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Title: CARBON AND NITROGEN DYNAMICS DURING INCUBATION OF MANURED SOIL

Author
item Calderon, Francisco
item Reeves Iii, James
item McCarty, Gregory
item Van Kessel, Jo Ann

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2004
Publication Date: 5/1/2004
Citation: Calderon, F.J., Reeves III, J.B., McCarty, G.W., Van Kessel, J.S. 2004. Carbon and nitrogen dynamics during incubation of manured soil. Soil Science Society America Journal. 68(5):1592-1599.

Interpretive Summary: While dairy manure is a valuable N source for crops, excessive manure application may lead to groundwater and atmospheric pollution. Laboratory incubations are used to estimate the N mineralization potential of manures. Nitrogen losses through denitrification during laboratory incubations may be an important source of error, resulting in an inaccurate estimation of mineralizable N during laboratory incubations. We hypothesize that measuring denitrified N should improve the correlation between manure N and mineralizable N. To achieve these objectives, we carried out six week laboratory incubations of manured soils. Soil mineral N, CO2 flux, and N2O flux after acetylene addition were measured weekly. Accomplishments include: a) Measured the effect of manure addition on soil nutrient dynamics on a wide variety of manures, b) Determined if manure chemical or nutritional properties correlate to C and N pools, gas fluxes or denitrification during a laboratory incubation of manured soil, and c) Measured the amount of N lost through denitrification during an mineralizable N assay. Our results show that denitrification, N immobilization, and C mineralization increase in manured soils, and that the N cycling dynamics can not be accurately predicted by the manure chemical properties measured in this experiment. Denitrification accounted for a small fraction of the total manure N added and adding the total denitrified N to the N mineralized did not improve the predictive value of manure properties on mineralizable N.

Technical Abstract: In this study we examined the relationship between denitrification, manure properties, gas fluxes, nutrient pools, and mineralizable N during laboratory incubation of manured soil. Different dairy manures (n=107) were added to soil at a rate of 0.1 mg N g-1. Manured and control soils were incubated and sampled weekly for soil mineral N, CO2 flux, and N2O flux for a six week period. The denitrifier enzyme activity (DEA) was measured at the end of the experiment. Weekly N2O and CO2 production increased in the manured soils during the first three weeks of incubation. There was a positive correlation between added manure C and cumulative CO2 production. Nitrate content increased in all soils throughout the six week period, but the increase was more marked in the manured soils. In most manured soils, ammonium concentration was initially high then declined, resulting in N immobilization. This N immobilization accompanied by relatively low cumulative denitrification in the manured soils suggests that N immobilization was important during the incubation. No correlation existed between denitrifier enzyme activity (DEA) and N pools or gas fluxes in the manured soils. On average, denitrification accounted for less than 5 percent of the added manure N. Higher proportions of denitrified N were observed in some manures, suggesting that N losses through denitrification may be important sources of error in manure mineralizable N assays. Our results show that denitrification, N immobilization, and C mineralization increase in manured soils, and that the N cycling dynamics cannot be accurately predicted by the manure chemical properties measured in this experiment.