Nitrate-N in the soil profile and tile drainage water as influenced by tillage

Conservation tillage systems facilitate the infiltration of greater amounts of precipitation into the soil profile by reducing surface runoff. Concern has developed among some scientists because higher infiltration and percolation rates are often linked to potentially higher leaching losses of agricultural chemicals. Soil samples were taken in 1 foot increments to a depth of 5 feet to ascertain the accumulation and distribution of nitrate-nitrogen (NO3-N) in the soil profile as influenced by tillage. Two long-term tillage studies on fine-textured, clay loam soils were sampled in July and November 1977 following 2 years of limited rainfall. Nitrate-N accumulation in the 0 to 3 foot profile in late July was reduced by 75% (no tillage) to 38% (chisel plow) compared with the conventional moldboard tillage system in this 8-year-old study. Accumulation in the 0 to 5 foot profile after harvest was 751, 546, 345, and 198 lb NO3-N/A for the moldboard plow, chisel-plow, disk-, and no-tillage systems, respectively. Another 3 year study showed accumulations of 625, 619, 468, and 391 pounds NO3-N/A after harvest with the moldboard plow, ridge-plant, chisel-plow, and no-tillage systems, respectively. These data indicate that tillage can have substantial effects on the accumulation of NO3 in soils and that additional research is needed to determine the mechanisms responsible for these differences.