Urea transformation and the adaptability of three leafy vegetables to urea as a source of nitrogen in hydroponic culture

Abstract

Substitution of urea for commonly used nitrate fertilizers in hydroponic culture of vegetables would not only avoid excessive accumulation of 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 toxicity per se. Differences in adaptability to urea were found among three species of leafy vegetables, Ipomoea aquatica Fossk., Lactuca sativa L. and Brassica chinensis L. I. aquatica showed the best adaptability, growing normally with urea as the sole nitrogen source in spite of the dramatic pH decrease in the nutrient solution. It was further found that I. aquatica had significantly lower urease activity in the roots than the other two species when urea was supplied to the solution. Tolerance of low pH and avoidance of urea toxicity may be possible mechanisms of I. aquatica's adaptability to urea application in hydroponic culture.

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