Crop production and environmental performance in organic and conventional farming systems. Results from a 42 years old field experiment

Abstract

Agricultural systems put severe pressure on the environment, and management practices balancing the need for agricultural production and environmental health are urgently needed. Key environmental challenges for agricultural systems include the reduction of nutrient losses, the mitigation of greenhouse gas emissions and the preservation of soil biodiversity. Organic farming systems are proposed as environmentally friendly alternative to conventional systems due to their focus on long-term soil quality, but often show lower yields. Long-term field trials are the backbone to assess the impact of farming systems on agronomic and environmental parameters. In this study we present the results from a 42-year-old field trial (DOK trial), located in Therwil, CH on key agronomic and environmental parameters. The trial compares two organic (BIODYN, BIOORG) and two conventional (CONFYM, CONMIN) farming systems with an unfertilized control (NOFERT) and follows a system comparison approach. Farming systems mainly differ in plant protection and fertilization strategy but follow the same tillage strategy and 7-year crop rotation. CONFYM receives the highest external inputs in terms of nutrients and chemical plant protection followed by CONMIN, BIOORG, and BIODYN. Across the five main crops, (grass-clover, wheat, potato, maize, and soybean) organic farming systems maintained yields at ~85% of conventional systems with distinct differences between legume and non-legume crops. Farming systems receiving organic inputs at a rate of 1.4 livestock units per hectare and year stabilized (BIOORG, CONFYM) or even enhanced (BIODYN) soil organic carbon and nitrogen stocks. Yet, soil organic carbon and nitrogen contents evolved slowly and differences became statistically significant only after 22 years. All fertilized farming systems showed a positive nitrogen balance when nitrogen fixation via legumes was included. Still purely mineral fertilized (CONMIN) and unfertilized (NOFERT) systems lost soil organic carbon and nitrogen on the long term. Organic farming systems significantly reduced soil borne climate impacts, which was rather driven by nitrous oxide emissions than by changes in soil organic carbon contents. Higher richness of soil fauna, and weed population was observed in organic farming systems, next to enhanced biological soil quality indicators. The functional potential of the soil microbiome showed a gradual change from organic (BIODYN, BIOORG) to conventional (CONFYM, CONMIN) systems highlighting the impact of farming systems on soil functions With the present study, we could show that with moderate yields gaps organic farming systems can reduce pressure on the environment by enhancing soil functionality for critical ecosystem services