Reduced tillage effects on soil properties and growth of cereals and associated weeds under organic farming

In organic farming, reduced tillage is often avoided because of potentially negative consequences for crops and weeds. On an experimental organic farm in Germany, we studied during three years the effects of the three tillage systems mouldboard ploughing (MP, inversion to 30 cm depth), two layer ploughing (TP, inversion to 15 cm, loosening to 30 cm) and layer cultivation (LC, only loosening to 30 cm) on soil properties, root and shoot growth of barley and rye and their associated weeds. The different tillage systems were applied for five consecutive years prior to the initiation of the current study within a five-course crop rotation consisting of green fallows, peas and cereals. During the current investigation, different tillage systems were applied after cereal harvests only resulting in different time periods between tillage and seeding for barley and rye. Generally, differences between tillage systems were most pronounced between LC and MP or TP while effects of MP and TP were similar. Soil aggregate stability under both crops was on average 46% and 18% higher at LC than at MP and TP, respectively. Soil penetration resistance under barley was on average 199% higher at LC than at MP (p = 0.012); under rye tillage systems had no effect on penetration resistance. Soil respiration was unaffected by tillage systems under both crops. Root length density (RLD) under barley was in the first two years 50% higher at MP than at LC in 20–30 cm soil depth; in the third year 32% higher under TP than MP or LC in the upper soil horizons. RLD under rye was unaffected by tillage treatments. Barley shoot mass was 38% lower at LC and 24% lower at TP than at MP (p = 0.044), rye shoot mass was in two years not influenced (p = 0.58). Weed shoot mass in barley was across years 88% and 65% higher at LC than at MP and TP, respectively; under rye no clear influence of tillage systems on weed shoot mass was observed. Experimental years differed considerably regarding annual precipitation and mean air temperatures and significantly influenced all parameters measured, however did not interact with the tillage treatments for most parameters.