CSIR Apple Orchard Water Use

With memories of the recent debilitating droughts still fresh in the minds of many in the major fruit

producing regions in South Africa, there is need to radically improve how water is managed to make

every drop count. The number of tools available to farmers to optimize their irrigation is growing

mostly by harnessing modern technologies. So, this CSIR Orchard Water Use Application (APP) adds

to the existing products.

Over the years, researchers from the Council for Scientific and Industrial Research (CSIR) in

collaboration with fruit industry partners have conducted research aimed at measuring the actual

water use of orchards using state-of-the-art techniques. This APP is a culmination of those efforts as

it pulls these data together to develop a tool that is both accurate and simple. Currently the APP is

designed to forecast the water requirements in apple orchards only. Other crops will be added in

future.

The APP follows the internationally acclaimed FAO 56 principles to predict the orchard water

requirements 1 to 7 days in advance. Reference evapotranspiration (ETo) for the orchard’s location

is calculated using data from reliable online weather forecasts. The weather forecast data is pulled

into the APP when the user enters the site coordinates. An experimentally validated algorithm runs

in the background to derive the orchard crop factors using readily available information e.g. the tree

canopy fractional cover (0-1), tree height, soil type, cover crop status (i.e. whether tall and dense,

average, or bare) and the irrigation system. In this way, appropriate crop factors are derived for each

orchard thereby avoiding the problem of over-irrigation especially in younger orchards whose crop

factors are not well known.

The outputs from the APP include the daily orchard transpiration and evapotranspiration including

the reference evaporation (in mm/d). These data are displayed in either graphical or tabular forms.

A weekly summary of each water use variable is also provided. Weekly crop factors are provided.

This free version of the APP has been validated with actual sap flow measurements of transpiration

and eddy covariance measurements in more than 12 apple orchards in different production regions

in the Western Cape. However, we would appreciate feedback on your experiences with the APP

and how the tool can be improved to make it more relevant to your operations.