Spectrum Agronomic Library

Knowledge is key to using your analytic results to their fullest. The Spectrum Agronomic Library provides you with useful information that will help you to better understand the complex science of agronomy. Our agronomists will be continually adding original and reprinted articles, so check the library regularly for new information.

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Alfalfa and Potassium

Everyone that grows forages knows of the importance of potassium for top alfalfa production. Next to nitrogen, it is the next most highly required element by the growing plant. For every 1 ton of dry matter production, alfalfa contains 55-70 lbs of K2O. This means that at 6 ton/acre the crop is removing 330-420 lbs K2O/acre (or 600-700 lbs of 0-0-60). If sufficient amounts of fertilizer are not applied, the crop will absorb these nutrients from the soil and lower the potassium level in the soil.

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Manure and Soil Organic Matter

Many people ask if manure can be applied to economically build soil organic matter. The following article was taken from the Penn State Field Crop News, Vol 01:11, 9/28/2001 and does a good job of explaining the amount and type of manure that can be used to help increase organic matter in the soil.

Organic matter is the bright star in the sky of soil quality. Soil organic matter improves soil tilth, infiltration rate and soil water holding capacity, contributes nutrients to the crop, and increases the CEC of the soil. Manure is an important source of raw or partly decomposed organic matter.

The question is if organic matter levels can be maintained with manure application only. In an 11-year corn silage experiment in Vermont, 20 T/A (wet weight, including bedding) of dairy manure were needed to maintain soil organic matter levels. Applying less than 20 T/A led to a decrease of soil organic matter contents. Twenty tons of dairy manure contains approximately 5200 lbs of dry matter, 200 lbs of N, 80 lbs of P2O5, and 160 lbs of K2O. Assuming a typical yield of 21 T/A, corn silage removes approximately 105 lbs of P2O5, and 230 lbs of K2O, so a 20 T/A manure application is not excessive. The answer in this case is yes, organic matter levels can be maintained with bedded dairy manure in a continuous corn silage system. You would have to apply more than 20 T/A to increase soil organic matter content.

Most dairy farmers use liquid manure which does not contain any bedding material. Liquid dairy manure contains less than 5% dry matter compared to 13% dry matter in solid manure. To apply the same amount of phosphorus as in the previous example, 6200 gallons/A would need to be applied. This amount of manure weighs 25.9 T (assuming 8.35 lbs/gal), contains 2600 lbs of dry matter (high estimate, based on 5% dry matter content), 174 lbs of N, 81 lbs of P2O5, and 155 lbs of K2O. With the same amount of nutrients, one applies approximately half the amount of dry matter in liquid manure as in solid manure. The conclusion therefore is that with liquid manure only, it will not be possible to maintain soil organic matter levels in a corn silage system without over-applying phosphorus.

These results correspond well with the experience of the long-term rotation experiment at the Penn State Research Farm at Rock Springs in Centre County. In this experiment, 15 years of liquid manure application (based on P-needs of the crop) in a continuous corn grain system resulted in an organic matter content of 2.8%, compared to 2.2% in the same system that received fertilizer but no manure. The increase of soil organic matter content was very small in this experiment.

These data show that liquid manure applications without the return of adequate amounts of crop or cover crop residue to the soil will result in a decline of soil organic matter contents.

Chlorine in Pool Water and Nearby Plants

Today there are many homes that have swimming pools as well as municipal pools in the cities. Many people ask, “Will the chlorine from the pool that gets on the plants around the pool harm them?”

It is important to remember that chlorine does not occur naturally in nature, chloride (Cl-) is readily soluble, highly mobile and easily taken up by plants. Chloride is the element that is found in fertilizer materials.

Chlorine (Cl2) is a corrosive, poisonous gas used to make bleaching agents and disinfectants. The form of chlorine most often added to pool water is solid calcium hypochlorite which forms hypochlorous acid (HOCl) when place in water. Sodium hypochlorite is the active ingredient of common household bleach. Commercial liquid chlorine (compressed chlorine gas) is used as a water treatment to kill bacteria. Hypochlorous acid is the effective agent that controls algae growths in pools.

According to Clemson University, “There should be no effect of pool water splashed on nearby plants from normal pool use. Larger plants (and animals) can tolerate the concentrations that are recommended for pool water.”

Dr. Alison Osinski (Aquatic Consulting Services, San Diego, CA) suggests, “If the pool or spa water has a high chlorine content, uncover it and allow the chlorine to dissipate before using the water for irrigating the landscape. Or, chemically remove the chlorine by adding solium thiosulfate of sodium sulfite to the water.”

Chloride (Cl-) is the ionic form of chlorine found in nature. It has a negative charge and is often associated with sodium (common table salt) or other positively charged ions like potassium. It is non-toxic and readily absorbed and used by plants.

Compare the concentrations of chloride and chlorine in water. Sea water, which contains high levels of bacterial life, contains chloride levels of around 20,000 ppm. Water treatment plants aim for chlorine levels of 1.7 ppm to disinfect water.

 
 
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