MANAGEMENT PRACTICES TO CONSERVE SOIL NITRATE IN MAIZE PRODUCTION SYSTEMS

Residual soil N following maize (Zea mays L.) harvest is susceptible t o leaching over winter. There is no available information regarding th e combination of intercropping system and water table control to conse rve soil N in maize production systems. A 2-yr study was conducted to examine the effects of cropping systems (monocrop maize, and maize int ercropped with annual Italian ryegrass [Lolium multiflorum Lam.]) and water table controls (free drainage, or subirrigation to establish wat er table depths at 70 and 80 cm below the soil surface) on conserving soil N, under climatic and soil conditions of southwestern Quebec. The resulting six treatments were fertilized in the spring with 270 kg N ha(-1). The effects of adding fertilizer at 0, 180, and 270 kg N ha(-1 ) on monocrop maize with free drainage were also investigated. Soil co res of 1 m in depth were collected in the spring and fall of 1993 and 1994. In 1993, intercropping decreased the amount of NO3--N in the top 1 m of soil profile by 47% (92.3 kg N ha(-1)) relative to monocropped maize at harvest time. Water table depth had less effect on soil NO3- -N content than cropping system. Both increasing water table depth and monocrop maize enhanced downward movement of NO3--N during the growin g season and following spring. More NO3--N was present in freely drain ed subsoil under maize given 270 kg N ha(-1) than under maize given 18 0 kg N ha(-1).