Several models of apple tree carbon balance have been developed, including a simplified model by our lab. Tree photosynthesis and total dry matter production is the best characterized except for root growth and root respiration. Once dry matter is produced and partitioned to the different organs (another key problem for modeling), the effects of carbon availability to the fruits on their growth and abscission needs to be modeled. Our approach is based on an observed relationship between increased abscission with decreased fruit growth rate of populations of fruit. From several empirical studies of fruit growth and abscission during chemical thinning or imposed stress early in the season, a relationship was found between % abscission and classes of fruit growth rates. It appears to be best if the fruit growth rate is expressed as a percent of the growth rate of the fastest growing group of fruits in each study. Thus in the model the fruit growth allowed by the available carbon each day is compared to a pre-determined maximum growth rate for the cultivar. The percent-of-maximum growth rate then determines how much abscission will occur. Then the growth rate of the remaining fruit is calculated. Additional parameters of the model allowed for a multiple-day buffer of carbon availability, an imposed fruit number reduction (i.e. equivalent to hand thinning), and temperature effects. Although there are more improvements planned, the initial tests have been promising with the simulations showing realistic patterns of fruit abscission and fruit growth.
Alan N. Lakso and Michael D. White
William J. Lamont Jr., Michael D. Orzolek, E. Jay Holcomb, Kathy Demchak, Eric Burkhart, Lisa White, and Bruce Dye
At the Pennsylvania State University (Penn State) High Tunnel Research and Education Facility, a system of production of high-value horticultural crops in high tunnels has been developed that uses plastic mulch and drip irrigation. The Penn State system involves small-scale, plastic-application equipment that prepares and applies plastic mulch and drip-irrigation tape to individual raised beds. It differs from the production system developed by researchers at the University of New Hampshire in which drip-irrigation tape is manually applied to the soil surface and then the entire soil surface in the high tunnel is covered with a black plastic sheet. An overview of the production system used in the Penn State high tunnels is presented in this report.
William J. Lamont Jr., Michael D. Orzolek, E. Jay Holcomb, Robert M. Crassweller, Kathy Demchak, Eric Burkhart, Lisa White, and Bruce Dye
The Center for Plasticulture's High Tunnel Research and Education Facility was established at Pennsylvania State University in 1999. Since its inception, applied research has been conducted at this facility by a team of researchers and extension specialists on the development of a new high tunnel design. The development of crop production recommendations for vegetables, small fruits, tree fruits and cut flowers grown in high tunnels has been a priority. To complement the applied research program, an aggressive extension education program was developed to extend information on the technology of high tunnels to county extension personnel, growers, industry representatives, students, master gardeners and the general public. The extension programming effort consisting of demonstration high tunnels, field days, tours, in-service training, publications and presentations made at winter meetings will be discussed in the report below.