Soil³ – Sustainable Subsoil Management

Project number: 031B1066
Contact: Prof. Dr. Wulf Amelung, INRES – University of Bonn
Project team: University of Bonn, Technische Universität München, Forschungszentrum Jülich, Freie Universität Berlin, Thünen-Institut, Ecologic Institute, Humboldt-University of Berlin
Duration: 1/10/2015 – 31/01/2025

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Project aim 

This project aims, to explore how and to which degree we can manage the subsoil to secure or even increase plant yields by improving the overall nutrient and water use efficiency for crops. We presume that nutrient and water uptake from the subsoil can be elevated at given or even increased crop yields when there are attractive options for the plants to invest into subsoil roots, like low physical resistance for the root channels, hot spots of higher microbially facilitated nutrient supply in the subsoil as well as plant available subsoil water under conditions of seasonal drought stress in the surface soil. 
With a growing global population, arable food production in 2050 should be 60 percent higher than that of 2005/ 2007 (FAO, 2012). Therefore, there is the need for “sustainable intensification” of production, which is a great challenge in front of the background of the current situation of agricultural production. However, immense water, carbon, and nutrient reservoirs can be found in subsoils. In order to secure the yield potential of soils and to increase their productivity in the long-term, it is inevitable that subsoils are integrated in sustainable management strategies. 
Expected results 

Aim of Soil³ is to provide scientific knowledge for practitioners. The coupling of strategies of research and production, services, arable management strategies, and providing of software tools are main bricks. Indicator systems of the acquisition of water and nutrients from the subsoil are applicable for monitoring success. Different technical means and manipulation options of the subsoil are tools for economic utilization. Identifying of genotypes could be coupled with commercial plant breeding industry. 


Project results from phase 1  and 2        


Subsoil is more heterogeneous in its physico-chemical properties than topsoil. Root access to subsoil resources is site-specific but can be enhanced by topsoil management, particularly N fertilization and liming, as well as by biopores and loosening, with greatest yield effects under seasonal drought. For specific subsoil management we developed a tool for strip-wise compost injection into subsoil. This stabilizes or even increases crop yields by 20%, depending on weather conditions and topsoil management. Subsoil management is most promising and sustainable in well-drained sandy soils, regions with layers restricting root growth, and regions facing extreme climatic events. Implementation of subsoil management might be best feasible under clear ownership conditions combined with organic farming.

Positive effects of stripwise subsoil melioration with compost with respect to crop yields and soil quality, e.g. microbial community, nutrient status and carbon storage, last for min. 4 years. Moreover, no enhanced nitrate leaching was found. With costs of 800 €/ha and yield increases of 23-55%, the technique becomes profitable after 4 years. Subsoil melioration could give access to 45-60% of nutrient and water resources in German farmland, with most promising success in Northeastern Germany characterized by summer drought. Acceptance of subsoil melioration by farmers varies among regions and is generally higher for biological measures (biopore formation via precrops) than for more invasive mechanical treatments.


Expected results phase 3               


We aim at i) determining longevity of yield gains and soil quality (carbon, water and nutrient storage) via both technical and biological subsoil melioration also in lower-value soils, ii) evaluating water and nutrient use efficiencies against conventional soil management techniques, iii) providing a systematic tool for selection of organic amendments, iv) monitoring the performance of various crops under subsoil melioration and v) regionalization of costs, risks and benefits. This will enable us to provide implementation advice and outreach materials for the public, farmers, industry and science.