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ISSUE 3  May 17, 2001

 

REVERE SOYBEANS AND THEY WILL RESPOND

Soybean varieties differ in their ability to emerge at different soil temperatures and from different depths of planting. Recognize varietal differences and you will be rewarded by producing a better crop of beans. All varieties germinate and emerge at 85E F but many have very limited germination below 59E F. Target soil temperatures of 60E F or above for optimum soybean planting conditions before proceeding into the field. Plant soybeans a maximum of 2 inches deep, trying to optimize planting depth to only 1-1.5 inches. Soybeans should never be planted in dry soil. The minimum seed moisture uptake required to germinate soybeans is 50% of the seed weight. Soil moisture should be sufficient to allow soybean seed to imbibe water, but not too flooded. Soil moisture levels too high combined with low temperatures allow soybean seeds to be attacked by soil fungi and decay. Soils too low in moisture can also be detrimental to soybean seed. Water stress can reduce both the rate and percentage of germination in very sensitive crops such as soybean.

Effect of Water Stress on Germinability* and Subsequent Radicle Growth
(
*Germinated for 96 hours at 29EC (84EF))

 

Radicle length (mm)

Species

0 bar

-3 bar

-6 bar

-10 bar (soil moisture conditions)**

Dandelion

13

6

6

0

Bitter sneezeweed

4

1

1

0

Hemp sesbania

10

7

0

0 (very sensitive)

Jimson weed

33

22

13

0

Soybean

68

12

0

0 (very sensitive)

Prickly sida

32

38

33

16

Pearl millet

124

125

94

102 (not very sensitive)

**Where field capacity is 0 bar and progressively drier soil conditions are -3 bar to -10 bar.

Be careful when moving or loading seed to the planter. Soybean seed is very fragile, more than most seed as can be seen at harvest when very low crop moisture can result in cracked soybeans. A 10% reduction is germination can occur simply from throwing soybean seed out of a truck and onto a concrete floor or onto hard ground. Try not to let seed fall more than a foot when handling bags for planting. Test any saved and stored seed for intactness of the soybean seed coat, germination under stress, germination percentage and seed viability prior to planting.

 

MULTIPLE STRESS SYNDROME PREVENTION IN SOYBEANS MATTER OF MANAGEMENT

Just as iron chlorosis can become more severe when multiple stresses are affecting soybeans, a stress such as water deficiency can influence glyphosate-tolerant varieties. In recent growth chamber, greenhouse and filed studies, researchers in Arkansas (published in Agronomy Journal 93:187-195 2001) have shown that while glyphosate-tolerant soybeans contain the ability to block the aromatic amino acid syntheses that kills plants that are not tolerant to glyphosate, the nitrogen-fixing symbiont in the soybean root nodules does not contain a resistant enzyme. Running trials with different spray timings to equate to several different stages of soybean development, early applications as compared to later sprayings generally delayed nitrogen fixation and decreased biomass and nitrogen accumulation, although early-sprayed plants recovered by 40 days after emergence. Even in soils with ample, available nitrogen, plant biomass and nitrogen content were decreased by use of glyphosate. There was, however, large variability in sensitivity to glyphosate by cultivars with biomass decrease ranging form 0 to 30% when measured 40 days after emergence. In growth chamber studies where environment could be more strictly controlled, nitrogen fixation was found to be sensitive to water deficits in the glyphosate-tolerant varieties while companion field studies with the tolerant varieties showed no change in nitrogen fixation as there was adequate soil moisture throughout the growing season. Under limited soil moisture conditions, a decrease in biomass and seed yield was commonly seen. Although glyphosate affected tolerant soybean growth, nitrogen fixation and yield in water-limited environments in the studies, this response may not be consistent across genetic backgrounds. Thus, careful selection of plant genetics and minimization of plant stress during early soybean growth and development are important in optimizing nitrogen fixation, plant biomass and ultimate yield.

 

FIELD CONDITIONS FOR CORN AND SOYBEANS GOOD FOR GROWTH

Warm soil temperatures on the surface have worked to make magic on early seeded varieties. Corn that was planted before May 5 is already emerging with adequate soil moisture promoting the process toward good physiological development. Recently planted soybeans are under less pre-germination stress with adequate soil moisture and warm day time temperatures, limiting cool season soil root rots. Continued warming temperatures and future dribbles of rain may make the early season optimum for plant growth. This is very good news, especially where tight supplies of seed or bin run seed for soybeans were testing below 85% germination scores and on fields that were not rotated from soybeans. Limited rain showers have encouraged optimum soil planting conditions and establishing plants to initiate good root growth and development that will help later in the season. Initiate scouting of fields on a weekly basis to insure crop condition.

Denise McWilliams
Extension Crop Production Specialist
dmcwilli@ndsuext.nodak.edu

 

HEAT CANKER

High temperatures in the 90+ F range this past week, brings on possibilities of heat canker damage. Heat canker often greatly reduces stands of flax, canola, sunflower and sugarbeets, especially in semiarid regions. Barley appears to be the cereal most susceptible to heat canker injury, but will recover as its growing point if still below ground when the damage occurs. Heat canker is not a disease but a stem tissue damage caused by high temperatures at the soil surface. Thin stands, dark colored soils, and formation of a surface-soil crust are conducive to heat canker. If the plants are injured when small, stems become sharply constricted at the ground line, tissues collapse, and the plants fall over and die. When the plants are larger, outer tissues are injured and plants respond by producing additional cork tissue as an overgrowth to the injury. This wound is brittle, and the plant may break off at the soil line later on if exposed to strong winds. Early sowing of sufficient seed and use of a surface mulch to reduce soil surface temperatures are the most effective control measures for heat canker.

 

PROBLEMS WITH CORN EMERGENCE?

Corn should begin emerging after about 100 to 125 GDDís have accumulated following planting. This can be anywhere from one to three weeks after planting depending on the temperature. Hereís a list of a few common things to look for if you encounter an emergence problem in corn this spring.No seed present. May be due to planter malfunction or bird or rodent damage. The latter often will leave some evidence such as digging or seed or plant parts on the ground.

 

CRUSTING PROBLEMS WITH FLAX, CRAMBE, MUSTARD, CANOLA, SAFFLOWER

Some parts of the state received a hard rain a week ago that caused some crusting problems. One question that is being asked is, "How can I break a crust when Iíve seeded a crop such as flax, crambe, canola, mustard or safflower?"

A light harrowing at a Ĺ inch depth can be safely done only if the crop has been seeded deeper than 1 inch. Three days after the crops has been seeded, harrowing should not be considered because if the seedling is within Ĺ inch of the surface, the seedling probably will be killed.

If the crop is trying to emerge through a heavy crust layer and the stand is in jeopardy, the best rescue treatment would be to run an empty disk opener drill at a right angle across the field. Keep the pressure off the drill disks; this will reduce the injury potential.

 

HARROWING FOR WEED SEEDLINGS

Populations of shallow emerging weed seedlings such as pigeongrass, kochia, Russian thistle, wild mustard, pigweed, nightshade and below ground white weed sprouts can be severely reduced by timely harrowing. Harrowing will not reduce wild oat, cocklebur and volunteer sunflower populations that much due to their deeper emergence, however control will be higher if they have not yet emerged and happen to be near the soil surface.

Light spring tooth harrows should be set shallow (Ĺ inch deep) and angled back to reduce the potential of crop injury.

Itís best to harrow wheat and barley at the two leaf stage and not later than the three leaf stage to minimize injury potential. Wheat can be harrowed twice while barley should be harrowed only once. Corn can be harrowed between the one and four leaf stage, and sunflower, 2 to 6 leaf stage. Soybeans and dry beans can be harrowed between the 1 to 2 trifoliolate stage. Itís advised not to harrow canola, mustard, crambe or flax seedlings. Refer to NDSU Extension Cir. W-1134 for additional information on mechanical weed control with the harrow or rotary hoe.

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

 

APPRAISING HAIL INJURY TO SMALL GRAINS

Areas in and around Grand Forks County experienced some heavy hail this week. Prior to jointing hail most often has a minimal effect on yield; however, as the crop approaches reproductive developmental stages, injury to the growing point is more likely and leaf damage or loss has greater impact on yield. This puts little if any of the small grain crop at risk. If any was damaged it would most likely be winter wheat.

Destruction of leaf area on young plants is seldom as serious as appearances may indicate. During early development the growing point is below the soil surface, with this protection, small grains can suffer loss of above ground foliage without dying. If the growing point of small grain is not damaged the plants will likely recover.  When the growing point moves above the soil surface at jointing in small grains it becomes vulnerable to damage.

When hail causes damage, it is advisable to wait several days after the injury occurs to make an accurate determination injury. After this period, new growth on plants with uninjured growing points can be observed. If no regrowth is observed, the stem of the plant may be split to inspect the growing point. The growing point should be white or cream colored. Darkening or softening of the growing point usually precedes plant death.

 

ALLEVIATING CRUSTING IN SMALL GRAINS

Heavy rains followed by hot temperatures is a recipe for crusting. Crusting is usually most noticeable is in areas with low organic matter and little surface residue, and especially in fields were excessive tillage was done.

Crusting sufficient to prevent the coleoptile of a germinating small grain to penetrate the soil surface can result in severe stand loss. When the crust is not broken the first leaf of the seedling will break through the coleoptile and grow under the crust. Once this has happened seed nutrient stores are quickly depleted resulting in plant death. Consequently, managing a crusting problem is a critical time issue especially during warm weather like that experienced this week.

Soil crusting can be alleviated in any number of ways as long as it does not disturb the sub soil. Light rain is idea but when this is not in the forecast, a light harrow, double disc drill set very shallow, or rotary hoe are examples of equipment that can effectively be used. The objective is to very gently break the soil crust.

 

HEAT INJURY

Hot temperatures during early growth of small grains can result in injury, often called heat canker, that appears as bands on leaves. These bands correspond to leaf tissue that was at the soil surface when the hot temperatures occurred, and are most likely on the first and second leaves.

When hot temperatures occur as the crop is emerging injury will appear as damage to the tip of the first leaf. Since much of the small grains around the state were just emerging during the 90E F temperatures this week the most likely injury will be to leaf tips.

Heat canker on small grains is usually cosmetic. If a crop was jointing injury to the growing point is possible; however, a crop in this stage will usually provide enough shade to prevent serious injury.

 

CROP INJURY AND REPLANTING DECISIONS

The decision to replant requires careful assessment of crop injury, alternate crop choices and cultural practices related to crop growth and development. Each case of injury should be considered individually.

Optimum plant population for maximum yield in both barley and wheat is about 30 plants per square foot. Reductions in the plant population will reduce yield albeit in a non not proportional manner. Under favorable growing conditions good yields have been obtained with plant populations below 10 plants per square foot. Replanting small grains should not be considered when populations are at 10 plants per square foot or greater.

The effect of planting date on yield is also important when considering replanting. Delays in planting small grains past May 15 typically result in yield reductions on the order of 0.5 to 1.5 % per day. It is difficult to compare yield of an early planted crop with a less than desirable stand and a much later planted crop with an optimum stand; however, when the original crop is planted well before mid May its yield potential may be better than that of a replant. Under dry conditions the availability of soil moisture must be considered, as it may be depleted by the current crop and will be further reduced during replanting.

The final decision on replanting should be an economic one, based on sound agronomic information. If the cost of replanting is equal or greater than any yield gains, then exercise is the only thing gained. The critical determination is the yield potential of the damaged crop compared to that of a replant, and the cost of replanting.

Michael D. Peel
Small Grains Extension Agronomist
mpeel@ndsuext.nodak.edu


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