Fertilidade do solo, características produtivas e valor nutritivo de Urochloa decumbens (Stapf) R.D. Webster e Mimosa caesalpiniifolia Benth em monocultivo e sistema silvipastoril

Abstract

Silvopastoral systems play an important role in livestock production. The use of forage legumes in areas of pastures has the potential to increase the efficiency in the use of resources, contribute to a better nutritional value of the forage and increase production, in addition, it improves the environmental and biological conditions of the soil. The present study aimed to evaluate the height, forage mass, forage density and leaf: stem ratio, the nutritional value of signal grass [Urochloa decumbens (Stapf) R.D. Webster] and sabiá (Mimosa caesalpiniifolia Benth.); botanical composition of the pasture, the proportion of uncovered soil, soil fertility and the presence of secondary components in the legume, in different evaluation systems, periods and years of evaluation. The research was carried out at the Experimental Farm of the Universidade Federal Rural de Pernambuco (UFRPE), located in the municipality of Garanhuns-PE (8°58'52''S 36°27'47''W). The experimental treatments were a silvopastoral system (SSP) of signal grass with sabiá, in addition to monocropping systems of each species, using a randomized block design, with three replications. The experiment was carried out for two years (2019 to 2021), at different seasons (dry and rainy). The legume was grown in three double rows in the signal grass pastures, spaced 2m between double rows, 1m between plants and 25 m between each set of double rows, totaling 600 plants.ha-1. In the monocropping systems cultivation, the same spacing between rows and plants was used, however, single rows were used, totaling 5,000 plants.ha-1. The cropping systems did not affect the height and forage mass of the grass, the variables were affected by the season and year of evaluation, as well as the interaction of these factors. Canopy height, stem forage mass (SFM), green forage mass (GFM), senescent material (SM) and total forage mass (TFM) of signal grass varied between seasons and years. The height of the signal grass was higher in the rainy season in both years (49.7 cm and 50.4 cm). The greater SFM was obtained in the rainy season of the first year of evaluation (1431 kg DM.ha-1). GFM was greater in the rainy season in both years of evaluation, on the other hand, SM was greater in the first year in the rainy season and the dry season of the second year 4702 and 5101 kg DM.ha-1, respectively, with TFM having similar behavior. The forage density was superior in the rainy season of 2019. The legume tree developed more under monocropping cultivation (3.61 m), also having a greater forage mass in this system (854 kg DM.ha-1), on the other hand, this forage mass varied according to year and season. The botanical composition of the pasture was not affected by the cultivation system, predominating the signal grass in all seasons and years of evaluation. Soil fertility levels were not influenced by the cropping system, being changed over the years. The greatest leaf: stem ratio was obtained in the first year of evaluation, reaching a ratio of 1.13. An interaction effect of the year and season was observed for the crude protein (CP) content of the grass, especially in the rainy season of 2019 (71.76 g.kg-1) and the dry season of 2020 (73.87 g.kg-1). No variation was observed in the crude protein content of the forage concerning cropping systems (P>0.05). An isolated effect of the evaluation period was observed for the contents of dry matter, ethereal extract (EE) and cellulose of the grass, with the greatest levels observed throughout the dry season 393.78 g.kg-1, 20.72 g kg-1 and 20.72 g.kg-1, respectively. An interaction effect of the year and season was observed for the contents of the mineral and organic matter fractions of the grass, not differing between years in the rainy season. The mineral fraction varied from 62.24 g.kg-1 to 66.64 g.kg-1, while the organic matter was the greater in the dry season of 2019 (951.58 g.kg-1). An interaction effect between the year and season was observed for the average levels of total carbohydrates, with greater levels in the rainy season of 2020 (871.70 g.kg-1) and in the dry season in the year 2019 (868.20 g.kg -1). No significant effect was observed for the contents of dry matter, organic matter, mineral matter and hemicellulose of the legume evaluated. The crude protein content of the legume differed between the interaction of years and seasons, ranging from 162.30 g.kg-1 in the rainy season of 2019 to 88.44 g.kg-1 in the dry season of the same year. In 2020, the results obtained ranged from 149.21 g.kg-1 to 140.24 g.kg-1, not differing between seasons. The NDF was not influenced by cropping systems, the interaction between year x season being significant, with greater NDF contents in the rainy season of 2019 (605.48 g.kg-1) compared to the year 2020 and the dry season of 2019. The dry season of 2020 was superior to the previous year and the rainy season, with an NDF of 536.12 g.kg-1. The ADF content differed in the interaction between year and season, with a lower content found in the dry season of 2019. A high concentration of condensed tannins was observed in the legume during the dry season compared to the rainy season. The nutritive value of the grass and the legume under evaluation was not affected when these species are used in the consortium, on the other hand, it varies over the years and evaluation periods, as well as the condensed tannins of the legume.