Yield and quality responses of summer annual grasses to different management regimes

Author

Rodney J. Creel

Date of Award

12-1978

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Henry A. Fribourg

Committee Members

John H. Reynolds, Daniel L. Coffey

Abstract

Sorghum-sudangrass hybrids (Sorghum bicolor (L.) Moench) and improved pearlmillets (Pennisetum americanum (L.) Leeke) produce large amounts of forage in summer when most cool season forage crops have slowed production.

To determine some plant and environment characteristics and the extent of cultivar x management interaction over a broad spectrum of managements, four summer annual grass cultivars were subjected to 19 different defoliation frequency and stubble height managements at Knoxville, Tennessee in 1976 and 1977. The cultivars were Chowmaker 235, Sweet Sioux III, FS-531 sorghum-sudangrass hybrids, and Millhy 99 pearlmillet. The plots were sidedressed with nitrogen (N) twice during the summer and two samples were taken at each harvest, one large one to determine DM production, and a smaller one for determination of leaf area, dry weights of representative parts, meristem heights, N content and in vitro dry matter digestibility (IVDMD). Predictive models were developed for yield at each harvest, regrowth per day (kg/ha/day), total N percent and IVDMD.

Quality, morphological characteristics, and quantity of DM produced varied with year, management, and cultivar. The sorghum-sudangrass hybrids outyielded the pearlmillet when harvested later than the 90-cm height, but high quality and similar yields (10 metric tons/ha) were obtained when harvested at 90 cm.

When cut at 90 cm, stubble heights of 15- or 8-cm had no effect on yields or IVDMD, and resulted in similar N content. However, a 90-cm harvest cut to 15— or 8-cm stubble before a boot or early bloom harvest resulted in greater season yields for Chowmaker than for Sweet Sioux. Generally, Chowmaker performed best when cut to 15-cm stubble, and Sweet Sioux when cut to 8—cm stubble, when the stage of growth at harvest was earlier than the boot stage.

The pre-boot, boot or early bloom harvests were delayed by a previous 90-cm harvest for all cultivars, and N content sometimes was increased. A previous 50-15 cm harvest before an early bloom or boot harvest delayed the early bloom and boot harvests of FS—531, but did not delay those of the other sorghum-sudangrass hybrids and pearlmillet. These had greater N content as a consequence of the previous cut. The first pre-boot stage harvest of Sweet Sioux following a 50-15 cm harvest also had a larger N percent than the first pre-boot harvest of plants managed 'PB-15'. Material harvested at more mature or taller stages of growth were low in total N percent but relatively high in IVDMD.

The number of days since March 1, average plant height and the number of days during regrowth all were important predictors of harvested yields, daily regrowth, total N and IVDMD. These four dependent variables were increased as the number of days during growth increased, except for the daily regrowth in the Chowmaker model. As average plant height at harvest increased, yields and daily regrowth increased, but N percent and IVDMD generally decreased. The number of days of regrowth generally increased yields and decreased all the other dependent variables.

Chowmaker plants performed best when growth before the boot stage was cut to 15-cm stubble. The performance of plants generally was related to rainfall, and many of the managements studied were suitable. Management '50-15, EB-8, 75-15' was favorable for quality and yield. Sweet Sioux plants performed best when growth was cut to 8 cm, and the dependent variables were related not only to the three independent variables listed above, but also cumulative rainfall and temperature.

The number of days of regrowth was related to all the dependent variables for FS-531. FS-531 plants yielded more than other cultivars when allowed to reach taller stages.

In addition to the number of days since March 1, the number of days for regrowth, and average plant height, leaf area of the stubble also were important in the Millhy models. This cultivar was not responsive to management.

Recommended Citation

Creel, Rodney J., "Yield and quality responses of summer annual grasses to different management regimes. " Master's Thesis, University of Tennessee, 1978.
https://trace.tennessee.edu/utk_gradthes/7929