Educational garden Nutrient deficiency and lime requirement

Fertilisation trial in the Educational garden

The fertilisation trial on display in the Educational garden shows the influence of omitted fertilisation with the nutrients nitrogen (N), phosohor (P) and potassium (K) as well as the influence of omitted liming. There are six experimental variants with different mineral fertilisation:

(1) full fertilisation, (2) without N, (3) without P, (4) without K, (5) without lime, (6) no fertilisation

The trial is embedded in a three-field crop rotation:

(1) Silage maize, (2) winter wheat, (3) winter rape

The experiment is repeated three times in the field (so-called block system with three blocks). In each of the three blocks, the crop rotation is offset by one year, so that all three crops are seen each year. In each block there are all six trial variants with different mineral fertilisation in random order:

Block system in 3 blocks

Statistical analysis

Every three years, i.e. at the end of each crop rotation, the experiment can be precisely evaluated statistically. Plant and soil data of the six fertilisation variants are compared with each other. Important data are the yields and the contents of nutrients in plants and soil.

pH value, soil acidification and liming

The pH value here is a measure of the acidic or alkaline character of the soil solution, i.e. the water in the soil with the substances dissolved in it.

The pH value influences many biological, chemical and physical properties of the soil. In addition, the availability of plant nutrients in the soil depends on the pH value. Thus, the pH value is a central indicator for soil fertility.

Under our humid climatic conditions, lime-free soils become increasingly acidic (soil acidification). The pH value decreases over time. This is a natural process. Any form of agriculture increases natural soil acidification.

Lime neutralises the acids formed. Regular liming stops acidification and can even reverse it if necessary.

Plant nutrients and fertilisation

17 chemical elements are vital for plants (essential nutrients). The elements carbon (C), oxygen (O) and hydrogen (H) are absorbed as gases or as water. All other nutrients are mainly taken up by the roots from the soil water as dissolved salts (minerals). The nutrients thus removed from the soil are replaced by regular fertilisation. Mineral fertilisers return nutrients to the soil as salts (minerals). Nutrient elements in organic fertilisers (e.g. in manure) must first be mineralised into minerals by microorganisms in the soil before they can be absorbed by plant roots from the soil water. Nitrogen (N), phosphorus (P) and potassium (K) are the most important nutrients in mineral fertilisation. They have important functions in plant metabolism:

N:  Component of all proteins and many other organic compounds in the plant's metabolism. ...

P:   Very important for the energy metabolism of every living cell. Component of the genetic material and cell membranes. ...

K:  Among other things, it plays a central role in the water balance of the plant. ...

Visual analysis

In addition to the exact statistical analysis, a simple visual analysis can also be carried out by laypersons by simply observing. Differences in plant height, in the appearance of the plants, differences in colour and the death of plant parts (necroses) can indicate nutrient deficiency or too low pH values in the soil. In addition to differences in the height of the plants, typical symptoms may be observed:

Nitrogen (N) deficiency: yellow discolouration of older leaves or of the whole plant (chlorosis).

Phosphorus (P) deficiency: purple discolouration (antocyanin discolouration) on stems (maize) and leaves (rape)

Potassium (K) deficiency: Unusually strongly upturned leaves in maize (stiff growth habit), limp leaves during drought (lack of turgescence), death of leaf edges (leaf margin necroses).

Lack of liming: mixture of different symptoms, as many nutrients and soil properties are indirectly affected.

The trial was established in 2018 on a site with a sufficient supply of nutrients. In the first years after the trial has been established, clear symptoms of nitrogen (N) deficiency are to be expected. In the following years, phosphorus (P) deficiency and potassium (K) deficiency are to be expected. Only with strongly decreasing pH values will the lack of liming become noticeable.