Productivity of new harvester prototype in willow plantations with different growing stock

A prototype of a mower-chipper type harvester was developed for cutting small stems in cooperation between LSFRI Silava and SIA Laflora. The prototype produces chips and eco-pellets of various lengths in short rotation coppice, shelter belts and overgrown agricultural lands. The innovative element of the harvester is use of gravity force (bending of stems by a tractor own weight and formation of bunch of shoots with header and underframe) to feed in circular saws and chipper, thus significantly reducing energy demand for bending of shoots into the chipper, which is the most energy demanding operation in other commercial willow harvesters. Time studies were implemented in Skrīveri region in August 2022 in short rotation coppice fields established in 2011. Willows of tree different ages (1, 3 and 5 years) were harvested. The main factor influencing productivity in the study sites was growing stock of the coppice crops. The driving speed of the base machine cannot be significantly increased to avoid clogging of the chipper infeed and to retain good quality of chips; therefore, reduction of growing stock cannot be compensated with faster driving in the field. It was also noted that wood chip quality becomes significantly worse if the stump diameter of an average shoot is less than 1 cm and the saw blades are more often blocked by thin, flexible shoots. Similarly, clogging related issues were found in the 5 year old plantation. Optimal work conditions were in the 3 year old coppice crop; however, the driving speed of the base machine (MTZ82 tractor) was still too high. The recommended speed in such conditions is 0.8–1.2 km·hE−1. The yield obtained in the tests under these conditions in the 3 year old coppice crop was 2.4 tons of dry matter per hour. The productivity could be raised by increasing the power of the base machine. There is still space for technical improvements to avoid clogging of material in the chipper and jamming of saw blades, as well as to improve the quality of chips.