Responses of Brachiaria brizantha cv. Marandu and soil properties to potassium and nitrogen fertilization in latosol in the Amazon region

The state of Rondônia is located in the Amazon region and contains approximately 8.1 million ha of pastures, most of which are in advanced stages of degradation. There are few regional studies with evaluating potassium and nitrogen fertilization in pastures. The study aimed to evaluate the productivity of Brachiaria brizantha cv. Marandu in response to potassium and nitrogen additions in the soil, as well as to assess the effects on some soil chemical attributes. The experimental design was in randomized blocks in a 5x5 factorial scheme with four replications. Factor 1 consisted of potassium doses (0, 100, 200, 400, and 800 kg ha-1 of K2O), and factor 2 consisted of annual nitrogen doses (0, 50, 100, 200, and 400 kg ha-1 of N), both applied on the surface. Five dry mass samples were collected in 2010, 2011, 2012, 2013, and 2017, and two soil samples were taken in 2012 and 2017 in the 0-0.10 and 0.10-0.20 m depth layers to verify the effect of treatments on soil chemical attributes. B. brizantha cv. Marandu did not show any interaction between potassium and nitrogen doses. Potassium had a three-year residual effect on dry mass production and exchangeable K content in the soil, even at the highest K2O doses. Nitrogen fertilization provided a linear and positive increase in dry mass production of B. brizantha in all years evaluated. The annual addition of the highest N doses decreased pH, Ca2+, and Mg2+ contents and increased Al3+ content in the soil.