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 interceptio n and the accumulation of plant biomass. Plant density has been reported to have a significant influence on the component processes of leaf area produ ction in hemp. This study investigates the response to plant density of lea f (node) appearance, leaf expansion at each node and leaf senescence, and d evelops relationships for use in the hemp model described in the final pape r of this series. Green and senesced node counts were made at regular intervals in a plant de nsity trial for treatments of 50, 80, 120, 200 and 300 plants/m(2). Measure ments were also made of the fully expanded leaf area at each node. Leaf pai rs were found to appear and senesce at constant thermal time durations; bet ween 84 and 97 degrees Cd for node production, and between 130 and 167 degr ees Cd for node senescence. Leaf area per node at first increased linearly with node number, then reached a plateau, and subsequently declined linearl y. Increases in plant density resulted in slower rates of node production a nd reduced the maximum leaf area per node.