Corn yield and fertilizer N recovery in water-tablecontrolled corn¯rye-grass systems

Concern about NO-3 leaching and groundwater pollution from corn monoculture has prompted an investigation of alternative production systems that reduce leaching. It is hypothesized that both intercropping and water-table control could increase N uptake and reduce the quantity of N that might be lost due to leaching. This study compared corn (Zea mays L.) with annual Italian rye-grass (Lolium multiflorum Lam) intercropping and corn monocrop systems under three controlled drainage levels [free drainage (water table 1 m below soil surface), and water-table depths maintained at 0.70 or 0.80 m, below the soil surface via subirrigation]. Annual Italian rye-grass was planted 10 days after the corn was planted. Grain yield, above-ground dry-matter production, N uptake and fertilizer N recovery (FNR) were assessed over 2 years on a fine, silty, mixed, non-acid, frigid Typic Humaquept sandy loam soil. Corn grain yields were unaffected by the annual rye-grass/weed component of the intercropping system or the various water-table depths in either year. Intercropping increased the total above-ground dry-matter production by 3.2 and 2.4 Mg ha-1 and N uptake by 71 and 49 kg ha-1 in 1993 and 1994, respectively. Fertilizer N recovery from corn was not different between the two cropping systems. Water table depth had no effect on grain yield and N uptake. Previous published results from the same site indicated decreased soil NNO-3 content in the top 1 m of the soil profile in the fall of 1993 and less denitrification due to intercropping, demonstrating that a corn¯annual rye-grass intercropping system, especially with rye-grass establishing well later in the season, may be an effective practice for increasing soil N uptake without reduction of corn grain yield when adequate N and moisture are present.