Department of Soil Science

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Browsing Department of Soil Science by Subject "Apple trees -- Grabouw -- South Africa"

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    The effect of irrigation scheduling on the performance of young apple trees in newly established orchards
    (Stellenbosch : Stellenbosch University, 2018-03) Stofberg, Aline; Hoffman, J. E.; Van Zyl, J. L.; Stellenbosch University. Faculty of AgriSciences. Dept. of Soil Science.
    ENGLISH ABSTRACT: During a study conducted in a newly established orchard on a gravelly soil in Grabouw, the most effective irrigation schedule for optimum performance, including root growth and root distribution, of young apple trees was determined. In order to be profitable, apple trees in newly established orchards must fill their allocated space as soon as possible. Soil water status and root growth distribution are believed to be major determining factors in achieving such a favourable effect. Malus domestica „Bigbucks‟ (a mutation of „Corder Gala‟) with an average size of 1.8 metres grafted on MM109 rootstocks were subjected to three different irrigation cycles from December 2016 to May 2017. Treatment one (T1) was a short irrigation cycle, treatment two (T2) was a medium cycle and treatment three (T3) was a long irrigation cycle. Between December 2016 and May 2017, T1 received ca. 10 mm of water every 3 to 4 days, T2 received ca. 20 mm water every 7 days and T3 received ca. 30 mm water every 14 days. Rainfall to an amount of 153 mm also added to the water supply of the trees. Physical and chemical properties of the soil were determined, followed by the installation of irrigation equipment, soil water measuring instruments and rhizotrons for studying roots in situ several times during the season. Irrigation systems were equipped with controllers that were operated remotely by cell phones and soil water measurements were logged continuously. At the end of the season (May 2017) tree response to irrigation treatments was determined by measuring stem circumference and shoot growth. Root studies using the soil profile wall method was carried out to evaluate final root distribution after the first season. The evapotranspiration (ET) of each irrigation treatment during the growing season was calculated using the root-zone water balance equation as described by Hillel (2004). The ET at the end of the growing season was 644.3 mm, 580.1 mm and 568.5 mm for T1, T2, and T3, respectively. All three treatments received a sufficient amount of water during the growing season as the lower ET values of T2 and T3 restricted neither vegetative nor root growth of the apple trees. There was no significant difference between the three treatments in terms of shoot growth and trunk circumference. Rhizotrons were used to determine total root length densities. At the end of the growing season T2 had the highest total root length density, followed by T3 and T1. The use of rhizotrons to study roots in situ proved to be successful and cost effective. The rooting index that was determined using the profile wall method showed that soil conditions were more favourable for the two driest treatments, T2 and T3, than T1. These two treatments (T2 and T3) had significantly higher rooting densities throughout the soil profile, grew to deeper soil layers at a greater distance from the tree and had a significantly higher mean amount of roots in the clayey textured subsoil than T1. This finding implies that longer irrigation cycles produced bigger root systems and that such trees will be less prone to drought.