Long-term Tillage Effects on Soil Erosion, Physical Properties, and Soil Moisture

Tillage plays a key role in production agriculture soil management and can influence myriad soil processes and properties, depending on its intensity. Tillage can chop and bury residue; change soil physical structure; and alter how water moves on, into, and through the soil matrix. If improperly implemented, it can lead to problems such as drought stress, poor root penetration, and erosion. Consequently, it is important to understand how soils are affected by long-term tillage practices. Our research examined tillage practices at a long-term (28 year) research site in the North Carolina piedmont. Our primary objectives were to determine the effects of tillage on: 1) soil erosion using ground-based lidar; 2) soil physical properties such as bulk density, particle size distribution, water retention, plant-available water, carbon, and carbon stratification ratio in three row positions (in-row, trafficked interrow, and untrafficked interrow) and to depths of 105 cm; and 3) soil profile moisture conditions to estimate water-use efficiency and depletion and recharge during and following dry periods. The tillage methods were no-till (NT), in-row subsoiling (IRS), chisel plow in spring (CHsp) or fall (CHfa), disk (D), chisel plow in spring or fall followed by disk (CHspD, CHfaD) and moldboard plow in spring or fall followed by disk (MPspD, MPfaD). Soil type at the site was a Casville sandy loam (fine, mixed, semiactive, mesic Typic Kanhapludult). Lidar elevation data showed that the natural elevation gradient (i.e., trend) at the site was best removed using a second order polynomial; the de-trended data were used for analysis of erosion losses. The elevation of MPspD was 13.3 cm lower than NT, which corresponded to a soil loss of 1891 Mt ha-1. In general, estimated soil loss was greatest in tillage treatments of higher tillage intensity. Bulk density was greatest in the trafficked row position of all treatments, an effect detected only at a depth of 10 cm. Particle size distribution was not affected by tillage and changed only with depth. Few differences were detected for water retention and plant-available water. Carbon content was greatest at 2.5 cm and decreased substantially with depth, especially in low tillage intensity treatments such as NT and IRS. The carbon stratification ratio that compared shallow (2.5 cm) vs. deeper depths (10 cm) was greatest in NT, CHsp, and D. Treatments with the greatest carbon stratification ratios tended to be the same treatments that produced the greatest yields over the life of the study. Water-use efficiency was highest in NT and IRS, and lowest in CHsp and MPspD in all five years that soil moisture data were collected. During periods of near-zero rainfall, more water was removed from the soil profile in low-intensity tillage treatments than others, and subsequently these treatments gained more water after rainfall, indicating the influence of tillage on a soil's ability to provide water during dry periods. Overall, results show that conditions conducive to crop growth, yield, and soil conservation coincided with long-term low-intensity tillage management.