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Abstract
To improve the growth of spinach (Spinacia oleracea cv, Okarne) and to decrease shoot nitrate contents, different concentrations of urea were used as a source of nitrogen in the nutrient solution For hydroponically grown plants. Spinach was grown in a hydroponic got culture amended with 0,20, or 58% urea with or without nickel addition (Ni; 0.05 mg L-1) while the dotal concentration of N (17.33 mmol L-1) remained constant in all the cases. In order to identify the most eEective conceniration of Ni for the growth of spinach, another experiment was conducted using various concentrations sf Ni in a 50% urea solution. Addition of 0.05 mg Ni L-1 to the nutrient solution gave the best results in terms of qualitative and quantitative charaeteristies Naximuna vegetative production was achieved with a 28% urea solution contaimnang Ni. Shoot NO3-N content significantly decreased with increasing level sf urea in the solution. The urea-N content in the shoots was significantly inc~easedw ith both 20 and 50% urea solution without Ni addition. The total-N content in the shoots was almost the same in all the experimental treatments except those utilizing 50% urea solution without Ni addition. The content of Ca in the shoots increased by the addition of Ni with urea in the nutrient soleation, Fe eontent in the shoots was slightly affected by nrea nutrition, except for the treatment utilizing 20% urea solution with Ni addition. The contents of K, Mg, and Zn were significantly agected by urea in the nutrient solution. Ni in the shoots was not detected when it was not supplied in the nutrient solution. Also, the Ni content in the shoots was within the range of natural abundance when Ni was added to the 20 and 50% urea solutions.