Subsoil water nitrate and phosphate dynamics in an organic integrated crop–livestock rotation system

Organic integrated crop–livestock systems (ICLSs) can improve nutrient cycling and soil cover, but subsurface nutrient dynamics in organic rotations that include small ruminants remain poorly characterized. This study evaluated nitrate–N (NO 3 –N) and phosphate–phosphorus (PO 4 –P) concentrations in subsoil water from a certified‐organic corn–soybean–goat pasture rotation in central Kentucky. Subsoil water was monitored at 1‐m depth for 5 years under seven treatments arranged in a randomized complete block design: corn–soybean no‐pasture treatment (CNP), ungrazed perennial pasture (PP), two crop phases (rotation corn phase [CS1] and rotation soybean phase [CS2]), and three goat‐grazed pasture phases (P1 [first‐year goat‐grazed pasture], P2 [second‐year goat‐grazed pasture], and P3 [third‐year goat‐grazed pasture]). NO 3 –N showed significant treatment, year, and treatment × year effects. Five‐year mean NO 3 –N ranged from 6.8 mg L − 1 in PP to 21.1 mg L − 1 in P3, with significantly high concentrations in CNP (19.4 mg L − 1 ). Peak seasonal NO 3 –N concentrations occurred mainly during annual crop phases and pasture‐to‐crop transition periods, whereas PP and early pasture phases generally maintained lower concentrations under continuous vegetative cover. Managed goat grazing did not consistently increase NO 3 –N relative to the ungrazed pasture. PO 4 –P responses differed from NO 3 –N, with a strong year effect but limited treatment separation. Five‐year mean PO 4 –P ranged from 0.6 mg L − 1 in CNP to 1.1 mg L − 1 in PP. Overall, maintaining continuous cover, minimizing soil disturbance during rotation transitions, and managing grazing to preserve vegetation may reduce nutrient movement into subsoil water in an organic ICLS.