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Tillage Influence on Soil Sulfur Characteristics in Winter Wheat-Summer Fallow Systems

Dep. of Agronomy, Univ. of Missouri, Delta Research Center, Portageville, MO 63873

D. G. Westfall and G. A. Peterson

Dep. of Agronomy, Colorado State Univ., Fort Collins, CO 80523

E. T. Elliott

Natural Resource Ecology Lab., Fort Collins, CO 80523

*Corresponding author.

ABSTRACT

Conversion of native prairie ecosystems to crop production leads to net losses of many essential plant nutrients. The purpose of this research was to monitor winter wheat (Triticum aestivum L.)-fallow rotations for seasonal soil S fractions and S dynamics as affected by tillage. Soil samples from plots that had been subject to 15 yr of no-till, stubble mulch, and conventional tillage were collected at monthly (cropped) and 2-wk (fallow) intervals, from May through October at depth increments of 0 to 2.5, 2.5 to 5, 5 to 15, 15 to 30, and 30 to 60 cm. Sulfate-S, carbon-bonded S (CB-S), and esterbonded S (HI-S) concentrations were determined for each soil sample. During fallow, SO₄-S accumulation in the surface 0 to 5 cm was 1.5 times greater in no-till than in tilled soils. After a rainfall of 49 mm, SO₄-S concentrations increased at 15 to 30 cm from 4.6 to 5.8 mg kg^–1 in no-till, 3.1 to 8.3 mg kg^–1 in stubble mulch, and 3.4 to 11.2 mg kg^–1 in plow treatments. No-till soils contained higher amounts of HI-S at 0 to 15 cm than either tilled soil. There was no difference in CB-S concentration at 0 to 15 cm between no-till and stubble mulch with both containing higher CB-S contents than plowed soils. Lower surface concentrations of SO₄-S, greater SO₄-S leaching, and lower HI-S and CB-S in tilled than in no-till soils indicates that S is conserved in low-soil-disturbance tillage systems.

Joint contribution from the Dep. of Agronomy, Natural Resources Ecology Lab. (NSF Project BSR 8605191) and Colorado Agric. Exp. Stn. (Project 1-53240 and 5-3230).

Received for publication November 29, 1989.