Tillage intensity influences nitrogen cycling in organic kura clover living mulch

Abstract

Perennial cover crops, also known as living mulches, have the capacity to improve soil quality, yet their effects on nitrogen (N) cycling and provisioning in organic systems are not well understood. We evaluated soil N contributions of kura clover (Trifolium ambiguum) between and within crop rows for four zone tillage approaches of varying intensity for corn (Zea mays). In 2015 and 2016, an established kura clover field was subjected to tillage treatments including no-till, traditional shank till, also known as strip-till (ST), novel, PTO-driven rotary zone till (ZT), and a combination of ST and ZT (DT; double till) in Rosemount, MN, followed by corn. An earlier planting date in 2015 (May 5, 2015 vs. May 18, 2016) contributed to a substantially lower rate of kura clover biomass at corn planting in 2015 (518 kg ha−1) compared to 2016 (3035 kg ha−1). The substantial difference in kura clover biomass contributions at tillage and planting between years appeared to govern N cycling indicators. For instance, soil inorganic N differed by tillage treatments only in 2016. After tillage, within row soil inorganic N was 68% and 106% greater than between rows for ST and DT treatments, respectively. At harvest, DT within row soil inorganic N was approximately double that of ST. We conclude that the N benefit from a legume living mulch depends on both the intensity of tillage and the amount of biomass present, and thus there may be advantages to delayed planting, particularly when used for organic production.