Spatiotemporal soil organic carbon dynamics in irrigated corn silage-alfalfa production systems receiving liquid dairy manure

Authors: Gamble, Joshua; Feyereisen, Gary; Schneider, Sharon; Wente, Christopher - Chris; Baker, John

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Proceedings
Publication Acceptance Date: 8/13/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: This study quantified the changes in mass of soil organic carbon (SOC) on adjacent 65-ha corn silage-alfalfa production fields receiving liquid dairy manure in west central Minnesota. We quantified the spatial variability in SOC in four soil layers as it relates to terrain and agronomic management and then predicted SOC at unsampled locations. High resolution (1 m x 1m) maps of SOC were then created for both 2006 and 2015, and changes over time were calculated. We found that elevation, wetness index, field (west/east), and irrigation (yes/no) improved SOC prediction in 0 - 15 cm and 15 - 30 cm soil layers, but were not useful for SOC below 30 cm soil depth. In the west field, SOC increased 7% in the 0 - 15 cm layer due to gains in the irrigated portion of the field, but did not change in the 15 - 30 cm layer. In the east field SOC stocks were similar in 2006 and 2015 for the 0 - 15 cm and 15 - 30 cm layers. In both fields, SOC increased by 13% in the 30 - 60 cm layer and by 24% in the 60 - 90 cm layer over the study period. These findings suggests that current rates of C removal in forage harvest and C addition in manure are sufficient to maintain or increas SOC. The findings of this research will be of interest to researchers and agency personnel with interest in rapidly assessing SOC, and also to producers/producer groups with interest in maintaining/improving soil productivity, soil quality, and soil carbon sequestration.

Technical Abstract: Accurately measuring soil organic C (SOC) stock changes over time is essential for verifying agronomic management effects on C sequestration. This study quantified the spatial and temporal changes in SOC stocks on adjacent 65-ha corn silage-alfalfa production fields receiving liquid dairy manure in west central Minnesota. We employed regression kriging to interpolate SOC in four soil layers in 2006 and in 2015 and then calculated stock changes over time. Regression kriging with elevation, topographic wetness index, field (west/east), and irrigation (yes/no) accurately predicted SOC in the 0 – 15 cm (R2 = 0.89) and 15 – 30 cm layers (R2 = 0.51 to 0.95), where variogram analysis indicated moderate to strong spatial correlation. From 0 – 15 cm, SOC in the west field increased by 7% (+ 4.5 Mg C ha-1) over the study period due to gains in irrigated portions of the field, but no changes were found in the east field or at 15 – 30 cm in either field. Below 30 cm, a lack of spatial structure and lack of relationships between SOC and auxiliary variables was found, but simple means indicated SOC gains of 13% (+ 4.7 Mg C ha-1) in 30 – 60 cm layer and 24% (+ 3.9 Mg C ha-1) in the 60 – 90 cm layer across both fields. Current rates of C harvest in forage and manure C addition are maintaining or increasing SOC. Regression kriging with easily acquired auxiliary variables offers a highly accurate method to monitor SOC stock changes over time to 30 cm depth.