A model for 'Gala' apple crop value grown in Chile: an approach that includes main weather condition effects

In central Chile, the size of the fruit and yield of 'Gala' apples depend mainly on crop load and maximum temperature during winter (WTmax), and the length of the growing season (SL). Therefore, differential regulation of crop load is required to optimize the crop value depending on the growing area. The objective of this study was to develop a model to estimate crop value that includes important weather characteristics for 'Gala' productivity. The data was obtained from 13 thinning trials performed in different apple growing areas during seasons 2012 to 2016, from orchards located between latitudes 34 degrees 20'S and 37 degrees 40'S. The prediction models for yield (R-2=0.86; RMSE=0.57) and fruit size (R-2=0.58; RMSE=215.27) were constructed from multiple regressions analysis based on the WTmax (12 degrees C to 14.5 degrees C), SL (122 to 146 days) and crop load (210,000 to 560,000 fruits ha(-1) intercepting 70% PAR). The proportion of fruit in each commercial category was estimated as a function of the average fruit weight. According to winter weather, simulations for contrasting growing areas (cold, 12 degrees C WTmax; warm, 14.5 degrees C) were carried out with an average season length of 136 days. The results show that under the current price scenario, the crop value in areas or years with warm winters is optimized with an average fruit size of similar to 138 g, which is reached with similar to 360,000 fruits ha(-1) (similar to 50 t ha(-1)); while with colder winters, it is still increasing with an average fruit weight of similar to 167 g, similar to 560,000 fruits ha(-1) (similar to 90 t ha(-1)). Thus, the crop value for warmer conditions is lesser than 60% of the colder condition. Although the validation of the model has not been tested yet, the model can be a promising tool to determine pruning and thinning assessing crop profitability under changing climate scenarios.