Development of a hemp (Cannabis sativa L.) simulation model 3. The effect of plant density on leaf appearance, expansion and senescence

The accurate prediction of leaf area production is an important element of many crop models, given that it is the key determinant of light interception and the accumulation of plant biomass. Plant density has been reported to have a significant influence on the component processes of leaf area production in hemp. This study investigates the response to plant density of leaf (node) appearance, leaf expansion at each node and leaf senescence, and develops relationships for use in the hemp model described in the final paper of this series. Green and senesced node counts were made at regular intervals in a plant density trial for treatments of 50, 80, 120, 200 and 300 plants/m2. Measurements were also made of the fully expanded leaf area at each node. Leaf pairs were found to appear and senesce at constant thermal time durations; between 84 and 97°Cd for node production, and between 130 and 167°Cd for node senescence. Leaf area per node at first increased linearly with node number, then reached a plateau, and subsequently declined linearly. Increases in plant density resulted in slower rates of node production and reduced the maximum leaf area per node.