THE EFFECT OF ANHYDROUS AMMONIA APPLICATIONS ON THE SOLUBILITY OF SOIL ORGANIC CARBON

Abstract

The rapid increase in anhydrous ammonia use in Western Canada has created concerns about possible detrimental soil effects, particularly solubilization of organic matter. Anhydrous ammonia was injected at rates of 0.206, 0.416 and 0.834 g NH₃-N into undisturbed soils taken in 20-cm-diameter cylinders. Both field capacity (FC) and permanent wilting point (PWP) moisture contents were used. Samples were taken at 0–2.5, 2.5–5.0, 5.0–7.5 and 7.5–10.0 cm from the injection point, 1 day after injection. For the 0.416 g NH₃-N rate samples were also obtained 35 days after injection. Soluble organic carbon (SOC) was measured in a 1:15 soil:water extract. The SOC was closely related to the NH₄⁺-N concentration (r² = 0.79 to 0.99; P < 0.001). The SOC was increased by NH₃ at all injection rates for samples within 2.5 cm of injection point, at the highest rate for the 2.5- to 5.0-cm zone but there were few effects in the 5.0- to 7.5-cm zone and none in the 7.5- to 10.0-cm zone. The solubilized C was 0.3–4.6%, 0.0–3.0% and 0.0–0.6% of the total C in the 0- to 2.5–cm, 2.5- to 5.0-cm and 5.0- to 7.5-cm zones, respectively. The 0- to 2.5-cm, 2.5- to 5.0-cm and 5.0- to 7.5-cm zones represent 4.3, 13.1 and 21.8%, respectively, of the total soil volume. Thus carbon solubilized is insignificant when expressed on a total soil basis. Key words: Anhydrous ammonia, soil organic C, soluble organic C, soil deterioration