Growth and development of lettuce plants at high NH4+:NO3- ratios in the nutrient solution

Abstract

Lettuce plants, cv. Vera, were grown at five NH4+:NO3- ratios in the nutrient solution in a 0.15 m deep sand growing bed. A standard nutrient solution was used, with the composition of, in mmol L-1, 11.0 NO3-; 1.5 H2PO4-; 6.5 SO4--; 7.5 Ca++; 10.0 K+ and 1.5 Mg++, and, in mg L-1, 0.42 Mn; 0.26 Zn; 0.05 Cu; 0.50 B; 0.04 Mo, and 4.82 chelate Fe. Ammonium nitrate was used to supply NH4+ concentrations of 2.5; 5; 7.5 and 10 mmol L-1, reaching NH4+:NO3- ratios of 0:11 (T1); 2.5:13.5 (T2); 5:16 (T3); 7.5:18.5 (T4) and 10:21 mmol L-1 (T5) as treatments. A completely randomized experimental design was used, with four replications and 20 plants per plot. Four plants of each plot were harvested at 25 days after planting, to determine shoot and root dry mass, shoot fresh weight and number of leaves per plant. Number of leaves, shoot fresh and shoot and root dry mass decreased 25.5%; 52.5% and 68.5% from T1 to T5, respectively, following polynomial models. Root dry mass was 1.7 g/plant for T1 and T2, and 0.82 g/plant for T3, T4 and T5, decreasing in a proportion of 51.8%. For lettuce crop production in hydroponical facilities, the NH4+ threshold limit of about 9-12% of the total N should be retained.

Effect of plant spacing on growth and yield of lettuce (Lactuca sativaL.) in a soilless production system

“…Soilless cultivation of lettuce recently gained popularity in South Africa because of improved yield and quality (Maboko & Du Plooy, 2008). A review of the literature showed conflicting results regarding the recommended spacing for lettuce in a soilless cultivation system (Niederwieser, 2001; Andriolo et al, 2006). Understanding the crop response to plant density is crucial for maximizing lettuce yield.…”

Mode of Managing Nutrient Solution Based on N Use Efficiency for Lettuce (Lactuca sativa L.)

“…Carbon, nitrogen and water uptakes rates are the key processes determining fresh yield of vegetables [5]. Improved water use efficiency (WUE) representsa key factor in increasing crop productivity under suchwater scarcity conditions [10], and improving NUE might help to limit use of N fertilizers and to preserve the environment and public health [14].…”

“…Besides, soilless systems have relatively small additional expense and save both fertilizers and water. Due to drain large amounts of residual nutrient solutions with high salinity for the environment has been the biggest problem for soilless plant cultivation, then recycling and reuse is a current trend of sustainable farming systems [5]. The N use efficiency for lettuce ( Lactuca sativa L. ) was researched by monitoring the concentration of NH 4 + , NO 3 − and gross-N in nutrient solution and NO 3 − on lettuce leaves under the conditions of different management modes of replacing the nutrient solution and initial pH values.…”

Nutrient Solutions for Hydroponic Systems

“…Therefore, recycling and reuse of solutions is a trend in searching for sustainable agricultural production systems (Andriolo et al, 2006). Brun et al (2001) reported recycling systems based on EC control, consisting of adding a water complement to the drainage to decrease the EC and a complement nutrient solution to obtain the desired EC.…”