Growth analysis of spinach (Spinacia oleracea L.) plants under the effect of different sources and doses of nitrogen

The behavior of physiological variables and growth rates in spinach under the effect of different doses and sources of nitrogen was studied. Spinach plantlets were transplanted into plastic bags filled with soil and located in a greenhouse, where remained during all the study. The treatments consisted of two fertilizer sources, urea and ammonium nitrate, and three doses, 50, 100 and 150%, taking into account the recommendation of soil analysis. The treatments generated soil salinity, where ammonium nitrate was the source of the highest incidence. Ammonium nitrate at the highest dose was associated with the highest leaf area and total fresh mass. Dry mass of plants and leaf dry mass had the highest values with the two sources at the highest doses. Ammonium nitrate at the highest dose contributed to the highest leaf area, total fresh mass and leaf area index (LAI) at day 49 after transplanting (dat). Relative growth rate (RGR), in general, was decreasing in time, where ammonium nitrate at 50% showed the highest values. Leaf area ratio (LAR) and specific leaf area (SLA) progressively decreased, with urea at 150% demonstrating the greatest decrease. The crop growth rate (CGR) had a slight increase in time, where 150% urea, ammonium nitrate at 100% and 150% had highest values of this rate. Net assimilation rate (NAR) decreased significantly over time and at 7 dat ammonium nitrate at 100% achieved the highest value. Additional key words: fertilization, growth curves, growth rates, electrical conductivity