PHOSPHORUS MOVEMENT AND ADSORPTION IN A SOIL RECEIVING LONG-TERM MANURE AND FERTILIZER APPLICATION

Long-term experiments offer unique possibilities to study time-depende nt effects of management practices on crops and soils. Phosphorus move ment in soil resulting from long-term manure and fertilizer applicatio n are an environmental concern when P reaches ground or surface waters . A long-term cropping-systems study was started in 1912 in western Ne braska. In 1953, each plot was divided into manure (27 Mg ha(-1) annua lly) and no manure sections to which fertilizer treatments of 0, 45, 9 0, 135, 180 kg N ha(-1), and 135 kg N ha(-1) + 80 kg P ha(-1) were app lied annually and continuous corn (Zea mays L.) was grown under irriga tion. Soil samples were collected to a depth of 1.8 m in 1993 from sev en depth increments and analyzed for plant-available P, adsorption cha racteristics using the Langmuir isotherm, and adsorption index. Availa ble P concentrations to a soil depth of 1.8 m were greater with manure application than without manure. In the no-manure plots, little ferti lizer P moved beneath the 1.1-m soil depth, the maximal depth of the c alcium 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 fertil izer. Possible explanations are that P from manure moved in organic fo rms, or chemical reactions of P occurred with compounds in manure, whi ch may have enhanced P solubility. Phosphorus from long-term manure or fertilizer application and from heavy loading of manure can leach int o groundwater in areas with shallow water tables or coarse-textured so ils.