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Project Buddies
Special thanks to Wesley Tuttle, USDA-NRCS geophyisicist, for assistace in conducting the geophysical surveys. We also point up the generous support of Michael G. Wagger, Department of Soil Science; the Monsanto Corporation for donating seed; Joe French, Superintentant, Upper Piedmont Research Station for keeping the doors open; Larry Shough, Auman French and the UPRS crew whose hands we busy early and often; Jennifer Etheridge, Steven Holland, Pukraj Deol, Matt Taggart of the Heitman group; and Bill Connolly and Chris D'Aiuto of the White group.

Project Overview

Many soybean producers in North Carolina's Piedmont shifted away from conventional clean-tillage to conservation-tillage planting systems in the 1980s. Sloping topography and erosion-prone, acidic soils developed in residuum of schist, gneiss, and granite are dominant geomorphic features of the southern Piedmont. Soil physical quality that has been degraded by exhaustive plowing or classified as inherently poor, combined with seasonal rainfall arriving mainly as intermittent showers interrupted by droughty periods lasting from 1 to 2 weeks, pose challenging situations for annual rain-fed row crops like soybean. Never the less, productivity gains have been realized on degraded Piedmont soils from conservation practices that reduce or eliminate tillage and maximize residue cover. The principal reasons cited for this are more efficient capture, utilization, and profile storage of available moisture, along with tillage cost savings.

The overarching goals of this research are to better understand the mechanisms governing soil profile moisture dynamics, and their relationships with soybean (and corn) productivity under different conservation and conventional planting systems in two, representative, North Carolina Piedmont Ultisols. Scientists have long recognized that physical properties like soil strength (penetration resistance) and air-filled porosity influence root growth and, consequently, water availability to plants. To account for this an integrated parameter, the Least Limiting Water Range (LLWR) was developed linking the root restraining characteristics of plant-available water holding capacity (PAW), soil strength, and soil aeration as a function of bulk density. Physical quality of the soybean rooting environment and thus, productivity may be inferred from the LLWR without excavation and quantitative measurement of the soybean (or corn) root system.

Specific objectives of this research funded by the Soybean Growers Association of North Carolina include 1) model the LLWR with respect to tillage, traffic pattern, and depth in the prime soybean (and corn) rooting zone in two Piedmont Ultisols; 2) assess the effect of soil physical properties on available moisture and characterize the physical quality of the rooting environment in terms of the LLWR; and 3) assess the long-term consequences of conservation and conventional planting systems on soil physical quality and their relationship to soybean productivity. We are using relatively new technologies like the multi-depth capacitance probe for measuring profile soil moisture; the multiple-probe soil cone penetrometer; soil sampling equipment designed to extract a relatively undisturbed subsoil core; and proximate remote sensing (scanning lidar, ground penetrating radar, and electromagnetic induction measurement of soil apparent electrical conductivity [ECa]) to characterize soil physical properties.

Two, long-term tillage trials, both on Typic Kanhupludults, at the Upper Piedmont Research Station, Reidsville, NC are the foundation for these investigations. Both trials are randomized complete block experiments in a corn-soybean rotation with controlled traffic, described here. Project leaders: Jeffrey G. White, Alan D. Meijer, Robert D. Walters, Joshua L. Heitman, Adam M. Howard, Robert Austin.


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This page was last modified on 12-Jan-2019 .