Efficiency of irrigation practices for table grapes in the Hex River Valley
Date
2008-03
Authors
Eustice, Tarryn
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
In order to produce table grapes of export quality economically, irrigation must be practised
conservatively without adversely affecting the crop. To use water as conservatively as possible
effective irrigation scheduling practices must be applied. The highest water use efficiency (WUE) is
only possible if irrigation scheduling practices lower the amount of water applied, while at the same
time they increase the yield.
The first aim of this project is to investigate whether current irrigation practices make efficient use of
water by comparing irrigation requirements determined using theoretical models with actual irrigation
applied for two seasons (2005/6 and 2006/7). Secondly, the effect of cumulative irrigation on the
chemical status of soil in 16 blocks was investigated to establish whether nutrient leaching as a result of
differential water use may have had an influence on yield.
Six blocks (three dripper and three microsprinkler blocks) were selected and irrigation requirements
were determined using evaporation pan calculations, SAPWAT and Vinet and compared with actual
irrigation applications. Furthermore, a yield-irrigation index (kg/m3) and an income-irrigation index
(R/m3) were determined for each of the six blocks and compared.
To investigate the effect of cumulative water use on the chemical status of the soils of 16 blocks, soil
samples were taken and analysed for pH (1M KCl), EC (1:5); soluble cations and anions (Ca, Mg, Na,
K, SO4, NO3, and Cl), ammonium acetate extractable cations (Ca, Mg, Na and K) and micro elements
(Zn, Fe, Mn, Cu and B).
The irrigation requirements predicted by the different irrigation scheduling methods are variable. For
Vinet, the irrigation requirement determined for microsprinkler irrigation is much higher than that
determined using the evaporation pan or SAPWAT approaches. Comparison of the irrigation applied
to each of these blocks does not clarify whether any irrigation scheduling takes place. Results showed
a relationship between the yield-irrigation index and income-irrigation index. It has not however been
verified whether this relationship is statistically significant.
Description
Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2008.
Keywords
Irrigation efficiency, Leaching, Table grapes, Irrigation scheduling, Dissertations -- Soil science, Theses -- Soil science