Biogas slurry added amino acids decreased nitrate concentrations of lettuce in sand culture

Abstract

Abstract Human health worldwide is being threatened by excessive nitrate intake through the dietary pathway, i.e. vegetables and drinking water, and the former is the primary source (about 80%) for large quantitative ingestion and the biological characteristics of nitrate accumulation, especially for leafy vegetables. In this paper, four kinds of organic nutrient solutions (biogas slurry dilution or biogas slurry dilution with added glycine) were developed to culture lettuce in order to lower the nitrate concentrations in leafy tissue. The results showed that all organic nutrient solutions significantly decreased nitrate concentrations of lettuce shoot, and simultaneously had an increased or unbiased yield compared with inorganic nutrient solution (containing NO3 −-N solely) in sand culture with high-level nitrogen supply (8.69–15 mmol/L). In addition, glycine addition only slightly decreased nitrate concentrations in lettuce shoot both at 1:4 and 1:5 dilution rates of biogas slurry. Leafy SPAD values indicated that there were differences in lettuce N nutrition of new and old leaves responding to various N-form supplies, and no correlations between nitrate concentration and SPAD values were found. It was concluded that application of organic nutrient solutions formulated from biogas slurry dilution and amino acid in soilless cultivation is an effective means for reduction nitrate concentrations in leafy vegetables.