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ISSUE 11  July 11, 2002

 

CANOLA-HIGH TEMPERATURES AND DROUGHT

Heat injury to seedlings occasionally occurs on hot sunny days, with air temperatures in the range of 85-95 F and soil temperatures of 120 F have been recorded. Heat injury is commonly associated with drought injury, but excessive heat will also injure or kill seedling plants even if moisture is plentiful.

When in the blooming stages, heat blasting and or flower abortion is a strong possibility. This can vary from field to field and is very dependent on time of flowering, soil moisture and humidity during the hot periods. Usually in this situation one would see no or limited pod growth and thus no seed set. It will usually be in patches on the main stem and branches as related to time of flowers pollinating and the heat stress. With good soil moisture under canola usually flower abortion will be minimized to some extent.

Both low and high temperatures can adversely affect development prior to and during flowering. Low, but non-freezing, temperatures just prior to flowering slow the rate of plant development. The start of flowering is delayed or, if begun, the rate of flower opening is slowed and the amount of pollen shed is reduced. High temperatures at flowering will hasten the plant's development, reducing the time from flowering to maturity. High temperatures during flowering shorten the time the flower is receptive to pollen, as well as the duration of pollen release and its viability. This can decrease the number of pods which develop and the number of seeds per pod, resulting in lower yields. It appears that Brassica rapa (Polish) is more susceptible to this type of damage than Brassica napus (Argentine). Very hot weather combined with drought may cause bud blasting wherein the flower clusters turn brown and die resulting in serious yield losses.

Once pods are formed, canola is more tolerant than at flowering to high temperatures. Cool night temperatures at this time also help the plant recover from extreme heat or dry weather.

However, during this stage, a combination of heat and extreme drought will severely affect the pod and seed development including formation of seeds, seed size and oil content. The seed oil content is highest when seeds mature under lower temperatures (50 to 70 F). High temperatures during seed maturation result in reduced oil content. High temperatures, drought and long days hasten maturity and in combination, can reduce yield through fewer pods, with fewer lighter seeds per pod.

 

CROPS AND WATER USE

"What crop uses the least water and which crops are the most resistant to drought?" These are questions being asked by many producers in drought stricken areas of North Dakota and to states south.

If water shortages appear to be a certainty, it is important to try to anticipate when those water shortages will occur and recognize the difference in the impact that a shortage of water will have on different crops. The crops to be least impacted by moisture shortages are the perennial forages - alfalfa, grasses, and hay crops. These crops have well established, deep root systems and are biomass accumulators - that means they produce biomass (forage) in direct response to the amount of water transpired through the plant. This is in contrast to seed producing crops such as wheat, barley, corn, sunflower, safflower, dry beans, sorghum and millet for grain, which require a specific amount of water to develop to the seed-producing stage and then require additional water to produce high quality seed. Similarly, root and storage crops, such as sugar beet and potatoes, accumulate storage in direct proportion to the amount of water transpired through the plant, but a significant degree of stress at specific stages will result in a significant reduction in both yield and quality.

One way to look at crop water needs is to determine the number of pounds of water needed to produce a pound of dry matter or yield. The list of crops included below shows a wide variation in water needs. From the relatively small amount of water needed by millet, sorghum and corn to the very large amount needed by alfalfa, bromegrass and quackgrass. Irrigators also need to consider that each crop may have vulnerable or critical periods when limited moisture is likely to reduce yields.

Millet is often considered a drought resistant crop but it is more correctly a fast maturing crop that develops so quickly that it utilizes any moisture stored in the relatively shallow soil layers. Beans mature fairly early and are somewhat similar to millet. Navy beans blossom over a short period of time and are damaged by high temperatures during blossoming so yields can be reduced.

Pinto beans, soybeans and buckwheat blossom over a prolonged period of time; thus, the critical period for pollination and filling is spread over a greater time period, giving some degree of drought resistance. While sunflowers are considered to be drought resistant, soybeans are able to withstand higher moisture tensions than sunflowers. Sunflowers, like safflower, however, have an extensive root system that is available to explore the root zone more completely and extract more of the available water from it. Wheat appears to be able to do comparatively well under limited moisture conditions, because of extensive root development to a depth of 5'. Wheat has the ability to produce under quite dry conditions.

Sorghum has the capacity to recover from drought stress and resume growth. Yield under these circumstances is often reduced, but some recovery is made when moisture comes. Sorghum exposed to severe moisture shortage and high temperature over a prolonged period is not likely to recover sufficiently to produce economic yields even though death of the plant does not occur. Corn, oats and flax show varying degrees of drought resistance. Moisture at pollination time and from then to maturity is critical for corn, wheat, and barley harvested for grain. On the other hand, crops like corn, wheat, and barley may prove to be excellent forage crops is not allowed to go to maturity and cut as high quality, high moisture, high protein crops before maturity.

For grain crops, the components that make up yield (the number of heads (ears) per acre, number of kernels per head and the weight per kernel) are the critical components. Environmental conditions have a large influence on these components of yield at different stages in a plant's life cycle.

Water Requirement of Plants

Low Water Requirement - remember that these figures are for dry weight of crop

Plants which require less than 400 lbs. of water  per lb. dry plant weight

Crop

lbs H20/lb

Millet
Sorghum
Corn
Sugarbeet
Sudan grass

274
274
361
377
380

Medium Water Requirement

Plants which require 400 to 700 lbs. of water
per lb. dry plant weight

Potatoes
Barley
Buckwheat
Wheat
Oats
Rye
Soybeans

499
523
540
584
594
634
646

High Water Requirement

Plants which require more than 700 lbs. of water per lb. dry plant weight

Red clover
Sweet clover
Flax
Alfalfa
Bromegrass
Quackgrass

759
784
835
866
977
1000

Source:
Modified version of Ag. Notes from Dr. Jim Bauder
Montana State University

 

DROUGHT AND SEEDLING ALFALFA

Alfalfa seedlings experiencing drought during their first summer may struggle to survive. Luckily, alfalfa seedlings are tough. Despite their slow rate of growth and tender appearance, many of them manage to survive stressful conditions and become productive hay-makers.

Years like 2002 are harder on these seedlings than others, and this is one of those years. Because of the extended heat and dry weather, alfalfa seedlings are experiencing more stress than usual. Anything you can do to reduce stress and competition will help.

The place to begin is weed control. Weeds use moisture and intercept light, two critical needs of seedlings. If weeds aren't too large and they are growing actively, herbicides are a good option. Otherwise, clipping may be necessary. If you must clip, be careful that you don't smother seedlings with your clippings. And leave a tall stubble so seedlings don't go into shock after clipping due to the sudden change in their micro-environment..

Also scout for insects. Leafhoppers, aphids, grasshoppers, and other insects cause extra problems during dry weather. Timely insecticide application or mowing is more important than ever.

Finally, consider mowing or topping off your dryland alfalfa, even if there isn't enough there to harvest. The larger the plant, the more soil moisture it needs to survive. Making plants smaller by clipping will reduce the plant's moisture requirement, relieving some stress and conserving what little precious moisture still remains.

 

SOYBEANS IN BLOOM AND MOISTURE IS CRITICAL

Many soybean fields are blooming throughout the state and in NW Minnesota. The beginning bloom stage or R1 stage in soybeans is marked by the plants having at least one flower on any node of the main stem. Soybeans are at 50% bloom when an open flower can be found on every other plant in a row. Flowering, unlike maturity on soybeans, begins toward the bottom of the plant (at the third to sixth node) and then progresses upward and back downward. Branches off of the main stem will flower a few days later than the main stem. While flowering begins at the base of the plant and proceeds to the top of the plant, physiological maturity of the beans will progress anywhere on the plant stem. Normally, soybean pods will be mature in the middle or top of the plant and down, thus remember to check pods toward the bottom of the plant when determining if harvest time has come. Flowering of soybeans is an important time in bean growth and development. At stage R2, full bloom, each plant has accumulated about 25% of its total dry weight and nutrients; it has attained about 50% of its mature height; and, it has produced 50% of its total mature node number. This later flowering stage begins the period of very rapid N-P-K and dry matter accumulation that will continue through R6. Also, during flowering the soybean plant gears up on its nitrogen fixation in order to provide for the demands of the plant. Scout for disease and insect problems (aphids) during this critical time period of flowering.

Duane R. Berglund
NDSU-Extension Agronomist
dberglun@ndsuext.nodak.edu


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