Treatments & Sampling
The regional salinity of this groundwater varies from 3 to 15 dS/m with 8 to 18 ppm boron.
Irrigation treatments consist of fresh (Aque), blended (Blend) and full strength saline well (Well) water (average EC of 0.5, 2.5 and 5 dS/m, and boron @ 0.3, 6 and 11 ppm, respectively). The highest salinity treatment is more than 4 times as saline as almost all irrigation waters currently used in the San Joaquin Valley.
All plots were irrigated with a total of 8 to 12 inches of fresh (Aqueduct) water during the winter and/or cotton germination, followed by 18 to 26 inches of treatment water, depending on seasonal demand. Pistachios received about 18 inches based on a 9.5 foot wide area between the cotton.
Due to contamination of the aquifer by oil field leachate water, the average salinity of the Well water eventually increased to 7.5 dS/m by July 2007. At this time we began blending some
Aqueduct water into the Well treatment and increased the amount of Aqueduct water in the Blend treatment to return to the salinity levels at the start of the trial.
|Control: Aqueduct water
|Well: Shallow groundwater||5.0 dS/m|
|Blend: 50/50 mix of above||2.5 dS/m|
Irrigation Water & Soil Sampling
- Soil samples at 4 depths up to 5 ft, and treatment water samples were taken at the beginning and end of the season. Samples were analyzed for EC, Ca++, Mg++, Na+, Cl-, HCO3, and B at the ANR lab at UC Davis.
- The EC of treatment water was recorded weekly using a handheld meter.
- To characterize the situation in the field, the EC of irrigation water samples at given distances from the drip hoses was measured at the beginning and end of the season
- A network of monitoring devices was installed to record water status of the soil: 1) neutron probe access tubes measured soil water content, and 2) electrical resistance blocks to measure matric potential, an indicator of soil water content.
Plant Tissue Sampling
- Pistachio leaf tissue was analyzed for these nutrients: Calcium (Ca), Magnesium (Mg), Sodium (Na), Chloride (Cl), Boron (B), Nitrogen (N), Phosphorus (P), and Potassium (K)
- Trunk circumference measurements were taken yearly from 2005.
- Several trees were sacrificed to measure Boron accumulation in woody tissue and tree weights at the end of the study.
- Field and aerial surveys were undertaken for EC. Aerial imaging uses a procedure which records various band widths of light and from these, These measurements ar used to calculate a numerical indicator of plant status called the Normalized Difference Vegetative Index (NDVI). NDVI is used as an indicator of plant health, because NDVI values are associated with plant constituents, such as water and pigments. In this study, NDVI values were calculated for individual plots in 2004, 2006 and 2008.
- Data collected on the cotton replicates included: 1) Leaf water potential as an indicator of water stress, 2) petiole tissue analysis for nutrients NO3, P, K and B, and 3) lint yield and quality at annual harvest.