Arrival at a Probable Cause of Yellow Strawberry Plants in Castroville

Aug 2, 2012

Arrival at a Probable Cause of Yellow Strawberry Plants in Castroville

Aug 2, 2012

Introduction: The following is a description of a second, more thorough evaluation of the situation described previously in this space of yellow strawberry plants in a field in Castroville.  This issue of yellow strawberry plants popping up in certain locations in the Castroville – Salinas production area has confounded us for years, but I believe the work described below allows us to make a strong argument as to the cause is of this malady at least in this case.

 

Materials and Methods:  A total of four samples (two from an area of severe yellowing, and two from an area of apparently healthy green plants) were taken.  Following the output example posted below (Figure 2), each sample consists of 10 zones of a bed, and each zone is tested for 14 parameters.  At each soil sampling site, a representative plant sample was uprooted and taken away for analysis of tissue mineral concentration.

 

Results: The data in the Tables 1 and 2 below represent an average of the two samples taken each for yellow and green plants.  In order to better interpret the data, several zones have been grouped together.  Zones 9 and 10 represent the surface of the bed, zones 1, 2 and 3 represent the soil straight underneath the drip tape, zone 8 the plant zone, zone 7 the root zone and zones 6, 5 and 4 being underneath the root zone 7.

 

Table 1: Evaluation of Zones 1- 6 of Bed in Yellow and Healthy Areas

 

Data (mg/Kg dw)

Zones 1,2 and 3

Zones 4,5 and 6

 

Yellow

Healthy

Yellow

Healthy

Moisture (%)

33.7

33.6

29.8

31.8

pH (units)

8.5

8.1

8.5

8.1

EC5 (umhos/cm)

269

267

381

355

Ammonia (NH3-N)

24

32

60

16

Nitrate (NO3)

204

49

443

94

Phosphate (PO4)

126

86

66

68

Potassium (K)

157

184

157

92

Calcium (Ca)

419

417

398

201

Magnesium (Mg)

169

375

174

130

Carbonate (CaCO3) %

2.3

1.8

2.7

1.7

Sulfate (SO4)

219

195

694

412

Sodium (Na)

454

417

578

426

Chloride (Cl)

175

184

181

242

Nitrite (NO2)

0

0

0

0

 

Table 2: Evaluation of Zones 7-10 of Bed in Yellow and Healthy Areas

 

Data (mg/Kg dw)

Zone 7- Root Zone

Zone 8- Plant Zone

Zones 9 and 10

 

Yellow

Healthy

Yellow

Healthy

Yellow

Healthy

Moisture (%)

30.6

32.1

33

33.1

22.8

26.3

pH (units)

8.7

8.2

8.7

8.3

8.3

8.2

EC5 (umhos/cm)

305

389

258

374

938

546

Ammonia

(NH3-N)

34

14

54

16

48

44

Nitrate (NO3)

314

30

199

25

968

452

Phosphate (PO4)

6.5

57

85

55

111

45

Potassium (K)

144

74

185

89

206

89

Calcium (Ca)

341

156

713

194

512

195

Magnesium (Mg)

140

83

383

127

384

104

Carbonate (CaCO3) %

2

1.3

2.0

1.9

2.0

1.9

Sulfate (SO4)

434

492

239

437

1216

622

Sodium (Na)

500

446

492

496

872

520

Chloride (Cl)

160

309

165

330

433

310

Nitrite (NO2)

0

0

0

0

0

0

 

 

Table 3: Comparison of Mineral Concentrations of Leaf Tissue for Green and Yellow Plants

Mineral

Yellow Plant

Green Plant

Total Nitrogen

2.4%

2.2%

Total Phosphorous

0.38%

0.44%

Potassium

1.1%

1.2%

Calcium

1.5%

1.3%

Magnesium

0.55%

0.38%

Total Sulfur

0.21%

0.18%

Copper

4.5 ppm

3.7 ppm

Zinc

23 ppm

18 ppm

Iron

515 ppm

365 ppm

Manganese

185 ppm

108 ppm

Boron

73 ppm

78 ppm

Molybdenum

1.1 ppm

1.9 ppm

Sodium

350 ppm

79 ppm

Chloride

4150 ppm

3000 ppm

 

I’ve also taken a look at the irrigation water.  As is common in northern Monterey county, the farm gets its water as a mixture of recycled water blended with well or river water.  A full report for an example of the blended irrigation water used on this farm is available from the Monterey Regional Water Pollution Control Agency at:

http://www.mrwpca.org/recycling/chem2012_blended.php

In the sample taken of the blended recycled and river water mix, conductivity (EC) was 1.3 dS/m, sodium 118 ppm, chloride 160 ppm and adjusted SAR of 3.4 (sodium adsorption ratio, an index of sodium hazard adjusted for the amount of calcium in the irrigation water). 

Discussion:  The pH of the soil in the beds in all zones is quite high, which is not surprising because of the high percentage of carbonates (lime) throughout.  One can also see accumulations of nitrates, phosphates and potassium are substantially higher in the areas of the yellow plants, which quite likely due to their declining ability to take up the nutrients being continually applied as fertilizer.   It is worth noting that nitrates in the high concentrations found in our soil tests can be toxic to plants, thus accelerating the decline of plants.

Nitrites, generated from ammonium in anaerobic conditions, are zero, indicating adequate aeration in the bed.

In terms of the irrigation water, referring to the water quality guidelines for crops developed by UC Cooperative Extension, we find that the water used on this farm can be used with some restriction to irrigate crops moderately susceptible to salinity such as strawberry.  In other words, this irrigation water isn’t great but is OK.

It seems that the real culprits in this field are the accumulated amounts of chloride and sodium.  Generally speaking, crops in our area perform best when the soil sodium levels are less than 250 ppm and soil chloride levels are less than 100 ppm. 

Across all the soil samples the average amounts of sodium and chloride are above 250 ppm and 100 ppm respectively.   High as they are, the concentrations of both ions do not vary greatly in the plant and root zones and the zones around them in either areas of green or yellow plants. There are, however, substantial differences in the concentrations of these ions at the crust (zones 9 and 10) between green and yellow plant areas. For example, on average soil from areas of yellow plants there is nearly a twofold accumulation of sodium in the crust of soil taken as well as a substantially higher amount of chloride over the soil sampled around green, healthy plants.  This tells us that while these large amounts of sodium and chloride (also known as salts) are accumulating away from the plant via evaporation, they are nevertheless passing through more sensitive plant zones to get there.  It is not difficult then to hypothesize that during this transition the yellow plants are picking up these salts obtaining the fourfold accumulation of sodium and 40% increase in chlorides that we observe in the leaf tissue of yellow plants over that of green.

Furthermore, it is notable that the amount of lime (CaCO3) in all the soil samples is high.   This indicates that a lot of calcium coming into the soil from irrigation water is precipitating out and not as capable of sufficiently limiting the amount of exchangeable sodium.   In turn the sodium hazard is high.  This may also explain to some extent why areas quite close to one another respond differently, since in some areas (perhaps even quite close together) more calcium precipitates out than others.

My conclusion drawn from all this work in this particular instance of severe plant yellowing of strawberry plants is that the uptake of sodium and chloride by these affected plants is very high and they are being poisoned by salt.

Thank you to Frank Shields and Soil Control Lab for their generous assistance in this work.  Thanks to other colleagues for their valuable insight and input which assisted me in the development of my conclusion.

This project was supported in part with funds provided by the California Strawberry Commission.