The impact of different growth media and ammonium-nitrate ratio on yield and nitrate accumulation in lettuce (Lactuca sativa var. longifolia)

Abstract

Ammonium (NH4+) to nitrate (NO3-) ratio and growth media significantly alter plant development and NO3- accumulation in lettuce. Nitrate accumulation is regarded harmful for environment and human health. The quality of lettuce is assessed by NO3-concentration, size, and weight. This study determined the impact of five different growth media (cocopeat, peat, bark, perlite and rockwool) and four different NH4+:NO3- ratios (0:100, 20:80, 40:60 and 60:40) on NO3- accumulation in lettuce, yield, and several growth attributes. The experimentation was conducted according to open feeding system of soilless agriculture. The ‘Cosmos’ variety of lettuce was used as experimental material in the study. Growth mediums and NH4+:NO3- ratios significantly altered NO3- accumulation, head, leaf, stem and root traits. The results revealed that instead of growing lettuce with NO3- only in peat and rockwool, addition of NH4+ (20:80 of NH4+:NO3-) into nutrient solution increased head weight. While head weight increased in perlite medium with the addition of NH4+, it decreased in cocopeat and bark media. It is concluded that growth media and NH4+:NO3- ratios pose significant impacts on NO3- accumulation in leaf and that the increase in NH4+ ratio decreased NO3- accumulation in all growing media. Therefore, it is recommended that NH4+ should be added in the nutrient solution to decrease NO3- accumulation, which will ultimately improve yield and quality of lettuce.