Intercropping Irrigated Corn and Soybeans for Silage.

Irrigated corn and soybean intercropping research was conducted at the Irrigated Research and Extension Center near Prosser, WA and was designed to fit into a triticale and corn rotation. On June 13, 2012 and June 20, 2013 soybeans were planted perpendicular to corn rows on June 15th, 2012 and July 1, 2013. Roundup Ready® soybean varieties Asgrow 1431 (Maturity Group 1) and Eagle Seeds Game Keeper (Maturity Group 7) were planted in 6” rows at four planting densities 0, 93,825, 187,650, 375,300 plants ha-1 both intercropped with corn and planted in monoculture. Mycogen x12301S3 corn seed was planted in 30” rows at 93,825 plants ha-1 both years. Monoculture and intercropped corn was fertilized according to soil test as if it was grown in monoculture. Silage was harvested October 8, 2012 and October 22, 2013. Land equivalent ratios (LER) was generally positive both years with Game Keeper and in 2013 with Asgrow 1431, whereas it decreased in 2012 with Asgrow 1431. Averaged over soybean varieties and years, silage yields were 22.86, 22.58, 23.19, 23.45 Mg ha-1 when intercropped with soybeans at a planting density of 0, 0, 93,825, 187,650, 375,300 plants ha-1, respectively. In 2012, as soybean intercrop planting density increased from 0 to 375,300 plants ha-1 soybean dry matter increased from 0 to 3.8% and 0 to 7.0% of intercrop production for 1431 and Game Keeper, respectively; whereas in 2013, soybean dry matter comprised 0 to 9.4% and 0 to 12.9% for 1431 and Game Keeper, respectively. In 2013, averaged over soybean intercrop density corn grain production was higher with 1431 at 9.3 Mg ha-1 compared with Game Keeper 7.6 Mg ha-1. In 2013 averaged over soybean varieties, grain yield was 8.41, 9.25, 8.42 and 7.67 Mg ha-1 for soybean intercrop planting densities of 0, 93,750, 187,500 and 375,000 plants ha-1, respectively. Averaged over intercrop soybean density, intercropped corn grain protein was higher with Game Keeper at 7.82% compared with 1431 at 7.46%. In 2012 and 2013, compared to the control, intercropping Game Keeper at what appears to be the optimum soybean planting density of 187,500 plants ha-1 increased LER to 1.10 and 1.16; increased soybean fraction of dry matter produced from 0 to 5.2% and from 0 to 10.4%; increased total dry matter production from 24.14 to 25.86 Mg ha-1 and 20.45 to 22.14 Mg ha-1 in 2012 and 2013, respectively. In 2013, compared to the control, intercropping Game Keeper soybean planting density of 187,500 plants ha-1 grain dry matter remained virtually unchanged from 7.72 to 7.63 Mg ha-1, however, it increased grain protein from 7.47 to 7.95%.