ARS | Publication request: Curve numbers for long-term no-till corn and agricultural practices with high watershed infiltration

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 5, 2013
Publication Date: N/A

Interpretive Summary: Available runoff data were used in a watershed study in the hill lands of east-central Ohio to quantify the low runoff potential of no-till corn (with a large earthworm population) and other high infiltration agricultural practices. Grassed watersheds and the wheat years in a rotation had the lowest runoff potential of those studied followed by no-till with an earthworm population. Conventionally grown corn with complete soil surface mixing and no surface residue with a moldboard plow had the largest runoff potential, however, this could be reduced significantly by minimum soil surface disturbance by disking in the spring - runoff potential was equivalent to a permanently managed meadow. The results of this study are important because it appears there is a physical limit to runoff reduction in the study area, however the runoff-reducing benefits of no-till enable producers to have a corn crop every year rather than one year in four and operate an environmentally sustainable enterprise. Producers, engineers, scientists, conservationists, and urban planners will benefit from this study.

Technical Abstract: The Curve Number (CN) method is an engineering and land management tool for estimating surface runoff from rainstorms. There are few watershed runoff records available during which a no-till crop was growing and hence there are few field-measured CN values. We investigated CN under continuous long-term no-till corn and compared it to other potentially high infiltration agricultural practices using data from three experimental watersheds (average area=0.74 ha) at the North Appalachian Experimental Watershed (NAEW) near Coshocton, Ohio. Practices compared were wheat, and first and second year meadow as part of a 4-yr corn-wheat-meadow-meadow rotation (CWMM), continuous meadow, and continuous no-till corn, mulch-tilled corn, and conventionally-tilled corn (i.e., moldboard plow). Double-mass curves of runoff for no-till and permanent meadow documented the significant and immediate reduction in runoff from the no-till management. Runoff was generated at a rate of 4.9 mm/yr during the no-till period compared with permanent pasture at 44.0 mm/yr (0.11 times the meadow rate). CNi for the 48-yr record of continuous no-till corn practice with an earthworm population at WS191 decreased substantially to 66.3, -24.3 CN units) from the period of conventional corn in rotation on the same site. The NRCS handbook value for CN was 16 CN units larger at 82. The CN for the mulch-tilled corn culture treatment (74.6) was lower than conventional corn (90.6 largest) by 16 CN units. CN was surprisingly high (77.4) for a watershed in continuous meadow, which was similar to mulch-tilled corn. The wheat years in rotation also had some of the smallest CN values (63.7), suggesting smaller CN for a practice similar to that used in organic agriculture today. Continuous no-till corn had a slightly larger curve number (66.3) than meadow (61.9) in rotation suggesting that simple grass establishment can be as effective as long-term no-till with a thriving population of earthworms and numerous earthworm-created macropores. CN of approximately 60 appears to be the lowest possible in the terrain, management practices, geology, soils, subsoil permeability, and climate of the NAEW.