WHEAT RESPONSE TO VARIOUS ROW SPACINGS IN RELAY INTERCROPPING SYSTEMS P.M. Porter and A. Khalilian'

1.93 m center wheel spacing and combines with a 2.44 m center wheel spacing.

INTRODUCTION In the southern USA there is considerable research interest in relay intercropping of soybeans and cotton into wheat before harvest. Sequentially doublecropped soybeans or cotton after wheat harvest delays the planting of those crops, and can result in poor stands (Beatty et al.. 1982) and reduced yields (Coale and Grove, 1990; Garner e t al., 1992). Numerous relay intercropping systems involving different planting schemes and associated equipment have been developed and successfully tested (Hood et al., 1991). The systems usually involve controlledtraffic for planting, fertilization, pesticide applications, and wheat harvest. Because controlled-traffic causes soil compaction only in non-cropped t r a f f i c lanes, spring tillage operations usually necessary o n Coastal Plain soils before planting the summer crop are n o t required, resulting in the potential for reduced fuel requirements (Khalilian e t al., 1 9 9 1 a and 1991b) for the intercropping system as compared to c o n v e n t i o n a l d o u b l e c r o p p i n g s y s t e m s Elimination of tillage operations prior t o summer crop planting and inhibition of weed emergence by shading f r o m the wheat crop can reduce herbicide inputs for the summer crop in the interseeding system (Buehring e t al., 1990; Khalilian e t al., 1990).

One interseeding scheme employs 1.93 rn wheel centers t o match t h e wheel traffic of many of the tractors currently used in t h e Southeast as well as several models o f older combines. This planting scheme provides for planting 11 r o w s of wheat spaced 33.0 cm apart with two zones of 61.0 c m provided for the tractor, interseeder and combine wheel traffic. W i t h this system, up t o eight r o w s of soybeans or four r o w s of cotton can be planted (Fig. 1 a ) . The cotton can be picked with a conventional 96.5 c m four-row cotton picker. Several newer model combines use a wheel center spacing of a t least 2.44 m., and thus another interseeding scheme w a s designed t o accommodate those combines (Hood et al., 1992). This scheme involves planting 14 r o w s of wheat with 5 row widths of 30.5 c m t o accommodate t h e interseeding of 5 r o w s of cotton or soybeans, 2 r o w widths of 61.0 c m t o accommodate the tractor, interseeder and combine wheel traffic zones, and 7 r o w widths of 15.2 c m (Fig. 1 b ) . This study compared the yield and yield component response o f wheat produced with these interseeding production schemes t o the yield a n d yield c o m p o n e n t response of conventionally g r o w n wheat.

Clemson University has been developing equipment and planting schemes t o interseed soybeans and cotton into standing wheat using controlled-traffic production methods since 1985. Hood et al. (1992) describes the evolution of the Clemson Interseeder. a planter which can be modified t o plant wheat, cotton and soybeans with a variety of r o w spacings

MATERIALS AND METHODS The study was conducted a t the Edisto Research and Education Center near Blackville, SC, on a Varina loamy sand. It involved four planting systems with six replications in a randomized complete block design. Treatment descriptions are detailed in Table 1. Treatment A involved conventionally planted wheat with r o w widths equally spaced. Treatment B utilized the Clemson lnterseeder and t h e 11-row planting system (Fig. 1 a ) . Treatments C & D utilized the Clemson lnterseeder and the 1 4 - r o w planting system (Fig. 1 b ) . A paraplow and French Durou p l o w was employed for deep tillage prior t o wheat planting f o r treatments C and D,

One of the problems in conducting controlled-traffic operations is that the wheel spacings can vary f o r the equipment employed for planting, combining, and fertilizer and pesticide applications. Many farmers in the Southeast currently are using tractors with a

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Depts. of Agronomy & Soils and Ag. & Biol. Engr., Clemson University, Edisto Research and Education Center, Blackville,

sc. 144

Table 1. Treatment descriptions of a two-year study conducted at the Edisto Research and Education Center near Blackville, SC.

Planting date Harvest date Number o f wheat r o w s Row width Seeding rate’ ha‘’ seed (linear Fall tillage’ Tire spacing

N O~2 .1 June 1

Dec. 14 June 7

16 19.6

24 15.2

112.1 64.4

112.1 50.3 Drill Chisel 193

Nov. 21 June 1

14 June 7

Nov. 21 June 1

14 June 7

14 15.2, 30.5

11 33.0 61

112.1 93.3 Clemson I. Paraplow 244

112.1 125.6 Clemson Paraplow 193

61

3 June 1

June 7

14 15.2, 30.5

61

112.1 93.3 Clemson I. Durou p l o w 244

’

Number o f seeds planted per meter o f r o w was calculated using an average seed weight of 0.034 g seed”. Trt A (conventionally planted wheat) was planted with 16-row Amazone in 1991 and a 24-row in 1992. All other treatments were planted with the Clemson Interseeder. The chisel p l o w h a d 30 c m shank spacings and operated 28 c m deep, the had 53 c m shank spacings and operated 30 t o 33 c m deep, and the French Durou p l o w had 96 c m shank spacings and operated 33 t o 36 c m deep.

’

occurred o n June 1. 1992 and June 7. 1993. with 61.0 c m of each r o w c u t at ground level, and oven dried at 60°C for 48 hours. Aboveground dry matter and number o f heads with viable seeds were determined. After threshing the wheat in an Almaco plot combine, the weight and number of seeds from each harvest r o w were determined.

respectively, t o compare the effect o f these t w o n e w conservation tillage implements for wheat production in coastal plain soils. The experimental area w a s limed with 2.24 Mg o n Oct. 8, 1991 and disked. O n Oct. 18 t h e area w a s fertilized with 30.8 kg N and 106.5 kg K and again disked. Plots in three of the four treatments were deep tilled o n Nov. 19 and planted with ’NK Coker 9835‘ wheat o n Nov. 21. The other treatment (Durou plow) was tilled t o 35.6 c m and planted o n Dec. 3, after the tillage equipment had arrived. Wheat was t o p dressed o n Feb. 5, 1992 with 67.3 k g N The second year of the study, 67.3 kg K was applied o n Dec. 8 and disked to 20.3 cm. Deep tillage occurred o n Dec. 14, and the same day all plots were planted. Planting occurred later than normal because o f the extremely w e t conditions in Nov. and Dec. o f 1992. The nitrogen application was split with 33.6 kg N applied as S-25 o n Dec. 16, 1992 and Feb. 18 and Mar. 2, 1993. Weeds and diseases were controlled using appropriate pesticides. Soybeans were interseeded into appropriate plots on M a y 19, 1992 and M a y 20, 1993. Wheat harvest

For each year, and for the 2-year combined data, statistical analysis comparing individual r o w s within each o f the four treatments was conducted. In addition, a system analysis of the four treatments was conducted employing t w o methods: a) using the entire set of individual r o w data, except the outside rows, t o eliminate the border effect of leaving 0.61 m between t w o adjacent plots, and b) using the entire set of individual r o w data. The area for the outside r o w was calculated b y adding 30.5 c m t o one-half the distance between the outside row and the adjacent row, and multiplying that sum b y the harvest length. SAS w a s employed for the statistical analysis, and t h e LSD reported only if the significance level was at

145

la.

33.0 61.0 cm

C

s

row

2

3

4

8

5

7

s

10

11

C S

Wheat row

2

3

4

7

13

Figure 1. Planting pattern f o r wheat, cotton and soybeans for a) the tractor wheel spacing, and the 2.44 m tractor wheel spacing schemes.

RESULTS AND DISCUSSION

14

m

o n each side of t h e plot w a s included in the analysis did n o t change t h e interpretation of the results (Tables 2 and 3). These data indicate wheat yields were n o t adversely affected by wide r o w planting under t h e given experimental parameters.

System Analysis Analysis of t h e entire system, whether including or excluding the outside r o w s in the analysis, did n o t affect the interpretation of the results for the yield and yield components measured (Tables 2 and 3). The climatic conditions were better for t h e 1992 growing season as compared t o the 1993 growing season, and there was a significant year effect for all yield and yield components measured. There was n o significant year b y treatment interactions for above-ground dry matter yield, seed yield, kernels per unit area, or kernel weight. However, there were year b y treatment interactions for heads per unit area and kernels per head.

In 1992 and t h e 2-year combined data, treatment D had fewer heads per unit area b u t more kernels per head than t h e other treatments. In the 1992 season, treatment D w a s planted t w o weeks later than t h e other treatments. Delaying the planting date probably resulted in poor tillering, and caused t h e reduction in heads per unit area and increase in kernels per head as compared t o the other treatments. The next season, w h e n all treatments were planted o n the same date, these differences were n o t observed. In 1992 and the 2-year combined data, the conventionally planted wheat (treatment A) had more heads per unit area than the other treatments. Both years treatment A had the lowest number of kernels per head. For the

In 1992, 1993 and for the 2-year combined data, there was no significant difference between the four treatments for the above-ground dry matter yield, seed yield, kernels per unit area or kernel weight. Whether or n o t the outside r o w 146

Table 2. Statistical analysis o f wheat yields for entire system including outside rows.

..................................................................................................................................................... Total dry wt.

Trt

Kernel wt.

Kernels per

Heads per

Wt. per kernel

Kernels per head

..................................................................................................................................................... 9

1992 A

1079 964 C 992 D 932 mean 992 cv 10.6 Analysis of variance Trt effect NS FLSD

516 483 490 466

549a 468b 464b

489 10.7

17246 15750 16106 15494 16149 9.7

NS

NS

***

466 9.3

0.0299 0.0307 0.0305 0.0300 0.0303 2.6

NS

53.2

35.1 8.4

*** 3.6

1993

618 607

A

C

604 566 mean 599 cv 10.6 Analysis of variance Trt effect NS FLSD

282 285 284 264 279 10.3

8580 8754 8882 8240 8614 9.2

37 1 346 349 336 351 7.5

NS

NS

NS

399 384

C

798

387

D mean

749 795

365 384 11

10.9

Analysis of variance Trt effect NS Year effect NS Trt FLSD

NS

24.6 5.5

** 1.7

2-year combined data A 848 786

cv

0.0328 0.0325 0.0320 0.0320 0.0323 2.6

NS NS

12913 12252 12494 11867 12302 10.1

460a 407b

0.0314 0.0316

406b

0.031 2 0.0310

408 8.8

0.0313 2.6

NS

***

***

***

***

NS

**

NS

29.9 7.7

NS

29.9

*** 1.9

.....................................................................................................................................................

and NS refer t o

0.01, 0.05, and

combined 2-year data, the number of kernels per head w a s significantly lower than for the other treatments. These data can be explained by looking a t t h e individual r o w data and the effect o f tire-traffic o n t h e wheat r o w s of the conventionally planted wheat.

respectively.

Individual Row Analysis For the conventionally planted wheat,

the

seed yield on both a linear and area basis, kernel weight and kernels per head all decreased dramatically in the rows where tire compaction occurred (rows 4 & 14 in 1992, and r o w s 6 & 7 147

Table 3. Statistical analysis of wheat yields for entire system excluding outside rows.

1993

639 633 C 622 D 587 620 mean cv 10.5 Analysis of variance Trt effect NS FLSD A B

2-year combined data A 850

793 C 795 D 779 mean 804 cv 11.5 Analysis of variance Trt effect NS *** Year effect NS

292 296 290 273 288 10.2 NS

8828 9043 9057 8473 8851 9.2

387 356 367 355 366

NS

NS

0.0329 0.0326 0.0320 0.0322 0.0324 2.9

8.7

NS 1.6

403 389 387 381 390 11.4 NS

***

NS

12984 12356 12478 12357 12544 10.4 NS

***

NS

478a 414b 419b 422 10.2

*** *** ***

0.0315 0.03 17 0.0312 0.031 1 0.0314 3.0

NS **U

NS

35.9

FLSD

**,

and NS refer t o

24.2 5.4

0.01, 0.05, and

and 18 & 19 in 1993) (Fig. 2a-d, treatment A). Tire-traffic rows had more, but smaller and later maturing heads than the other rows. The tire

compaction was a result of three passes over the wheat plots for application of a herbicide, spring N and a fungicide. In the other treatments n o wheat was run over b y those passes over the

29.4 8.3

*** *** 2.0

respectively.

plots because of the wheat-row spacing

allowance f o r the tire track (Fig. 1a and 1b).

For the 1 1 -r o w wheat system (Fig. 1 a ,

treatment B) t h e r o w s most widely spaced (rows

1, 3, 4, 8, 9 & 11) tended to have t h e highest

148

b

C

d

L5D

-

1993

1

2

-

3

4

N.S

5

6

7

0

ROW

Figure 2. Seed yield on a linear basis (a) and area basis (b), kernel weight (c), and kernels per head (d) from individual wheat rows of treatments A and B.

149

C I

a t

a

I

40

-

t

*

b

I

I

600

b

400

196

=

-

-

II =

200

=

0

36

L

-

a, 34

L

1993

=

1992

= 1.6

a,

a

1-

N.S.

32

-

-

...

1993

=

1992

N.S.

N

26

d

d LSD

-

1992

=

1-

35

30

-

25

20 15

1993

LSO

-

-

3.7

10

1 2

3

09101112

1 3 14

I 2

3

4567

12

13

ROW

Figure 3. Seed yield on a linear basis and area basis kernel weight kernels per head from individual wheat rows of treatment C and D.

150

and

Coale, F.J., and J.H. Grove. 1990. Root distribution and shoot development in no-till fullseason and double-crop soybean. Agron. J.

seed yield o n a linear basis (Fig. 2a. treatment B), but w h e n calculated o n an area basis, the r o w spacing did n o t affect yield Fig. 2b. treatment B). Kernel weight and the number of kernels per head were unaffected by r o w spacing (Fig. 2c & 2d. treatment B).

82:606-612. Garner. T.H., A. Khalilian, C.E. Hood, and M.J. Sullivan. 1992. Wheatlcotton cropping systems for Coastal Plain soils. pp. 509-512. In Proc. 1992 Beltwide Cotton Conf., Vol. 1, Nashville, TN. 6-10 January 1992. Nat. Cotton Council of Am., Memphis, Tenn.

For the two 1 4 - r o w wheat systems (Fig. 1b), the r o w s m o s t widely spaced (rows 1, 2, 3, 12, 13 & 14) consistently yielded more than the other r o w s o n a linear and area basis (Fig. 3a and 3b. treatments C & D). Kernel weight was generally unaffected b y r o w spacing (Fig. 3c. treatments C & D), b u t the r o w s m o s t widely spaced tended t o have more kernels per head than the narrower spaced r o w s (Fig. 3d. treatments C & D).

Hood, C.E., A. Khalilian, T.H. Garner, and J.H. Palmer. 1992. Improved interseeding methods and equipment. pp. 1-12. ASAE 1992 International Winter Meeting. 1 5 - 18 December, 1992. Nashville, Tenn. Paper no. 92-1595. Hood, C.E., A. Khalilian, J.H. Palmer, T.H. Garner, T.R. Garrett and J.C. Hayes. 1991. Double-cropping interseeding system for wheat, soybeans, and cotton. Applied Eng. in Ag. 7(5):530-536.

In summary, yield of conventionally planted wheat w a s n o t significantly different f r o m yields of skip-row schemes designed t o allow f o r relay intercropping of either soybeans or cotton. For the conventionally planted wheat, tractor traffic o n t o p of certain wheat r o w s reduced yields of those r o w s as compared t o non-traffic rows. Wheat g r o w n in wider-spaced r o w s adjacent t o the controlled-traffic tire lanes in the schemes designed t o allow f o r relay intercropping compensated yield-wise on an area basis as compared t o narrower-spaced rows.

Khalilian. A., T.H. Garner, C.E. Hood, and M.J. Sullivan. 1991a. A progress report o n cotton production s y s t e m s f o r soil and w a t e r conservation. pp. 4 4 9 - 4 5 2 . In Proc. 1991 Beltwide Cotton Conf., Vol. 1, San Antonio, Texas. 8-12 June 1991. Nat. Cotton Council of Am., Memphis, Tenn.

LITERATURE CITED Khalilian, A., C.E. Hood, J.H. Palmer, T.H. Garner, and G.R. Bathke. 1991b. Soil compaction and crop response t o wheatlsoybean interseeding. Transactions of the ASAE. 34(6):2299-2303.

Beatty, K.D., I.L. Eldridge, and A.M. Simpson, Jr. 1982. Soybean response t o different planting patterns and dates. Agron. J. 74:859-862. Buehring, N.W., D.B. Regnielli, and M.A. Blaine. 1990. Long term, wheat and soybean response pp. 65-68. In t o an intercropping system. Conservation tillage for agriculture in the 1990s. Proc. 1990 Southern Region Conserv. Tillage 16-17 July 1990. North Conf., Raleigh, N.C. Carolina State Univ. Spec. Bull. 90-1.

Khalilian, A., C.E. Hood, J.H. Palmer, T. Whitewell, a n d S.U. Wallace. 1990. Conservation tillage interseeding of soybeans into standing wheat. pp. 72-76. In Conservation tillage for agriculture in the 1990s. Proc. 1990 Southern Region Conserv. Tillage Conf., Raleigh, N.C. 16-17 July 1990. North Carolina State Univ. Spec. Bull. 90-1.

151