DIVISION S -3—SOIL MICROBIOLOGY AND BIOCHEMISTRY The Role of Nitrate Diffusion in Determining the Order and Rate of Denitrification in Flooded Soil: I. Experimental Results

presence and activity of denitrifiers. These factors have The effect of NO3--N diffusion on the order and rate of debeen studied bv several workers, for example, Bremner and nitrification reaction was studied in IS soils from various locations in Shaw (1958a, 1958b), Nommik (1956), Patrick (1960), the U.S. The soils were amended with 0.5% rice straw and incubated Broadbent and Clark (1965), and Terry and Nelson (1975). under saturated conditions without O2, either with no excess floodThe question is still open regarding the dependence of the water or with a 3-cm overlying layer of floodwater. The disappeardenitrification rate on NO3~-N concentration. Earlier, ance of added and native NO3--N and its conversion to N2 and N2O Patrick (1960), Broadbent and Clark (1965), and Keeney followed apparent zero-order reaction kinetics when all the NO3"-N (1973) considered that the rate of denitrification was was present in the active soil layer (no excess floodwater). When independent of NO3--N concentration (zero order), while MO'*°.T W8S ?,, "f *' floodwater °" tbe soil ' other investigators have reported that denitrification folNOa -N disappearance followed apparent first-order reaction ki, , ,. ».. , ,. i » , • . fr, netics. A decree in NC^-N concentration in the soil layer caused *[* ̂ ^f " Michaehs-Menten kinetics (Bowman N03--N in the floodwater to diffuse into the soil layer (a first-order and Focht, 1974; Stanford et al., 1975a, 1975b; Kohl et al., reaction with respect to NO3~-N concentration) where it was de1976). nitrified. Thus where NO3~-N loss involved both diffusion from the The usual experimental procedure for determining the overlying floodwater and denitrification, NO3~-N disappearance order and rate of denitrification is to submerge the soil in a appeared to be a first-order rather than a zero-order reaction. test tube or beaker and to then measure the disappearance The rate of denitrification was faster in soils incubated with no of added NO3~-N and/or the appearance of nitrogen gases excess floodwater compared to soils incubated under 3 cm of (Stanford et al., 1975a, 1975b; Bowman and Focht, 1974; floodwater. One soil (Crowley silt loam), when incubated with no Koh] et £ ^ 1916) 7^ NQ3--N in Such a System is present added carbon source and no excess floodwater, showed NO3--N Jn bo{h ^ floodwater ^d the soil layer Since de. h^TH ®S7 ^""t* '-^ x ̂ ̂ nitrification occurs primarily in the soil layer (Engler and IT^ord'er. ""^ ««* Patrick, 1974), the diffusive flux of NOr-N from the overlying layer of floodwater to the underlying soil layer Additional Index Words: nitrogen loss, NOj'-N reduction, firstwill influence the apparent order and rate of the reaction. order kinetics, zero-order kinetics, submerged soil, anaerobic soil The objective of the investigation reported here was to layer, floodwater. determine the effect of NO3~-N diffusion from the overly________________ ing floodwater to the soil layer on the order and rate of denitrification. This paper presents the experimental results T HE KINETICS of the denitrification process in soil are Of this study; interpretation and mathematical analyses of influenced by several factors such as available carbon, these data are reported in a companion paper (Phillips et temperature, pH, 02 concentration, redox potential, moisal., 1978). ture content, possibly NO3~-N concentration, and the ————— MATERIALS AND METHODS 'Contribution from the Lab. of Flooded Soils & Sediments, Dep. of Agronomy, Louisiana Agric. Exp. Stn., Louisiana State Univ., Baton Fifteen surface soils collected from various locations in the Rouge, LA 70803, and Dep. of Agronomy, Uriiv. ofKentucky, Lexington u.S. were used in this study. Certain properties of the soils are KY 40506. Received 28 Feb. 1977. Approved ,7 Nov. 1977. shown in Table 1 These soils had been stored air drv since 'Post-Doctoral Research Associate, Professor.of Agronomy, Louisiana shown in 1 able_1. Ihese soils had been stored air dry since State Univ., and Professor of Agronomy, Univ. of Kentucky. The first collection in 1975. All soil samples were ground to pass a 20author is currently with Biol. & Agric. Eng. Dep., North Carolina State mesh sieve before incubation. All soils were incubated with: (i) no Univ., Raleigh, N.C. and the second author is currently with the Center overlying layer of floodwater (saturated condition), or (ii) a 3-cm for Wetland Resources, Louisiana State Univ., Baton Rouge, LA overlying layer of floodwater. For soils 1 and 2, another treatment "?? '̂ . . . . j , v / o T i u r > » , r j i . r » e consisting of a 6-cm overlying layer of floodwater was also MS&ST^SES K'^iK•£££?££: includeAne soi.s were amendld 4h 0.5% rice straw prior to A. E. Erickson, W. J. Upchurch, O. W. Bidwell, J. L. Young, and A. R. incubation to provide a readily available energy supply dunng Swoboda for providing 12 of the soils used in the study. denitrification and 100 /tg NC>3~-N/g (oven dry basis) of soil. One REDDY ET AL.: NITRATE DIFFUSION AND DENITRIFICATION IN FLOODED SOIL: I. 269 Table 1—Certain selected properties of the soils collected across the United States.