Water shortage is becoming a severe problem in arid and semiarid regions worldwide, reducing the availability of agricultural land and water resources. In Spain, citrus is one of the most economically important crops, with 74,000 ha devoted to its cultivation. Since water resources are increasingly more insufficient, the efficient use of water is becoming more essential. Deficit irrigation in many agricultural crops has frequently proved to be an efficient tool for improving water-use efficiency. This paper examines the effects a deficit irrigation during the ripening period on yield and the most representative fruit quality properties. The study was conducted during two consecutive years (2009-2010) in a commercial 12-year-old orange orchard (
Citrus is one of the most important crops in Andalusian agriculture, with 74,000 ha devoted to its cultivation. In the last 25 years, this surface has grown by 2.04% annually; and it has therefore been promoted that the citrus production will be close to 2.3 million tons by 2015 (30% of the national production). Of the total area of citrus in Andalusia, 51,500 ha are dedicated to sweet orange, being the Navelina variety the second most representative of them with 13,000 ha García-Tejero [
Considering that water is a scarce resource in Spain, the irrigated agriculture accounting for 80% of global water consumption [
Considering the previous researches by Pérez-Pérez et al. [
The trial was conducted during two consecutive years (2009-2010), in a commercial 12-years-old orchard of mature orange trees (
The local climate is Mediterranean dry, with an average potential evapotranspiration (
The experimental design was a randomized complete block, with four replicates per treatment. The experimental unit had three rows, with five trees per row, and the three central trees (central row) were established for measuring fruit properties and final yield.
A deficit-irrigation treatment (DI) was applied during the ripening period, with a water stress ratio of 0.75, defined as the ratio between the actual water-limited supplied in this treatment versus the water supplied to control treatment. Also, a fully irrigated treatment at 100% of crop evapotranspiration (ETc) was considered as a control. Thus, in 2009 year the water-restriction period was from 301 day of the year (DOY) to harvest (322 DOY), ranging this period from 308 to 330 DOY in 2010.
The seasonal values of
According to this, Table
Irrigation water applied (mm) in each treatment during the studied period.
Period (DOY) | Year | |||
---|---|---|---|---|
2009 | 2010 | |||
Control | DI | Control | DI | |
1–31 | 0 | 0 | 0 | 0 |
32–59 | 7,7 | 7,7 | 0 | 0 |
60–90 | 17,2 | 17,2 | 3,6 | 3,6 |
91–120 | 21,4 | 21,4 | 11,4 | 11,4 |
121–151 | 44,1 | 44,1 | 44,6 | 44,6 |
152–181 | 70,8 | 70,8 | 65 | 65 |
182–212 | 82,5 | 82,5 | 98,6 | 98,6 |
213–243 | 93,5 | 93,5 | 95 | 95 |
244–273 | 81 | 81 | 83 | 83 |
274–304* | 72,8 | 70,4 | 56 | 56 |
305–334* | 21,4 | 15,6 | 20 | 14,6 |
335–365 | 0 | 0 | 0 | 0 |
| ||||
Total | 512,4 | 504,2 | 477,2 | 471,8 |
DOY: day of the year; Control: control treatment; DI: deficit irrigation treatment; *periods in which DI was applied.
During the studied period three different samples were established in each season (301, 315, and 322 DOY in 2009 and 308, 316, 330 DOY in 2010). For each sample there were determined 11 fruit-quality parameters, analyzing 5 fruits per tree. The external fruit colour index (
The content of total soluble solids (TSS) in the juice was measured with a refractometer, and titrable acidity (TA) was determined by titration with NaOH and phenolphthalein indicator in 100 mL of juice. Maturity index (MI) was expressed as the relation TSS/TA. Rind weight (RW), juice weight (JW), and the ratio of juice weight versus fruit weight (JR) were determined using a digital scale with a precision of ±0.01 g. Total C vitamin (C-vit) and total flavonoids (TF) were determined by liquid chromatography (HPLC), expressed as mg of ascorbic acid and mg of hesperidin in 100 mL of juice, respectively.
At harvest, fruit yield was determined for each tree by weighing the orange fruits. One sample of 100 fruits per tree was collected to determine average fruit weight.
An exploratory and descriptive analysis was made of yield and its components, followed by an analysis of variance (ANOVA) with a mean separation analysis applying a Tukey’s test. SPSS statistical software package was used (SPSS 15.2 for Windows, 2006, SPSS Inc., Chicago, IL).
There was no clear response of the tree yield related to deficit irrigation (Figure
Effects of deficit irrigation on yield. Control, control treatment fully irrigated at 100% ETc; DI, deficit irrigation treatment. Vertical lines represent the error bars in each treatment.
In our case, the DI strategy imposed in this experience did not show significant effects on yield, further more, there was not observed an accumulative effect of water stress in subsequent years, and in the second year DI showed a higher yield, with an increment of 11,000 kg ha−1. These results are in line with those showed by García-Tejero et al. [
The lack of effects of DI on final yield along with the water savings promoted increments on irrigation water productivity, this being especially remarkable during 2010 year (Figure
Irrigation water productivity in each treatment during the studied period. Control, control treatment fully irrigated at 100% ETc; DI, deficit irrigation treatment. Vertical lines represent the error bars in each treatment.
Increasing crop-water productivity may be a means of achieving efficient and effective water use. In agriculture, the interest is to produce more with less water, because available water for irrigated land is a limiting factor in many world areas [
Figure
Timing evolution of fruit size components. Control, control treatment; DI, deficit irrigation. Vertical lines represent the error bars in each treatment.
During 2010, the obtained results are in line with those in the previous year. There were non significant differences in any parameter, although, again, there were observed increases in juice weight in DI (Figure
On overall, these results argued that a moderate water-stress during the ripening period does not promote negative effects on fruit size and juice content, this stage being a good time for introduce water savings and maintain an optimum fruit development. Ballester et al. [
Figure
Timing evolution of fruit quality parameters. Control, control treatment; DI, deficit irrigation; TSS, total soluble solids; TA, titrable acidity; MI, maturity index. Vertical lines represent the error bars in each treatment.
Many studies have been pointed out that water stress in citrus crops affects these properties [
Finally, the effects of DI during the ripening period in the temporal evolution of external colour index were studied. The obtained results did not show significant differences between treatments (Figure
Effects of deficit irrigation on colour index (CI) during 2009 (a) and 2010 year (b). Vertical lines represent the error bars in each treatment.
In recent years research activities in agriculture have been aimed to find new production strategies for improving the foods nutraceutical properties. Among the possibilities for improving the quality of them are those designed to achieve an increase in the components recognized as healthy. In this sense, Flavonoids and vitamin C are highly beneficial antioxidant compounds found in many fruits and vegetables, and it’s now well established that a plentiful intake of antioxidants through foods, drinks and supplements is vital for optimal human health. It has been recognized that orange juice is an important source of vitamin C and hesperidin for human nutrition. In this sense, we have tried to address a study on the effects of deficit irrigation in the synthesis of these compounds. In line with the previous results, there were no detected significant differences between treatments during the monitoring period. In this sense, moderate deficit irrigation during the ripening period was not reflected with a decrease in the ascorbic acid (Figure
Effects of deficit irrigation on ascorbic acid (a) and hesperidin contents (b). Control, control treatment; DI, deficit irrigation treatment. Vertical lines represent the error bars in each treatment.
Navarro et al. [
According to the results of the present study, we have not been able to prove that a moderate water stress during the ripening period in sweet orange citrus trees induce a deterioration of fruit quality properties. In this sense, a descend in juice content and in fruit weight was not observed. This fact supports the obtained results on final yield, which was not affected by deficit irrigation, even with an increase on yield values of deficit irrigation.
In terms of fruit organoleptic and nutraceutical properties, there were not detected pernicious effects on them. Moreover, DI treatment showed higher values of maturity index due to the keeping of ratio between the contents of total soluble solids and titrable acidity.
Considering these results, we can affirm that a moderate water stress applied during the last fruit-growth period is a sustainable strategy for saving water, increasing the irrigation productivity and obtaining fruits with similar properties to those without deficit irrigation.
The authors thank Antonio Caballero for his excellent technical support as personal of Rio Tinto Fruit S.L., where experimental assay has been development. This work was supported by funds from the Project between IFAPA and the Companies Arvensis Agro S.A (CAICEM 09-46), Cultifort S.L. (CC09-009), and Sustineable Agro Solutions S.A. (CEM 09-009).