Study On Substrate-Root Multiple Properties Of Tomato Seedlings And Damage Of Transplanting Pick-Up

China is a leader in the world’s vegetable production and it is expected that the coun-try increases the production of such crops. Among other vegetables, the production of tomatoes is crucial since it has the potential of providing favorable amount of vitamin A and C and reducing the risk of certain types of cancers and heart diseases. It is a major vegetable, of which China is the leading producer in the world with production reaching more than 50.6 million tonnes in 2013. In an attempt to increase production, it is essential to automate the transplanting process which is a very important cultural practice. However, the performance of the machine is inextricably linked to the agro-nomic conditions of the seedling soil. At the moment, it is challenging to come up with the most effective vegetable transplanter to suite growing conditions in the coun-try. This is partly due to the fact that most designers do not have full knowledge of the agronomic properties of the seedlings in order for them to incorporate such infor-mation into the design process. There is a general lack of information that matches the development of pick-up end-effector design and the seedling breeding technique in terms of soil and root development. This makes successful automatic vegetable trans-planting difficult. In recent times, X-ray micro-computed tomography (micro-CT) has been used to evaluate soil-root morphological and mechanical features. In some cases, they are combined with other techniques for comprehensive analysis of such media. In the area of machine dynamics, field conditions also help in optimizing such mechani-cal process. This dissertation focuses on substrate-root multiple properties of tomato seedlings and damage of transplanting pick-up using advanced techniques such as mi-cro-CT. The main research content of this study therefore is as follows:1) In the first study, micro-CT was used alongside destructive root washing method for assessing tomato seedling soil substrate-root physical, mechanical and agronomic properties. Three growth media having sphagnum peat moss, perlite and vermiculite were mixed in percentage proportions of 60:20:20,60:40:0 and 60:0:40 for substrate 1 (SI), substrate 2 (S2) and substrate 3 (S3) respectively. The respective substrates were repacked into the 72 cell tray at bulk densities of 0.28,0.32 and 0.36 gem-3. After 30 days growth period and subsequent micro-CT scanning and analysis, the result showed mean range of porosity for S1, S2 and S3 as 17.8-24.7%,40-52.8%,11.3-14.2% respectively. Finite element simulation performed on the micro-CT images al-so showed the maximum von-Mises stress distribution and stiffness to be greater in S1 followed by S2 and S3. In using the destructive method for measuring agronomic properties, it indicated that increasing bulk densities (0.28,0.32 and 0.36 gcm-3) nega-tively affected root length in S2 and S3. Also, at 0.28 gcm-3, the highest root volume and length were recorded in S1. The results suggest that the combination of sphagnum peat, perlite and vermiculite (S1) in the proportion of 60:20:20, especially at a bulk density of 0.28gcm-3, proves to produce optimum substrate-root morphological and mechanical properties for quality assessment of tomato seedlings for successful auto-matic transplanting.2) The second study considered the utilization of scanning electron microscopy (SEM) with its energy dispersive spectroscopy (EDS) technique for substrate-root nutrient elemental composition in addition to monitoring the above-ground properties of seed-lings grown using water applications of 4,6 and 8 mL daily. Three growth media S1, S2 and S3 were used for the SEM-EDS analysis. Six samples from each 72 cell tray was randomly selected and thin sections (20 mg) taken as sub-samples for scanning and analysis. The experiment was conducted in triplicates. Subsequently, seedlings were grown under the three water application treatments to monitor their above-ground morphology. The SEM-EDS analysis indicated that the soil media under in-vestigation composed mainly of C, O, N, C, Si, P, S, K, Ca, Fe and Cl. The concentra-tion of O, Si, N, P, K, Fe and Mg which are essential nutrients for proper growth of plants were found to be significantly present in SI compared to S2 and S3. These findings indicate that the application of substrate mix in proportion of 60:20:20 with respect to sphagnum peatmoss, perlite and vermiculite give the best nutrient composi-tion for the production of tomato seedlings. The other part of the study showed that the application of 8 mL water application results in the production of stronger stem diameter, higher seedling plant height and greater number of leaves compared to 4 mL and 6 mL water application respectively.3) In the third part of the study, models were formulated with the aim of simulating the root growth and connecting force in the substrate as well as to determine the soil-root mechanical properties. Tomato seedlings were grown up to 37 days and the sub-strate-roots scanned on the 25th,28th,31st,34th and 37th days using micro-CT. The im-ages were analyzed using VGStudio Max 2.2 to estimate the volume of roots at the above mentioned stages of growth of seedlings. The atomic force microscopy (AFM) was also utilized to gather data on the root force and other elastic properties of 28 days old seedlings. Also TA.XTPlus texture analysis was utilized to assess the com-pressive strength of the substrate-roots. In all, the results are as follows:the highest root growth rate was to be recorded in the experiment using X-ray micro-CT at 7.639 x 10-3 mm3/sec while that of the maximum root growth rate by simulation was found to be 7.854 x 10-3 mm3/sec; the maximum root connecting force was estimated to be 1.568 x 10-7N and 1.254 x 10-7 N from the experimental and simulation results re-spectively; the tomato seedling root recorded index of plasticity in the range of 0 and 1 which shows that it is visco-elastic in nature; the maximum force recorded in the soil-root loading case was 2.52 N.4) The fourth study focussed on the quantification of the damage of the substrate-root. With focus on using a gripping force device designed in-house, an experiments on the visualization of the structure and morphology of the seedling under gripping forces of 1.5N,3.0N and 4.5N were performed and the results quantified using X-ray micro-CT. Strain sensors placed on the two fingers and turning knob of the device were used to control the amount of force applied which was then recorded by the strain instrument. The result showed that as the compressive gripping force increased, the damage in terms of area estimation also increased.5) The last study considered developing pick-up force models, analyzing the vibrat-ing properties of the pick-up device and performing optimization of the transplanting pick-up success. The pick-up force model was developed to establish the relationship between the force and pin penetration angle. The result of the model gave a high coef-ficient of correlation (R2) of 0.960. The vibration simulation of the pick-up device recorded natural frequency ranges of 75.51,118.25,316.67 and 400.04 Hz for four mode numbers. As a result of modification, the experimental vibration test recorded natural frequencies of 60.45,72.51,82.25,101.56 and 121.45 N for the five mode numbers. In optimizing the transplanting pick-up success, a frequency range of 30 to 40 number of seedlings per minute was established with minimum and maximum suc-cess ratios of 90.24% and 91.40% respectively. This indicates that under the best conditions of using peat-perlite-vermiculite in the proportion of 60:20:20 at a bulk density of 0.28 gcm-3 and water application of 8 mL, tomato seedling was found to be more successfully transplanted. Hence the growth conditions arrived at in the study indicates optimum conditions for successful transplanting of tomato seedlings.