A field trial study on long-term effects of organic farming on the retention of plant available soil water

With regard to an increasing intensity and frequency of drought and heavy rainfall, there is a need to adapt arable farming to these climatic changes. In this respect, organic agriculture has a higher adaptation potential than conventional agriculture, since organic farming leads to an enrichment of soil organic carbon and a stimulation of soil biological activity in the long term. As a result, an improvement of soil structure, water infiltration and soil water retention can be expected as compared to conventional agriculture.

In April 2023, a study of soil hydraulic properties after 15 years of recognised organic management was commenced in the Czech Republic. The objective is to compare an organic farming system to a conventional farming system in terms of retention of plant available soil water. The hypothesis is that the retention of plant available soil water is higher in the organic farming system than in the conventional farming system.

The studied site is a long-term field trial on a clay loam soil in Praha-Uhříněves (P = 584 mm, T = 8.3 °C). In either farming system inversion soil tillage is carried out by mouldboard ploughing to a depth of 20 cm. For either farming system two plots with summer wheat (Triticum aestivum L.) are sampled in 2023 and 2024. In order to analyse soil water retention functions, saturated hydraulic conductivity, and soil organic carbon content, soil samples are taken in 10 cm and 30 cm soil depth each year in spring, summer, and autumn. In order to unravel the sources of plant available water, further soil samples are taken bimonthly in 10 cm, 30 cm, and 45 cm soil depth. The soil water’s isotopic composition (δ²H, δ¹⁸O) of these samples is analysed and compared to the rainwater’s isotopic composition. The volumetric soil water content is continuously recorded in 10 cm, 30 cm, and 45 cm soil depth.

Preliminary data from the first experimental year indicate that the volumetric soil water content in the organic farming system is higher than in the conventional farming system. In contrast, soil water retention and soil organic carbon content do not show differences between the two systems. However, for robust results with statistical validation, further data and analyses need to be waited for. Therefore, reliable conclusions regarding the hypothesis of a better retention of plant available soil water in the organic system will be possible in the course of the project.

This project is funded by the institutional support of the Czech Academy of Sciences (RVO: 67985874) and by the Faculty of Environmental Sciences of the Czech University of Life Sciences Prague (IGA grant No. 2023B0042).