modeling leaf production and senescence in wheat

this experiment was conducted to quantify leaf production and senescence in wheat. the experiment was carried out at research farm of the gorgan university of agricultural sciences and natural resources, gorgan, iran in 2005 using a randomized complete design considering sowing dates as environment. treatments were sowing date (14 december, 20 jan and 21 feb, 2005) and cultivars (aria, atrak, koohdasht, shirodi, tajan, taro and zagros). the results revealed that the start of leaf production, leaf appearance rate and time of cessation of leaf production on main steam aren't different in between cultivars but leaf production rate on main steam for sowing dates was 0.01 leaf day-1. leaf senescence on main steam commenced after 475 growth degree day (gdd) and it continued at 0.07% per gdd. production of leaves in plant consisted of two phases and that were closely related to the leaf production on main stem. at the first phase, one leaf were added to the whole plant leaves by each leaf increase on the main stem. the second phase started when there were three leaves on main stem. at this phase, 2.7 leaves were added to the leaves of the whole plant by each leaf increase on main stem. leaf death on whole plant was closely related to leaf senescence on the main stem, and it had two phases. with each percent of leaves death on main stem 0.83 and 1.03 percent of whole plant leaves died at first and second phases, respectively. mean leaf longevity was about 616 gdd. the results suggest that leaf production and senescence in wheat could be quantified using different equations.