Evaluation of Nitrogen Response Pattern Between Early-Season Biomass Production and Biomass Yield at Harvest in Energy Cane.

The concept of using optical sensors to estimate energy cane yield potential based on canopy reflectance readings early in the season adopts the premise that biomass production at early growth stages is related to yield level at harvest.  This study was conducted to evaluate the nitrogen (N) response pattern between early-season biomass production and total biomass yield at harvest. An experiment was initiated in 2013 at the LSU AgCenter Research Station in St. Gabriel, Louisiana. The experiment layout was split plot in randomized complete block design using two varieties (Ho 02-113 and US 72-114) as main plots and four N rates (0, 56, 112, and 224 kg N ha^-1) as sub plot treatments with four replications.  Biomass samples were taken from a 1-m long section of each plot at three, four, and five weeks after N application. At harvest, a single-row chopper harvester with a loader was used to cut and discharged stalks to a wagon fitted with load cell. The proportion of leaves and stalks was estimated from 15 randomly selected plants from each plot. No effect of N was observed on early-season biomass production across sampling dates in 2013. However, this lack-of-response to N was not reflected at harvest. Nitrogen uptake of both varieties was significantly increased at N application rate of 224 kg ha^-1 while increase in total biomass yield at the same rate of N fertilizer was observed only on variety Ho 02-113. The high rate of lodging of US 72-114 may have contributed to the lack of biomass yield in response to N application. The effect of N has not reached its full potential by the time the early-season biomass sampling was initiated which could partly explain the lack of similarity on N response pattern between early-season and at harvest biomass yields.