Models to Estimate Chilling Accumulation Under Subtropical Climatic Conditions in Brazil

Abstract

Chilling requirement is a characteristic that limits temperate fruit crops cultivation under subtropical climate. Several mathematic models, differing on the relative value of chilling units have been developed, in order to estimate the chilling accumulation on a given site. The present work compared eight of these models using data from hourly temperatures from May to August, from a period of 11 years, collected in Pelotas, RS, Brazil, aiming to characterize the region regarding the chilling accumulation for the cultivation of deciduous fruit trees and it also had as objective to check if a model using average temperatures is suitable enough to be used when hourly temperatures were not available. The eight tested models were: Chilling Hours (≤7.2°C); Chilling Hours (≤11°C); Utah; Low Chill; Dynamic; Mean Temperatures; Positive Utah and Taiwan. The results showed large differences between years, regardless of the used model. However, the Taiwan and Low Chill models seemed more suitable for the estimation of the accumulation of cold in the Pelotas region. The Medium Temperatures model can be used as a valid option since it has a high correlation with the other models and easy data availability.

Análise de tendência das componentes do saldo de radiação e número de horas de frio em Cruz Alta - RS

“…Os resultados indicaram, além do melhor modelo a ser aplicado, que no sul do Brasil há grande variação do NHF, com os locais mais favoráveis associados as maiores altitudes. Milech et al (2018) comparam oito modelos de estimativa do NHF para 11 anos de dados de inverno em Pelotas-RS. Geirinhas et al (2017), mostraram que existe tendências positivas e significativas da frequência de ondas de calor desde a década de 80 nas diferentes regiões brasileiras.…”

Cold hardiness-informed budbreak reveals role of freezing temperatures and daily fluctuation in chill accumulation model

“…In the studies that contributed data for the DM, some observations demonstrate a chill negation effect, but where negation only happens within the first few days of experiencing the warm temperatures (≥19 °C; Erez et al, 1979; Couvillon and Erez, 1985). However, studies of woody perennials in warmer, subtropical climates (particularly of temperate horticultural crops) have seen the need to adapt models by omitting such chill negation from warm temperatures, or accumulate chilling in a much warmer range (Ou and Chen, 2000; Lu et al, 2012; Milech et al, 2018), and the use of UT model is discouraged in warm climates (Luedeling et al, 2023). Our artificial treatments did not include temperatures where possible effects of chill negation were expected.…”

Chilling requirement of four peach cultivars estimated by changes in flower bud weights

“…Chill units (or cold units) were calculated for each collection date using Low Chill (Gilreath & Buchanan, 1981) and Taiwan (Ou & Chen, 2000) models. These models were chosen based on previous work in which they seemed to be the most suitable for the Pelotas area (Milech et al 2018a(Milech et al , 2018b.…”