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

Abstract

SummaryThe 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 ratios (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.