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Sara Epps
Dr. Howes
BRAE 331
2 March 2015
Irrigation of Sugar Beet Crops
In 2014, California was responsible for only 1.9% of the United States’ 1,147,200 acres
of sugar beets harvested (USDA 2014). Sugar beets are a biennial crop grown in 11 different
states in the US, with Minnesota leading in acreage (USDA 2014). Sugar beets account for a
little over half of the US domestic production of sugar, with the other portion being raw
sugarcane. The sugar beet is an industrial crop, grown for the use of sucrose stored in the roots of
the crop (Kenter et al. 1996). Temperate climates are ideal for maximizing yield and sugar
production, but can be grown in a variety of climates. They are usually a summer crop in regions
such as northern US, where the roots will not survive the cold winters. However, they can be a
winter crop in more southern regions with semi-arid climates. The sugar beet, or Beta Vulgaris,
is a deep rooting crop with maximum root zone depth of 39.37 inches, or a little over 3 feet
(Gonzalez-Dugo et al. 2007).
Crop Coefficients
Evapotranspiration rates and crop coefficients are two very important values that are
necessary for scheduling irrigation. The ET rate of a crop is a weather-based value that is
calculated using a variety of climate variables. CA uses CIMIS weather stations to provide us
with this data. Williams et al. (2001) defines the crop coefficient, Kc, as “the fraction of water a
non- water-stressed crop uses in relation to that of ET.” The Kc is a value that changes as the
crop grows and develops. To find the ET value for a specific crop (ETc), the reference ET value
(ETo) must be multiplied by the crop coefficient specific to the crop being grown. Figure 1
shows the different crop coefficient values for the four different growth stages of sugar beets in
California. According to the FAO (2015), the crop coefficients for the initial, mid, and end
growth stages are 0.35, 1.20, and 0.70, respectively.
Since there are many different variables that go into computing crop coefficients, there
are different methods of estimating or calculating these values. This results in slightly different
coefficients used by different growers. For example, Sahin et al. (2007) found the mean seasonal

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crop coefficient to be 0.65 for sugar beets. Tasumi et al. (2005) found a large variation in the
crop coefficients for sugarbeets with differences in crop growth among individual fields. The
mean Kc found during crop development was 0.25, 0.97 when there was full canopy cover, with
a maximum Kc of 1.05 (Tasumi et al., 2005).
Fig. 1: Crop Coefficient for Various Growth Stages of sugar beets. Values from FAO (2014).
Optimum Soil Moisture Content
Soil moisture content is a large determining factor for maximizing yields for most crops.
Sugar beets are found to be fairly tolerant to water stress. Qi et al. (2005) sandy loam soils are
amongst the most common soils for the growth of sugar beets, having available soil water
content of about 14% when at field capacity. The amount of water in the soil that is available to
the plant varies for different crops and soil types. Hassanli et al. (2009) says that soil moisture
and root zone control have a large affect on conserving water, which is very important in times
such that water availability is scarce. Sugar beets are often times not irrigated and only use the
water from rainfall in Mediterranean climates. In drier regions, irrigation is used to keep
appropriate soil moisture content. Neibling et al.,states that to prevent water stress, irrigation
should occur when soil moisture in the 12-18 inch depth depletes about 50%. Too much rain or
drainage doesn’t affect the crop directly, but can leach needed Nitrogen out of the root zone
(Cooke et al. 1993). Typically, roots can extract water from soils at depths around 39.47 inches
(Pervin et al. 2015). Tognetti et al. (2002) states that drought stress is the main cause of yield
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decline in sugar beets. Hoffmann et al. (2011) quotes Durrant (1988) and Lexander (1993), and
noted that the two main factors that influence field emergence of the crop are temperature and
soil moisture. Since emergence of the crop is a very important stage of growth, it is important not
to have too much water stress when the plants are in such sensitive states. Richard et al. (1995)
found in his study that soil water potential of -500kPa was a critical value for sugar beet
germination, agreeing with Gummerson (1986).
Optimum Leaf Water Potential
The leaves of a sugar beet plant are very susceptible to wilting. Stegman et al. (1997)
found in his study about optimal leaf water potential that there was no decrease in yield when the
leaf xylem pressure was at -11 to -12 bars. When the leaf water potential exceeds the optimal
values found by Stegman et al. (1997), the leaf stomata begins to close. The closing of the leaf
stomata regulates the flow of CO2 into the plant, directly affecting the plant’s photosynthesis.
The higher the salinity, the lower the leaf water potential at which the turgor potential attains
zero (Katerji et al. 1997).
Critical Irrigation Times
Sugar beets are found to have long vegetative phases without sensitive flowering stage
(Werker et al. 1998). Sugar beets can be grown and harvested for their seeds, or grown for the
sucrose accumulation in their roots. The main purpose of sugar beet crops is for sugar production
from their roots. When farming sugar beets for their roots, the crop never actually sees the
flowering stage, making emergence and germination the most sensitive stages of growth. Light
frequent irrigations are ideal for emergence and early growth stage of sugar beets because of
their sensitivity to water stress (FAO 2014). When speaking to Colace (2015), a sugar beat
farmer in the Imperial Valley, he agreed that germination and emergence is the most sensitive
growth stage to water stress even though sugar beets are known to be less affected to water stress
when compared to other field crops. Stegman et al. (1977) found that frequent irrigation before
full canopy development can increase ET rates. However, it is important not to over irrigate at
these sensitive growth stages, due to the increased risk of disease (Neibling et al. 1995). After
crop establishment, allowable depletion of 45-50% of the soil moisture is found to be acceptable
(Neibling et al. 1995)). Discontinuing irrigation 2-4 weeks prior to harvesting has been found to

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increase sucrose accumulation in the roots (FAO 2014). Yet, soil that is too dry can complicate
and decrease the quality of root harvests.
ET vs. Yield
Every 1% loss in potential evapotranspiration resulted in a 0.24% loss in potential yield
(Werker et al. 1998). Werker et al. (1998) claims that in sunny environments, yield depends on
ET. With higher temperatures, evaporation increases, causing the plant to lose more water.
Temperature and weather play a vital role in ET rates. Slow growth rates at emerging and young
sugar beets were correlated with large ET values (Werker et al. 1998). Pervin et al. (2015) claims
that ET values of 500-550 mm ensure high yield values of sugar beets. Yield potential of sugar
beet crops depends primarily on site and year effects (Pervin et al. 2015). Soil type and climate
in different regions can drastically change the ET, which in turn fluctuates the yield of sugar
beets. Leaf area has been found to have a higher affect on transpiration than stomata closure in
the plant (Gonzalez-Dugo et al. 2005). The stomata are the pores in the plant’s leaves that allow
water vapor to transpire into the atmosphere, and allow CO2 into the leaves. Stegman et al.
(1977) found that there was no root yield produced until ET reached values of 20 cm.
Figure 2a: Relative Yieldvs. Relative ET. FAO (2014) Figure 2b: Yieldvs ET (mm) of sugarbeets from Katerji (1997)
Sensitivity to Waterlogging and Salinity
Werker et al. (1998) quoted Dunham (1993) in saying that sugar beet ancestors were
originally grown on sea coasts, which is why they are thought to be a more salt and drought

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tolerant field crop than most. The most common effect of high salinity in soils, is the reduction
of growth rate and decrease in size (Plaut et al. 1985). Soils high in salinity largely affect the
availability of water to the plant roots. It is important to find threshold EC values for crops to
ensure maximum yield. Katerji et al. (1997) quoted work from Ayers and Westcot (1985) who
found the threshold ECe to be 7 dS/m, which agrees with many other sources. Figure 3 shows the
% yield decline as ECe values of the soil increase. FAO (2014) says that yield is not affected at
all until ECe values exceed 7. The yield declines by 10% at EC values of 8.7, 25% at 10 EC,
50% at 15 EC, and 100% yield decline once EC values reach 23 and above (FAO 2014).
Although many sources say that sugar beets are a salt tolerant crop, (Bor et al. 2002) states that
in the germination and emergence stage, sugar beets are especially sensitive to salinity. After
emergence, the crop is able to osmotically adjust to the salinity levels in the soil. Full osmotic
adjustment was obtained after just 14 days of being exposed to the salinity in the soil (Plaut et al.
1985).
Fig 3. Yield Decline vs. ECe. Values from FAO (2014).
Katerji et al. (1997) found that soil texture has a larger affect on sugar beet yield than salinity
does. Soil texture can greatly affect the soil water tension, which depicts how available the water
in the soil is to the plant roots. Root and crown rot are at maximum potential when the soil
moisture is at 100% and decreases as the soil dries (Neibling et al).
Special Considerations
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Most sugar beet crops are spring-sown and harvested in autumn. This increases the root
survival rate, as they are not subjected to freezing temperatures in the winter. However, recent
studies are showing that winter-sown sugar beets have increased yields if they can survive
through the winter. Loel et al. (2014) states that compared to autumn sown sugar beets, winter
sown sugar beets can increase yields to about 26-34% according to Hoffmann and Kulge-Severin
(2010). Loel et al. (2014) found that sugar beets at optimal growth stage can survive minimum
temperatures of about 7 degrees Celsius. There are different advantages and disadvantages to
growing both winter-sown and autumn-sown sugar beets.