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977798 
Journal Article 
Nitrite and Ammonium Toxicity on Lettuce Grown under Hydroponics 
Hoque, MM; Ajwa, HA; Smith, R 
2007 
Yes 
Communications in Soil Science and Plant Analysis
ISSN: 0010-3624
EISSN: 1532-2416 
39 
1-2 
207-216 
WOS:000252667100016 
Nitrite (NO2--N) toxicity symptoms have been observed on lettuce (Lactuca sativa) at various locations in California. The objective was to evaluate the symptoms of ammonium (NH4+-N) and nitrite (NO2--N) toxicity on Sundevil iceberg lettuce and Paragon romaine lettuce and to determine lettuce growth and biomass production under different levels of NO2--N. Hydroponic studies under greenhouse conditions were conducted using nutrient solutions containing nitrate (NO3--N) and two other forms of nitrogen (NO2--N and NH4+-N) applied at a constant concentration (50 mg NL-1) or using different NO2--N levels (0, 5, 10, 20, 30, and 40 mg NL-1) and a constant NO3--N level (30 mg NL-1). Crown discoloration (brownish color) was observed for lettuce grown in both NO2-N and NH4+-N solutions approximately 3 weeks after transplanting into the hydroponic systems. Lettuce grown in NO3--N solution produced larger biomass and greater number of leaves per plant than lettuce grown in NO2--N or NH4+-N solutions. Increasing the concentration of NO2--N suppressed plant height, fresh and dry biomass yield, and number of leaves and increased the root vascular discoloration. Lettuce growth was reduced more than 50% at NO2--N concentrations greater than 30 mg NL-1. Even at 5 mg NO2--NL-1, growth was reduced 14 and 24% for romaine and iceberg lettuce, respectively, relative to that obtained in nitrate solution. Although concentrations between 5 and 40 mg NO2--NL-1 reduced dry biomass similarly for both lettuce types, toxicity symptoms were more severe in iceberg lettuce than in romaine. 
ammonium; iceberg lettuce; Nitrite; romaine lettuce