UREA TRANSFORMATION AND THE ADAPTABILITY OF 3 LEAFY VEGETABLES TO UREA AS A SOURCE OF NITROGEN IN HYDROPONIC CULTURE

Substitution of urea for commonly used nitrate fertilizers in hydropon ic culture of vegetables would not only avoid excessive accumulation o f nitrate in plants but would also reduce the cost of production. This substitution, however, might have adverse effects, such as a dramatic decrease in solution pH, reduced nutrient uptake and possibly urea to xicity per se. Differences in adaptability to urea were found among th ree species of leafy vegetables, Ipomoea aquatica Fossk., Lactuca sati va L. and Brassica chinensis L I. aquatica showed the best adaptabilit y, growing normally with urea as the sole nitrogen source in spite of the dramatic pH decrease in the nutrient solution. It was further foun d that I. aquatica had significantly lower urease activity in the root s than the other two species when urea was supplied to the solution. T olerance of low pH and avoidance of urea toxicity may be possible mech anisms of I. aquatica's adaptability to urea application in hydroponic culture.