Situation: The complaint we were invited to evaluate in this field was less typical than what one often finds with yellow plants in Salinas or Watsonville. These patches of yellow plants were typically dispersed in patches of various sizes in the field (photo 1 below), but on one side of the field this was particularly pronounced.  This area corresponded with a farm road from a previous artichoke plantation as well as being the end of the drip tapes installed by the strawberry grower.

The bed tops tended to be dry and moisture has been adequate but not excessive, so my running thesis of excess water actually did not fit so well in this situation. 

I had the good fortune on this particular call of being accompanied by Frank Shields from Soil Control Lab, who did a thorough evaluation of a bed and plant tissue (photo 2 below) and arrived at the results as depicted in photos 3 and 4 below.

Evaluation: As readers can assess from the attached analyses, this sampling was extraordinarily detailed.  The soil analysis breaks down the bed into ten zones and evaluates no less than 14 parameters of each zone.  Furthermore, in zone 7, Frank took a general sample of the soil texture and shrinkage, which gives an assessment of at what moisture percentage cracks form in the soil.

As a standard operating procedure, Frank sampled one bed containing symptomatic plants according to a pattern of ten different areas, the cross section of which can be seen in the soil report attached below.  Additionally, Frank uprooted several plants for evaluation of the roots and tissue mineral contents in the foliage.

This soil test strives to accomplish a number of things.  First, it is designed to monitor the movement and location of accumulated soluble salts for the purpose of determining the water pattern from the irrigation system. Similarly, since during the season strawberry fertilizer is supplemented via the water it is useful to know where the nutrients are ending in the bed to confirm that they are getting to the plant and not being leached out of range or being affected by adverse pH or salt conditions.

Plant available nutrients are both water soluble and exchangeable. This analysis is designed to monitor the water soluble fraction for the water soluble plant nutrients nitrate, nitrite, chloride, and sulfate as well as cations which accumulate with the water soluble fraction like calcium, potassium, sodium and ammonia. 

Interpretation of Results:

Moisture: All zones were very wet indicating recent irrigation of sufficient volume to completely fill the bed and should leach salts and nutrients down and out of the bed.   Additionally, there were no shrinkage cracks visible when observing the fifty foot section of row again indicating that the soil had been kept sufficiently moist.

The pH is on the high side and evenly distributed between 7.8 and 8.4 though all zones.  However, this pH is not unusually high and normally would not be said to be problematic for strawberries.

Soil potassium is this sample low.   It is typical for soils in Salinas and the Pajaro Valley to have potassium concentrations above 150 ppm, but with the exception of zone 10 of the bed this particular sample ranges around 50 ppm or below.  This is reflected in the leaf potassium concentration of 0.9% when a range of 1.3 – 1.8% is ideal for this time of year.

Soil nitrate appears to be substantially leached out, and indeed the percentage in the leaves of the sampled yellow plants is 2.0%, which is somewhat less than the optimum of 2.4- 3.0 % for this time of year.   Still, 2.0 % dry weight tissue nitrogen would not explain the substantial yellowing we observe in the field.

Phosphorous, calcium, magnesium and the other micronutrients appear to be sufficient according to the attached tissue analysis.

Nitrites, which are oxidized to plant available nitrate in the process of nitrification but toxic to plants in quantity are absent from the sample.  This is quite probably because of the well aerated soil and lack of packing. 

EC5: This is a measure of the amount of water soluble components in a zone. Zone six has the highest in the root zones (1 – 8) but all within values to support plant growth. With proper watering, salts should accumulate in zone six, nine and ten. In this sample, salt accumulation is highest at zone ten typical of a pattern of a bed having full mulch and plenty of water.

We can also look at the ratio of water soluble cations to get an idea on the ratio of plant available constituents like the SAR value and soluble Ca/Mg ratio. The very high sodium and chloride compared to the low calcium and magnesium in this sample is significant and indicates a problem.   Indeed, sodium and chloride are excessively high in the plant tissue and very likely to be interfering with normal plant function.

Outside of the carbonates, the soil minerals are an accumulation both from the irrigation water and nutrients added to the soil. If most of the salts accumulated in the bed are naturally found in the irrigation water (as is the case here), it means that the nutrients are being leached out of the root zone with excess water and additional fertility could be considered.  

Conclusion:   Rather than being a problem of the deficiencies of nitrogen or potassium, Frank maintains that at issue here is a buildup in the affected areas of chloride and accumulated salts as a result of irrigation.  Carrying this thesis further, perhaps if the amount of current irrigation water could be limited in the areas experiencing yellow plants, one would also be reducing the amounts of apparently damaging sodium and chloride.  That might be one way to address the problem.

The scattershot pattern of yellow plants across the field is the major confounding point of the problem being evaluated here.  On the one hand it would indicate that the toxicities and deficiencies described above are occurring in the same scattershot pattern across the field but it does beg the question why the differences are so dramatic, sometimes even from one plant to the next.

So, while this evaluation has given us a good look at what is going on around these yellow plants, we still don't conclusively know what exactly is the cause of this problem.  It absolutely merits further work. 

Thank you to the grower who invited us out.  I thank Frank Shields of Soil Control Lab for the contribution of his time and expertise to working on this problem. 

I have an update on the strawberry field described in the January 6 post of this blog suffering extensive salt damage .

As you may recall, the determination on finding all of that salt damage was to immediately overhead irrigate to wash the accumulated salts away from the plant roots, and the grower did indeed do that already on the next day as shown in the first photo below.

As the reader can see from the second and third photos below, the recovery of this field is now near complete.  The plants are large, green with flower and fruit formation just beginning.  While the field seems to be have been set back some on the production cycle from the injury caused by salt, there is no doubt that the situation is a much happier one right now than in January, with nary a sign of salt burn anywhere and plants well into recovery.

Three soil samples taken from the field April 24, 2012 gave salinity at 1.3 dS/m, 1.5 dS/M and 2.3 dS/M, giving the impression that much of the salt from January had been now leached out.

A few things that growers and field people might being seeing this time of year in strawberry plants.

Salt Toxicity: By far the biggest issue so far in 2012 has been salt damage.  This issue is well described in the January 6 post, but a photo is included below for the sake of comparision with the other disorders.  To re-iterate, most notable characteristic of salt damage is the burnt margins of the leaves, especially on the more developed leaves.  Photo 1 below.

Fumigant Toxicity: Fumigation toxicity is another, fortunately not too common, issue that one will see at this time of year.  Every case I have been called out to has involved drip fumigation, and this makes sense, since for several reasons drip fumigants take much longer to exit the soil than shanked in materials like methyl bromide.  The process of moving out of the soil was delayed even more in the case depicted below in Photo 2 because of application into the cooler temperatures of late October, 2011.  It is notable that, in an attempt to mitigate the fumigant remaining in the beds post fumigation, this field was flushed via the drip tape with a large quantity of water and beds slit several days before planting.  Nevertheless, these activities still did not suffice, and the field languishes.

In photo 2 (taken the week of January 9) below, one can see the affected plant is struggling to establish itself and is undersized and yellow.   This is probably because its root system was compromised by remaining fumigant (doesn't need to be a lot either, it could have just been a trace) at planting and its root system is still struggling to function normally.  While this plant will undoubtedly still survive, it is unlikely to reach full yield potential.  The die was cast and its fate determined at the point of planting.

Leaf Blotch Disease:  Leaf blotch disease of strawberry normally is found all over Central Coast strawberry fields this time of year. However, since it is dependent on splashing water, it is pretty doubtful that there is much of this disease around this year. Nevertheless, since symptoms superficially mimic those of salt damage it is worth a review. 

Generally the lesions of leaf blotch disease consist of tan to gray leaf blotches that commonly, but not always, develop along the margin or edge of the leaflets. The leaf blotches are irregular in shape and are very often surrounded by a purple margin. Affected areas can grow to some size and are able to expand and cover from 1/4 to 1/2 of the leaflet surface.  To distinguish leaf blotch disease from salt damage one needs to look for the presence of tiny, brown to black, fungal fruiting bodies in the gray to tan blotches.  Photo 3 below.

As a postscript to last week’s post regarding salt and ammonium damage to area strawberry plantings, I will outline the results of the soil samples taken from a field demonstrating the symptoms described in that article.

Steve Koike and I collected soil samples from the affected field last Thursday, January 5.  Soil samples were collected from four blocks, one of which had been overhead irrigated the day previous, and consisted of composites of at least five 5” deep samples taken from around the fertilizer band by the plant roots.

Samples were immediately taken to Soil Control Lab in Watsonville for analysis.

Results are as follows:

The results are pretty clear in showing that the block (Sample 4 ) which had been watered by overhead irrigation had three times lower nitrate concentrations and about half the EC (which is electrical conductivity, a measure of salt) of the other three averaged as a group, but more equivocal on the reduction of ammonium.

To interpret the data in the table above, we can refer to work done some time ago which demonstrated EC’s in excess of 1.0 were related to loss in yield of strawberry, suggesting that real damage could occur at the 4x levels in the table above.