Stand Establishment, Fertility & Water Use

Base Replanting Decision On Calendar, Stand
Some crops such as small grains, canola, sunflower and soybean can compensate for low plant populations that may occur as a result of poor stand establishment.  These crops will compensate for stand reduction through tillering, branching or increased head or kernel size. Following are minimum stands of several crops to avoid major yield reductions when making decisions on tearing up the field and replanting.

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. Even stands below 12 plants per square foot of barley and oats have yielded near normal because they typically tiller more than spring wheat, which typically tillers more than durum.  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.

About the only replant choice in mid June is flax, buckwheat, early-short season sunflower or 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. 

What about replanting to improve stands? Remember that a replant decision costs dollars and extra time. In many cases the later planted crops will yield less that the early planted and lower stand established crop. The later replant also may put the development of the crop into a more stressful period, such as a high temperature, drought or risks of fall frost. Also, the harvest period would be extended into the fall when weather conditions can be difficult.

Refer to NDSU Extension Circular A-934, “Replanting after Early Season Crop Injury” for further information, available on the web at: www.ext.nodak.edu/extpubs/plantsci/crops/a934w.htm. 

Minimum stand levels to consider before replanting

Crop	Minimum Stand	% of Normal Stand
Small Grains	8-10 plants/sq. ft.	40-60
Flax	12-15 plants/sq. ft.	20-40
Safflower	2-2.5 plants/sq. ft.	40-50
Canola, Mustard	3-4 plants/sq. ft.	40
Sunflower	11-13,000 plants/A	50-60
Soybean	60-75,000 plants/A	35-50
Field peas	3-5/sq. ft.	40-70
Dry Beans: Navy	45-60,000 plants/A	50-60
Dry Beans: Pinto	28-40,000 plants/A	40-50

Spring Wheat Replanting Guidelines

• 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.

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.

Soybean Stand Evaluation
Under normal planting conditions and soil temperatures, soybean seedlings should emerge five to nine days following planting.  Early planted soybeans without a fungicide seed treatment are more vulnerable to fungi like Pythium which thrives in cool wet soils. Once soil temperatures warm up, other diseases like Phytophthora root rot and Rhizoctonia can reduce soybean stand. It is critical to evaluate soybean fields after emergence and determine what kind of stand you have. The good news is soybean is a very forgiving crop and has a great capacity to compensate for reductions in stand. University of Minnesota research on stand reduction suggests that substantial reduction in plant stands has little effect on yield (figure 1).  It takes a 50% stand reduction to reduce potential yield by 10%. Evaluate stands closely before deciding to replant, also considering the calendar date. Weigh yield loss because of stand reduction against the penalty for delayed planting. U of M research on planting date suggests that substantial yield reduction does not occur until after June 1 (figure 2).

Checking Nodules on Field Peas, Soybeans
Field Peas: Field peas that have been emerged for 2 to 3 weeks should have nodules forming on root hairs of both the primary root and lateral roots. Healthy nodules actively fixing nitrogen for the plant are pink or red inside. White, brown or green nodules indicate that nitrogen-fixation is not occurring. If the pea plants appear yellow and the roots appear not to be nodulated, then it’s suggested to get the field top-dressed with nitrogen. Nitrogen fertilization after planting is not generally recommended, as too high levels of nitrogen fertilizer applied can and will inhibit nodule formation and ability to fix N for the legume plant for later grain development and protein content of the seed. When checking the health of nodules also check root proliferation, and look for any root rot diseases or insect damage. Diseased roots will have low nodule formation.

Soybeans: nodulation can be seen shortly after emergence (VE), but the plant is not actively fixing nitrogen until the V2 to V3 stages. Soybean plants that are 5 to 6 inches tall should have their second unfolded trifoliolate leaflets (V2 stage) totally unrolled. The number and nodules formed on the soybean roots along with the amount of nitrogen fixed increases until the R5.5 stage. Nodules actively fixing nitrogen for the plant are pink or red inside. White, brown or green nodules indicate that nitrogen-fixation is not occurring. Nitrogen fertilization after planting is not recommended as nitrogen fertilizer applied to active nodules will render these nodules inactive or inefficient, depending on the amount of nitrogen applied. Soil nitrogen is utilized over fixed nitrogen, if available in large amounts. Check the health of your soybean nodules and check root proliferation. At V2, soybeans should be rooting down six inches into the soil and by V5 will completely reach between 30-inch rows, making any cultivation at V5 needing to be very shallow.

When checking soybean and pea plants for nodules, don’t pull the roots directly from the soil, since that will slough off nodules and result in an inaccurate count. It’s best to use a small shovel, spade or trowel and dig the soybean roots carefully and shake gently or place in a bucket of water to wash soil off the roots. Nodules then can be counted and examined for viability. It’s suggested to check at a minimum of five sample sites in a field to make a good assessment.

Also, one should go back and check again just before the flowering stage to ensure that the N fertility for the legume will be adequate. Nitrogen fixation ceases with the onset of pod formation in peas and lentils. Good nodulation and N fixation not only benefits the growing crop but also is most beneficial to the crop that will follow in next year’s rotation. These principles and methods of checking for nodules are also suggested for lentils and chickpeas.

Approximate Yield, Water Use, Water Use Efficiency Crops differ significantly in their water requirements, drought tolerance and water use efficiency.  Strictly defining the water use by a crop is difficult because water use is affected by the amount and timing that water is available. For example, a crop like corn is water use efficient (produces more dry matter per inch of water), but also has a relatively high water requirement as it has a higher yield potential than most crops. Furthermore, crops differ in how water stress might affect them. Corn, for example is very sensitive to drought during the flowering process. Wheat on the other hand, is sensitive during several weeks proceeding flowering. A crop that is stressed early in its growth cycle, may not be able to recover to the extent that it will be able to use the water that is available, even though rainfall during the latter stages of development is plentiful Crop Average Yield/A Average Water Use, Inches Water Use Efficiency Yield/A/Inch H20 Alfalfa 5 tons 24 0.2 ton Grain Corn 120 bu 21 6 bu Potatoes 400 cwt 20 20 cwt Sugarbeets (Sugar) 3.2 tons 19 0.2 ton Soybean 35 bu 16 2.2 bu Spring Wheat 40 bu 15 2.7 bu Sunflower 1500 lb 14 110 lb Flax 25 bu 12 1.7 bu Pinto Bean 2200 lb 12 180 bu Barley 55 bu 11 5 bu Source: J.W. Bauder and M.J. Ennen, NDSU Soil Science Department .

Tips for Managing Soil Crusting
Heavy rains on fields not yet emerged can lead to questions of whether soil crusting will be a problem. Consider waiting at least 5 days after a crop is beginning to emerge to determine what percentage of the stand will be established. If a heavy crust does occur, a harrow or rotary hoe will be the best option once the soil starts to dry. Before deciding to rotary hoe or harrow, be sure that seedlings are unable to emerge through the crust. Harrowing can break off an emerging coleoptile or hypocotyl resulting in more damage than good. It is not advised to harrow canola, flax, mustard, or other crop seedlings which can be small and near the soil surface. If the plant is leafing out under the crust layer and the stand is poor, then breaking the crust layer is recommended. A harrow, rotary hoe or any empty press drill with disc openers has been used successfully to break up a crust. Light, spring tooth harrows should be set shallow (½ inch deep) and angled back to reduce the potential of going too deep. Harrowing at a right angle to the rows and driving as slow as possible will also reduce the injury potential to the crop that has emerged.

Average Water Use for Wheat in Inches/Day for North Dakota

Temperature o F	1	2	3	4	5	6	7	8	9	10	11	12	13	14
50-59	.01	.03	.04	.06	.07	.08	.08	.08	.08	.08	.07	.06	.04	.03
60-69	.02	.04	.07	.10	.12	.14	.14	.14	.14	.14	.12	.10	.07	.04
70-79	.03	.06	.10	.13	.17	.19	.19	.19	.19	.19	.17	.14	.10	.06
80-89	.04	.08	.12	.17	.22	.24	.24	.25	.25	.25	.22	.17	.12	.08
90-99	.05	.10	.15	.21	.26	.29	.30	.30	.30	.30	.27	.21	.15	.09
Growth Stages			Tillering		Jointing	Boot	Heading		Early Milk		Early Dough	Hard Dough

Water Use of Wheat
A wheat crop of about 50 bu/ac 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 N.D. 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: http://ndawn.ndsu.nodak.edu and also for Minnesota: www.soils.wisc.edu/wimnext.

Determining Wheat, Barley Yield Probability Based On Soil Moisture For high yields, small grains need 14 to 17 inches of water (soil or rainfall), depending on weather conditions and length of growing season. Small grains require about five to six inches of water as a threshold for grain yield. Each additional inch of water will provide four to seven bushels per acre. In deep, well-drained soils, the roots of small grains will extract water to a depth of 3 to 3.5 feet. Sandy soils hold about 1 inch of plant available water, clay soils about 2 inches and loam soils 2.25 inches per foot of soil at field capacity. Small grains are most sensitive to water stress in the boot to flowering stage of growth. Total Water  Available Wheat Yield  Bu/A Barley Yield  Bu/A 8 12-21 21-30 9 16-28 28-40 10 20-35 35-50 11 24-42 42-60 12 28-49 49-70 13 34-56 56-80 14 38-63 63-90 15 42-70   16 46-77

Water Stress in Corn
Water stress during flowering and pollination delays silking, reduces silk elongation, and inhibits embryo development after pollination. Moisture stress during this time reduces corn grain yield 3-8% for each day of stress. Moisture or heat stress interferes with synchronization between pollen shed and silk emergence. Drought stress may delay silk emergence until pollen shed is nearly or completely finished. During periods of high temperatures, low relative humidity, and inadequate soil moisture level, exposed silks may desiccate and become non-receptive to pollen germination.

Silk elongation begins near the butt of the ear and progresses up toward the tip. The tip silks are typically the last to emerge from the husk leaves. If ears are unusually long (many kernels per row), the final silks from the tip of the ear may emerge after all the pollen has been shed. Another cause of incomplete kernel set is abortion of fertilized ovules. Aborted kernels are distinguished from unfertilized ovules in that aborted kernels had actually begun development. Aborted kernels will be shrunken and mostly white.

Water stress during grain filling increases leaf dying, shortens the grain-filling period, increases lodging and lowers kernel weight. Water stress during grain filling reduces yield 2.5 to 5.8% with each day of stress. Kernels are most susceptible to abortion during the first 2 weeks following pollination, particularly kernels near the tip of the ear. Tip kernels are generally last to be fertilized, less vigorous than the rest, and are most susceptible to abortion. Once kernels have reached the dough stage of development, further yield losses will occur mainly from reductions in kernel dry weight accumulation.

Severe drought stress that continues into the early stages of kernel development (blister and milk stages) can easily abort developing kernels. Severe stress during dough and dent stages of grain fill decreases grain yield primarily due to decreased kernel weights and is often caused by premature black layer formation in the kernels. Once grain has reached physiological maturity, stress will have no further physiological effect on final yield. Stalk and ear rots, however, can continue to develop after corn has reached physiological maturity and indirectly reduce grain yield through plant lodging. Stalk rots are seen more often when ears have high kernel numbers and have been predisposed to stress, especially drought stress.

Critical Growth Stages for Major Crops
See the NDSU web site www.ag.ndsu.edu/drought and SDSU web site, http://sdces.sdstate.edu/drought   for more information on coping with drought and dry conditions, covering various crop and livestock issues, with links to other drought-related web sites as well. 

Critical growth stages for major crops1
Crop	Critical period	Symptoms of water stress	Other considerations
Alfalfa	Early spring and immediately after cuttings	Darkening color, then wilting	Adequate water is needed between cuttings
Corn	Tasseling, silk stage until grain is fully formed	Curling of leaves by mid-morning, darkening color	Needs adequate water from germination to dent stage for maximum production
Sugar beets	Post-thinning	Leaves wilting during heat of the day; abnormal dark green color	Most sensitive to moisture shortages in early growing stages but peak moisture use comes later in the season when they have complete ground cover
Soybeans	Bloom and fruit set	Leaf wilting	Any stress from R4-R6 (late pod development/early seed fill) causes more yield reduction than at any other time
Small grain	Boot and bloom stages	Dull green/bluish color, rolled up leaves; firing of lower leaves	Small grain crop injury from drought stress can appear similar to herbicide injury symptoms
Potatoes	Tuber formation to harvest	Wilting during heat of the day	Water stress during critical period may cause cracking of tubers
Sunflower	Preplant, bud and bloom	Leaf wilting	Most sensitive to moisture stress during flowering; least sensitive during vegetative period (emergence to early bud)
1 NRCS Colorado Irrigation Guide, NDSU, Colorado State University
See the NDSU web site www.ag.ndsu.nodak.edu/drought/drought.htm for more information on coping with drought and dry conditions, covering various crop and livestock issues, with good links to other drought-related web sites as well.

UM Research Links Iron Chlorosis to high N levels
University of Minnesota research indicates that the severity of iron deficiency chlorosis may be linked to high levels of nitrate-nitrogen in the soil that subsequently increases the concentration of nitrate N in the soybean plant. Higher concentrations of nitrate N apparently can inhibit the soybean plant’s metabolism of iron, resulting in lower concentrations of chlorophyll in the soybean plant and subsequently lower yields. Thus, management practices in soybeans need to keep concentrations of nitrate-nitrogen in the soil to a minimum. One approach would be to avoid using excessive amounts of fertilizer nitrogen for the preceding corn crop. Another approach is to use a competition crop such as oats. See research results online: www.extension.umn.edu/cropenews/2007/07MNCN03.htm.

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.

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 online at www.ag.ndsu.edu/procrop/syb/ironchlorosis.htm. 

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

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 top dress, use of stream nozzles or stream-bars and liquid fertilizer is strongly recommended. Sometimes, 28% has been known 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/ac 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/ac 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 (about  ½”) to move the N into the soil so that roots can utilize it. 

Topdressing N in Wheat for Protein
The first question is whether there will be an economic benefit to higher protein this year – consult with a grain market advisor or local grain handler to see what they think about prospects for premiums.  With N prices hovering around 30 cents/ lb N or more, the cost of N plus application would be somewhere around $15/acre. That means that the ½ % protein enhancement possible with 30 lb N/acre would have to cover at least those costs to be profitable.

With 40 bu/ac wheat, that means a protein premium of about 38 cents/1/2 point.

Another consideration is weather; if hot temperatures and dry conditions may have chipped away at yield potential, the N already applied may be sufficient to produce higher protein without help from added N.

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