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Title: Studies on the biology of sourgrass (Trichachne insularis (L.) Nees) and of its competition with buffelgrass (Cenchrus ciliaris L.) and guineagrass (Panicum maximum Jacq.);
Sourgrass 
Author: Pyon, Jong Yeong
Date: 1975
Abstract: Sourgrass (Trichachne insularis (L.) Nees) is one of the most serious pasture weeds in Hawaii. It has ruined many good dryland pastures on Maui, Molokai, and Oahu. Studies were conducted on its distribution, seed germination, seedling emergence and growth and development under natural and controlled conditions and on its competition with the improved pasture species, buffelgrass (Cenchrus ciliaris L.) and guineagrass (Panicum maximum Jacq.). Field surveys showed that sourgrass was most abundant below 540 meters elevation, in dry zones of 120 to 760 mm of annual rainfall. Sourgrass occurred on hillsides or on gentle basal slopes where Prosopis pallida (Humb. and Bonpl. ex Willd) HBK. or Leucaena latisiliqua (L.) Gillis and Stearn grew. Distribution of sourgrass corresponded to shade conditions. The soils of infested areas were commonly silt clay to silt clay loam with shallow soil profiles. Low rainfall, high temperatures, and shade were the more important factors in the distribution of sourgrass. Optimum germination of sourgrass seed was obtained under light with alternating temperatures of 20-30 C or 25-35 C or with constant 30 C. Germination in complete darkness was very poor at most temperatures. Germination of sourgrass seed was best under 8 or 12 hour photoperiod but was reduced under 16 and 24 hour photoperiods. Gibberellic acid, kinetin, and thiourea were effective in enhancing germination at 22 C in the dark. Germination percentages of sourgrass, buffelgrass, and guineagrass decreased as moisture stress simulated with mannitol was increased. Guineagrass and buffelgrass were more affected by moisture tension than was sourgrass. The capacity of sourgrass to germinate rapidly under low soil moisture could give it a competitive advantage over buffelgrass and guineagrass under semi-arid to arid conditions. Sourgrass seedling emergence was greatest from seeds planted near the surface and decreased as the depth of planting increased. Sourgrass was capable of emerging from a maximum depth of 5 cm in the clay loam used in this study. Plant height, dry weight, tillers per plant, and seed yield per plant were greatly decreased as the plant density was increased from 5 plants to 160 plants per pot. Intraspecific competition was probably a major factor affecting seedling development and survival of sourgrass. Sourgrass flowering was found to be day-neutral in response to photoperiod. The plants under longer photoperiods flowered earlier than those grown under shorter photoperiods probably because floral development was slow in response to insufficient light energy under shorter photoperiods. Plant height and dry matter production of shoots of sourgrass, buffelgrass, and guineagrass increased but dry weight of roots and tillers per plant decreased with increasing shade. In addition, flowering was delayed as shade increased. Nitrogen fertilization increased plant height, dry weights of shoots and roots, and tillers per plant for all species. A pot study was conducted to evaluate the competitive ability of sourgrass, buffelgrass, and guineagrass under different levels of shade and nitrogen fertilization. The growth of sourgrass was severely suppressed when grown with buffelgrass, guineagrass or both. Highly significant reductions in height, dry weight, and tillers per plant of sourgrass resulted from competition with associated grass species. Sourgrass was thus less competitive than buffe1grass and guineagrass. It is evident from these results that sourgrass in pastures can be controlled through competition from buffelgrass and guineagrass under proper management of grazing and fertilization. Practices which would enhance the competitive advantage of buffe1grass and guineagrass over sourgrass would include the following: (1) ensuring adequate moisture for germination, (2) fertilization, and (3) prevention of over-grazing.
Description: Typescript. Thesis (Ph. D.)--University of Hawaii at Manoa, 1975. Bibliography: leaves [123]-133. xi, 133 leaves ill. (some col.), maps
URI: http://hdl.handle.net/10125/12041
Rights: All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Keywords: Grasses -- Hawaii

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