Conservation tillage affects root growth of dryland spring wheat under drought

In dryland cropping, no-tillage ran increase small grain crop growth compared with conventional tillage. Because root systems develop ahead of aboveground growth and are affected by soil environment, observation of root growth will show the mechanisms by which no-till enhances crop growth. Wheat (Triticum aestivum L.) was grown in a spring wheat-winter wheat-sunflower (Helianthus annus L.) rotation begun in 1984 on Temvik-aWilton silt loam (fine-loamy, mixed TS pic and Pachic Haploborolls) under conventional till (CT: spring dishing), minimal till (hlT: spring undercutting) and no-till (NT). Root length growth OULG) was measured by microvideo camera in pressurized-wall minirhizotrons, and soil water was measured by neutron moisture meter. Relative to CT, NT generally enhanced RLG more than aboveground growth; RLG averaged 65, 130, and 145 km/cm(2) in 1988, 1989, and 1990, respectively. In 1988, RLG was 37% greater than hlT (P < 0.1), with CT intermediate. In 1989, RLG was 40% greater in NT than in CT, with ILIT intermediate, and RLG in 1990 was 112% greater in NT than CT (no MT). Final biomass averaged 380, 1730, and 3090 kg/ha in 1988 through 1990, and was 36% greater, not significantly different, and 44% greater in NT than CT, respectively. Root penetration was shallow (1.1 m or less) in dry subsoil, but in each year roots penetrated to greater soil depths under NT than under hlT or CT. Amounts of stored soil water were generally not significantly different among tillages, but more water was depleted in 1990 under NT than CT. Cooler soil under NT (measured in 1989) and superior soil water conservation in the near-surface zone appear to confer a root growth advantage to the NT treatment.