Deep-rooting cover crop mixtures: Creating highways to subsoil water and nutrient resources (RootWayS)

Organic farming systems traditionally consider subsoil resources for crop production. As increasing drought frequencies and intensities will reduce nutrient availability in dry topsoils, future conventional agriculture has to manage subsoils as valuable water and nutrient sources. This project aims at optimization of deep rooting winter cover crop mixtures as a strategy for fast access to subsoil resources by root channel re-use in conventional cropping systems. The niche complementarity principle will be used by combining a shallow and a deep-rooting species of one functional cover crop group (Brassicaceae, grasses, legumes) to form deep-reaching root channels even during short winter growing season. Species-specific root-channel re-use of cover crop mixtures by maize will be quantified .

Figure 1: Conceptual idea.

(Physico-)chemical and microbiological characterization of cover crop root channels and their interactions with the maize rhizosphere will explain the preferential use of species-specific root channels by the cash crop maize. Tracer approaches (13C, 15N, D2O, Cs, Rb, Sr) will unravel the fast and efficient access of maize to subsoil nutrients and water using cover crop root channels. Drone-based thermography will allow upscaling of water and nutrient use by maize to the field scale. Implementation of these data in crop models will allow prediction of maize yield depending on cover crop management. The relevance of cover cropping as subsoil-exploring management practice will be determined depending on two key factors: 1) Soil properties by conducting experiments on the three key agricultural soil types in Germany and 2) Soil water supply by simulated drought events by rainout shelters. We will deliver clear recommendations on soil type-specific cover crop mixtures for maize cultivation facing increasing drought risks. We will bring these outcomes to practice by direct cooperation with cover crop seed suppliers and professional agricultural organizations.

Figure 2: Theoretical project design.