Orchard recycling improves climate change adaptation and mitigation potential of almond production systems

Abstract

There is an urgent need to develop climate smart agroecosystems capable of mitigating climate change and adapting to its effects. In California, high commodity prices and increased frequency of drought have encouraged orchard turnover, providing an opportunity to recycle tree biomass in situ prior to replanting an orchard. Whole orchard recycling (WOR) has potential as a carbon (C) negative cultural practice to build soil C storage, soil health, and orchard productivity. We tested the potential of this practice for long term C sequestration and hypothesized that associated co-benefits to soil health will enhance sustainability and resiliency of almond orchards to water-deficit conditions. We measured soil health metrics and productivity of an almond orchard following grinding and incorporation of woody biomass vs. burning of old orchard biomass 9 years after implementation. We also conducted a deficit irrigation trial with control and deficit irrigation (-20%) treatments to quantify shifts in tree water status and resilience. Biomass recycling led to higher yields and substantial improvement in soil functioning, including nutrient content, aggregation, porosity, and water retention. This practice also sequestered significantly higher levels of C in the topsoil (+5 t ha-1) compared to burning. We measured a 20% increase in irrigation water use efficiency and improved soil and tree water status under stress, suggesting that in situ biomass recycling can be considered as a climate smart practice in California irrigated almond systems.

Fig 1

Effects of soil treatments (a) and soil treatments × irrigation regimes (b, P = 0.25) on kernel yields and irrigation water use efficiency (IWUE). (*) indicate significant difference at P ≤0.05.

Fig 2

Impact of WOR on (a) total carbon and (b) nitrogen content in aggregate fractions. (*) indicate significant differences at P ≤0.05.

Fig 3

Effect of Grind and Burn treatments on (a) Proportion of soil aggregate fractions, (b) mean weight diameter (MWD), (c) water retention curves, and (d) infiltration rate. (*) indicate significant differences at P ≤0.05.

Fig 4

Effect of Grind and Burn treatments on (a) Cellulase (CB); (b) β -glucosidase (BG); (c) β-N-acetylglucosaminidase; (NAG), and (d) Leucine Aminopeptidase (LAP) enzyme activities. (*) indicate significant differences at P ≤0.05.

Fig 5. Principal Components Analysis (PCA) of soil health indicators and treatment clusters.

BD, bulk density; Cmpt, compaction; Inflt, infiltration; MWD, mean weight diameter; EC, electrical conductivity; TN, total nitrogen; SOM, soil organic matter; SOC, soil organic carbon; POxC, permanganate oxidizable carbon; CB, cellulose; BG; β –glucosidase; NAG; β-N-acetylglucosaminidase.

Fig 6. Average of neutron probe readings at different soil depths during the deficit irrigation period (6/5-7/3) as affected by soil (grind and burn) and irrigation treatments.

Fig 7

Effect of soil (Burn and Grind) and irrigation treatments on (a) average of weekly stem water potential readings (b) weekly measurements of stem water potential, and (c) stomatal conductance measurement (7/3). (*) indicate significant differences at P ≤0.05.