Influence of N rates on nitrate accumulation and distribution in peanut

Pot experiment was conducted to understand the influence of N rates on accumulation and distribution of nitrate and yield in peanut.Results showed that the pod yield increased quadratically with N rate and the maximum yield could be reached at the N rate of 150.9 kg/ha.The relative content,accumulated amount and accumulating rate of nitrate in peanut plant increased with N rate.The nitrate content in various organs,at the same N level,differed with growth stages.The content was high in stem at seedling stage and pegging stage and in underground-organs at pod-filling stage.Nitrate content decreased in leaves and stems and increased in pod with plant growth and development.At maturing stage,increasing N rate could result in an increase of the distribution percentage of nitrate in stem and kernel(N135 kg/ha) while a decrease in root and no obvious trend in other organs.The excessive application of N(for example,N180 kg/ha) may increase the distribution percentage in vegetable part and reduce that in kernel.The nitrate content of kernels and all other organs for all treatments was less than the nitrate-content standard set up by WHO and FAO,indicating no nitrate pollution in peanut products.But excessive N was able to greatly enhance the nitrate concentration in both peanut products and tillage layer of soil.The suggested N rate was 90 kg/ha that would optimize yield,quality of product and ecological effect.