The effects of forage grasses and legumes on subsequent potato yield, nitrogen cycling, and soil properties

Abstract

To balance economic potato production with environmental risks, it is crucial to understand the effects of forage crops preceding potatoes on soil nitrate (NO 3 - ) leaching potential, soil quality and potato yield. This study compared a legume forage (red clover, RC), a grass forage (timothy, T), and a red clover-timothy mixture (M) over two cycles of a 3-yr rotation (barley underseeded with forage-forage-potato) from 2013 to 2018. The forage crops were grown under low input maintenance system receiving only starter N fertilizer during the establishment year. Legume-based forages (i.e., RC and M) had greater dry matter accumulation and lower C:N ratio, and therefore added a greater quantity and quality of organic matter inputs to the soil compared with the grass-based forage (T). This resulted in increased soil N supply to the subsequent potato crop, and improved soil quality as indicated by increased aggregate stability, permanganate oxidizable carbon (POX-C), autoclaved citrate extractable soil protein (ACE), and flush of CO 2 upon rewetting a dried soil for legume- than grass-based forages. Under N limited conditions (i.e., no N fertilizer applied) forage legumes were associated with higher potato yield than forage grass. However, tuber yield was not increased when N fertilizer was applied, a finding attributed to a better synchrony between potato N uptake and soil N supply in the presence of N fertilizer with the forage grass treatment. The legume-based forages improved soil quality, increased soil N supply as well as NO 3 - leaching losses. Results of this study suggest that there may be a trade-off between selecting forage crops to reduce NO 3 - leaching and to enhance soil quality. • Compared forage legumes and grasses on soil quality, N cycling, and potato yield. • Soil quality improved, soil N supply and nitrate leaching increased with legumes. • Higher potato yield with legumes than grasses only under N limiting conditions. • Trends towards higher potato yield with forage grasses with N fertilizer applied. • Trade-offs between improving soil quality and potato yield and reducing N leaching.