Number 209 September 11, 2009

Transcription

1 Number 209 September 11, Preplant and planting time fertilizer decisions for wheat 1 2. Adjusting wheat seeding rates for unfavorable conditions 3 3. The importance of fall tillers in wheat yields 5 1. Preplant and planting time fertilizer decisions for wheat Wheat producers know that fertilizer application decisions made at or before planting can have a big impact on yields. Common questions they have are: * How much nitrogen (N) and phosphorus (P) should be applied? * Should or could all the N be applied at planting time? * How should the N and P be applied for best economic efficiency? * Are there other nutrients such as chloride, sulfur, or zinc which also might be needed? These are not easy questions to answer, since many factors are involved, such as tillage system, soil test levels, soil type, texture and drainage, normal winter rainfall, previous crop, equipment limitations, cost, and others. But the following are a few general guidelines to consider: Nitrogen. * Nitrogen timing and application method. There are a couple of key issues to consider when deciding when to apply N to wheat. One of the keys is soil drainage and likely winter rainfall. Another key issue is the need to ensure there is adequate N available to stimulate fall growth and tillering. On well-drained, medium- to fine-textured soils in Kansas, and where winter rainfall is normally low, all of the N needed for the crop can be applied prior to planting wheat. This would include much of the area west of the Flint Hills, except where sandy soils or poor drainage would create N loss risks. Ammonia is probably the most cost-effective N source available to many growers for total-fall-preplant systems, though other sources (such as urea) can also be used. Where tillage is used, application of ammonia is a natural fit with sweeps, secondary tillage tools, or narrow-spaced toolbar applicators. Adding coulters to knife applicators can also make preplant anhydrous ammonia an option in no-till systems. A key when using ammonia is to use band spacings closer than 20 inches. With dry broadcast materials, using tillage or a no-till drill 1

2 to incorporate the N fertilizers will likely improve efficiency by reducing the potential for losses due to immobilization and/or volatilization. The area suitable for total-fall N programs can be extended to include some of the poorly-drained heavy soils in south central Kansas and higher rainfall areas of northeast and east central Kansas through the use of slow-release N products, such as coated urea, or by adding a nitrification inhibitor to anhydrous ammonia. On most soils across the state, a split application system using pounds of N applied in the fall and the balance topdressed in winter to early spring at greenup performs as well as totalpreplant systems. A topdressing system will generally outperform preplant systems on sandy soils prone to leaching or poorly drained soils prone to denitrification, such as the claypan soils of southeast Kansas. Unlike Europe or the intensive Eastern U.S. wheat production areas, additional yield responses to multiple topdress applications are rarely seen in Kansas. Ideally, producers would apply at least 15 to 30 lbs N per acre to wheat before or at planting to ensure sufficient N for fall growth and tiller development. This is especially important for no-till wheat, continuous wheat, or wheat after sorghum. That s not as easy as it may sound, however. It is difficult to apply that much N with the seed by using liquid , or dry or starter products with the drill. Producers should not try to spike their starter fertilizer with extra N from urea or UAN to raise the N rate at planting. This practice is tempting to no-till producers who want to get as much of the N as possible applied below the soil surface. However, urea-containing N fertilizer can injure the wheat if it is placed in direct seed contact because urea hydrolizes to ammonia, which is toxic to the germinating seed. While at times, producers get by doing this with no adverse effects, we get reports every year from farmers who had to replant due to seedling injury. Placing urea, or urea containing fertilizers such as UAN in direct seed contact is a risky practice. If injury occurs and stands are thin, the reduction in yield potential can be quite costly. How should the additional N needed at planting time be applied? For highest N use efficiency, band applications of N below the soil surface are always preferred, especially in no-till, since placing N below the soil surface minimizes N immobilization (tie-up in residue) and eliminates the potential for volatilization loss. If knifing/banding N is not an option, apply the N to the soil surface prior to planting and incorporate it with the drill. * Nitrogen rates. The factor that causes the most variation in N rates is residual nitrate-n in the soil. A survey in 2006 showed residual N varied from 8 to more than 300 pounds N per acre in central and western Kansas. So a profile N test is the best tool for fine-tuning N rates. No-till wheat production systems generally require about lbs/acre more N than wheat planted on tilled ground throughout the season, especially when surface applications of urea or UAN are used. A higher percentage of the applied N in a no-till system is immobilized by decomposing residue on or near the soil surface, which will lower N use efficiency for that year. This is especially true with liquid sources broadcast-sprayed on residue, such as UAN. Surface banding liquids prior to planting can reduce immobilization, but the most consistent performance comes with incorporation or subsurface banding. 2

3 If wheat is planted immediately after grain sorghum or sunflowers, producers will also need to add another 30 lbs N per acre to their total N rate (in addition to no-till adjustment). This is due to the extremely low levels of N in the residue of these crops, slowing the release of N from the previous crop residues. Phosphorus. Phosphorus fertilizer should always be applied based on a current soil test. When soil test P is below 20 ppm, producers will usually get a good response to applying P to wheat. At low soil tests (less than 20 ppm), producers should try to apply at least lbs P per acre with the seed. It is not necessary, however, to band all the recommended P below the soil surface, even under no-till conditions. Research at K-State shows that a combination of starter fertilizer and broadcast application is just as effective as deep-banding systems or placing all with the seed. Is there an advantage to using a build-up approach to applying P for wheat vs. the traditional, and lower, sufficiency recommendations? Not really, if a starter fertilizer is used at low soil test levels. Research has shown that the results will be similar. But the use of starter fertilizer is the key to making efficient use of P fertilizer at low soil test levels, and under no-till conditions. When soil-p test levels are low, it is also important, when using the sufficiency approach, to use starter P fertilizer for every crop in the rotation, including soybeans. Other nutrients. Soil testing is the key to determine if a response to other nutrients, such as sulfur or chloride would be expected. Responses to both are becoming more common in Kansas. But soil testing is the best way to determine if they are needed. -- Dave Mengel, Soil Fertility Specialist dmengel@ksu.edu -- Dorivar Ruiz Diaz, Nutrient Management Specialist ruizdiaz@ksu.edu 2. Adjusting wheat seeding rates for unfavorable conditions The basic seeding rate recommendations for wheat are: Western Kansas (less than 20 inches/year of rainfall): lbs/acre Central Kansas (20-30 inches/year of rainfall): lbs/acre Eastern Kansas (30 inches/year or more of rainfall): lbs/acre Irrigated: lbs/acre However, there are several conditions under which producers may need to adjust these basic seeding rate recommendations, such as: * Early planting for grazing. When planting wheat early for grazing, it s best to use a seeding rate of lbs/acre. 3

4 * Planting later than the recommended dates. When wheat is planted later than the recommended dates, it typically produces fewer productive fall tillers and a less developed secondary root system in the fall. This often results in lower grain yields unless the producer compensates by using a higher seeding rate. By November 1, seeding rates should be increased by 50 percent (to a maximum of 120 lbs/acre). By mid to late November, seeding rates should be 90 lbs per acre in western Kansas and 120 lbs/acre in central and eastern Kansas. * No-till planting into heavy residue. In general, when planting no-till, producers should increase their seeding rate by about 15 lbs/acre. This is especially true during the first few years of notilling, until the producer becomes more familiar with any adjustments needed on the drill to get good seed-soil contact and uniform seeding depth under no-till conditions. However, it is common to see longtime no-tillers to use seeding rates similar to conventional-till planted wheat. * Planting immediately after grain sorghum. If wheat is planted directly behind grain sorghum, producers in western Kansas should use a seeding rate of lbs/acre. In central and eastern Kansas, producers should use a seeding rate of lbs/acre. Wheat planted directly after grain sorghum does not tiller as well as wheat planted under other conditions. * Varieties with unusually large or small seed. The basic seeding rate recommendation applies to most varieties, and results in roughly the same number of seeds per acre regardless of the variety. Some varieties, such as Overley, have unusually large seed. In these cases, seeding rates should be increased by about percent to compensate. The higher end of that range of increase should be used for varieties that do not tiller well, such as Overley. Likewise, some varieties, such as Bond CL, have unusually small seed. Seeding rates of these varieties can be decreased by about percent. Seed size can be measured in terms of the number of seeds per pound. The normal range is about 14-16,000 seeds per pound. I use 15,000 seeds per pound when I don t know the seed count and I want to calculate seeds planted per acre. * Planting under adverse seedbed conditions. This is not recommended, but may be necessary at times for any number of reasons. If soils are too wet, too dry, or too cold, producers should increase seeding rates by percent or more, up to a maximum of 90 lbs/acre in western Kansas and 120 lbs/acre in central and eastern Kansas. * Planting poor quality seed. This is not recommended, of course. But if good quality seed cannot be found for various reasons, producers may have to use lesser quality seed. In this situation, the seed should always be tested for germination first. If the germination rate is less than 85 percent, seeding rates should be increased accordingly to compensate. Even if germination is acceptable, if the seed has a test weight below 56 lbs/bushel or has seed-borne diseases and is not treated with a fungicide, then producers should increase their seeding rate by about 30 lbs/acre. What if more than one of these factors applies? Should producers just add up all the suggested increases in seeding rates? No. If that were the case, the recommended seeding rate might be a high as 200 lbs/acre, which is clearly absurd. The maximum rate producers should use, under any conditions, is about 120 lbs/acre. -- Jim Shroyer, Extension Agronomy State Leader jshroyer@ksu.edu 4

5 3. The importance of fall tillers in wheat yields With wheat, the main stem usually produces the most productive head in wheat. However, primary and secondary tillers play a very important role in grain yield as well. In fact, under normal conditions, as much as 70 percent of the grain yield comes from the tillers. Management decisions made at planting time and in the early fall -- such as planting date, seeding rate, and nitrogen management can have a big effect on fall wheat growth and tiller development. It is a good idea to try to keep the wheat from growing too much in the fall, since excessive fall growth will deplete soil moisture and put the crop at risk of drought stress later in the season. On the other hand, it doesn t make sense to intentionally hold back too much on nutrients or alter seeding rates in the fall. Producers should try to encourage fall tillering for the most part, since fall tillers are the most productive tillers the wheat produces. A K-State study from several years ago by former graduate student Duane Thiry looked at the relative contribution of fall vs. spring tillers in final grain yield, and the effect of planting date on tiller development. Planting date effects on tiller development and grain yield: Hutchinson Fall tillers (no/sq yd) Spring tillers (no/sq yd) Planting date Plants (no/sq yd) Maximum Productive Maximum Productive Total spikes (no/sq Yield (bu/acre) yd) Sept Oct Oct Nov LSD (0.05) Mean weight of straw and grain, harvest index, kernels per spike, and kernel weight Tiller wt (g) Planting date Fall or spring tillers Straw Grain Harvest index Kernels/spike Kernel weight (mg) Sept. 28 Fall Spring Oct. 11 Fall Spring Oct. 28 Fall Spring Nov. 13 Fall Spring LSD (0.05) NS Early planting led to the highest number of both fall and spring tillers. However, the high number of tillers produced in the fall led to intense competition, and less than 25 percent of the fall tillers produced were productive. This intense competition also showed up in the low harvest index numbers for both the fall and spring tillers. (Harvest index is the ratio of grain yield to total above-ground biomass) A low harvest index means that less carbohydrates and other nutrients were put into grain production at the early planting date than at the other planting dates. 5

6 At the Oct. 11 planting date, which is optimum for this location, there was a high number of productive fall tillers and a high harvest index for both the fall and spring tillers. Fall tillers were especially important. About 69 percent of the total grain yield came from fall tillers and only 31 percent came from spring tillers. When wheat was planted on Oct. 28, a high percentage of the fall tillers was productive, but the number was considerably lower than the Oct 11 date. This planting date is later than optimum. Wheat at this planting date did tiller profusely in the spring, and both fall and spring tillers had a high harvest index. In this case, only 44 percent of the grain yield was from fall tillers and 56 percent was from spring tillers. Wheat planted Nov. 13 did not produce many tillers, either fall or spring. The stand was too sparse to produce high grain yields. A few of the main conclusions from this study: * Planting date greatly affects grain yield by influencing the development and survival of tillers. * Early planting causes excessive tillers, which have low survival, low harvest index, and low grain yield. * Late planting causes inadequate fall tillers, which are not compensated for by spring tillers. * Planting wheat within the optimum period promotes development and survival of fall and spring tillers, with high harvest index and high grain yield. -- Jim Shroyer, Extension Agronomy State Leader jshroyer@ksu.edu These e-updates are a regular weekly item from K-State Extension Agronomy and Steve Watson, Agronomy e- Update Editor. All of the Research and Extension faculty in Agronomy will be involved as sources from time to time. If you have any questions or suggestions for topics you'd like to have us address in this weekly update, contact Steve Watson, swatson@ksu.edu, or Jim Shroyer, Research and Extension Crop Production Specialist and State Extension Agronomy Leader jshroyer@ksu.edu 6