Masters Theses

Date of Award

8-1979

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Gary M. Lessman

Committee Members

John H. Reynolds, R. J. Lewis

Abstract

A greenhouse experiment was conducted with tall fescue (Festuca arunidacea Schreb.) to evaluate the effects of NO3 and NH4 fertilization on mineral composition, yield and components related to grass tetany potential. A nitrification inhibitor [2-chloro-6-(trichloromethyl)- pyridine] was used to slow the conversion of NH4 ions to the NO3 form. In the experiment a factorial combination of three levels of N; 34, 67, and 134 kg N/ha; three levels of K; 56, 112, 224 kg K/ha; two levels of Mg; 0 and 112 kg Mg/ha; at two Soil pH levels; pH 5.2 and 6.2; was evaluated with and without a nitrification inhibitor. Two cuttings of plant material were analyzed for Mg, Ca, K, total N, and NO3-N. The use of a nitrification inhibitor such that primary N fertilization was from the NH4 form was found to lower Mg, Ca, and NO3-N concentration of first cutting forage. However, N in the NH4 form increased Ca and K in the second cutting. The ratio of K/(Ca + Mg) was not affected at the chosen probability level by the NH4 form of N fertilization. Total Mg uptake by forage was reduced when the NH4 ion was the primary form of available N. Yield was not affected by NH4 fertilization in either of the two cuttings, but was lowered when combined yield data were statistically analyzed. First cutting forage grown at the 224 kg rate of added K/ha, at the 0 kg/ha rate of added Mg, with NH4 as the primary form of N, contained Mg concentrations below 0.20%. Also in the first cutting, forage contained less than 0.20% Mg when grown at pH 5.2, at the 0 kg/ha rate of Mg, and with the 67 and 134 kg/ha rates of N fertilization. Addition of the higher levels of K used in the experiment increased K concentration and the K/(Ca + Mg) ratio of forage while lowering Mg concentrations in both cuttings. However, K concentrations were not high enough to limit Mg availability to animals as some authors have suggested. The ratio of K/(Ca + Mg) did not approach or exceed 2.2 in any cutting. The addition of Mg at the 112 kg Mg/ha rate was found to increase Mg concentration but did not significantly affect K/(Ca + Mg) ratios. Fertilization with the higher levels of N increased total N concentration of both cuttings, with total N being higher in the first cutting than the second. In neither cutting was total N concentration great enough to decrease Mg availability to animals consuming the forage. First cutting results revealed higher NO3-N levels in forage from pots receiving NO3-N as the primary form of N fertilization when compared to the NH4 form. Levels of NO3-N did approach or exceed the 0.35% level some have suggested as toxic to animals consuming forages in a few treatments. An increase in soil pH from 5.2 to 6.2 significantly lowered the K/(Ca + Mg) ratio in the first cutting and increased forage Mg concentration in both cuttings.

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