Productivity of mechanized whip harvesting with the Stemster MkIII in a short-rotation coppice established on farmland

Abstract

The success of short-rotation coppice (SRC) will rise with increasing biomass prices. One of the main constraints for establishing SRC today is the unpredictable cost of (whip) harvesting. Therefore, the harvest of a 9 ha SRC in Belgium was monitored, in order to develop a whip harvesting cost model to estimate harvesting productivity and costs as a function of various input data. The harvest was executed in February 2017 with a Stemster MkIII, after a three-year rotation of SRC with poplar. A biomass inventory was combined with a time-motion study and an economic analysis. The field stocking (fresh weight basis) ranged from 40 to 100 Mg ha−1. The average load of 2.4 Mg was obtained from a 220 m long double row and took 6.4 min, resulting in an average productivity of 26 Mg h−1 (excluding delays). Genotype, field stocking and their interaction significantly affected the harvester's productivity. Border limited headlands (<8 m width) had a significant impact on turning time and, thus, increased the total harvesting cost by 6%. The offload time was stable at 23 s Mg−1, while the harvesting cost varied from 7 to 22 € Mg−1, depending on work conditions and costing assumptions. Even though the Stemster MkIII produces whips instead of wood chips, its productivity is still lower than the modified foragers' productivity, but the Stemster MkIII is lighter and may offer better mobility. Optimal performance can be obtained with a high field stocking, appropriate spacing and adequate headlands.