Row spacing effects at different levels of nitrogen availability in maize

No-tillage maize (Zea mays L.) grown without adequate N intercepts less than 95% of the incident radiation at flowering. Reducing the distance between rows could increase radiation interception and grain yield. A 2-yr experiment was conducted at INTA Research Station, Balcarce, Argentina (37 degrees 45' S; 58 degrees 18' W), to study the effect of row spacing and N availability on intercepted radiation, kernel number, and grain yield of no-till maize. Treatments consisted of a factorial combination of row width (0.35 and 0.70 m) and N (0 and 120 or 140 kg ha(-1) each year) at a constant plant density. Low N decreased kernel number and grain yield. Narrow rows significantly increased kernel number per unit area and grain yield. Average increases in response to narrow rows were 14.5 and 20.5% fbr kernel number and grain yield, respectively. However, relative increases in response to narrow rows were greater at low N. A close association between kernel number and intercepted radiation during the bracketing-silking period was observed. With conventional row spacing, relative grain yield responses to narrower rows decreased as crop radiation intercepted at flowering increased. A decrease in row distance when N was limiting partially offset the negative effects of N deficiency on grain yield. Our results indicate that 27 to 46% increases in grain yield were obtained in response to narrow rows in N-deficient maize crops.