By Randy Weisz and Ron Heiniger
Nitrogen management is one of the most important keys to successful small grain production. It is also one of the easiest management strategies to misuse, resulting in both environmental damage and yield reductions. To achieve optimum small grain yields, follow different nitrogen guidelines in the fall, winter, early spring, and spring.
When planting on time, 15 to 30 pounds preplant nitrogen per acre are generally suffcient to promote maximum growth and tillering. This application may be very important for high yields, since nitrogen stress early in the season will prevent adequate tillering. When small grains follow soybeans or peanuts, carryover nitrogen may be present at quantities high enough to meet small grain fall requirements. However, the availability of carryover nitrogen is difficult to predict. In many years and locations, the nitrogen released from a previous legume crop many not be available until spring, which is too late to support fall tillering. Consequently, unless experience with specific fields indicates otherwise, when small grains are planted on time, a small amount of preplant nitrogen is recommended even when following soybeans or peanuts.
Research has shown that late planted small grains generally do not respond to preplant nitrogen applications. When temperatures are too low to promote tillering, preplant nitrogen cannot be taken up by the plants and is easily leached out of the soil. Even high rates of preplant nitrogen cannot stimulate tillering in cold soils. Consequently, when planting after the opening planting dates (see Chapter 7, Small Grain Planting Dates for North Carolina, which is at http://www.smallgrains.ncsu.edu/Guide/Chapter7.html), application of preplant nitrogen to small grains is not recommended.
Small grains planted before the optimal planting dates risk freeze damage. Preplant nitrogen applications to early planted small grains promote increased tillering, but it can also increase the risk of freeze damage. While applying nitrogen to early planted small grains will often result in better looking stands, research has shown that it generally does not increase yields. Consequently, preplant nitrogen is not recommended for early plantings.
Preplant nitrogen management for no-till small grains is similar to conventional-till. In tests conducted by NC State University, preplant nitrogen only resulted in increases in no-till yields when the grain was planted on time. Preplant nitrogen has not been beneficial in no-till test plots planted before or after the optimal planting dates.
Cold temperatures slow small grain growth and tillering, and consequently limit nitrogen uptake. Since little nitrogen can be taken up by the crop during the winter months, nitrogen applied may leach away and is generally of little value to the crop. Nitrogen management during the winter months consists of making sure the crop does not become nitrogen deficient. Small grains under nitrogen stress in the winter can lose tillers, which may reduce yield.
Indications of a possible nitrogen deficiency are a pale green color, thin, poorly developing stands, and a history of heavy leaching rains after planting. A small application of 15 to 30 pounds nitrogen per acre may be made to help green the crop back up. This application can stimulate growth, but the potential for losses to the environment is great. Growers who apply nitrogen in the winter should be prepared to check the tiller density at Feekes Growth Stage 3 and apply more nitrogen if needed.
At Feekes Growth Stage 3 (see Feekes Growth Stages for Small Grains in this guide), which usually occurs in North Carolina around late January or early February, small grains begin to develop more tillers if nitrogen is available. If sufficient numbers of tillers developed in the fall, further tillering will not be necessary and an application of nitrogen at this time will not benefit the crop. If fall tillering was limited and there are not enough tillers to produce adequate heads, yields will be reduced, unless nitrogen is made available and more tillers develop in the next few weeks. Determine nitrogen requirements for Feekes Growth Stage 3 by counting the number of tillers (with at least 3 leaves).
Wheat
When wheat reaches Feekes Growth Stage 3, count the number of tillers with at least three leaves per square foot. If tiller density is greater than 50 per square foot, do not apply nitrogen until Feekes Growth Stage 5 (usually in March). Splitting nitrogen applications when tiller densities at Growth Stage 3 are high can reduce yield! If tiller density is less than 50 per square foot at Growth Stage 3, the crop needs nitrogen as soon as possible. Waiting until Growth Stage 5 to apply nitrogen may reduce yields. Under these conditions, splitting nitrogen applications will usually be of benefit. This strategy is outlined in Figure 8-1.
Figure 8-1. Timing spring nitrogen applications for wheat
Determining Tiller Density at Feekes Growth Stage 3
To determine tiller density, count well-developed tillers (i.e., those with at least three leaves). Ignore small tillers that have only one or two leaves. Do not be concerned with differences between the main plant and younger side tillers. Just count any stem with at least three leaves as a tiller. The final count will include main plants, tillers, and side tillers. Count all the tillers that have at least three leaves in a yard of row. Do this in several places and take an average. Tiller density is then computed as:
Tillers per square foot = (tillers per yard of row) x 4 / (row width in inches)
For example, in five counts of tillers in a yard of row, the average was found to be 102. The row spacing is 7.5 inches. Tiller density is then:
102 x 4 / 7.5 = 54.4 tillers per square foot.
An alternative is to mark out a square foot of ground, and count all the tillers in that area that have at least three leaves. Do this in several places and take the average.
Oats, Barley, Triticale, and Rye
Research on counting tillers to time nitrogen applications for these crops has not been done. Growers will need to rely on past experience to judge when splitting nitrogen will benefit oat, barley, or triticale stands that are thin at Feekes Growth Stage 3.
During stem elongation, which occurs during Feekes Growth Stage 5 (see Feekes Growth Stages for Small Grains), small grain crops begin to take up large amounts of nitrogen. The future grain head is formed at this time although still underground, and nitrogen stress at this growth stage will result in smaller heads. Nitrogen is needed now by the small grain crop, and the bulk of spring nitrogen fertilizer needs to be applied at this growth stage.
Wheat
At Feekes Growth Stage 5, apply the optimum amount of nitrogen based on past experience with a specific field. In the absence of such experience, or if there has been a lot of rain during the early spring that may have leached out earlier applied nitrogen, use a tissue test to determine the optimum nitrogen rate. Tissue tests are most effective on thick stands of wheat and should not be used on extremely thin wheat stands. Nitrogen regulations in the Neuse River basin limit the amount of nitrogen that can be applied to wheat grown in that area, but a tissue test at Growth Stage 5 supersedes these regulations. So if a tissue test indicates that your wheat needs more nitrogen than the regulations allow, producers are permitted to apply the additional nitrogen. This is an additional benefit of taking a tissue test!
Once the tissue nitrogen concentration is known, use Figure 8-2 to determine the appropriate nitrogen rate.
Figure 8-2. Nitrogen recommendations during stem elongation (Feekes Growth Stages 4 and 5) based on whole plant tissue test.
Oats, Barley, Triticale, and Rye
Research on using tissue samples to optimize nitrogen requirements for these crops has not been done. Use Table 8-1 to determine the crop’s total spring nitrogen requirement.
Table 8-1. Spring nitrogen requirements for oats, barley, triticale, and rye |
||||
Region |
Total Nitrogen Recommendations (lb per acre) |
|||
Oats |
Barley |
Triticale |
Rye |
|
Coastal Plain & Tidewater |
100 |
100 |
120 |
80 |
Piedmont & Mountains |
80 to 100 |
80 |
120 |
80 |
Taking a Tissue Test at Feekes Growth Stage 5
First, be sure the wheat is really at this growth stage. Stage 5 occurs when the leaf sheaths of the wheat are strongly erected and splitting the stem shows the growing point to be about 1/2 inch above the root crown (see Feekes Growth Stages for Small Grains in Chapter 1 at http://www.smallgrains.ncsu.edu/Guide/Chapter1.html). Once the first node of the stem, or joint, is visible at the base of the plant, the crop has reached Growth Stage 6. Samples taken during Growth Stage 6 or later usually show lower nitrogen concentrations, which can result in higher-than-needed nitrogen fertilizer recommendations. Sampling before Stage 5 can result in nitrogen recommendations that are too low.
Obtaining a representative tissue sample is similar to obtaining a representative soil sample. Unusual areas of the field should be avoided. If major differences in top growth or apparent residual nitrogen availability are evident in large areas of the field, these areas should be sampled and fertilized separately.
The tissue sample is taken by cutting a handful of wheat tissue at 20 to 30 representative areas in the field. The top growth should be cut approximately 1/2 inch above the ground. Soil particles clinging to the tissue must be brushed from the tissue, and dead leaf tissue must be removed. The individual sample should be placed in a clean paper bag that is large enough to allow good mixing of the total sample. After thorough mixing of the sample, take approximately three handfuls of tissue from the mixed sample, place them in a sample envelope or a clean paper bag, and send or take them directly to the laboratory. Samples not delivered within 24 hours need to be dried in a 160-degree oven to prevent spoilage. Never package tissue samples in plastic bags.
Applying nitrogen after the plants have jointed (Growth Stage 6) generally will not increase yield. In fact, liquid nitrogen applied at Stage 6 or later will severely burn the plants and reduce yield. Nitrogen applications may sometimes be of benefit at Stage 6 if the crop is yellowing and showing visible signs of nitrogen deficiency. Little research has been done on late spring nitrogen applications, but at flag leaf emergence (Feekes Growth Stage 8), up to 20 pounds of nitrogen per acre can be applied to wheat using granular urea dissolved in water. (Do not use UAN solution, which will damage the head and the flag leaf and thus reduce yields severely.) The granular urea (prilled granular urea should not be used unless it is not coated) should be tested to be certain it dissolves readily. Twenty-five to 30 gallons of water per acre are needed to get good wetting of the foliage.
Crop residue, left on the surface in no-till systems, can tie up nitrogen needed by developing tillers. For this reason, making an initial application of 15 to 30 pounds of nitrogen per acre in the fall is especially important in no-till. Applications at the high end of this range are recommended. Since fall tiller development can be slow in no-till, determining tiller density at Feekes Growth Stage 3 is especially important. If the density is low, splitting spring nitrogen will help achieve a high yield.
Several satisfactory sources of nitrogen are available for topdressing small grain. Nitrogen solutions (approximately one-half ammonium nitrate and one-half urea dissolved in water) are popular and widely used. These solutions contain from 30 to 32 percent actual nitrogen. Although the solution may cause slight foliar burn, there is little likelihood of reduced yields from this effect if the fertilizer is applied before jointing.
A third source of nitrogen is ammonium sulfate (21 percent nitrogen). Ammonium sulfate is readily available, especially in eastern North Carolina. This source also contains sulfur (24 percent). Sulfur may be important in fields with rather deep sandy surfaces if no other sulfur has been applied within the past 1 or 2 years.
In recent years, urea (45 percent nitrogen) has been readily available. Its popularity stems from its high nitrogen content, usually competitive prices, and low degree of metal corrosion. Under certain conditions, volatility losses can occur when urea is applied to sandy soil. However, if it is broadcast as early as possible in the spring when the soil surface is moist, wind speed is at a minimum, temperature is relatively low, and humidity is high, no loss should occur. When urea is applied to silty or clayey soil surfaces, volatilization does not seem to be a problem.
Preplant nitrogen is important to promote fall tillering when small grains are planted on time. For small grains planted before or after the opening planting dates, preplant nitrogen is not recommended. Tiller density at Feekes Growth Stage 3 can be used to tell if nitrogen is needed in early spring and if split applications will be beneficial. If tiller density is high, all spring nitrogen can be applied at Feekes Growth Stage 5. Whether making a single spring nitrogen application or split spring nitrogen application, a tissue test at Feekes Growth Stage 5 can provide valuable information about how much nitrogen is required and if other nutrients are at adequate levels.
Some materials adapted from Intensive Soft Red Winter Wheat: A Management Guide, Blacksburg: Virginia Polytechnic Institute Cooperative Extension Service.
This file is a chapter from Small Grains Production Guide, 2004-05. Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the NC Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension Center.
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Last Revised Sept. 2004