- North Dakota State University
- Side Dressing Fertilizer: Nitrogen in Corn
- Sidedress Applications
- Nitrogen Applications: Sidedress it Right
- Soil Basics Part V: Topdressing and Sidedressing Nitrogen
- Managing N
- Pre-sidedress Soil Nitrate Test (PSNT)
- Nitrogen source
- Applying additional N
- Trickle irrigation
- Water problems
- 3 Tips for sidedressing nitrogen on your corn crop
- Sidedress options
- Over-the-top nitrogen
- Smart nitrogen and sweet corn
North Dakota State University
The greatest need for nitrogen is from the V12 stage to the corn blister stage in a corn plant’s life. Typically, corn is side-dressed at the 6 leaf (V6) stage; however any time prior to V12 will achieve management goals.
Soil type heavily influences the side-dressing decision. High clay soils should have a planned split-application of nitrogen fertilizer due to the risk of nitrogen loss by denitrification. Fine-textured sandy soils also have high risk of nitrogen loss due to leaching.
Corn at 2-3 leaf staging can withstand a broadcast application of urea. Urea can used in older corn plants can cause fertilizer burn or plant death and the least favorable nitrogen choice. Urea broadcast should be limited at 60 lb actual N/acre.
By 4 leaf crop staging, nitrogen should be applied between the rows. In older corn, anhydrous ammonia can be applied if the soil will seal up. The second most desirable application method is the application of UAN (28%) with a coulter which places fertilizer at an approximate 2 inches depth. The third-best alternative is to apply UAN as a surface band using orifice nozzles between the rows. Corn injury can be reduced if a stiff hose which drags or nearly drags on the ground is configured to the stream bar.
Fertilizer placed in every other row is sufficient. Slow-release formulations should be avoided.
Side Dressing Fertilizer: Nitrogen in Corn
To determine the best option for an in-season N application, consider the source of N to be used, crop growth stage, and the ability to minimize N loss. After considering these factors, injecting N fertilizer between rows is often the best option. With applications between rows, N is kept at a safe distance to avoid crop injury and is placed where the crop roots will be growing. Also injecting or incorporating N minimizes the potential for N loss.
Applying N in every other row can help increase the speed of application and research indicates that yield may not be negatively impacted because every row will have N applied on one side.1 Using this every other row system, injection points can be adjusted to avoid placing an injector in a wheel track, where higher N losses may occur.
Anhydrous Ammonia. Applications should be made under soil conditions that ensure proper sealing of the knife track. Ammonia vapor can escape with shallow injection or if improper sealing occurs, corn leaves can be damaged. If only a portion of the leaves are damaged, corn plants usually grow out of the leaf damage. Also, sidedressing should occur early to avoid root pruning or anhydrous ammonia “burn” damage to seedling roots (Figure 2).
Urea-Ammonium Nitrate (UAN).When using UAN solutions such as 28% or 32% N, injection between the rows is the preferred application method which minimizes volatilization N loss. The probability of N loss is higher if not incorporated appropriately. Half of the N content in UAN is urea. Up to 30% of the urea component could be lost due to volatilization if no rainfall is received within ten days and temperatures are warm.3
Broadcasting UAN solutions can be implemented; however, foliar leaf “burn” may occur resulting in leaf loss and reduced early growth. (Figure 3). Due to injury concerns, it is recommended not to exceed 90 lbs N/acre of broadcast UAN when corn plants are at the V3 to V4 growth stage and 60 lbs N/acre broadcast at the V7 growth stage. Also, if plants are larger than V7 growth stage, UAN solution should not be broadcast applied across the foliage. For applications after V7, use drop hoses for UAN “dribble” application directly to the soil surface between the rows.
Urea. Broadcasting urea may cause some leaf “speckling” or browning of the leaf edge when granules fall into the corn whorl. The potential for this to occur increases with higher application rates and taller plants. However, leaf burning is generally less with broadcast urea granules compared to broadcasting UAN solution, ammonium nitrate, or ammonium nitrate.3 To minimize adhesion of urea granules to the plant, apply when the foliage is dry. Using an urease inhibitor when sidedressing urea early in the season can minimize volatilization loss.
SIDEDRESS NITROGEN IN CORN
Nitrogen (N) is an essential nutrient for successful corn production and there is never a good time to be short of N. The chart below illustrates how much N is accumulated by a corn plant during the growing season.
Approximately 60% of the total amount of N needed by the plant is accumulated from V4 to pollination, making that an especially important time to be mindful of the N available in your fields. N deficiency after V6, when the plant is relying solely on soil supplied nutrients, can have severe impacts on yield. The rate of N uptake diminishes after pollination as a high percentage of the N used during grain fill is supplied via remobilization from leaf and stalk tissue.
Various application methods can be used to ensure N availability to the crop all season long. Pre-plant applications of N are common as it’s typically easier to find time to do the application. Pre-plant applications have a higher risk of N loss because of the amount of time between application and plant uptake. To better understand the dynamics of N loss, please refer to the previous Between The Rows “Understanding Nitrogen Loss”. The application method that poses the least risk of N loss is applying after corn emergence, commonly referred to as sidedressing.
sidedress n determination
Sidedressing N is essential if little or no N was applied before planting and applications should be made by the V3 growth stage. Sidedressing is often a planned part of N application programs where part of the N is applied before planting and the remainder is applied after emergence. Split N applications are a common practice of growers striving to get maximum yield, such as in yield contests. In other cases, sidedressing is used to supplement or replace N lost from pre-plant applications due to weather. This is often the case in wet springs, especially in June, where a significant amount of N can be lost due to leaching or denitrification in warm, saturated soils.
There are various soil and tissue testing methods available to determine if supplemental N is needed after crop emergence. All these methods have their pros and cons and should be studied before using. A more recent popular method of predicting post emergence N applications is the use of internet based N modeling tools. These e-based tools use algorithms that account for current N availability, crop growth stage, weather, and soil parameters.
A simple method for determining N need is observing the plant’s growth and color. This method is best if N check strips were previously applied for comparative purposes. Regardless of method, if the crop is expressing N deficiency symptoms at any point from the V4 stage through pollination, a sidedress application of N is usually a wise investment.
Late season N uptake can differ among hybrids, but no hybrid will yield well in N deficient conditions. To ensure maximum yield, regardless of hybrid, use a N management program that supplies a readily available amount of N to the crop throughout the growing season. Rather than choosing which hybrid to sidedress for supplemental N, choose which field is more likely to respond.
The best response to sidedress will come from fields with:
- Little or no pre-plant applied N, apply N before V3
- Saturated soils in warm conditions, especially poorly drained fields
- Coarse (sandy) soils that received heavy rainfall after planting
- High pre-plant N losses due to weather
- N deficiency symptoms from the V4 growth stage through pollination
- High stand counts, uniform growth and yield expectations that are higher than the planned pre-plant N rate
Sidedress N application methods
Anhydrous ammonia – This application method provides an efficient in-season N source. Applications should be made prior to the V6 growth stage to avoid excessive root pruning. It’s important to make sure the application knife track is properly sealed to avoid N loss and crop damage.
Broadcast urea – This is a time efficient application method but is vulnerable to volatilization loss. To avoid N loss, applications should be made shortly before an expected rainfall. In warm conditions, as much as 30% of broadcast urea can volatilize if there is no rainfall within 10 days after application. Urea stabilizer products such as Agrotain® Plus can be used to reduce volatilization. Urea granules can cause leaf burn. To minimize leaf burn, apply granules to V4 or smaller corn when leaves are dry. If urea is applied in emergency situations to larger corn, leaf burn will be more apparent but is worth the risk if the only alternative is not having enough N available for the crop.
Urea Ammonium-Nitrate (UAN) solutions – This method has the widest application window and is only restricted by the height of the crop for the application equipment used. High clearance machines allow application up to tasseling. Liquid N solutions can be dribbled on the soil surface or injected using a coulter system. Avoid broadcast applications after V3 growth stage due to the potential of extreme leaf burn. Dribble applications are prone to volatilization loss if not incorporated by a rainfall.
N stabilizers can be used to reduce the risk of N loss.
Fertigation – Applying N through sprinkler irrigation systems is a common and efficient practice. Proper equipment to avoid backflow into the water source is required when using this method. Fertigation should begin with the first irrigation and be complete by the R1 to R2 growth stages. Application rates of 20-30 lb N/acre per irrigation event are recommended. However, higher rates of up to 50 lb N/acre per irrigation are unlikely to cause crop damage because the fertilizer is diluted in water. It is important that water is applied uniformly, without runoff, to ensure even distribution of N.
There is never a good time for a corn crop to be short of nitrogen. Pre-plant N applications have an increased risk of N loss, leading many corn growers to use sidedressing as part of their nitrogen plan. For others, it’s a way to add supplemental N in fields that have sustained high N loss. In either case, there are factors to consider to ensure the best return on your investment.
Fertilizer side-dressing gives extra nutrients to vegetable crops so that they can produce to their full potential.
Side dressing is the application of fertilizers in a shallow furrow or band along the side of vegetable row crops or in a circle around individual plants.
Side dressing gives extra nutrients to vegetable crops so that they can produce to their full potential.
To side dress create a furrow 1 to 2 inches deep along a row of plants or in a circle around each individual plant. Create the furrow just beyond the plant’s drip line (the drip line is the distance from the central stem of a plant to the end of its widest branches). Apply the fertilizer in the furrow and cover with soil.
Side dressings include solids such as granular fertilizers, aged compost and manure, bone meal, and rock phosphate and also liquid fertilizers and fish or seaweed emulsion or compost and manure tea.
Side dressing is commonly done when plants need extra nutrients for growth–at flowering or fruiting time and in the second half of the growing season. From midseason on vegetable crops make rapid growth and quickly use nutrients put in place before sowing or transplanting.
Side dressing also resupplies nitrogen, phosphorus, potassium, and trace elements leached form root zone by irrigation.
How Much to Side Dress Vegetables
One handful of good compost is sufficient to side dress most vegetable plants. That is equal to about one tablespoon of 5-10-10 fertilizer. Adding liquid fertilizers to your watering can is an easy way to side dress. A cupful of compost tea is a good side dressing.
It is important to apply commercial fertilizers according to the instructions on bags or bottles. Over fertilized vegetables tend to be less productive.
Fertilizers should not be placed right next to the stem of a plant; they might burn the roots. Fertilizers side dressed outside the drip line will encourage roots to extend beyond the drip line.
When to Side Dress Vegetables
One side dressing at midseason is usually enough to sustain and encourage a vegetable plant to harvest. Heavy feeding crops–mostly summer fruiting crops that take a long time to mature such as tomatoes, peppers, and eggplants–will benefit from more than one side dressing.
Here are suggested times to side dress vegetables:
- Beans: not necessary.
- Beets: add bone meal or phosphorous at planting time; side dress when plants are 4 to 5 inches tall.
- Beet greens: 2 weeks after leaves appear.
- Broccoli: 3 weeks after transplanting and again when heads begin to form.
- Brussels sprouts: 3 weeks after transplanting; again when sprouts are marble size.
- Cabbage: when the head begins to form; side dressing is not necessary if soil was well fertilized at planting.
- Carrots: add bone meal or phosphorous at Cauliflower: when heads begin to form; not necessary if soil was well fertilized at planting.
- Celery: 3 weeks after setting out starts; again 6 weeks later.
- Chard: after each cutting when substantial leaves are taken from plant.
- Corn: 3 weeks after planting or when plants are 8-10 inches tall; again when tassels appear.
- Cucumbers: just before vines start to spread and again when blossoms set.
- Eggplant: 3 weeks after transplanting and again at blossom time.
- Kale: when plants are 6-8inches tall.
- Leeks: when plants are 12 inches tall.
- Lettuce, head: a few weeks after planting.
- Lettuce, loose-leaf: after second and third cuttings for cut-and-come again crops.
- Melons: just before vines begin to spread; a week after blossom set; again 3 weeks later.
- Okra: at blossom time.
- Onion: 3 weeks after setting out; when tops are 4 to 8 inches tall; when bulbs begin to form.
- Peas: not necessary.
Peppers: 3 weeks after transplanting; again at blossom time.
- Potatoes: before second hilling; when plants bloom.
- Pumpkins: when plants start to run; again at blossom time.
- Radishes: no need to side dress.
- Spinach: when plants are about 1/3 grown; at second and third cuttings for cut-and-come again crops.
- Squash, summer: when plants are 6 inches tall; again at blossom time.
- Squash, winter: just before vines begin to spread; again at blossom time.
- Sweet potatoes: before second hilling.
- Tomatoes: 2 to 3 weeks after transplanting; at blossom time; before first picking; 2 weeks after first picking–always light on nitrogen.
- Turnips: add bone meal or phosphorous at planting time.
- Zucchini: at blossom time.
More tips at Vegetable Plant Nutrients and Fertilizers for Tomatoes, Peppers, and Eggplants.
An application of fertilizer between the rows of growing crops is known as a “sidedress” application. The application of N fertilizer between the rows of a growing corn crop is the most common sidedress application on dairy farms.
The decision to make a sidedress N application should be based on a Pre-Sidedress Nitrate Test (PSNT). This test assesses whether or not the corn crop will have a yield response to the addition of sidedress N. If the PSNT indicates that a yield response is likely, then the sidedress application of N should be made when the corn is 12-24 inches tall. This roughly represents the last time we can access a corn field to apply N before the crop moves into a phase of high N demand. Sidedress N applications are geared to supply N when the crop needs it and can handle it (i.e. ample root system, ability to photosynthesize, etc.), so it’s highly efficient.
Nitrogen can be sidedressed using three methods:
1. Urea Ammonium Nitrate (UAN) solution can be applied with a pesticide sprayer fitted with drop nozzles. The solution is dribbled on the soil surface.
2. Urea Ammonium Nitrate (UAN) solution can also be injected into the soil between the rows with disc openers.
3. Anhydrous Ammonia is another N fertilizer used in sidedress applications. Use of anhydrous ammonia is on the decline, because it poses a risk to the applicator, must be injected, and transport over the road is regulated.
What are the pros and cons of sidedress nitrogen applications?
- Sidedress applications allow the use of the PSNT to decide whether money should be spent on sidedess N applications or not.
- Nitrogen can be applied with a high nutrient use efficiency, because the N is applied to a rapidly growing crop at the stage of growth when N is needed most.
- Sidedress timing (often late June) can interfere with other crop management activities or be difficult due to field wetness.
- Injection is slow. Although spray rigs with drop nozzles can be much faster.
- Anhydrous ammonia has downsides due to handling safety, transportation regulations, and the risk of theft.
Continue to the next pages for a focus on fertilizer materials.
Nitrogen Applications: Sidedress it Right
Switching products and application from preplant to sidedress requires availability of needed fertilizers and equipment. So have a plan in place.
By John Sawyer, Department of Agronomy, Iowa State University
Options for sidedress N
If decisions are made to plant corn and then apply N sidedress, be certain to check that needed fertilizer products and application equipment will be available. Best options for sidedressing, in order from most to least preferable, include:
- Injected anhydrous ammonia, UAN or urea,
- Broadcast dry ammonium nitrate, ammonium sulfate or urease treated urea,
- Surface dribbling UAN solution between rows,
- Broadcast UAN, and
- Broadcast urea.
Sidedress injection can begin immediately after planting if corn rows are visible or GPS guidance positioning equipment is used. Be careful so that soil moved during injection does not cover seeded rows or small corn plants. It is easiest to inject in the row middle and there is no advantage in attempting to place the band close to the row. Corn roots will reach the row middle at a small growth stage. Injected N can also be applied between every other row. That technique will provide equivalent response as when placed between every row. For many soils, when planting corn after soybean there should be adequate N in the root zone to meet the needs of small corn plants. For corn after corn, there is a greater chance that additional N is needed for early growth. Preplant or starter N can help meet that need, and is especially important if sidedressing is delayed significantly in either rotation.
Broadcasting urea or ammonium sulfate across growing corn might cause some leaf spotting or edge browning where fertilizer granules fall into the corn whorl. The chances of this happening increases with larger corn. As long as the fertilizer distribution is good and not concentrated over plants, the leaf damage should only be cosmetic.
Because UAN solution is comprised of one-half urea and one-half ammonium nitrate, it has less volatile loss concern than dry urea. A urease inhibitor with surface applied and non-incorporated urea and UAN will help reduce volatile loss. Rainfall will eliminate volatile loss and is needed to move surface applied N into the root zone.
Broadcast application of UAN solution across growing corn has the potential to cause leaf burn and reduced early growth. Depending upon the severity of damage, reduced plant growth may be visible for several weeks after application. Research conducted in Minnesota indicated that when corn plants were at the V3 growth stage (vegetative leaf stage defined according to the uppermost leaf whose leaf collar is visible – in this case three leaf collars visible), phytotoxic effects were worse at rates above 60 lb N/acre (rates applied were 0, 60, 90, and 120 lb N/acre), but damage was not permanent and did not adversely affect stand or yield. When plants were larger than the V3 stage, plant damage was worse and some yield depression occurred with the 120 lb N/acre rate. Many pre-emergence herbicides are applied using UAN as the carrier to minimize trips across fields. However, this strategy is only recommended prior to crop emergence. Almost all herbicides prohibit application in N solutions after corn has emerged. Check herbicide labels closely.
If N is going to be sidedress applied, then rates can be adjusted from results of the late spring soil nitrate test (LSNT). Soil samples, 0-12 inch depth, are collected when corn is 6-12 inches tall with rate adjustment based on the measured nitrate-N concentration. Using the LSNT could be especially helpful this spring when there is question about N supply in manured fields. The large rainfall this spring has moved carryover nitrate deeper in the soil profile. A concern with the LSNT this spring is that it will miss that nitrate and therefore over-estimate needed application.
Late sidedress N considerations
If corn becomes too tall for normal sidedressing equipment, it is possible to use high clearance equipment to apply N. The N source typically will be UAN solution, with equipment available to either dribble the solution onto the soil surface with drop tubes or shallow inject with coulter-shank bars (coulter-disk injected) or dry urea, which can be broadcast spread across the top of corn.
Research in Iowa has shown corn can respond to mid- to late-vegetative growth stage N application when there is deficient N supply, but there can be loss in yield potential. Reduced yield occurs more frequently when soils are dry at and after application (applied N not getting into the root zone) and with severe N stress. Best responses occur with sufficient rainfall shortly after application to move N into the active root zone.
If attempts to get N applied preplant or early sidedress have failed, or there are concerns about N supply from prior fertilizer or manure applications, then mid- to late-vegetative-stage application can be a helpful rescue. If possible, have some non-N limiting (approximately 50 percent more than normal rate) reference strips or areas in the field to use for comparison. These areas can be used to visually determine if corn would respond to additional N, or as a check to see if earlier N applications or carryover N is not sufficient. These reference areas are also needed for N stress sensing tools (such as chlorophyll meters or canopy sensors) to help guide application rates. These reference areas should be planned and N applied early in the season, or be field areas that are known to be non-N deficient. Plant and canopy sensing can begin when corn is at approximately the V9-V10 growth stage. If late N application is needed, it should be applied as quickly as possible and not later than the tassel stage.
Soil Basics Part V: Topdressing and Sidedressing Nitrogen
In the last fact sheet, we discussed soil testing and nutrient application. Routine soil tests are not good predictors of nitrogen (N) availability, but we discussed how we can estimate N availability based on sources such as soil organic matter, cover crops, manure and compost. Generally, it is best to apply only a small amount of N at planting and supply more as plant demand increases during the growing season. Decomposition of organic materials in the soil will supply some or all of the required N and sidedress or topdress applications should be adjusted accordingly. A pre-sidedress soil nitrate test (PSNT) is helpful in determining if an application of additional N is needed. This fact sheet will address using the PSNT and methods of topdressing and sidedressing N, including application using trickle irrigation.
Regardless of its source, most soil N is converted to nitrate-N, which is highly soluble and easily leached. It is not desirable to have high levels of soil nitrate when crop demand is low. When we broadcast large amounts of N prior to planting, most of it will be converted to the nitrate form several weeks before crops can utilize much of it. In the mean time, the N is subject to leaching. The degree to which leaching actually occurs is dependent on the amount of rainfall and irrigation and soil characteristics. Leaching risk from pre-plant N applications can be reduced somewhat by using a slow release N fertilizer such as sulfur-coated urea. Soil organic matter, compost and residues from previous crops are generally considered to be slow-release sources of N, but certain organic sources of N are readily available. Up to half the N in dairy manure and 75% of the N in poultry manure is readily converted to nitrate-N. A large part of the N in legumes is converted to nitrate shortly after plow down. Pre-plant incorporation of manures and legumes can result in leaching risks similar to fertilizer N.
Plastic mulch protects N from leaching from the portion of the field that is covered by the mulch. However, the bare soil between the plastic strips is not protected, and in fact, may be more susceptible to leaching because, during a rain storm, it receives water being shed from the plastic in addition to that which falls directly on the soil. Many growers are applying N in wide bands and covering them with plastic.
Good N management involves supplying the right amount at the right time for crop needs. Lack of sufficient N can reduce yields, but any N in excess of crop needs is subject to leaching. Studies in New York have shown that even a small amount of over-fertilization with N increased nitrate levels above drinking water standards in ground water. In one study, when N was applied to corn at 30 lbs/A above the optimum rate, 40% of the excess was lost to leaching. The study was done on a sandy soil, typical of many agricultural soils. Leaching becomes less likely as soil texture becomes finer.
In some crops, such as corn, application of excess N is simply a waste of money, costing a grower as much as $30 to $60 per acre (depending on the N source) without any benefit. With other crops, over-applying N can also suppress yields or quality. In studies in New York and Massachusetts, pumpkin and butternut squash yields were reduced by applying more N than required by the crop. High levels of N can increase the incidence of blossom-end rot in tomatoes and delay maturity of onions and potatoes.
For most crops, it is appropriate to apply 20 to 40 lb of N per acre as a band at planting, or if banding is not practical, up to 50 lb per acre as a pre-plant broadcast. This practice should be adequate because crops use small amounts of N during the first few weeks after germination or transplanting. As the plants grow, their need for N increases, and additional N can be applied as a sidedress or topdress. When the soil is warm and if soil conditions are appropriate (see Soil Basics IV), N will be released or mineralized as microbes break down soil organic matter. This N can supply some, and sometimes all, of the crop’s remaining N requirement, reducing or eliminating the need for additional N.
Pre-sidedress Soil Nitrate Test (PSNT)
The PSNT was developed originally for use in field corn on dairy farms where manure is routinely applied and legumes are often included in the cropping system. It is now well established that if the nitrate-N level in the soil is above a threshold level of 25 ppm when the corn is six to twelve inches tall, additional N from fertilizer will not increase yield. Most vegetable growers do not include manure or legumes in their cropping systems. However, several years of research and experience on vegetable farms shows that decomposing soil organic matter can release substantial amounts of N which can be measured by the PSNT.
Samples for the PSNT should consist of a well-mixed composite of 10 to 20 cores or slices of soil to a depth of 12 inches. Avoid sampling fertilizer bands or areas that may have received extra N. About one cup of the composite should be dried to stabilize the nitrate. A good method is to spread the soil thinly to air dry. A fan will reduce drying time. Do not place damp samples on absorbent material because it can absorb some of the nitrate. You can skip the drying step if you can deliver the samples to the soil testing lab in less than 24 hours. Fields should be sampled for the PSNT about a week before the time when side or topdressing is normally done. This should allow adequate time for drying, shipping, and testing (turn around time in the lab is about 24 hours) and for you to plan your program. See Soil Basics IV for mailing information and prices for soil testing.
As with field corn, sweet corn does not respond to N application if the soil nitrate-N level exceeds 25 ppm as measured by the PSNT. Based on research and experience, a threshold of 35 to 40 ppm seems appropriate for peppers, tomatoes, butternut squash or pumpkins. This suggestion may appear contradictory since the N requirement for peppers and tomatoes is about the same as sweet corn and it is lower for pumpkins and squash. However, sweet corn has a deeper and more extensive root system than most other vegetables and is better able to extract N from the soil. Vegetables with shallower root systems would logically require a higher concentration of N in their root zones to supply their needs.
Nitrogen is available in a number of forms. These include urea, ammonium and nitrate. Common fertilizer sources of N used in New England include urea, ammonium nitrate, diammonium phosphate, monoammonium phosphate, calcium nitrate and potassium nitrate. In the soil, urea is converted by hydrolysis to ammonium, which in turn is converted through nitrification to nitrate. In warm soils these reactions usually happen fairly quickly if soil pH is over 6.0 and soil moisture and aeration are adequate. Nitrate is the predominant form of N taken up by most plants, but any of these fertilizers can be used because they will be converted to nitrate. However, high ammonium levels can interfere with calcium uptake and induce calcium related disorders such as blossom-end rot of tomatoes, tip burn of cabbage and greens and cavity spot of carrots. This problem is exacerbated by heat and moisture stress and may not be an issue every year. Many growers use calcium nitrate and sometimes potassium nitrate for topdressing or sidedressing N on crops subject to calcium related disorders. High ammonium levels can also be injurious to soil microbes leading to a prolonged period of high ammonium. Ammonium nitrate provides half the N in the nitrate form and half in the ammonium form. Urea N is converted to ammonium N and then to nitrate N. In effect, applying urea is similar to applying N in the ammonium form. Application of urea and ammonium phosphates are most likely to interfere with calcium uptake whereas calcium nitrate and potassium nitrate are not likely to do this. Ammonium nitrate is intermediate in this regard. When a slow release form of urea is used, only a small amount of ammonium is present at a given time and is unlikely to cause a problem with calcium nutrition, but N may not be available quickly enough to meet the demands of a rapidly growing crop.
Applying additional N
Supplemental N is typically applied during the growing season as a sidedress or topdress. A sidedress application involves placing a band of N into the soil at a desired distance from the row of plants and is done with a fertilizer applicator mounted on a cultivator. The machine should be adjusted so that the fertilizer band is far enough from the crop row to avoid root damage by the equipment. For a topdress application, fertilizer is broadcast over the entire field, usually with a spin-type spreader. Most of the fertilizer granules bounce off the plant, but a few remain on the leaves. The adhering granules can burn the leaves, leaving small dead spots. Other than leaf crops, this injury is not much of a problem, but if the leaves are moist during application, more fertilizer sticks to the foliage and serious leaf burn can occur. Many growers cultivate the crop after topdressing to incorporate the fertilizer, and others try to apply it just prior to rain or irrigation, which can move soluble N into the soil. Some growers are using liquid solutions of N in water. Typically, these are sidedressed. There are no significant differences between liquid or dry materials from a horticultural standpoint. The main considerations in deciding which of these to use are equipment and convenience.
Trickle, or drip irrigation has become increasingly popular with vegetable growers and is frequently used under plastic mulch. By using a fertilizer injector, trickle irrigation can be used effectively to apply N during to growing crops. (NOTE: Certain precautions must be followed when injecting fertilizers. See recent articles in Vegetable Notes by Anne Carter on components of a trickle irrigation system.) The need for supplemental N can be determined using the PSNT as it is with other application methods. Samples for the PSNT should be take from under the plastic, if used. The best way is to use a soil sampler which will punch a small hole in the plastic and remove a core of soil. Be sure to avoid cutting the irrigation tape when sampling under plastic.
When topdressing or sidedressing, it is common to apply all the N in one or two applications. Smaller, but more frequent applications are desirable from a N management standpoint, but are time consuming, and may be impossible when plants grow large. With trickle irrigation, it is convenient to apply small amounts of N weekly or even daily. For example, if you want to apply about 50 lb N per acre, you can inject a little over seven lb N per acre per week for seven weeks, or about one lb per day if you prefer. Small weekly applications provide for more efficient crop use of N than one or two larger applications. Daily application offers little advantage over weekly application, but may be necessary if the injector can not inject a week’s worth of N during the appropriate irrigation run time. To prevent leaching, the irrigation system should not be run longer than necessary to effectively wet the root zone of the crop. If there is not enough time to inject all the fertilizer needed for the week in one injection, then smaller, daily injections are preferable. Before injecting fertilizer, the entire system should be filled with water and at full operating pressure. When all the fertilizer has been injected, the system should be run long enough to flush all fertilizer from the lines. If fertilizer is left in the lines, clogging may occur due to chemical precipitates or growth of bacterial slimes.
There is a potential for certain fertilizer materials to react with chemicals in irrigation water. If the water pH is below 7.0, there is little potential for problems, but at pH 8.0 and above, the risk is high. At levels above 40 to 50 ppm, calcium and magnesium are likely to react with phosphorus, if present in the fertilizer, causing precipitation of phosphates. If fertilizer containing calcium is added to water with concentrations of bicarbonates above 2 meq/liter, calcium carbonate may precipitate. Sulfates in fertilizers can react with calcium in the water resulting in the precipitation of gypsum. These precipitates can clog emitters.
Phosphorus- and sulfate-containing fertilizers, if needed should be applied before planting because we are not concerned about these leaching. Nitrogen is the element that is most appropriate for injection into trickle irrigation water. Calcium nitrate has the potential to cause clogging if the water pH and bicarbonate levels are high as noted above. If calcium nitrate causes clogging, potassium nitrate or urea can be used as an alternative N source.
Water testing labs can analyze water for pH, calcium, magnesium and bicarbonates. You can also perform a simple test: Mix fertilizer into a container of irrigation water at the same concentration it will be after injection into the trickle system. Cover the mixture to exclude dust and let it sit for at least the length of time it will be in the system before it reaches the soil. If the water becomes cloudy or a precipitate collects on the bottom of the container, you can expect this to happen in the irrigation system with the likelihood of clogging. If it is necessary to lower the water pH, acid can be injected into the irrigation water. This requires special handling precautions and special injection equipment. Be sure to carefully follow directions to avoid personal injury or damage to crops or equipment.
Nitrogen is easily leached from the soil. If this happens, money is wasted and ground water may be contaminated. Nitrogen applications should be timed to meet crop demands. Large pre-plant broadcast N applications should be avoided. A PSNT should be used to determine the need, if any, for additional N during the growing season. If needed, additional N can be applied by topdressing, sidedressing or injection into a trickle irrigation system.
This is the last of a series of fact sheets on soil and nutrient management for vegetable growers. Special thanks are extended to Dr. Allen Barker for reviewing these fact sheet and making helpful suggestions.
John Howell, Department of Plant and Soil Sciences
CAN YOU AFFORD TO TAKE RISKS WITH YOUR NITROGEN?
There has been a lot of discussion on nitrogen timing and the best methods to apply nitrogen. The University of Missouri states it well, “The BMP for timing of nitrogen (N) fertilizer applications is to apply fertilizer as close as possible to the period of rapid crop uptake (Figure 1). Managing N in this way will minimize losses of N from the field and will ensure adequate N availability to the crop during critical growth periods.”
In addition, the University of Purdue states that ear size is first determined at V5-V6; “Kernel row number determination of the uppermost ear begins shortly after the ear shoot is initiated (V5 to V6) and is thought to be complete as early as V8.”
Therefore, we know that the primary goals of applying nitrogen is to apply it as close to when your crops need it as possible and also to apply it in a way that will minimize your risk of nitrogen loss to ensure nitrogen is in the soil, available for your crops when they need it.
First let’s take a look at nitrogen timing
- If you apply all your nitrogen in the Fall you will have around 7 months from when you applied nitrogen to when your crops need it. This seems to be a big gamble and puts you at the mercy of weather to ensure that your nitrogen is still there and available in the Spring. If you get heavy rains in the Fall or Spring, you could lose a very significant portion of your nitrogen through leaching, which is also not as environmentally friendly since this nitrogen has nowhere to escape but deeper into the soil.
- If you apply all of your nitrogen pre-plant you have cut down on some of your risk of nitrogen loss but you are still applying 1-2 months before your crops need it so there is still some unnecessary risk of nitrogen loss through leaching.
- If you wait to apply a significant portion of your nitrogen until mid-summer right before the reproductive stage, you may not have all of you nitrogen needs met at V5-V6 when ear size is determined and you may have starved your crops during the early critical growth stages that give a baseline for future yield. In addition, what individuals pushing late-season side dress do not mention is that the microbes and organic matter in your soil contain a significant amount of nitrogen that is naturally released as the soil warms up through the summer.
Therefore, early sidedress strikes the perfect balance between applying your nitrogen just before it is needed by your crops and also ensuring that all of your crops nitrogen needs are met during the critical growth stages.
Next, let’s take a look at nitrogen application methods, Dribble vs. Injection
The University of Purdue states that as much as 15-20% of surface applied urea-based nitrogen may volatilize (lost) within a week after application. They also stated that this risk is essentially zero if the product is injected into the soil.
If your nitrogen is applied on top of the soil you are relying on rain to take the nitrogen down to the roots where it is need for uptake. If we have a dry period in the summer, you are subjecting your nitrogen to significant risk of volatilization as it will convert into ammonia gas and escape into the atmosphere, never to be utilized in boosting the yield of your crops.
Injecting your nitrogen in the soil helps reduce this risk of volatilization and helps ensure that the nitrogen that you apply will still be there when your crops need it most.
Our crops are dependent enough upon timely rain, why would we also build this into our Nitrogen Program? Inject your N with a FAST Applicator and minimize this risk!
The University of Purdue sums it up best by stating “One of the keys to managing costs of nitrogen fertilizer or maximizing nitrogen use efficiency is to manage N sources wisely to minimize the risk of nitrogen loss due to leaching, denitrification, or volatilization. The use of a sidedress application strategy remains one of the easiest and least expensive ways to maximize nitrogen use efficiency.”
Invest in your operations with a FAST Applicator to maximize your nitrogen investment and yield by providing a boost of N just before ear size is determined and also minimizing your risk of N Loss by injecting your Nitrogen IN THE GROUND rather than taking an unnecessary risk and dribbling it on top.
University of Purdue – https://www.agry.purdue.edu/ext/corn/news/timeless/CornRespLateSeasonN.html
University of Missouri – http://plantsci.missouri.edu/nutrientmanagement/nitrogen/practices.htm
University of Purdue – https://www.agry.purdue.edu/ext/corn/news/timeless/earsize.html
3 Tips for sidedressing nitrogen on your corn crop
Fernandez says most corn is around the V5-V6 stage across the country by the middle of June. Up to this point corn has taken up around 20 to 25 lbs N/acre. That’s about 10 percent of the total N it will need by the time it reaches physiological maturity in the fall.
Corn is now entering a very rapid growth phase. Between now and the time it silks, corn will accumulate an additional 100-120 lb N/ac. If the crop has insufficient nitrogen now, it will translate in reduced grain yield at harvest.
If you already applied all the nitrogen the crop will need and that nitrogen has not been lost due to excessive precipitation, you are set. But your earlier application may have been subject to loss. If you had a lot of leaching in heavily tiled fields, soils with a lot of natural drainage, or denitrification in waterlog soils, you may need to apply more nitrogen.
If additional nitrogen is needed, Fernandez offers a few reminders for growers to consider.
1. When should I apply nitrogen?
The crop needs little nitrogen during early vegetative stages to about the fifth leaf development stage. The largest portion of the total nitrogen taken up by corn occurs during the eighth leaf to VT (tasseling) development stages. Nitrogen uptake is mostly done shortly after pollination. Thus, applying N before the V8 development stage is best. Research has shown that if applications are done around V6, it is very rare to see yield loss due to N stress.
Research shows that there is little or no benefit waiting to apply nitrogen much past the V8 development stage. In fact, depending on the year, it can reduce yields. Some of our studies have shown that with split applications, delaying sidedress to V12 reduced yields compared to sidedress at V8.
2. What are the best options for sidedressing nitrogen?
Injection into the soil or dribbling the nitrogen fertilizer between rows are the best ways to sidedress because this application can reduce volatilization of urea and protect the crop from foliar damage. If ammonia is used for the application, it is important to watch soil conditions to ensure that the knife track closes properly to avoid foliage damage by free ammonia escaping to the atmosphere.
When injecting or dribbling are not viable options, broadcast applications of nitrogen would be the next alternative. Urea granules will have the least impact on leaf burn compared to UAN or dry products such as ammonium nitrate or ammonium sulfate. To minimize adhesion of dry products to the leaves, it is best to apply when the foliage is dry. Remember, urea is subject to volatilization if rain does not fall within three to four days after application. As much as 30% of broadcast urea can volatilize if there is no rainfall within approximately 10 days after the application.
If UAN solution is broadcast over corn when plants are small (about 6 in.), it’s likely the damage will not result in yield loss. Even when plants are bigger (V4), the foliage damage caused by a rate as high as 90-100 lbs. nitrogen/acre typically does not cause significant yield reduction.
One way to reduce damage from UAN is to apply in advance of rain. If rain falls within a few hours after application, it will wash the fertilizer off the foliage and will also reduce the potential for volatilization of urea. If a broadcast application of UAN is the only option available, do it as soon as possible because the smaller the plant, the lesser the potential for foliar damage. If you plan to include herbicide with your UAN application, be sure you read the herbicide label first to make sure such application is allowed. Additionally, be aware that including herbicide with the UAN solution can intensify leaf burn. In Minnesota, addition of 2 lbs. atrazine/acre at a rate of more than 90 lbs. N/acre at V3 caused severe leaf burning. Applying 2 lbs. atrazine/acre at 60 lbs. N/acre causes similar leaf burning as applying 120 lbs. N/acre with UAN alone.
3. If my crop is too tall already, can I apply nitrogen “over the top?”
In some fields, crops are getting tall and some still need additional nitrogen. Application of dry products, such as ammonium nitrate and urea, “over the top” can result in foliar damage. Typically, this damage is an aesthetic concern and rarely translates into yield reduction.
Over the top applications of UAN are the least desirable way of applying nitrogen. However, if this is the only alternative and the plant needs more N, the yield benefit from the additional nitrogen will likely outweigh the leaf burn caused by the application. Research has shown yield reduction when a rate of more than 60 lbs. nitrogen/acre was applied at V8. To avoid extensive foliage damage, when nitrogen applications are needed later than V8, it’s very important to fit the high-clearance equipment with drop hoses so UAN is applied directly on the soil surface without touching the crop canopy.
“If additional nitrogen is needed, sidedress earlier rather than later in crop development if at all possible,” Fernandez says. “If you have an option on how to apply nitrogen at sidedress, choose first injection applications or dribble UAN solution between rows; second, broadcast of solid ammonium-containing fertilizers; and third, broadcast UAN solution.”
For more information about nitrogen, read the post at the University of Minnesota Extension.
Smart nitrogen and sweet corn
Sweet corn is a heavy user of nitrogen. Depending on days to maturity, plant density, soil type, irrigation and other cultural practices, sweet corn can use 150 or more pounds of nitrogen per acre. Applying that much nitrogen to many soils requires careful application management. For most nitrogen fertilizers, if that much was applied all at once there would be significant nutrient loss to leaching, volatilization or both – an economic waste to the producer and potentially damaging to the environment. Therefore, growers use split applications applying a third to half (depending on soil type) of the nitrogen prior to planting and the rest as a sidedress when plants are 18 to 24 inches tall.
Several nitrogen sources are suitable, but the more common ones include ammonium nitrate (33-0-0) and urea (46-0-0) pre-plant and then ammonium nitrate, urea or anhydrous ammonia (82-0-0) as a sidedress. Each is a good source, but each also has limitations. Ammonium nitrate has become fairly heavily regulated due to its potential in making explosives. Urea is quite mobile and volatile and needs to be applied under the correct conditions or much is lost. Finally, ammonia is dangerous to handle and requires specialized application equipment.
“Smart nitrogen” was developed to help solve these limitations. Smart nitrogen is urea covered with a polymer-coating and has a slightly less nitrogen value (42-0-0) than regular urea. The polymer coating slows the rate at which urea is dissolved and therefore released to the soil to eventually be utilized by the plant. Theoretically, one pre-plant application of ESN (Environmentally Smart Nitrogen) should be enough to satisfy the nitrogen requirement for the entire season. To test this on sweet corn, a trial was conducted by Michigan State University Extension at the Southwest Michigan Research and Extension Center in 2015 and tested the following treatments:
- 150 pounds as ESN prior to planting.
- 25 pounds as urea plus 125 pounds as ESN prior to planting.
- 25 pounds as urea plus 100 pounds as ESN prior to planting and 25 pounds as urea as a sidedress when plants were 18 inches tall.
- 50 pounds as urea plus 100 pounds as ESN prior to planting.
- 50 pounds as urea prior to planting and 100 pounds as urea as a sidedress when plants were 18 inches tall.
Cabo sweet corn (Syngenta Seed Company) was planted 6 inches in the row with rows 30 inches apart. The trial was irrigated as needed and weeds controlled using a combination of Dual and Aatrex. Plant height was measured over time and at harvest the number and quality of ears was determined. After analyzing the data, it was found that all treatments produced similar growth, yield and ear quality.
The benefit of a onetime nutrient application using ESN is labor and equipment savings of the sidedress application. ESN for this trial was $1.16 per pound of nitrogen while urea was $0.80 per pound. A 150 pounds per acre application of ESN cost $174 while urea cost $120, a $54 difference. Labor and equipment costs for a second application are estimated to be between $40 and $50 per acre. So urea is slightly less expensive from the standpoint of product and application. For some producers, there may be a benefit in a “once and done” approach. It is also possible ESN rates lower than 150 pounds per acre may provide a similar performance as 150 pounds per acre regular urea. This is something that will be evaluated in a 2016 trial.
A full report of this trial will be given during the Sweet Corn session Tuesday, Dec. 8, 2015, at the Great Lakes Fruit, Vegetable and Farm Market EXPO. More information can be found at the Great Lakes EXPO website.