No-till, no-herbicide forage soybean (Glycine max (L.) Merrill) cropping system with an Italian ryegrass (Lolium multiflorum Lam.) living mulch

Abstract

We conducted a field experiment to identify appropriate agronomic practices for a no-herbicide cropping system for the production of forage soybean (Glycine max (L.) Merrill) in northern Japan. We sowed a winter habit Italian ryegrass (Lolium multiflorum Lam. ‘Ace’) in the early spring and then soybeans using a no-till planter after harvesting the first crop of Italian ryegrass in June. Italian ryegrass then served as a living mulch for the soybean crop. Soybeans were harvested in October along with the Italian ryegrass dead aboveground biomass. We tested this cultivation method using different Italian ryegrass seeding rates, and replicated the experiment in two consecutive years and in two fields with different levels of weed pressure. Italian ryegrass yield tended to increase with increasing seeding rate. Few weeds remained in the plots in which Italian ryegrass was sown at a rate of 50 kg ha−1 and greater, and there was no significant difference in soybean yield between those plots and plots in which herbicide was used. Soybean yield in the plots where Italian ryegrass was sown at 20 kg ha−1 was no different from that at higher sowing rates in the field with medium weed pressure, but was significantly lower in the field with high weed pressure. We conclude that cropping with an Italian ryegrass living mulch is an effective system for producing forage soybean without herbicide, but to ensure sufficient weed suppression for adequate production of soybean forage, sowing rates of Italian ryegrass should be at least 50 kg ha−1.