Small-Scale Mechanical Harvesting and Tractor-Caused Soil Compaction Reduce Early Growth in Sugarcane

Sugarcane is an important crop for sugar and biofuel production worldwide. It is mostly grown on hilly area by smallholders in China, which makes harvesting by a combine harvester impractical. Harvesting sugarcane by a small-scale harvester could be more practical. However, information about the impact of small-scale mechanical harvesting on soil compaction (SC), early growth and cane yield, and its yield components is still limited. The scarcity of quantitative information is equally true for the genotype and harvesting method interaction for traits describing early growth and final yield in sugarcane. Field experiments were conducted in a plant and two consequent ratoon crops (RCs) during 2016–2018 in Kaiyuan, Yunnan Province, China, to determine the impact of small-scale mechanical harvesting followed by tractor passages (SMH) on SC, sugarcane early growth and yield, and yield components, and to determine the genotype x treatment (harvesting methods, GT) interactions. The results indicated that, when compared to manual harvesting (MH), SMH significantly (p < 0.05) increased SC at 5, 10, and 20 cm depths by 0.6, 0.71, and 0.69 MPa for the first ratoon crop (RC), respectively; and increased by 1.4, 2.02, and 1.72 MPa at 10, 20, and 30 cm depths for the second RC, respectively. The amounts of underground bud bank (UBB) in RCs were nearly nine times the buds for establishing the plant crop (PC); positive correlations between the UBB and seedling counts were observed, with the highest correlations (r = 0.8453) occurring in May for the second RC. As compared with MH, stool damage and gaps were significantly higher in SMH; meanwhile, the UBB was lower in two RCs; the amount of seedlings, plant height, and height uniformity were significantly lower in SMH. Cane yield declined more in SMH, particularly declining by 20.59% from the first RC to the second RC. With respect to sugarcane production by SMH, the existence of significant GT interactions for stool damage, gaps, early seedling, millable stalks, and height uniformity at the maturing stage suggested that genotype selection trials should be conducted under the SMH rather than in MH.