5.1.7. The dilution effect

Often there is one apparent limiting factor for crop growth as recognised by Justus von Liebig (1803–1873) for nutrients. If this limiting factor is removed the crop might directly run into a second limiting factor or growth will be increased. When the crop shows fast growth, present nutrients will be “diluted” that is more carbon, oxygen and hydrogen molecules (carbohydrates, water) relative to the mineral and more complex phytochemicals, i.e. growth and defence machinery, will be produced. This “dilution effect” arises when cultivation practices become more optimal and could thus arise from improvement of each and every one of the cultivation practices mentioned in this document. Figure 5.3 provides a nice example of the “dilution effect” of additional CO₂. Especially in mineral nutrition the dilution effect is a well-known phenomenon. It might even result in very counter intuitive results. For example, a plant has a shortage of mineral X as identified by its retarded growth and determined by dry matter analysis. When mineral X is supplied in higher quantities this might result in a dramatic plant growth response leading to further diluted concentrations of mineral X in the dry matter. In other words, fertilisation of the plant deficient mineral might lead to a decrease of that same mineral in the edible plant parts. A very good paper on the dilution effect in agriculture has been written by Jarrell and Beverly (1981).