Lime and Nutrient Addition Affects the Dynamics and Fractions of Soil Carbon in a Short-term Incubation Study With 13C-Labeled Wheat Straw

Abstract

Lime and nutrients are common agricultural amendments and when applied with fresh organic matter can alter the cycling of carbon (C) in soils. Previous research has focused on assessing either the impact of nutrients on C associated with specific soil fractions or the application of lime on C dynamics in the whole soil, without fully considering the potential interactions of lime and nutrients on changes in soil C. A short-term (77 days) incubation experiment was conducted to investigate the effects of lime and nutrients (nitrogen, phosphorus, and sulfur) when added with 13C-labeled wheat straw on the incorporation of the wheat straw C into soil C. Respiration was measured throughout the incubation, and soil (a Yellow Chromosol or acidic Alfisol) was analyzed for C in the fine (<0.4 mm) and coarse (>0.4 mm) soil fractions after 77 days. There was greater C loss from the coarse fraction soil across all treatments when straw was incorporated, and lime application increased C loss from both fractions. Lime plus nutrients led to positive soil priming, a decrease in the preexisting soil C tracked through changes in 13C, and reduced conversion of straw C into the fine fraction soil C as compared with nutrients alone. The lime and lime plus nutrients added with straw reduced the net humification efficiencies (9.3 and 8.1%, respectively), compared with the unlimed or nutrient-only treatments (18.4 and 15.5%, respectively). Lime with supplementary nutrients was less effective in promoting the conversion of straw C into the fine fraction soil C compared with nutrients alone in this incubation experiment. Where lime and supplementary nutrients as fertilizer are routinely used to improve agricultural production, the lime may offset any benefit of the nutrients for conversion of straw C into the fine fraction soil C.