The influence of hail net on the water balance and leaf pigment content of apple orchards

Highlights

• Hail net offsetting the negative effects caused by heat and drought stress in apple production.

• Integrating the effects of hail net on the water supply and some of the parameters of photosynthesis of apple orchard.

• Differences between the response of Golden Reinders and Early Gold varieties on the effect of hail net.

Abstract

Apple production accounts for 60–65 % of all fruit production in Hungary, as one of the most important areas of the fruit production sector. Extreme weather conditions in the continental climate can cause significant problems in apple production. The most important solutions to decrease their effects are irrigation and hail net. In addition to protection against hail damage, the hail net has effect on microclimatic factors, its shading effect has a positive effect on the growth of fruit trees and it reduces the risk of sunburn and transpiration. The aim of our research was to evaluate the effect of hail net on the water balance of Early Gold and Golden Reinders microclimatic factors on the basis of thermal imaging, water potential measurement, canopy dry matter content and to analyze the effect on pigment content. The research was carried out on a weekly basis in July and August 2019 at the Horticultural Unit of Pallag, University of Debrecen, Hungary. Based on our results, the air temperature was 2.91 % lower (p = 0.150) and the relative humidity was 3.16 % higher (p = 0.0001) under the hail net. Results also revealed that the foliage temperature was 7.28 % lower (p = 0.006), the water potential value of the foliage was 20.80 % higher (p = 0.399) under the hail net, while the dry matter content of the leaf was 4.76 % lower than in orchards outside the hail net. Canopy chlorophyll concentration was 10.24 % (p = 0.066) higher and carotenoid values were also higher (16.24 %, p = 0.004) in hail net protected circumstances. Based on the results, the hail net has a favorable effect on the water balance of apple orchards and pigment content of apple leaves through microclimatic conditions, partially offsetting the negative effects caused by summer heat and drought stress.

Introduction

Apples are an extremely important part of both the world's fruit production and consumption because approximately 80 million tons of apples are produced in the world each year. It is also a significant industry at European level a production of approximately 12 million tons/year (USDA, 2019). It accounts for 60–65 % of all fruit production in Hungary, making it one of the most important areas of the fruit growing sector with an average of 550–600 thousand tons/year, so making it the 5th largest production area in Europe. Due to the continental climate, frost damage in autumn, spring and winter and the development of atmospheric drought in summer causes significant problems in apple growing areas (Csihon et al., 2015; Dremák et al., 2016). Nowadays, active protection methods against hail damage and various extreme weather conditions are available. One of them could be the use of hail nets. In 30–70 % of the most significant apple growing areas in Europe hail net is already used (Szabó, 2016), as no other protection equipment has proven to be so effective in controlling ice damage (Lakatos et al., 2011). The hail net has an effect on the physiology of the tree, its shading effect in warm, sunny areas has a positive effect on the growth of fruit trees (Giaccone et al., 2012), reduces the appearance of the effects of sunburn on trees and animal pests (Middleton and McWaters, 2002; Gindaba and Wand, 2005; Iglesias and Alegre, 2006). It has an effect on the microclimatic factors especially temperature, wind speed and relative humidity, which changes will have an effect on the amount of water transpired by the individuals (Bosco et al., 2015; Mupambi et al., 2018) and the temperature of foliage (Iglesias and Alegre, 2006). The use of hail net provides a favorable environment for the synthesis of photosynthetic enzymes, thereby for the photosynthesis to occur (Mditshwa et al., 2019) and the chlorophyll content to increase (Manja and Aoun, 2019). The increased photosynthetic activity and water use efficiency of the canopy increase carbohydrate production and eventually contribute to better yield quality (Sivakumar and Jifon, 2018). Since the long term effect of the hail net on the canopy plays significant role in yield production, this research focuses on the effect of hail net on the canopy. The main aim of the present research is to evaluate and integrate the effects of hail net on the water supply and some of the parameters of photosynthesis of apple orchard where drought and heat sensitive Golden Reinders and Early Gold varieties are grown on sandy soil with very poor soil conditions. The effects of hail net on several water supply related parameters and pigment content of canopy were analyzed, and furthermore the relationship among the examined parameters were explored.