MECHANISTIC PROCESS-LEVEL CROP SIMULATION MODELS FOR RESEARCH AND ON-FARM DECISION SUPPORT
Title: APPROACHES TO MODELING POTATO LEAF APPEARANCE RATE
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 22, 2005
Publication Date: May 1, 2006
Citation: Fleisher, D.H., Shillito, R.M., Timlin, D.J., Kim, S., Reddy, V. 2006. Approaches to modeling potato leaf appearance rate. Agronomy Journal. 98:522-528.
Interpretive Summary: Crop growth models are used to predict plant responses to factors including light, temperature, nutrients and water. Scientists and farmers can use these predictions to help make decisions such as when to irrigate or add fertilizer. However, the model predictions need to be reliable in order to provide realistic data. One way to improve the accuracy of potato models is to include equations that simulate the growth of individual leaves. Experiments were conducted to generate data on the development of potato leaves in the plant canopy under different air temperatures. Methods for using that data to improve the potato models were evaluated. Farmers, scientists, and policy planners who need improved predictions on potato responses to nutrient, water, climate, and land-use changes will benefit from the research.
Two approaches for modeling potato (Solanum tuberosum cv. Kennebec) main and apical stem leaf appearance rates were evaluated, one based on thermal time using the phyllochron, and a second based on a nonlinear temperature response function using a beta distribution. In order to build and test the models, two data sets of leaf appearance measurements at different temperatures (14/10, 17/12, 20/15, 23/18, 28/23, and 34/29°C thermoperiods with a 16/8 hour cycle) were obtained from SPAR (soil-plant-atmosphere-research) chambers. A third set of leaf appearance data from a field trial was obtained for partial validation purposes. Leaf appearance rate linearly increased with growth temperature from 14/10°C to 28/23°C in the first SPAR data set, but declined at the 34/29°C treatment. A phyllochron of 28.2 GDD4°C/leaf was obtained with all the data and 23.5 without the 34/29°C treatment. Parameters for the beta distribution function, which included all data, were Tmax = 40.46°C, Topt = 27.98°C, and Rmax = 0.979 leaves/plant per day. Simulated leaf appearance numbers were accurate in comparison with the 2nd SPAR data set with both the 23.5 GDD4°C/leaf phyllochron and nonlinear temperature response approaches. Partial validation performed with the field data set showed that both models were suitable for simulating potato leaf appearance rates. However, the temperature function approach has advantages in that nonlinear relationships can be included in a single equation.