Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 18, 2005
Publication Date: May 10, 2005
Citation: Calderon, F.J., Reeves III, J.B., Mccarty, G.W. 2005. Nitrapyrin delays denitrification on manured soils. Soil Science. 170(5):350-359. Interpretive Summary: Excessive application of manure may lead to NO3 leaching to ground water and fluxes of nitrogen oxides to the atmosphere. Nitrification inhibitors such as nitrapyrin (N-serve; 2-chloro-6-(trichloromethyl)pyridine) may help to conserve manure N in the root zone. However, the effect of applying nitrapyrin and manure to wet, denitrification-prone soils has not been well studied. The objective of this study was to test the effect that nitrapyrin has on the N cycling of manured soils under high moisture and NO3-N content. The study consisted of a laboratory incubation of soils under aerobic conditions. Three agricultural soils, as well as a sand and a forest soil were included in the study, all with high moisture and initial NO3-N content. Each soil received three treatments: 1) NM- Manure plus nitrapyrin (190 mg nitrapyrin kg-1 soil), 2) M- manure alone (0.15 mg manure N g-1), and 3) C- soil alone controls. Nitrapyrin was mixed with the manure prior to addition to soil. Destructive samplings were carried out weekly for 10 weeks. At each sampling, soil extractable mineral N, microbial biomass N, denitrified N, and N2O fluxes were measured. Nitrapyrin was effective in reducing net nitrification, thus enhancing soil NH4-N accumulation during the entire incubation period. Neither manure nor nitrapyrin consistently affected net mineralizable N in the five different soil types. Microbial N immobilization and/or denitrification were strong sinks of N that precluded net N mineralization. Nitrapyrin did not increase cumulative denitrification, but some soils had delayed denitrification when nitrapyrin was added. Manure had a strong effect on N2O fluxes, and denitrified N in some soils, but the effects of nitrapyrin were inconsistent. In summary, while nitrapyrin was effective in reducing nitrification in manured soils, the effect on soil mineral N and potential N supply to plants varied across soils because of the interaction between nitrification, denitrification, and N immobilization.
Technical Abstract: Nitrapyrin is a soil additive that has been commercialized to block nitrification in agricultural soils. In this experiment, we show adding nitrapyrin when manuring moist soils has the potential to reduce N leaching from soils by reducing the relative amount of NO3 in the soil extractable mineral N. However, no consistent benefit in N2O emissions to the atmosphere were found under the high moisture conditions used in the experiment. Adding nitrapyrin to the manured soils did not increase net mineralizable N due to high denitrification N losses, suggesting no positive effect on the soil N status.