Sociologia

NITRATE REDUCTASE ACTIVITY, BIOMASS, YIELD, AND QUALITY IN COTTON IN RESPONSE TO NITROGENOUS FERTILIZATION Armando Edgar Hernández-Cruz1, Esteban Sánchez-Chávez2*,Arturo Palomo-Gil1, Armando Espinoza-Banda1, Pablo Preciado-Rangel1

ABSTRACT In the production of cotton (Gossypium hirsutum L.), nitrogenous fertilizer, one of themost costly crop practices, is important to reach high yields, although a high nitrogen (N) content in the plant does not always translate as high fibre production. Oneway of assessing the efficiency of the N fertilizer is through the enzymatic activity of nitrate reductase (NR), which is the key enzyme in N assimilation regulated by anumber of endogenous and exogenous factors that determine yield. The aim of the present study was to assess the effect of the N dosage on yield, fibre quality, biomass,NR enzymatic activity in vivo in the cotton variety Fiber Max 989. The application rates evaluated were 0, 50, 100, and 150 kg ha-1 of N, using urea as a source (46%N) in a random-block design with three replicates. At harvest, the results indicated that the maximum yield of seed cotton and the greatest accumulation of total foliarbiomass through time was reached on applying 150 kg de N ha-1. The different N-application rates did not affect the components of cotton-fibre quality. The activity ofendogenous NR was greater in plants where 150 kg of N ha-1 were applied, which in any case resulted in the highest cotton yield and N content, and therefore the NRactivity in vivo could be used as a bioindicator of the nutritional state of the N in cotton.

Key words: Gossypium hirsutum L., nitrogen application rate, yield.