NITROGEN FRACTIONS IN A GRAY WOODED SOIL AS INFLUENCED BY LONG-TERM CROPPING SYSTEMS AND FERTILIZERS

Abstract

A study was undertaken to determine long-term effects of two cropping systems and various fertilizer treatments on the distribution of N in a Gray Wooded soil of Alberta. The relative amount (expressed as percent of total soil N) of total acid hydrolyzable N in soils from plots in the five-year rotation of grains and legumes was significantly greater than in the wheat-fallow sequence. A similar effect was also noted from the proportion of soil N present in the form of amino sugar N, amino acid N, hydroxyamino acid N and unidentified N in the acid hydrolyzates. The relative amounts of ammonium N in the acid hydrolyzate, the non-hydrolyzable N and the non-exchangeable ammonium N in soil were greater in the wheat-fallow plot soils than in the rotation. The relative amount of total hydrolyzable N was significantly lower in the manure, NPKS, NS, lime or P treated soils than in the control. The proportion of amino sugar N increased following the manure treatment. Long-term application of mineral fertilizers had no significant effect upon the percentage distribution of the different forms of hydrolyzable soil N and the non-exchangeable ammonium N in the soil. The relative distribution of amino acids was not affected by the two cropping systems or various fertilizer treatments, but differences were noted in the absolute amounts.