WUE Part 2: Kernel Yield per Inch of Water

Water use efficiency (WUE) within agriculture has became a bit of a buzz word over the past few years. This is mostly due to the heightened awareness of the public due to the drought. This has placed a lot of emphasis on water usage within agriculture, in which many are demanding that water should be used at the highest efficiency. Almonds are no exception to this.WUE is essentially how much crop we can produce with a given amount of water. This is not an easy value to determine due to the complexity of many farming systems. Once determined, however, it provides an insight into determining issues affecting productivity.Within almonds, there have been attempts to determine optimal WUE. Monitoring of yields in several orchards over the last 10 years has determined a theoretical WUE of 83 lbs of crop for every inch of water use (essentially 1000 kernel lbs of crop for every acre foot of water use). Previous work within a production almond orchard from a single site in California found it to be around 70-72 lbs per acre inch of water use. This range was supported by research work in Australia. Interestingly, anecdotal evidence from water cuts experienced during the drought suggests a similar range, with many farmers experiencing yield losses around 800-1000 lbs/acre for every acre foot of water reductions.To further explore this concept and expand the findings across may locations, three trials were established across California. These trials are located in Kern, Merced, and Tehama Counties and are studying the effects of varying water use amounts on yield. Results from a previous year have been written about earlier. As shown in table 1, our results from the Merced County trial found an average of 73 kernel lbs per acre inch of water use. This is based on a three year average across all five irrigation treatments within a block. Water use is being presented as acre inches of water use from the postharvest period through harvest. Of interest is the amount of crop produced per inch of water use can vary widely - even within a field. Although not shown, the data also varies significantly from year to year due to the tendency of alternate bearing.

Block	Water Use in Acre Inches(Sept - August)	Yield	Yield/Inch Applied
West	37.7	2704.9	72.4
East	35.6	2832.9	81.0
Middle	32.5	2151.5	66.9
Average:	35.2	2563.1	73.4

 If an orchard's 2-3 year average yield  is not performing to this level, consider reviewing orchard history for a variety of problems. These could include:

• Poor water infiltration that leads to an increase in evaporative losses of water applied;
• Incorrect irrigation duration or scheduling in which too much water is being applied and lost to deep percolation;
• The effects of salinity;
• Insect infestation, blossom and foliar diseases that reduce field weights by infesting nuts, killing flowers or nuts, or cause defoliation in which the subsequent refoliation reduces fruit buds;
• Nutrient deficient trees;
• and other considerations.