Effect of mineral and organic fertilization on crop yield, nitrogen uptake, carbon and nitrogen balances, as well as soil organic carbon content and dynamics: results from 20 European long-term field experiments of the twenty-first century

Assembled results from 20 European long-term experiments (LTE), mainly from the first decade of the twenty-first century, are presented. The included LTEs from 17 sites are the responsibility of institutional members of the International Working Group of Long-term Experiments in the IUSS. Between the sites, average annual temperatures differ between 8.1 and 15.3 degrees C, annual precipitation between 450 and 1400 mm, and soil clay contents between 3 and 31%. On average of 350 yield comparisons, combined mineral and organic fertilization resulted in a 6% yield benefit compared with mineral fertilization alone; in the case of winter wheat, the smallest effect was 3%, the largest effect, seen with potatoes, was 9%. All unfertilized treatments are depleted in soil organic carbon (SOC), varying between 0.36 and 2.06% SOC. The differences in SOC in unfertilized plots compared with the respective plots with combined mineral (NPK) and organic (10t ha(-1) farmyard manure) fertilization range between 0.11 and 0.72%, with an average of 0.3% (corresponding to approximate to 15t ha(-1)). Consequently, the use of arable soils for carbon sequestration is limited and of low relevance and merely depleted soils can temporarily accumulate carbon up to their optimum C content.