Optimizing Nitrogen Application in Root Vegetables from Their Growth, Biochemical and Antioxidant Response to Urea Fertilizer

Abstract

Nitrogen is one of the most influencing inorganic nutrients for improved plant growth and yield in crops. However, excessive fertilizer application may have adverse impacts on the environment. Therefore, we strive to investigate in this work by examining the impact of different nitrogen (N) doses in the form of urea (46% N) on the growth, yield, photosynthetic pigment content, nitrate reductase activity, carbohydrate content, protein content, and antioxidant enzyme activity of the carrot and beetroot. A pot experiment was conducted under natural conditions with four nitrogen levels as basal treatment (Control = Nil N, U50 = 145.57 mg/kg N; U100 = 291.14 mg/kg N; U150 = 436.71 mg/kg N; U200 = 582.28 mg/kg N). Results found that U150 (436.71 mg/kg N) is the optimum N fertilizer dose at which significant (p ≤ 0.05) improvements in all the growth, yield and biochemical attributes of carrot and beetroot were observed. However, the further increment in N doses did not affect the observed parameters and, therefore, excessive N level was observed beyond U150 = 436.71 mg/kg N. The principal component analysis presented significant correlations among the various parameters observed. Two principal components account for a total of 98.86% variance (PC1 = 92.96%; PC2 = 5.90%) in carrot and 99.2% variance (PC1 = 92.64; PC = 6.56) in beetroot of the overall data variability in plants supplemented with different N treatments.