Annually repeated traffic in delayed Miscanthus × giganteus harvests; effects on crop response and mitigation measures

Harvest traffic in Miscanthus can damage the crop if new shoots have emerged when trafficking occurs. This research was conducted in Miscanthus to determine the effects on crop response and soil compaction of annually repeated harvest traffic, applied before shoot emergence but after the initiation of new growth in the rhizome. Three treatments were used; (a) an untrafficked control, (b) trafficking with equipment that simulated the baler harvesting system (baler) and (c) trafficking with equipment that simulated the forager harvesting system (forager). The experiment was conducted on an Umbrisol at the Teagasc Crops Research Centre, Oakpark, Co. Carlow, Ireland in 2009 and repeated in 2010 and 2011. Effects on crop response were determined by measuring stem numbers, stem height, biomass yield and overall stem yield. Effects on soil compaction were assessed by measuring soil penetration resistance, bulk density and water infiltration rate. A comparative analysis was conducted on soil temperature data from sites across northern Europe to determine when growth was likely to begin each year and thus estimate when harvest traffic was likely to cause damage. An analysis of traffic patterns in both the baler and forager harvest systems was also conducted to determine which system was likely to minimise crop damage. Trafficked zone stem yield was significantly lower in 2011 (5.24 tdm ha−1) when compared with 2009 (11.17 tdm ha−1). Significantly lower stem yield was recorded in the trafficked zones of both the baler (5.98 tdm ha−1) and forager (6.01 tdm ha−1) treatments when compared with the untrafficked control (13.90 tdm ha−1). Soil penetration resistance and bulk density were significantly higher at a depth of 30 cm in 2011 (3.08 MPa and 1.82 g cm−3, respectively) when compared with 2009 (2.74 MPa and 1.58 g cm−3, respectively). Water infiltration rate was significantly lower in the baler (0.3 cm h−1) and forager (0.9 cm h−1) treatments when compared with the control (1.7 cm h−1). Across northern Europe the annual Miscanthus harvest should be completed by late March to minimise the risk of damage to new growth by harvest traffic. If delayed harvests are unavoidable, crop damage can be minimised by using the forager system because of its reduced traffic intensity (number of passes) when compared with the baler system.