RELATING UPROOTING RESISTANCE TO STEM BASAL DIAMETERS OF PLANTS FOR EROSION MITIGATION

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 7, Issue 3, May June 2016, pp , Article ID: IJCIET_07_03_013 Available online at Journal Impact Factor (2016): (Calculated by GISI) ISSN Print: and ISSN Online: IAEME Publication RELATING UPROOTING RESISTANCE TO STEM BASAL DIAMETERS OF PLANTS FOR EROSION MITIGATION Nwoke, H.U., Dike, B.U., Nwite, S.A., Nwakwasi, N.L. Department of Civil Engineering, Federal University of Technology, Owerri. P.M.B 1526 Owerri, Imo State, Nigeria. ABSTRACT The strength with which a plant resists uprooting from erosion is influenced by a number of morphological traits including the stem basal diameter. The objective of this study is carry out in-situ lateral uprooting tests for various plant species and develop models that relate uprooting resistance to plant stem basal diameter. The study area is the erosion prone land of Nguzu Edda in Ebonyi State, Nigeria. Several lateral uprooting tests were carried out to determine the uprooting forces for twelve plant species. The stem basal diameters of the plants were also measured. Linear, quadratic and cubic regression models were used in data analysis. The results showed that maximum uprooting force has a linear relationship with stem basal diameter with coefficients of determination ranging from to The r 2 value was for Saccharum officinarum, for chrysopogon zizanioides and for paspalum notatum while other plants studied had r 2 values ranging from to The p-values for all species using linear regression were less than 0.05 hence the model results are significant at 95% confidence level for all plant species studied Key words: Lateral Uprooting, Basal Diameter, Uprooting Force, Erosion, Statistical Analysis. Cite this Article: Nwoke, H.U., Dike, B.U., Nwite, S.A., Nwakwasi, N.L., Relating uprooting Resistance to Stem Basal Diameters of Plants for Erosion Mitigation, International Journal of Civil Engineering and Technology, 7(3), 2016, pp editor@iaeme.com

2 Nwoke, H.U., Dike, B.U., Nwite, S.A., Nwakwasi, N.L. 1. INTRODUCTION The role played by lateral roots and root hairs in promoting plant anchorage and specifically resistance to uprooting forces cannot be over emphasized in Bioengineering. In terms of flash flood mitigation, it refers to the combination of biological, mechanical and ecological concepts to reduce or control erosion, protect soil and stabilize slopes using vegetation (Finney, 1993). The effects of roots in protecting the soil from being eroded can therefore not be neglected (Gray and Sotir, 1996). Resistance to uprooting for plants could be resolved into series of events associated with the breakage of individual roots. When a plant is pulled from the soil, force is transmitted to the root system, which will fail at a point determined by the strength of the root, the soil shear strength and soil bond. In non woody roots, such failure generally occurs in the proximal region of the roots (Ennos, 1993). The role of both lateral and tap roots in the anchorage of a plant remains unquantified. Stokes et al. (1996) used wire model to predict that branching should increase uprooting resistance, however, the rigid wire models are obviously not close mimics of nonwoody roots and indeed models that bent during uprooting behaved differently. In most plants, a single force applied to stem will be transmitted to numerous roots either because of lateral branching or because of adventitious roots from the stem base. This allows more efficient transfer of the load to the soil because many narrow roots have a greater surface area than a single thick one (Ennos, 1993). Quantifying the role of laterals and more generally, root architecture on anchorage will allow a better understanding of the relative importance in determining the evolution of the diversity of root system form (Fitter, 1985). It has been demonstrated that when subjected to mechanical stress, some species of plant have higher number of roots and greater lateral root branching (Stokes et al, 1997, Mickovski and Ennos, 2002). It should also be pointed out that other traits such as root stiffness (Mickovski et al, 2007), changes in cell wall properties (Scippa et al, 2006) and root system asymmetry (Nicoll and Ray, 1996) can also play roles in plant anchorage. 2. MATERIALS AND METHODS This study was conducted in Nguzu-Edda Erosion site of Ebonyi State, Nigeria. Twelve plant species from the local vegetation were sampled as shown in Table 1. Table 1 sampling and classification of plant species S/N Species Family Growth form Sampling site 1 Oxytenanthera abyssinica Poaceae Shrub 1 2 Vernonia amygdalina Asteraceae Shrub 1 3 Saccharum officinarum Poaceae Shrub 1 4 Pennistum purpureum Poaceae Herb 2 5 Paspalum notatum Poaceae Herb 1 6 Chrysopogon zizanioides Poaceae Herb 1 7 Cynodon dactylon Poaceae Herb 2 8 Citrus sinensis Rutaceae Tree 1 9 Mangifera indica Anacardiaceae Tree 2 10 Anacardium occidentale Anacardiaceae Tree 1 11 Azadirachta indica Meliaceae Tree 1 12 Milicia excels Moraceae Tree editor@iaeme.com

3 Relating uprooting Resistance to Stem Basal Diameters of Plants for Erosion Mitigation The species selected represent different families and were at juvenile stage of growth. Uprooting tests were carried out at the peak of vegetative growth. During the experiment, plants were selected to represent different stem-root basal diameters and thus to represent species anchorage strength and morphology throughout the range of diameters studied (2-20mm). Lateral in-situ uprooting tests were done using a scale force gauge which measures the uprooting force. The tests were performed on six samples per specie. Before each test, the superficial litter layer was removed to clear the stem base. A non-stretch rope was bound to the stem base at one end and to a portable force gauge at the other end. A horizontal traction force was then applied slowly and regularly manually until the plant was uprooted. During the valid tests, the maximum force (in each case) reached before uprooting was noted. To prevent soil moisture content differences, the tests were carried out in the morning hours, about two days after a rainfall of high intensity. Soil shear strength at 5cm and 10cm depths were measured to determine the soils mechanical properties. After uprooting, the plants were cleaned using stream of water to remove soil particles, the stem basal diameters were measured using venire caliper and micrometer screw gauge. Statistical tools were used in the analysis of results obtained from the tests. The linear, quadratic and cubic models were applied to establish the relationship between plant uprooting resistances and stem basal diameters as presented in Equations 1 to 3. (1) (2) Where a 0, a1, a 2 and a3 are regression coefficients. 3. RESULTS AND DISCUSSION Result of the soil s shear strength measured at two points in the study area is presented in Table 2. The result shows that the soil cohesion increased with soil depth but there was no significant difference in soil shear strength between the two locations. Table 2 Soil shear strengths (KPa) at two points on the site Depth Characteristics Point 1 Point 2 5cm Mean Standard error (3) 10cm Mean Standard error The results of the maximum uprooting forces ( ) and the stem basal diameters (D) of the twelve species studied are shown in Table editor@iaeme.com

4 Nwoke, H.U., Dike, B.U., Nwite, S.A., Nwakwasi, N.L. Table 3 Maximum Uprooting forces and stem basal diameters Species Test No O. abyssinica D(mm) C. Sinensis D(mm) V. amygdalina D(mm) C.dactylon D(mm) P. Purpureum D(mm) S. officinarium D(mm) M. indica D(mm) A. occidentale D(mm) A. indica D(mm) M.excelsa D(mm) P.notatum D(mm) C.zizanioides D(mm) Tables 4 and 5 show the linear, quadratic and cubic regression models obtained for various plant species using the data presented in table 3. The coefficients of determination and p-values for the various models are also presented. The r 2 - values are positively correlated with Fmax for all models. However, the linear model had the highest coefficient of determination and lowest p-values (P<0.05) which implies that the model results are significant at 95% confidence level for all plant species studied. Therefore, the linear regression model can be applied in the determination of maximum uprooting force using stem basal diameter editor@iaeme.com

5 Relating uprooting Resistance to Stem Basal Diameters of Plants for Erosion Mitigation Table 4 Regression and statistical parameter for various plant species Specie Linear Quadratic Cubic Saccharum Officinarum r 2 =0.90 r 2 =0.65 r 2 =0.69 P= P= P= Mangifera indica 50.2 r 2 =0.99 r 2 =0.98 r 2 =0.93 P= P= P= Anacardium Occidentale 69.8 r 2 =0.99 r 2 =0.98 r 2 =0.99 P= P= P= Azadirachta indica 60.9 r 2 =0.99 r 2 =0.99 r 2 =0.91 P= P= P= Milicia Excelsa r 2 =0.99 r 2 =0.99 r 2 =0.99 P= P= P= Paspalum Notatum r 2 =0.98 r 2 =0.89 r 2 =0.83 P= P= P= editor@iaeme.com

6 Nwoke, H.U., Dike, B.U., Nwite, S.A., Nwakwasi, N.L. Table 5 Regression and statistical parameter for additional plant species Specie Linear Quadratic Cubic Oxytenanthera abyssinica r 2 =0.99 r 2 =0.88 r 2 =0.713 P= P= P= Citrus Sinensis 156 r 2 =0.99 r 2 =0.99 r 2 =0.65 P= P= P= Vernonia Amygdalina 43.2 r 2 =0.99 r 2 =0.88 r 2 =0.92 P= P= P= Cynodon Dactylon 5.1 r 2 =0.99 r 2 =0.99 r 2 =0.94 P= P= P= Penniston Purpureum r 2 =0.99 r 2 =0.98 r 2 =0.99 P= P= P= Chrysopogon Zizanioides r 2 =0.98 r 2 =0.72 r 2 =0.25 P= P= P= CONCLUSION It has been the practice in most erosion devastated areas for people to use plants for mitigation and control of the erosion. However, the strength of such plants in resisting uprooting by erosion has been given little or no consideration. This study therefore focused on establishing the relationship between the uprooting forces and the basal diameters of plants used in erosion control. Twelve plant species were studied. This involved measuring the uprooting forces and the basal diameters of the plants. Six editor@iaeme.com

7 Relating uprooting Resistance to Stem Basal Diameters of Plants for Erosion Mitigation independent tests were carried out on each of the twelve species selected. Regression analysis was employed to establish the relationship between maximum uprooting forces and stem basal diameters. It was observed from the result that though some quadratic and cubic models related the variables well, the linear models gave the best relationships in all cases. These results will help in informed choice of plants for erosion and flood control. REFERENCES [1] Ennos, A.R (1993), The Scaling of Root Anchorage, J. TheorBiol 161: [2] Finney, K. (1993), Landscape Architect, 11 th Annual California salmonid Restoration Federation Conference in Eureka. [3] Fitter, A.H. (1985), Functional Significance of Root Morphology and Root System Architecture Ecological Interactions in soil. Blackwell Scientific, Oxford, UK, pp [4] Gray, D.H. and Sotir, R.B. (1996), Biotechnical and Soil Bioengineering Slope Stabilization, John Wiley and sons, New York. [5] Mickovski, S.B., Bengough, A.G., Bransby, M.F., Davies, M.C. and Haallett, P.D. (2007), Material Stiffness, Branching Pattern and Soil Matrix Potential affect Pullout Resistance European Journal of Soil Science 58: [6] Mickovski, S.B. and Ennos, A.R. (2002), A Morphological and Mechanical study of the Root Systems of Suppressed Crownscots Pine Pinussylvestris, Tree (Berl) 16: [7] Nicoll, B.C. and Ray, D. (1996), Adaptive Growth of Tree Root Systems in Response to Wind Action and Site Conditions, Tree physiol 16: [8] Scippa, G.S., Di Michele, M., Di Lorio, A. (2006), The Response of Spartiumjunceum Roots to Slope: Anchorage and Gene Factors, Ann Bot (Lond) 97: [9] Stokes, A., Ball, J. and Fitter, A.H. (1996), An Experimental Investigation of the Resistance of Model Root Systems to Uprooting, Ann Bot (Lond) 78: [10] Stokes, A., Nicoll, B., Coutts, M.P. and Fitter, A.H. (1997), Responses of Young Sitka Spruce Clones to Mechanical Perturbation and Nutrition: Effects on Biomass Allocation, Root Development and Resistance to Bending, Can J. Res27: [11] Nwoke H.U, Dike B.U, Okoro B.C and Nwite S.A., Uprooting Resistance Andmorphological Traits of Plants Used In Erosion Mitigation, International Journal of Civil Engineering and Technology, 7(3), 2016, pp editor@iaeme.com