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Massachusetts | I am considering using urea as a primary N source for my potato crop next year, mostly because it is cheap. I have been reading online about it, and have discovered that many feel that excessive ammonium N will prevent Ca uptake by plants, causing disorders like tomato blossom end rot and potato hollow heart. Is this really a problem, or will the ammonia from the urea convert to nitrate quickly enough to not matter?
Do any growers here feel that this is true, and avoid urea as a result?
Here are some links:
http://pubs.caes.uga.edu/caespubs/horticulture/blossom-rot.html
"The uptake of calcium is inhibited by ammonia. Use nitrogen in the form of potassium or calcium nitrate and avoid ammonium nitrate if possible. Apply potassium, phosphorus, and magnesium as recommended because balancing these nutrients with calcium is also important in preventing blossom-end rot. Applying too much fertilizer, especially ammoniacal nitrogen, at one time can result in blossom-end rot -- use several smaller side-dress applications."
http://www.umassvegetable.org/soil_crop_pest_mgt/soil_nutrient_mgt/...
"Nitrogen is available in a number of forms. These include urea, ammonium and nitrate. Common fertilizer sources of N used in New England include urea, ammonium nitrate, diammonium phosphate, monoammonium phosphate, calcium nitrate and potassium nitrate. In the soil, urea is converted by hydrolysis to ammonium, which in turn is converted through nitrification to nitrate. In warm soils these reactions usually happen fairly quickly if soil pH is over 6.0 and soil moisture and aeration are adequate. Nitrate is the predominant form of N taken up by most plants, but any of these fertilizers can be used because they will be converted to nitrate. However, high ammonium levels can interfere with calcium uptake and induce calcium related disorders such as blossom-end rot of tomatoes, tip burn of cabbage and greens and cavity spot of carrots. This problem is exacerbated by heat and moisture stress and may not be an issue every year. Many growers use calcium nitrate and sometimes potassium nitrate for topdressing or sidedressing N on crops subject to calcium related disorders. High ammonium levels can also be injurious to soil microbes leading to a prolonged period of high ammonium. Ammonium nitrate provides half the N in the nitrate form and half in the ammonium form. Urea N is converted to ammonium N and then to nitrate N. In effect, applying urea is similar to applying N in the ammonium form. Application of urea and ammonium phosphates are most likely to interfere with calcium uptake whereas calcium nitrate and potassium nitrate are not likely to do this. Ammonium nitrate is intermediate in this regard. When a slow release form of urea is used, only a small amount of ammonium is present at a given time and is unlikely to cause a problem with calcium nutrition, but N may not be available quickly enough to meet the demands of a rapidly growing crop. "
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Vegetable Growers...Ammonia N Question
