Soil carbon increase from crop roots and amendments still present twelve years later.

Soil organic carbon was measured after surface application of equal C amounts from various C sources to fallow soil or a winter wheat crop for five consecutive years. Municipal biosolid produced the largest gain, followed by manure and alfalfa (Medicago sativa L.) foliage. Wheat (Triticum aestivum L.) straw, sucrose, and wood sawdust were not different than no addition. These effects were additive to and independent from the effect of fallow soil versus cropped soil. Soil cropped to winter wheat increased in C comparable to the biosolid application or to plots planted to perennial grass. Measurements 4, 6, and 12 years after a return to normal farming practices produced no change in relative or quantitative differences. These results illuminate the durability of above‐ and below‐ground contributions to soil C. Core Ideas: Increased soil organic carbon (SOC) produced by crop roots or amendments is still present 12 years later.The effect of wheat straw and sucrose on SOC was not significant, but biosolids, manure, and alfalfa increased SOC.Five years of wheat or perennial grass produced a substantial gain in SOC compared to fallow. [ABSTRACT FROM AUTHOR]