The objective of this work was to evaluate the effect of phytomass accumulation, soil cover, and nutrient cycling promoted by cultivation systems with annual and cover crops on the grain yield of soybean sown in succession in the Cerrado, in the state of Mato Grosso, Brazil. The experiment was carried out in a randomized complete block design with nine cultivation systems and four replicates, in two crop seasons. In 2014/2015, forage grasses and legumes were evaluated, besides fallow treatments. In 2015/2016, forage and legume intercropped or not with corn or sunflower and fallow were assessed; the soybean crop was evaluated following cover crops. Phytomass, soil cover, and nutrient cycling provided by cultivation systems, as well as soybean mass and yield, were determined. Urochloa ruziziensis alone or intercropped, compared with the fallow systems, promotes significant increases in phytomass production, soil cover and nutrient cycling, with an increase in the grain yield of soybean planted in succession. N and K are the most accumulated nutrients in the aerial part of the cover crops and are released in larger quantities in the soil in the two years of evaluation. Crotalaria spectabilis promotes an increase in soybean yield in the 2015/2016 crop season, compared with U. ruziziensis, due to the synchronism between N release and uptake under no-tillage system.

The objective of this work was to evaluate the effect of cover crops on weed suppression in no-tillage soybean production systems in Rondonopolis, Mato Grosso. The experiment was carried out in an experimental area and consisted of the evaluation of nine cover treatments and soil management in a randomized complete block design. The treatments were: NT fallow, CT fallow, Crotalaria spectabilis, Crotalaria breviflora, maize + Crotalaria spectabilis, Pennisetum glaucum, Urochloa ruziziensis, Cajanus cajan, sunflower + Urochloa ruziziensis, Stylosanthes, Vigna unguiculata, Urochloa brizantha, maize + Urochloa ruziziensis. The evaluations were carried out before the desiccation for soybean sowing in the crops (10/23/2014) and (09/21/2015), before the post-emergence of soybean (09/12/2014) and (12/11/2015) and in the second season (12/06/2015). The useful area was 5 x 5 m and all weeds were counted and identified, but only the four species with the largest population were collected. The weeds evaluated were: Digitaria horizontalis, Digitaria insularis, Porophyllum ruderale and Tridax procumbens. Fallow treatments presented higher weed populations in relation to the others, in all periods of evaluation. Digitaria horizontalis presented the highest phytomass production in most seasons. The production systems with Urochloa ruziziensis, Pennisetum glaucum, Crotalaria spectabilis and intercropped with maize + Urochloa ruziziensis, sunflower + Urochloa ruziziensis and maize + Crotalaria spectabilis were the best alternatives for integrated weed management, reducing the incidence and increasing control of the main species that were detected during the conduction of the experiment.

For mitigation of negative effects of human activities on the soil density, the use of cover crops in no-tillage system (NTS) has been strongly recommended. This study aims to evaluate the shoot and root development of Urochloa ruziziensis subjected to soil density levels in dystrophic Oxisol. The experiment was conducted in a greenhouse with a completely randomized design, with five treatments and four replications. The treatments consisted of U. ruziziensis submitted to five levels of soil density (1.0, 1.2, 1.4, 1.6 and 1.8 Mg m -3 ), twenty experimental units in total. The Urochloa ruziziensis showed reduced plant height, leaf area and number of leaves with increasing soil density, resulting in morphological and physiological changes from densities higher than 1.6 Mg m -3 . However, these results demonstrate the ability of this species to break the compacted ground and form biopores. The Oxisols value of 1.4 Mg m -3 is restrictive for the plant growth and development.