A large amount and consistent supply of seed is needed if switchgrass becomes a major cellulosic biofuel crop in the U.S. Good management practices are critically important for producing good yields of high quality seed. Most switchgrass seed is produced in the central and southern Great Pains, including Oklahoma, as part of traditional farming practices. The dry weather in August and September in Oklahoma is conducive for producing highquality switchgrass seed.
Burning crop residues, which helps switchgrass green up early, can be performed in February each year before switchgrass starts to grow. Burning fields also helps control the few weeds in mature stands. Fertilization with 50 to 100 lbs N/acre each year is important for good seed production. Fertilizer works best when applied in the spring after plants have started to grow for two or three weeks. Phosphorous and potassium should be applied if soil tests indicate available soil P and/or K are low. Generally switchgrass does not need irrigation, but some supplemental water may be beneficial during the period of seed development under drought conditions.
In Oklahoma, emergence of switchgrass seedheads varies, primarily due to different ecotypes and varieties. For example, emergence of seedheads of upland varieties starts in late June or early July. However, inflorescences of lowland varieties come out in August. Normally, upland switchgrass seed matures in August, while lowland switchgrass seed is ready for harvest at the end of September or early October. Additionally, the variety Kanlow seed matures about two weeks earlier than Alamo, both lowland switchgrass types.
A switchgrass panicle (seedhead) with ripe seed.
Switchgrass seed can be produced in solid- seeded stands or in specialized row plantings. Row plantings tend to produce more seed than solid stands. Row widths of 15 to 40 inches can be highly productive. Switchgrass plants are likely to lodge if row spacing is less than 12 inches. Likewise if rows are wider than 45 inches, seed yields in the first few years tend to be relatively low.
Switchgrass growing in 40-inch rows for seed production.
Switchgrass seed is
harvested by directly combining the standing maturing crop
or by first windrowing the crop and then combining the windrowed crop after the panicles have dried for a few days.
Switchgrass seed crop may be directly combined in the field.
Switchgrass seed crop may be windrowed with a swather.
The optimum time to harvest is when most of the spikelets have mature seeds and a few seeds are beginning to shatter from seedheads. The main advantage to direct combining is one less operation across the field is required. The windrow harvesting method allows cutting while stems are still green and before seed begins to shatter. Seed shattering in some lowland switchgrass varieties can result in total seed loss. Following the harvest, seed must be conditioned in preparation for sale. Conditioning involves removal of trash, weed seeds, other crop seeds, and other materials. Seed yield of switchgrass varies from 150 lbs/acre in the first year post establishment, to approximately 300 lbs/acre when stands are fully established. Under ideal conditions, seed yields could potentially be much higher.
Alamo switchgrass seed is completely shattered from
inflorescences by the third week in November in Stillwater, Okla.
View from combine of switchgrass as it is harvested
for seed next to an area already harvested.
View from combine of switchgrass as it is harvested for
seed next to an area already harvested.
Switchgrass stubble after seed harvest.
To assure the variety identity, genetic purity, and high quality of seed sold to consumers, seed producers are encouraged to produce certified switchgrass seed. Oklahoma Crop Improvement Association (http://okcrop.com/) is the seed certifying agency in the state.