Does Crop Species Diversity Influence Soil Carbon and Nitrogen Pools?

Crop species composition and richness exert a strong influence on soil C and N dynamics through the proportion of decomposable organic compounds returned to the soil. Under no-till, soil C and N pools were compared for five crop rotations, (1) continuous corn (Zea mays L.; CC), (2) spring wheat (Triticum spp.)soybean [Glycine max (L.) Merr.; SWS], (3) spring wheatcornsoybean (SWCS), (4) spring wheat winter wheatcornsoybean (SWWWCS), and (5) spring wheatwinter wheatflax (Linum usitatissimum L.)corn cornsoybean (SWWWFCCS), in the northern Great Plains. Soil organic matter (SOM) content was highest under CC and significantly higher than SWWWCS (P < 0.05). Highest organic C, C/N ratio and potentially mineralizeable carbon pool (PMC) was observed under SWCS rotation, similar to CC and significantly greater than SWWWFC CS. Pearson correlation coefficients indicate rotation length had negative relationship with PMC; whereas, PMC had positive relationship with soil organic carbon (SOC) and C/N ratio. Increasing rotation length might increase the substrate diversity that reduces decomposition rate. Similar soil C and N pools of CC and SWCS rotations with annual fertilizer N inputs of 220, 111 kg N ha1 yr1, respectively, indicate SWCS rotation can be a potential alternative to CC to minimize the fertilizer N input and maintaining species diversity.