The effect of climatic factors on the visit of pollinators and the seed yield
of alfalfa
Jevtić G., Radović J., Lugić Z. and Vasić T.
Agricultural Institute Serbia, Center for Forage Crops, Kruševac, Trg Kosturnice 50, Serbia.
Abstract
In the course of a two-year research the effect of meteorological factors on the visit of pollinators,
pollination and seed yield of alfalfa (Medicago sativa L.) was studied. Pollinator activity and
meteorological factors were monitored in the morning, at noon and in the afternoon during 10 days of
flowering during summer regrowth. The temperature was recorded at three different heights above
ground level (0.3 m, 0.6m and 1m). In the first year, characterized by abundant precipitations, the
pollinators of alfalfa such as Megachile rotundata, Nomia ssp. and others were dominant (63.92%). In
the second year, drier and warmer, honeybees prevailed (87.63%). The second year was much more
favorable for seed production so the seed yield was considerably greater than in the first year. Seed yield
and seed yield components (except for 1,000 seed weight) were significantly different between the
studied years.
Keywords: climatic factors, pollinators, seed yield, seed yield components.
Introduction
Production of alfalfa seed is highly dependant on meteorological conditions (Erić, 1995; Marković,
1997). Among meteorological factors, air and soil temperature and humidity during flowering have the
greatest effect on seed yield, together with precipitations, light, velocity of the wind, etc. The optimal
mean daily temperature for successful alfalfa pollination range from 25 to 300 C (Erić, 1995), and the
optimal relative air humidity is from 30 to 50% (Žarinov and Kljuj, 1995). Increased relative air
humidity has a negative effect on the concentration of sugars in nectar which decreases the activity of
honeybees (Ciurdaresku, 1974). The highest seed yields of alfalfa are achieved in dry and warm
summers, while in damp and rainy years the yield is lower (Hoopingarner and Waler, 1992). The best
regions for alfalfa seed production are those with average precipitations of 600-650 mm m-2 (Bošnjak
and Stjepanović, 1987). The activity of honeybees is affected primarily by wind. Wind speed of about
24 km h-1 is limiting for honeybees activity (Martin, 1976). The objective of this paper was to
determine how certain climatic factors affect the activity of pollinators and seed production of alfalfa.
Materials and Methods
Our research was carried out in 1997 and 1998 at experimental field of Center for forage crops in
Krusevac. The following meteorological factors were studied: air temperature, air humidity,
precipitations and wind speed. All measurements were taken simultaneously with the counting of the
pollinators in three terms (morning, noon and afternoon). The temperature was measured at three
heights (30 cm, 60 cm and 1 m) above ground. Air humidity was measured by a mobile thermohygrograph placed in a meteorological shelter facility 250 m far from a trial field. Precipitation was
determined by pluviometer while the wind speed was measured by anemometer. The number of all
pollinators on 1 m2 of flowering alfalfa seed crop in 30 min were counted every ten days. Seed yield
was determined after harvest on three 2m2 plots and seed yield components were determined on ten
selected plants per plot. The number of seeds per pod and 1,000 seed weight were determined. The
percentage of inflorescences forming pods and the percentage of florets forming pods was calculated.
For all climatic factors mean, minimum and maximum values were determined, while seed yield and
seed yield components were subjected to analysis of variance.
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Results and discussion
In the first experimental year the temperatures in the morning were lower while at the two other times of
observation they were optimal for activity of pollinators (Table 1). In the second year, the temperatures
recorded in the morning were suitable for pollinator activity while those at noon and in the afternoon
were slightly higher than optimal. The difference between temperatures at different heights was,
depending on the day, even greater than 1C0.
Table 1. Temperatures recorded during the trial in 1997 and 1998 (10 days analysis).
Morning
Noon
0.3m
0.6m
1m
0.3m
Mean
22.9
23.57
23.4
Min
19.6
20.5
Max
25.8
27.8
Afternoon
0.6m
1m
0.3m
0.6m
1m
27.4
27.7
27.3
26.9
27.0
26.8
20.4
21.8
22.3
21.8
24.2
23.4
23.2
26.8
31.5
32.8
32.7
30.8
31.7
31.4
31.9
31.7
30.9
30.9
30.8
1997
1998
Mean
24.8
24.8
24.6
31.9
Min
18.1
18.8
18.1
24.0
23.4
23.2
22.2
19.73
19.7
Max
29.0
28.6
28.2
37.8
37.3
36.9
35.7
35.5
35.8
Optimal humidity ranging from 50 to 70% was present only in the morning in both years of
investigation. while humidity at noon and afternoon was lower than optimal. Air humidity at noon and
afternoon was higher in the first year than in the second year. The first year was a rainy one. with
rainfall occurring during the whole alfalfa flowering period (85 mm m-2). During measuring in 1998 the
rain fell only once but abundantly (45 mm m-2). Velocity of wind was never limiting for pollinator
activity.
Table 2. Meteorological factors in 1997 and 1998.
Precipitations
(mm day-1)
Air humidity (%)
Morning
Noonday
Afternoon
Mean
Min
Max
67.9
56
81
41.4
29
61
42.0
29
69
Mean
Min
Max
67.6
60
74
34.5
23
60
33.4
21
70
1997
8.5
1998
4.5
Wind velocity (km h-1)
Morning
Noonday
Afternoon
7.1
3.0
12.0
8.3
3.6
18.6
10.1
4.2
18.6
3.2
1.8
7.7
7.5
4.2
12.0
8.3
1.2
14.4
As regards pollinators. there was a marked difference between the first and the second year (Table 3). In
the first year which was considerably more humid and cooler. there were 1,264 pollinators recorded
daily on average. Other pollinators (63.92%) were much more active in comparison with honeybee
(36.08%). In the second year. drier and warmer. we counted 159.2 pollinators daily with a strong
prevalence of honeybees (7:1) with respect to other pollinators (Megachile rotundata Fab., Nomia spp.
and others).
Sustainable Grassland Productivity
313
Table 3. Number of honeybees and other pollinators (10 days analysis).
Pollinators
Year
Honeybees
Times
II
III
16.8
11.4
1997
I
17.4
min
2
2
5
max
37
33
34
∑
456
139
5
I
26.6
Other pollinators
Times
II
III
32.8
21.4
10
14
6
45
49
49
9.3
5.1
5.3
1998
43.5
52.3
43.7
min
5
24
18
3
2
0
max
72
69
68
18
11
13
∑
808
Total
pollinators
Honeybees
(%)
Others
(%)
1264
36.08
63.92
1592
87.63
12.37
197
The second year proved to be more suitable for seed production than the first one. Seed yield and seed
yield components in the second year had considerably greater values than in the first year. except for
1,000 seed weight (Table 4).
Table 4. Seed yield and seed yield components.
Trait-Year
1997
1998
Average
Lsd
0.05
0.01
Seed Yield
(kg ha-1)
199.0
409.2
304.1
71.7
97.4
Inflorescences
forming pods (%)
44.44
83.71
64.07
8.96
11.17
Florets forming
pods (%)
30.46
44.02
37.24
11.65
13.89
Number of seeds
per pod
2.97
3.49
2.23
0.17
0.24
1,000 seed
weight (g)
2.27
2.28
2.28
0.24
0.32
Conclusions
Our two-year research on the effect of climatic factors on the activity of pollinators and seed production
confirmed that the climatic factors studied, especially temperature and precipitations. had a great
influence on the activity of pollinators and seed production of alfalfa. In the first year which was colder
and more humid there were significantly more other pollinators in comparison with honeybee (2:1).
Climatic conditions were rather unfavorable for seed production. In the second year which was dry and
warm. honeybees were predominant. This year was also much better for seed production since seed
yield was about double in comparison with the first year.
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