cannot be selectively absorbed, but is taken up consistently with water. If the nitrogen cannot be immediately transformed in the plant to ammonium or further to amino acids and finally to proteins, it is stored in vacuoles. A high nitrate concentration in the leaves is then coupled with very high susceptibility to obligate parasites such as mildew and rust. Furthermore, an oversupply of nitrogen leads to dense crops which dry poorly and are thus more susceptible to disease.
Particularly with micro-nutrients, supply deficiencies can occur even with high levels in the soil.
In addition, it may be that plants show deficiencies, particularly of manganese, zinc or boron in spite of high levels in the soil. This lack of nutrients is often caused by unfavourable local conditions such as excessively high pH values or excessively low soil moisture. This can lead to the temporary or permanent determination of [a lack of] micro-nutrients. In the short-term, a latent or acute lack of nutrients may be remedied by foliar fertilization measures. Moreover it is possible to boost the acidity of the soil slightly and thus bring about an increase in the availability of micro-nutrients.
