Impact of tillage, cover crop, and in situ bioreactors on nutrient loss from an artificially drained Midwestern Mollisol

Nutrient losses via subsurface tile cause environmental degradation of aquatic ecosystems. Various management practices are primarily aimed at reduction of nitrate leaching in tile discharge; however, studies on leaching of other nutrients are limited. A replicated plot experiment was initiated in 2016 as part of the Long-Term Agroecosystem Research (LTAR) network Croplands Common Experiment to quantify the effectiveness of management practices on leaching of NO₃-N, total P, K, and S from drained soils. Corn (Zea mays L.) and soybean (Glycine max L. Merr.) were grown under five different treatments: (1) BP: basic practice with fall chisel plow; (2) NT: no-till crop production; (3) RC: no-till with a winter rye (Secale cereale L.) cover crop; (4) DW: no-till with woodchip denitrification walls parallel to both sides of the tile; and (5) ZN: zero N; no-till without N fertilization. Compared to BP, both RC and DW treatments reduced NO₃-N load by 63% and 47%, respectively; 15.5, 5.8, and 8.2 kg N ha^-1 year^-1, while omitting N fertilization did not impact N loads (12 kg N ha^-1 year^-1). The DW resulted in greater K loss compared to BP, presumably due to decomposing woodchips. No-till practices increased drainage flow and K and P loads compared to conventionally tilled BP plots but had no impact on other nutrients. The BP produced the highest corn yield, whereas soybean yields were not affected by treatments. These findings indicate that while some conservation practices are effective in reducing nutrient leaching, others are likely to increase their loss and reduce crop yields.