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

30% more VWC at field capacity (FC) (Fig 3C). Water infiltration, measured as hydraulic con- ductivity (Fig 3D), was also significantly improved compared to the burn treatment (0.003 vs 0.001 cm s-1). Soil biology and SHI WOR significantly increased soil MBC by 28% compared to the burn (Table 2). While MBN trended higher (+13%), this increase was not significant (P = 0.41). Soil enzyme potential activ- ity, which indicates potential rates of C and N cycling, was generally higher in the grind soil compared to the burn (Fig 4A–4D). The grind treatment soils had relatively higher levels of soil C cycling enzyme activity, with significant increases for both BG and CB (Fig 4A and 4B). Soil N cycling enzyme activity for NAG was also significantly increased under WOR, but not for LAP despite trending higher (Fig 4C and 4D). Additions of woody biomass into the orchard soil significantly increased estimated soil respiration rates (1-day CO2 evolution; +76%; P � 0.05, Table 2). Because of these changes and shifts in WEOC, the soil health index (SHI) significantly increased from 4.24 in the burn treatment to 6.13 in the grind treatment (Table 2). Principal component analysis and correlations Principal component (PCA) and correlation analysis were used to further identify relation- ships between soil properties across treatments (Fig 5, Table 3). We observed clear clustering of the two management practices and two principal components accounted for 64.3% of the total variance (PC1 and PC2 explaining 45.6% and 18.7% of total variance, respectively) (Fig

5). Soil parameters with high impact on treatment separation (>0.5) were soil C (SOC, SOM), total N, microbial biomass (MBC, MBN), soil enzymes (BG, CB, NAG) and physical properties such as aggregation (MWD), infiltration, and compaction. Total soil C (SOC) was strongly positively correlated with increases in total nitrogen, microbially stored C pools (MBC) and two enzymes (BG, NAG) (Table 3). Improvements in aggregation, infiltrations, soil water con- tent and mitigation of compaction issues also trended with increases in SOC. 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. https://doi.org/10.1371/journal.pone.0229588.g001 Table 1. Impact of WOR on soil physical and chemical properties (0–15 cm) in 2017. Treatment BD (g cm-3) Cpt (MPa) EC (ds m-1) CEC (meq†) NO3- (mg kg-1) NH4+ (mg kg-1) TN (%) SOC (%) C Stock (T ha-1) SOM (%) POxC (mg kg-1) Grind 1.58 142 0.57 8.28 11.93 1.39 0.069 0.79 18.72 1.52 250 Burn 1.64 165 0.58 7.78 12.66 1.31 0.056 0.55 13.53 1.07 153 P Value 0.05 0.05 0.45 0.28 0.73 0.35 0.05 0.001 0.01 0.001 0.04 Treatment pH Ca Mg K Na Cl B Fe Cu Mn Zn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . mg kg-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Grind 6.94 60.52 17.74 11.06 20.38 22.6 0.3 33.23 9.25 9.03 9.69 Burn 7.02 61.12 17.37 11.68 16.49 15.51 0.31 28.01 9.26 6.79 9.64 P Value 0.39 0.48 0.47 0.39 0.03 0.003 0.4 0.11 0.5 0.01 0.47 BD, bulk density; Cpt, compaction; EC, electrical conductivity; CEC, cation exchange capacity († Per 100 g of soil) TN, total nitrogen; SOC, soil organic carbon; SOM, soil organic matter; POxC, permanganate oxidizable carbon https://doi.org/10.1371/journal.pone.0229588.t001 PLOS ONE Whole orchard recycling PLOS ONE | https://doi.org/10.1371/journal.pone.0229588 March 27, 2020 9 / 22