Potato pulp as a composting substrate

Potato pulp is a waste, which is produced in considerable quantities by starch manufacturing industry. Addition of pulp fibre residue to soil results in beneficial effects on soil physical and biochemical properties. In this study, organic potato pulp was mixed with organic grass in three concentrations (75:25 (A), 50:50 (B) and 25:75 (C) % w/w) with the aim of comparing the dynamics of the composting process during a 30-day period. A mini-field experiment was conducted in 0.7 m³windrows which were left without covering and additional mixing during composting process, except sampling procedure. During 30-days' experiment the C:N ratio decreased from 25÷30 to 13÷17 indicating the active conversion of organic matter in windrows with three different combinations of the substrate. An increase of grass concentration led to an increase of the temperature in the windrow at the thermophilic phase of the process. This effect can be explained by higher porosity of the composting substrate containing 75% grass and 25% (w/w) potato pulp. Fourier transform infrared (FT-IR) spectra of compost water extracts indicated the heterogeneity of compost. The water content in two windrows was 59÷75% and 81÷86%, respectively, thus indicating considerable differences in the dynamics of physico-chemical and microbiological processes. The order of earthworms' preference for compost samples can be listed as follows: A < C < B. Therefore, the ratio potato pulp:grass as 1:1 could be considered as the most optimal under the tested conditions.