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.
A pot study was conducted to investigate influences of salinity on sugarcane (Saccharum spp.) plant growth, leaf photosynthesis, and other physiological traits during tillering and stalk elongation. Treatments included two commercial sugarcane cultivars (Canal Point (CP) 96-1252 and CP 00-1101) and an Erianthus with five different soil salt concentrations (0 [Control], 38, 75, 150, and 300 mM of NaCl added). Growth (tillers, plant height, and nodes) and physiological (leaf net photosynthetic rate [Pn], stomatal conductance [gs], intercellular CO2 concentration, and leaf water soluble sugar concentrations) characters were determined during the experiment. Responses of sugarcane growth, photosynthesis, and photoassimilate translocation to salinity depended on soil salt concentration. Plant height was the most sensitive while the number of nodes was the most tolerant to soil salinity among the three growth traits measured. CP 96-1252 differed from CP 00-1101 significantly in response of shoot:root ratio to high salt concentration. Leaf Pn of plants treated with the 38 mM salt did not differ from that of the control plant, but plants treated with the 75, 150, and 300 mM salt had 12.7, 18.7, and 35.3% lower leaf Pn, respectively, than the control. The low leaf Pn due to salinity was associated with not only the decrease in gs, but also the non-stomatal factors. Results of leaf sugar composition and concentrations revealed that high salt concentration also depressed photoassimilate translocation from leaves to other plant tissues. These findings are important for better understanding of some physiological mechanisms of salinity influence on sugarcane growth and yields.
The relationship between natural defoliation rate and endogenous ethylene, indole-3-acetic acid (IAA), and abscisic acid (ABA) levels in four sugarcane cultivars possessing different defoliation traits was investigated. Leaf sheath, leaf scar, and leaf blade samples were collected from the 10th leaf position below the fully expanded leaves during sugarcane maturation stage. Ethylene, IAA, and ABA levels were measured using gas chromatograph, liquid chromatograph, and external standard methods. The results showed that during sugarcane maturation, the highest natural defoliation rate was observed in CYZ03-194, followed by CYZ01-1413, CMT02-467, and CYA99-91. Ethylene production and IAA levels in the leaf scars, leaf sheaths, and leaf blades were the highest during the early-to-mid-maturation stage and decreased afterwards. The ABA levels showed a mono-peak curve change and peaked at the late-to-mid-maturation stage. Ethylene production in leaf scars during the early-to-mid-and midmaturation stages as well as ABA levels in leaf scars at the late-to-mid-maturation stage significantly differed among the cultivars, with the highest levels in CYZ03-194, followed by CYZ01-1413, CMT02-467, and CYA99-91. On the other hand, the IAA levels in leaf scars and leaf sheaths at the early-to-mid-maturation stage were highest in CYA99-91, followed by CMT02-467, CYZ01-1413, and CYZ03-194. Correlation analysis demonstrated a positive correlation between the natural defoliation rate and ethylene production, ABA level, ethylene/IAA ratios, and ABA/IAA ratios, whereas a negative correlation was observed with IAA level during the early-to-mid-and midmaturation stages.
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