Companion crops compete with underseeded alfalfa, which can affect the stand that can be established. Our objective was to determine if delayed take-out of the companion crop reduces the forage yield and stand establishment of alfalfa.

Paul oats was seeded at about 1,000,000 seeds/acre and DKA34-17RR Roundup Ready alfalfa was seeded immediately after the oats at an angle to the oat seeding on April 18, 2006. The soil test indicated adequate P and K, and 50 lb N/acre as urea was applied to insure adequate N. Plot size was 6 by 25 feet. Six treatments as listed in Table 1 were established at the appropriate time. A RCBD was used with four replicates. Stand was determined on May 22 by counting one 6-inch row 40 inches in length in each plot. Forage yield of the alfalfa in the first harvest (first three treatments) was taken when 30 to 50% bloom occurred due to the droughty conditions and short growth. Oat was harvested at the boot, heading, and soft dough stage in the last three treatments. Alfalfa was harvest on September 13 for the first four treatments.

The stage that the companion crop was taken-out by Roundup did not affect the forage yield (Table 1). Apparently the availability of soil water was the determining factor for yield level and not the date of companion crop removal. Delaying oat harvest to soft dough increase the oat forage yield, but the alfalfa stand was very poor in the heading and soft dough treatments so no harvest was obtained. Harvesting the oat companion crop at the boot growth stage allow some alfalfa regrowth, but the forage yield was significantly less than treatments sprayed with Roundup. Oat contributed little to the forage yield of Roundup treatments.

The first year’s data suggest that oat competition must be removed before the boot stage in a dry year or alfalfa establishment may fail. This may explain why producers are reluctant to re-establish stands in the drought-prone areas of North Dakota where companion crop establishment is common.

Forage yield in 2007 was significantly lower from plots harvested at soft dough growth stage in 2006 (Table 2) than other treatments. The stand was thinner, indicating the competition effects of the comparison crop. However, the yield at the soft dough stage was better than anticipated in 2006. Forage yields in 2008 were not significantly different among treatments (Table 2).

These data suggest that the crown development of the plants in the soft dough treatment offset the higher number of plants in other treatments. The data also indicates that the window for weed control with Roundup is relatively wide since the oat competition up to 15 inches in growth had no effect on seeding and subsequent alfalfa forage yields. Finally, using an oat companion crop to establish Roundup Ready alfalfa on erosion-prone soils would appear to be an excellent establishment method.