Planting, Fertility & Water Use

The Ideal Spring Wheat Stand
Agronomists generally agree that an optimum spring wheat stand ranges between 28 to 32 plants per square foot (1 acre = 43,560 square feet; thus 28 to 32 plants per sq ft is about 1.2 million to nearly 1.4 million plants per acre. Thirty plants per square foot would be about 1.3 million plants per acre).

A stand much below 1.2 million plants/ac may reduce yield potential, while a stand much over 1.4 million plants per acre will increase lodging potential. Varieties with strong straw strength can be seeded at higher rates, while varieties with less straw strength may need to be seeded at lower rates. If you plant early into good soil moisture, you can also reduce rates as you will take advantage of tillering. However, increase the seeding rate by 1 to 2 plants per square foot for every week planting is delayed past your early optimum seeding date.

A number of growers use a ballpark seeding rate of bushels or pounds per acre, but differences in kernels per lb amongst varieties, as well as seed lot germination, can result in under/over seeding and less than optimum stands.

A more accurate seeding rate calculation considers desired plant population, historic field stand loss, seed lot germination, and seed count per pound.  For example, if the desired population is 1.25 mil plants/ac, estimated stand loss is 10%, estimated germination is 95%, and the seed lot seed count is 15,000 seeds/lb, then:

• 15,000 x 0.95 = 14,250 viable seeds/lb
• 1,250,000 seeds x 110% = 1,375,000 viable seeds needed per acre
• 1,375,000 seeds divided by 14,250 seeds/lb = 96.5 lbs/ac seeding rate, or 28 seeds per sq ft.

Wheat Replanting Guidelines

Use the following guidelines to determine if replanting spring wheat is worthwhile:

• If reduced stand is uniform (no big skips or holes) keep stands of 15 plants/sq ft.
• If skips are larger (3 to 6 ft) or holes are 4 to 6 ft in diameter and the stand is 18 plants per sq ft or less, then replant if moisture is adequate.
• After June 1 in ND and northern MN, and May 15 in southern MN, replant with a crop other than wheat or barley since yields are reduced by about 50% when planting after these dates compared with normal planting dates.

N.D. Soybean planting dates
Soybean grown in central North Dakota have performed well when planted during mid-May, as indicated by a recent six-year NDSU study at Carrington. During 1999 to 2001, soybean planted during mid-May (May 18 to 21) improved yield an average of 2.3 bushels/acre, or 6%, compared with yield from planting during the first week of June. Average yield with ‘Traill’ (0.0 relative maturity) declined 5% when planted late, while yield with ‘Daksoy’ (00.5 relative maturity) was similar between planting periods.

From 2002 to 2004, soybean planted from May 10 to 15 did not provide a yield advantage, compared with planting 10 to 15 days later (May 20 to 30). Due to a more favorable soil environment for plant establishment, the later planted soybean generally resulted in less time needed for stand establishment, greater plant density and similar date of physiological maturity time, compared with the earlier planting time. However, in one of three times the trial was conducted, ‘Barnes’ (0.3 relative maturity) had an 8 bushel/acre, or 19%, greater yield when planted May 10, compared with May 20, while ‘Walsh’ (0.0 relative maturity) had a similar yield between planting dates.

Planting Dates and MN State Average Corn Yields, 1968-2005
Since 1968, the average planting date for Minnesota’s corn acreage has been earlier by about 1/2 day per year. The average planting date for corn was May 20 in 1968 and was May 3 in 2005. On average, corn is now planted 23 days earlier in Minnesota compared with planting dates of the mid 60s. Based on several years of research in Minnesota, 23 days earlier has resulted in substantially higher corn yields.  A UM analysis shows that corn planted prior to May 1 has averaged more than ten bushels per acre higher than trend yields. Corn yields decreased almost ½ bushel per acre with each one-day later planting date from April 28 to May 21 during the 38 years of 1968 through 2005. While early planting is important to achieve high corn yields, increased yields over the years are due to a combination of factors, including higher yielding hybrids, good weed control, good fertility programs, higher plant populations, earlier planting, and weather factors.

More Facts & Figures on Seeding Rates Online:
www.ag.ndsu.edu/procrop/sds/seedingrate.htm

Base Row Crop Replanting Decision On Calendar, Stand
Around June 10, a corn crop with stands of less than 12,000 plants per acre could be torn up and replanted to a crop like sunflower or soybeans that can be planted at this date and still mature. By June 15, however, the decision may be to keep a stand of 12,000 to 14,000 plants per acre because it would be too late to plant a good alternative.

Uniformity of stand is the key to evaluating a poor stand. If there are no large skips in the field, fairly low plant populations of soybeans (75,000/ac), dry beans (50,000/ac) and sunflower (10,000 to 11,000/ac) can still maintain yields. These plants have the ability to branch or flex and fill in space. This is not as true with corn, and weeds also become a bigger problem.

Water Use of Wheat
A wheat crop of about 50 bushels per acre has a water requirement that is about equivalent to 10 inches. However, because water also evaporates from the soil surface, the actual amount of water needed to produce a crop is higher. Under most conditions in the Northern Plains, small grains will need between 14 and 16 inches of soil moisture per season, depending on climactic conditions and the length of the growing season.

Daily crop water use, also called evapotranspiration or ET, depends on canopy development and will generally peak between heading and early dough stage. Daily ET during this peak period can range from 0.10 to 0.30 inches depending on air temperature and cloud cover. The table below shows estimated daily ET rates figured for spring wheat in central Minnesota at different stages of growth and selected maximum daily air temperature ranges. As weather is variable by location, so too will daily ET estimates vary by location. Real-time estimated daily crop ET may be observed over the Internet during the growing season at: ndawn.ndsu.nodak.edu.

Average Water Use for Wheat in Inches/Day in Central Minnesota

Temp.(°F)	Week After Emergence
	1	2	3	4	5	6	7	8	9	10	11	12	13	14
50-59	.02	.03	.05	.06	.08	.09	.10	.10	.09	.09	.07	.05	.03	.02
60-69	.03	.05	.07	.09	.12	.13	.15	.14	.13	.13	.10	.07	.05	.03
70-79	.04	.07	.10	.12	.17	.17	.19	.19	.18	.17	.13	.10	.07	.04
80-89	.05	.08	.12	.16	.20	.22	.24	.24	.22	.21	.16	.12	.08	.04
90-99	.06	.10	.15	.18	.24	.26	.29	.28	.26	.25	.19	.15	.10	.05
Growth Stage		Tillering						Early Milk			Soft Dough	Hard Dough
			Jointing			Heading

Source: U of M

About the only replant choice in mid June is flax, buckwheat, early-short season sunflower or proso millet. Other options to consider would be to grow a crop for hay, or plant winter wheat in the fall. Remember to take crop insurance into consideration, and herbicide used in the prior planted crop and whether it may create a problem with injury to a crop change.

Spring Frost Tolerance Varies by Crop, Conditions
Canola, Flax, Mustard: These crops can handle a frost of 24° F for a short time with canola the most tolerant to cold temperatures. Frosted leaves/plants will be dark green or black in color. If discolored or injured, wait at least 2-3 days before any decisions are made to see if the growing point is alive. Within 3 days, there should be a new leaf emerging from the growing point located in the center of the plant. The best indication that the plant has been killed by a frost is the stem. If the stem below the cotyledons is wilted and doesn’t straighten out within 48 hours of the frost, the plant is more likely dead.

Pulse crops (field peas, lentils and chickpeas): Similar to small grains, the growing point is below the soil surface to the fifth node stage or about the 4” height stage. If the stem is collapsed, wilted on the soil surface for 48 hours and regrowth has not occurred, that plant has most likely been killed. Recovery is usually quick with the newest leaf emerging from the stem within 3 days.

Sunflower: When in the cotyledon stages, can withstand temperatures in the 25-26° range for short periods of time if they are just emerging from the soil. Sunflower true leaves in the 2, 4 or 6 leaf stages become more sensitive with each development stage and the terminal bud can be permanently damaged. It’s believed that when sunflower are in the V2 stage, then the lower limit would be 26-27°, whereas if sunflower are in the V4 or V6 stages then the lower limit would be 28-29°. If sunflowers become brown or blackened and the terminal bud is damaged then the plants will not recover.

Corn: Historically very few northern corn fields have been destroyed by spring freezes, although research is limited on this subject. Plants less than six inches tall (V-5) will usually recover from frost, because the growing point is still below the soil surface and usually not damaged. Lethal cold temperatures (28° or less) can penetrate the upper inch or two of soil, especially if the soil is dry, and kill plant tissue including coleoptiles and growing points. Non-lethal injury by cold temperatures may cause deformed elongation of the mesocotyl or physical damage to the coleoptile in non-emerged seedlings, resulting in the “cork-screw” symptom and subsequent leafing out underground.

Soybeans: Broadleaf crops that have the growing point at the top of the plant are more susceptible to frost damage than grass species. Thus, soybeans are quite sensitive to frost, and are easily damaged by frost in the 28-32° range. Temperatures of 28° for any extended period of time can completely kill soybean plants (buds, stems and leaves). During the early seedling stage (VE to VC), soybeans have some tolerance to temperatures of 29-30° for short periods of time. If the seedlings have been somewhat hardened off by cool temperatures for several days, then temperatures as cool as 28° can be tolerated. Once true leaves emerge (V1 and V2), soybeans become more susceptible to freezing temperatures below 32° for any extended period of time. Soybeans in the unifoliolate leaf stage are slightly more frost tolerant than soybeans in the first or second trifoliolate stages.

Average Date of Last Spring Frost   28° 32° Fargo May 4 May 12 Williston May 4 May 13 Oakes May 5 May 13 Bowman May 6 May 14 Mandan May 7 May 12 Grand Forks May 6 May 16 Fessenden May 8 May 17 Dickinson Exp. Sta. May 12 May 19 Minot Exp. Station May 12 May 20 Langdon Exp. Sta. May 17 May 28 Source: National Climatic Data Center/ND Ag Statistics Service. Number of years used in average varies by location.

Soybean Fertility Tips

• Inoculation is most useful in first and second-year soybeans. Thereafter, if nodulation was good in the first years, only occasional inoculation is suggested.
• Nitrogen is only needed on first-year soybeans, or soybeans where nodulation was poor the last time the field was in soybeans, or in fields where iron chlorosis has been a serious problem in the past. Rates including residual soil N should be about 50 lb N/acre. Soybeans in fields well nodulated in the past and in fields where chlorosis is only a spotty problem do not need supplemental N regardless of soil test nitrate level.
• Phosphate is needed at soil tests below medium levels. Broadcast is desirable, even in no-till fields, but banded P can be applied if rates of N in 7-inch rows do not exceed 10 lb/acre and do not include urea-N. MAP is probably most safe, but DAP can be used if rates are low.
• Micronutrients have generally not been found to be helpful in North Dakota. Sometimes iron applied with the seed or foliar has helped greenup plants, but EDDHA, the soil applied form most helpful, is often too high priced to be practical at rates required for yield increases. Zinc has not been found to increase yields in local studies, nor has manganese been shown to be beneficial in our region. If foliar micronutrients are used, separate the glyphosate and micronutrient applications by about 5 days, as tankmixing them may reduce weed control.

Iron Chlorosis in Soybeans
Cool, wet weather along with soil high in pH, carbonates and salinity are ideal conditions for iron chlorosis to develop. Chlorosis associated with iron deficiency does not appear until the first trifoliate leaves appear in the plant.

Wheel tracks being yellow or green compared to the rest of the field is likely the result of the difference in soil wetness under the tracks. In dry conditions, the soil tends to be more moist under tracks because of capillary pull of water into the track similar to the press wheels of a planter pulling moisture into the seed zone. More moisture, more bicarbonate, more chlorosis. In wet years, wheel tracks and compacted areas tend to dry first, thence less moisture, less bicarbonate, green tracks.

The adoption by growers of more chlorosis/salt tolerant varieties has resulted in more soybean fields withstanding this stress. Warmer, drier weather helps improve chlorosis symptoms, although NDSU research suggests that even fields which recover quickly may have yield affected due to the condition.

To date, foliar applications of micronutrients or iron sprays on soybeans have not shown consistent yield increases from this condition. Some herbicides may further stress soybeans already stressed by chlorosis; see more information www.ag.ndsu.edu/procrop/syb/ironchlorosis.htm .

Farming Myth: Soybeans build soil organic matter
Soybeans only build soil organic matter if they are tilled under before harvest as a green manure. Rotation studies have shown that when soybeans are introduced, organic matter levels decrease at a greater rate than previous non-annual legume rotations. Research has suggested that under soybeans, rate of organic matter breakdown is increased, evidently helping soybeans by providing additional soil N so that the soybean carbohydrate contribution to nodules is reduced. The increased rate of organic matter breakdown and N mineralization is part of the source of our soybean previous crop N credit we give crops following soybeans.

Topdressing N in Wheat for Yield
Some spring wheat growers may consider topdressing with another 30 to 60 lb N if growing conditions are favorable for wheat, and preplant N rates were based on conservative yield estimates.

Topdressing N deficient small grains from emergence to the 6-leaf stage may serve to increase yield provided a timely rain incorporates the application prior to jointing. The application and its incorporation by rainfall needs to be completed before jointing for yield enhancement. The interval between 3-5 leaf is best; NDSU data indicates that wheat yield response to topdressing is greatest through tillering. Topdressing after the 3-leaf stage and before the 6-leaf stage may help head size, spikelet number and kernel number decision, all of which are yield component decisions that the wheat plants make.

To topdress, use of stream nozzles or stream-bars and liquid fertilizer is strongly recommended. Sometimes, 28% has been know to result in foliar burn; one alternative is 25-0-0, a manufactured urea solution. Some studies have shown this material to be less likely to burn foliage than 28%. However, it is often more expensive to use, so the pros and cons of using this product should be weighed.

On taller wheat, stream nozzles are preferred because the stream-bars have a habit of catching on foliage and breaking off sometimes. However, they do work well and with care can last a long time. Because the stream application is not a foliar treatment, rather a concentrated soil band in effect, it needs rain to work it into the soil. If rain doesn’t fall before the wheat reaches jointing, the N may help boost protein, but will do little to increase yield.

Topdress Dry or Liquid N?
Both dry and liquid N products can be used for topdressing wheat. Dry products may be less expensive, while liquid products may offer the advantage of being used as a herbicide carrier. Urea solutions offer an added advantage of reduced leaf burn. Dry granular products can be applied at any rate. If dry urea is used, it might be wise to also have it coated with Agritain®, which is a tried, tested and proven urease inhibitor, and gives about 10 days of protection from volatility.

The amount of liquid N that can be applied without leaf burn diminishes as temperatures rise and crop growth accelerates. Forty lb N/acre as liquid N is a relatively safe rate when temperatures are cool and small plants provide 40-60% ground cover. With high temperatures and a ground covering crop canopy, safe rates drop to 10-25 lb N/acre with increased margins of safety for urea solutions.

If topdressing applications using liquid N (UAN, 28-0-0), it’s recommended to use streamer bars to minimize and reduce leaf burning and crop injury. Streamer bars concentrate the application into bands, which tend to drive most of the fertilizer to the soil surface rather than coat the leaves, where it could damage the leaf tissue. A concentrated band also slows the rate of urea volatilization from the urea portion (the N in UAN is about 50% urea) of the UAN.

Leaf burn potential when applying liquid N increases as the wind increases. Under windy conditions, the wind breaks the stream apart and converts it into a poor broadcast application, coating leaves and increasing burn. Do not broadcast UAN; the burn will be great and may cause a yield reduction in some cases.

Whichever source is used, rain is needed (¼ to ½”) to move the N into the soil so that roots can utilize it. 

Topdressing N in Wheat for Protein
Topdressing N in an appropriate and timely manner has resulted in a protein boost from ½ to 1 % in N.D. trials, with ½ % being more common.

Topdressing N before the first joint extends will not leave wheel tracks in fields. Traffic across fields later breaks the stem below the joint and will leave tracks visible through harvest.

Topdressing from jointing through the watery ripe stage of grain development will often serve to increase protein content of grain, but will have little if any effect on yield. Applications of N past the watery ripe stage would have no real effect on grain protein content. By the time the wheat crop starts heading out, it has accumulated nearly all of the nitrogen that will eventually show up in either grain yield or protein. It is also logical to conclude that since leaf area decreases as the plants mature, especially with disease and natural senescence, foliar fertilization efficiency will decrease thereafter. Thus, once the grain is in the dough stage, the grain is basically drying and uptake of nutrients is over.

Consequently, it’s generally recommended that nitrogen applications for enhancing protein be made as soon after tillering as possible and before flowering and pollination. (A foliar N application is not recommend before pollination at flag leaf emergence or at pollination, because of leaf burn potential. The need to protect the flag leaf is crucial, and pollination is also a critical time to protect sensitive anthers.)

Apply a foliar application of 10 gal/ac (30 lb N) as 28%, mixed ½ and ½ with water at the watery -ripe stage of kernel development (right after pollination, but before starches have formed). This would be applied as a foliar application during the cool of the day. Although some leaf burn with a foliar application is expected, it will be minimized when the fertilizer is applied during the cool of the day. In years with night temperatures in the 40s and daytime temperatures in the 60s and low 70s, low levels of burn have been reported. With daytime temperatures in the high 80s and 90s, the best times would be early in the morning from 4 a.m. until perhaps 9 or 10 a.m., then again in the evening after 7-8 p.m.

A good choice for nozzles would be flat fans, not forward/back.  The forward and back nozzles used for scab fungicide application are meant to cover the head. We don’t want to cover the head. This fertilizer application is meant to cover the leaf, so flat fans are better.

Leaf burning in trials conducted in N.D. have shown little if any decrease in yield when precautions are taken. Still, this is an art, not a science, and there is no guarantee against leaf burn. Sometimes despite best efforts there is some leaf burning, although if precautions are taken, the effects will not normally be severe. Make sure not to apply streamer N in a high wind which breaks up spray particle stream into a broadcast application. This will result in a high leaf burn risk.  Leaves that are burned do not recover; however, bushels lost due to burn are usually low following pollination, and if protein premiums are expected to be high, a modest protein increase may be worth more than a slight loss in bushels due to superficial burning. 

It is highly recommended that no fertilizer N be applied during small grain heading. Often, scab fungicides are applied at this time for maximum effect.  However, fertilizer should not be applied during a heading application.

Approximate Pounds of Nitrogen Per Plant Per Acre for 45 bu/a Hard Red Spring Wheat (based on Bauers wheat growth studies)

Leaf Stage 4 5 6 7 8 9 Boot 10 Heading 11 Flowering 13 Milky 15 Mealy GDD 511 657 803 949 1095 1241 1416 1591 2191     Pounds of Nitrogen Leaf 15 25 30 35 45 50 50 40 25 5 Stem     10 20 30 35 40 45 40 15 Heads             5 20 55 105 Total 15 25 40 55 75 85 95 105 120 125 The season patterns of accumulation of nitrogen in the different parts of wheat plants are illustrated above. (Source: NDSU Extension Service)

Sidedressing Corn, Sunflower
Corn yield decisions can be made later in growth than in small grains. Sidedressing corn (a practice usually reserved for sandy soils prone to leaching) can start when the corn is tall enough that dirt clods do not cover the young plants. Corn can be 8-10 leaves and still have close to full yield potential if N application is delayed until then, although it’s better to apply it earlier than that – usually 4-8 leaf corn is ideal.

If the corn becomes too tall for injecting with anhydrous or liquid, set up a boom on a high-clearance sprayer with drop nozzles placed between the rows. The nozzles should be weighted or braced so they don’t ride above the canopy. Don’t broadcast N either dry or liquid. Remember that corn isn’t like wheat. Wheat sheds dry and liquid fertilizers to some extent, while corn gathers most of what lands on it into the whorl, which concentrates the fertilizer, resulting in significant and often serious burn and yield reduction potential.

Successful post-N applications with drop nozzles are possible until the corn is taller than the high -clearance sprayer platform. The taller the corn, the more damage will be done turning on the field ends and corn breakage from crowding rows (especially in 22 inch rows).

Estimating Additional N Need For Corn, Other Crops

It is difficult even with soil testing and plant analysis to determine rates of N needed to supplement N loss from leaching, or denitrification following excessive rainfall. The following decision chart developed by the University of Minnesota may help.

Decision Table for the Need for Supplemental N   Question #1 When and how was the N applied?   A. In the fall, less the 4 inches deep and soil temperatures were above 50oF 6 B. In the fall, 4 or more inches deep and soil temperatures were above 50oF 5 C. In the fall, less than 4 inches deep and soil temperatures were below 50oF 4 D. In the fall, 4 or more inches deep and soil temperatures were below 50oF 3 E. In early spring (March/April) 3 F. Broadcast on the soil surface in the fall, unincorporated 4 G. Broadcast on the soil surface in the fall, incorporated, below 50oF 3 H. N applied in May, incorporated. 2 Question #2- What was the predominant spring (May/June) soil condition? A. Normal or drier than normal 1 B. Wetter than normal 3 C. Standing water in low areas 4 Question #3- What does the crop look like?   A. Crop is tall and moving on in maturity, showing N deficiency* 5 B. Crop is short and early in maturity, showing N deficiency* 3 C. Crop is short and early in maturity, showing no N deficiency* 2 D. Crop is tall, moving on in maturity, green 1 TOTAL SCORE

* N deficiency symptoms vary for each crop. Generally, crops are yellow, more so in lower leaves, with upper leaves greener. Lower leaves on corn will become yellow from leaf tip in a V pattern following the mid-vein with the V-tip aimed towards the stalk.

• Add the points for each of the three questions.
• Total is 7 or less- Supplemental N for yield not necessary
• Total 8-9- Supplemental N may or may not be necessary
• Total of 10 or more- Supplemental N is suggested

Supplemental rates from 30-50 lb N/acre are suggested for most crops, on the higher of that range for crops with high yield potential and low risk of quality reduction from application of N (any crops except flax, barley, sugarbeet, safflower).  Also, for canola, if N appears lost, assume that sulfur was also lost and include some in the supplement.

Sidedressing Sunflower
Sunflower can be sidedressed after emergence when soil clod movement won’t damage young plants , to when they are too tall to physically get through. Usually 6-18 inches is best.

Troubleshooting Nutrient Deficiencies
Back-to-Basics, an informative crop fertility web site sponsored by Mosaic (IMC Global/Cargill Crop Nutrition), has one of the most comprehensive photo illustration guide to troubleshooting crop nutrient deficiencies on the Internet. Go to www.back-to-basics.net and click on the link “Nutrient Deficiency Symptoms.” There, visual nutrient deficiency symptoms can be found for various field crops, including corn, canola, soybeans, and wheat.

A flow chart for identifying nutrient deficiencies in corn, compiled by the University of Minnesota Extension Service, can be found online at www.extension.umn .edu/cropenews/2002/nutrientdeficiencyflowchart.pdf.

Nutrient deficiency symptoms for a number of crops can also be found online at www.nrs.mcgill.ca/whalen/nutrient/Symptom.html, web site of Joann Whalen, Soil Fertility Program, MacDonald College of McGill University, Canada.  The images (prepared by the Potash & Phosphate Institute) take time to download, but are unique in that deficiency symptoms of secondary and micronutrients are illustrated, along with N-P-K.

Critical growth stages f