BIOMASS PRODUCTION AND NITROGEN UPTAKE IN CORN-RYEGRASS SYSTEMS

Cropping systems, plant growth stages, and applied N fertilizer rates all directly affect N uptake. A 2-yr study was conducted to evaluate t he effects of cropping system [monocrop corn (Zea mays L.) and corn in tercropped with annual ryegrass (Lolium multiflorum Lam.)] on dry matt er (DM) production and distribution and on N uptake and allocation in the plants during the development of corn. Each of these corn systems was produced on a fine sandy loam (Typic Humaquept), using an applicat ion of 270 kg N ha(-1) in each spring. Zero N (control) and convention al N rate (180 kg N ha(-1)) treatments were included for monocropped c orn with conventional drainage. Plant tissues of all treatments were s ampled at six-leaf, tasseling, and mid-grain filling stages, and after physiological maturity. In both years, DM production and N uptake of intercropped corn were lower than, or not different from, the monocrop ped corn (depending on growth stage). The total N uptake and DM produc tion of the intercropping system (corn + ryegrass + weeds) were greate r than those of the monocrop system. Application of 270 kg N ha(-1) re sulted in 20% less N recovery than 180 kg N ha(-1) with monocropped co rn production using free drainage. Both the corn-ryegrass intercroppin g system and applied N rates altered the allocation of DM and N among different parts of the corn plants. The ryegrass and weeds were not ab le to take up enough of the extra N after the high N rate was applied for two consecutive years. The effect of precipitation on annual ryegr ass growth was an important factor in N uptake by the intercropping sy stem.