Annual denitrification rates in agricultural and forest soils: a review

Abstract

Denitrification is an important soil process for assessing nitrogen cycling and controlling nitrogen pollution in the environment. Numerous studies of denitrification rates in soils have been reported over the last decade, many with sampling protocols that are more reliable than in the past. In this paper, we review denitrification rates for agricultural and forest soils that have been reported in the literature, discuss factors that appear to be important in controlling the amount of denitrification that occurs in these soils, and summarise modelling approaches that have been used to predict annual denitrification rates. Most studies of in situ denitrification in upland soils have been conducted in agricultural grassland and forest ecosystems, with a paucity of studies reported from other ecosystems. A large range of annual, in situ, denitrification rates have been reported (0–239 kg N/ha.year), with the highest rates typically occurring in irrigated, nitrogen-fertilised soils. However, most annual denitrification rates reported in the literature appear to be fairly low, with over half of the rates in forest soils being <1 kg N/ha.year (mean of 1.9 kg N/ha.year). Rates of denitrification in agricultural soils tend to be higher than in forest soils, with 85% of rates reported being >1 kg N/ha.year, and a mean rate of 13 kg N/ha.year. Numerous soil, site, and management factors have been reported to affect the denitrification process in situ. The literature indicates that the highest rates of denitrification can be expected in nitrogen-fertilised soils, or where site management increases soil nitrate availability. Where nitrate is non-limiting, denitrification rates appear to be highest in irrigated loam soils. The review suggests that it is difficult to predict denitrification rates based on our current understanding, and that pilot studies should still be conducted if soil nitrogen balances are required.

Assessing ways to combat eutrophication in a Chinese drinking water reservoir using SWAT

“…Losses of nitrogen by denitrification are influenced by various factors (for rice paddies, for instance, the fertilizer-application method, timing and applied nitrogen compound) (Craswell et al 1981), which challenges comparisons between land-use management practices. Nevertheless, the denitrification rate simulated in the present study lies within the combined span of annual soil denitrification rates for forests (,0.1-40 kg N ha À1 ) and agriculture (0-239 kg N ha À1 ) reported by Barton et al (1999), where irrigated and inorganic fertilised soils tend to exhibit higher rates (ranging from 49 to 239 kg N ha À1 ). Moreover, our simulated ranges of annual diffuse nutrient exports from the watershed (3.4-14.1 kg N ha À1 and 0.1-0.8 kg P ha À1 , Fig.…”

“…Hence, SDNCO was changed to allow denitrification processes to begin at lower moisture conditions (95%) (Pohlert et al 2007). SDNCO was set slightly higher than reported as in situ values (ranging between 50-83%) (Barton et al 1999), because denitrification is initiated before vertical water movement in SWAT when SDNCO is set below field capacity (Pohlert et al 2007), which might lead to overestimated nitrogen losses by denitrification. Moreover, a higher threshold may moderately influence the timing of nitrogen dynamics.…”

Nitrogen budgets of urban lawns under three different management regimes in southern California

“…However, there was a high degree of spatial variability in these fluxes and consequentially large uncertainties of N losses through this pathway. At the annual scale, gaseous N losses through denitrification were 16.4 ± 13.2, 27.9 ± 20.9, and 12.8 ± 19.0 kg -1 ha -1 year -1 for Typical, Low Input, and Low Impact, compared to the mean denitrification rates of 13 kg -1 ha -1 year -1 for fertilized agricultural soils estimated by Barton et al (1999) and 14 ± 3.6 kg -1 ha -1 year -1 for fertilized suburban lawns (Raciti et al 2011b). Denitrification accounted for 7.9 ± 6.3, 20.2 ± 15.2, and 20.2 ± 30.4 % of total annual N inputs in Typical, Low Input, and Low Impact.…”

“…With relatively large uncertainties due to spatial variation, the estimated fluxes at the annual scale might have a large possible range, from 0 to 50 %, of total N inputs (Table 1b). Relatively large gaseous N losses through denitrification are expected if N fertilization rates exceed plant needs (Barton et al 1999;Raciti et al 2011b), while long-term fertilization could substantially increase the denitrification potential of soil (Drury et al 1997;Horgan et al 2002b;Šimek et al 2000). Although denitrification may help reduce NO 3 --N leaching from fertilized lawns by converting NO 3 --N to N 2 , high denitrification rates may also increase soil emissions of NO, an air pollutant, and N 2 O, a greenhouse gas.…”

Effects of the clear-cutting of a Douglas-fir plantation (Pseudotsuga menziesii F.) on the chemical composition of soil solutions and on the leaching of DOC and ions in drainage waters

“…The behaviour of gravitational solutions with very low and constant concentrations seemed to eliminate a control of their nitrate content by denitrification because this flux is usually strongly discontinued. Changes in soil moisture (less than 2%) could increase the denitrification rate, but would remain too limited to modify drastically the denitrification process in the present ecosystem [5].…”