Winter-annual cover crops reduce soil erosion by providing ground cover, while producing energy-cheap N for a subsequent crop. Incorporated cover crops or those left as no-till mulch can enhance soil structure and water infiltration. A series of studies was designed to test agronomic advantages of growing mixtures of rye plus hairy vetch and hairy plus bigflower vetches. Plots were arranged in randomized complete blocks and the study conducted for two consecutive cover crop/corn sequences. I measured N yield of cover crops, their ground-covering ability, and their influence on soil structure and a subsequent corn crop.

Nitrogen yields ranged from 53 to 187 kg/ha using either pure stands of hairy vetch or mixtures of hairy vetch plus bigflower vetch. Nitrogen yields for rye plus hairy vetch mixtures ranged from 90 to 179 kg/ha. Rye growing in association with vetch had lower C:N ratios (47:1) than pure rye (59:1), apparently deriving additional N from vetch. Vetches were poor at covering the ground in the fall (< 15% cover) as compared to rye (> 41% cover) or mixtures of rye and vetch (25 to 45% cover).

When compared to vetch pure stands, corn yields were suppressed 5 to 42% by including rye with vetch due to N immobilization from the rye component and reduced N yield from the vetch component. Corn yields from hairy vetch or hairy: bigflower vetch mixtures were 15.5 Mg/ha and 16.2 Mg/ha respectively and statistically similar to rye + 140 kg N/ha (16.7 Mg/ha). Corn following the two-vetch mixture took up 129 kg N/ha, while corn following hairy vetch took up 114 kg N/ha. Using N fertilizer, corn N uptake was 183 kg N/ha following 140 kg N/ha fertilizer and 213 kg/ha following 210 kg/ha N fertilizer. Increased soil moisture seemed to be related to the presence of a surface mulch.

I was unable to detect any changes in water-stable soil aggregates in the upper 15 cm after 2 years of cover cropping. During 1988, water infiltration in no-till plots was lower than in plots that had been disk incorporated, but a tillage effect was not seen in 1989.