Enhancing nitrogen use efficiency in urochloa brizantha cv. marandu: physiological and molecular responses to foliar inoculation of plant growth-promoting bacteria alongside different 15N doses for sustainable nitrogen fertilization management

Abstract

In Brazil, the basis of livestock feed is pastures. The sustainability of the system involves the production of greater quantity and quality of forage, with reduced inputs, providing less impact. The objective of the work will be to evaluate the ability of Azospirillum brasilense, Bacillus S26 and Bacillus N72 strains applied via foliar, associated with doses of N, to promote the growth of Urochloa brizantha cv. Marandu, evaluating the use of applied urea, through the isotopic technique, and influence on nutrition, physiological and molecular parameters, development and production of dry mass of the aerial part and roots. The experimental design will be four randomized blocks with four replications, there will be 11 treatments, totaling 44 experimental units. The treatments were: 1) control - without nitrogen fertilization, 2) fertilized with 40 kg ha-1 of urea and without inoculation, 3) fertilized with 80 kg ha-1 of urea and without inoculation, 4) fertilized with 40 kg ha-1 of urea plus foliar inoculation of A. brasilense, 5) fertilized with 40 kg ha-1 of urea plus foliar inoculation of Bacillus S26, 6) fertilized with 40 kg ha-1 of urea plus foliar inoculation of Bacillus N72, 7) fertilized with 40 kg ha-1 of urea plus foliar inoculation of A. brasilense + Bacillus S26 + Bacillus N72, 8) foliar inoculation of A. brasilense + Bacillus S26 + Bacillus N72, without nitrogen fertilization, 9) foliar inoculation of A. brasilense, without nitrogen fertilization, 10) foliar inoculation of Bacillus S26, without nitrogen fertilization, 11) foliar inoculation of Bacillus N72, without nitrogen fertilization. The variables to be analyzed will be plant height, number of tillers, relative chlorophyll index, leaf/stalk ratio, root dry mass, macronutrients (N, P, K, Ca, Mg and S) and micronutrients (Zn, B, Fe, Mn and Cu). The use efficiency (NUE) and recovery of N applied via fertilizer in palisade grass will be determined using the isotopic dilution technique with 15N. The data will be tested for normality of errors and variance. Significant results will be subjected to a mean comparison test using the Scott-Knott test and correlations. After identifying the most important comparisons, differential proteomic analysis will be carried out, the objective of which will be to identify the metabolic processes responsible for the plants' best response. The work should allow us to observe that the efficiency of forage production with high nutritional quality and good rational management of pastures is fundamental to guarantee animal production, as well as pasture persistence. (AU)