Switchgrass for bioenergy

 Article summary

INTRODUCTION

Switchgrass can be used as a bioenergy crop. It holds up well to drought and flood, and has less of a need for herbicide and fertilizer. It grows in poor soil and rough climates, and adapts well to changes in its environment. It is also a good choice for carbon sequestering. It has demonstrated a higher carbon yield than other crops like corn, soybean, alfalfa, and reed canarygrass. Switchgrass also works well as a cover crop between planting seasons because it keeps the soil in place when it rains, due to its deep root system.

MATERIALS AND METHODS

The Cave-in-rock switchgrass was planted on a small patch of farmland near Ligonier PA, about 42 miles east of Pittsburgh. Perennial grasses were grown there for the previous five years. They prepared the land by spraying to prevent woody weeds from growing and cut the vegetation with a rotary mower. Then they planted an oat cover crop to try and prevent weeds from taking over, but it didn’t work so they had to completely till the soil and plant winter wheat. The switchgrass’ moisture content was determined by weighing bales that were oven dried at 55° C. CO₂ and water vapor were measured on a daily basis and recorded as a weekly average in graphs.

RESULTS

The older the switchgrass got, the more biomass was available to be harvested. The ecosystem respiration decreased substantially in the first three years and soil moisture gradually increased at the deeper depths measured. The efficiency of water use also stabilized.

DISCUSSION

142g CO₂/m²/yr but mature stands are able to sequester as much as 440-3700g CO₂/m²/yr. When the soil is tilled repeatedly over many years it can reduce its organic carbon content by over 50% in comparison to having a permanent crop of plants growing. Even tilling the land once can make a significant loss of carbon held in the dirt. CO₂ isn’t the only greenhouse gas, N₂O also affects the environment, however it was not taken into account with this experiment. The switchgrass was harvested before the spring because it’s the driest at that time so it weighs less which makes it cheaper to transport and easier to burn for energy. It also reduces the amount of nutrients removed from the soil, since when plants go dormant for the winter they put all their nutrients in their roots.

 CONCLUSIONS

Aside from growing switchgrass for bioenergy, it can also sequester carbon dioxide into the soil. It uses less water than other crops that can be used for the same reasons, and is more efficient at using that water. Another thing I found out looking around online was that a genetically modified switchgrass is able to produce polyhydroxybutyrate, which is a nontoxic, biodegradable polyester plastic, which I also thought was pretty cool.

Source

Carbon dioxide and water fluxes from switchgrass managed for bioenergy production. By R. Howard Skinner, Paul R. Adler. Published in Agriculture, Ecosystems and Environment. June 18 2010