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Subject: search.filters.subject.Stylosanthes hamata

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    A study of the effects of defoliation and water stress on growth and development of Stylosanthes hamata (L.) Taub. cv Verano : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Agronomy at Massey University
    (Massey University, 1986) Sayan, Tudsri
    Verano stylo (Stylosanthes hamata (L.) Taub.) is an important pioneer legume in the tropics and its potential as a pasture legume under grazing appears to be promising in Thailand. This thesis was carried out in two parts - the first part was conducted in the Controlled Climate Rooms at the Plant Physiology Division, DSIR, Palmerston North, New Zealand. The aim of these studies was to obtain basic information on growth patterns and the response of Verano stylo to cutting at different intensities, frequencies and stages of growth and at two levels of water stress in terms of quantity and quality of herbage produced. The second part was a grazing trial conducted at Muaklek, Thailand, to test the grazing management hypothesis derived from the Controlled Climate Room studies. The results from the Controlled Climate Room studies showed that the growth and development of intact Verano stylo was slow at the pre-flowering stage and increased rapidly after the onset of flowering. Maximum growth rate of 2.04 grams/plant/day was recorded between 70 and 80 days and maximum dry weight of 105 grams/plant was achieved approximately 108 days after seedling emergence. During this post-flowering stage, plant growth in terms of plant dry weight, branch development, leaf number and leaf area increased rapidly. Flowering commenced 35 days after seedling emergence and continued throughout the experimental period. Stem was the major plant component, followed by the inflorescence and leaf fractions. In terms of the response to various cutting regimes, the results showed that the more severe the cutting the more deleterious was the effect on regrowth. Cutting the primary branches had a greater effect on plant regrowth in terms of plant dry weight, branch number, leaf number and leaf area than defoliating the main stem. Severe cutting of primary branches (i.e. to node 0) plus hard cutting of the main stem (i.e. to node 3) resulted in the death of the plant after two cuts. When defoliation was delayed to the later stage of growth (near maximum growth rate), severe cutting of the primary branches (i.e. to node 0) caused extensive plant death following only a single cut. All growth parameters recorded were markedly reduced when the interval between cutting was decreased. It is suggested that the response of Verano stylo to defoliation is dependent upon the number and especially the size of the primary branches, the number of growing points, the amount of stubble reserves and the residual leaf area immediately after cutting. The differences in yields were largely due to changes in the stem and to a lesser extent the inflorescence and leaf fractions. Growth of the plant in terms of plant dry weight, branch number, leaf number and leaf area were reduced to a greater extent under severe than under mild water stress. The differences in plant dry weight between the two levels of stress were largely due to the size of the stem fraction. After rewatering there was a rapid increase in growth by both the previously mild and severe water stressed plants, resulting in a marked increase of all the variables recorded. However, growth of plants previously under severe water stress was less than those previously under mild water stress. The increase in total plant dry weight was due to an increase in all plant components, especially leaf and inflorescence fractions. Severity of cutting had less effect on plant variables than water stress. The effect of cutting was more apparent under mild water stress than under severe water stress in terms of plant dry weight, branch number and leaf area, and continued to show this effect on rewatering with respect to leaf number and leaf area. Verano stylo herbage quality, as measured by crude protein concentration, was relatively high even in the uncut control plants. Defoliation increased the protein concentration, but within the cutting treatments there was little effect of cutting intensities and frequencies on the crude protein concentrations of all plant components, except the stem fraction which was slightly superior under frequent than infrequent cutting. The protein concentration was higher in the leaf and inflorescence and lower in the stem at all cutting intensities and frequencies. Severe moisture stress increased the crude protein content in the leaves, stems and inflorescences compared with mild moisture stress and continued to show this effect on rewatering with respect to the leaf and stubble fractions. Hard cutting in the drought period also increased protein concentrations in the leaves, stems and inflorescences compared with lax cutting and continued to show this effect on rewatering with respect to the stubble and stem fractions. Although the crude protein concentrations in different plant parts and for different cutting intensities, frequencies and stages of cutting and for different water regimes were relatively small, the amounts per plant were large due to the substantial and significant differences obtained in dry weight between treatments. The increase in crude protein was largely due to the inflorescence fraction, especially under lax cutting. Crude protein yields were also seriously reduced under frequent and hard cutting of the primary branches. Previously stressed plants at either mild or severe levels greatly increased their crude protein yield after rewatering, and this was largely due to the crude protein yield of the leaf and inflorescence components. In terms of carbohydrate reserves, the results of this study clearly showed that the concentration of these reserves in the residual top and roots of Verano stylo were low (< 3% of dry weight), were comprised mainly of sugar and were independent of the stage, intensity and frequency of cutting. However, carbohydrate concentrations were substantially increased by severe and especially mild water stress. Starch was the major component and accumulated in all plant parts especially the stubble, stem and tap root fractions. The effects of cutting during the drought period were only evident in the stubble, inflorescence and tap root fractions - the levels declining with increasing intensity of defoliation, particularly of the starch fraction. However, these carbohydrates, especially the starch fraction in the stubble, stem and tap root, almost totally disappeared during the rapid recovery phase, suggesting it was used for regrowth. In terms of the amounts of carbohydrates, the results showed that the differences between cutting intensity were largely due to the differences in the residual dry weights especially in the stubble. Generally the more severe the cutting, the lower the amount of carbohydrates in the stubble. However, cutting frequency had no significant effect on carbohydrate accumulation. Severe water stressed plants accumulated only half the reserves of the mild water stressed plants during the drought period. Under both mild and severe water stress, the stem was the major accumulator of these reserves, particularly of the starch fraction. On rewatering, there was a marked increase in the accumulation of sugar akin to the increase in dry matter yields. However, starch yields in the stem and tap root showed a substantial drop during this period. During the drought period, hard cutting significantly depressed the accumulation of sugar and starch especially under mild water stress. In the roots only the starch fraction was affected. On rewatering, previous hard cutting continued to depress carbohydrate yield but only of the starch fraction of those plants under previous severe water stress. The results from the field experiment confirmed the importance of residual leaf and branch numbers on plant regrowth in terms of dry matter production, branch development, leaf number and leaf area and their persistence. Under climate room conditions, 6 weekly cutting produced significantly higher yields of all growth components than did 3 weekly cutting. However, under field grazing conditions frequent grazing (every 4 weeks) produced significantly higher yields than infrequent grazing (every 8 weeks). Frequent grazing also maintained a higher density of Verano stylo plants and a lower weed content. The results are discussed in relation to the possible grazing management of Verano stylo in Thailand.
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    A study of the effects of water and cutting on seed production of Verano stylo (Stylosanthes hamata) and Siratro (Macroptilium atropurpureum) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand
    (Massey University, 1983) Waikakul, Phanna
    Tropical pasture legume seed production in the North-east of Thailand first began in the early 1970's. Stylosanthes hamata cv. Verano and Macroptilium atropurpureum cv. Siratro were two of the forage legumes proposed to fill the requirement for improved pastures in this region of Thailand. This study was initiated to provide information on the effects of water stress, stage of plant development at the time of cutting and cutting intensity on seed production of these two tropical forage legumes, in the field at Khon Kaen, Thailand. A second and more intensive study on the reaction of Verano stylo to water stress, and stage and intensity of cutting was carried out to provide a better understanding of possible plant adaptation and the contribution of plant components to seed yield of this species under controlled environment conditions at the D.S.I.R., Palmerston North, New Zealand. Initially, field experiments were carried out in two different seasons, (dry season and wet season). The dry season experiment studied the effects of irrigation, non-irrigation, and cutting on seed yield. In the wet season field experiment only the effect of cutting was studied in both Verano stylo and Siratro. The results from the dry season study showed that species are responsive to irrigation. Irrigated plants produced about 25% more seed yield than non-irrigated plants in Verano stylo but only about 10% more in Siratro. The response of the plants to cutting was variable depending on the stage and intensity of cutting. Light cutting at either the vegetative or floral initiation stages gave higher seed yields than uncut plants in Verano stylo, while in Siratro all cut plants gave higher seed yields than uncut plants. Planting Verano stylo or Siratro in the wet season resulted in plants taking longer to reach the reproductive stage than in the dry season. This protracted vegetative stage resulted in bigger plants and more sites for seedheads. In stylo both cut and uncut plants gave higher seed yields than those obtained in the dry season planting, while in Siratro plants heavily cut at the vegetative stage gave the highest seed yield. Siratro plants grown in the wet season tended to produce strong vegetative growth and good inflorescence development. However, seed yield was lower because of poor pod development and low numbers of seeds per pod. The second experiment on verano stylo was carried out under controlled environment conditions designed to simulate as closely as possible the different growing seasons previously used in the field. The results confirmed that water plays an important role in increasing seed yield in both cut and uncut plants, and especially in cut plants provided they received high water levels throughout the growing period. Water stress appeared to change plant structure, both vegetative and reproductive growth being greatly reduced during the stress period. Water also had an effect on the number of sites for seedhead formation and the contribution to seed yield. In plants which were water stressed from about 30 days after sowing (vegetative stage) both cut and uncut plants remained small resulting in low branch numbers, shorter branches and fewer sites for seedhead development. Water stress applied following peak flowering (55 days after sowing) also reduced seed yield, compared with the yield from plants receiving water throughout the period of seed development. The maximum yield obtained varied from 1.2-9.3 grams per plant between the three water treatments. Studies on the contribution to seed yield from each branch order and seedhead position indicated that in both cut and uncut plants most of the seed yield came from secondary branches (60-75%). The contribution to seed yield, however, was different between water treatments. In early stressed plants seed yield was apportioned almost equally between primary and secondary branches. However in plants which had been placed under water stress at peak flowering, the seed yield obtained from primary branches was only half that produced from secondary branches. In non-stressed plants 70% of total seed yield came from seedheads produced on secondary branches and only 20% from primary branches. The position of seedhead formation on each branch was also important. The results showed that about 75-90% of total seed yield came from seedheads formed at nodal sites. The number of seedheads formed at terminal sites was low. In later stressed plants and in well watered plants the contribution of nodal sites to seed yield was higher than in early stressed plants. The results of the field study on Verano stylo and Siratro, and the second experiment on stylo grown under controlled environment conditions were incorporated into practical recommendations which lead to conclusions on the most economically, socially and agriculturally acceptable management system for the seed production of Verano stylo and Siratro by Thai farmers.