An extensive literature review was conducted of corn and soybean research that compared yields of no‐tillage to conventional fall tillage systems. The objective was to test the hypothesis that no‐till has a different effect on corn and soybean yields in different regions of the United States and Canada. The trial results were mapped to look for geographic and environmental patterns in the relative performance of no‐tillage to conventional tillage on corn and soybean yield. The national average difference in corn and soybean yield between no‐tillage and conventional tillage was negligible. A map of the tillage yield comparisons was created for the U.S. and Canada. No‐till tended to have greater yields than conventional tillage in the south and west regions. The two tillage systems had similar yields in the central U.S., and no‐till typically produced lower yields than conventional tillage in the northern U.S. and Canada. No‐tillage had greater corn and soybean yields than conventional tillage on moderate‐ to well‐drained soils, but slightly lower yields than conventional tillage on poorly drained soils. Corn and soybean yields tended to benefit more from crop rotation in no‐till as compared to continuous cropping. Future tillage research should focus on optimizing successful high residue no‐tillage or strip‐tillage production systems instead of making comparisons to conventional tillage systems.

No abstract

No abstract

The efficient operation of reservoirs relies on the effective release of water during flooding, requiring a good understanding of spillways and their hydraulics. A series of experiments was conducted in a laboratory flume on a stepped spillway model with moderate slope (26.68) for discharges up to 0.0121 m 3 /s. Using regular uniform horizontal steps of 5 cm height, then several new step configurations including inclined and horizontal curved steps with and without reflector blocks, the flow patterns were investigated. The energy losses over a horizontal stepped spillway were compared with those obtained in a number of similar, previous studies, and with the results obtained for the new step configurations. Good agreement was shown with previous results for horizontal steps, and the inclined and horizontal curved steps dissipated about twice as much energy as the horizontal steps. The results highlight the importance of considering a variety of step forms in spillway design where flows are unpredictable and energy dissipation is important.

No abstract