Biological soil quality and soil organic carbon change in biodynamic, organic, and conventional farming systems after 42 years

Abstract

Soils are the basis of life on land and the ways in which we manage them for crop production, impact their role, functions and quality. Conventional farming uses industrial inputs to a level that is economically justified, whilst organic farming systems avoid mineral fertilizers and synthetic chemical pesticides. This study investigates the long-term effect of organic and conventional farming systems on soil quality. The DOK trial (bioDynamic, bioOrganic, Konventionell (German for conventional)) running since 1978 in Therwil (CH), compares bioorganic (BIOORG), biodynamic (BIODYN), and conventional (CONFYM) farming systems at two farmyard manure intensities corresponding to 0.7 and 1.4 livestock units per hectare with a purely mineral fertilized system (CONMIN) and an unfertilized control (NOFERT). The treatments in the DOK trial vary in plant protection and receive system-specific organic matter inputs differing in rate and quality. With this work, we revisit the soil organic carbon (SOC) dynamics across 42 years and redefine the previous perception of mainly declining SOC contents after 21 years of organic and conventional management (Fliessbach et al. 2007). After 42 years, we found SOC contents to be increased in BIODYN 1.4 and to a lesser extent also in BIOORG 1.4. CONFYM 1.4 showed stable SOC contents, while systems fertilized with manure of 0.7 livestock units and CONMIN lost SOC. SOC loss was highest in NOFERT. Enhanced biological soil quality under organic and particularly biodynamic management highlights the close link between soil biology and SOC changes. The impact of farming systems on SOC was detectable after 2 decades of continuous management. We conclude that recycling manure at a level of 1.4 livestock units per hectare permits maintenance of SOC levels and that composting manure, as performed in BIODYN 1.4, helps to further increase SOC levels and improve biological soil quality.

Microbial resistance and resilience to drought under organic and conventional farming

“…Moreover, microbial communities were similarly affected by drought in all cropping systems. Hence, we found no clear indication that the application of composted or stacked manure in BIODYN and CONFYM, the associated increase in SOC [29] and microbial diversity [25], the reduction of pesticide application, or other factors like the biodynamic preparations in BIODYN could increase microbial resistance to drought. Additionally, this long-term field trial already includes some regenerative practices such as shallow tillage, cover cropping, and incorporation of grass-clover into the crop rotation in all cropping systems.…”

“…An on-field drought simulation experiment was conducted in the long-term DOK trial, which has been described in more detail by Krause et al (2022) [29]. Briefly, the field site is located on a haplic luvisol in Therwil, Switzerland (47°30'9.48"N, 7°32 '22.02"E).…”

“…The trial compares five different organic and conventional cropping systems differing in fertilization and pesticide management since 1978. The average annual precipitation at this field site is 840 mm and the mean annual temperature is currently around 11 °C [29].…”

“…Systems receiving organic amendments generally show higher soil microbial biomass, enzyme activity, microbial diversity, and activity [25,27,28]. Higher soil organic carbon (SOC) contents have been reported in organic cropping systems due to manure application, revealing higher SOC contents in systems receiving composted manure compared to stacked manure [29]. Increased SOC is considered to increase soil aggregation, porosity, and water retention [30].…”

Long‐term organic management: Mitigating land use intensity drawbacks and enhancing soil microbial redundancy

“…Indeed, the enhancement, or at least the maintenance, of soil fertility is one of the pivotal benefits of organic farming systems (Barnwal et al., 2021). Soils under organic farming systems usually exhibit better quality and higher biological activity than conventional farming systems (Krause et al., 2022). The soil manuring considerably stimulates microbial biomass and activity by improving soil chemico‐physical properties and supplying easily assimilable C and nitrogen (N) sources (Ferreira et al., 2021; Ren et al., 2019).…”