Tech Tuesday

Reviewing Biomass Yield

Study looks at a key biomass crop in detail and identifies the switchgrass "sweet spot" for the U.S.

There's been a lot of research done on biomass from crops targeted for the future biofuels industry, but so far little work has been done with that information to evaluate the response of biomass yield to soils, climate and crop management...until now. A team of researchers from Oak Ridge National Laboratory and Dartmouth College published a study - released today - for the July-August 2010 Agronomy Journal from the American Society of Agronomy. The researchers used peer-reviewed publications to evaluate switchgrass yield as it relates to site location, plot size, stand age, harvest frequency, fertilizer application, climate and land quality. Switchgrass is considered by many to be a key player in the biomass crop arena for the future.

Looking at 1,190 yield observations for both lowland and upland types of switchgrass grown from 39 field sites across the United States, the researchers pulled date from 18 publications that reported on field trials in 17 states. Among the factors examined, statistical analysis revealted that much of the variation in yield could be accounted for by variation in growing season precipitation, annual temperature, nitrogen fertilization and the switchgrass type.

Lowland switchgrass was a yield winner at most locations, except in northern latitudes. Annual yields averaged 12.9 metric tons per hectare (or about 6 tons per acre) for lowland varieties and 8.7 metric tons for upland ecotypes (or about 4 tons per acre). In some locations of Alabama, Texas and Oklahoma, there were reported biomass yields topping 28 metric tons per hectare with lowland cultivars (about 13 tons per acre).

One field in the study topped 39 metric tons per hectare (more than 17 metric tons per acre) in an area with high fertilization (200 pounds of N per acre) and in a year with high precipitation.

The research also shows that switchgrass will respond to N applications noting that even though there was yield variability across the reviewed data. they note that for lowland ecotypes of switchgrass, the optimum use of N is about 100 pounds per acre - however in many cases zero-fertilized plantings did as well as fertilized plantings. Upland ecotypes also respond to N use at about the 100 pounds per acre range, but above that yields dropped off.

It appears timely rains have a key role to play as well. For example, in the high yields researchers found in five east Texas locations, rainfall from April to September was high.

Researchers didn't observe any bias for higher yields associated with experimental plot size, row spacing or with preferential establishment of stands on high quality lands. Using a model developed from the data, based on long-term climate records, they projected top yields in a corridor westward from the mid-Atlantic coast to Kansas and Oklahoma. Low precipitation west of the Great Plains limited yield in that region.

The researchers say findings showing no bias for plot size or land productivity is important. They see promise in applying their model to additional bioenergy crops at a global scale in combination with a range of land-use scenarios.

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