Soil microbial quality associated with yield reduction in continuous-pea

The negative impact of continuous production on soil productivity has been demonstrated but is not well understood. The impacts of continuous-pea on soil health and functioning, as compared to pea–wheat rotation, were assessed as part of an 11-year study conducted on a thin Black Chernozemic soil to understand how crop rotation affects soil microbial communities, nutrient availability, and pea nutrition and productivity. Soil and plants from the field pea phase of the rotations receiving one of three nitrogen treatments (0, 20, 40 kg N ha−1) were sampled three times during the growing season of 2005. Reduction in pea plant productivity in the continuous-pea system seemed attributable to multiple causes. In continuous-pea, tissue N and P concentrations were reduced by over 10%, and tissue Fe and Mn concentrations were increased 2- and 1.7-fold, respectively. High tissue micronutrients (Fe, Mn, Cu, and Zn) concentration was related with the abundance of the Gram negative bacteria phospholipid fatty acid (PLFA) biomarker 2OH-14:0. In the continuous-pea rotation, the soil microbial community was smaller, the abundance of beneficial Gram positive bacteria and arbuscular mycorrhizal (AM) fungi was reduced as indicated by phospholipids fatty acid biomarkers, and the percentage of AM root colonization was lower. These differences in soil microbial biodiversity could be related with increased susceptibility of continuous-pea to root rot injury, as continuous-pea root abundance was reduced 2-fold as compared to pea–wheat rotation. Fusarium root rot was more severe in the continuous-pea than pea–wheat rotation (assessed in 2001 and 2008). Depressed soil organic carbon level, and dehydrogenase, phosphatase and urease activity in continuous-pea, revealed a negative impact of continuous-pea on nutrient cycling. Greater residual NO3 level in the soil profile indicated inefficient use of N and increased risk of N leaching with continuous-pea.