Structural differences in wheat (Triticum aestivum), hemp (Cannabis sativa) and Mischanthus (Mischanthus ogiformis) affect the quality and stability of compost as growing medium

Summary

Physical properties as well as process parameters were examined in three different composts based on plant residues. The wheat compost was a mixture of clover-grass and wheat straw in a ratio of 3:5, the Mischanthus compost was composed of the same materials and contained Mischanthus straw in addition in a ratio of 3:2.5:2, and the hemp compost was based on clover-grass, wheat and hemp straw also in a ratio of 3:2.5:2. The wheat and Mischanthus composts both had an initial C/N ratio of 26 and process parameters such as nitrogen losses and mineralisation pattern did not differ between the two compost types. The hemp compost had a much lower initial C/N ratio of 16 as the hemp straw was harvested fresh, resulting in higher losses and more mineralised nitrogen during composting. Particle size distribution was determined by image analysis of scanned samples. No differences were observed between the percentages of particles in the selected length intervals, however the largest number of particles was observed in the Mischanthus compost. Particles in the hemp compost had more uneven surfaces than the other composts and had the highest water retention capacity. Thus, the geometry and surface characteristics of the particles and the pores created are important in determining suitability of plant based growing media.