Monday, November 18, 2019

Using NDVI for BioStimulant Assessment

By Fabian Sanchez
RD4AG is working to expand knowledge on the modes of action and effectiveness of biostimulants in agricultural crops. One of the tools we rely on is the Normalized Differential Vegetative Index (NDVI) to assess live green vegetation in our BioStimulant product performance trials.
With the advent of numerous innovations, there is more opportunity than ever to improve our ability to evaluate the health and well-being of plants in the field. Achieving accurate and useful field assessment data can be challenging and costly and the data is often fraught with background noise from human error and subjective variabilities.  NDVI measurements can help us monitor research plots more efficiently. These measurements can also lead to a larger analysis of vegetative properties to assess BioStimulant impact including; leaf area index, chlorophyll concentration, plant productivity, vigor, fractional vegetation cover, accumulated rainfall, basic nutrient response, crop condition (identify diseases), yield potential, stress, biomass, herbicide efficiency and the list could go on.
            NDVI uses the photosynthetically active radiation spectral region of plants in the near-infrared and red (visible) spectral region. The chlorophyll reflectance value needs to be determined in order to understand the NDVI readings which are based on the reflectance values from the plants using the two different wavelengths. Chlorophyll is known to strongly absorb visible light from 400nm to 700nm for use in photosynthesis therefore, NDVI functionally obtains the equivalence of simple infrared/red ratio as shown on the figure below.
NDVI is directly related to the photosynthetic capacity and thus energy absorption of plant canopies. Our instrumentation is the Greenseeker handheld crop sensor by Trimble (Fig. 2.) and its sensor displays the measured value in terms of an NDVI reading (ranging from 0.00 to 0.99) on its LCD display screen as described in their website. Therefore, the greener plant material there is the higher the NDVI reading is which complies with the principle of having low red-light absorbed by the chlorophyll in the plant and high near-infrared light reflectance.
The Greenseeker is an active light source optical sensor which means it provides its own light so that the time of the day will not be a factor affecting the measurement. There are some environmental variables that can have an impact on data quality.  If wind is blowing plants sufficiently to change which side of the leaves the sensor is reading, there can be substantial differences, especially in crops that may have small hairs or different textures on the undersides of foliage. Naturally, the sensor does not differentiate between weed and crop species so care must be taken when weeds are present to assure accurate data.
Operational use after calibration and charging consists of holding the device with the sensor directed at the foliage, pressing the trigger button, and walking at a steady pace through the target plot areas maintaining a specific height range of 24” to 48” (60-120 cm) above the crop canopy (depending on the size and type of the crop).
 Fig. 3 to the left, illustrates the sensor’s oval field of view showing how the size is proportional to height and approximates 10” (25cm) wide at 24” (60cm) above the ground and 20” (50cm) wide at 48” (120cm) above the ground, Trimble. An error message will be displayed on the screen if you are too high or too close to the crop.
The sensors on the instrumentation are emitting brief bursts of red and infrared light and automatically measuring each type of light that is reflected from the plant to obtain the NDVI reading. The device will display an NDVI value once per second during operation and reaches a maximum interval of 60 seconds, therefore, we want to record at least 10 seconds for each plot to collect a representative data set. After walking the desired area, release the button and the sensor will display the final average value of all the readings that were taken.
In order to establish favorable results, consistency in the plant population and agronomics are key components to success.  It is important that only the same crop and relative growth stage be compared.  In other words, taking a reading of one plot at 6 leaf and another at 30 leaf is not an accurate comparison.  Intuitively, comparing a wheat reading with a spinach reading does not provide useful information. The algorithms in these instruments require at least 50% of the field of view of the sensor to be covered by vegetation for accurate measure of “Greenness” that equates to productivity.  Bare ground typically reads 0.13, so less than 50% plant coverage of the soil in our experience is most useful in evaluating weed control if weeds are dying or breaking through the program.  If we want % ground cover with plants, we are now using imagery and color thresholding as discussed in RD4AG’s white paper on Canopy Coverage by Connor Osgood.  For plant productivity evaluations of crops, we tend to wait for the crop to grow a bit larger before we start the NDVI assessments in our trials.  Since NDVI also depends on the geometry of illumination and anisotropy of the target we continue to evaluate crops using the same standard procedure and hence maintain the position of the target of interest within the swath of the instrument at a specific range so we have consistency that can be relied upon to tease out subtle differences in crop performance.

Monday, November 20, 2017

Drought Trials--- what kind of drought are we trying to test?

We do our share of drought work.  Yuma Arizona is drier than most of the Sahara Desert—we receive only 2.8 inches (75mm) of precipitation a year!  When combined with our two growing seasons for most crops, this region lends itself to this kind of work.  But all not drought programs are created equal.  Giving some thought to what the type of drought situation you want to simulate is paramount to determining the right approach.

Drought means that the plant is in moisture stress for a period of time.  That period can be anything for a couple of hours on a hot afternoon to being severely water deficient for most of the plants life. 

The cause or reason for the drought is also pertinent. 
  • ·         A situation where there is rationing of water, and now a grower is forced to grow his crops on 10, 20 or 50% less water than “normal”. 
  • ·         Perhaps the situation is that the water is only available on a schedule, and the grower gets it every 7, 14 or? Days regardless of the plants need.
  • ·         It could be a dry land situation, and the rains do not come for 3 weeks when the plants need it most.

How to administer the drought becomes critical.  Typically, we like to use drip irrigation as we can assure uniformity, and we can regulate and confine it accurately.  Surface water can be utilized in some situations.  Sprinklers can also be used, but again, only in some situations.

The generic program we see requests a percentage reduction in water applied.  Reductions of 25 and 50% are common requests.  So, getting to the first discussion above… What is the “normal 100%” amount of available moisture?  We have worked with some very high-tech software to predict moisture needs using soils, crop growth stages and forecast temperatures.  To date we have watched them all FAIL miserably.  Corn in a full “pineapple roll” at 9 am when it should be fine for several more days.  And we have followed conventional wisdom on irrigation and cut back 20% only to have no effect on yield at all.  All this means is that drought work is as much art as it is science.

When do we want drought stress? Do we want to get the crop out of the ground and then reduce it?  Most places with wet or snowy winters and then spring plantings come out of the winter wet.  This means that the crop comes up in moisture, and the suffering is later.  Many in the corn belt feel it is V-8 before they can dry things down significantly.  This is the most common scenario, and based on our experience, much drought stress at germination is next to impossible to overcome and have a normal yield.

Do we want to grow the crop with just enough water and then at fruit set, or tasseling, etc, we want to stress for a month as if the rains did not come or the reservoir went dry?  To do this effectively we need to keep the lower soil horizons water quantity as dry as possible so when we induce the stress, the roots don't make up the deficit by getting the water from the lower depths. (The same concept holds true for nutrient deficiency trials.)  In our experience, a full flood irrigation will fill those lower profiles and deep-rooted crops like corn or tomatoes will take 30-60 days to show much stress.  But this strategy can backfire.  In summer of 2017 here in Yuma, we were keeping our tomatoes and watermelons on the light side of wet, with not much at all for available moisture in the second foot of soil.  June 20, the first day of summer we had 120 Fahrenheit. —the 4th hottest day on record, and abnormally early.  We were caught flat footed and the crops went down in a hurry without having a reserve of deep water to pull from.

Whatever scenario is targeted, a decision has to be made about frequency of the water.  Are we putting on a little bit every day or three with “normal” being an acre inch and the reduced regimes ¾”?  Or are we watering every other day with the normal amount one day and a reduced quantity every other irrigation?  Another possibility is to water Several acre inches every 10-14 days like we would with a surface irrigation, and then withhold water Longer on the dry section.  Part of this decision is if we are mimicking a situation of water rationing, or if we are looking at a dryland scenario of no rain for a few weeks.

When in a water rationing situation, most growers will water it out of the ground well, and then irrigate for a good fruit set and try to cut back some during the bulking stage.  But so much depends on the crop.  Shorting tomatoes or peppers during the fruit bulking growth stage will typically cause blossom end rot, even if there is enough water to make most of the tonnage.

This discussion can be endless!  Determining the situation you want to mimic is the starting point.  The more we understand what the product might do, combined with lots of discussion about what might and might not work is the foundation of a good trial.

Sunday, January 11, 2015

Mite we talk Strawberries?

Strawberries at
We have been doing strawberry work off and on for the past few years.  The low Desert of CA/AZ has been producing December-March fruit for 10 years or so, and there are around a thousand acres down here each year.  The majority of the plantings are in the Coachella Valley, closer to Palm Springs, with the rest scattered around. For the past few years we have planted a small acreage here in Yuma of commercial style Strawberries--raised beds with plastic and drip irrigated, with a first of October planting of a commercial variety.  Steve Lucich with Norcal Nursery in Red Bluff, California has been a great help to our efforts, and we sincerely appreciate his and the rest of the staff at Norcal Nursery's support.  Ron Sakuma, one of the original brothers who formed Norcal actually worked with us 25 years ago when we played with Strawberries in Colorado, but that is another story...

For pest issues we have the usual Botrytis fruit rots, and more interestingly, we typically have a significant amount of Anthracnose as a flower / fruit issue.  To the point where we won't harvest much if we do not control it.  Powdery mildew is sporadic here.

Two Spotted Mites (Image by J. Bundy)
We also have our fair share of issues with two spotted mites.  Last year they surprised us and were a real issue in our trials--except of course in our mite trials, where they were welcome!!  The planting we have in this winter has a low level of pressure as the weather is cool, and we are nurturing them so that when the weather warms back up in a month or so, we will have a thriving population where we can do trials without the concern of either a) over spray from the commercial grower, or b) complaints from the commercial grower about how we are bombing his field with mites parachuting in...

Iron is an issue in Desert Strawberries
You can also see in the image at the right that Iron can be an issue in our soils, and strawberries are the proverbial Canary ... we do a reasonable amount of fertility work since at 15 or 20 thousand dollars an acre for commercial fields, getting the growers to shut down their fertilizer program is challenging.  Same is true with transplant issues such as Phytophthora. We have the option to keep the fumigation off the blocks, and the mortality from damping off problems is somewhat frightening in the non-fumigated areas.

The one on the right does not look too happy--
root diseases strike again! The one on the left has
worm damage and the center of the flower is frosted 
Phytophthora--Killer of Youth...

One of the more interesting things about strawberries is that there is a limit on how many people want... at the beginning of harvest (December), our staff are arm wrestling to see who gets to take them home... and by March, everyone looks the other way when they walk past the boxes...

Whatever your testing needs are for Strawberries, let us know and we will work with you on a method!

Saturday, November 8, 2014

Planting in Yuma

Planting more plots, this time in the Yuma area... in the Winter Wheat Planting in Montana post from last month, we were working at some points, only 50 miles from the Canadian border... here in this series, we are only 5 miles from the Mexican Border...

We are using a PlotSpider, a self propelled planter / tool bar system set up to plant trays of seeds rather than envelopes as we usually do.  This is a fairly specialized piece of equipment, and this is an older model we are resurrecting in cooperation with Dr. Oly Cantu at Arizona Plant Breeders.

The system and machine worked fine.  Oh there were the usual new equipment blues like forgetting to put the drills in the ground, but overall, it worked great.  And hopefully our alleys will be straight!!!

Calibrating to plant 4 foot plots
Kenny watching the cone and trip marks as we calibrate.
Kenny working to keep the rows straight while Cody runs the
tray planter in some 25 foot Canola plots

Canola seed in the cone

Daniel driving as Brandy runs the trays and Cody calls the trip points
in some 8 foot long wheat plots

Things moving smoothly--the buckets are to put spent trays into.

Tuesday, October 28, 2014

Winter Wheat Planting in Montana

A quick photo essay of the Winter Wheat planting season this fall, with lots of seed treatment trials...

Saturday, August 23, 2014

GPS Steering and Plot Work

Auto-steer has been around for a while in the more expensive tractors.  I remember the first time I saw someone making vegetable beds with a GPS system and auto-steer—WOW!!  Traditionally, a farm would have one guy—a Prima Donna usually—who was the Lister Driver (a lister is the shovel implement which makes beds)... and this guy was revered for being able to drive straight and with consistent guess rows. 

Guess Rows are the bane in row crops… a guess row is the space between implement passes… Let’s say you have an 8 row Lister, which means it has 9 identically shaped shovels spaced EXACTLY the same distance apart, and at exactly the same depth mounted on a perfectly level tool bar.  So those 8 rows are all the same.  Same height, and of course, all the same distance from peak of the row to the peak of the adjacent rows.  In our case with vegetables, that peak to peak distance is 42.0 inches. 

So you make a pass and you have 8 beautiful beds…you get to the other end of the field and then you get ready to drive back.  In the old days we used a marker.  The marker was a shank with a small shovel of some flavor which was set so that it was in the middle of the next pass with the tractor.  The idea being that you would drive over that line and everything would be straight and even.  And this is where the “Lister Driver” excelled… he could drive that line straight as an arrow, and be only an inch or two off.  And he was king.  Everything else hinged on his straight rows.  The cultivating, the spraying, harvesting all went much better when the rows were straight and even.

So our mystical Lister Driver would make his turn and then get lined up on the mark… usually requiring a couple of backups and pull forwards to get this 28 foot implement mounted on a 300 horse tractor exactly right.  The advent of GPS accuracy, brought about after President Clinton, (during lulls between sessions with Monica) signed the bill which removed the distortion from the navigation satellites and allows sub-inch precision with the right receivers.  So now most anyone can drive a lister, do a better job and be quicker.  Why? Because when you make your turns, you don’t have to line up adjacent to the previous pass, you can make a broader and easier turn, kick on the auto-steer when you are close and the machine takes over and puts you right where you want to be.
4 Little Devils Farming's 28 foot Lister completing
 a pass in an RD4AG field soon to be in Lettuce.  Take a
tape, every bed is 42.0 inches apart

Back when, the suggestion that you could list 28 feet, move over 112 feet, and have that pass end up being in the right spot, and I mean DEAD ON, was the dream at beer bashes and whiskey parties.  And today, most anyone can do it. But these systems work best at 3 mph plus and they are a 30-50 thousand dollar add on to the hydraulic systems on to a new or used tractor.  And they don’t really put them on small tractors like we use in research. A few years back Trimble decided to appease the Tulip growers in Holland, designing a system which would be accurate at the 2 kph (1.2 mph) speed they used when transplanting.

But those are still expensive ad ons—to do the plumbing into your existing tractors hydraulics was pushing 20 grand, plus another 10 for the GPS system.  For most of us, that would more than double the tractor value!  We have been working with our friends at Triangle Ag in Fort Benton, Montana on this for a while.  DeImna worked in research while getting her degree at University of Idaho, so she was sympathetic to our issues, and she made the error of not hanging up on me the first time I called…

With her help, we found a good used Trimble FMX GPS machine and then we bought the components to put Trimble’s gear based steering wheel auto steer system.  It still cost us 10 grand but we felt like this was a bargain for technology we needed as the precision required of us gets tighter and tighter each season.  We have been playing with this for the past couple months, and we are finally getting it dialed into where we want.  The first tries found the machine not sure which line it should be taking… we are doing passes of 5 or 6 or 7 feet at 1.5 mph when planting, and that takes different settings than 28 feet at 5mph… but as you can see from the photos from yesterday’s corn planting, we are getting the hang of it.  Our guess rows are 41-42-43 inches, on a nominal 42, so things are good.  And this makes such a huge improvement in the other tasks later…  
Straight rows... Magical!  The angled dirt ridge is from a previous operation.
Those are Medjool Date palms in the back ground.

Our Excellent SRES Runabout Research Planter