Fertilizer, Tillage, and Dairy Manure Contributions to Nitrate and Herbicide Leaching

Few studies have examined the water quality impact of manure use in no‐tillage systems. A lysimeter study in continuous corn ( Zea mays L.) was performed on Maury silt loam (fine, mixed, semiactive, mesic Typic Paleudalf) to evaluate the effect(s) of tillage (no‐till [NT] and chisel‐disk [CD]), nitrogen fertilizer rate (0 and 168 kg N ha −1 ), and dairy manure application timing (none, spring, fall, or fall plus spring) on NO 3 –N, atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐ s ‐triazine), and alachlor [2‐chloro‐2′‐6′‐diethyl‐ N ‐(methoxymethyl)acetanilide] concentrations in leachate collected at a 90‐cm depth. Herbicides were highest immediately after application, declining to less than 4 μg L −1 in about two months. Manure and manure timing by tillage interactions had little effect on leachate herbicides; rather, the data suggest that macropores rapidly transmitted atrazine and alachlor through the soil. Tillage usually did not significantly affect leachate NO 3 –N, but no‐tillage tended to cause higher NO 3 –N. Manuring caused higher NO 3 –N concentrations; spring manuring had more impact than fall, but fall manure contained about 78% of the N found in spring manure. Nitrate under spring “only fertilizer” treatment exceeded 10 mg L −1 38% of the time, compared with 15% for spring only manure treatment. After three years, manured soil leachate NO 3 –N exceeded that for soil receiving only N fertilizer. Soil profile (90 cm) NO 3 –N after corn harvest exceeding 22 kg N ha −1 was associated with winter leachate NO 3 –N greater than 10 mg N L −1 Manure can be used effectively in conservation tillage systems on this and similar soils. Accounting for all N inputs, including previous manure applications, will be important.