LONG-TERM N FERTILIZATION OF A SOLONETZIC SOIL - EFFECTS ON CHEMICAL AND BIOLOGICAL PROPERTIES

A field experiment was conducted at Vegreville (east-central Alberta) to determine the residual effect of various amounts of fertilizer N on chemical and biological properties of a Solonetzic soil. The experiment was established in 1961 and soil samples were taken in 1986. Five fertilizer treatments were applied from 1961 to 1978: 0, 76, 152 and 305 kg N ha-1 as ammonium nitrate (AN) and 74 kg N ha-1 plus 139 kg P ha-1 as monoammonium phosphate (MAP). Nitrogen fertilization with AN depressed the pH of the Ap horizon from 5.7 in the unfertilized N treatment to 4.2 with 305 kg N ha-1 and this acidification effect was more pronounced with MAP than at the equivalent rate of N with AN. Fertilizer N caused a significant decrease in extractable Mg in the Ap horizon. There was a trend towards sodium adsorption ratio (SAR), soluble Na, and extractable Na and Ca, with applied N. Microbial biomass C and N, and thc amount of mineralizable C and N decreased with N fertilization, with the lowest values at the highest rates of fertilizer application. However, total soil organic carbon and soil organic N increased with N application.