Raymond C. Ward, Ph.D.
Jolene F. Ward, B.S.
A Refresher On Pop-Up Fertilizer
By Dr. Ray Ward
Starter fertilizer has been shown many times to be an effective method of fertilizer application. The "2 x 2" placement requires separate fertilizer openers that have a number of disadvantages including cost, weight, residue clearance, available planter space, and soil disturbance. Therefore, many producers are placing phosphate fertilizers with seed at planting which is generally a good method of placement, except for the possibility of germination injury.
Factors that impact germination or seedling injury are crop sensitivity row width seed-fertilizer spread width, rainfall after planting, and closeness of fertilizer and seed. Soil factors that need to be considered are soil pH, organic matter, soil texture, and soil moisture. Fertilizer factors affecting germination include fertilizer grade and rate.
Phosphate is known to have a low salt index. However nitrogen and potash have high salt indexes. Also, it is known that thiosulfate present in 12-0-0-26 fertilizer is toxic to germinating seeds. Therefore sulfate fertilizers should be applied with the nitrogen application where practical. We have always used a factor of 8 pounds of N plus K20 as a limit of fertilizer that can be applied with corn seed in 30-inch row width. Conceivably, 16 pounds of N and K20 could be placed with the corn seed in 15-inch rows because there are twice as many feet of row in 15-inch rows compared to 30-inch rows
Many producers are thinking about fertilizing another crop besides corn. South Dakota State University has compared many crops for their sensitivity to the amount of N plus K20 that can be applied with the seed. The amount depends on the crop and the row spacing. The following table gives a guideline for some crops.
Phosphorus Soil Test
lbs P2O5/A Cool Season Warm Season 0-5 55-70 35-45 6-12 40-55 20-30 13-25 20-35 0-20 26-50 0-20 0 51+ 0 0 Potassium Soil Test lbs K20/A Cool Season Warm Season 0-40 85-150 55-100 41-80 50-75 30-50 81-120 30-45 15-25
0 200+ 0 0 Sulfur
Soil Test lbs S/A Cool Season Warm Season 0-2 12-17 0-7 3-4 5-10 0 5-7 0-5 0 8+ 0 0 - 2 -
Pounds on N plus K20
Another alternative to placing fertilizer in direct contact with the seed is dribbling the starter behind the press wheel about 2 inches to the side of the seed. Kansas State University experiments at the Belleville location found this placement to perform almost as well as the 2 x 2 placement.
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The View From My Windshield
Have you noticed how slow the grass is growing with the moisture we have received in the last month? As I travel the country I have been noticing that the grass looks good from the pickup, but when I walk around the pastures I find the grass to be pretty thin which is understandable considering the severe drought we have had in the summer of 2002. However, I see much improved growth of grass where some nitrogen fertilizer has been added, especially with cool season grasses.
I think the reason for the great response to nitrogen fertilizer is the weak root system caused by drought. Producers that need extra forage may want to consider an application of at least 30 to 40 pounds of N per acre. It is getting pretty late for fertilizing cool season grass such as brome grass. However, some response can be expected if plenty of rain is received in early June. Wheat grasses and orchard grasses should respond well with N applied now Warm season grasses should be fertilized around the first of June with about 30 pounds of N per acre.
Research has shown that 40 pounds of N should increase cool season grass yield by 3/4 to 1 ton per acre, depending on water and temperature. The warm season grasses need about 27 pounds of N per acre to increase yield by one ton per acre.
There has been a lot of interest in irrigated grass production for grazing. Nitrogen is very important for grass production. The nitrogen should be split so about 40 pounds of N per month is applied per acre during forage production. The rate of N will depend on the amount of grass needed and if the grass present will produce at that period of time. Hopefully, most producers will have a good mixture of grass species for a long period of grazing.
Some steps to follow when considering fertilization of grasses include:
Fertilizer Requirement For Grasses
Nitrogen Fertilizer Calculations
Cool Grass = (Yield Goal * 40) - soil nitrate to 2 ft - legume - manure
Warm Grass = (Yield Goal * 27) - soil nitrate to 2 fi - legume - manure
Answering Questions On Urea Application
Ward Laboratories professionals often get questions about surface application of urea and UAN solutions. Urea is a dry fertilizer that dissolves with water after application creating urease enzyme that is naturally present in all soils at some level. Urease enzyme converts urea to ammonia (NH3) and bicarbonate (HCO3) in the presence of water.
If there are hydrogen ions present (as in an acid soil - soil pH below 7.0) bicarbonate combines with another hydrogen ion to form water and carbon dioxide (C02) The CO2 escapes as a gas. The hydrogen ions are used forming water causing soil pH to increase. Very little ammonia (NH3) exists at pH of 7 and below, but at higher pH, the NH3 increases especially above 8.0. If NH3 is present in the soil it will transform into NH4 and be held on the soil exchange complex. If the NH3 is held on organic residue there is a greater chance of ammonia volatilization as the crop residue dries.
Urease activity and rate of urea hydrolysis is faster in warm temperatures. So urea and UAN solutions applied during the cool part of the season have less chance of ammonia volatilization. For example, a rise in temperature from 44 F to 80 F increases the rate of conversion to ammonium four times faster. Soil moisture is also very important for conversion of urea to ammonium. Urease activity is very low in dry soil and dry residue. The better the moisture the faster the conversion.
So, what is the best way to apply urea? First, it should be noted that UAN solutions contain about 1/2 urea and 1/2 ammonium nitrate, so the liquid N solutions are only 50% urea. Dry urea, conversely, is all urea. Research shows that it is best to incorporate the N fertilizers by tillage or with 1/2 inch of rain. The second best method of application would be to apply UAN in surface strips spaced 12 to 20 inches apart depending an which crop is being fertilized. Spreading dry urea has about the same effect as UAN surface stripping. The least effective method of applying UAN is surface broadcasting. If rainfall or irrigation occurs within 3-5 days after broadcast application the effect is generally the same as incorporation. All methods of application are much better of course, than not applying nitrogen that is needed for the crop.
For conventional farming where a considerable amount of crop residue is incorporated by tillage any method of application of nitrogen fertilizer performs well. The discussion above is written for the no-till and residue management operations.
Another reason that surface application of UAN solutions may not perform quite as well is crop residue tie-up. When UAN solution is sprayed on the residue soil microbes begin using the nitrogen to break down the residues. The more time the fertilizer is on the residue, the more N fertilizer used by the microbes. Once the N fertilizer is used by the microbes it becomes part of the organic matter of the soil and then the N is released slowly over a period of years. If the N fertilizer is knifed-in or washed in, then the N fertilizer is available for the intended crop. The point is that sometimes there may not be any ammonia volatilization, but may be N immobilization.
Late Spring Nitrate Test or PSNT
Have you wondered if the manure or past legume crop is supplying enough nitrogen for the crop? A late spring nitrate test or PSNT may help supply the answer to that question. PSNT is the soil test for nitrate taken when corn is 6 to 12 inches tall or as a pre-side dress nitrate test. Iowa State University has evaluated the method of N recommendations. Take the soil sample from 0 to 12 inches deep using 15 composite soil cores from the sampling area. The area could be up to 80 acres per composite sample. Be sure to ship to Ward Laboratories for analysis ASAP. After nitrate-N analysis, estimate N fertilizer needs by subtracting the concentration of soil test nitrate from 25 ppm N. Twenty-five ppm is the critical nitrate-N concentration where no additional N is needed.
Example: A soil nitrate test is 16 ppm nitrate-N.
25 ppm N-16 ppm N = 9 ppm N differenee
The difference is multiplied by 8 lb of N/A/ppm N
Therefore the N recommendation is 9 ppm N * 8 lb of N/A/ppm N or 72 lb of N/A.
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The rapid growth of alfalfa this spring has produced several questions from producers. One of the diseases cropping up is Spring Black Stem. The leaves develop many small dark brown spots on the lower leaves and on the stems. If the disease continues, the lower leaves will turn yellow and drop off. The lesions on the stems enlarge and may blacken large areas near the base of the plant. Severe infestation girdles the stem, which destroys the plant. The plant dies when infection spreads to the crown. If you see leaves dropping off or large lesions appear, it is best to harvest as soon as possible to reduce disease injury. As weather warms and dries, the disease symptoms will be less,
Some alfalfa had severe hail damage this spring. The growing point of alfalfa is at the top of the plant. As the plant develops toward bloom, a plant hormone sends a signal to the crown to start sending new shoots out of the crown. If the top is cut off then the same signal is sent to the crown. However, if hail breaks the top of the plant but the plant still remains taller than a cutting, the signal is not sent to the crown therefore the branches of the main plant try to grow. If this happens the alfalfa should be harvested. If there is not enough growth for a harvest just shred the alfalfa so new growth will begin at the crown. The reason it should be cut is the growth from the branches will be slow and yield will be lower than getting new growth from the crown.
We also observed Phytophthora root rot on alfalfa. Lesions develop on the roots, usually about 3 inches below the crown. Look for dark spots on the taproot. With a knife cut into the lesion and observe how far the lesion goes into the taproot. A dark spot will penetrate into the taproot about 1/3 of the diameter. Eventually the taproot will completely rot and the plant will die. Usually the disease appears on established plants in poorly drained soil and whore water stands for 3 days or less. Plant growth is reduced, eventually plants wilt and leaves turn yellow to reddish brown.
Good management practices include the following:
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