Trees under an SDI regime appeared more resilient and for deficits equal to or below 70% were also more productive than those under an RDI regime. (Figure 2 and Figure 4). A higher percentage of nut damage due to carob moth was seen compared with previous seasons. Damage was greater on trees under deficit irrigation because their hulls split sooner and therefore were exposed for a longer period of potential infection and damage. Conclusion Reducing irrigation application by 15% below normal plant requirement using either an RDI or SDI strategy had no negative effect on kernel size and yield over the three seasons of investigation. Deficits that reduced normal plant water requirement by more than 15% are likely to reduce both kernel size and yield. Trees appear to better adapt to a sustained (SDI) rather than regulated deficit irrigation (RDI) strategy where deficits are imposed before harvest.
Figure 3: Influence of irrigation strategy on kernel growth during the 2009-2010, 2011-2012 and 2012-2013 growing seasons at Lake Powell
Figure 2: Influence of irrigation strategy on midday stem water potential in the 2009-2010, 2010-2011 and 2011-2012 growing seasons at Lake Powell
Figure 4: Influence of irrigation strategy on kernel yield at the end of the 2009-2010, 2011-2012 and 2012-2013 growing seasons at Lake Powell