ANR Publications
6701 San Rablo Avenue
Oakland, CA 94608-1239
Telephone: (510)642-2431
A full stand of property spaced plants is the first step in the production of a profitable crop of sugarbeets. Sugarbeets in California are usually grown on raised planting beds of two types: single-raw beds spaced 30 inches apart, and doublerow beds with 14 inches between rows on the bed and 26 inches between rows of adjacent beds. Field experiments summarized in table I show that the double-row system tends to produce slightly more sugar but that the difference is small and of little practical significance. Table I also shows that there is little to be gained by greatly increasing the number of plants that can be grown per acre by planting two rows, spaced 10 inches apart, on. beds spaced 30 inches from center to center (see fig. 1 for row spacing).
The number of sugarbeet plants required per acre for maximum sugar yield depends on the row spacing used. Although plant populations can vary considerably for a given row spacing, it is important to know the range of in-row spacings that will produce top yields.
The results of an experiment to evaluate the effect of varying the distance between plants within the row when the row spacing is 30 inches or 14 and 26 inches (double row) are shown in figure 2. Root and sucrose production were near maximum when plants were spaced from 4 to 10 inches in 30-inch rows and 6 to 12 inches in 14- and 26-inch rows. In these experiments, root yield was determined by hand harvest of roots 2 inches and more in diameter. For commercially grown sugarbeets, the safe minimum distance between plants on 30- and 14- and 26-inch rows should probably be 5 and 7 inches, respectively, because some roots 2 inches in diameter may not be recovered by a mechanical harvester or may be eliminated by cleaning devices at the beet-receiving station. As spacing increased beyond 12 inches, a decline in root yield occurred. The decline was greater for plants grown on 30-inch rows. Two-raw beds (14- and 26-inch raw spac- ing) therefore offer some protection from loss in yield when plants are spaced further than 12 inches apart or when gaps occur in a stand.
Effects of Soil Salinity
Sugarbects are quite tolerant to salinity at later stages of growth, but are sensitive during germination. Soil salinity is measured by the electrical conductivity of a water extract drawn from a saturated soil sample. Conductivity is usually expressed as millimhos per centimeter (mmhos/cm) at 25C. At a conductivity of 4 mmhos/cm, germination is delayed and some suppression occurs. At higher salt readings, germination is progressively lower. Once established, beets will grow well at a conductivity of 8 mmhos/cm; higher concentrations will progressively reduce growth. In general, it is the initial soil salinity at planting time that causes germination prob- lems, rather than the salt in the irrigation water. Consequently, it is advisable to take salinity samples of the soil from which the beds will be made.
Soil with an initial salinity of only I or 2 mmhos/cm can become quite saline (5 to 10 mmhos/cm) in the seed zone of single-raw beds after one irrigation with good quality water. This marked buildup of salts around the seed, resulting from continued evaporation and movement of soil water to the seed line, exposes the germinating seedling to salt concentrations many times greater than those encountered by the roots at later stages of growth. The margin of safety for singlerow crops, therefore, is narrow, and stand failures frequently occur in soils not thought to be saline. If single-row beds are used and the salinity of the plow layer is I mmho/cm or higher, irrigate every other row when germinating seed and wet the beds completely across so that salt will be moved by the water away from the seed row as illustrated in figure 3.
Double-row beds provide a greater margin of safety against salt damage. An initial salinity of 2 to 5 mmhos/cm can be tolerated when double rows are used, because the salt accumulates in the center of the bed, In this case, salinity in the seed line seldom exceeds that of the initial plow layer, and often is somewhat less.
When the salt in the soil exceeds 4 to 5 mmhos/cm, beets can be grown by using specially shaped beds or using sprinkler irrigation during the germination period. If the salinity of your soil is 4 mmhos/cm or higher, consult your local office of Cooperative Extension regarding appropriate cultural techniques.
Seedbed Preparation
Ideally, fields should be leveled to a grade of 0.05 to 0.15 percent slope in the direction the irrigation furrows are to run, so that beets can be irrigated without flooding the top of the seedbed. Steeper slopes will make it more difficult to irrigate for germination. Use a plane before each beet crop to remove minor variations in slope-do this when the soil is loose, such as after discing in the fall of the year preceding the sugarbeet crop.
In preparing the seedbed, soil must be tilled to shatter compacted layers and loosen soil deeply enough to allow listing shovels to operate to the desired depth. it is best to do such tilling, which may consist of chiseling to a depth of about 14 inches followed by one or two discings, when soil is relatively dry.
Most sugarbeets are grown on beds, and listing is the first operation in making beds. Be sure listing shovels go deep enough to leave ridges that will provide sufficient soil to make well-formed finished beds about 5 inches high. In areas where winters are wet, it is advantageous to list in the fall, particularly for heavy soils because it provides drainage, saves working the soil deep when it is wet in the spring, and allows more timely spring planting with a minimum of work. Falllisted beds may be weedy at planting time. These weeds can be controlled with an herbicide or special tilling equipment.
With a modern, multipurpose bed-shaper, it is possible to shape beds, apply herbicides, rototill bed tops to incorporate the herbicides into the soil, firm beds, and plant in a single operation. Good seedbeds should be:
Even low concentrations of free ammonia are toxic to germinating seeds. If anhydrous ammonia or ammonia solution is to be applied when beds are formed, do not place it directly below the seed. It is best to place this material about 8 inches outside the seed row and at least 6 inches from the top of the bed so that the material is I or 2 inches below the level of the furrow bottom. In this position there should be adequate soil between the point of application and the seed row to trap and hold all free ammonia (fig. 4). Most damage from ammonia fertilizer is the result of careless placement, especially in sandy or dry soils where free ammonia gets to germinating seeds or roots of young plants.
If experience or soil tests indicate that seedlings may need more phosphorus than the soil can supply, 20 pounds of phosphorus per acre (46 pounds Of P205) can be placed about 3 inches below the seed to insure rapid seedling growth. At this depth, up to 20 pounds of nitrogen per acre can be com- bined with the phophorus to insure adequate nitrogen for early seedling growth.
Another method for making phosphorus available to seedlings is to broadcast it before the beds are formed and list it into the beds. Again, some nitrogen can be broadcast with the phosphorus and incorporated into the beds. It is not advisable, however, to apply more than 40 pounds of nitrogen per acre in this manner unless sprinkler irrigation is used. Under furrow irrigation, the nitrogen moves with the water to the top of the bed where it cannot be absorbed by plants and may contribute to high salinity in the seed row. Later, this nitrogen may be leached into the root zone by rain, stimulate vegetative growth, and reduce the sugar concentration of storage roots.
Disease, Weecl, and Insect Control
Seedling diseases, weeds, and insect pests can seriously reduce stands and therefore must be controlled. All seed issued to growers by California sugar companies has been treated with appropriate materials to protect germinating seedlings from soilborne fungi and, often, from certain insects.
You should know what weeds to expect in your field and plan to control them with the proper herbicide. Publications are available from county Cooperative Extension offices concerning weed control and how to control pests of younger sugarbeets.
Planting
It is essential to use a planter capable of placing single seeds at the spacing desired, and several such makes of planter are available. Use monogerm seed processed and graded to uniform size and property treated with fungicides and an insecticide. Seeds may be pelleted, but this is not essential if the raw seed is properly sized and graded. Be sure to use the correct planter plate or belt for the particular seed you use. Sugar company field representatives will know the correct seed plates and belts for their grade of seed and for your planter. The purchase of new planter plates each season is a good investment, since worn platescan drop double or multiple seeds in a single hill. After selecting the proper gear ratios for the seed spacing to be used, check the drop pattern of the planter on a uniform surface.
If you anticipate good yield emergence (50 percent or better), you can plant to a stand by placing seeds from 4 to 6 inches apart. If a synchronous thinner is to be used, seeds should be spaced 3 inches apart. If thinning is to be done with long-handled hoes, plant seeds 2 to 21/2 inches apart.
Plant at a uniform depth of 3/4 to I inch; deeper planting reduces emergence. Avoid heavy press-wheel pressures that make marked indentations over the seed row. These make thinning more difficult and increase crusting from heavy rains or heavy sprinkler irrigations. During planting, check your seed boxes frequently and clean out accumulated dust and broken seed pieces. Operate the planter at the recommended speed for proper plate or belt cell fill. This is usually 21/2 miles per hour or slower.
Irrigation for Germination and Crust Control
Probably no other single factor affects emergence as much as does correct, well-timed irrigation. Adequate soil moisture for the seed is essential; excesses are harmful. Moisture is also of prime importance in crust formation and alleviation.
When irrigating by furrow, the initial stream of water should be capable
of reaching the end of the raw quickly without overflowing the seed rows
at any point. Then the flow should be cut back to maintain water throughout
the length of the furrow and minimize runoff. Furrow ends should connect
with drains to keep from flooding the lower ends of the beds.
Apply water at the reduced rate until the soil is thoroughly wetted
well past the seed line. Beds will wet more rapidly if the water surface
in the furrows is a short distance below the bed surface. Water levels
can be raised temporarily by blocking furrows at intervals with small earthen
dams that overflow and wash out before flooding the seed rows, or more
permanently with plastic dams that overflow when the desired level is
reached. If beds tend to wet slowly, they can be constructed lower than
the standard height, provided the land is precisely graded and planed to
minimize overtopping.
After the initial irrigation, watch for two critical conditions: crusting and a lack of adequate moisture for germination. A well-timed second irrigation is usually sufficient to replenish the soil moisture. If you time this second irrigation to coincide with seedling emergence, it can be valuable in alleviating crusting.
Properly operated solid set sprinklers assure a high percentage of emergence. (The advantages, selection and management of these systems are discussed in Solid Set Sprinklers for Seed Germination, Leaflet 2265, available from county Cooperative Extension offices.) Sprinklers can be operated once or twice daily to soften crust, leach salts from around the seeds, and maintain optimum soil moisture around seeds. The sprinkler system should be designed to apply low precipitation rates that will reduce puddling of surface soil. The main disadvantage of solid set sprinkler systems is the high investment cost.
Growers who have sprinkler systems available for irrigating other crops might use those systems for germinating sugarbeets, since the system is needed only until seedlings emerge. This may be from 10 to 20 days, depending on the season.
Synchronous Thinning
Synchronous or selective thinning involves the use of a device that detects the presence of a beet seedling with a probe or an electric eye. The thinning knife skips the detected plant, and then removes a portion of the raw equal in length to the length of the knife (fig. 5). The synchronous thinner significantly reduces the number of excessively long gaps in the row as compared to the random mechanical blocker.
Because the thinning device can also be activated by contact with a clod or weed, careful seedbed preparation and good weed control are essential. The soil should not be disturbed by cultivating or hoeing before synchronous thinning. If clods are a problem, rolling may help.
Plant beet seeds no closer than 3 inches apart to prevent leaving too many blocks with double or multiple plants. If seedlings are less than 21/2 inches apart, both plants usually will be left'when the thinning knife is activated. An abundance of doubles will reduce yield.
Set the thinner to remove 4 or 5 inches of row adjacent to each plant sensed. If seedlings are 3 inches apart (as in fig. 5), the minimum spacing between plants after thinning will be 9 inches. However, because of irregularities in emergence, some spaces between plants will be greater. Table 2 shows the theoretical average distance between plants after thinning when seeds are spaced 3 inches apart, their emergence percentage varies, and the synchronous thinner is set to remove plants for 5 inches each time it is activated.
The synchronous thinner should be operated when plants are in the two-
to four- true-leaf stage. If plants are too large, the sensor may sense
a leaf at its extremity, and the cutting blade may remove the plant that
should have been left.
Field trials have shown that synchronous thinning can produce yields
comparable to those produced as a result of careful hand thinning. Table
3 summarizes the results of some of these trials.
Long-handled Hoe Thinning
When seeds are planted closer than 2 inches apart, long-hoe thinning
becomes difficult, the cost may be excessive, and workers usually leave
too many double- and multiple-plant hills. Seedlings from monogerm seeds
planted 2 to 21/2 inches apart are easily thinned with long hoes. Removing
two seedlings between the plants to be left will result in minimum between-plant
distances of 6 and 7 1/2 inches when seeds are spaced at 2 and 21/2 inches,
respectively. A 4-inch hoe blade is convenient to use for seedlings spaced
at 2 inches, and a 5-inch hoe is useful with plants spaced at 2 1/2 inches.
Stand Evaluation
"Do I need to thin?" Use the following procedure to decide whether a
stand is adequate for good production, or whether it needs thinning.
• Count the number of plants per 50 feet of row at six or more locations
scattered throughout your field.
• Average these counts. For example:
• Divide this average into 600 inches (50 feet) to determine the average
distance between plants. For example:
600/143 = 4.2 inches per plant
On 30-inch beds, beets should not be closer together than 5 inches, and on 14- and 26-inch beds they should not be closer than 7 inches. If plants are closer than this, additional thinning is in order. Additional thinning can be done with long-handled hoes if the field has already been synchronously thinned, or, if a synchronous thinner was not used initially, it can be used to do the additional thinning.
"Do I have enough plants for a profitable crop, or should I replant?" A grower may be faced with the question of replanting if there seem to be too many gaps between plants. In 30-inch rows, gaps of up to 18 inches are of little consequence, since plants at the ends of the gaps will grow larger and for the most part compensate for the empty space. With longer gaps, however, the loss in yield is about proportional to the space in excess of 18 inches. Two-row, 40-inch beds have less risk of loss from gap space, and gaps of up to 24 inches may be tolerated. You can estimate your crop loss resulting from a gappy, 30-inch-row stand by following these steps (substitute "24 inches" for "18 inches" if you use two rows on a 40-inch bed).
• At several locations in the field (at least eight), mark off 50 feet
of row and measure and record all gaps greater than 18
inches. Be sure to measure each gap entirely.
• For each location, add up the inches in gap space, and subtract
from that the total number of gaps multiplied by 18, to give excess gap
space (EGS). For example, if you have a total of 174 inches in gap space
from seven gaps:
If you would normally have expected 30 tons of roots per acre from your
date of planting when the stand was good, you would now anticipate a loss
of 9 percent (or a little less than 3 tons per acre), and a resulting crop
of about 27 tons. During warm weather you can anticipate a loss of about
I ton per acre for each week of growing time you give up by replanting.
Thus, if you replant 6 weeks later than your original planting, you will
lose 6 tons per acre. In addition, you will incur the expense of establishing
the new stand. In this situation, replanting does not pay. The loss from
replanting after an original cold-weather planting may be less, perhaps
only 112 ton per acre per week. In this case, replanting 6 weeks later
results in a loss of only 3 tons per acre, and a yield comparable to
that anticipated from the gappy stand; again in this situation, it is not
economical to replant. Replanting decisions are not simple, and they can
be costly-consult your local Farm Advisor and sugar company field representative.
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