Nutrient Acquisition from the Subsoil: N Uptake in Biopores

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In sustainable agricultural production systems relying on nutrient acquisition from the solid phase, the subsoil has to be considered for crop nutrition. Large continuous biopores generated by plant roots and earthworms provide elevated concentrations of nitrogen and plant available phosphorus as well as increased microbial abundance and activity. They are thus potential hot spots for the nutrient acquisition from the subsoil.To determine the amount of nitrogen taken up from the subsoil by crops, it is therefore essential to consider the structural heterogeneity, addressing the effect of the drilosphere. In the proposed project, nitrogen uptake by spring barley from i. the subsoil in total and ii. a subsoil biopore will be quantified in pot experiments by means of labeling i. the topsoil or ii. the subsoil drilosphere using 15N labelled lucerne litter. Treatments with biopore will be compared with treatments without biopore. Furthermore, by labeling the drilosphere in different soil depth sections, nitrogen uptake analyses from different soil depths will be linked to monitoring root growth in biopores throughout the cultivation period with a permanently installed flexible videoscope. With the proposed approach, it will be investigated whether earthworm casts are an appreciable source of nitrogen for crops and if consequently structuring the subsoil with biopores increases the share of N derived from the subsoil. Moreover, the pattern of N uptake from the drilosphere throughout the cultivation period will be elucidated monitoring root-soil contact in biopores as a function of time. This way, a further step will be taken towards understanding the role of biopores for the nutrient acquisition from the subsoil.