Since 2002, the federal research programme for organic agriculture has supported research projects on soil fertility. Research projects at the beginning studied specific subject areas such as comparison of various mulch materials, nutrient mobilisation (especially phosphorus), humus balance and soil erosion. This addressed gaps especially in methods in organic practice, where data acquired from conventional agriculture are not applicable. From 2008, the research on soil fertility significantly increased and there was a special focus on interdisciplinary systems approaches. The joint research project on the management of soil fertility in organic farming, for example, examined a number of factors that interact in this field, such as tillage and soil compaction, fertilisers, green manures and cover crops, weed and disease pressure, crop species and yield levels, energy consumption and the use of machinery, but also cost-benefit analyses of promoting soil fertility and recommendations for farmers. Other projects addressing the need to increase soil fertility investigated the influence of agronomic management measures on soil quality, and of various aspects of reduced tillage; these projects continue the idea of the systems approach. In 2011 a status quo analysis of long-term field experiments in German-speaking countries was conducted, which included comparisons of systems employed to study the long-term impact of management measures on soil fertility, and to identify further research needs.
Important results from individual projects on soil fertility are presented below. Based on new data, recommendations are given on the use of different mulching materials and effects on soil moisture and nutrient content. Also results relevant for practitioners were derived from the revision of the method for estimating soil erosion, and concrete suggestions for new methods were made. Similar to the case of the method for estimating humus balance, this method could also be adapted for the conditions of organic farming in Germany. From on-going projects (started since 2008) important first results have been obtained. For example, the status quo analysis of long-term field experiments produced new findings on the long-term effects of different management systems, and new research gaps were identified. Further results from the BÖLN research on soil fertility are regularly published at www.bundesprogramm-oekolandbau.d
