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Effects of irrigation scheduling on soybean growth and yield.

Kurt Thelen, Mark Bernards and Michael Staton

Michigan State University, E. Lansing, Michigan, 48824 thelenk3@msu.edu

Abstract

Five irrigation schedules based on soybean growth stage and soil water deficit were evaluated. Soybean varieties responded similarly to the irrigation treatments, i.e., the variety x irrigation treatment interaction was not significant (p=0.05). Average yields were equal between the full season, flowering (R1-R2), and pod elongation (R3-R4) treatment timings, at about 3025 kg/ha. Waiting until seed fill (R5-R6) to begin irrigating cost approximately 335 kg/ha in yield (2690 kg/ha), and plots that were not irrigated (except to keep soil moisture above the 75% soil water deficit level) produced yields of only 1950 kg/ha. Yields averaged across all five irrigation treatments of seven of the varieties were equal, 2755 to 2950 kg/ha. Soybean aphids were present in large numbers between late July and mid-August. Although the trend showed higher aphid populations in irrigated plots, there was not a statistical difference between irrigation treatments. Based on three years of data, it appears that maximizing soybean yield in the Northcentral Corn Belt is dependent on maintaining adequate soil moisture beginning at full bloom (R2) or beginning pod (R3), provided that the soil water deficit (SWD) does not exceed 75% prior to that growth stage.

Media Summary

Northcentral United States soybean growers can conserve water and maintain soybean yield by holding off on irrigation until the soybean reaches full flower. Maintaining adequate soil moisture beginning at full bloom (R2) or beginning pod (R3), provided that the soil water deficit (SWD) did not exceed 75% prior to that growth stage resulted in maximum soybean grain yield. Irrigation to above 75% SWD prior to full bloom had little effect on soybean yield.

Key Words

Soybean, Irrigation, Water Use, Yield.

Introduction

North Central United States seed corn producers have been encouraged by seed companies to include soybean in their crop rotation to break up crop pest cycles associated with continuous corn. In Michigan, seed corn is often produced on sandy soils, and most growers have installed center pivot irrigation systems. Because soybean is not typically grown under irrigation in Michigan, very little information is available on scheduling irrigation for soybean and growers have reported inconsistent yield responses. Previous studies have evaluated soybean response to irrigation and the temporal pattern of rainfall in more southern latitudes (Ashley and Ethridge 1978; Elmore et al. 1986; Runge and Odell 1960). In most studies, soybean seed yield increased with irrigation, although the degree of increase varied significantly depending upon the year, time of application, soil type, and variety grown (Heatherly 1985).

The objectives of this study were: 1) To determine what irrigation schedule optimizes soybean seed yield in Michigan, and 2) to evaluate how high-yielding Michigan soybean germplasm responds to irrigation treatments.

Materials and Methods

The experiment was conducted during the 2001-2003 growing seasons on a Spinks fine sandy loam at Michigan State University’s Southwest Michigan Research and Extension Center (SWMREC), near Benton Harbor, MI. The field was chisel plowed and disked each year. The field was limed in 2001 to a pH of 6.5, and fertilized each year with K2O (2001, 78 kg/ha, 2002-2003, 123 kg/ha). Fertilizer was incorporated by disking. Daily max and min air and soil temperatures, solar radiation, wind, and precipitation were recorded by the Automated Weather Station located on the research station and operated by the Michigan State University Agricultural Weather Office.

Five irrigation treatments, based on soybean growth stage and soil moisture levels, were evaluated (Ritchie et al., 1997). Soybeans were irrigated before the soil water deficit reached 50% beginning at each of the following growth stages: 1-Full Season (FS), 2-Flowering (F) (R1-R2), 3-Pod Development (P) (R3-R4), 4-Seed Filling (S) (R5-R6), 5-Dryland (D). The soil water deficit was not allowed to exceed 75% during the growing season for any treatment, and irrigation was applied to the dryland treatment at least once each year. No irrigation was applied after soybeans reached the R7 growth stage. Irrigation was applied using Senninger Wobbler Sprinklers from 2 m tall risers. The nozzle size was 0.55 cm and pressure was regulated at 103 kPa. Risers were spaced 18.3 m apart and were mounted on 7.6 cm aluminum solid-set pipe. The radius of the spray circle was approximately 8.2 m. Irrigation distribution was measured by attaching 1.0 L beverage cups to 1.3 cm PVC pipes 1.0 m above the soil surface. The cups were spaced 1.4 m apart along the N/S axis for all plots, and the E/W axis for the full season irrigation plots. The water in each cup was measured using a graduated cylinder shortly after the irrigation was completed and precipitation was then calculated.

Soil moisture was measured weekly using TDR technology. A Trime-T3 tube access probe and the Trime-FM3 moisture meter were then used to measure volumetric soil moisture in 17.8 cm intervals to a depth of 0.9 m. Soybeans were planted on 26 April 2001, 7 June 2002, and 3 May 2003 in 15 inch rows using planters equipped with John Deere MaxEmerge Plus planting units. The late planting in 2002 was a replant because the first planting was infected by pythium rot and emergence was poor. The varieties planted were: 2001, Asgrow 2703RR; 2002, Asgrow 2703RR and Stout; 2003, glyphosate resistant Asgrow 2703RR, D.F. Seeds 8316RR, DynaGro 3200RR, and Garst 2502RR and non-glyphosate resistant Asgrow 2553, Dairyland DSR 300, Garst D308, and Stout. The seeding rate was 475,000 seeds/ha, with the exception of Stout in 2002, which was seeded at 686,000 seeds/ha.

Plots were 6 rows wide and 7 m long, and were trimmed to 4.3 m for harvesting. Plots were harvested using an Almaco small plot combine. Plant heights were obtained by measuring two or three plants in each plot to the top of the stem. Lodging ratings were made on a scale of 1 to 5, where 1=no plants lodged, and 5=all plants lodged.

Results and Discussion

Weather conditions for the duration of the study are reported in Table 1. Seed yield of Asgrow 2703RR was statistically equal for the full season, flowering, and pod elongation treatments in 2001 and 2002 (Table 2). When data from both years were averaged together, the seed fill treatment yielded significantly less than the full season, flowering, and pod elongation treatments, but significantly more than the dryland plots (p=0.05). In 2002, there were no statistical differences in seed yield for the five irrigation treatments on Asgrow 2703RR. However, Stout yields responded positively to increasing amounts of irrigation (see Table 1). In an extensive study using 16 cultivars Kadhem et al. (1985) reported a wide variation of response to irrigation with some cultivars responding positively and others negatively. It is possible that the timing of drought stress can be more important than the total number of days of drought stress or the total amount of water applied to the crop. If plants lack water at key reproductive stages (flowering, pod elongation or seed fill), yield will be reduced because of pod and/or seed abortion. However, indeterminate soybeans, the type grown in Michigan, are more drought tolerant than determinate soybeans because they are able to flower and set pods for a longer period of time.

Irrigation increased soybean yield. In 2001 and 2003, Asgrow 2703RR yields for each of the irrigated treatments exceeded those of the dryland treatment. In 2002, average yields of Asgrow 2703RR and Stout increased as the amount of irrigation water applied increased. In 2003, the average yields of 8 varieties also were greater for irrigated treatments than the dryland treatment. These results confirm what has been reported earlier by Ashley and Etheridge (1978). Irrigation applications prior to pod elongation (R3-R4) did not increase soybean yield significantly. As has been shown in other studies (Korte et al., 1983), it is not necessary to irrigate soybeans prior pod elongation to achieve increased yields from irrigation. In 2001 and 2002 significantly less water was applied to the pod elongation treatment than the full season and flowering treatments. Yields of the seed fill treatment may have been significantly less than the other irrigated treatments in 2001 and 2002 if the minimum soil moisture level (75% depletion) had not been maintained prior to soybeans reaching the R5 growth stage. All eight varieties tested responded similarly. In both 2002 and 2003 the ‘irrigation treatment x variety’ interaction was not significant (p=0.05). This contrasts with reports of a wide range of responses to irrigation treatments among soybean varieties (Kadhem et al., 1985), but may be attributable to our choosing varieties that had yielded well in irrigated variety trials. In 2003, the average yields of seven varieties were equal for each of the irrigation treatments. Only DynaGro 3200 yielded less, likely due to poor emergence (~50%). Plant height and susceptibility to lodging increased as the amount of irrigation applied increased. The variety Stout was most susceptible to lodging each year. Yields in 2003 were less than in 2001 and 2002 due to a cool summer and a period in mid-August when soil moisture dipped below 50% for all treatments.

Table 1. Weather conditions in half-month increments during the growing season.

 

2001

2002

2003

30 year average

 

air max

precip

rad

air max

precip

rad

air max

precip

rad

air max

precip

 

C

mm

kJ/m2

C

mm

kJ/m2

C

mm

kJ/m2

C

mm

April 16-30

18.1

30.2

323193

16.5

27.7

265135

17.2

20.1

284780

14.4

47.8

May 1-15

23.6

29.2

300534

16.3

57.4

282127

18.3

83.8

240211

20.5

76.2

May 16-31

19.7

39.6

297368

19.0

28.4

347171

18.5

25.7

339468

June 1-15

21.7

69.4

258917

24.2

59.7

293495

21.8

7.4

302357

25.9

87.6

June 16-30

26.8

20.3

360013

29.5

11.2

394555

27.6

8.1

408219

July 1-15

25.7

17.8

400430

29.4

34.8

416154

28.2

66.3

372480

27.7

77.7

July 16-31

30.0

28.7

355101

30.3

6.1

355130

26.2

12.7

396687

Aug 1-15

29.4

19.6

355696

28.7

44.7

352479

27.2

24.1

324111

27.0

81.0

Aug 16-31

25.6

79.0

266885

26.5

87.6

304845

29.2

5.1

352927

Sept 1-15

25.2

28.9

292035

27.4

3.6

299925

25.1

25.1

275937

23.7

85.9

Sept 16-30

18.5

39.9

185475

23.8

25.9

235725

19.1

51.1

226213

Oct 1-15

17.8

98.3

145380

19.0

27.7

187465

18.1

45.5

222192

17.4

40.6

Table 2. Soybean yield (kg ha-1) as affected by variety and year. Data include all plots treated with herbicide. The irrigation X variety interaction was not significant, p = 0.05.

 

2001

2002

2003

 

FS

F

P

S

D

avg

FS

F

P

S

D

avg

FS

F

P

S

D

avg

Asgrow 2703RR

5055

4684

4566

4055

2635

4199

4670

4362

4441

4037

4214

4344

3289

3110

3276

2800

2316

2958

Stout

           

3884

3952

3115

2883

2630

3293

3143

2797

3490

2757

1954

2828

Asgrow 2553

                       

3139

2965

3195

2802

2077

2835

Dairyland DSR 300

                       

3573

3026

3159

3145

1959

2972

D.F. Seeds 8316RR

                       

3174

3304

3079

2967

2190

2943

DynaGro 3200RR

                       

2306

2390

2134

1932

1497

2052

Garst 2502RR

                       

3252

3283

3349

2926

2100

2982

Garst D308

                       

3169

3115

3146

2846

1813

2817

avg

5055 a †

4684 ab

4566 ab

4055 b

2635 c

 

4277 a

4157 a

3778 ab

3460 bc

3422 c

 

3131 a

2999 ab

3104 a

2772 b

1988c

 
 

‡ SE, irrigation trt: 274

SE, variety: 100
SE, irrigation trt: 158
SE, irrigation x variety: 223

SE, variety: 88
SE, irrigation trt: 70
SE, irrigation x variety: 197

† Means of irrigation treatments with the same letter within a year are not statistically significant, p = 0.05, Tukey adjusted.
‡ SE = Standard error.

Conclusion

Based on three years of data, it appears that maximizing soybean yield in the Northcentral Corn Belt is dependent on maintaining adequate soil moisture beginning at full bloom (R2) or beginning pod (R3), provided that the soil water deficit (SWD) does not exceed 75% prior to that growth stage.

References

Ashley, D.A. and W.J. Ethridge. 1978. Irrigation effects on vegetative and reproductive development of three soybean cultivars. Agronomy J. 70:467-471.

Elmore, R.W., D.E. Eisenhauer, J.E. Specht, and J.H. Williams. 1988. Soybean yield and yield component response to limited capacity sprinkler irrigation systems. J Prod Ag 1:196-201.

Heatherly, L.G. 1985. Irrigation management for soybean yield enhancement. In World Soybean Research Conference III, edited by Richard Shibles, Boulder, Colorado, Westview Press. pp 980-987.

Kadhem, F.A., J.E. Specht, and J.H. Williams. 1985. Soybean irrigation serially timed during stages R1 to R6. I. Agronomic responses. Agron. J. 77:291-298.

Korte, L.L., J.H. Williams, J.E. Specht, and R.C. Sorensen. 1983b. Irrigation of soybean genotypes during reproductive ontogeny. II. Yield component responses. Crop Sci. 23:528-533.

Runge , E.C.A. and R.T. Odell. 1960. The relation between precipitation, temperature, and the yield of soybeans on the Agronomy South Farm, Urbana, Illinois. Agron. J. 52:245-247.

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