Masters Theses

Date of Award

8-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Donald D. Tyler

Committee Members

Mike Essington, Mike Mullen

Abstract

Soil acidity is a major concern in crop production in the southeastern United States and is influenced by several factors, including N-rate, cover crops, and tillage. A field experiment was established in 1981 to examine the influence of these practices on soil properties on a Lexington silt loam (Ultic Hapludalf) soil. In 1995 the effect of limestone application, as determined by a 1:1 water pH and the Adams and Evans buffer test, was added to the experiment on the existing soil treatments at the full recommended rate and half the recommended rate. Soil samples were taken in the spring prior to fertilization at the following depths: 0-7.5 cm, 7.5-15 cm, and 0-15 cm. Laboratory analyses of soils included 1:1 soil pH, Adams and Evans buffer test, organic carbon, cation exchange capacity, exchangeable bases (Ca, Mg, Na, K), exchangeable Al, and exchangeable Mn. As N-rate increased soil pH decreased throughout the experiment and the amount of exchangeable Al and exchangeable Mn tended to increase with increasing N-rate. The use of a cover crop significantly influenced soil pH, Ca, Mg, Mn, and SOC. The vetch cover crop added to the acidic characteristics of the treatments, and typically added approximately 40-60 kg N ha1 to the treatments. TUlage practice significantly influenced CEC, exchangeable Al and pH. No-till treatments tended to have lower pH values and had higher amounts of SOC, exchangeable Al, and exchangeable Mn than corresponding tilled treatments. The difference in pH in the full rate of limestone and the half rate of limestone were not significant, however the full rate of limestone did tend to increase the soil pH more and at a faster rate than the half rate of limestone. Both rates of limestone displaced most of the exchangeable A1 and Mn for the exchange complex, usually within one year of application. Both rates of limestone appear to be adequate in raising soil pH>6.0 in either system, however neither rate was adequate in raising the soil pH>6.0 in the NT vetch plots that received ≥67 kg N/ha. Excessive amounts of acidity are avoided when proper N-fertilizer practices are used, and additional N from legume cover is accounted for. The Adams and Evans buffer test does appear to be adequate in determining lime requirement for NT cotton production in Tennessee, however if pH ≤ 4.8, incorporation of limestone or a increased lime rate is advised.

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