ISHS Acta Horticulturae 533: VIII International Symposium on Timing Field Production in Vegetable Crops
A SIMPLE WEATHER DRIVEN MODEL TO DETERMINE HARVEST DATE OF GREEN BEANS FOR FREEZING USING QUANTITATIVE AND QUALITATIVE CRITERIA |
| Authors: | M.E. Ferreira, A. Ferreira, L. Andrada, A.A. Monteiro, J.P. de Melo Abreu, V.V. Bianco |
| Keywords: | Phaseolus vulgaris L., pod yield, pod characteristics, modeling, simulation |
| Abstract:
The aim of this study was to construct a simple model to simulate the time-course of pod yield and quality in order to determine the best harvest date of green beans for freezing. In 1992 and 1993, two field trials with green beans (Phaseolus vulgaris L., cv. Alcade) were conducted in Central Portugal. Three plant populations, two irrigation levels, and various harvest dates were studied. Simultaneously, two complementary field trials were conducted, consisting of eight sowing dates per year. Plant population significantly influenced biomass and pod yield, while soil water level only affected these quantities in 1993. Developmental stage (i.e., thermal time after first flowering) was by far the most important effect to determine pod quality. Soil water level and plant population had no consistent effect on pod quality characteristics. Empirical sub-models of the changes of the pod quality characteristics, in relation to phasic development, were obtained by regression analysis. Except for the color determinations, the proportion of the variation accounted for by the sub-models was high (r2 ranged from 0.70 to 0.93). Since, in practice, soil physical characteristics are seldom available, and irrigation tends to suppress water stress, the model assumes that mineral nutrition and water are non-limiting. Minimal weather data required are minimum and maximum temperatures, and sunshine hours; no soil information is needed. Daily dry matter yield is calculated by the minimum of the estimates from two commonly used approaches. Phasic development is simulated through thermal time. Quality pod characteristics are statistically determined by thermal time and optionally shown in relation to pod yield. Model validation showed that the predicted values of biomass and pod yields, and quality variables were in general good agreement with the measured values. The outputs of this simple model can be used to assist the freezing industry in scheduling sowing dates, and therefore, production of green beans. | |
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