Establishing an almond water production function for California using long-term yield response to variable irrigation

Abstract

The consumptive use of water by almond trees in California has become a controversial topic due to a worsening drought that began in 2011. The research reported herein was designed to provide information that could be used in irrigation decision-making including how to evaluate the risks/rewards of seeking/acquiring additional supplies in a drought. Ten irrigation levels ranging from 1000 to 1350 mm per season were applied in a mature southern San Joaquin Valley ‘Nonpareil’ almond orchard over a 5-year period. Nut load was invariant over the range of irrigation regimes with no evidence of any sustained negative impacts. Individual kernel weight was reduced commensurate with the level of deficit irrigation; the lowest irrigation resulted in a 15% lighter kernel. Maximum yield (3900 kg/ha) was achieved with 1250 mm of applied water. There was statistically significant tree stress in the 1250-mm application regime with midday shaded leaf water potential about 0.2 MPa more negative than trees receiving additional water. Maximum marginal water productivity (WPM) was 0.30 kg/m3 at 1080 mm of applied water, falling to zero at 1290 mm. With almond prices of $8/kg, this is equivalent to water valued at $2/m3. Estimated annual statewide almond orchard evapotranspiration based on this study is 1100–1350 mm which is about 25% higher than estimates made four decades ago. However, yields have increased in the 250% range since that time. This tenfold difference between yield and evapotranspiration means that WPM is much higher now than in the past, and at current prices, it demonstrates that almond trees are suited for high water cost areas.

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Irrig Sci (2017) 35:169–179
DOI 10.1007/s00271-016-0528-2
ORIGINAL PAPER
Establishing an almond water production function for California
using long‑term yield response to variable irrigation
David A. Goldhamer1 · Elias Fereres2
Received: 21 January 2016 / Accepted: 24 October 2016 / Published online: 28 November 2016
© Springer-Verlag Berlin Heidelberg 2016
difference between yield and evapotranspiration means that
WPM is much higher now than in the past, and at current
prices, it demonstrates that almond trees are suited for high
water cost areas.
Introduction
As California entered the fourth year of what has been
called an unprecedented drought in 2015, news stories
and editorials appeared in the popular press, including the
New York Times (Kristof 2015), about the “excessive”
water needs of almond trees, and there were suggestions
that water use by almond growers should be legally cur-
tailed (Philpott 2015; Fresno Bee 2015). While researchers
and others involved with consumptive use have long rec-
ognized that crops use lots of water, the almond water use
values reported, including “1 gallon per nut,” shocked the
public. The almond industry was accused of exacerbating
the impacts of the drought on the general public who had
already been forced by the state to cutback water use by
25% (Megerian et al. 2015). Discussion in the media gen-
erally focused on the rights of the almond growers to con-
tinue their livelihood versus the publics’ right to water.
The growth the California almond industry was driven
by worldwide demand and progressively higher prices paid
to the grower, approaching $12/kg in 2015. This led to the
replacement of traditionally grown row crops, such as cot-
ton, with almonds which has gone from 45,700 ha in 1960
to 157,500 ha in 1980 to 413,000 ha in 2014 (USDA 2011;
Almond Board of California 2015). Little attention was paid
to the fact that annual potential almond evapotranspiration
(ETc) was reported as 900–1350 mm (State of California
DWR 1986; Goldhamer and Girona 2012) compared with
700–800 mm for cotton (Goldhamer and Snyder 1989).
Abstract The consumptive use of water by almond trees in
California has become a controversial topic due to a wors-
ening drought that began in 2011. The research reported
herein was designed to provide information that could be
used in irrigation decision-making including how to evalu-
ate the risks/rewards of seeking/acquiring additional sup-
plies in a drought. Ten irrigation levels ranging from 1000
to 1350 mm per season were applied in a mature south-
ern San Joaquin Valley ‘Nonpareil’ almond orchard over
a 5-year period. Nut load was invariant over the range of
irrigation regimes with no evidence of any sustained nega-
tive impacts. Individual kernel weight was reduced com-
mensurate with the level of deficit irrigation; the lowest
irrigation resulted in a 15% lighter kernel. Maximum yield
(3900 kg/ha) was achieved with 1250 mm of applied water.
There was statistically significant tree stress in the 1250-
mm application regime with midday shaded leaf water
potential about 0.2 MPa more negative than trees receiving
additional water. Maximum marginal water productivity
(WPM) was 0.30 kg/m3 at 1080 mm of applied water, fall-
ing to zero at 1290 mm. With almond prices of $8/kg, this
is equivalent to water valued at $2/m3. Estimated annual
statewide almond orchard evapotranspiration based on this
study is 1100–1350 mm which is about 25% higher than
estimates made four decades ago. However, yields have
increased in the 250% range since that time. This tenfold
Communicated by J. Knox.
* David A. Goldhamer
dagoldhamer@ucdavis.edu
1 Department of Land, Air, and Water Resources, University
of California, Davis, Davis, CA, USA
2 IAS-CSIC and University of Cordoba, Córdoba, Spain
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