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Thunderstorm Effects

County Agent News
Dan Folske
August 5, 2019 

Thunderstorm Effects

            Thunderstorms may bring needed rain but they can also do a lot of damage. The thunderstorm that came through the county last Saturday is a good example of both positive and negative effects. 

            Did you know that thunderstorms can fertilize your crops, lawns, and gardens? The tremendous energy released from a bolt of lightning breaks apart the inert nitrogen gases in the air.  This allows allows the nitrogen to combine with oxygen forming water soluble nitrogen oxides. Thus rainfall from a thunderstorm with lots of lightning is very rich in nitrogen which is an essential nutrient for plant growth.  A rough estimate of the efficiency of fixation yields the value of 1026 NO2 molecules per lightning stroke. I have no idea how that might convert to pounds per acre because it still needs the rainfall to get it to the soil surface.

            Severe storms can produce strong winds and hail which can and do cause millions of dollars worth of damage to crops, vehicles, and buildings. The storm Saturday afternoon did plenty of damage. I don’t have an estimated dollar amount for the damage caused but I know that numerous crops which were near maturity were hit hard. I lost two windows on the south end of my house and heard of other houses in the area with broken windows. My metal roof looks like it was worked over with a hammer to give it an embossed appearance.

            For producers trying to put up a very short hay crop, thunderstorms can really be a mixed blessing. Rainfall is almost always welcome but when it falls on hay that is cut and ready to bale it can do a lot of damage causing both nutrient and dry matter losses. Here is an article by Karl Hoppe, NDSU Extension Livestock Specialist, explaining those losses.

 

How much does rainfall reduce yield?

 

Several research studies have addressed the effects of rainfall on cut alfalfa. In Wisconsin, Collins measured dry matter losses of 22% when alfalfa was exposed to 1-inch of rain after 1 day of curing. Similar hay cured without rain damage lost only 6.3% of the initial potential yield. Losses appear to be greatest after partial drying of the forage has occurred. In this same study, alfalfa exposed to 1.6 inches of rain over several days suffered a 44% loss in dry matter.

 

How does rainfall reduce yield?

Three primary factors are involved: leaching, respiration, and leaf loss.

Leaching is the movement of cell solubles out of the plant. Components of the plant that are very water-soluble are leached out of the forage and lost during a rain event. Unfortunately, most of these compounds are those highly digested by the animal. They include such things as readily available carbohydrates and soluble nitrogen, minerals, and lipids. About one-half of the dry matter leached by rain is soluble carbohydrate. Excessive leaching of soluble carbohydrates by rainfall impacts its value to make good silage. Reduced soluble carbohydrates provide less substrate for bacteria involved in the fermentation process. In situations where soluble carbohydrates are in low concentrations, silage additives that provide fermentable substrate might provide some benefit to ensure proper fermentation.

Respiration, the breakdown of soluble carbohydrates by plant enzymes, will cause dry matter losses regardless of whether wilted forage is subjected to rain or not. Respiration losses occur while crop moisture levels are above about 30 percent. These losses are reported to be about 3 to 4 percent of the potential DM harvest.  Each time cut forages are wetted by rain, respiration is prolonged or begins again in cases where the cured forage is already below 30 percent moisture. In either situation, additional dry matter is lost.

Experience and common sense tell us that rain damaged alfalfa is more susceptible to leaf shatter after it dries. Rainfall often means additional raking or tedding to speed up drying; hence, more lost leaves.

 

How does rainfall intensity and forage moisture affect losses?

Research is conclusive on these two points. Given the same amount of total rainfall, a low intensity rain will result in more leaching of soluble compounds than a high intensity rain. In addition, as forage moisture declines, it is more prone to DM loss from rain. In Wisconsin rainfall studies, the maximum loss in DM (54% DM loss) was a treatment where 2.5 inches of rain fell on hay that was nearly cured.

 

Does rainfall affect forage quality?

Perhaps nothing is more frustrating than to see excellent quality alfalfa turn into cordwood with each passing rainstorm and subsequent raking. Most rainfall studies agree that wetting of field cured alfalfa has little impact on crude protein concentration. In fact, it is common to see relatively high protein values in comparison to fiber concentrations. However, because rain leaches soluble carbohydrates, structural fibers (acid and neutral detergent fibers) comprise a greater percent of the forage dry matter. Depending on numerous factors previously discussed, the digestibility of rained-on hay may decline from 6 to 40 percent.

 

“Make hay while the sun shines” is an old adage that still rings true today. Watch the weather forecast and hope for better weather; or consider making haylage.

 

 

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