Atributos do solo e produção de forragem em sistema agrossilvipastoril adubado no ecótono Amazônia - Cerrado

Abstract

Adequate levels of nitrogen supplementation can provide mutual gains between the components of agrosilvopastoral systems. The objective of this study was to evaluate soil attributes and chemical composition of Megathyrsus maximus Jack cv. Massai intercropped with maize (Zea mays L.) between double rows of sabiá (Mimosa caesalpiniaefolia Benth), spaced 30 × 3 × 2 m, and babassu (Atallea speciosa Mart.). The experiment was laid in a randomized complete block design with four treatments and three replications. Each block of 1 ha was subdivided into four paddocks of 0.25 ha, with an average of 35 babassu palm trees/ha and 276 sabiá trees/ha. The treatments were 0, 100, 200 and 400 kg ha-1 year-1 of nitrogen (N), the fertilizations were with urea. Beef steers were used, with initial average body weight (BW) of 200 ± 35 kg, according to the put-and-take technique, with two tester animals per paddock, and adjustment animals according to forage availability [2 kg dry matter (MVS) kg BW-1]. Two soil collections were carried out (Aug/2020 and July/2021). The evaluation of soil attributes was carried out at five distances (0; 3.5; 7.0; 10.5 and 14 m) perpendicular to the double rows of thrush. Mini trenches (30 x 30 x 30 cm) were opened to collect undisturbed samples at depths of 0 – 10, 10 – 20, 20 – 30 cm, and density, macroporosity, microporosity and total porosity were analyzed. Deformed samples at the same depths perpendicular to the mini-trenches were collected for soil chemical analysis (P, K+ , Mg+2 and Ca+2). The masai was evaluated from Jun/2021 to Feb/2022 every 28 days, and the total forage mass (MFT), percentage of green (%FV) and senescent (%FS), forage height and density (DF), green forage crude protein (PBFV) and senescent (PBFS), green forage mineral matter (MMFV) and senescent (MMFS); neutral detergent fiber from green (FDNFV) and senescent (FDNFS) forage; green (FDAFV) and senescent (FDAFS) forage acid detergent fiber, green (LIGFV) and senescent (LIGFS) forage (LIGFS) lignin. The SAS Proc Mixed program was used, and the means of each treatment were compared using Tukey's test, at a 5% probability level. The distance from the tree component did not significantly influence (P < 0.05) the physical attributes of the soil, however, there was a difference (P < 0.05) for microporosity, treatments 0 and 100 Kg N ha-1 year- 1 showed values 11.2% higher than the other treatments. For soil chemical attributes, there was no difference (P > 0.05) between treatments, only between depths. P, Ca2+ and K+ nutrients were 31%, 8.82% and 23.53% higher in the superficial layer (0-10 cm) compared to the other layers. The year 2020 showed lower concentrations of P, Mg2+ and K+ in the interaction of fertilization and distances. Forage mass was not influenced by fertilization levels (variation from 2128 Kg N ha-1 yr-1 to 2203 Kg N ha-1 yr-1. Lower percentage of green forage (51.50%) and higher percentage of senescent (48.89%) was observed in the treatment without fertilization. The percentages of MM, PB, NDF and LIG were not influenced by fertilization. January 2022 showed a higher value of MM (17.54% more), LIG was also higher in this month (31.07% more, together with the months of August and October 2022. The lowest value of PB was in July 2021 (24.43% lower). FDN was higher in August 2021 and February 2022 (15 % and 12.15% higher respectively. The agrosivilpastoral systems under nitrogen fertilization, improves the physical and chemical conditions of the soil, providing the formation of macroaggregates. The chemical attributes present relevant results, but it requires more time to be observed. Nitrogen fertilization influenced positively in the production of MSV in agrosivilpastoral systems, as well as in te forage crude protein, being the treatments with higher applications of protein, presented higher concentrations in the forage