Influence of soil pH on NO_xand N₂O emissions from bovine urine applied to soil columns

Abstract

The nitrous oxide (N 2 O) molecule is both a greenhouse gas and a precursor to the formation of nitric oxide (NO) in the stratosphere, which is subsequently involved in catalytic destruction of ozone (O 3 ). Tropospheric NO can form NO 2 with both gases (NO x ) able to react with volatile organic compounds to produce the detrimental O 3 molecule. Information on how NO and N 2 O emissions respond to agricultural management is lacking. Limited data suggest N 2 O emissions following bovine urine deposition may vary with soil pH. This work hypothesised that soil liming would also reduce NO x emissions due to enhanced nitrification and reduced opportunity for HNO 2 formation as soil pH increased. Bovine urine was applied (575 kg N/ha) to repacked soil cores (34% water-filled pore space) that ranged in pH from 4.4 to 7.6, and these were maintained at 218C. With the exception of the pH 4.4 treatment, increases in NOÁN fluxes occurred during the first 11 days, when nitrification was proceeding. Increasing the initial soil pH enhanced the net ammonium depletion rate. The loss of NOÁN, expressed as a percentage of the net ammonium depletion rate, decreased with increasing initial pH during this first 11 days with NOÁN fluxes reduced due to competition between abiotic and biological demands for NO 2 ( . After 21 days, the optimal pH for the net NOÁN flux was observed to be 5.7 to 6.0. However, cumulative NOÁN fluxes after 35 days showed little variation due to initial soil pH and ranged from 0.02 to 0.05% of urineÁN applied. The cumulative N 2 OÁN flux ranged from 0.04 to 0.09% of urineÁN applied with a linear increase from pH 5.7 to pH 7.6. Based on these results, where soils are relatively dry, liming acid soils from pH 5.5 to pH 6.5 will not affect cumulative NO fluxes from urine patches. However, cumulative N 2 O fluxes may be enhanced.

Excessive use of nitrogen in Chinese agriculture results in high N2O/(N2O+N2) product ratio of denitrification, primarily due to acidification of the soils

“…Khan et al . () measured N 2 O emissions induced by bovine urine 2 weeks after manipulating the pH by liming, and found that the accumulated emissions increased with liming. Goodroad et al .…”

Nitric and nitrous oxide fluxes following bovine urine deposition to summer-grazed pasture

“…Soil chemical and physical characteristics were previously reported by Khan et al (2011). In brief, the soil had a pH of 6.0, bulk density of 0.95 g/cm 3 , and total C and N contents of 2.9 and 0.26 mg/kg, respectively.…”

“…Thus factors affecting these processes, such as soil pH and moisture content, also affect NO x emissions (Davidson 1992;Khan et al 2011). Since NO is an obligate intermediary in denitrification there is less opportunity for the emission of NO when soil water-filled pore space (WFPS) becomes elevated because complete denitrification is favoured as a result of the lower relative gas diffusivities .…”

Emission Laws and Influence Factors of Greenhouse Gases in Saline-Alkali Paddy Fields

“…In comparison, the effect of pH on N 2 O emission is complex. Soil pH is an important factor affecting both nitrification and denitrification [38]. Low pH may affect both the nitrification and denitrification processes and inhibit the activity of the N 2 O reductases responsible for the conversation of N 2 O during denitrification, which then leads to increased N 2 O emissions [39].…”