Int J Biometeorol (2001) 45:191–195
© ISB 2001
O R I G I N A L A RT I C L E
Nadia Valentini · Giovanni Me · Roberto Ferrero Federico Spanna
Use of bioclimatic indexes to characterize phenological phases of apple varieties in Northern Italy Received: 25 October 2000 / Revised: 6 August 2001 / Accepted: 6 August 2001
Abstract The research was designed to characterize the phenological behaviour of different apple varieties and to compare different bioclimatic indexes in order to evaluate their adaptability in describing the phenological phases of fruit species. A field study on the requirement for chilling units (winter chilling requirement) and the accumulation of growing degree hours of 15 native apple cultivars was carried out in a fruit-growing area in North West Italy (Cuneo Province, Piedmont). From 1991 to 1993, climatic data were collected at meteorological stations installed in an experimental orchard (Verzuolo, Cuneo). Four methods were compared to determine the winter chilling requirement: Hutchins, Weinberger-Eggert, Utah and North Carolina. The Utah method was applied to determine the time when the chilling units accumulated become effective in meeting the rest requirements. A comparison of the different methods indicated that the Weinberger-Eggert method is the best: as it showed the lowest statistical variability during the 3 years of observations. The growing degree hour requirement (GDH) was estimated by the North Carolina method with two different base temperatures: 4.4°C and 6.1°C. More difficulties were met when the date of rest completion and the beginning of GDH accumulation was determined. The best base temperature for the estimation of GDH is 4.4°C. Phenological and climatic characterizations are two basic tools for giving farmers and agricultural advisors important information about which Prepared in conjunction with the international conference ‘Progress in Phenology: Monitoring, Data Analysis and Global Change Impacts’ held in Freising, Germany, October 4–6 2000 N. Valentini (✉) e-mail:
[email protected] Fax: +39-11-6708823 G. Me, R. Ferrero Università di Torino, Dipartimento di Colture Arboree, Via Leonardo da Vinci, 44 10095 Grugliasco, Italy F. Spanna Settore Fitosanitario regionale – Sez. Agrometeorologia – Regione Piemonte, Corso Grosseto 71/6, 10100 Torino, Italy e-mail:
[email protected] Fax: +39-11-4323710
varieties to choose and which are the best and the most correct cultivation practices to follow. Keywords Malus pumila Miller · Phenology · Dormancy · Winter chilling requirement · Growing degree hours
Introduction The study of the phenological behaviour of crops as a part of a well-characterized environment is important both to obtain satisfactory production results and to determine the most suitable agronomic techniques. Research studies on interactions between climate and cultivation have involved the setting up of specific bioclimatic indexes (Fatta Del Bosco and Tuccio 1968; Richardson et al. 1974) with the aim of explaining vegetative and productive behaviour. This field investigation was carried out to characterize the phenological behaviour of 15 different apple cultivars and quantify their development characteristics. Another aim of this research was to evaluate and to compare the applicability of various bioclimatic indexes to the environmental conditions of North-West Italy by using statistical methods.
Materials and methods The experimental orchard is located in Verzuolo (province of Cuneo), 470 m above sea level, in a fruit-growing area in North-West Italy. This area is characterized by climate conditions typical of Italian pre-alpine regions. The mean rainfall is about 860 mm, with the primary maximum in April–May and the secondary in autumn. The minimum occurs during summer (principally in July) and winter. December and January are the coldest periods while July and August register the maximum temperatures. During winter, frequent frosts occur and sometimes temperatures are lower than –12/–15°C. The orchard is located on a medium slope and is characterized by loamy, slightly acid soil (pH 6.1) with a medium depth and a good organic matter supply. The research was carried out from autumn 1991 to spring 1994. During this period the climatic data were collected at SIAP (Bologna, Italy) meteorological stations installed in the experimental orchard. The temperatures were measured hourly from the end of summer till the end of spring.
192 Fig. 1 Phenological phases of the apple tree (Gautier 1988)
Phenological data were determined in the orchard by weekly observations from bud breaking (stage B, Fig. 1) until the fall of the leaves, following the Fleckinger stages (Gautier 1988). The study of the requirement for chilling units was carried out on the following 15 apple cultivars native to Piedmont’s mountain valleys: Bela d’Barge, Bouras, Buta d’la Cascina, Carla, Carpendù Rusulent, Dominici, Fiandrine, Gambe Fine Piate, Gris Canavoeit, Magnana, Poum d’la Madlena, Poum d’la Porta, Ravè Valle Gesso, Rous Giachè, Runsè. The trees were planted in 1990, using M111 as rootstock. The training system was a free palmette. Four methods were compared during the 1991–1992, 1992–1993 and 1993–1994 seasons to determine the winter chilling requirement (WCR): Hutchins, Weinberger-Eggert (Fatta del Bosco and Tuccio 1968), Utah (Richardson et al. 1974) and North Carolina (Shaltout and Unrath 1983). These methods use different calculations to obtain the chilling units from the hourly temperatures. In the Hutchins method, 1 h of exposure to a temperature lower than 7°C equals one chilling unit (CU). The WeinbergerEggert method does not consider that temperatures lower than 0°C and higher than 7°C contribute to the chilling unit value. In the Utah method 1 CU equals 1 h of exposure at 6.1°C; CU accumulation becomes less than 1 as temperature deviates from that opti-
mum; above 15°C the contribution is negative and 0 units are accumulated below 1.4°C (Table 1). The North Carolina model proposes a broader range of effective temperatures and incorporates a greater negative effect when temperatures exceed 21°C. The optimum chilling peak is at 7.2°C (Table 2). Moreover, the Utah model suggests a mathematical method to determine the date when chilling unit accumulation begins. This method was applied to all the four models considered. Positive chilling units begin to accumulate immediately after the day in autumn when the largest negative accumulation is experienced (Richardson et al. 1974). The accumulation of CU was terminated at the beginning of bud break (stage B, Fig. 1). From this moment, until full bloom (stage F2, Fig. 1), the requirement for growing degree hours (GDH) was estimated according to the North Carolina model (Shaltout and Unrath 1983) by using two different base temperatures:
[ ] GDH = ∑ [∑ (T – 6.1 °C)] Bud 24
GDH = ∑ ∑ (Th – 4.4 °C) FB
0
Bud 24 FB
0
h
where Bud=bud breaking, FB=full bloom and Th=hourly temperature.
193 Table 1 Corresponding temperature and chill unit (CU) value of the Utah model
Temperature °C
CU
18.0
0.0 0.5 1.0 0.5 0.0 –0.5 –1.0
Table 2 Corresponding temperature and chill unit value of the North Carolina model
Temperature °C
CU
–1.1 1.6 7.2 13.0 16.5 19.0 20.7 22.1 23.3
0.0 0.5 1.0 0.5 0.0 –0.5 –1.0 –1.5 –2.0
Table 3 Comparison of four methods to determine winter chilling requirement (WCR; mean 1991–1993) Method
WCR (CU)
CV
Hutchins Weinberger-Eggert Utah North Carolina
2559.4* 2223.7*** 2538.8* 2683.9**
0.0587** 0.0393*** 0.0567* 0.0560*
*–***Means followed by the same symbol are not significantly different for P=0.01 Table 4 WCR values obtained by the Weinberger-Eggert method for 15 apple cultivars (mean 1991–1993)
Fig. 2 Estimation of the beginning of accumulation of chilling units (CU) by Utah method
Cultivar
WCR (CU)
SD
CV (%)
Bud break date
P. Madlena Runsè Bouras Gambe F.P. Carla Magnana Carpendú R. Bela d’B. Fiandrine Dominici P. Porta Gris C. Buta C. Ravè V.G. Rous Giachè
2138 2193 2193 2193 2196 2207 2222 2236 2236 2238 2238 2245 2247 2252 2323
41.8 61.6 61.6 61.6 62.8 74.5 87.8 91.0 91.2 93.0 93.0 99.0 109.7 110.1 174.9
1.95 2.81 2.81 2.81 2.86 3.38 3.95 4.07 4.08 4.16 4.16 4.41 4.88 4.89 7.53
4 March 10 March 10 March 10 March 10 March 14 March 14 March 15 March 17 March 17 March 17 March 19 March 19 March 19 March 26 March
For each method the standard deviation (SD) and coefficient of variability (CV) were calculated and the data were examined with analysis of variance. Mean values were compared by the Tukey test.
Results When WCR is calculated by the Utah method from September on, there is an initial decrease of the curve followed by an increase. The lowest point is assumed to be
the beginning of CU accumulation. In 1991 the estimated date was the 5 October, in 1992 it was 1 October and in 1993 it was 26 September (Fig. 2). A comparison of the four methods of determining WCR shows no significant differences between the results obtained from the Hutchins and Utah models during the three seasons. By contrast, the Weinberger-Eggert and the North Carolina models gave the lowest and the highest value respectively. Comparing the means of co-
194 Table 5 Comparison of different base temperatures for the determination of the growing degree hour requirement (GDH) (means 1991–1993)
Base temperature (°C)
CV
GDH
4.4 6.1
0.1457 * 0.1850 **
4793.4 ** 3554.0 *
*,**Means followed by the same symbol are not significantly different for P=0.05
Table 6 GDH requirement of 15 apple cultivars with two different base temperatures (means 1991–1993) Cultivar
GDH 6.1°C
CV (6.1°C) %
GDH 4.4°C
CV (4.4°C) %
Full bloom date
P. Madlena Carpendú R. Ravè V.G. Carla Buta C. P. Porta Magnana Runsè Fiandrine Dominici Bela d’B. Rous Giachè Bouras Gris C. Gambe F.P.
2934 3018 3198 3442 3481 3449 3463 3497 3512 3598 3665 4000 3900 4034 4115
27.8 25.6 10.9 19.3 26.1 11.8 12.4 22.9 8.4 2.6 18.1 27.3 24.9 25.9 13.6
4066 4079 4325 4663 4675 4680 4730 4742 4775 4843 4927 5161 5296 5387 5552
18.3 19.2 8.6 13.6 21.4 9.4 6.7 16.6 7.3 3.6 15.6 25.0 19.5 23.6 10.2
7 April 11 April 19 April 15 April 18 April 20 April 18 April 14 April 22 April 20 April 19 April 25 April 18 April 25 April 20 April
efficients of variability for each method, the WeinbergerEggert method shows the lowest statistical variability during the 3 years of observations (Table 3). With the Weinberger-Eggert method the WCR for the 15 cultivars varies from 2138 (Pum d’la Madlena) to 2323 CU (Rous Giachè). The standard deviation and the coefficient of variability increase when going from the more precocious cultivars to the later ones. The CU requirements for each cultivar and their precocity in bud breaking are show in Table 4. The comparison between the two base temperatures used to determine the GDH requirement shows that the lower coefficient of variability was obtained when the 4.4°C base temperature (Table 5) was used; with this base temperature, GDH varies from 4066°C (Pum d’la Madlena) to 5552°C (Gambe Fine Piate) for the years 1991–1993. The GDH requirement and the date of full bloom of each cultivar are shown in Table 6.
Discussion The comparison of the different methods indicated that the Weimberger-Eggert method supplies the best result and, in fact, it showed the lowest statistical variability during the 3 years of observations. The Utah method is the more correct and objective way of calculating the date when CU accumulation begins. However, the moment when dormancy is effectively broken seems to precede bud breaking. In fact, in our region, apple varieties satisfy their winter chilling requirement during December or January, but there are
great difficulties in determining the exact date when the chilling requirement is completely satisfied. For bud sprouting to begin, the accumulation of both chilling units and degree hours is required. In consequence, in this study WCR are probably overestimated and therefore GDH are underestimated. Studies of this kind attempt to determine the actual moment when the chilling requirement is satisfied in order to adopt it as the starting point for the calculation of GDH accumulation. In practice, to determine when the winter chilling requirement is satisfied it is necessary to cut off some branches and put them into a laboratory under controlled conditions (Guerriero and Scalabrelli 1991); if the WCR is satisfied, some days later the flower buds begin to open. In this way we can determine the right date for starting the GDH calculation. The choice of the base temperature for the GDH calculation was based on the lower variability calculated over 3 years; the results have demonstrated that 4.4°C is the best base temperature for estimating GDH, but it is important to test other base temperatures and other methods for this estimation. This approach should be applied to other fruit species to describe the behaviour of different cultivars and their adaptability to different climatic conditions. Phenological and climatic characterizations can be important indicators for farmers and agricultural advisors, informing their choice of varieties and applications for the best cultivation practices.
195 Acknowledgements We wish to thank Dr. Luigi Pellegrino for the elaboration of dates and the Istituto Professionale di Stato per l’Agricoltura di Verzuolo. The experiment complied with the current laws of Italy.
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