Doses of potassium and nitrogen sources affect radish root quality parameters and nitrate reductase activity

Abstract

Nitrogen and potassium are the nutrients most extracted and exported by the radish culture, being essential for the productivity and quality of the roots produced. Thus, the present study was developed with the objective of evaluating changes in plant growth and radish root quality as a function of potassium doses and nitrogen sources. The experiment was conducted in a completely randomized design, with treatments arranged in a 4 x 2 factorial scheme, with four doses of potassium (K), 0, 70, 140 and 210 kg of K₂O ha^-1 and two sources of nitrogen (N), ammonium sulfate and calcium nitrate, with four replicates. The plants were evaluated for growth, yield, biochemical quality of the roots and nitrate reductase activity in the leaves. The treatments did not influence the growth and yield characteristics: leaf and root fresh mass, leaf dry mass, total leaf area, root length and diameter. Potassium fertilization increased the vitamin C content in the radish roots and the nitrate reductase activity in the leaves, especially when the N source used was calcium nitrate. The highest SPAD index value was obtained at a dose of 51 kg ha^-1 of K₂O. The use of ammonium sulfate provided a higher content of soluble solids in the roots. The application of potassium increases the quality of the roots and the activity of nitrate reductase, thus reducing the accumulation of nitrate in radish.