Soil organic carbon pools and soil quality indicators 3 and 24 years after a one-time compost application in organic dryland wheat systems

Abstract

Quantifying changes in soil organic carbon (SOC) is essential for understanding the effect of managements on carbon (C) sequestration, especially in cultivated marginal lands. The objectives of this study were to determine the short- (<3 yr) and long-term (>24 yr) effects of a one-time compost application on soil organic matter (SOM) pools and stocks: coarse particulate organic matter (cPOM), fine particulate organic matter (fPOM), mineral-associated organic matter (MAOM), and soil physical quality (SOC:clay ratio) in surface- and sub-soils. Manure compost (0, 25, and 50 Mg dry weight ha–1) was applied to three organic dryland winter wheat-fallow systems (WW-F): Historic, (HT, >24 yr), Snowville (SN, < 3 yr), and Blue Creek (BC, <3 yr), in northern Utah. At HT, cPOM-C concentrations in amended plots were higher than under the control plots at the 0–10- (84.6 vs 54.4 g OC kg-1 fraction) and 10–30-cm (34.4 vs 19.4 g OC kg-1 fraction) depth. Compared to control plots, compost increased MAOM-C concentration from 1.8 to 3.4 g OC kg-1 fraction at the 30–60-cm at SN and from 2.35 to 3.99 g OC kg-1 fraction at the 60–90-cm depth at BC. Similarly, cPOM-C concentration was also increased at SN (5.5–23.6 g OC kg-1 fraction, 30–60-cm) and BC (8.3–31.2 g OC kg-1 fraction, 60–90-cm). The SOC:clay ratio was significantly higher at the 30–60-cm depth at BC (1:50–1:40) and at the 60–90-cm depth at SN (1:70–1:30), which suggests that compost application can impact subsoil physical quality. Thus, one-time compost application at 16.5 Mg C ha-1 every two decades might constitute a reasonable management option for managing C in dryland WW-F agroecosystems.