The kinetics of nonexchangeable-K release using H-saturated resin were investigated on Kalmia (fine-loamy, siliceous, thermic Typic Hapludults) and Kennansville (loamy, siliceous, thermic Arenic Hapludults) soil profiles from the Coastal Plain of Delaware. Calciumsaturated soil samples were equilibrated with H-saturated resin from 0.5 to 960 h. Equilibrium in K release in both soil profiles was attained in about 960 h. The kinetics of K release were evaluated using the Elovich, parabolic diffusion law, first-order diffusion, and zero-order equations. The first-order diffusion equation described the K-release kinetics best as evidenced by the highest correlation coefficient (r) and the lowest value of the standard error of the estimate (SE). The parabolic diffusion law also described the data satisfactorily indicating diffusion-controlled exchange. The zero-order and Elovich equations did not describe the data well as shown by higher SE values than those found with the first-order diffusion and parabolic diffusion law equations. Nonexchangeable-K release rate coefficients (k 2) ranged from 1.20 to 2.2 X 10~3 h~' in the Kalmia soil and from 1.5 to 2.9 X 10 3 h ' in the Kennansville soil. The magnitude of the /c 2 values suggested low rates of nonexchangeable-K release from the two soils.

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Nitrification inhibitors may reduce loss of fertilizer N from the root zone by reducing leaching and denitrification. This reduced N loss should be reflected in increased crop yields. These studies were con· ducted to determine if potato yield, specific gravity, or leaf N at flow· ering would be increased by use of nitrification inhibitors. Nitrification inhibitors dicyandiamide (DCD) and 2-chloro-6-(trichloromethyl)· pyridine (nitrapyrin) were evaluated in five studies on potato (So· Ianum tuberosum L. cv. Atlantic) in Northeast Florida on an Arenic Ochraqualf, a Grossarenic Paleudult, and a Grossarenic Paleaquult. Treatments were combinations ofN at 67, 134, and 202 kg ha-•; DCD at 0, 5.6, and 11.2 kg ha-•; nitrapyrin at 0.56 and 1.12 kg ha-•; and isobutylidene diurea (IBDU) applied as one-third of the N. Tuber yields were not affected by nitrification inhibitors in four of five tests but were increased 14% in one test. Nitrification inhibitors increased leaf N concentration at flowering in three of four tests. Tuber yields were higher with DCD than with nitrapyrin in three of five tests. In several year-location combinations, use of IBDU resulted in greater tuber yield and leaf N concentration at flowering than did nitrification inhibitors. Based on these results, nitrification inhibitors can not be recommended for potato production on hyperthermic, sandy, irri· gated soils.