Growth and development of soybean under changing light environments in relay intercropping system

Maize-soybean relay-intercropping (MS_R) is a famous system of crop production in developing countries. However, maize shading under this system directly affects the light quality and intensity of soybean canopy. This is a challenging scenario in which to implement the MS_R system, in terms of varieties selection, planting pattern, and crop management since the duration of crop resource utilization clearly differs.

Therefore, this experiment aimed to elucidate the effect of leaf excising treatments from maize top to fully clarify the needs and balance of light quality and intensity of intercrop-soybean under MS_R in field conditions. The effects of different leaf excising treatments (T0, no removal of leaves; T2, removal of two topmost leaves; T4, removal of four topmost leaves; T6, removal of six topmost leaves from maize plants were applied at first-trifoliate stage (V₁) of soybean) on photosynthetically active radiation transmittance (PAR_T), red to far-red ratio (R:FR), morphological and photosynthetic characteristics and total biomass production at second-trifoliate stage (V₂), fifth-trifoliate stage (V₅), and flowering-stage (R₁) of soybean were investigated through field experiments for 2-years under MS_R.

As compared to T0, treatment T6 increased the PAR_T and R:FR ratio at soybean canopy by 77% and 37% (V₂), 70% and 34% (V₅), and 41% and 36% (R₁), respectively. This improved light environment in T6 considerably enhanced the leaf area index, SPAD values and photosynthetic rate of soybean plants by 66%, 25% and 49% at R₁, respectively than T0. Similarly, relative to control, T6 also increased the stem diameter (by 29%) but decreased the plant height (by 23%) which in turn significantly increased stem breaking strength (by 87%) by reducing the lodging rate (by 59%) of soybean plants. Overall, under T6, relay-cropped soybean produced 78% of sole soybean seed-yield, and relay-cropped maize produced 81% of sole maize seed-yield. Our findings implied that by maintaining the optimum level of PAR_T (from 60% to 80%) and R:FR ratio (0.9 to 1.1), we can improve morphological and photosynthetic characteristics of soybean plants in MS_R. Therefore, more attention should be paid to the light environment when considering the sustainability of MS_R via appropriate planting pattern selection.