Inoculação com rizobactérias e adubação nitrogenada no crescimento, produção e acúmulo de nutrientes em grão-de-bico

Abstract

The biological activity of nitrogen-fixing and growth-promoting bacteria is important in legume crops, as they reduce the use of fertilizers and increase agricultural production. However, this information in the cultivation of chickpeas is considered scarce in tropical regions. In this context, the objective was to evaluate the effect of inoculation of Rhizobium tropici, Bacillus spp. and nitrogen fertilization in the growth, production and absorption of nutrients in chickpeas. For this, three studies were carried out, all with the same randomized block design, with four replications. The first experiment consisted of a 2 x 6 factorial scheme, consisting of the presence and absence of Rhizobium tropici inoculation and six doses of N: 0, 25, 50, 75, 100 and 125 kg ha-1, in the form of urea. The study was carried out in two areas with different levels of soil organic matter (MOS) and cultivation time. The second and third studies were conducted in a 2 x 6 factorial scheme, consisting of the absence or presence of Bacillus spp. (concentration of 1 x 107 CFU per mL) of root isolates, and six doses of N identical to those of the first study. The second study evaluated the characteristics of production and productivity of chickpeas and the third study characterized the dry matter biomass and the absorption of macronutrients in the flowering phase. The responses in nutrient production and accumulation differed between the factors studied. In the area with the lowest MOS content, in the first study, inoculation with Rhizobium tropici or the application of 125 kg ha-1 of N increased the production of chickpeas and the leaf contents of N, P, K and Mg, increasing productivity by 65% when compared to the control treatment. However, the greater natural availability of N from the soil with a higher MOS content supplied the plant's demand for maximum productivity, indicating only the inoculation response with Rhizobium tropici for some production components (mass of grains per plant, number of pods with a grain, dry leaf mass, total and chlorophyll index). In the second and third studies, seed inoculation with Bacillus spp. increased productivity, nodulation with rhizobia and favored K, Ca and Na absorption, contributing to the production of more than 4 t ha-1 of grains, especially in the area with lower MOS content (longer cultivation time). In the second study, the application of 25 kg ha-1 proved to be sufficient to obtain greater productivity in the chickpeas, with no response in the area with the highest MOS. The decreasing order of nutrient accumulation in the aerial part of the chickpeas was as follows: nitrogen (109.71 kg ha-1)> potassium (68.94 kg ha-1)> calcium (25.28 kg ha-1) > magnesium (10.17 kg ha-1)> phosphorus (4.98 kg ha-1)> sodium (2.23 kg ha-1). The addition of Bacillus spp. as a management practice in chickpea crops it is recommended because it increases nodulation, dry biomass and nutrient absorption. The recommendation of nitrogen fertilization in chickpeas is dependent on the natural condition of MOS in soils and cultivation time.