Morphophysiological responses, water, and nutritional performance of the forage cactus submitted to different doses of nitrogen.

The application of nitrogen fertilization can promote different morphological, productive, and efficient responses in forage cactus. Therefore, the objective was to determine the morphophysiological, productive, nutritional, and economic responses of the forage cactus clone Orelha de Elefante Mexicana (Opuntia stricta (Haw.) Haw.) subjected to four doses of nitrogen (N) under irrigated conditions in the semi-arid region. Four treatments were applied: 50 (T1), 150 (T2), 300 (T3), and 450 (T4) kg ha−1 of N. For growth analyses, biometry and biomass data were collected to determine phenology, rates morphophysiological characteristics, ideal cutting time, and fresh (FM) and dry (DM) yields. From data on soil moisture, physical-hydric properties, and productivity, the components of water balance, water use efficiency, and economic gain of the crop were calculated. From analyzes of forage cactus plant tissue, nutrient concentrations, biological utilization coefficient, and nutrient use efficiency were determined. The FM and MS yields showed a quadratic (cycle 1 and 2) and positive linear (cycle 3) response to the increase in nitrogen dose. In the first two cycles the maximum dose for FM was 286.19 kg N ha−1 and 413.33 kg N ha−1, to DM productivity the maximum dose was 299.12 kg N ha−1 and 416.79 kg N ha−1. The specific cladode area and the net assimilation rate had better responses at the lowest N doses (50 and 150 kg ha−1), and the absolute and relative growth rate, phenology, and cutting moment were under little influence of N levels. The concentrations and the coefficient of biological utilization of the nutrients showed a positive response to the quadratic model. For concentrations, nitrogen (T4 = 6.72 g N kg−1 DM), phosphorus (T1 = 6.28 g P kg−1 DM), and potassium (T1 = 33.18 g K kg−1 DM) showed significance at 5 % probability, and the quadratic model accounted for 99 % of the data variability. It was concluded that the clone characteristic influenced the relative and absolute growth rates more than the different nitrogen doses. Fertilization from 300 kg N ha−1 increased DM and FM productivity and nutrient concentrations. Lower doses of N were more efficient in DM production. Based on real evapotranspiration, N use efficiency increased with increasing doses, and for other nutrients, the greatest efficiencies occurred in cultivation periods with a smaller amount of water inserted into the system. [ABSTRACT FROM AUTHOR]