Crop rotation diversity to improve water quality and increase soil health
Extended crop rotations that include a perennial forage crop are a key component of the Iowa Nutrient Reduction Strategy. In addition to reducing nitrate loss to Iowa waterways, extended crop rotations can also increase soil organic carbon content in surface and subsoils. Greater C storage in extended crop rotations may be attributed to greater root inputs, which can form organic matter more efficiently than aboveground inputs. The purpose of this study was to compare the biochemical composition of soil organic matter between an extended rotation (corn-corn-oat/alfalfa-alfalfa) and a simple rotation (corn-soybean). We hypothesized that the soil organic matter would reflect greater contribution of root inputs in the extended crop rotation. We collected soil samples from extended and simple crop rotations at four depths. We measured total fatty acids and fatty acid biomarkers that represent root and shoot compounds using pyrolysis-gas chromatography-mass spectrometry and extraction by cupric oxide. Results indicate fatty acids dominate subsoil carbon pools. Ongoing research using the cupric oxide method will quantify root and shoot biomarkers. High levels of root inputs are desirable because they promote resilience and stability of Iowa crop production.