ENVIRONMENTAL EFFECTS ON CORN EAR MORPHOLOGY, PLANTING TO SILKING

Numerous studies describe the morphological events in corn, Zea mays L., from planting to tasseling and silking. However, the effects of the environment on the rate of development are not clearly defined during this period. Therefore, a study was conducted to define and model the environmental effects on corn development with special emphasis on ear development. A scheme was developed that would allow for the simultaneous modeling of the vegetative, tassel and ear development. Tassel initiation was found to be complete by the time seven leaves were fully emerged. Ear initiation was complete by the time nine leaves were fully emerged. Row initiation and the start of kernel primordia set was observed on plants with as few as six leaves fully emerged and was complete by the time ten leaves were fully emerged. The initiation of kernel primoridia stopped three to five days before silking when a moisture stress occurred, and continued until silking when the crop was well watered. As a general rule, the rate of development from planting to silking was governed most by the daily temperature regime. The daily temperature range affected the rate of development whenever the temperature approached the critical threshold. Rate of development during the period from tassel initiation to ear initiation was related to water stress as well as temperature. Water stresses also tended to delay silking. The computer model framework determines the dates of emergence, tassel initiation, ear initiation, tasseling, and silking using growing degree units. Six methods of calculating thermal units were used. All six methods predicted the dates of the critical development events described above better than using days after planting. In addition to determining dates of specific developmental events, the model predicts the number of leaves initiated and emerged each day and the cumulative number of kernel primordia initiated each day. The computer model was designed to allow easy substitution of developmental subroutines, and provisions were made for including a tassel development submodel. The model can be used alone or can be adapted to interface with a physiologically based crop model. As a subroutine for a larger crop model, it would serve as a biological clock for various physiological processes