Features Agronomy Corn Seeding/Planting
Intercropping can improve irrigated corn silage

In an effort to capture the ears of silage corn growers in Saskatchewan, the Irrigation Crop Diversification Corporation (ICDC) in Outlook conducted a demonstration project to see if intercropping corn and faba bean under irrigation or dryland conditions could produce high energy, protein and yield compared to mono-crop corn. 

“It was hoped that yields of the intercrop will be similar to those of corn as a monocrop, but the result will be a more balanced forage with appropriate levels of energy and protein,” says Garry Hnatowich, research director with ICDC. “Faba bean is a long season crop and is expected to mature at a similar date as corn facilitating harvest when both crops are at an ideal stage for silaging.”

The corn-faba bean intercrop demonstration was established on June 2, 2020, at the ICDC location in Outlook for the irrigated site, and on May 22, 2020, at Wheatland Conservation Area in Swift Current as the dryland site. The trials were replicated four times at Outlook and three times at Swift Current. 

At Outlook, the corn monocrop was direct seeded into wheat stubble with 30-inch (76.2-cm) row spacing. The faba bean monocrop and corn-faba bean intercrop were also direct seeded into wheat stubble on 10-inch (25.4-cm) row spacing. For the intercrop, the corn was seeded on 30-inch rows, with the faba bean seeded on 10-inch row spacing between the corn rows. This resulted in a seeding pattern of one row of corn – two rows of faba beans – one row of corn.  

At Swift Current, the trials were also direct-seeded into wheat stubble. The corn monocrop was seeded on 25-inch (63.5-cm) row spacing, while the faba bean monocrop and corn-faba bean intercrop were seeded on 8.25-inch (21-cm) row spacing. 

Irrigated corn was seeded at a target plant population of 32,000 plants/acre (79,000 plants/ha) or 28,000 plants/ac dryland. Faba bean was seeded to obtain 4.5 plants per square foot (45 plants/m2). 

Nitrogen (N) fertilizer treatment rates accounted for soil available N from zero to 24 inches (zero to 60 cm) in Outlook, with residual measured at 16 pounds per acre (18 kg/ha). At Swift Current, soil test N was from zero to 12 inches (zero to 30 cm) measuring 42 lbs./ac (47 kg/ha). All N fertilizer applications were applied as side-banded urea (46-0-0) in corn rows only. 

In the monocrop treatments, corn received 142 lbs. N/ac (160 kg/ha), with 0 N applied to faba bean. The corn-faba bean intercrop treatments included a 0 N control, and 36, 71, 107, and 142 lbs. N/ac (40, 80, 120 and 160 kg N/ac).

At seeding, all plots also received 44.5 lbs. P2O5/ac (50 kg P2O5/ha) as seed placed monoammonium phosphate (MAP; 11-52-0). At both sites, faba bean was inoculated with a faba bean inoculant.

At Outlook, there were 2,156 cumulative Corn Heat Units (CHUs) from May to August. Hail and extremely high winds caused damage to corn plants on Aug. 27, 2020 and a killing frost terminated the trial on Sept. 8, 2020. Total in-season precipitation and irrigation was 11 inches (279 mm). Swift Current received 2,081 CHUs from May to August and total in-season precipitation of 6.1 inches (154.9 mm).

Irrigated intercrop was superior
At Outlook, irrigated dry matter yields were highest in the corn-faba bean intercrop 160N treatment. This intercrop treatment had a dry matter yield of eight tonnes per acre (19.74 T/ha), while the corn monocrop 160N treatment yielded 6.9 tonnes per acre (16.95 T/ha), which was 14 per cent less. There were no significant yield differences between the corn monocrop and the 0N, 40N, 80N, or 120N intercrop treatments. Faba bean monocrop was significantly lower than all treatments at 3.24 tonnes per acre (8.01 T/ha).

“Corn plants were shorter when less than 160 kg N/ha was applied. This suggests that corn yield was reduced in most intercropped treatments but the faba bean contributed enough yield that there were no significant yield differences between the corn monocrop and the 0N, 40N, 80N, or 120N ontercrop treatments,” Hnatowich says.

The 120N and 160N intercrop treatments had a higher protein content than the corn monocrop, but they had less TDN, so overall forage quality was not superior. Otherwise, there were no major differences in forage quality between treatments. 

A basic economic analysis was conducted to provide a relative overview each treatment at the irrigated Outlook site. Wet yield, estimated silage price, gross revenue, and net revenue were calculated. The 120N intercrop treatment had a net revenue of $636.52 per acre ($258/ha) and the 160N intercrop netted $652.12 per acre ($264/ha). These were more profitable than the 160N monocrop corn treatment at $571.49 ($231/ha).

Dryland intercrop didn’t provide an advantage
Under dryland production, although monocrop corn yielded 3.27 tonnes per acre (8.07 T/ha) dry matter, 160N intercrop yielded 2 tonnes per acre (5.03 T/ha) and faba bean monocrop yielded 1.15 tonnes per acre (2.83 T/ha), yield differences between any treatments were not statistically significant. Hnatowich says this can be attributed to extensive variability within treatments.

Some components of forage quality including crude protein and macrominerals were higher in the faba bean monocrop, but generally, treatment differences were small and variable. 

Based on the demonstration, a faba bean corn intercrop under irrigation has good potential when fertilized with higher rates of nitrogen, but the benefit of an intercrop may not be there for dryland silage corn growers.