CORN RESPONSE TO RESTRICTED NODAL ROOT GROWTH WITH RELEVANCE TO ZERO TILLAGE

In Ontario, corn (Zea mays L.) yields with zero tillage are 10–15% lower than those with conventional tillage. Slower growth with zero tillage usually begins at the four-or five-leaf stage and continues until the 10- to 12-leaf stage. We hypothesized that restriction of nodal root development occurs with zero tillage and causes the reductions in shoot growth and final yield. Two greenhouse experiments were conducted in which nodal root development of corn plants was restricted by soil compaction or dry soil while the seminal roots grew in flowing nutrient culture. Compaction reduced nodal root length by 54%, and dry soil reduced it by 90% at the 10-leaf stage. Shoot dry weight at the 12-leaf stage was significantly reduced by dry soil but not by compaction. Leaf water potential and stomatal conductance at the 12-leaf stage were reduced by dry soil despite a negligible drop in pressure potential across the mesocotyl. Dry soil reduced shoot growth in terms of plant height after the eight-leaf stage. It was concluded that restriction of nodal root growth in zero tillage systems probably would not account for the reduced yields. Key words: Corn, Zea mays L., growth regulator, seminal roots, mesocotyl, xylem resistance