Vol. 80 No: 2

Title:
High irrigation frequency and transient NH₄ concentration: effects on soilless-grown bell pepper

Authors:
A. SILBER, M. BRUNER, E. KENIG, G. RESHEF, H. ZOHAR, I. POSALSKI, H. YEHEZKEL, S. COHEN, M. DINAR and S. ASSOULINE

pp: 233-239

Abstract:
The effects of irrigation frequency, N concentration, and NH₄-N/NO₃-N ratio on rhizosphere NH₄ concentrations and plant yield were investigated for bell pepper (Capsicum annuum L., cv. ´Mazurka`) grown in perlite. The experiment comprised eight treatments, with two concentrations of N (120 or 60 mg l^-1), two NH₄-N/NO₃-N ratio (3:7 and 1:9), and two irrigation frequencies (3 d^-1, or for 1.5 min every 30 min throughout the day). The combination of high NH₄ concentration in the irrigation water and high irrigation frequency reduced yield significantly. Decreasing the NH₄ concentration by decreasing the NH₄-N/NO₃-N ratio, or by decreasing the total N concentration, improved yield. The impaired growth of plants exposed to high irrigation frequency and high NH4 concentrations was a result of high transient NH4 concentrations in the rhizosphere. Time-dependent processes, such as nitrification, reduced transient NH4 concentrations in the rhizosphere and, therefore, actual NH₄ concentrations were lower under low-frequency irrigation. Modification of the NH₄/NO₃ ratio under high frequencies of irrigation is recommended to diminish the risks of NH₄ toxicity in sensitive crops.

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