Soil Carbon, Nitrogen, and Bulk Density Comparisons in Two Cropland Tillage Systems after 25 Years and in Virgin Grassland

Abstract

Stubble mulching is advocated as a desirable soil management practice, but no data are available for the northern Great Plains showing the effect of its long‐term use on soil properties. Neither have any comparisons been made of organic carbon (C) levels in cropland and virgin grassland in this region since 1947. Four farm field sites, each of moderately coarse‐, medium‐, and fine‐textured soils under conventional tillage, stubble mulch tillage, and virgin grassland (never cultivated) were sampled at 0 to 7.6, 7.6 to 15.2, 15.2 to 30.5, and 30.5 to 45.7 cm to measure organic C, total nitrogen (N), and bulk density. Average organic C and total N to a depth of 45.7 cm, % by weight, were significantly higher under stubble mulch than conventional tillage management. Organic C concentration in moderately coarse‐ and fine‐textured soils was 44 and 13% higher, respectively, under stubble mulch than conventional management, but it did not differ between the two management systems in medium‐textured soils. The percentage loss of C and N from the 0‐ to 7.6‐ and 7.6‐ to 15.2‐cm soil zones due to cropping as compared to virgin grassland was no greater than the percentage loss found in 1947 at field stations after nearly 40 years of cropping. In another comparison considering only medium‐textured soils on farm fields, percentage loss of organic C after about 70 years of cropping, using 1979 virgin grasslands as a reference, was no greater than loss after about 40 years of cropping, using 1950 virgin grasslands. Continued cultivation of dryland soils, especially with stuhble mulching, has maintained organic C and total N at higher levels than was projected from earlier research. Cropland bulk densities to 30.5 cm ranged from 7 to 20% higher than on grassland but did not differ between conventional and stubble mulch tillage management.