Nitrogenous Fertilization, Tropical Fodders, Model Curves.
Objective: To determine and compare the parameters of the nitrogen curve and the nutritive nitrogen index of cultivars of Cenchrus purpureus with and without nitrogenous fertilization.
Design/Methodology/Approach: Five cultivars of C. purpureus with or without fertilization were evaluated, and the dose was 141N-43P-20K. The grass was harvested every 21 d with production of dry matter (DM) and nitrogen (N). Growth rates and Critical Nitrogen (Nc) were obtained. The negative power equation with its parameters Nc and the Nitrogen Decrease Coefficient (Cd) were used. The Nutritive Nitrogen Index (NNI) was obtained with the Nc parameter of each curve, divided by the N content of the cultivar in each sampling. The data were analyzed with a completely randomized design in a factorial arrangement of five (cultivars) and two levels of fertilization.
Results: Nc of 2.6 and a Cd of 0.65 fertilized, and 1.14 of Nc and 0.68 of Cd without fertilization, and in turn all of them supplemented the amount of N for their growth from soil. The NNI was 0.8 for the fertilized cultivars, with classification of excess and sufficient for the first 56 d.
Study Limitations/Implications: Variables to determine the availability of water and the balance of soil-plant N could further expand the knowledge of these tools.
Findings/Conclusions: Parameters obtained such as Nc and NNI help to determine nutritional status of the fodders.