Evaluation and prediction of corn stover biomass and composition from commercially available corn hybrids
High consumption of imported energy in the United States and other countries has increased the interest in bio-renewable sources of energy. This interest has fueled research into crop residues as one potential alternative fuel source. At issue is how to balance economic viability with the sustainability of the endeavor.
The objective of this project was two-fold. The first objective was to quantify the amount and distribution of dry matter, moisture, fiber, and minerals in corn stover from a number of corn hybrids, grown at varying population densities. In this multi-year study we found that of the stover material remaining after harvest roughly 55% is found in the stalk and leaf material below the ear, 25% in the stalk and leaf material above the ear and the remaining 20% is found in the cob (12%) and husk (8%). The moisture, composition, and mineral concentration were significantly affected by year, planting density, and hybrid. Due to the highly variable quantities of biomass and the composition and nutrient concentrations within the stover fractions our guidance is to collect and analyze representative samples from each field level treatment in order to accurately predict stover constituents.
The second objective was to develop a predictive model which can be used to quantify corn stover biomass present on a given field. Harvest index (HI) values were calculated in order to evaluate their value in predicting stover biomass. However the significant variability observed in the two years tested limited the usefulness of this ratio in predicting stover biomass. Given the variation in HI, its utility as a stable, predictive measurement across years and productivity levels for the estimation of stover biomass is questionable. In the evaluation of HI in highly productive environments commercially available corn hybrids averaged 0.55 kg kg-1and can achieve HI levels of 0.60 kg kg-1. However, under stressful conditions these levels are significantly lower. Plant density is a significant variable for HI in stressful conditions.
Additional morphological measurements were collected for the development of an allometric model. A trend was observed for the fractions evaluated and a composite model fit the corresponding measured biomass with an adjusted R2 of 0.55. However, when the model was applied to the validation data set, very poor predictions were observed for each fraction and in composite.
The data gathered from this research, which was gathered and utilized to develop predictive models for the estimation of corn stover biomass, characterized a large amount of variation which exists across current corn production variables. To characterize this variation properly the data suggest adequate sampling across all field level variables is necessary to accurately predict corn stover biomass. If estimates must be made it is suggested to use conservative estimates of stover biomass, for example a HI ratio of 0.55 : 0.45 kg kg-1 of grain to stover. It is hoped that with this conservative estimate and other field level considerations such as slope and soil type that adequate residue remains on the soil to protect and build our natural resources in a sustainable manner.