Synergy of biochar rate and no-tillage and its effects on field-grown onion nutrition and yield

Combining cover crops and biochar is an efficient strategy that can synergistically improve nutrition and increase onion yield and resilience to the dry season. This study aimed to evaluate onion yield and nutrition in two cultivation systems: one bare soil with biochar application (without cover plants) and another under no-tillage, both with increasing biochar rates. Two field experiments were carried out with growing onion in a Humic Dystrudepts treated with a single biochar application only in 2016. Over three years (2016, 2017, and 2018), onion was cultivated without cover crops with biochar (bare soil) and under no-tillage with biochar (NTS). In both experiments, increasing biochar rates of 0, 5, 10, 20, 40, 80, and 100 t ha⁻¹ were added to the soil only in the first year of onion cultivation. Besides yield, nutrient uptake (N, P, K, S, Ca, Mg, B, Cu, Fe, and Zn) was evaluated in both the onion bulb and the whole plant (shoot + bulb). In 2017, the onion yield in the no-tillage (NTS) experiment showed a linear response to increasing biochar rates. In contrast, in the bare soil experiment, onion yield exhibited a quadratic response to biochar application, with the optimal biochar rate being 53.2 t ha⁻¹. In general, nutrient uptake by both the bulb and the whole plant was higher in the NTS experiment with increasing biochar rates compared to the bare soil experiment, where biochar was applied without cover crops.