Evaluation of Iron Chelate Starter Fertilizer Use for ...

Evaluation of Iron Chelate Starter Fertilizer Use for Irrigated Soybean Merrick County - 2010 University of Nebraska-Lincoln Richard B. Ferguson Professor of Soil Science Glen P. Slater Research Analyst

Objective The study was conducted to evaluate the potential for soybean yield increase with the use of an iron chelate starter fertilizer (Soygreen) on soils known to be prone to iron chlorosis. Additionally, we wanted to evaluate the degree of chlorosis pressure spatially across the field, and efficacy of the iron chelate fertilizer in areas of varying chlorosis pressure. Such variation could result in economic benefits from site-specific use of iron chelate starter fertilizer. Soygreen is a dry water soluble powder (6% Fe) iron chelate (ortho-ortho Fe-EDDHA). It is manufactured by Laboratorio Jaer, S.A. of Barcelona, Spain and distributed by West Central Inc. of Willmar, MN. Soygreen is recommended as an in-furrow soil or foliar applied fertilizer. Recommended rates for in-furrow application are 1-3 lb product/acre, in 2-10 gallons of water/acre. Materials and Methods The study was conducted in 2010 on a producer’s field in northern Merrick County, Nebraska with moderate Fe chlorosis pressure potential. Soils within the study area were Leshara silt loam, Wann loam, and Janude sandy loam (Figure 1). The cooperator was responsible for most agronomic activities including pivot irrigation. Management practices (variety selection, fertilizer other than starter, pesticides, etc.) were at the discretion of the farmer with the intent to optimize yield potential. The previous crop at this location was corn. The field was disked in the spring. Prior to planting, the field was mapped with a Veris 3100 soil apparent electrical conductivity instrument, coupled with a Trimble 442 RTK-GNSS receiver, providing shallow (0-30 cm) and deep (0-90 cm) apparent electrical conductivity and 2 in. accurate elevation. All starter treatments were applied with a 10 ft JD Maximizer (4-row) planter with a John Blue piston pump for liquid fertilizer application in-furrow with the seed. The Soygreen formulation was a mix of 80 lbs of dry Soygreen into ~320 gallons of water, mixed using a dry inductor and a 1000 gal. liquid nurse tank. Soybeans were planted May 24 (Croplan variety RT2722 @ 140,000 ppa). Plot dimensions were 8 rows (20 ft) wide by field length (~2000 ft). The study, which covered 16 acres, was a randomized complete block design with 4 treatments and 4 replications. Specific treatments were: TRT Fertilizer Formulation Fe Chelate 1. No starter (check) none 2. Soygreen starter 2 lb /acre 3. Soygreen starter 3 lb /acre 4. Soygreen starter 4 lb /acre The crop was sprayed with 1qt/ac Roundup on June 30 to control a weed problem. Chlorophyll data (Minolta SPAD 502 meter) was collected from treatment strips June 28, 2010. Multispectral aerial imagery (RGB – NIR) of the study field was obtained July 16, 2010. The field was harvested using the

cooperator’s yield mapping combine October 2, 2010. Directed soil samples of the field were collected October 8, 2010.

Figure 1. Merrick County study site, with 2009 FSA aerial image as background. Study area bounded by green outline. Study area soils are: Leshara silt loam (Le), Janude sandy loam (Jm), and Wann loam (Wm).

Results and Discussion Soil sample results from the study field are shown in Table 1. Soil pH was on average neutral – no sites had a pH greater than 8.0. Patterns of deep apparent soil electrical conductivity are shown in Figures 2 and 3. Generally conductivity was lower in the eastern part of the study area, coinciding fairly closely with the Janude sandy loam soil. The soybeans showed minor signs of iron chlorosis in patches as early as June 15 (Figures 4 and 5). Differences in chlorosis were evident with treatment, with darker green foliage where iron chelate was applied. There appeared to be no visual difference among Fe rates in foliage color. Figure 6 illustrates approximate growing season rainfall (obtained from a nearby weather station). The early part of the season – through mid-July, was relatively wet, followed by dry conditions the rest of the season.

Soybean Response to Fe Chelate Starter Fertilizer

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Table 1. Directed soil sample results.

pH

Buffer pH

OM (%)

Mehlich 3 P (ppm)

K (ppm)

Fe (ppm)

Mn (ppm)

DPTA Zn (ppm)

0-8 in. NO3-N (ppm)

0-8 in. (lb N/acre)

0.24

7.0

7.1

2.0

19.8

241

20.7

6.5

1.69

10.2

24.7

0.08 0.38

5.7 8.0

6.8 7.2

0.8 3.1

5.0 46.0

150 392

4.8 79.2

2.2 15.5

0.63 4.14

4.0 21.2

10.0 51.0

Soluble Salts

AVG Min. Max.

Figure 2. Shallow apparent electrical conductivity.

Figure 3. Deep apparent electrical conductivity.


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Figure 4. Untreated (left) and treated (right) strips, June 15, 2010.

Figure 5. Untreated (left) and treated (right) strips, June 15, 2010.


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Figure 6. Growing season rainfall from nearby automated weather station (approximately 8 mi west).

Figure 7. Aerial image (RGB) of study field July 16, 2010. The area bounded by the orange outline within the study area had evident chlorosis in June, shown in Figures 4 and 5.


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Figure 7 is an aerial photograph of the study area taken July 16, 2010. There are evident areas of reduced vigor in the western portion of the study in the Leshara soil. This is the area where chlorosis was most evident earlier in the season, and where the photographs in Figures 4 and 5 were taken June 15. The area towards the east within the Janude soil is a former drain which has been filled and leveled, but is quite coarse-textured. The drain still exists as an extended pond to the south of the study area. Poor crop growth was noted in this area throughout the growing season.

Table 2. Treatment means over entire study area. Yield means with different letters are significantly different (PR=0.05).

Fe Chelate (lb/acre)

Chlorophyll Meter June 28

Grain Yield (bu/acre)

Grain Moist. (%)

Check

0

25.3

64.7 c

9.39

2

Soygreen

2

22.7

66.5 ab

9.46

3

Soygreen

3

25.6

66.6 a

9.46

4

Soygreen

4

22.6

65.7 bc

9.48

Trt No.

Fertilizer Source

1

Table 2 provides mean values for treatment effects on in-season chlorophyll, grain yield, and grain moisture over the entire study area. Overall, there were small but significant differences in yield among treatments (SAS Proc GLIMMIX). Yield increases with Soygreen treatment ranged from 1.0 to 1.8 bu/acre across the entire study area. Treatment response was also evaluated spatially, according to mapped soil series and the chlorotic patch evident in June, shown in Figure 6. Table 3 illustrates grain yield by soil series and within the chlorotic zone, by treatment. The highest yields were observed within the Wann loam soil series, and lowest yields in the Janude sandy loam. There were no significant treatment effects on yield within the Janude soil series, but significant increases in yield with Fe chelate application in the Leshara and Wann soil series. There was also a significant increase in yield with Fe chelate application within the observed chlorotic area. The largest yield increase to Fe chelate starter fertilizer was approximately 4 bu/acre, observed in both the Leshara soil series and in the evident chlorotic zone. Table 3. Treatment means within mapped soil series, and treatment means within observed the chlorotic area (Figure 6). Yield means with different letters are significantly different (PR=0.05).

Trt. No.

Fertilizer Source

Fe Chelate (lb/acre)

Leshara silt loam

Wann loam

Janude sandy loam

Chlorotic Area

1

Check

0

64.2 c

69.0 b

60.6 a

64.9 c

2

Soygreen

2

67.9 b

69.9 b

61.7 a

67.8 b

3

Soygreen

3

68.9 a

71.5 a

60.2 a

68.7 a

4

Soygreen

4

67.9 b

66.2 c

61.4 a

63.7 c


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Figure 8 illustrates yield patterns over the entire field, and Figure 9 illustrates yield patterns for just the study area. Yields in the study area to the west of the pond in the field tend to be lower than the bulk field to the south. This may be partly due to increased weed pressure in the study area. The entire field was treated with Roundup, but the non-study area of the field was also cultivated. The study area could not be cultivated due to planter guess rows from the research 4 row planter not matching the guess rows from the cooperator’s 12 row planter. Mean soil nutrient levels shown in Table 1 are generally considered adequate for soybean production. The average soil pH was not high, though the highest pH’s did coincide with the Leshara soil and the region of the field with more visual evidence of Fe chlorosis (Figure 10). The chlorotic area also tended to have the highest laboratory EC values (Figure 11) and lowest soil Fe (Figure 12).

Figure 8. Soybean yield, entire field.


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Figure 9. Study area soybean yield.


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Figure 10. Soil pH distribution.

Figure 11. Soil EC distribution (lab analysis).


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Figure 12. Soil Fe distribution.

Summary There was not severe Fe chlorosis in this field in 2010. Consequently, yield increases due to Fe chelate starter fertilizer were small, but statistically significant in some areas of the field. The largest yield increase to Fe chelate fertilizer was observed on the Leshara soil, and within the area of the field with visual symptoms of Fe chlorosis in June. There was no benefit to increasing Soygreen rate above 3 lb Fe/acre. Depending on relative costs of use of Soygreen as a starter fertilizer, and the value of the soybean crop, it may be profitable to use Soygreen as a starter treatment on this and similar soils – and especially so in areas of the field known to be more prone to iron chlorosis.

Acknowledgements We appreciate the provision of this field for research by the cooperator Paul Jarecke, and his general care of the study site throughout the growing season. We also appreciate funding provided by West Central, Inc., in support of soil fertility research efforts of the University of Nebraska.


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