Modelos De Regresion

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Scientia Horticulturae 138 (2012) 165–170

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Scientia Horticulturae
journal homepage: www.elsevier.com/locate/scihorti

Prediction of harvest start date in highbush blueberry using time series regression models with correlated errors
˜ Carlos Munoz a , Julio Ávila a , Sonia Salvo b,∗ , Juan I.Huircán a
a b

Department of Electrical Engineering, Universidad de La Frontera, Chile Department of Mathematics and Statistics, Universidad de La Frontera, Chile

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a b s t r a c t
This work proposes a model for predicting the harvest start date sufficiently far ahead to enable the farmer to make a well-informed plan. The heat unit method is widely used in agriculture asthe phenological unit of time, which offers the least variation in date predictions, and heat units have been used to estimate the start of harvesting in various crops. The problem is that the farmer needs to know the number of days and not the number of heat units that are needed until the harvest can begin. It is proposed that the daily maximum and minimum temperature time series be modelledthrough regression models with errors correlated using a sine curve. Using the requirements reported by Carlson and Hancock (1991) for the start of harvest of 13 varieties of blueberry over 15 years, a model has been developed that allows the requirements of heat units to be translated into days remaining until harvest. The models are estimated at intervals of 3 months, 2 months, 1 month, 14 days and7 days before the date at which the heat unit requirements are reached. Three months ahead, the error was less than 10 days late, and 7 days ahead, it was 2 days late. A blueberry orchard in Temuco, Chile, was used as a case study and had similar results. All the errors are within the variability of the heat unit models. The models can be used by farmers to predict and plan the blueberry harvestwith adjustments for location and variety. © 2012 Elsevier B.V. All rights reserved.

Article history: Received 8 January 2012 Accepted 16 February 2012 Keywords: Blueberry Vaccinium Heat units Time series regression Harvest date

1. Introduction Blueberry cultivation is an important economic activity in Chile, where it is practiced between the Valparaíso and Los Lagos regions and covers morethan 7000 ha (ODEPA and CIREN, 2010). In the 2010 season, more than 50,000 tons of blueberries were exported, mainly to the United States and the European Union (Bravo, 2011). Blueberries can be exported either frozen or fresh; however, the latter draw a higher sale price in the final markets. In 2011, for example, frozen blueberries drew only 40% of the value of fresh fruit (ODEPA, 2011). Theseexports to the northern hemisphere are favoured by the high sale prices achieved in the early and late varieties produced in the off-season. There are two important aspects for fresh blueberry exporters to consider: estimating the yield, which has been addressed (Hancock et al., 2000; Salvo et al., 2012), and the harvest start date. Knowing the harvest start date accurately at least 2–3 weeks in...