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Alfalfa Date of Planting
and Phenological Development
Steve Orloffl , Randy Dovel 2, and James Rainey 3
INTRODUCTION
Planting date can have a profound influence on the potential profitability of an
alfalfa field. It can affect stand density, seedling development, weed pressure, and
eventually, yields. When to plant is a decision that growers must make every time a
new field is going to be established. Currently, insufficient information is available
for the Intermountain alfalfa production region to adequately advise growers on this
critical issue.
Greenhouse studies, conducted at U.C. Davis by Teuber, determined effects of
photoperiod and temperature on alfalfa seedling development. Results provided the
basis for a model to predict optimum alfalfa planting date using seasonal
photoperiod and average soil temperature curves. Research conducted in Yolo and
Fresno Counties in California supported the predictions of optimum planting date by
this method. This research demonstrated a 1 ton/A per year yield reduction from
planting one month late, and this effect continued beyond the first year. The model
predicts that the optimum time to plant in the Klamath Basin is from mid-June to
the beginning of August. Experience at the U.C. Intermountain Research and
Extension Center (IREC) suggests this planting period may be optimum.
Common grower practice is to plant from as early as March to early June, or to
plant in August. Hence, growers are currently planting at all possible planting dates
during the growing season except those predicted to be the optimum planting dates
using this model. Field validation in the Klamath Basin is needed to determine if the
model fits the unique environment of this area. Knowing the optimum planting date
can improve yields, reduce or possibly negate the need for herbicides, and possibly
prolong stand life.
Phenology is the study of the development of an organism as influenced by
genotype and the total environment. Since alfalfa forage quality is affected greatly by
age or development stage, a 10-stage classification system has been developed to
assess alfalfa stage of development. The mean stage by count (MSC) procedure
estimates the mean stage as the average of observed stages weighted for the number
of shoots in each stage. MSC is a relatively simple procedure that can be performed
1
/ Siskiyou County Farm Advisor, Yreka, CA.
/ Associate Professor, Klamath Experiment Station, Klamath Falls, OR.
3 / Biological Sciences Research Technician, Klamath Experiment Station, Klamath
Falls, OR.
2
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in the field. By correlating stage and forage quality values, the MSC has provided a
quick way to estimate forage quality of growing alfalfa in some areas. However,
initial studies in Oregon do not support the correlation found elsewhere. It may be
necessary to modify the equation for Oregon conditions to accurately estimate
forage quality using MSC values.
A joint project was initiated at both KES and IREC to evaluate the
appropriateness of both date of planting and phenological models in the Klamath
Basin. Procedures and results reported below are from KES only.
PROCEDURES
Alfalfa was planted at 3-week intervals throughout the summer of 1992 on April
1, April 22, May 14, June 3, June 24, July 15, August 5, and August 26. Three alfalfa
cultivars were planted; Vernal, Centurian, and WL 320; with fall dormancy ratings of
2, 3, and 4, respectively. The experimental design was a split-plot, with planting dates
as the main plots and cultivars as sub plots, resulting in a total of 24 treatments.
Treatments were replicated four times. The plots were seeded using an
"experimental scale" grain drill. Plot size was 1.5 X 6 meters. The crop was irrigated
by solid set sprinklers.
In 1993, the first cutting was harvested when alfalfa plants for a given planting
date were at the 10 percent bloom stage or when they had sufficient crown bud
elongation (elongation averages 2 cm). Subsequent cuttings were made when the
alfalfa was in the bud stage. Stand density was determined at the first trifoliate leaf
stage, after the first alfalfa harvest, and at the end of each production season.
Destructive plant sampling was done outside of the harvest area to determine the
effect of planting date on crown development. Phenological stage was determined at
approximately biweekly intervals in the year following establishment until first
harvest. This was done to document planting date effects on phenological
development the following year. Forage quality samples were analyzed for crude
protein (CP), acid detergent fiber (ADF), and neutral detergent fiber (NDF) using
standard laboratory procedures.
RESULTS
Date of planting significantly affected forage yield in the establishment year
(Figure 1). There was no difference in yield due to delaying planting from April 24
to May 13; however, delaying planting after May 13 resulted in severe yield
reductions. No harvestable hay was produced on plots seeded on July 15 or later.
From an economic point of view, either early spring planting or late summer
planting seems to be more advantageous. Early spring planting maximizes yield in
the planting year, while late summer planting would allow for a short-season grain or
hay crop to be grown prior to planting. A mid-summer planting would greatly reduce
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alfalfa production in the establishment year and preclude planting a short-season
crop prior to seeding the alfalfa. There was no difference in forage yield between
the three varieties in the establishment year.
It was hypothesized that date of planting the previous year would affect yield in
the first cutting the year after planting. First cutting yields of the varieties Centurian
and WL 320 were significantly lower in the August 31 planting date than the
previous planting dates (Figure 2). First cutting yields of Vernal declined below
earlier planted yields in both the August 6 and 31 planting dates. When averaged
across all planting dates, yields of the three varieties were not significantly different.
Sampling date had a greater affect on forage quality than either planting date or
variety. Average CP concentration declined from 24.0 percent on May 27 to 18.5
percent on June 21 (Figure 3). Average ADF and NDF values increased from 25.7
and 33.3 percent on May 27 to 33.1 and 42.1 percent on June 21, respectively. When
averaged over all three sample dates, ADF and NDF values of the last two planting
dates were significantly lower than earlier planting dates (Figure 4). Planting date
did not have a statistically significant effect on forage CP concentration.
Trends in forage quality parameters were correlated to phenological stage as
measured by MSC. Both ADF and NDF increased as MSC increased, and CP
decreased with advancing phenological stage (Figure 5). Although correlations were
significant, only about 60 percent of the variability in forage quality was accounted
for by phenological stage. That is too poor a correlation to depend on for precise
forage quality prediction, but could be a useful tool in determining cutting schedules.
Further study is needed to determine the usefulness of this management tool in the
Klamath Basin.
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3.5
< 3
Z 2.5
0
H 2
0
_ j 1.5
0
4/24 5/13
6/03 6/24 7/15 8/06 8/31
PLANTING DATE
Figure 1. Alfalfa Yield in 1992. Total alfalfa yield (tons dry matter/A) in
the establishment year of alfalfa planted at three-week intervals
throughout the summer of 1992. Data points represent the
average of three varieties. Plots were planted at the Klamath
Experiment Station, OR.
VERNAL
-
H CENTURIAN
WL 320
I
1
I
f■
4/24 5/13 6/03 6124 7/15 8/06 8/31
PLANTING DATE
Figure 2. First Cutting Yield in 1993. First cutting yield (tons dry
matter/A) in 1993 of three alfalfa varieties planted at three-week
intervals throughout the summer of 1992. Plots were planted at
the Klamath Experiment Station, OR.
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45
NDF
40
35
C.) 30
25
CP
20
15
6/07
5/27
6/21
SAMPLE DATE
Figure 3. Sample Date Effect on Forage Quality. The effect of sample date on three
measures of forage quality, crude protein (CP), acid detergent fiber (ADF), and
neutral detergent fiber (NDF) of 1993 first cutting alfalfa. Samples were collected
on May 27, June 7, and June 21 prior to first cutting. Data points represent the
average of seven planting dates. Plots were established at three-week intervals
throughout the summer of 1992 at the Klamath Experiment Station, OR.
40
NDF
35
ADF
0 30
OL
a25
CP
20
4/24 5/13 6/03 6/24 7/15 8/06 8/31
PLANTING DATE
Figure 4. Planting Date Effect on Forage Quality. The effect of date of planting the
previous year on three measures of forage quality, crude protein (CP), acid
detergent fiber (ADF), and neutral detergent fiber (NDF) on 1993 first cutting
alfalfa. Data points represent an average of three sampling dates. Plots were
established at three-week intervals throughout the summer of 1992 at the Klamath
Experiment Station, OR.
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50
40
30
w
a-
Cp
20
10 0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
40
MEAN STAGE BY COUNT
Figure 5. Correlation of Phenological Stage and Forage Quality. Correlation of three
measures of forage quality, crude protein (CP), acid detergent fiber (ADF), and
neutral detergent fiber (NDF) to phenological stage as determined by mean stage
by count (MSCNT). Regression equations and correlation coefficients of forage
quality parameters with MSC:
%CP = 27.537 - MSC * 3.6529
%ADF = 19.344 + MSC * 5.657
%NDF = 26.284 + MSC * 6.329
R2 = 62.3%
R 2 = 68.6%
R 2 = 68.4%