I read already a lot that UREA may cause damage to plant and soil in emerging Asian agriculture. But how can we identify that high fertilized (irrigated) UREA or other N-fertilizers are the causing reasons. We know that metabolized compounds like toxic nitrite NO2 or complex N-carbamate occure for short time and might be some reasons. But what causes and how we can identify the intrinsic factor for plant damage and yield loss?
UREA may lower pH. But reported soil analysis is:
pH:6.0－8.5
phosphorus: 5-20 ppm
potassium: 70-180 ppm
humus: 1.2%.
What can indicate soil EC, even soil is high fertilized (irrigated) with UREA?
Many thanks for your incoming experiences here.
J HUMER
May it be that already the simple AMMONIA (NH3) procuded by the hydrolysis of urea by urease is the crucial cytotoxin for bad germination and bad root growing and thefore diminishing plant growth and yield, due to overfertilization?
Thank you Dr. Hani for the attached interesting references .Among the possible causes of seedling toxicity due to urea application,biuret, ammonium/ammonia and nitrite ,the excess ammonium in plant cells and the nitrite derived from ammonium appears to be the cause of the ill affects of urea or any ammonium containing fertilizer, when ammonium accumulation is more than nitrification in soil.When ammoniuum ions get converted into nitrate quickly ,possibly the bad affect may not manifest. However it is often heard from farmers that the proximity of high concentration of urea to seed may cause the toxicity to seedlings.So in effect ,the excess ammonium in soil during germination may be the causitive factor for seedling injury.
Most likely it is the ammonium toxicity. Under high pH, this form may persist for a longer time period. Further, excess ammonium may impair uptake of other cations apart from the seedling injury caused (as mentioned in previous replies).
Nitrite toxicity may be expected only in waterlogged conditions with impaired nitrification and consequent build up of nitrite. Under normal conditions, ammonium form of nitrogen gets rapidly transformed to nitrate.
Important also to consider the crop grown. Crops differ in their sensitivity to the toxicity of ammonia.
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