Evaluation of Pre-side Dress Soil Nitrate Test for Sugarbeet in Iran

Field experiments were conducted to evaluate the accuracy of PSNT (pre-side dress soil nitrate test) in semi-arid region of Iran where sugarbeet is grown under irrigation water. In a randomized complete block with three replications, urea-N was side dressed at 0, 90 and 180 kg ha⁻¹ N based on nitrate concentration of soil at V4 to V6 growth stage and 180 kg ha⁻¹ N applied at planting and mid season pre-side dress based on farmers practice. Sugarbeet responded to nitrogen application in all sites where the soil nitrate was low. The high applications of N where the soil nitrate were higher than 17 mg kg⁻¹ resulted insignificant increase in concentration of impurities such as sodium, potassium and nitrogen content of roots. The amount of measured nitrate in soil at V-6 stage of growth was significantly correlated (at 1% level of significant) with root yield and sugar content of beet (r² = 0.64 and 0.58, respectively). The lower critical level on nitrate test could be due to lack of conversion of organic matter and accumulation of nitrate in depth higher than 0.3 m, as a result of lower leaching rate in semi-arid area which can be utilized by sugarbeet during late stage of growth. The pre-side dress Soil Nitrate Test method proved to be a very reliable method to predict nitrogen requirement of sugarbeet in order to produce high yield and quality of sugar.