Alfalfa in rotation with annual crops reduced nitrate leaching potential
Arshdeep Singh, Tahseen Afzal, Bryan L. Woodbury, Charles S. Wortmann, Javed Iqbal
Abstract
Abstract Rotation of perennial alfalfa ( Medicago sativa L.) with annual crops has the potential to reduce nitrate‐nitrogen (NO 3 ‐N) in the vadose zone and increase soil organic carbon (SOC) sequestration. The objective of this study was to determine the long‐term effects on SOC, NO 3 ‐N, ammonium‐N (NH 4 ‐N), and soil water in the 7.2 m depth with an alfalfa rotation compared with continuous corn ( Zea mays L.). Soils from six pairs of alfalfa rotation versus continuous corn observation points were sampled to 7.2 m depth in 0.3 m increments. The uppermost 0.3 m was divided into 0–0.15 and 0.15–0.30 m. For the 0–7.2 m depth, the alfalfa rotation compared with continuous corn had 26% less soil water (0.29 vs. 0.39 g cm −3 ) and 55% less NO 3 ‐N (368 vs. 824 kg ha −1 ). The cropping system and NO 3 ‐N concentration did not affect NH 4 ‐N in the vadose zone. The alfalfa rotation compared with continuous corn had 47% higher SOC (105.96 Mg ha −1 vs. 72.12 Mg ha −1 ) and 23% higher total soil nitrogen (TSN) (11.99 Mg ha −1 vs. 9.73 Mg ha −1 ) in the 0–1.2 m depth. The greater depletion of soil water and NO 3 ‐N with alfalfa rotation was primarily below the rooting zone of corn, suggesting no negative implications for corn following alfalfa but greatly reduced potential of NO 3 ‐N leaching to the aquifer with the alfalfa rotation. Alfalfa rotation compared with continuous corn is a means to greatly reduce the leaching of NO 3 ‐N to the aquifer and improve the surface soil with the potential to increase SOC sequestration.