Precision of sugarcane biomass estimates in pot studies using fresh and dry weights

Authors: Zhao, Duli; Glaz, Barry; Edme, Serge; Del Blanco, Isabel

Submitted to: American Society of Sugar Cane Technologists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2010
Publication Date: 5/3/2010
Citation: Zhao, D., Glaz, B.S., Edme, S.J., Del Blanco, I.A. Precision of sugarcane biomass estimates in pot studies using fresh and dry weights. American Society of Sugar Cane Technologists. 30:37-49. 2010.

Interpretive Summary: Measurements of biomass of sugarcane components are generally calculated as fresh weight for field experiments. For sugarcane pot studies that harvest plants before they become too large, often dry weight rather than fresh weight is measured under the assumption that dry weight provides a more precise estimate of treatment effects. However, particularly for stalks, measuring dry weight can be difficult and time consuming. The purpose of our research was to compare experimental precision of fresh and dry weights on sugarcane green and brown leaves and on stalks. We conducted four pot studies with 2-6-month-old plants from 2005 to 2009 with each experiment being a combination of some of the following treatments: genotype, crop cycle (plant-cane or first ratoon), water-table depth, water availability, soil type, or nitrogen fertilizer rate. We measured fresh and dry weights of green leaves, brown leaves, and stalks and calculated their dry to fresh weight ratios. Analyses of variance, regression, and estimates of coefficient of variation and repeatability were used to compare treatment responses and evaluate experimental precision. Except for the water-availability treatment, dry weight to fresh weight ratios ranged from 28 to 29% for green leaves, from 17 to 20% for stalks, and from 39 to 64% for brown leaves. Treatment responses were generally similar for fresh and dry weights for all parameters. Similar coefficients of variation and highly significant regressions were consistently found between fresh and dry weights. Repeatability values were generally low for all traits, but similar between fresh and dry weights. Therefore, measuring biomass as fresh weight in sugarcane pot studies would save substantial resources and obtain comparable experimental precision as measuring dry weight.

Technical Abstract: Sugarcane (Saccharum spp.) field studies generally report fresh weight (FW) rather than dry weight (DW) due to logistical difficulties in drying large amounts of biomass. Pot studies often measure biomass of young plants with DW under the assumption that DW provides a more precise estimate of treatment effects than FW. The purpose of our research was to compare experimental precision of FW and DW measurements on sugarcane green and brown leaves, and on stalks in pot studies. Four pot studies harvested after 2-6-months growth were conducted at Canal Point, FL from 2005 to 2009 with each experiment being a combination of some of the following treatments: genotype, crop cycle (plant-cane or first ratoon), water-table depth, water availability, soil type, or N rate. For green leaves, brown leaves, and stalks, we measured FW and DW, and calculated DW:FW ratio. Analyses of variance, regression, and estimates of CV and repeatability were used to compare treatment responses and appraise experimental precision. Except for the water-deficit stress treatment, DW:FW ratios ranged from 28 to 29% for green leaves, from 17 to 20% for stalks, and from 39 to 64% for brown leaves. For all parameters, treatment responses were generally similar for FW and DW. Similar CVs and highly significant regressions (r2 = 0.74-0.99****) were consistently found between FW and DW. Repeatability values were generally low for all traits, but similar between FW and DW. Results suggest that measuring biomass as FW rather than DW would save substantial resources in conducting pot studies.