Growth and Nitrogen Uptake Curves in Papaya Grown under Protected Crop

The knowledge of the crop development and nutrient extraction curves, allows developing suitable nutrition programs for each crop, with the consequent reduction of costs and pollution that are caused by the excessive application of fertilizers. Some nutrients, like the nitrogen (N), besides being very important in plant metabolism, are very dynamic, so their excessive use may cause their accumulation in the soil or the substrate in forms that are not assimilated by the plants or the change of the pH in the media, affecting the uptake of other nutrients. The objectives of this work were: generate information about the development of the papaya crop (Carica papaya L.) and the N extraction, under protection in a low-tech greenhouse with a closed hydroponics system. A standard nutrient solution and the 'Red Maradol' variety were used. To record the variables, four plants in full competency were sampled monthly, and the leaves, roots, stems and fruits were separated for their analysis. The total dry matter (DM) and the N concentration were determined. A DM accumulation curve was developed for each part of the plant and for the whole plant. The results were analyzed using the Sigma Plot 10.0 program; obtaining sigmoid adjustment curves of three points in all the cases. The R-2 value for the model of total DM during the year of evaluation was 0.964. The R-2 values for the leaves, stems, roots and fruit were 0.88, 0.945, 0.918 and 0.9659 respectively. With the results on the N concentration, the total nutrient extraction was estimated by period; the accumulated extraction was adjusted to the same model of the DM and the R-2 obtained value was 0.988.