Integration of Liquid Manure into Conservation Tillage Corn Systems

Intensive cultivation and chemical fertilizer application resulting from traditional management practices in southwestern Ontario, Canada, require high energy input and cause soil loss. Four field experiments were conducted over three years in four mixed farms under no-tillage and minimum tillage corn ( Zea mays L.) systems. The effects of fertilizer source and manure application timing, rate, and method on soil nutrient concentrations, corn grain yields, and groundwater nitrate concentrations were investigated. Three experiments included three basic treatments of fertilizer source: inorganic (chemical) fertilizer, liquid manure, and a combination of inorganic fertilizer and liquid manure. The other experiment included five treatments: pre-plant manure with and without incorporation by an aeration implement, side-dress manure with and without incorporation by a disc implement, and side-dress inorganic fertilizer. Soil samples (0-300 or 0-600 mm depth) for analysis of soil nitrate-nitrogen (NO 3 -N), phosphorus (P), and potassium (K) concentrations were taken periodically each year, including soil residual NO 3 -N concentrations measured in the fall after harvest. Weed biomass and corn grain yields were also measured. In general, higher NO 3 -N concentrations were observed in those plots where nitrogen sources had been applied shortly before soil sampling. Trends of residual NO 3 -N concentrations varied among experiments, and results were inconclusive. Two-fold higher P concentrations were observed in the manured plots than in the inorganically fertilized plots as a result of higher P 2 O 5 inputs from swine manure. Farmers who apply liquid manure to their no-tillage cornfields should be prepared for the possibility of additional weed pressure, especially using pre-plant manure application or side-dressing manure without a starter fertilizer. A 6% increased or comparative corn grain yield was achieved using liquid manure as a fertilizer source when weeds were not a problem. Considering the reduced risk of P runoff and the increased yield potential, the combined treatments, including pre-plant manure with side-dress inorganic fertilizer and starter fertilizer with side-dress manure, are recommended.