Physical, chemical and biological subsoiling for sustainable agriculture

Subsoil degradation – mainly through strong compaction (to density > 1.6 g cm−3) by intensive agriculture with heavy machinery – is a global problem for soil health, crop production, carbon sequestration, and the environment. Subsoiling is a field measure to improve the physical, chemical, and biological properties of the soil below the common plowing depth to increase crop yields, water and nutrient use efficiency, economic benefits, and ecological functions. Traditionally, physical (phy-), chemical (chem-) or biological (bio-) subsoiling approaches are used to recover degraded subsoils, whereas their combination was disregarded. This review summarizes current knowledge on subsoiling approaches and their effects on soil properties, crop production, carbon storage and other ecosystem functions. A meta-analysis showed that phy-subsoiling boosts crop yields by 19 % on average, with a temporal decrease in organic carbon content in the topsoil compared to no-till cultivation. Phy-subsoiling is necessary but not sufficient to completely resolve tillage pan compaction problems. Bio- and chem-subsoiling combined with phy-subsoiling very efficiently increase the full range of soil fertility properties for a long duration, raising crop yields and strengthening economic benefits because the combination retains the advantages while reducing the shortcomings of individual subsoiling approaches. Thus, farmers should upgrade phy-subsoiling with bio-approaches, including the use of deep-rooted crops and straw incorporation, and chem-subsoiling modes, including manuring and liming.