September 26, 2000
PRODUCTIVITY OF DIVERSE PASTURES IN A WET VS DRY YEAR
Jim Gerrish and Matt Sanderson1
Abstract
Cool-season pasture species vary in their ability to remain productive
during dry summer conditions. Productivity of sixteen grass and
grass-legume mixtures varying in degree of species complexity were
compared in two years of markedly different precipitation levels.
Forage production in 1999, when growing season precipitation was 40% of
normal, averaged 65% of production measured in the more favorable year of
1998. Range in variation in 1999 yield as percentage of 1998 among
mixtures was from 57 to 78%. In 1999 tall fescue (Festuca arundinacea Schreb.)
receiving 120 lb N/acre yielded 78% of 1998 yield but 90% of the
production occurred before July 5. Mixtures containing birdsfoot trefoil
(Lotus corniculatus L.) as the primary legume provided the best
pasture performance in terms of both total annual yield and seasonal yield
distribution. Both binary grass-birdsfoot trefoil mixes and a complex
eight-species mix provided greater mid to late-summer forage yield than
either tall fescue or smooth bromegrass (Bromus inermis Leyss)
receiving N fertilizer.
Introduction: Livestock producers relying on pasture to provide
most of the nutrients for their stock sometimes face the challenge of
drought. Across a large part of the Central US, 1998 and 1999 were very
contrasting growing seasons. While 1998 was an excellent growing
year with adequate rainfall distribution throughout the growing season,
1999 was the driest June through September period recorded in 25 years of
weather records kept at the University of Missouri-Forage Systems research
Center and, on the average for the state of Missouri, June through
December, 1999, was the driest seven-month period of the 20th century.
An ongoing study comparing forage yield and quality of 16 different
pasture mixtures varying in species complexity from one to eight has
provided a comparison of pasture performance between a near normal
precipitaion year and a very dry year. Our objective was to compare total
yield and yield distribution among the pasture mixtures in the two
contrasting years.
Material and methods: Sixteen grass or grass-legume mixtures were
established in 50 ft X 50 ft plots in a completely randomized design with
four replications. Mixtures varied in degree of species complexity. Base
grasses were tall fescue (TF) and smooth bromegrass (SB). These two
species were established as monocultures and one or the other were present
in all mixtures. Grass components were seeded on September 5, 1994 on a
prepared seed bed. Grass seed was broadcast and rolled in with a
cultipacker. Legume components were frost seeded on March 10, 1995. Red
clover (Trifolium pratense L.; RC) and birdsfoot trefoil (BFT)
establishment with frost seeding was very good while alfalfa
(Medicago sativa L.;A) establishment was very poor. Due to the near
absence of alfalfa in the designated plots, the plots originally intended
as TF or SB +A were reassigned as grass + 0 N treatments for comparative
purposes. Legumes were seeded first as binary mixtures with each base
grass and then in combination with one another within each base grass.
More complex mixtures were created by adding orchardgrass (Dactylis
glomerata L.;OG), timothy
(Phleum pratense L.;T) and big bluestem
(Andropogon gerardii Vitman;BB) to the tertiary base grass-legume mixtures.
Thus, the most complex mixture contained eight seeded species. Each
mixture was formulated to provide 80 seeds/sq-ft with the base grass
always providing 50% of the seed in mixtures and all other components
equally represented. The one exception was the eight species mix where
all components were allocated in equal amounts.
Swards were uniformly managed to encourage establishment during the 1995
growing season and were mechanically harvested in 1996. Tall fescue and
smooth bromegrass monocultures received 120 lb N/acre annually as three
40-lb applications applied in March, June, and September. For
interpretation of all of the figures in this report refer to the reference
number beside each pasture mixture.
Ref. No.Tall Fescue Base Ref. No. Smooth Bromegrass Base
1)TF + 120 lb N/acre 9) SB + 120 lb N/acre
2)TF + 0 N/acre 10) SB + 0 N/acre
3)TF + BFT 11) SB + BFT
4)TF + RC 12) SB + RC
5)TF + A +BFT 13) SB + A + BFT
6)TF + A + BFT + RC 14) SB + A + BFT + RC
7)TF + A + BFT + RC + OG + T 15) SB + A + BFT + RC + OG + T
8)TF + SB + A + BFT + RC + OG + T 16) SB + A + BFT + RC + TF + OG
+ T + BB
In both 1998 and 1999, individual plots were grazed on an as-needed basis
whenever a particular plot reached 8 to 10-in. mean sward height. Prior to
grazing, six 2.7-ft2 quadrats were clipped from each plot. At the same
site, sward surface height was measured and the species composition was
visually estimated. Plots were grazed with six to eight steers for four to
seven hours to remove approximately 50% of the forage biomass. Residual
forage was measured after each grazing event. Total annual forage yield
and yield by month were determined.
Results and Discussion: Rainfall in April and May, 1999, was
excellent and temperatures were favorable for very rapid pasture growth.
Pasture growth rate and forage yields early in the season actually exceeded
the rates and yields measured in 1998. Rainfall for the next three months
was less than 40% of the long term norm. Pasture mixtures which remain
productive under these latter conditions should allow producers to better
weather the economic and biological stresses of drought.
In 1998 average sward height at turn-in was slightly greater than our
target of eight to ten inches (11.0 in.) while in 1999 the average sward
height was slightly less than the target
(7.75 in.). Herbage mass at
turn-in was similar for both years with 2415 and 2315 pounds/acre for
1998 and 1999, respectively.
Total annual forage yield in 1999 was about 65% of the 1998 forage yield
when averaged across all pastures (Figure 1). The first
assumption might be that any pasture which provided greater than 65% yield
potential could be considered to be lower risk pastures when planning for
future drought protection. This might be a safe assumption if the goal were only
total forage production. For example, a single-cut hay production system that
might have that objective. Total forage yield for the sixteen pastures is
shown in Figure 2.
Tall fescue receiving 120 lb N/acre was quantitatively the highest
yielding pasture as well as the pasture providing the highest percentage
of yield in a poor year compared to the very good 1998 growing season.
Statistically, four other pasture mixtures were not significantly lower
yielding than TF + 120 N. The common characteristic of the other higher
yielding mixtures is that they all contained birdsfoot trefoil as the
primary legume. Red clover contribution to pastures was much lower in 1999
compared to 1998. While this may have been a drought effect, it may also
have been a reflection of timing in the red clover persistence cycle. In
stands managed for natural reseeding as this study is, there are generally
two years of strong clover production followed by an off year. Stand
measurements made in October of 1999 did find a significant presence of
young red clover plants in most plots designated as red clover mixtures.
Smooth bromegrass response to N fertilization was disappointing in both
years. While addition of 120 lb N/acre to tall fescue produced almost
3500 lb/acre additional forage per acre compared to 0 N, 120 lb N applied
to smooth bromegrass produced only 300 pounds more forage than unfertilized
bromegrass in 1999. Even with the excellent growing conditions of 1998, N
fertilization produced less than 1000 pounds of additional forage on smooth
bromegrass pastures. Obviously, the economics of fertilization of these
two species must be quite different. Smooth bromegrass responds much better
to N fertilization in hay situations compared to grazing because so much
of the biomass is produced above typical grazing heights. Tall fescue, on
the other hand, produces an abundance of dry matter in the lower 6 to 8
inches. The economics of N fertilization on grazed tall fescue can be
quite good due to potentially high production in relatively short pastures.
Coupled with high stock density which can enhance nitrogen recycling in
the system, N fertilization of tall fescue looks quite good.
The primary drawback of N-fertilized fescue pastures in dry years is yield
distribution. While 1999 total production appeared quite good, the monthly
distribution of available forage was a different matter. Mixtures which
compared most favorably to TF + N in both total yield and 1999 yield as
percent of 1998 yield were those mixtures containing birdsfoot trefoil.
Monthly production of TF + BFT compared to TF + N was quite favorable,
particularly in late summer (Figure 3). Over 90% of TF + N total yield for
the season was produced before July 15. While this may be acceptable for
hay production, it is unacceptable for pasture production. The pasture
with greatest species complexity, including a C-4 grass exhibited a
unimodal yield distribution pattern for the season compared to the typical
bimodal distribution curve associated with most cool-season
forages
(Figure 4).
Summary: While N-fertilized grass pasture produced the most total forage
in a very dry year, 90% of the forage production occurred before July 5.
Total season forage yield of grass mixtures containing birdsfoot trefoil
were not significantly different from N-fertilized grass but did produce
significantly more forage during the late summer period compared to
N-fertilized grasses. Mixtures appear to be more drought resistant than
grass monocultures.
Figure 1. Total forage yield in 1999 averaged 65% of total forage yield
in 1998.
(DMY=Dry Matter Yield)
Figure 2. Total forage dry matter yield in 1999 with least significant
difference compared to tall fescue receiving 120 lb N/acre.
Figure 3. Tall fescue + birdsfoot trefoil pastures exhibited
significantly more late summer regrowthcompared to tall fescue + 120 lb N/acre
during the 1999 dry season.
Figure 4. Pasture mixtures vary significantly in yield distribution
through the season with more complex mixtures exhibiting more unimodal
yield distribution compared to a simple binary mixture.
PRODUCTIVITY OF DIVERSE PASTURES IN A WET VS DRY YEAR
Jim Gerrish and Matt Sanderson1
Drought is a problem which livestock producers must periodically
face. Dry conditions typically reduce total pasture yield and reduce
livestock carrying capacity. We compared productivity of 16 different
cool-season pasture mixtures between a season with favorable rainfall
for optimum pasture production and very dry year. Treatments included
grass monocultures receiving 120 lb/acre nitrogen fertilizer as well as
grass legume mixtures. The most complex mixture in the study consisted of
eight different forage species including a warm-season grass which
would be better adapted to hot, dry conditions. Forage yield in the dry
year was reduced by about one-third over all mixtures but individual
pasture mixtures varied from less than 25% reduction to almost 50% product
ion. Pasture mixtures which yielded greater than the mean of all treatments
in the dry year on a percentage basis relative to the favorable year
should be those mixtures which are best adapted to withstanding drought
stress. Tall fescue fertilized with nitrogen produced the most total
forage in both the wet and dry years, but the distribution of yield
through the dry weather was very poor. Tall fescue and smooth bromegrass
pastures containing birdsfoot trefoil provided the best overall balance of
total yield and distribution through the dry season. This research
indicates that in cool-season dominant pasture areas, grass-legume
mixtures provide more stable forage production compared to
nitrogen-fertilized grass.
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1 Research Assistant Professor, University of Missouri-Forage
Systems Research Center, 21262 Genoa Road, Linneus MO 64653.
(GerrishJ@missouri.edu) and
Research Agronomist, Pasture Systems and Watershed Management Research
Laboratory, USDA-ARS, Building 3702, Curtin Road, University Park, PA 16802-3702.
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