2002 Cutting Height Study Data

Cutting Management for Brown MidRib Sorghum Sudangrass


Thomas Kilcer1, Paul Cerosalletti1, Peter Barney1, Alice Pell2, Denis Molina2,

Quirine M. Ketterings3, J.H. Cherney3

1Cornell Cooperative Extension, 2Dept. of Animal Science, Cornell University,

3Dept. of Crop and Soil Sciences, Cornell University



In a study at the Valatie Research Farm in 2000 we found considerable changes in feed quality parameters with delay in harvest of brown midrib sorghum sudangrass hybrids. A field trial conducted in 2001 in Delaware County (see the article by Cerosaletti and others in “What’s Cropping Up?” (2002) 12(3): 1-3) showed that for optimum quality stand heights should not be greater than approximately 54 inches. The objective of the 2002 research trials was to determine if dry matter production and yield quality could be improved when stand heights were shorter than 54 inches.

Materials and Methods

        In 2002 growing season height at harvest studies were established at three locations: 1) St. Lawrence County (P. Barney), a northern-cold lake-laid silt in northern NY; 2) Delaware County (two trials called P. Cerosalletti-1, and P. Cerosalletti-2), glacial outwash in high cool elevation; and 3) Columbia County (Kilcer), an excessively drained, outwash gravel in a low elevation-warm location, in eastern NY (Figure 2). Complete randomized block designs were used. The P. Barney site was planted using a Tye drill. The two Cerosalletti sites were planted with a farmer’s grain drill while the Kilcer site was planted with a John Deere drill with press wheels. Plot size was 12 ft. x 12 ft. with 3 ft. x 5 ft. of harvest area oriented north-south in the upper center of each plot. This was to provide a 4.5 ft buffer on the east, south, and west, to avoid shading of harvest area by neighboring plots. Each plot received the equivalent of 150 lbs N, 26 lbs of P2O5 and 90 lbs of K2O before planting. At each location, five harvest heights (30, 36, 42, 48, and 54 inches) were implemented on each of four replications. Harvest was taken when the tallest plots of the four replications were at the required height as measured at the horizontal curve of the tallest leaf. A 3.5-inch cutting height was used with hand harvesting. The biomass on the rest of the plot was removed after sample harvest. The re-growth was re-fertilized with 150 lbs of nitrogen (ammonium sulfate - 21%N) and harvested when it again reached the correct height. Plant height, stem counts, yield and dry matter content were taken at each harvest. All samples were analyzed for total N, P, K, Ca, Mg, lignin, sugar, non-structural carbohydrates (NSC), neutral detergent fiber (NDF), digestibility of neutral detergent fiber (dNDF at 30 hr), and in vitro total digestibility (IVTD at 30 hr) at the forage laboratory of Dairy One Cooperative Inc. in Ithaca, NY.  Milk2000 version 7.4, a software model developed at the University of Wisconsin was used to estimate milk yields in lbs per ton and in lbs per acre. We used the alfalfa-grass Milk2000 worksheet with standard values for neutral detergent insoluble crude protein (NDICP; 2.4% on a dry matter basis) and ether extract (3.6% on a dry matter basis) as reported for sorghum Sudangrass silage in the 2001 Nutrient Requirements for Dairy Cattle (National Research Council, 2001). The 30 hour dNDF was multiplied by 1.16 to obtain an estimate of the dNDF at 48 hours (J.H. Cherney, unpublished, 2003).

Dr Pell of Department of Animal Science, Cornell University, randomly selected samples from a range of heights from all three locations. For each of the selected samples, the unfractionated forage and its isolated NDF were fermented in vitro using the computerized gas measuring system of Pell and Schofield (1993), with the modifications described in Schofield and Pell (1995). This protocol was repeated in two different days using inocula from separate ruminal fluid collections. The cumulative gas curves produced from the 48-h digestion trial generated 145 time points that were used to provide an estimate of fermentation rate.  For this purpose, the gas production curves were fitted to a single pool exponential equation with lag (Mertens and Loften, 1980) using the TableCurve program, version 2.0 (Jandel Scientific, San Rafael, CA) under Microsoft Windows 95. The final output was the rate of digestion of the A1+B1 and the B2 fractions. The results of these analyses were formulated into comparable dairy rations holding grain inputs constant, using The Cornell Net Carbohydrate and Protein Synthesis Model. (Fox, and Barry, 1994).

Results and Discussion

The northern site (P. Barney) was not planted until July 1 due to wetness, and as a result of the drought that followed, only one harvest was possible. The drought limited the tallest height (54 inches) to one cut for the season at Kilcer and one of the P. Cerosalletti sites as well. One P. Cerosalletti site was able to secure three cuts at the shortest (30 inch) height. The delayed planting at P. Barney and droughts at all sites reduced yields as compared to previous studies.

Yields equaled or exceeded neighboring, earlier planted corn silage, at the P. Cerosalletti (corn silage =12 tons 35% DM) and Kilcer locations (corn silage =6.5 tons 35% DM). At the three sites that achieved two cuts, the highest dry matter yield occurred at the tallest stand height given a minimum of 3 cuts were obtained. Stand height determined the number of harvests/season.

Graphs 1-8 (see link below)

Milk/Acre and Milk/ton encompass the sum of the quality components. For all sites in 2002, as well as the Kilcer sites in 2000 and 2001, there was a very high correlation (R2=0.97) between dry matter yield/acre and milk/acre. For the 2002 data (see graph #9) it was a 0.99 R-sq.  Milk/Ton showed no significant change as affected by the variable of height at harvest. Thus, we conclude that yield per cut rather than individual quality changes drives the harvest timing decisions and that a two-cut system with stand heights of ~50 inches at harvest was optimum. Above 54 inches reproductive organs may be forming and moving up the stem, therefore changing the nutrient sinks, and affecting quality parameters.

Figure 9 (see link below)

The harvest height decision (harvest for optimum yield will maintain optimum quality) was also substantiated by the digestibility work by Dr. Alice Pell and Dr. Denis Molina (see Figure 10). The rate and amount of digestion of BMR sorghum-Sudan grass from the different studies was incorporated into the Cornell Net Carbohydrate and Protein model to produce the potential milk from energy and milk from protein. As height increased, the milk produced by the energy of BMR sorghum-Sudan calculated from their rate of digestion studies remained the same throughout 50+ inches. The milk produced from protein decreased with increasing height. The same trends were found in the 2000 and 2001 trials. Since protein levels are greatly influenced by N management, further research is needed to determine optimum N rate for maximum yield.

Figure 10 (see link below)

The lack of quality change with harvest height may enlarge the harvest window, but it does not change the fundamental problem of drying the crop to 35% from an average 16.4% DM at harvest. Farmers’ concern over moisture reduction for proper fermentation has been a major impediment to proper management of BMR sorghum-Sudan and expanded adoption by area farmers. Using the average dry matter of all cut heights (percent DM was not affected by stand height) and predicted tons of DM/height from 109 samples in 2002 height at harvest study, the amount of water per acre for each height was estimated (Figure 11). This total amount of water is in stark contrast with the amount of water contained in a first cutting of an alfalfa crop yielding 4 tons DM/year (first cut alfalfa contains approximately 47% DM - Cherney personal communication).

Figure 11 (see link below)


 Height of harvest of BMR sorghum-Sudan grass did not significantly affect quality components of lignin, NDF, dNDF, IVTD, sugar, predicted milk/ton. There was a trend toward decreasing crude protein with increasing height, but it was not robust enough to be significant in this test, and other studies suggest it could be affected by N management. Since dry matter yield was highly correlated with milk yield/acre, we conclude that BMR sorghum-Sudan grass has a relatively large harvest window in which to achieve quality forage able to compete with corn silage, but that for optimum quality, the forage should be harvested when stand-heights are less than 54 inches. The low dry matter of the fresh crop and the tremendous amount of water to remove present a challenge to proper management of this crop. There is a major need to explore the genetic ability to produce BMR sorghum-Sudan with a higher percent dry matter at harvest.  



 1.      Cerosaletti, P., Q.M. Ketterings and T. Kilcer (2002). 2001 Delaware County BMR sorghum sudangrass trials "What's Cropping Up?" 12(3): 1-3.

2.      Guyer, P.Q. and D.D. Duey (1986). Estimating corn and sorghum silage value. Univ. of Neb. Coop. Ext. Publ. G74-99-A, Univ. of Nebraska, Lincoln, NE.

3.      Kilcer, T., Q.M. Ketterings, T. W. Katsvairo and J.C. Cherney (2002). Nitrogen management for sorghum sudangrass: how to optimize N uptake efficiency? "What's Cropping Up?" 12(5): 6-9.

4.      National Research Council (2001). Nutrient requirements of dairy cattle. 7th edition. National Research Council. National Academy Press, Washington, D.C. 408 pages.

5.      Fox, D.G. and M.C. Barry. 1994. Using Whole Animal Models to Evaluate and Refine Cattle Diets Under Widely Varying conditions.  Proc. Of IV Inter.Workshop on Modelling Nut. Util. In Farm Animals. p. 143

6.      Lazarus, W. and Shelley, R. 2002 Farm Machinery Economic Cost Estimates for 2000. U of Minn Publ. FO-6696, Univ. of Minnesota

7.      Pell, A. N. and P. Schofield. 1993. Computerized monitoring of gas production to measure forage digestion in vitro. J. Dairy Sci. 76:1063-1073.

8.      Schofield, P. and A. N. Pell. 1995a. Measurement and kinetic analysis of the neutral detergent-soluble carbohydrate fraction of legumes and grasses. J. Anim. Sci. 73:3455-3463.

9.      Schofield, P. and A. N. Pell. 1995b. Validity of using accumulated gas pressure readings to measure forage digestion in vitro: a comparison involving three forages. J. Dairy Sci. 78:2230-2238


                             This research was funded by a research grant from Townsend and Garrison Inc.

For Further Information

 For further information on BMR sorghum sudangrass projects in New York contact Thomas Kilcer at the Rensselaer Cooperative Extension Office at tfk1@cornell.edu or 518-272-4210 or visit our websites (http://nmsp.css.cornell.edu/projects/bmr.asp and http://www.cce.cornell.edu/rensselaer/Agriculture/new%20bmr_sorghum.htm.


Cutting Height Study Graphs