AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Winter 1997, No. 5
Is chloride harmful to the environment? No. Many people confuse chlorine and chloride. Chlorine is a component of bleach, is used to sterilize pools, and is poisonous as a gas. Chloride is an essential plant nutrient and provides many benefits.
Why is chloride important? Research on wheat has shown that chloride can increase plant resistance to several diseases as well as enable the plant to better withstand disease pressures. Diseased leaves, most importantly the flag leaf, suffer from reduced photosynthesis. This results in lower grain fill, reduced kernel weights, and lower yields. Diseased roots and stems cannot adequately provide nutrients and water to developing heads. Chloride has been shown to increase the resistance of wheat to the foliar diseases tanspot, stripe rust, leaf rust, and septoria and to take-all root rot and common root rot.
Can I predict where chloride applications will be beneficial? Soil testing is proving to be a valuable tool in assessing the chloride status of soils. Data from responsive spring wheat varieties at 36 locations in South Dakota have shown that 60 pounds of chloride is an appropriate level to be maintained within the upper two feet of soil. To determine the amount of chloride to apply, simply subtract the soil chloride test level (two-foot samples) from 60. Divide this number by the chloride content of the fertilizer expressed as a fraction. As an example, suppose the soil test is 25 pounds per acre for the two-foot composite sample. The amount of chloride to apply is 60-25 = 35 pounds per acre chloride. The amount of muriate of potash to apply is 35/0.47 = 74 pounds of 0-0-60 per acre. Chloride content of muriate is 47 percent. These recommendations are based on research results that showed that at chloride levels less than 30 pounds per acre at a 2 foot depth, an average of 4 bushels per acre yield increase was observed. When soil samples to a two-foot depth tested between 30 and 60 pounds per acre chloride, more than a 2.5 bushel per acre yield increase was observed.
What causes soils to become too low in chloride? Chloride enters the soil through atmospheric deposition. Therefore, coastal soils are naturally higher in chloride than soils farther inland. On farm land, chloride gets applied with muriate of potash fertilizer. In much of the western half of North America where soils can have very high levels of potassium, potassium fertilization is not a common practice. In addition, wheat removes, on average, almost .03 pounds of chloride per harvested bushel. The lack of muriate of potash applications combined with chloride removal by wheat has created insufficient levels of chloride in many areas. It is also important to remember that chloride, like nitrate, is mobile in soils and can leach from the root zone. Therefore, soils should be tested regularly for chloride.
How do I know if my crop is getting the chloride it needs? One of the best ways to check the status of the crop is by tissue testing. The sample should be a collection of whole shoots in the boot to flowering stage. If the plant concentration is less than 0.12 percent, there is a 78 percent chance that the crop will respond to chloride fertilization. At concentrations of 0.13 to 0.40 percent, there is about a 49 percent chance of response. Above 0.40 percent, little chance of response exists. Applying chloride at this stage in the crop is made possible by implementing tramlines. Tramlines are wheel tracks that are not planted. By driving along the tramlines, applications such as fungicide, growth inhibitor and fertilizer can be accomplished without knocking down wheat plants.
Will I always see yield increases from chloride fertilization? Whether or not you can expect to see disease suppression and yield increases depends upon many factors. First of all, remember that chloride applications are part of an entire management strategy for wheat. Yield increases from chloride applications may not be readily apparent when other factors become more limiting. In addition, not all spring or winter wheat cultivars will respond to chloride. Research is currently being conducted on spring and winter wheat varieties to identify the responsive cultivars. On-farm research, done correctly, will provide more insight into identifying responsive varieties and understanding the importance of chloride fertilization within the complete wheat management system.