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

high quantity of it is microbially immobilized. The recycling of woody biomass could lead to increased N needs to sustain tree growth in the first year; however, it appears to increase the retention of N within the orchard system without affecting yields later on. Whether immobi- lized within microbial biomass, assimilated back into orchard biomass (as represented by sig- nificantly higher leaf N content and yield under WOR), or retained through binding to SOC and/or soil mineral surfaces, WOR likely decreases soil N leaching potential. Biomass recycling also improved soil physical properties of importance to growers and effi- cient use of irrigation water. Soil compaction was alleviated, and it was negatively associated with improvements in SOC and BG enzymatic activity, indicating that microbial decomposi- tion of woody inputs and subsequent enhancements in soil C may partially drive reductions in soil compaction. Increased volume of pore space resulting directly from chunky woody bio- mass additions to the topsoil might have also led to better porosity and reduction in compac- tion. Low soil surface compaction is an important component of fertile soils since it facilitates root growth, infiltration, and water and nutrient retention [56,57]. We observed a negative correlation between compaction metrics and soil water infiltration rates. Improvements in infiltration rates were likely attributed to an increase in soil porosity as shown previously [58] and increased preferential flow pathways and rates of hydraulic conduc-

tivity created after decomposition of large woody residues. Infiltration rate also positively cor- related with aggregation, with macroaggregate stability understood as a key attribute impacting soil water movement [59]. In addition to infiltration rates, neutron probe readings and moisture retention curves indicated significant improvements in hydraulic properties. The 30% improvement in water retention at field capacity in the grind treatment could be in part attributed to increased formation and stabilization of soil aggregates associated with C Table 3. Correlation coefficients among almond kernel yield, soil physicochemical, and biological properties as well as tree-water relations. Yield MWD Ift Cpt BD TN SOC SOM POxC MBC MBN BG CB NAG SWP SCt SWC Yield 1.00 MWD 0.62 1.00 Ift 0.74� 0.60� 1.00 Cpt -0.17 -0.30 -0.61� 1.00 BD -0.90� -0.59� -0.83� 0.75� 1.00 TN 0.75� 0.41 0.36 -0.40 -0.81� 1.00 SOC 0.74� 0.43 0.51� -0.43 -0.82� 0.99�� 1.00 SOM 0.83� 0.50� 0.64� -0.40� -0.87� 0.98�� 0.98�� 1.00 POxC 0.46 0.54� 0.48 -0.15 -0.46 0.22 0.23 0.27 1.00 MBC 0.38 0.66 0.76� -0.07 -0.59 0.48 0.52� 0.52� 0.55� 1.00 MBN 0.32 0.42 0.36 -0.15 -0.10 0.69� 0.15 0.19 0.49 0.57� 1.00 BG 0.80� 0.64 0.44 -0.66� -0.62� 0.68� 0.68� 0.74� 0.48 0.14 0.13 1.00 CB 0.08 0.14 0.20 -0.32 -0.22 0.54� 0.53 0.44 0.18 0.18 0.62 0.31 1.00 NAG 0.50 0.57 0.41 -0.75� -0.51 0.72� 0.74� 0.68� 0.51 0.35 0.17 0.77� 0.50 1.00

SWP -0.56 -0.08 0.30 0.17 0.71 -0.16 -0.46 -0.75� -0.06 -0.26 -0.58 -0.28 -0.56 -0.19 1.00 SCt 0.43 0.66 0.22 -0.07 -0.25 0.24 0.27 0.21 0.73 0.64 0.45 0.12 0.18 0.52 -0.64� 1.00 SWC 0.53� 0.72� 0.39 -0.27 -0.34 0.11 0.57� 0.55� 0.79 0.32 0.45 0.39 0.47 0.22 -0.30 0.59 1.00 �Significant at P � 0.05 ��Significant at P � 0.01 Abbreviations: MWD, mean weight diameter; Ift, infiltration; Cpt; compaction; BD, bulk density; TN, total nitrogen; SOC, soil organic carbon; SOM, soil organic matter; POxC, Permanganate-oxidizable C, MBC, microbial biomass carbon; MBN, microbial biomass nitrogen; BG, β -glucosidase; CB, Cellulase; NAG, β-N- acetylglucosaminidase; SWP, stem water potential; SCt, stomatal conductance; SWC, soil water content. https://doi.org/10.1371/journal.pone.0229588.t003 PLOS ONE Whole orchard recycling PLOS ONE | https://doi.org/10.1371/journal.pone.0229588 March 27, 2020 15 / 22