Measuring Effects of Surface Mulches on Abiotic Properties of Drip-Irrigated Xeric Landscapes

1.Fourteen 30 ft x 30 ft plots (in a 2 x 7 grid) were established in 1998 on a Rillito gravelly, loam soil with 0 to 1 percent slopes.Established plants on each plot include: Nerium oleander (6/plot), Leucophyllum frutescens (6/plot), Eucalyptus microtheca (1/plot), Quercus virginiana (1/plot) and Opuntia violaceae santa-rosa (1/plot).

2. These trees and shrubs were administered a 2x4 factorial treatment of irrigation (high volume vs. low volume) and pruning (6 week, 6 month, 1 year ans control) for 4 years previous to the ground cover study.

3. Two shrubs native to the southwest, Encelia farinosa (4/plot) and Atriplex canescens (2/plot), were introduced in January 2004.

4.In April 2004, four mulch ground cover treatments were applied at a minimum depth of 2 inches to the established plots.

5. Mulch assignments were made with respect to former irrigation and pruning treatments.

6. PB (Ponderosa pine residue) was assigned to plots with 6 month irrigation, with 2 plots historically having high irrigation (HV) and 2 plots low (LV).

7. YW (tree trimmings) and DG (decomposing granite) were half assigned to 1 yr and half to 6 week.

8. Pruning was given priority over irrigation for due to sever effect of 6 week pruning.

9. DG was assigned to plots nearest the north end of the research plots due to difficulty of installation.

10. BS control plots were assigned to plots that were historically not pruned, one with HV and one with LV (previously control plots).

11.All plots are irrigated at the same rate which simulates water use in a xeric southwest landscape (based on residential water use values collected in Tempe, AZ).

12. Water usage for each plot is monitored with water totalizer gauges which are read in gallons/month.

13. Repeated measures collected quarterly (Apr/May, July/Aug, Oct/Nov and Jan/Feb) at the research site include:

• Leaf morphology (annually)

• Leaf relative water content (RWC)

• Tree and shrub biovolume measurements

• Chlorophyll content measures

• Flower/color assay (annually)

• Net radiation and pyranometer measurements

• Soil respiration (Rs)

• Ground cover surface and soil interface temperature measurements

• Canopy temperature measurements

• Soil temperature measurements

• Mulch thickness quantification

• Mulch C:N ratio and total P testing

• Ground arthropod surveys

Leaf Morphology

Protocol performed Fall 2004 on Nerium oleander and Leucophyllum frutescens.

o Collect 3 leaves per plant per species in pre-labeled Ziploc baggies and keep cool after collection and while transporting samples to lab

o Weigh leaves for fresh mass (FM or FW) and take leaf area measurements (LA)

o Place leaves in pre-labeled envelopes and dry @ 60°C for at least 48 hours

o Weigh dried leaves for dry mass (LM or DW)

Data labels specified on excel worksheets and are analogous with leaf RWC labels.

SLM (specific leaf mass) = LM / LA

Leaf RWC

Leaf RWC (%) protocol performed quarterly on Nerium oleander and Atriplex canescens (and Opuntia violaceae santa-rita in Fall 2004).

o Collect 3 leaves per plant per species at dawn, each in its own pre-labeled zip-close baggie; transport in cooler with wetted paper towels

o Weigh as soon as possible for initial weight after harvest (fresh weight, FW)

o Soak leaves for 24 hours at room temperature (this done in zip-close baggies), ~20°C (saturated weight, SW)

o Dry 24-72 hours in drying oven at 60-85°C to constant weight (dry weight, DW)

o Apply data to relative water content formula:

Data labels: plot, taxa, plant #, leaf # (Ex: 01111 = plot 1, Nerium oleander, inside middle plant, leaf #1; 01121 = plot 1, Nerium oleander, inside last plant, leaf #1; 01211 = plot 1, Atriplex canescens, not irrigated, leaf #1; 01221 = plot 1, Atriplex canescens, irrigated, leaf #1).

RWC = (FW-DW) / (SW-DW)*100

(HortSci. 36(4):682-686 2001)

Sunrise 24-Apr-2004: 5:48am; collected leaves from 5:20am to 5:49am; back to lab by 6:25am for FW; all in H2O by 10am.

Sunrise 24-Jul-2004: 5:35am; collected leaves from 5am to 5:30am; back to lab by 6:15am for FW; all in H2O by 9:15am.

Sunrise 23-Oct-2004: 6:39am; collected leaves from 6:14am to 6:48am; back to lab by 7:31am for FW; all in H2O by 10:35am.

Opuntia pad RWC Sunrise 13-Nov-2004: 6:57am; collected leaves from 6:30am to 6:45am; back to lab by 7:30am for FR; all in H2O by 10am.

Tree and shrub biovolume measurements

Shrub , Shape

Nerium oleander , Cylinder

Leucophyllum frutescens , Cropped sphere

Atriplex canescens , Cropped sphere

Encelia farinose , Cropped sphere

Shrubs were measured for height and canopy spread in two directions (N/S and E/W) and described as basic geometric shapes such as truncated spheres for Luecophyllum frutescens and cylinders for Nerium oleander (m3). Measures were taken in cm with a measuring tape.

Trees were measured for height of tree, height of canopy from the ground, canopy spread in two directions (N/S and E/W) and diameter at breast height (DBH). DBH is usually 4.5 ft and this measure was used on Eucalyptus microtheca. DBH was modified to 30 cm on Quercus virginiana due to smallness of trees. Height of tree and height of canopy on Eucalyptus microtheca was triangulated with a Brunton Clino Master clinometer at a distance 25-50 ft, due to tallness of trees. Height of tree and canopy were measured in cm with a measuring tape. DBH on both species of trees was quantified with a Lufkin Executive Thinline diameter measuring tape.

All trees and shrubs were measured quarterly (except Nerium and Leucophyllum were measured monthly to follow longevity of irrigation and pruning effects).

Chlorophyll content measures

Chlorophyll content of trees and shrubs was measured with a Minolta Chlorophyll Meter, SPAD-502. Eight measurements were taken per shrub/tree. Measurements were taken quarterly. Chlorophyll extractions (mg/g) will be performed to relate SPAD readings to leaf chlorophyll content.

Flower/color assay

Digital photographs of Nerium oleander were taken annually from the east side of each shrub with an Olympus Camedia D-560 zoom digital camera during flowering season to determine differences in color composition between shrubs in each treatment.

Net radiation and pyranometer measurements

Two Campbell Scientific Q-7.1 net radiometers were used to measure the algebraic sum of incoming and outgoing all-wave radiation* (short-wave and long-wave components) on all ground cover types (plus turf (TF) at ASU East) on relatively cloudless days for a 24 hr period (MJ/m2). Two Campbell Scientific LI200X pyranometers were used to measure incoming solar radiation. Measurements were taken every 300 sec, averaged and uploaded into a data point every 15 min (Watts/m2). Integrated values were uploaded every 6 hours (MJ/m2). Measurements were taken quarterly.

*From Q-7 net radiometer instruction manual: Incoming radiation consists of direct (beam) and diffuse solar radiation plus long-wave irradiance (flow of electromagnetic energy incident per unit area upon a surface) from the sky. Outgoing radiation consists of reflected solar radiation plus the terrestrial long-wave component.

Soil Resipiration (Rs)

Quarterly Rs measurements were taken with a LI-COR LI-6200 Portable Photosynthesis System with an attached LI-6000 Soil Respiration Chamber (closed mode) to quantify root respiration and soil microbial activity differences in soil between mulch types. Because soil respiration is highly dependent on soil temperature measurements were taken between 3-5pm (corresponding to daily increases in soil surface temps). CO2 concentration is measured in ppm. Out put files show soil temp, ambient CO2, change in chamber dCO2, and Rs flux (?mol/m2/s).

From LI-6000 Soil Respiration Chamber instruction manual:

Before starting the measurement, the ambient CO2 concentration at the soil surface is measured. Once the chamber is installed, the CO2 scrubber is used to draw the CO2 concentration in the closed system down below the ambient concentration. The scrubber is turned off, and the soil respiration causes the CO2 to rise. Data are logged while the CO2 concentration is below, at, and above the ambient level.

Ground cover surface and soil interface temperature measurements

Quarterly surface temperature measurements were taken with an Oakton InfraPro Infrared Thermometer in °C. Nine measurements were taken per plot (36 on DG, PB and YW, 18 on BS and TF) in three N/S transects per plot. Measurements were taken for one 24 hr period at 4 hr intervals (600, 1000, 1400, 1800 and 2200). Emissivity was set at 0.96 for turf and 0.94 for mulch and soil.

Quarterly soil-ground cover interface measurements were taken with copper-constantine thermocouples in °C. Measurements were taken every 300 sec, averaged and uploaded as a data point every 15 min for one 24 hr period per plot.

Canopy temperature measurements

Quarterly canopy temperature measurements were taken on Nerium oleander (and Lecuophyllum frutescens beginning October 2004) for one 24 hr period (co-temporally with mulch surface temperature measurements) at 4 hr intervals (600, 1000, 1400, 1800

and 2200) with an Oakton InfraPro Infrared Thermometer in °C set on average temp mode. Emissivity was set at 0.96 for shrubs.

Soil temperature measurements

Soil temperature was measured in °C at two levels in the soil profile (5-10cm and 30-35cm) with Spectrum Technologies Model 100 WatchDog Data Loggers. Two loggers (one at each depth) were positioned 20 cm from the base of the middle inside Nerium oleander (under canopy) and 2 loggers were placed out in an un-shaded portion of each plot (open) for a total of 4 loggers in each plot (installed in January 04). In addition four loggers (2 at each depth, 10 meters apart) were placed in soil under turf at ASU East (installed in July 04). Data points were taken every 2 hours all day every day.

Data identification labels: plot, location w/in plot, depth (Ex: 0111 is plot 1, location 1 (open), depth 1 (5-10cm); Ex: 0222 is plot 2, location 2 (under Nerium canopy), depth 2 (30-35 cm)).

Mulch thickness quantification

Mulch (including turf) thickness (inches) was measured by taking a minimum of 3 transects across each plot with a minimum of 4 depth measurements in each transect. Thickness was quantified quarterly.

Mulch C:N ration and total P

This analysis was performed April 2004 and October 2004 by IAS Laboratories.

Arthropod Survery

Three pitfall traps per plot were installed July 04 (for a total of 42 traps). One in the middle of each plot and one co-located with Nerium and one co-located with Leucophyllum.

The first round of arthropods were collected the first weekend of February 2005.