Document Type

Thesis - Open Access

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Master of Science (MS)

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The purpose of this study was to determine the effects of 1) plant growth stage at the time of initial harvest, 2) stubble height, and 3) frequency of harvesting on switchgrass herbage yields and carbohydrate reserves. The research site was located on the South Dakota State University Dairy Research Unit, 1 km north of Brookings. Climatological data were gathered at the Agronomy Research Farm, 3.2 km southeast of the experimental site. Average annual precipitation over the years 1893-1965 was 52 cm of which 80% or 41.6 cm occurred during the April to September period. Average annual temperature is 6 C. Monthly air temperature and precipitation data for the research period are presented in Tables 1 and 2. The soil is described as a Vienna loam with level to very gently sloping topography. Soil analyses gathered each fall showed the following information for the 1970 to 1972 period: organic matter, 3.3 to 3.9%; phosphorus, 70 to 155 kg/ha; potassium, 450 to 653 kg/ha; and pH, 7.3 to 8. 0. Fertilizer was applied on June 1, 1971 and May 31, 1972 at the rate of 72 kg/ha of elemental nitrogen. On May 28 and June 12, 1971, 0.83 kg/ha active ingredient of 2,4-D [(2,4-dichlorophenoxy) acetic acid amine was applied to the experimental area for broadleaf weed control. A similar application was made on May 17, 1972. The experimental design was a split-split plot with three replications. Growth stage at the time of initial harvest was the whole plot factor with the cutting stages being: 1) vegetative, 2) late jointing, and 3) 100% headed. Stubble height was applied to the first split at levels of 6.4 cm and 25.4 cm. The second split treatment, frequency of cutting after the initial harvest, had levels of 14 days and 28 days. All forage was harvested with a 1.6 m flail chopper equipped with a manual height adjustment. The machine was adjusted for 6.4 cm and all plots to be cut at that height were harvested. It was then set for 25.4 cm to cut the remaining treatments. Herbage was collected in a burlap bag held at the end of a spout extension. This galvanized stovepipe extension enabled an individual to carry the bag while walking behind the chopper. Initial harvests for 1971 were taken on June 17, when the grass was at 40.6 cm of vegetative growth, July 9 at the late jointing stage, and August 12 when the stand was 100% headed. "Headed" was defined as having any part of the panicle exposed above the flag leaf. At this stage there were numerous small tillers visible at the base of the plants. These were considered new growth and therefore not included in our classification.

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South Dakota State University