Date of Award:

1988

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Ecology

Department name when degree awarded

Range Science

Advisor/Chair:

Frederick D. Provenza

Abstract

Lack of forage quantity and quality limit livestock production during the dry season in northeast Brazil. Coppice produced following cutting of tree species in this area has the potential to increase forage quantity and quality during the dry season, because trees that coppice retain green foliage throughout most of the dry season. However, the palatability of coppice is often low.

From a theoretical standpoint, woody plants with inherently slow growth rate should be less palatable to herbivores than plants with inherently fast growth rates, because plants that grow slowly allocate more carbon to compounds such as tannins and resins that reduce palatability. I tested this hypothesis with four tree species (Mimosa caesalpiniaefolia, Croton sonderianus, Auxemma oncocalyx, and Caesalpinia bracteosa) growing on both fertile (non-calcic brown) and infertile (lithic) soils. Inherent plant growth rates were determined by growing young plants of all species on both soil types in a greenhouse. Plants were fertilized with NPK (150 or 300 kg/ha) and watered to field capacity. Urea ((NH2)2CO),diammonium phosphate ( NH4)2 Po4 and KCL were used as sources of fertilizer. On fertile soils, Mimosa had the highest inherent growth rate, followed by Auxemma, Croton, and Caesalpinia. In pen and field trials, Mimosa was preferred by goats, followed by Auxemma, Croton, and Caesalpinia. Results were similar on infertile soils, but Croton had a higher growth rate than Auxemma, and Croton was preferred to Auxemma by goats . Fertilization with 150 or 300 kg/ha of NPK increased palatability of coppice of all plant species to goats on both fertile (non-calcic brown) and infertile (lithic) soils.

Fertilization affected the chemical and physical characteristics of the four plant species. Concentrations of tannins and lignins decreased as did leaf toughness, while nitrogen, phosphorus, and calcium increased. In vitro organic matter and neutral detergent fiber digestibilities did not change. The prediction that fertilized plants would be lower in carbon based compounds than the unfertilized plants was supported by the results of my study.

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