Articles
UREA AS A NITROGEN SOURCE FOR POT PLANTS
Many workers have demonstrated that for plants grown with a restricted root volume growth rate is more dependent on nitrogen than other nutrients.
Uptake of nitrogen depends largely on the prevailing osmotic value of the soil solution in addition to the availability of water = the total moisture stress.
Nitrogen as nitrate or ammonium salts add a considerable osmotic value to soil water.
In most of the nutrient solutions used an excess of 50% of the OP is caused by nitrogen.
In early days pot plant production the nitrogen source was often of organic nature, rotted manure, hoof and horn, giving a slow release nitrogen supply.
The change towards constant liquid feed and a low moisture stress in the pot has induced an interest in finding a way to an optimal nitrogen supply combined with low OP.
Urea-carbamide has possibilities in that respect.
It is a highly concentrated salt with high nitrogen content (46%) and with no ballast kations or anions.
It is not ionized and a very soluble, pure, non corrosive, non toxic, rather cheap chemical.
Problems caused by urea could be a possible content of biuret, a rather strong toxicate.
The risk is now rather small due to a strict production control.
Some questions concerning the effect of urea on plant growth have been brought forth:
Can roots assimilate urea as such or must it be decomposed to ammonium and further to nitrate before uptake?
If so, how do these processes occur in soil or inert media? Can any harmful effect be expected of the intermediate products of decomposition NH4+, NO2–, NO3– and the change in pH during such processes?
Urea will hydrolyse with alkali and acid to NH3 and CO2, but the process is rather slow at low temperatures.
In a biological active environment the hydrolysis on the other hand can be very rapid accellerated by urease.
The process will be the following: