Abstract

For the evaluation/assessment of the C_org content of arable land, only the nutrient humus C is of importance. On average, this is 0.3% C_org and is below 0.2% in more than 40%. The difference between “good” and “bad” is often within the error limit. The C_org content of long-standing bare fallow land has proven to be a suitable criterion for permanent humus. The levels of total humus C in Long-Term Field Experiments (LTE) are between 0.22% C_org and 4.17 % C_org. In about 40% of the experiments, the C_org content of the optimally organically and minerally fertilized variants is less than 1% C_org (=1.724% humus). The humus balancing method [1] is the only way to assess the humus supply status of the soil. It urgently needs to be revised after 50 years. The mineral fertilization ensures the nutrition of the people through the high yields and is also the basis of an adequate supply of humus. Long-term field experiments are an indispensable experimental prerequisite for practice-oriented humus research.