Acúmulo e valor nutritivo da forragem e atividade microbiológica do solo em pastagens consorciadas de sorgo-sudanense e capim-ruziziensis sob fertilização nitrogenada e potássica em segunda safra no bioma Amazônia

Abstract

The Integrated Systems (SIPA) can improve forage production during the off-season, reducing the fluctuation of feed supply in quantity and quality for the animals, and with the possibility of producing straw to cover and protect the soil. these results can be maximized with the use of forage plants with high production associated with fertilization, mainly nitrogen and potassium, which stand out as the main limiting factors in forage production. Among the main designs of the SIPA, mixed pasture is considered an alternative to increasing forage production during the off-season in soybean areas. Thus, our objective was to evaluate the forage accumulation and nutritional value of the Sudanese sorghum intercrop [Sorghum bicolor(L.) Moench. × Sudanese S. (Piper) Stapf. cv. BRS 810 bmr] with ruziziensis grass (Urochloa ruziziensis (R. Germ. & C. M. Evrard) Crins cv. Kennedy) fertilized with doses of nitrogen and potassium during the off-season period and to verify the effect of fertilization on the enzymatic activity of the soil after the consortium. The experiment was carried out in a randomized complete block design, with a combination of three fertilization levels (0, 25, and 50 kg of N and K ha-1 ) and three harvest cycles. Fertilizations were performed with the commercial formula 20-00-20 (urea, ammonium sulfate, and potassium chloride). There was an interaction between fertilization × harvest cycle for forage accumulation (FA) of sorghum (p= .0174), ruziziensis (p= .0051), and rate effect on the mixed pasture (FA of forage sorghum + FA of Urochloa ruziziensis ) (p< .0001), in which, regardless of the level of fertilization, the AF of the mix was 20% higher than the control. The straw in the soil had a rate effect (p= .0283), with an amount of 25% higher in the rate of 50 kg of N and K ha-1 (3590 kg DM ha-1 ) compared to the other fertilizations. The highest CP contents of both plants were at the rate of 50 kg of N and K ha-1 in cycle 1. The highest content of CBM was recorded at the dose of 25 kg ha-1 , registering a value 9.9% higher than the other rates. The enzyme urease and arylsulfatase showed higher activity at the rate of 25 kg of N and K ha-1 . Fertilization with doses of 25 kg of N and K ha-1 is recommended in the off-season, as it increases the mixed pastures AF and the morphological characteristics (LAI and leaf proportion), as well as the greatest levels of CP and NDF for an off-season pasture, and showed the highest soil enzyme activities. The fertilization of 50 kg of N and K ha-1 contributes to improving the residues for the next row crop.