Effects of Italian Ryegrass (Lolium multiflorum) Cultivation for Green Manure and Forage on Subsequent Above- and Below-Ground Growth and Yield of Soybean (Glycine max)

To diversify upland cropping systems, Italian ryegrass (Lolium multiflorum; IRG) can be incorporated as forage or green manure to soybean (Glycine max L.). The current study was conducted to analyze the effect of IRG cultivar and usage methods on the subsequent soybean above- and below-ground growth, as well as the yield, under different conditions. Three cycles of crop rotation were implemented with the combination of IRG cultivar (early maturing “Kowinearly”; late maturing “Winterhawk”), IRG usage (green manure for which both above- and below-ground biomass was incorporated, +CC; and forage for which only below-ground biomass was incorporated, −CC), and fallow soil as control. The soybean yield of +CC was consistently high regardless of the IRG cultivar, and it demonstrated an increase even under unfavorable weather conditions, while −CC treated did not differ from control. Incorporated IRG could serve as a starter fertilizer (79 to 156 kg ha⁻¹ of N input). Soybean root characteristic differences showed substantial variability depending on the year and treatments. However, when compared to the control, no adverse effects of IRG were evident. Thus, using IRG as a green manure has the potential to enhance soybean yield, while using IRG as a forage could bring additional harvested matter to the rotational system.