CORN ROOT DRY-MATTER AND NITROGEN DISTRIBUTION AS DETERMINED BY SAMPLING MULTIPLE SOIL CORES AROUND INDIVIDUAL PLANTS

Although models of nitrogen (N) flow in agroecosystems describe total plant N uptake, only limited data on roots exists. Underground dry mat ter and N distribution patterns in com (Zea mays L.) were determined b y isolating root segments from soil cores collected around plants at a nthesis from a Typic Kanhapludult. Samples were collected from two tre atments: no-till with 70 kg N/ha and conventional tillage and planting with crimson clover (Trifolium incarnatum L.) as a N source. Seven so il cores (4.2 cm diameter) per plant were taken to recover roots in th e 0- to 15-cm and 15- to 30-cm depth intervals. Sampling positions wer e at the base of the plant and at distances (perpendicular to the row) of 6, 16, and 27 cm into the trafficked interrow, and 11, 22, and 32 cm into the untrafficked interrow. Underground shoot and root segments were isolated from soil cores by hydropneumatic elutriation. Root dis tribution patterns in the no-till treatment were similar in trafficked and untrafficked interrows, but more roots were detected in the untra fficked interrows than in the trafficked interrows in the tillage trea tment. Averaged over treatments, 85% of the root weight and 81% of the root N were in the 0- to 15-cm depth interval. The root:shoot dry mat ter ratio was 0.27:1 and the root:shoot N content ratio was 0.20:1. Ca rbon:nitrogen (C:N) ratios were higher in underground shoot (118:1) an d coarse root fragments (78:1) than in aboveground shoot (42:1) or fin e root fragments (33:1).