The University of Arizona

Macronutrients in soil and bromegrass after long-term N fertilization

J. T. Harapiak, S. S. Malhi, K. S. Gill, N. Flore


Information on the long-term impact of repeated annual fertilizer applications of different nitrogen (N) sources on soil and plants is needed to develop sustainable grassland production systems. The concentration of macronutrients in the 0–5, 5–10, 10–15, 15–30, 30–60, 60–90 and 90–120 cm layers in a thin Black Chernozemic (Typic Boroll) soil and in bromegrass (Bromus inermis Leyss.) hay were compared after 15 annual applications of 168 and 336 kg N ha−1 as ammonium nitrate, urea, calcium nitrate, and ammonium sulphate, and a zero-N check. The concentration of NO3-N was increased by ammonium nitrate and ammonium sulphate at both N rates in most soil layers, by calcium nitrate at both N rates and by urea at 336 kg N ha−1 in the 15–60 cm soil. The accumulation of NO3-N increased with soil depth down to 60 cm, except for urea and ammonium sulphate at 168 kg N ha−1, and then it declined in deeper soil layers. The concentration of NH4-N was increased with fertilizer applications in some of the surface soil layers. The concentration of P was increased in the top 15 cm soil by ammonium nitrate and ammonium sulphate. The concentrations of Ca, Mg and K in the surface soil declined with most of the N fertilizer treatments while some treatments increased the Ca and Mg concentrations in the deeper soil layers. Increasing the N rate from 168 to 336 kg N ha−1 usually accentuated the above stated N effects on the concentration of macronutrients in the soil. The nitrate-based fertilizers caused more accumulation of NO3-N in some soil layers than the ammonium-based fertilizers. The relative increase in the concentration of NH4-N and P and the decline in the concentration of Ca, Mg and K in the soil by N addition was usually associated with the concomitant lowering of soil pH by N fertilization. In bromegrass hay, the total N concentration was increased by N fertilization but the concentration of other elements, except K, usually declined because of the dilution effect of the extra hay yield associated with N addition. Increasing the N rate from 168 to 336 kg N ha−1 further elevated the total N concentration but had no effect on the concentration of the other elements. Total N concentration in the hay tended to be greater with ammonium sulphate and ammonium nitrate than with the other 2 fertilizers. The concentration of total S was greater with ammonium sulphate than the other N fertilizers, and the concentration of P, Ca, Mg and K was not affected by the N fertilizer type. Fertilizer-induced high levels of NO3-N, NH4-N and P in soil may present potential for environmental pollution at these high N rates.



concentration; forage; N source; rate of N

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