The objective of this work was to evaluate the effect of roots and straw of palisade grass (Urochloa brizantha) and Ruzi grass (U. ruziziensis), used as cover crops in autumn-winter, on soybean performance. Seven treatments were evaluated in a randomized complete block design, with four replicates: fallow, during autumn-winter; straw of U. ruziziensis or U. brizantha 'BRS Piatã', distributed in plots kept under fallow in the winter, without roots; plots only with roots of U. ruziziensis or U. brizantha, without straw; and plots with straw and roots of U. ruziziensis or U. brizantha. The grass species were planted during the 2014/2015 crop season, and treatments were evaluated at the end of the 2015/2016 crop season, without drought during the soybean cycle. The oil and protein contents of soybean grains were not affected significantly by the treatments. However, the cultivation of grass species during autumn-winter increased soybean grain yield in comparison with fallow. Grass root effects are more expressive than those of straw. The combined presence of roots and straw confers a better performance to soybean than the isolated presence of roots or straw.

Soybean seeding rate (SR) is commonly subject to genotype x environment interactions, and characterization of this interaction is necessary to improve yield potential of future cultivars, especially in late sowing. The objectives of this study were to evaluate yield and yield components of three soybean cultivars in different SR under late sowing in Southern Brazil. We observed an interaction between SR and cultivars under late sowing, in which the increase from 25 to 45 seeds m-2 increased yield by 12% and 23% for cultivars BMX Energia and TMG 7262, respectively, while for cultivar AFS 110 there was no SR effect. The cultivars used in this study can be classified from more to less responsive to SR in late sowing as follows: TMG 7262 > BMX Energia > AFS 110. Also, the cultivars used in this study can be classified from higher to lower yield potential in late sowing as follows: TMG 7262 > AFS 110 > BMX Energia. The yield components most correlated to yield were as follows: seeds per area, plant height, 100-seed weight and nodes in main stem, mainly. The increase in SR increased seeds per area and pods per area, while decreased seeds per pod, stem diameter and node number in branches. The identified plant attributes related to yield increase will contribute for developing future cultivars with greater yield potential under late sowing.