The aim of the experiment was to compare and estimate (i) the water retention capacity of granule/sand mixtures of different proportions and (ii) absorption of the most important nutrients (NPK) provided by the granules.
L100 – 100% sand, GR100 – 100% granule, L25 – 25% sand and 75% granule, L50 – 50% sand and 50% granule, L75 – 75% sand and 25% granule.
- L100 had the lowest water retention capacity, 23% of initial dry sand weight of water was absorbed. GR100 had the highest water retention capacity with the largest amount of water absorbed (876% of initial granule weight).
- The fastest water loss happened in L100, where all added water had either drained or evaporated from the test pot by day 14. Water loss was slower in test pots with a higher granule proportion and about 30% of the amount of water added was still present after two weeks.
- Out of the main plant nutrients, the concentrations of nitrogen and potassium in the granule drainage were 100% and 90% respectively. However, the concentration of phosphorus in the drainage was only 17%.
- In the case of NPK complex fertilizers, the mobility of larger potassium and phosphorus compounds, which are less soluble in water, may be slowed down significantly in 100% granular substrate.
- For fertilization, it can be assumed that about 100% of the nitrogen applied to the substrate reaches the plants. In the case of phosphorus and potassium, only one-fifth of the amount in the granules may be available to plants.
Estonian University of Life Sciences, Chair of Crop Science and Plant Biology