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.