Effects of tillage on the root length and depth distribution of stubble cover crops

Tillage after the main crop is harvested may impact the growth of roots of the successive stubble cover crops (CCs). A three-year field experiment was conducted at the warm and dry Ruzyně and cold and wet Lukavec sites from 2021 to 2023. The root length density (RLD) to a depth of 60 cm was determined for seven variants of CCs, namely, two single species and five mixtures of two species: white mustard (Sinapis alba L.), phacelia (Phacelia tanacetifolia, Benth.), clover (Trifolium alexandrinum L.) and camelina (Camelina sativa (L.) Crantz), cannabis (Cannabis sativa L.) and setaria (Setaria italica (L.) Beauv.), buckwheat (Fagopyrum esculentum Moench) and phacelia, buckwheat and mustard, and oats (Avena sativa L.) and vetch (Vicia sativa L.). Two types of tillage, namely, mouldboard ploughing (PLO) and reduced shallow tillage (RET), were examined. Tillage did not significantly influence the RLD of the surface or subsoil layers or the average RLD of the 0-60 cm layer at either site, but the impact of tillage on the RLD interacted with CC variant. Reduced tillage decreased the RLD of the 0-60 cm layer by 0.25 cm cm^-3 on average in mustard, phacelia, and the mixture of buckwheat and phacelia and increased it by 0.24 cm cm^-3 in the other variants at Ruzyně. At Lukavec, RET decreased the RLD by 0.23 cm cm^-3 in phacelia and mixtures of cannabis and setaria, buckwheat and phacelia, and mustard and oats, whereas the increase in the other variants was negligible (0.06 cm cm^-3). The CC variants significantly affected the RLD of the 0-60 cm and 0-10 cm layers at both sites and in both tillage treatments, whereas this effect was not confirmed in the subsoil layer. The average RLD of 0-60 cm zone of the mixture of oats and vetch was greatest in both tillage treatments and at both sites (1.55-2.09 cm cm^-3), followed by that of mustard (1.20-1.68 cm cm^-3) and the mixture of buckwheat and mustard (1.05-1.51 cm cm^-3). Reduced tillage increased the proportion of the root length in the top 30 cm layer by 3.81% and 3.58% on average at Ruzyně and Lukavec, respectively, and slightly reduced it in the subsoil layer at both sites. At both sites, the aboveground dry mass of CCs corresponded significantly with the RLD of the 0-60 cm layer and the subsoil layer (40-50 and 50-60 cm) under PLO. The observed differences in the root density and distribution of CCs, as well as their responses to tillage, could be important for the uptake of limited resources, water, and nutrients and should be considered when designing CC mixtures.