Abstract
Insufficient and unbalanced biomass supply inhibited soybean [Glycine max (L.) Merr.] yield formation in the maize-soybean relay strip intercropping (IS) and monoculture soybean (SS). A field experiment was conducted to explore the soybean yield increase mechanism of DA-6 in IS and SS treatments. In this 2-year experiment, compact maize “Denghai 605” and shade-tolerant soybean “Nandou 25” were selected as cultivated materials. DA-6 with four concentrations, i.e., 0 mg/L (CK), 40 mg/L (D40), 60 mg/L (D60), and 80 mg/L (D80), were sprayed on soybean leaves at the beginning of flowering stage of soybean. Results showed that DA-6 treatments significantly (p < 0.05) increased soybean grain yield, and the yield increase ratio was higher in IS than SS. The leaf area index values and net photosynthesis rate of IS peaked at D60 and were increased by 32.2–49.3% and 24.1–27.2% compared with the corresponding CK. Similarly, DA-6 treatments increased the aboveground dry matter and the amount of soybean dry matter accumulation from the R1 stage to the R8 stage (VDMT) and highest at D60 both in IS and SS. D60 increased the VDMT by 29.0–47.1% in IS and 20.7–29.2% in SS. The TRG at D60 ranged 72.4–77.6% in IS and 61.4–62.5% in SS. The MDA content at D60 treatment was decreased by 38.3% in IS and 25.8% in SS. The active grain-filling day in IS was about 7 days longer than in SS. In D60 treatment, the Vmean and Vmax increased by 6.5% and 6.5% in IS and 5.7% and 4.3% in SS compared with the corresponding CK. Although the pod number and hundred-grain weight were significantly (p < 0.05) increased by DA-6 treatments, the grains per pod were maintained stable. The pod number and hundred-grain weight were increased by 30.1–36.8% and 4.5–6.7% in IS and 6.3–13% and 3.6–5.6% in SS. Thus, the grain yield at D60 was increased by 36.7–38.4% in IS and 21.7–26.6% in SS. DA-6 treatments significantly (p < 0.05) increased soybean grain yield and peaked D60 treatments both in IS and SS.
Highlights
The leaf area index (LAI) continuously increased from the the beginning flower stage (R1) to beginning seed stage (R5) stages, LAI was higher in monoculture soybean (SS) than in maize-soybean relay strip intercropping system (IS) (Figure 2)
In 60 mg L−1 of DA-6 (D60) treatment, the LAI was increased by 32.2–49.3% in IS and 23.6–25.2% in SS compared with the corresponding 0 mg L−1 of DA-6 (CK)
In D60 treatment, the Pn was increased by 24.1–27.2% in IS and 17.1–19.8% in SS compared with the corresponding CK
Summary
Intercropping systems, two or more crops planted on the same farmland, have many advantages such as better exploitation of sunlight, water, nutrients, and other environmental resources and higher land equivalent ratio (Li B. et al, 2020). The IS increases the compensation effect of gramineous and leguminous intercropping (Li S. et al, 2020), improves resource utilization in the spatiotemporal niche (Ahmed et al, 2020), increases farmland productivity with less environmental costs, and provides a potential approach to achieving sustainable agriculture development (Darch et al, 2018). This system produced additional soybean yields when maintaining the stability of maize yield production (Chen et al, 2019). The higher maize shading during the co-growth period inhibited the vegetative growth and yield formation of relay intercropped soybean (Raza et al, 2019b)
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