Methods for measuring nutrient mineralization in growing media with organic fertilizers incorporated

The rate and timing of mineralization is a key factor in order to meet the plant's need for nutrients when using organic fertilizers in horticultural plant production. However, there is a lack in international standards for analyzing the plant available nutrients in growing media and organic fertilizers. In order to track the mineralization and uptake of organically bound nutrients from organic sources, an experiment including three different measurement methods was carried out. Plants (Capsicum annuum) were cultivated in a greenhouse in containers filled with peat-based substrate mixtures with incorporated organic fertilizers. Two different treatments were included in the study, one with dried pelleted chicken manure + Kalimagnesia (K-Mg-S: 25-6-18), and one with a pelleted vegetable fertilizer (composed of malt, vinasse, seaweed and potassium sulfate) + Kalimagnesia. Both treatments had the same initial content of N. No fertilizers were added during the cultivation period. The analysis methods used were i) total analysis of the growing medium (Dumas method), ii) analysis of plant available nutrients (Spurway analysis) and iii) leaf analysis (total analysis). Analysis revealed that at the start of the experiment, 3-30% of the nutrients in the growing medium were plant available (detected using Spurway extraction), depending on nutrient, with the lowest value for nitrogen and the highest for sulfur. At the end of the experiment, <0.01-13% of the total nutrients originally present in the growing medium had been taken up by the plants. There were still plant available nutrients in the growing medium at the end of the experiment, however, for nitrogen at low levels.