2.2.1. Biomass and seed yield
At each harvest, we randomly selected thirty plants of maize and soybean in each plot. The aboveground was cut and separated into leaves and stem. All plant samples were oven-dried at 105°C for 30 min and then 80°C for 72 h. In each plot, root samples were taken at three locations of each plot, i.e. top, middle and down sides of the plot with a root sampler (8 cm of diameter × 10 cm of depth) to sample roots up to 30 cm of soil depth at each location. The root samples were washed with tap water until free of soil, and were placed in a plexiglass tray with 4 mm of clean water in depth. Total root length, surface area and diameter were analyzed with the Win-RHIZO 2004 (Regent Instruments, Quebec, Canada) (Costa et al., 2002; Jin et al., 2012). After scanning, root samples were oven-dried to determine dry weight.
At the full maturity, two central rows of each plot were hand-harvested for yield estimation in 2016, 2017 and 2018. Grain yield was adjusted to 130 g kg-1 moisture content.