ISSUE 1   May 6, 1999

FERTILIZING FLAX

    The acreage of flax is on the rebound. Flax has its own unique challenges with regards
to production and nutritional requirements. Much of the fertility work on flax has been
conducted in North Dakota and Canada.

    Flax has a requirement for nitrogen. The soil should be sampled at the 0-2 foot depth
and the results of a soil nitrate test used to modify the standard recommendation for N.
The standard recommendation equation for N is-

3 X Yield goal (in bushels/a) = N needed

From the result, subtract the soil test nitrate level. For example- Yield goal is 45 bu/acre.
Soil test is 40 lb/a.
    The recommendation in this example is therefore-

(3 X 45) - 40 = 95 lb N/a

    Phosphorus is required by flax, but flax is generally a good scavenger of P compared to
small grains. Placement is important. NDSU circular SF-717 (1992) allows that up to
10 lb N+K₂O may be applied with the seed in a 6 inch spaced double-disc drill. However,
some Canadian provinces recommend no fertilizer with the seed, while others allow up to
18 lb/a P₂O₅ with the seed (35-40 lb/a MAP or DAP). There is also a paper that states that
broadcast was better than seed-placed, suggesting some stand reductions with seed-placed
treatments.

    A recent Manitoba study shows that yields actually decreased with application of greater
than 10 lb/a P₂O₅ either seed-placed or side-banded. In this study, stand was reduced when
fertilizer was seed-placed at greater than the 10 lb rate (1 lb N/a with the seed). Using
air-seeders and fertilizer spread within the air-seeder bands, some fertilizer applied with the
seed is probably safer with this method than with the double-disc drills, but caution is still
advised, especially in soils with high pH and free carbonates which allow a higher volatility
and longevity of free ammonia from the phosphate source to linger in the seed zone.

    Rates of P recommended by NDSU charts at low and very low P soil test levels are given
to encourage buildup of soil test P levels when rates are higher than 10 lb/a P₂O₅. If the
decision is made to band fertilizer with the seed, low rates are suggested, perhaps deferring
the additional P recommended towards crops in the rotation that will respond better to it,
such as small grains or corn.

    Banded phosphate is also associated with a greater frequency of zinc deficiency. In some
studies, broadcast treatments of P showed no zinc deficiency symptoms, but symptoms were
evident and sometimes severe on treatments of seed-placed or 2X2 banded P. The
zinc/phosphate interaction with banded P is commonly found on other zinc sensitive crops
as well.

    High potassium (K) levels for flax are defined as any test level higher than 120 ppm. No K
fertilizer is recommended at K levels higher than 120 ppm. K levels lower than 120 ppm
would usually only be found in coarser textured soils along the Red River Valley beach ridges,
outwash plains or some of the older sediments west of the Missouri River Valley.

    Flax is sensitive to low soil zinc levels. According to a recent survey (Extension Report 52),
about 90% of the crop land in North Dakota has zinc soil test levels lower than 1 ppm.
Responses to zinc in flax have been seen at soil test levels lower than 1 ppm, but seldom are
seen at soil test levels higher than 1 ppm. Zinc deficiency is called "chlorotic dieback" and
was identified as early as 1943 at NDSU and later was attributed to low soil zinc levels and
was corrected with zinc fertilizer application.

    Zinc deficiency usually appears in patches, with the first sign being a stunting of the stem
and a bunching of new leaves, forming a rosette at the growing point or meristem. The leaves
in the rosette may yellow, forming the chlorotic feature the condition is named for. Older
leaves are not affected. The upper leaves and meristem may become necrotic. If the plant
survives, lateral buds may develop and form a branched plant, with the stunted main stem still
intact, but the dominant and seed-bearing branches growing from either side of the main stem.

    Zinc deficiency is more pronounced when soil temperatures remain cool ( less than 60^oF)
and soil zinc levels are low. Banded P application may also contribute to the condition.

    Much of the zinc fertilizer work on flax in North Dakota was conducted in greenhouse
studies at NDSU by Dr. J.T. Moraghan in the 1970's and early 1980's. However, these studies
were extensions of personal field observations during this period and the knowledge gained
would be expected to be transferable to the field. Some field work that agreed with this later
greenhouse work was done in the early 1960's by Dr. Zubriski at NDSU. Some of these data
appear below.

Influence of fertilizer applications to a Bearden silty clay loam soil on the yield of flax, Casselton, ND, 1963.

Influence of zinc applications to a Fargo silty clay soil
(pH 7.5, P very low) on yield of flax, Argusville, 1963).

    Rates of zinc suggested are 10 lb zinc as zinc sulfate as a broadcast treatment, or 3 lb/acre
in a band or foliar application. Zinc chelates may also be effective in a banded application.

    Along with soybeans, flax is one of the most sensitive crops to iron deficiency. The iron
deficiency will be most severe when soils are cool and when the soil is wet. Unlike zinc deficiency,
iron chlorosis will not result in branching of the plant, but will turn parts of fields yellow. Plants
will yellow in the upper, youngest leaves and yellowing may progress to necrosis if the condition
lingers. The deficiency may be serious, and may require an application of iron to improve the
condition of the crop. Iron applications are not always successful, and may require a second
application. Iron chelates may be used, but also cheaper sources, such as iron sulfate may also
be used effectively. Often, soil warming will cause most symptoms to disappear.

    Sulfur is not commonly found to be deficient in flax. It is most likely to be found in low
organic matter, sandy soils on higher landscape positions. Response to sulfur fertilization is
modest in comparison with canola.

Anhydrous Ammonia Waiting Period

    A common spring question is how long to wait following an anhydrous ammonia application
before seeding. There is no absolutely safe time. The standard answer is about 5-7 days, however,
few producers actually sit home and play cards waiting for the ammonia to settle out. A more
practical approach is to apply the ammonia at an angle to the future planting direction and go
ahead and plant. Any longer time between anhydrous application and planting is helpful, but
again it is no guarantee of absolute safety. Injured plants and loss of stand have been seen even
the spring after a fall application. The goal is to reduce large gaps in stand that can occur if
anhydrous and planting are done in the same direction.

    So how do producers get by when they seed and fertilize at the same time? They do it by rigging
up the air-seeder with a shoe that separates the seed and ammonia by at least 3 inches laterally
all the time. The ammonia band never crosses the seed row because the two are continuously
separated by steel. The down-side to that approach is that it is usually a shallow application which
may result in loss of ammonia through volatilization if the ground is cloddy, wet, or the
application made less than 3 inches deep. But in terms of seed and fertilizer separation, it is fine.

Micronutrient Update

    During the summer of 1998, a series of copper trials were conducted in Barnes, Wells and
Benson counties on spring wheat. The results supported previous Canadian work that showed a
copper response in low organic matter, sandy soils. The results of this study are presented in
Extension Report #50, available from the Extension Distribution Center at 701-231-7882.
This year, the study is being expanded to ten sites, seven in spring wheat and three in durum to
determine if the results can be duplicated and to determine what rates may be effective.

    There will be boron studies on sunflower conducted out of the Carrington and Dickinson
Research Centers this summer. The results of both of these studies will be made available this
coming winter.

    A chlorosis study on soybeans was concluded in 1998 that showed that the factors most
influencing iron chlorosis in North Dakota were a combination of carbonate level and soluble
salts. When evaluating varieties for chlorosis tolerance in this area, it is suggested that areas
having free carbonates and salt levels higher than 0.5 mmhos/cm in sands and 1.0 mmhos/cm
in heavier soils be selected for the screening area. The degree of chlorosis in any given year is
also greater in wet soils and when soil temperatures are cool.

    Care should be given when selecting soybean postemergence herbicides while soybeans are
chlorotic according to the first year of a two year study to determine the herbicide and chlorosis
interaction. Yields of soybeans were relatively high when Pursuit and Raptor were used in soils
with low salt levels, but yields were relatively low when salt levels were high. Cobra, Pinnacle
and Blazer treated plots were most consistently lowest yielding, while Galaxy treated plots were
most consistently highest yielding. These trials will be repeated in 1999.

Soil Survey of Micronutrients and Soil pH Levels is Available

    During the summer of 1998, a survey of North Dakota zinc, copper, boron and soil pH levels
was made. Every county in the state was sampled at three locations, georeferenced using DPGS
and an upland (hilltop), slope and depressional sample was gathered from each location. Each
nutrient map of the state consists of a separate landscape position. The survey is available as
Extension Report #52 at the Extension Distribution Center (701-231-7882).

    The survey contains some surprising features. It shows that most of the state may benefit from
zinc on sensitive crops such as corn, flax, potatoes and dry beans. It shows that copper should be
sampled by landscape position, not a composite field test. It shows that boron levels are much
lower than previously believed. It also shows that significant areas of low pH are present,
especially in the neighborhood of the Missouri River and areas within the central till plain.

    The survey is a picture of the state as a whole. A large amount of variability is still expected
between farms within regions, but it shows that in certain areas similar features should be
anticipated and testing called for when sensitive crops are planned and when future research
suggests.

HIGH SUGARBEET PLANT POPULATIONS WILL REAP HIGHER REWARDS

    Research conducted at NDSU and U of M indicates that plant populations of 35,000 plants
per acre at harvest will result in maximum yield of high quality sugarbeets. This population
corresponds to have about 150 beets per 100 feet of 22 inches row width at harvest time. To
achieve this ideal population, we need to have about 170 beets per 100 feet of 22 inches row
at thinning to compensate for 10% stand losses that occur from thinning to harvest.

    Growing sugarbeets at these populations has several advantages. Higher plant populations use
available soil water and nutrients more effectively, maximizing percent sugar and recoverable sugar.

    Plant populations below 125 beets per 100 feet of row result in reduced yields and poor quality
beets. Low plant populations compete poorly with weeds and close in the rows later than good
stands. Growers with poor stands are limited to fewer weed control options. For example,
harrowing or rotary hoeing may not be practical when stands are low since it will further reduce
the plant populations.

    So, for maximum yield, percent sugar and recoverable sugar, plant sugarbeets at the
recommended high plant populations.

Mohamed Khan
Extension Sugarbeet Specialist
mkhan@ndsuext.nodak.edu