1. Potassium deficiency in corn and soybeans 1 2. Residue treatment in continuous no-till wheat systems 3

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1 Number 61 December 15, Potassium deficiency in corn and soybeans 1 2. Residue treatment in continuous no-till wheat systems 3 1. Potassium deficiency in corn and soybeans We have been seeing a number of fields exhibiting potassium (K) deficiency symptoms in both corn and soybeans in recent years, particularly in eastern Kansas. In most cases diagnostic soil tests indicate that the soil is marginal or deficient in K, and broadcast applications of potash have fixed the problem. Low soil potassium levels in Kansas are more common than many realize, and K levels may actually be declining in many cases, especially in eastern Kansas. While many soils in Kansas are inherently high in K, that is not always the case. A summary of soil test results from in eastern Kansas showed that 25% of the samples taken in that three-year period had K soil test levels that required K fertilization. Thus it shouldn't be surprising to see some potassium deficiencies across the region. Why are soil test K levels apparently dropping in eastern Kansas? There are probably two underlying causes. Soybean production has increased significantly in the past 20 to 30 years. Soybeans are an important crop today and are big users of potassium. Soybeans remove about 1.4 pounds K 2 O per bushel, compared to 0.25 and 0.30 for corn and wheat respectively. A 35-bushel soybean crop would remove about 49 lbs K 2 O, and a 150- bushel corn crop would remove about 45 lbs K 2 O in the grain alone, which gets trucked off the field. Forage production to support the cattle industry is also important in the region, and hay removes from 30 to 60 pounds of K 2 O per ton depending on the hay crop grown. Thus crop removal is a major contributor to a gradual decline in soil K levels. Still, low soil test levels alone can not explain some of the situations where K deficiency is seen today. In some cases, soil test levels are high, and deficiencies would not have been predicted. Many fields exhibit K deficiency symptoms, particularly early in the growing season, even with high soil test K levels, especially in no-till or strip till production systems. Why would that be the case? 1

2 Part of it can be explained by the pathway of nutrient cycling during plant growth, harvesting, and residue management. That same 150-bushel corn crop mentioned above actually takes up over 200 pounds of K 2 O per acre if you count the stalks and leaves, as well as the grain. When the crop is harvested as much as 80% of the K is returned to the soil in the crop residue. In a traditional tilled production system, that K is incorporated throughout the top 6 to 8 inches of soil. However, in a no-till system the residue (and the K present in the residue) remains on the soil surface. As a result, nutrients become stratified in no-till soils, with the highest concentrations in the top 2 to 3 inches. With K stratified in the upper layer of soil and residue in no-till systems, crop uptake of K will ultimately depend on rooting patterns, environmental conditions, and the soil s reservoir of K below 3 inches. In most cases, under no-till conditions, soils are wetter and cooler than where tillage has been used. As a result, root growth of no-till crops often starts out slowly in early spring. Roots tend to concentrate at first in the surface few inches of the soil, in the same areas where nutrients concentrate. If environmental conditions are good, with plenty of soil moisture, this acts to benefit nutrient uptake in no-till crops. However, in dry years, or during dry periods during the year, that surface few inches of soil dries out and lacks water to support nutrient uptake. The plant is forced to utilize water from deeper in the soil profile, where nutrients may be less concentrated in no-till systems. Under those conditions nutrient uptake in general can be reduced under no-till. This may or may not result in K (or other nutrient) deficiency symptoms in no-till, depending on many factors -- when the stress occurs, how long it lasts, soil test level in the surface, and how high the nutrient concentration is deeper in the soil profile. If the problem develops early in the growing season and only lasts for a short period of time, the crop may well grow out of it with little lasting effect. If it continues long enough, or occurs at a critical growth stage, top-end yield potential may be reduced. An example in corn would be at the 5 to 7 leaf stage when the number of rows of kernels is being determined. Plants also have the ability to compensate if stress is relieved. For example, late rains can improve kernel fill in corn and seed size in soybeans. There has been work in Kansas, and other states, on using different potassium placement techniques to correct potassium deficiency problems. Barney Gordon at the Northcentral Kansas Experiment Field has gotten good responses to adding K to starter fertilizers, in long-term ridge-till corn which is flood irrigated. In that situation the K levels below the row have been gradually depleted, creating stress on seedlings. Providing some K at planting near the seed corrected the deficiency and gave significant yield increases. (Caution: Potassium fertilizers can cause seedling injury if placed in contact with the seed.) Work in southwestern Minnesota and northcentral Iowa on ridge-till corn showed that knifing K into the ridge, below the row, in the fall also was effective at supplying young plants with additional K. 2

3 Keith Janssen at the East Central Kansas Experiment Field has observed that adding K to the N and P being applied with strip-tillage in the fall or late winter has reduced the incidence of K deficiency in east central Kansas. Work in Indiana found that knifing K a few inches off the row in long-term no-till was much more effective than broadcasting K. Knife applications required only half as much K as broadcast applications (25 lbs K 2 0 vs. 50 lbs K 2 0) for similar yield responses. So if a producer observes K deficiency in their crop, what should they do? The first thing is take comparison soil samples from areas showing deficiencies and areas that appear normal. This will help determine if they are dealing with low soil K, or perhaps a nutrient stratification/weather related problem. In most low-k soils, broadcasting potash, in combination with some K applied as starter should fix the problem. If the farmer has access to equipment which can knife some K into the soil 3-6 inches deep, that would reduce the potential for positional unavailability during dry periods. In the case of plant deficiencies at high soil test levels, > 135 ppm, the answer isn't as straightforward. But based on the current body of work, the best strategy would be to use a starter fertilizer to address early-season issues, and knifed applications to reduce the risk from positional availability during dry periods. There are still a number of questions that we need to answer, and hopefully the applied research group at K-State will be able to give us some better answers in the near future. -- Dave Mengel, Soil Fertility Specialist dmengel@ksu.edu 2. Residue treatment in continuous no-till wheat systems In continuous wheat, there is always a question about how to handle the residue between crops. Specifically, should the residue be left intact, burned, or tilled? There can be conservation compliance restrictions involved in this decision. And in the future, there may be limitations on residue burning from the EPA. But those issues aside, what are the agronomic factors involved? Crop residue burning in continuous wheat is primarily an issue in central Kansas. In this part of the state, there has been one major 10-year study and a large 3-year demonstration plot coordinated by K-State agronomists in recent years that have looked at crop residue management in long-term continuous wheat. Another study was recently completed on continuous wheat in central Kansas by Scott Staggenborg and graduate student Mauro Carignano, and the resulted will be reported in a future Agronomy e-update. * The 10-year study has been conducted by Mark Claassen at the Harvey County Experiment Field. There are several cropping and tillage systems involved in this study, but part of it compares burning, chiseling, and no-till in continuous wheat. This experiment was conducted on a relatively fine-textured Ladysmith clay loam. With 3

4 inclusion of the findings in 2006, the results are as follows. Data for each treatment represent the average of 40 observations. Effect of Residue Treatment in Continuous Wheat Harvey County Experiment Field Residue Treatment 10-year Average Burn 48.8 Chisel 46.5 No-till 49.7 In these plots, the burning was done in July and followed by shallow tillage as necessary. After 10 years of burning (preceded by 10 years of moldboard plowing), there appears to be less internal drainage in the soil compared to the other residue treatments, Claassen reports. Ponding and drainage problems occurred on the burned plots following heavy rainfall in 2003 and 2005, which notably reduced the corresponding wheat yields. If the data for those years are not considered, there would be an average annual yield advantage of about 3.2 bu/acre for burning vs. chisel or no-till treatments. The continuous no-till treatment has resulted in surprisingly good long-term wheat yields. Importantly, good to excellent cheat control was maintained in most years, and varieties with good tan spot resistance were grown. In these plots, there seems to have been established some sort of biological equilibrium resulting in yield stabilization, Claassen speculates. The plots were in continuous no-till for 10 years prior to the start of the study, for a total of 20 years of continuous no-till. Cheat herbicides, such as Maverick and Olympus, have helped improve yields. Tan spot apparently has not reduced yields much in the continuous no-till plots. Variety 2137 was used in this study for a period of years. Overley subsequently replaced Both varieties have relatively good resistance to tan spot. Hessian fly has not been a problem in this experiment, in part because the wheat has been planted sufficiently late. Take-all has not been a problem in continuous no-till wheat in this study because of acid soil and the long history of monoculture. Growers might expect increased levels of disease with time in continuous no-till wheat. In historical research, take-all was found to increase by the third or fourth year and then stabilize or decline thereafter. * In Saline County, Tom Maxwell, district Extension agent for Central Kansas District 3, has had a large-scale demonstration plot on a cooperator s field since 2004 comparing residue burning vs. not burning in continuous no-till wheat. In these plots, which were not replicated, the residue was burned just 2-3 days prior to planting. The results are: 4

5 Burned vs. Unburned in No-till Continuous Wheat: Saline County Extension 2006 Variety No-till Burned (5th year wheat) No-till Unburned (4th year wheat) Jagger Jagalene Neosho Overley Overley + Gaucho XT Santa Fe Average Burned vs. Unburned in No-till Continuous Wheat: Saline County Extension 2005 Variety No-till Burned (4th year wheat) No-till Unburned(3rd year wheat) Jagger Overley Jagalene Cutter Dominator Karl Jagger/2137/Dominator Average Burned vs. Unburned in No-till Continuous Wheat: Saline County Extension 2004 Variety No-till Burned (3rd year wheat) No-till Unburned(2nd year wheat) Jagger Overley Jagalene Cutter Jagger/2137/Dominator Average Year Average Yields: No-till Burned vs. No-till Unburned Variety No-till Burned No-till Unburned Jagger Jagalene Overley

6 Cheat was a major issue in these plots, and had to be controlled with herbicides at times, Maxwell says. The no-till burned plots had less cheat than the no-till unburned. In 2005, the no-till unburned plots had uneven emergence and stand problems caused by hair pinning of the wheat stubble, due to light rain as the plot was being planted. There were no problems planting into the no-till burned plots. Overall, burning the wheat stubble immediately prior to planting wheat in continuous notill wheat systems seems to result in a favorable seedbed, Maxwell says. There doesn t seem to be a need for burning residue the first year of wheat after wheat. Wheat residue can become heavy after 2 or 3 years of continuous wheat, however, and burning can enhance yields and provide a better seedbed to drill into even with no-till drills. The demonstration plot results would indicate an advantage to burning the wheat stubble ahead of planting 3rd and 4th year continuous no-till wheat. Some varieties are better adapted to no-till wheat on wheat. Select varieties with good tan spot resistance, such as Overley. In addition, no-till wheat needs an extra 20 lbs/acre of N above recommended rates for conventional-till wheat. And be prepared to control cheatgrass, especially the 3rd and 4th year of continuous wheat, Maxell says. Again, these test results only indicate some of the agronomic factors involved in residue treatment in continuous wheat. Conservation compliance considerations, erosion concerns, and smoke issues must also be taken into account. -- Steve Watson, Agronomy e-update Editor swatson@ksu.edu These e-updates are a regular weekly item from K-State Extension Agronomy. 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 Jim Shroyer, Research and Extension Crop Production Specialist and State Extension Agronomy Leader jshroyer@ksu.edu 6