Cover crops and tillage effects on carbon–nitrogen pools: A lysimeter study

Cover crops (CCs) and tillage practices influence C and N pools in soil, which can affect dissolved organic C (DOC) and N leaching from agricultural fields. Previous studies on cover crops have focused mostly on nitrate leaching and total C (TC). Therefore, a study was conducted in southern Illinois from 2015 to 2018 to evaluate the effects of tillage systems (conventional till [CT] and no-tillage [NT]) and CCs on C and N pools including water-extractable C (WEC), permanganate oxidizable C (POXC), TC, water-extractable N (WEN), and total N (TN) in soil and on TN and DOC leaching collected with zero-tension lysimeters. Crop rotations included were corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation without winter CC (C–S), corn–cereal rye (Secale cereale L.)–soybean–hairy vetch (Vicia villosa Roth) (C–R–S–HV), corn–cereal rye–soybean–oat + radish (Avena sativa L.+ Raphanus sativus L.) (C–R–S–OR). The WEC decreased over time under CT system at a depth to 0–15 cm in rotation C–R–S–OR having cereal rye and oat+radish CCs. The POXC at depths of 15–30 and 30–45 cm increased significantly over time from fall 2015 to spring 2018 for all rotations under both tillage systems. The cumulative DOC leaching was greater in C–R–S–HV rotation than in C–S rotation in fall 2015 and spring 2018. Inclusion of cereal rye in C–R–S–HV and C–R–S–OR rotations reduced cumulative TN leaching compared with the C–S having no CC in spring 2018. Increased DOC leaching losses with the introduction of CC should be addressed and need further evaluation for its impact on C cycling in surface and subsurface waters.