Evaluating Physico-Mechanical Behaviour of Pyrethrum Using Principal Component Analysis and Response Surface Modeling for Optimal Design and Performance of Precision Harvesters
Pyrethrum (Chrysanthemumcinerariaefolium L.) is an industrial crop with complex morphology and diverse physico-mechanical properties that jeopardize the optimal design of precision harvesters. This study adopted multivariate correlation, Principal component analysis (PCA) and Response surface methodology (RSM) to characterize mechanistic relationships among morpho-physio-mechanical properties of pyrethrum plant to optimize design and performance of precision harvesters. Mature stalks were established in a completely randomized design of three (3) diverse field sites, with triplications (3) in Kenya’s Nakuru, Uasin Gishu, and Kericho counties, under irrigated and rainfed agriculture. Results showed that all bio-physical-mechanical parameters had bell-shaped frequency distribution, indicating generalized normality and good statistical range for adoption in mechanized harvesters. Multivariate analysis revealed a strong positive correlation (0.91) of wet floral unit volume (Vf) with unit floral mass (MIF). In contrast, floral diameter (FD) with porosity (Ф), and dry floral volume (Vd) with volumetric coefficient of expansion (Ψv) had the most significant negative correlation (？0.98). However, MIF with shoot internode length (SIL), actual density (ρt) with MIF, biomass repose angle (θ) with floral head diameter (FHD), θ with ρt, shear strength (τ) with FD, and Ψv with bulk porosity (ε), respectively, were uncorrelated (0.0). Cutting resistance force (Rc), plucking force (Fp), and mechanical compressibility (？) were non-linearly correlated. First-order linear model characterized the relationship between Rc, moisture content (MC), and mature stalk height (MSH). The first-order regression model best described Vd as a function of ？v and Vf. The first-order surface response model also characterized MSH, flower canopy width (FCW), and SIL. Second-order surface response characterized Fp, Rc, and ？ forces during mechanized harvesting. Further, a downward second-order open parabola characterized Rc, MC, and
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