Loss of nitrogen in compacted grassland soil by simultaneous nitrification and denitrification

• Published in: Plant and soil Vol. 200; no. 2; pp. 265 - 277
• Main Authors: Abbasi, M.K. (Wales Univ., Aberystwyth (United Kingdom). Inst. of Biological Sciences), Adams, W.A
• Format: Journal Article
• Language: English
• Published: Dordrecht Kluwer Academic Publishers 01-03-1998; Springer; Springer Nature B.V
• Subjects: Acid soils; Agricultural soils; Agronomy. Soil science and plant productions; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; Clay soils; COMPACTACION DEL SUELO; COMPACTAGE DU SOL; Cores; DENITRIFICACION; DENITRIFICATION; Fertilizers; Forest soils; Fundamental and applied biological sciences. Psychology; GALES; GRASSLAND SOILS; Grasslands; Incubation; MINERALISATION; MINERALIZACION; MINERALIZATION; NITRIFICACION; NITRIFICATION; Nitrogen; NITROUS OXIDE; Organic matter; OXIDO NITROSO; OXYDE NITREUX; PASTIZALES; Pastoralism; Pasture; PASTURES; PATURAGES; PAYS DE GALLES; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Soil amendment; SOIL COMPACTION; Soil depth; Soil science; Soil treatment; Soil water; Soils; SOL D'HERBAGES; SUELO DE PRADERAS; WALES; Monocotyledones; Weed; Compactness; Loss; Nitrogen; Inorganic element; Nitrogen cycle; Gramineae; Mineralization; Angiospermae; Nitrification; Agrostis capillaris; Denitrification; Nutrient; Spermatophyta; Fodder crop; Simultaneity; Lolium perenne; Inceptisols; Grassland soil
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1023/A:1004398520150

The soils of mid-Wales in grazed permanent pasture usually exhibit stagnogley features in the top 4-10 cm even though on sloping sites, they are freely drained. Nitrogen is often poorly recovered under these conditions. Our previous studies suggest that continuing loss of available N through concurrent nitrification and denitrification might provide an explanation for poor response to fertilizer N. The work described was designated to further test this proposition. When $NH_4^ + $-N was applied to the surface of intact cores, equilibrated at —5kPa matric potential, about 70% of $NH_4^ + $-N initially present was lost within 56 days of incubation. Study of different sections of the cores showed a rise in $NO_3^ - $ level in the surface 0-2.5 cm soil layer but no significant changes below this depth. The imbalance between $NO_3^ - $ accumulation and $NH_4^ + $ disappearance during the study indicated a simultaneous nitrification and denitrification in the system. Furthermore, the denitrification potential of the soil was 3-4 times greater than nitrification potential so no major build-up of $NO_3^ - $ would be expected when two processes occur simultaneously in micro-scale. When nitrification was inhibited by nitrapyrin, a substantial amount of $NH_4^ + $-N remained in the soil and persisted till the end of the incubation. The apparent recovery of applied N increased and of the total amount of N applied, 50% more was recovered relative to without nitrapyrin. It appears that addition of nitrapyrin inhibited nitrification, and consequently denitrification, by limiting the supply of $NO_3^ - $ for denitrifying organisms. Emission of N₂O from the $NH_4^ + $ amended soil cores further confirmed that loss of applied N was the result of both nitrification and denitrification, which occurred simultaneously in adjacent sites at shallow depths. This N loss could account for the poor response to fertilizer N often observed in pastoral agriculture in western areas of the UK.