Blogs 1 and 2 from May and June were rather complicated discussions of remote sensing imagery (focusing mostly on CERES images of these pistachio demo fields) and why the red (dry) to blue (wet) colorized image scale doesn't always remain constant from one image event to the next.
BOTTOM LINE: for any given image, the color separation across the field of red to blue is always showing the true relative drier to wetter areas of the field on that date. So many different colors across the block means the water status of the trees is quite variable. You want 90% of the field to be green and blue. BUT depending on the spread of canopy temperature (hottest to coolest areas) over the field on a given date some trees that showed up as green the month before might show up as yellow for the current month – even though the actual canopy temperature in degrees and a ground-based pressure bomb stem water potential (SWP) measured on the same trees are the same for both images. Both images provide valuable information for that date – especially on field uniformity – but for an absolute verification of the degree of real tree stress, you need additional ground data. Using this data, we verified that all fields were successfully winter/spring recharged with sufficient root zone soil moisture. So for this BLOG we are looking at the combined data snapshot for our fields from 6/19/2020.
PRESSURE BOMB COMPARISON ACROSS ALL FIELDS
The above figure for 2020 shows that the non-saline Eastside and Westside fields are closer than they were for 2019. As of June, the semi-saline Mid Salt site is about -2 bars more SWP stress than the non-saline fields and the saline HiSalt site is about -4 bars more stress. This is NOT for lack of water but the result of the additional salt-caused osmotic resistance to water uptake.
NON-SALINE EASTSIDE FIELD
AERIAL IMAGERY: This makes for good feeling as the fields are nearly all blue and green in all the fields, and we have -10 to -11 bars SWP in the west and SE fields (numbers in white) – so we are good to go! But wait, we have a -15 bar SWP in the NE field, which indicates stress. This was not obvious from looking at the trees and this field was irrigated with almost exactly the same amount of water as the other fields
TREE STRESS: Using the tree as the continuous integrated moisture sensor is somewhat possible using a dendrometer that measures the real-time daily shrink/swell and growth of the tree. The Phytech company is helping us do that by generating this average growth information in the below figure over 3 trees instrumented with dendrometers:
This is exactly the pattern that you want to see – steadily increasing growth running 15-30 microns/day over the spring and early summer. From Mid-June to July 17 these trees averaged 6000 microns (6 mm) additional radial growth. That's a 12 mm, or almost ½ inch increase in trunk diameter. The blue bars indicate the timing and duration of irrigation of this high frequency double-line drip system.
So what about the -15 bar SWP stress we measured on the NE block? We are fortunate to have 3 dendrometers on this block also which show a similar steady growth increase as the west 80 acres, but the slope is a little less so we only get 4000 microns increased growth (10-20/day) instead of the 6000 we have in the west 80 acres. This would confirm a bit more water stress in this block but not a big deal.
SOIL MOISTURE:
The ROOTZONE SUM chart below from the Jain Logic monitoring system using a Sentek Drill & Drop capacitance probe that measures soil moisture to a depth of 46 inches shows that the total root zone soil moisture has increased about 10% since the start of May. The numbers on the left access are the sum of the percent soil moisture measured by each sensor placed every 4 inches. If these numbers were absolutely accurate, it would mean that this Nord Series fine sandy loam soil would hold 42% water (5.0”/ft) at field capacity, which is impossibly high. The correct number is about 28%, 3.4 inches/foot as measured by a neutron probe. But the good news is that the trends in increased and decreased water content are very real and dependable. So the infiltration chart (below right) is an accurate
indicator of how deep water penetrates (dark blue columns) every irrigation. This shows that the water only went to 46” a total of four times over 3 months, so there is virtually no deep percolation lost below the root zone.
NON-SALINE WESTSIDE FIELD
AERIAL IMAGERY: Okay, this picture makes me feel a little more stressed than the Eastside CERES image – less blue and more yellow and red. The SWP (numbers in white) are only -1 to -1.5 bars more negative (stressed) then the eastside SWP and this block did receive about 1.4 inch less water since 5/16 than the Eastside. This is also a 300 acre block with ½ mile rows N to S with only 2 hose runs of ¼ mile each that appear to show weak pressure and water delivery in the middle and at the N and S sides of this block.
TREE STRESS: Unfortunately, cell phone/web reception at this field is not good and only a little of the Phytech dendrometers data came through. However, the 4 days data show as good of growth as the best Eastside block.
SOIL MOISTURE: We have two sites in this field with instrumentation. The NO COVER site below is 80 rows east of the west edge of the field with the soil classed as a Cerrini sandy loam. The soil at this site is sandier than the Eastside field. The irrigation system is a single-line drip with four 1 gallon/hr drippers per tree. Irrigation is typically a 24 hr set every other day starting in June. The Root Zone Sum chart shows a fairly steady water content, but the Infiltration chart on the right shows that 5 straight irrigations in mid-June penetrated to 46”, indicating possible deep percolation earlier.
The COVER crop site is 30 rows from the eastern edge of the field and is a Calflax clay loam with a definitely higher water holding capacity than the Cerrini SL in the NO_COVER area. This location and the NO_COVER location are in the same irrigation set, receiving water at the same time and duration – typically 24 hours. But with a heavier soil, this site is showing water infiltrating nearly every irrigation as opposed to the sandy loam area just 50 rows to the east. There is possibly a crack adjacent to a dripper that connects with the Sentek probe and pipes water down the side. Of all the sites to have a failure in the Phytech dendrometers, this was possibly the worst one, and these trees did receive 1 inch less water over the last month than the Eastside.
SEMI-SALINE, SALINE LEMOORE FIELD
AERIAL IMAGERY: As expected, the significant variability in canopy growth caused by excess salt and poor soil structure in this field produces the lowest and most variable Normalized Differential Vegetative Index (NDVI, left) and more WATER STRESS than in any other field. Should more leaching have been done during the winter to further reduce root zone salt loads? Perhaps the grower could have done more, but he applied 10 inches during the winter, which takes forever to penetrate in this saline-sodic Lethent silty clay loam, and his June 2020 SWP was less negative than June 2019. This is square quarter-section field with a double-line high frequency automated drip system with two ¼ mile hose runs, running in 3 to 8 hour sets. There is a distinct stress patter along the hose ends in the center and N and S borders of this field very similar to what we saw in the non-saline westside field with similar length of hose run. These are all pressure compensated drip emitters and any time I have checked the pressure at the hose end it is >12 psi which should be sufficient for max flow. So I'm guessing more emitters just get clogged and don't clean out during flushing. Maybe it would help to increase filter station/booster pressure and flush hoses more often. The grower used to run longer sets but that exacerbated the waterlogging problem.
TREE STRESS, SEMI-SALINE: Even though there is definite canopy size, ET and yield reduction in the best semi-saline area of this block compared to our non-saline fields, there was still excellent growth recorded by the Phytech dendrometers from May to July. In fact, the three trees with dendrometers in the NE area (D05) of this block have put on an average 10,000 microns (10 mm) additional radial growth. That's a 20 mm, or ¾ inch increase in trunk diameter – the highest growth rate of all our monitoring sites even with extra stress from the salt! Must be the seaweed extract Bart uses, hmmm.
TREE STRESS, SALINE: This severely affected saline area in the south central part of the block surprised us last year with about half the growth of the D05 Area. But this year has had essentially ZERO growth
SOIL MOISTURE, SEMI-SALINE: The second highest total Root Zone Summed water content is this area – reflecting a soil texture finer than any of the non-saline problem fields and very slow drainage through the profile. The deepest penetration during an irrigation is only 18”. The impact of this anoxia, waterlogging, has just as much negative impact on pistachio growth as does the higher salinity.
SOIL MOISTURE, SALINE: The highest total Root Zone Summed water content is in this area (D03) of the field. Frequently prone to ponding many trees have died here. The deepest recorded irrigation penetration for any 3 to 8 hour event is 6”. Installing an automated WiseCon irrigation system to run very short sets as often as daily has been the best strategy the grower found to reduce anaerobic conditions in the root zone and improve tree growth.
