Growth of Young Orchardgrass ( Dactylis glomerata L.) Plants in Different Environments 1

Growth and development of young ‘Boone’ orchardgrass plants were studied in a factorial experiment involving two temperature regimes, two photoperiods, three levels of N, and four levels of P. Seed was planted in a growth medium of Hartsells fsl soil and washed sand. Three days after emergence, seedlings were subjected to the experimental temperatures and photoperiods. Harvests of whole plants were made 3 weeks after the temperature‐photoperiod treatments were initiated and at 2‐week intervals through the eleventh week. Photoperiod effects were evident at the first harvest. With essentially equal radiant energy supplied to the two groups, the leaves of plants in the shorter, 10‐hour, photoperiod (SD) emerged more rapidly. Also, SD plants had a greater total length of exposed leaf blades during the early weeks and a lower shoot: root ratio than did plants in the 20‐ hour photoperiod. Weights of shoots, roots, and whole plants were greater under SD during the first 7 weeks. No response to supplemental N was detected during the first few weeks, but later it increased rate of leaf appearance, length of exposed blades, and weights of shoots and roots. With all measurements, marked responses to P were obtained. For the most part, interactions were relatively unimportant, but a strong N × P effect was operative after the 5th week. It is concluded that the observed plant‐weight increases may be accounted for, in part, by the morphological responses and their effects on light interception and absorptive capacities of the root systems.