Acidity generated by N fertilizers depends on factors such as the composition of the fertilizer, climatic and soil conditions, and the crops grown. Our objective was to quantify the acidifying effects of urea and anhydrous NH3 when used as fertilizers for cereal production in Saskatchewan, Canada. The fertilizers were injected annually (at 10‐cm depth) into a medium‐textured, moderately acid (pH ≈5.5) Typic Haploboroll, at rates of 0, 45, 90, and 180 kg N ha−1 for 9 yr. Soil acidity increased as N application rate increased, with anhydrous NH3 causing greater acidification than urea. Although pH values as low as 4.3 were recorded in soil treated with anhydrous NH3, KCl‐exchangeable acidity remained low. The major effect of acidification was a depletion of exchangeable Ca and Mg. The solubility of Mn (but not Al) increased substantially as pH decreased, with solution concentrations of almost 30 mg Mn L−1 being recorded 6 d after injection of NH3. Acidity generated by anhydrous NH3 compared well with values predicted assuming that all of the applied NH3 was oxidized to NO3− (with the production of 1 mol H+ mol−1 of N) and that these protons were partly neutralized by OH− released when NO3− was taken up and assimilated by plants. Acidification due to export of bases in grain was insignificant because wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) remove only a slight excess of cations over anions. Urea failed to realize its full acidification potential because of an apparent loss of urea‐N from the soil by NH3 volatilization.
O. T. 1996. Soit microbial and biochemical properties after ten years of fertilization with urea and anhydrous ammonia. Can. J. Soil Sci. 76: 7-l4.The influence of nitrogen (N) fertilizers, eipecially anhydrous ammonia, on soil quility has been qr:estioned frequently by pro_ponents of organic farming uoO to* input sustainabie agriculture. A 10-yr experiment wis conducted on an Orthic Dark Brown Chernozemic loam, at Scott, Saskatchewan, to examine ih. influ.n.. of uiea and anhydrous ammonia, at rates of N up to I 80 kg ha-l' on yields of cer-eals and oilseeds. In the 10th yr, we sampled soil from the 0-to 7.5-and 7.5-to l5-cm depths of each treatment 3 d before and 6 and 26 d after fertilization to'aisess the impact of applied N on microbial populations and soil biochemical properties. The^long-term residual effects ofN fertilization on ioil properiies were evident prioitothe 1Oth annual N application. The short-term effects were most pronounced 6 d after the 1gth N application. Generally, effects were greater in the7.5-to 15-cm depth, where N was.placed. the s'oit, which was already acidic (pH ='5.2 in 0.01 M CaCl2), decreased in pH in proportion to N_rate and more so for anhydrous ammonia than urea. Geneially, fungal and bacterial populations (plate counts) were positively related to N rate and were greater in soil treated with anhydrouj imm6nia than in urea-treated soil. In contrast, the actinomycete population was inversely related to N rate and was less for anhydrous ammonia than for urea. Nitrifier counts were increased by low rates of N (added substrate) but were similar to the check at high N rates (high acidity). There were no significant effects of N treatment on denitrifiers or yeasts. In contrast to the plate coun-t results, *i.t6bial biomass decreased with increasing rates of N and was lower for anhydrous ammonia than for ur.u. fio*.u.., the authenticity of this response is questionable because the fumigation-incubation method of biomass determination is compromised under acid conditioni. Carbon mineralization was unaffected but N mineralization and nitrification tended to decrease at the 1 80 kg N ha-l rate of anhydrous ammonia. Significant nitriflication occurred at pH < 5.0 suggesting possible adaptation of nitrifiers in this acid soil. Wet aggregate stability (WAS) was ulgffecled by N treatments. We conItua"ittrut, if producers in the Dark Brown soil zone apply fertilizirs at rates less than 90 kg N hr', deterioration of soil quality should be minimal.
UKRAINETZ, H. aNo CarvrpnlLL, C. A. 1988. N and P fertilization of bromegrass in the Dark Brown soil zone of Saskatchewan. Can J. Plant Sci. 68: 457-470. A 5-yr study was conducted on a Dark Brown Ioam at Scott, Saskatchewan to determine the effect of rate of ammonium nitrate-N (34-0-0) and urea-N (46-0-0) on bromegrass (Bromus inermis Leyss.) production and quality, N recovery and N use efficiency when the N was applied either annually or as a single application at the start of the experiment. The effect of phosphorus (P) on the above listed parameters was also assessed. Each N source was applied at once-only rates of 0, 100, 200, 400, and 800 kg ha-t and annual rates were 0, 50, 100 and 200 kg ha-r. Phosphorus was applied in 1976, 1979 and 1981 at 100 kg ha-r P2O5. Forage dry matter was positively related to precipitation received in April-June (r:0.91**) and in April of the crop year plus the previous September (r:0.80**). Dry matter response to N rates generally increased at a decreasing rate in early years but linearly in later years. Over the first 4 yr, annual applications of N resulted in up to 31% more dry matter than the single applications. Dry matter production was generally greater when ammonium nitrate was applied than when urea was used; these differences were more consistent at medium N rates-Dry matter was increased by P only when N was applied. Nitrogen concentration in forage was directly related to N rate in years ofgood precipitation, was greater in dry than wet years, and when N was applied annually, but was unaffected by N source. Phosphorus fertilization increased P concentration of forage but heavy dry matter production reduced P concentration. Annual N applications increased P concentration in forage only in the first year and N source had no effect. Toxic concentrations of NO3-N in the forage occurred in the first year only at N rates > 200 kg ha-r and were directly related to the amount of N applied. Except for the 800 kg ha I N rate in the second year, there were no further indications of NO3-N toxicity. Accumulated N use efficiency decreased linearly with increasing N rate and was greater for ammonium nitrate than for urea except at very high N rates. Accumulated N recovery was inversely related to N rate for the single method of application but unaffected by N rate applied annually. Over the first 4 yr, accumulated N recovery was greater for the single application at low N rates, but was greater for annual applications of N at high N rates. P fertilization increased N recovery.
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