Effect of different methods of subsoil loosening on the physical soil properties, root growth, soil water withdrawal and crop yield of a dry sandy soil

Compaction of the subsoil on intensively used arable land is one of the main causes of restricted vertical root growth. As a result, nutrient and water resources from the subsoil can only be used by the plant to a very limited extent. Particularly during temporary drought, the drying out of the topsoil and the associated reduction in nutrient availability, is no longer possible to compensate by using the water and nutrient reserves from the subsoil.

Subsoil loosening is increasingly discussed as a suitable method to increase crop yields in drought-prone areas. In the “Soil^3”project funded by the Federal Ministry of Education and Research of Germany, a field trial with winter rye and silage maize has been carried out on a dry highly compacted sandy soil in Thyrow (Germany) since 2019. The soil of the experimental site is classified as a Retisol, the climate is humid continental.

Five treatments are tested in the trial, where mechanical subsoiling using the Soil^3 method (Schmittmann et al., 2021) in 45 cm deep furrows with a spacing of 1 m (FU), in furrows with incorporation of organic compost (FU+CO) or with incorporation of straw (FU+ST) is compared with subsoiling with Paraplow to a depth of 50 cm (PP) and with reduced tillage to a depth of 15 cm (RT) as a control treatment. The effects of subsoiling on physical soil properties, penetration resistance and soil moisture profile as well as on root growth (vertical distribution of root length density down to a depth of 90 cm) and crop yield are being investigated.

The results of the first four years of the trial have shown that soil loosening with Soil^3 technology improved the physical soil properties within the furrows, with the water holding capacity of the soil only being increased in the furrows with incorporated organic matter. Root growth was limited to the first 20 cm of soil depth in the control treatment and in the area between the furrows. In the furrows, root length increased uniformly up to a depth of 50 – 60 cm. Total root length and rooting depth was highest in furrows with compost. The incorporation of straw can inhibit root growth. The cultivation with the Paraplow also led to an even vertical root distribution up to a depth of 50 cm, but not to a greater total root length.

The net water removal from the furrows in treatments with Soil^3 technology, but also from the areas between the furrows, was up to 50 % higher than in the control treatment. However, significant furrow effects were observed in winter rye during prolonged drought, with emergency ripening occurring in the areas between furrows.

On average over the first four years of the field trial, subsoiling achieved a maximum yield increase of 0.8+0.1 t ha^-1 DM ha for winter rye in the "PP" treatment and 2.3 +1.4 t ha^-1 DM ha for silage maize in the "FU" treatment of the Soil^3 technology. Thus, loosening in furrows appears to be particularly effective for row crops.