<b>Nitrate reductase activity on coffee leaves in relation to nitrogen supply</b> - DOI: 10.4025/actasciagron.v29i2.270

Abstract

The nitrate reductase (RN) is the first enzyme in the nitrogen reduction process on crops incorporated to carbonic skeletons that can indicate the nitrogen entrance level on plants. This work aims to investigate the effects of different rates and times of nitrogen application on RN activity and nitrogen content in leaves; and to establish correlations with coffee plants productivity. The experimental design used was completely randomized in a factorial outline 5 x 3 x 3, constituted by the combination of 5 nitrogen(urea) rates (0, 50, 150, 250 and 350 kg ha^-1) in three application times (a single application in December); two applications (November and January); three applications (November, December and January) and enzyme activity on three plant crown positions (apex, middle and base). The RN activity, the concentration of nitrogen in leaves and its productivity were evaluated during the frutification period. The enzyme activity was correlated positively both to N content in leaves (r = 0.96) and to grain productivity (r = 0.89). These results were adjusted to a linear and a quadratic model functions, respectively. The rate of 210 kg N ^ha-1 promoted higher productivity. The estimative of RN activity showed good results for detecting N deficiencies in coffee crops.