Field Scale C Input in an Intensive Tilled and Irrigated Field: Implications for Soil C Changes

Juhwan Lee, Richard Plant, Johan Six, Chris van Kessel

Department of Plant Sciences

University of California

Davis, CA 95616

Net primary production (NPP) in croplands plays an important role in the global C and other nutrients. In agricultural systems, field or larger-scale NPP is likely affected by climate, soil type, and management practices (e.g., tillage), affecting soil C levels via C input. As the greenhouse effect is of global concern, a potential to mitigate this effect through CO₂ sequestration in soils should be evaluated at various scales. This suggests that field variability of crop residue input can become an essential tool for better understanding of soil organic C dynamics in relation with best management practices. In the Mediterranean climate of California, soil C levels by organic C input and tillage intensity is expected to change more rapidly than ones in other climatic systems as soils typically have low organic matter content (≈ 1%) and weak structure. However, C sequestration at field or larger spatial scales has rarely reported. We used yield monitor data collected from 1997 to 2005 and soil C data from 2003 to 2005 across the field to evaluate the effect of soil type and levels of residue input in the soil in combination with tillage intensity on soil C levels and turnover. The study site was established on a laser-leveled, furrow-irrigated agricultural field of 30 ha in the Sacramento Valley, California. Three soil types occur at the site. Soil and crop processes controlling the field scale variability of residue input were discussed.