Experiment 1

The germplasm evaluation experiment was performed from 2013 to 2014 after two years of acclimation. The field experimental design consisted of a two-factor randomized block design with three replicates. The two factors—nine soybean varieties and planting patterns (sole cropping and maize-soybean intercropping)—were analyzed for various agronomic characteristics based on our previous method with some modifications⁴². All tested soybean germplasms were intercropped with maize (Zea. mays L. cv. Chuandan No. 418), and the maize planting patterns that were used are shown in Fig. 4A. In the intercropping treatments, the ratio of maize to soybean rows was 2:2, and a single strip of each row had the same width (200 cm). Soybeans were planted in wide rows before the reproductive stage of maize with a row spacing of 40 cm and plant spacing of 10 cm. The maize-soybean intercropping pattern was 160 + 40 cm wide-narrow row spacing. The PAR transmittance of the soybean canopy was 47.5%, which was measured using LI-191SA quantum sensors (LI-COR Inc., Lincoln, NE, USA). In the sole cropping system, all soybean germplasms were planted in solid rows with 50 cm row spacing and 20 cm plant spacing (Fig. 4B). The PAR transmittance of the soybean canopy was 100%⁴³. Each plot measured 6 × 7 m. Maize was sown on 26 March and harvested on 5 August. Soybean was sown on 13 June, when the maize plants were at the V12 stage, and had a 53-day coexistence period. Ten plants were randomly selected for each genotype in each replication, and those plants were averaged to provide one number per replication.

Planting patterns of relay strip intercropping (A) and sole cropping (B). The yellow triangles and green circles represent maize and soybean, respectively.