Association Between Morphological Characteristics and Agronomic Performance of Different Leaf Sized White Clover Varieties

ABSTRACT White clover ( Trifolium repens L.) adoption on commercial farms is promoted by improving agronomic performances and persistence in new varieties. Morphological characters are measured annually through statutory ‘spaced plant’ assessments (DUS—distinct, uniform and stable), but only to establish variety identity for market release. The opportunity to utilise this plant trait approach to indicate agronomic potential was investigated. Five white clover varieties were examined as isolated plants inserted into perennial ryegrass (PRG; Lolium perenne L.) plots, managed at 150 kg N/ha under a simulated rotational grazing protocol from 2024 to 2025. Isolated plant morphological characters (leaf, petiole, peduncle and stolon) were measured seasonally and compared to their respective spaced plant records. Isolated plant morphology was several orders of magnitude smaller than spaced plants and displayed significant ( p < 0.001) seasonal variations, with general declines from autumn to spring and recovery thereafter. Large varietal plasticity was evident in all characters ( p < 0.001). However, isolated versus spaced plant variety ranking was conserved for leaf size, petiole length/thickness plus stolon thickness, with less repeatability for peduncle length/thickness, internode length, flowering propensity. Two parallel varietal evaluation experiments (simulated and animal grazing), were conducted on these five clovers, conventionally sown with PRG at 150 kg N/ha. This agronomic data was correlated with isolated plant morphologies and revealed that leaf size, petiole characters and stolon thickness maintained close positive associations with clover proportion and production, particularly in summer and autumn. Plant area changes aligned with clover content but not yield. In spring, many morphological associations with yield were negative when most varieties did not maintain leaves at the canopy surface. Light penetration proportion to soil was greatest in spring and least in autumn, when larger leaf sizes of all plants intercepted more light, that is, created most shade. Some varieties developed thicker stolons and more growing points in spring suggesting greater robustness but did not yield more. This study identifies several traits that breeders could modify to enhance agronomic performance but needs further work to quantify relationship strength and repeatability before adoption by variety evaluators.