Dynamics of soil water-extractable organic C following application of dairy cattle manures

Abstract

Water-extractable organic C (WEOC) is a determinant driver of several soil and environmental processes, and can be influenced by management practices such as organic amendment. Our objective was to study the dynamics of soil WEOC following application of liquid and solid dairy cattle manures to a loamy and a clay soil under field conditions. Manures were applied in 2 consecutive years to silage corn fields at rates equivalent to 150 kg total N ha-1. Soil WEOC was monitored the day after application and weekly or biweekly thereafter in manured and control (mineral fertilizers) plots. Liquid and solid manure S brought on average 39 and 13 g WEOC m-2, respectively. These amounts are much larger than the increases measured in soil WEOC during the hours and days following manure application (0 to 30 mg kg-1, equivalent to 0 to 3 g m-2). Moreover, manure addition had little effects in the 10- to 30-cm soil layer. The rapid and extensive adsorption of manure WEOC onto mineral surfaces likely explains the limited effects of manure on soil WEOC. This adsorption process was presumably exacerbated by the mixing of manure and soil resulting from the tillage operation. Soil temperature and respiration appeared to have determinant influence on the level of soil WEOC content in the post-harvest period. Overall, temporal variations in soil WEOC contents were large and generally greater than the fluctuations directly attributable to manure addition. Key words: Soil organic C, extractable C, dairy manure, silage corn