Phosphorus movement and adsorption in a soil receiving long-term manure and fertilizer application

Long-term experiments offer unique possibilities to study time-dependent effects of management practices on crops and soils. Phosphorus movement in soil resulting from long-term manure and fertilizer application are an environmental concern when P reaches ground or surface waters. A long-term cropping-systems study was started in 1912 in western Nebraska. In 1953, each plot was divided into manure (27 Mg ha(-1) annually) and no manure sections to which fertilizer treatments of 0, 45, 90, 135, 180 kg N ha(-1), and 135 kg N ha(-1) + 80 kg P ha(-1) were applied annually and continuous corn (Zea mays L.) was grown under irrigation. Soil samples were collected to a depth of 1.8 m in 1993 from seven depth increments and analyzed for plant-available P, adsorption characteristics using the Langmuir isotherm, and adsorption index. Available P concentrations to a soil depth of 1.8 m were greater with manure application than without manure. In the no-manure plots, little fertilizer P moved beneath the 1.1-m soil depth, the maximal depth of the calcium carbonate layer in this soil. Phosphorus adsorption maximum and index were unrelated to P movement. At about similar P loading rates, P from manure application moved deeper in the soil than P from fertilizer. Possible explanations are that P from manure moved in organic forms, or chemical reactions of P occurred with compounds in manure, which may have enhanced P solubility. Phosphorus from long-term manure or fertilizer application and from heavy loading of manure can leach into groundwater in areas with shallow water tables or coarse-textured soils.