Changes in Biological and Chemical Soil Properties in an Austrian Long-Term Tillage Experiment

Conventional tillage, including ploughing after harvest and/or for seedbed preparation, aims to incorporate crop residues and weeds and to loosen, mix and aerate the soil. However, less beneficial effects, such as a loss of soil organic carbon (SOC), are also associated with intensive tillage. This has made reduced and minimum tillage systems without ploughing increasingly popular in agriculture, contributing to soil health and climate change mitigation. We studied the effects of different tillage systems on chemical and microbial soil properties in a long-term field experiment established on a fine-sandy loamy Haplic Chernozem in Fuchsenbigl, Austria, in 1988. The tillage treatments include conventional tillage (CT) with a plough and a cultivator down to 30 cm soil depth, reduced tillage (RT) with a cultivator down to 15 cm two to three times a year, as well as minimum tillage (MT) treated with a rotary driller once a year down to 5–8 cm soil depth. In 2016, a soil sampling campaign was conducted, and alkaline phosphatase, phospholipid fatty acids (PLFAs), and the nitrogen (N) mineralisation potential were analysed along with chemical properties including SOC, active C, total nitrogen (N_t), CAL extractable phosphorus (P_CAL) and potassium (K_CAL). Under MT, these properties were significantly higher compared to CT in 0–10 cm. In deeper soil layers, these parameters showed very few significant differences between the tillage treatments. RT yielded intermediate values but not always significantly different from CT. PLFA indicators significantly correlated with SOC and, even more distinctly, with N_t and active carbon. The high ratio of Gram-positive to Gram-negative bacteria indicates more recalcitrant organic matter in the top layer in MT than CT.