Changes in Soil Test Phosphorus and Phosphorus in Runoff From Calcareous Soils Receiving Manure, Compost, and Fertilizer Application With and Without Alum

Intensification of the dairy industry in southern Idaho has led to the overapplication of manures and a buildup of soil phosphorus (P), which is a potential threat to water quality in the region. As the use of alum has been shown to reduce both soluble manure P and runoff P from alum-treated manures, the objective of this study was to determine if surface applications of alum to dairy manure and compost before soil incorporation would reduce P losses under furrow irrigation on a calcareous soil. The effects of manure, compost, and fertilizer application with and without alum treatment on soil P, runoff'P; and aluminum under furrow irrigation, crop yield, tissue P concentrations, and P removal during a 4-year period were investigated in Kimberly, Idaho, on a Portneuf silt loam (coarse-silty, mixed superactive, mesic Durinodic Xeric Haplocalcids). Fertilizer and manure addition had the greatest potential to increase soluble P in soils compared with compost, which translated to greater soluble P losses with irrigation in some instances. The addition of alum to manure did not have any effect on soilextractable P or soluble P losses from furrow irrigation and therefore, when surface applied to manure before incorporation, is not a good best management practice for stabilizing P in manure-treated calcareous soils.