The following is a summary of a recent article that appeared in the Journal of Animal Science (Sept 2001). The title of the paper is "Effects of nitrogen fertilization and harvest date on yield, digestibility, fiber, and protein fractions of tropical grasses". This paper was published by a group from the Univ. of Florida. Tifton 85 bermudagrass and Pensacola bahiagrass were fertilized at 5 different rates: 0, 35, 70, 105, and 140 pounds of N per acre. Hay was cut at 28-day intervals: harvest 1 was early June, harvest 2 was late June, 3 was July, 4 was August and harvest 5 was in September. Results were as follows:
N rate
Harvest date
Bahiagrass
0 35
70 105
140
1 2
3 4
5
Yield (lb/ac/cutting)
686 1255 1320
1302 1223
887 1268 1376 1102
1168
IVOMD (%)
52.1 51.7 51.2
51.9 52.6
54.3 53.8 48.8
51.2 51.5
CP (%)
9.0 10.5 12.5
14.1 15.2
12.4 11.5 12.0
12.0 13.4
N rate
Harvest date
Bermudagrass
0 35
70 105
140
1 2
3 4
5
Yield (lb/ac/cutting)
585 1386 1626
1644 1613
1235 1760 1593 1142
1124
IVOMD (%)
58.0 56.3 56.0
57.2 60.0
61.0 58.6 54.3
57.4 56.2
CP (%)
9.8 10.9 13.8
15.8 18.1
14.6 13.2 12.4
13.2 14.9
For yield, both grasses were optimized at a nitrogen
rate of 70 pounds per acre. IVOMD is similar to TDN which is an index
of the energy content of the forage and N rate did not effect this; however,
cutting date did. This would have been even more dramatic if the
cutting interval had exceeded 4 weeks. N rate did continually effect
the protein content of the hay and kept increasing with increasing application.
A lactating cow requires approximately 62% TDN and
11% crude protein in her diet. Thus, to me, the take home message
is that these two grasses can be fertilized with 70 pounds of N per acre
and this will optimize yield and quality as long as a short cutting interval
is practiced. Obviously, these results will vary with location and
are highly dependent upon rainfall. I should also note that this
was over two years, one dry and one wet. That is certainly similar
to Alabama!! Drought - Flood - Drought - Flood!!! As always
if you have questions or comments please let me know.