Optimization of Irrigation Management in Mango Trees by Determination of Water and Carbon Demands to Improve Water Use Efficiency and Fruit Quality
Report No. 1136/1/03
December 2003

EXECUTIVE SUMMARY

Background

The production of agricultural crops and in particular subtropical fruits for the export market is a very important contributor to the South African economy. Production of these crops of high value is influenced by the amount of water the crops receive at certain growth stages. Due to the low and erratic rainfall, irrigation is widely practiced in South Africa. However, water resources in South Africa are scarce and the demand by agricultural, domestic, and industrial users is increasing continuously. Irrigation strategies are, therefore, changing and shifting towards increasing water use efficiencies instead of obtaining maximum yields accompanied by low water use efficiencies. In other words, the goal of modern agriculture is to use less water for irrigation without a decrease in fruit quality and yield and to conserve water.

The research objectives were:

• to manage irrigation for minimum water and nutrient losses in mango trees, simultaneously maintaining or even improving fruit quality and shelf life, by manipulating the water supply to trees,
• to determine vegetative and reproductive growth patterns critical for the application of regulated deficit irrigation treatments, and to expose trees to water deficits at specific growth periods to reduce excessive vegetative growth while not affecting fruit growth,
• to study photosynthesis and tree water relations, stem water potential and stomatal conductance, in response to different irrigation regimes in mango trees under field conditions over the season, and
• to adapt the PEACH growth model to mango trees.

An economical evaluation of the various irrigation strategies was not conducted, since this would require a separate study and was not part of our aims. Mango was chosen as an example for subtropical tree crops, since Hans Merensky Holdings provided the necessary field facilities. The research was carried out in a commercial mango orchard (1 ha) of the Westfalia Estate Moriah (Hans Merensky Holdings) in Hoedspruit (latitude: 24ºS, longitude: 31°E), Limpopo Province, and in laboratories of the Department of Plant Production and Soil Science, University of Pretoria. Five to eight year old mango (Mangifera indica L. cv. 'Kent' trees grown on 'Sabre' rootstock) trees planted at a density of 1.5 x 6 m were used in the study. Cultural practices, such as pruning, fertilizing, and harvesting, were conducted as in commercial orchards. Fertilization was applied separately from irrigation applications.