Resource Conservation District
Data Collection Protocol
To determine the impacts of mulch and compost applications on lemon bed SOM content, each bed within an experimental unit will be sampled using a 8” soil probe and these subsamples will be composited into a single sample, one per experimental unit, for a total of 18 samples. These 18 samples will be analyzed for organic matter at an accredited lab following University of California protocols. Baseline sampling will occur in Spring 2019 followed by three more sampling events each year of the study, e.g. 2020, 2021, and 2022.
To study the impacts of mulch and compost addition on bedded lemon GHG fluxes, 18 non-steady-state flow-through chamber systems (dynamic chambers) will be constructed and permanently placed in a lemon bed within each experimental unit. The change in concentration of GHG gases collected within these chambers will be measured using a portable GHG analyzer, a model DX4040 Fourier Transform Infrared (FTIR) analyzer manufactured by Gasmet Technologies Inc.
In dynamic chamber systems, a closed volume of air is circulated between the chamber, which is sealed to the soil surface, and an analyzer, in this case the DX4040. The DX4040 is a portable, battery operated unit specifically designed for in situ GHG analysis. It measures carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) concentrations simultaneously and, since FTIR is a rapid and non-destructive analysis method, it is ideally suited for field-based GHG flux studies.
GHG sampling will be conducted weekly (W), biweekly (BW), and after rain events (RE) starting in August 2019 and ending March 2022. Generally, higher fluxes, particularly of nitrous oxide, will coincide with rain events so it is expected that sampling will be more frequent in the wet season (Nov-Mar). In Spring and Fall, when soil moisture levels are relatively high, it is expected that weekly sampling will be needed to capture accurate, representative flux data. In the summer, when soil moisture levels are low and low fluxes are expected, sampling will be reduced to once every two weeks (biweekly).
The study applies mulch and/or compost on bermed lemon within a 45-acre block. This 45-acre block will be split into 3 replicates (A, B, & C) and each 15-acre replicate will be further divided into 6 experimental units - one control (C), two variable rate compost treatments (C2, C8), and three rate mulch treatments (M2, M3, M6) - for a total of 18 experimental units. Each experimental unit has 6 berms (about 400 trees).
Beginning in the Summer of 2019, compost and mulch will be applied at the various rates outlined in the experimental design. Each treatment will be tripled and each replicate will also have a control that has no applied mulch or compost.