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IV. Some Agronomic Factors Influencing Productivity and Efficiency

IV. Some Agronomic Factors Influencing Productivity and Efficiency

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62



FRANCIS OFORI AND W. R. STERN



crop, usually the cereal (Osiru and Willey, 1972;Lakhani, 1976). This can

be illustrated with 5O:SO mixture data from a replacement series experiment

in a sorghum-bean intercrop (Osiru and Willey, 1972). The optimal density

of either crop of 200,000plants/ha gave an LER of 1.41;this was due to increase in intercrop sorghum yield, because the intercrop bean yield remained unchanged.

In a study of maize intercropped with cowpea at densities ranging between 10,000and 40,000plants/ha for either crop and planted in the same

hill, maize (cv. TZPB composite) was more competitive than cowpea (cv.

TVu-1209)(Fawusi et af., 1982). The response of intercrop maize to increasing component density was similar to that of sole maize. At the lowest mixture density, the intercrop maize yield was 2300 kg/ha, 15% less than the

sole maize, and increased to 4600 kg/ha (8% less than sole maize) at 40,000

plants/ha. Pod yield of intercrop cowpea with the lowest density of maize

was 941 kg/ha, a reduction of 41(70 of sole cowpea yield at optimum density. At the highest overall density, intercrop cowpea yield was 700 kg/ha,

i.e., a yield reduction of 66%. When sole crop yields of maize and cowpea

in the optimum density treatment were used to standardize mixture yields,

LER values rose with increasing mixture density. From the lowest to the

highest density, the LER values were 0.91, 1.14, 1.20,and 1.26.

The growth and yield of legume component is reduced markedly when intercropped with high densities of the cereal component. In a maize-bean intercrop system, increasing maize density three-fold, from 18,000to 55,000

plant/ha, caused reductions of 24% in leaf area index and 70% in seed yield

of the associated bean (Gardiner and Craker, 1981). Using repacement

series designs in a maize-cowpea intercrop system, Chang and Shibles

(1985b)showed that the level of the maize population generally imposed a

limit on the yield of the intercrop cowpea, and that there was no effect of increasing cowpea density.

Even though the cereal component usually contributes a greater proportion of the mixture yield, the magnitude of intercropping advantage or efficiency seems to be determined by the legume component (Ofori and Stern,

1986, 1987). Fisher (1977)studied maize-bean intercrop systems at varying

densities which at harvesting were 13,700,27,000,and 47,700plants/ha of

maize combined with 23,300, 56,300, and 121,000 plants/ha of beans,

respectively, designated as low, medium, and high densities. At each density, the yields of intercrop maize did not differ from those of the sole maize.

However, intercrop bean yield significantly increased with a rise in bean

density. The seed yields of beans were 320 kg/ha, 650 kg/ha, and 940 kg/ha

from the lowest to the highest density. Although maize contributed more

than 80% of the mixture yield at each density, the LER values followed the

trends in intercrop bean yields: 0.57,0.92,and 1.39 from the lowest to the

highest density. These observations are consistent with the data of Francis



CEREAL-LEGUME INTERCROPPING SYSTEMS



63



et al. (1982a,b) on maize intercropped with bush or climbing beans at different component crop densities.

Results from two separate studies using sorghum and pigeonpea also

show that the cereal contributes a greater proportion to mixture yield, but

that the efficiency of the system measured in terms of LER follows the

trends in the intercrop legume yields (Freyman and Venkateswarlu, 1977;

Natarajan and Willey, 1980a). When intercrop sorghum densities were

varied from 55,000 to 220,000 plants/ha and combined with constant

pigeonpea density of 37,000 plantdha, the intercrop sorghum yield reponse

was linear. In contrast, the intercrop pigeonpea yield decreased with rising

sorghum density (Freyman and Venkateswarlu, 1977). The highest LER

value was obtained at the lowest sorghum density and decreased with rising

sorghum density (Table VI).

It seems that density of the cereal component determines the level of combined mixture yield, but that the efficiency of cereal-legume intercropping

systems, measured in terms of LER, follows the trend of the legume component.

B. PLANT ARRANGEMENT

AND SPACING

Row arrangements, in contrast to arrangements of component crops

within rows, improve the amount of light transmitted to the lower legume

canopy. Such arrangements can enhance legume yields and efficiency in

cereal-legume intercrop systems (Mohta and De, 1980). In a maize-groundnut intercrop system, Evans (1960) obtained LERs of 1.09 in the same row

arrangement compared to 1.30 in alternate rows and 1.38 in a hill arrangement (Table VI).

In two separate studies involving pigeonpea and soybean, maize yield was

not significantly reduced when planted in alternate rows with the legume in

comparison to planting in the same rows (Dallal, 1974, 1977). From Table

VI, it may be seen that biological efficiency measured as LER was higher

when component crops were sown in alternate rows rather than in the same

row. In the maize-pigeonpea system, maize yield was not affected in the

alternate row arrangement, but this was reduced by 20% when the

pigeonpea was in the same row (Dallal, 1974).

From these studies, it was found that arrangement of component crops in

alternate rows is more beneficial than in the same rows. In contrast to these

observations, Agboola and Fayemi (1971) did not observe any difference

whether maize and cowpea were planted in the same or alternate rows

(Table VI).

The use of double rather than single alternate row arrangements of component crops improve the yield and light penetration to the canopy of the



Table VI

Effects of Plant Arrangement and Spacing of Component Crops on Productivity and

Efficiency of Various Cereal-Legume Intercrop Systems

Yield’ (kg/ha)

Crop combination

and treatment

Maize with

Groundnut

Same row

Alternate row

In hills

(Sole crop)

Cowpea

Same row

Alternate row

(Sole crop)

Pigeonpea

Same row

Alternate row

(Sole crop)

Soybean

Same row

Alternate row

Alternate 2-rows

(Sole crop)

Soybean

Alternate rows

Alternate 2-rows

(Sole crop)

Soybeanb

(alternate rows)

70 x 30cm

70 x 60cm

70 x 90cm

(Sole crop)

Sorghum with

Pigeonpea

Same row

(60 cm)‘

Alternate 2-rows

(90

Alternate 2-rows

(135 cm)‘

(Sole crop)

Soybean

Alternate rows

Alternate 2-rows

(Sole crop)

Groundnut

Alternate 2-rows

(60

Alternate 2-rows

(90

Cowpea

Alternate 2-rows

(60

Alternate 2-rows

(90



Intercrop

cereal



Intercrop

legume



2,851

2,554

2,580

(3,330)



74 1

744

851

(1,422)



LER



Reference



1.09

1.30

1.38



Evans (1960)



593



1.54



Agboola and Fayemi (1971)



590



1.55



1,915

1,950

(L990)



(1.033)



2,4%

2,979

(3,130)



1,239

1,481

(1,871)



1.46



4,480

5,118

5,051

(5,353)



170

517

303

(1,634)



0.94

I .27

1.13



Dallal (1977)



3,530

3,700

(3,344)



550

720

(2,783)



1.25

1.37



Mohta and De (1980)



6,980

7,095

6,910

(7Jm



460

650

820

(3,405)



1.05

1.12

1.14



Chui and Shibles (1984)



8,380



1,040



1.24



Freyman and Venkateswarlu (1977)



8,840



1,070



1.29



9,110



1,150



1.35



(10,483)



(1,634)



1,540

1,500

(1,760)



1,247

(2,783)



990



Dallal (1974)



1.74



1.23

1.30



Mohta and De (1980)



Singh (1981)



3,055



323



I .47



3,185



386



1.52



3,605



418



1.87



3,635



716



2.19



Singh (1981)



‘Figures in parentheses are sole crop yields for calculating LER.

bData of 1981 experiment.

‘Denotes cereal row spacing.



CEREAL-LEGUME INTERCROPPING SYSTEMS



65



legume component. In maize-soybean and sorghum-soybean studies conducted by Mohta and De (1980), the yields of the cereals were not affected by intercropping with soybeans when arranged in either single or double alternate

rows. In the maize-soybean combination, there was a 3 1070yield increase in the

intercropped soybeans when components were arranged in double alternate

rows relative to single alternate rows. The LER was 1.37 in the double alternate

row and 1.25 in the single alternate row arrangement. With sorghum, intercrop

soybean yield in the double alternate rows was 1247 kg/ha, an increase of 26%

over the single alternate row arrangement. The LER was 1.30 in the double

alternate row arrangement and 1.23 in the single alternate row (Table VI).

When alternating pairs of sorghum rows 90 cm apart with two rows of an

associated legume, Singh (1981) found that LER was greater compared to

sorghum at 60 cm between rows with two rows of the legume in between (Table

VI). In a parallel study, Wagmare et al. (1982) found that light penetration

was markedly increased in the wider row arrangement. At 60 days, light incident on the intercrop legume canopy with sorghum rows spaced at 60 cm was

52% of the incoming radiation, and 70% when sorghum was spaced at 90 cm.

Widening interrow spacing of the cereal component to accommodate more

rows of the legume component improves legume yield and efficiency of the intercrop system (Table VI). In a study of sorghum at 220,000 plantslha intercropped with pigeonpea at 37,000 plants/ha, 90-cm interrow spacing of

sorghum improved the yield of intercrop sorghum by 5% and that of associated

pigeonpea by 3% when compared to 60cm rows (Freyman and Venkateswarlu,

1977). Further widening of sorghum interrows to 135 cm gave a 9% increase in

sorghum yield over the 60-cm spacing, and pigeonpea yield was increased by

11070. The LER values for the three spacingswere 1.20 for 60cm, 1.29 for 90cm,

and 1.35 for 135 cm. The yield of intercrop soybean increased by 78% when

spacing between hills with associated maize was adjusted from 30 to 90cm; the

LER for the 30-cm spacing was 1.05 and 1.14 for the 90 cm (Chui and Shibles,

1984).



From several studies, it would appear that the yield of the cereal component is

usually less affected by component densities and manipulation of spacing between component crops. Intercrop legume yield usually is reduced significantly,

however, depending on the proximity of the cereal component. This could be

due to the intensity of shading at the top of the legume canopy, as observed

recently in a cassava-soybean combination by Tsay (1985) (see Fig. 1).



c.



RELATIVE TIMEOF SOWING OF COMPONENT CROPS



The relative time of sowing of component crops is an important management variable manipulated in cereal-legume intercrop systems but has not

been extensively studied. Andrews (1972) pointed out that differential sowing improves productivity and minimizes competition for growth-limiting



66



FRANCIS OFORI AND W. R. STERN



factors in intercropping. Willey (1979)also pointed out that sowing component crops at different times ensures full utilization of growth factors

because crops occupy the land throughout the growing season.

Francis et al. (1976)found that sowing maize and beans 5-15 days apart

reduced yields of the intercrops compared to sole crops (Table VII). In contrast to simultaneous sowing, maize sown 5-15 days earlier than beans

increased maize yields by 13-43'70,and the associated bean yields were rcduced by 20-27%. On average, intercropping efficiency measured as LER

was 39% higher when beans were sown 5-15 days before maize. In studies

on maize intercropped with four contrasting bean cultivars sown 5-10 days

apart, results suggest that near-simultaneous sowing of component crops is

optimal to attain the highest combined yields and intercropping efficiencies

(Francis, 1978;Francis et al., 1982a).

In Columbia, Francis et al. (1982b)varied dates of sowing maize and indeterminate beans (types I1 and 111) and found maize to be more competitive than beans at all sowing dates, except when beans were sown 10 days

earlier. Simultaneous sowing resulted in a bean yield reduction of 51 070 and

maize yield reduction of 3 1 Yo. Sowing maize 10 days before beans reduced

bean yield by 69% and maize by only 7%. Beans sown 10 days earlier reduced maize yield by 53% and bean yield by 21 %. In terms of LER, similar

results were obtained by staggered and simultaneous sowings. However, the

LER followed the trends in bean yields rather than the maize yield, because

sowing maize 5 and 10 days before beans gave relatively lower LER values



Table VII

Yield and LER of Component Cereal and Legume Sown Less Than 1 Week Apart

Yield (kg/ha)

Sowing dates



Cereal



Legume



LER



Reference



Maize-bean combination

Sole crop

Maize, 5-15 days before beans

Simultaneous sowing

Beans, 5-15 days before maize



7270

5040

5710

69106



939

394

500

483



-



Francis et at. (1976)O



1.11

1.32

1.46



Millet-greengram combination

Sole crop

Millet, 7 days before greengram

Simultaneous sowing

Greengram, 7 days before millet



2288

2115

1825

1528



349

26

87

229



1 .o

1.05

1.32



-



May (1982)



OBean variety Pijoo planted at 300,000 plants/ha and maize H-207 at 40,OOOplantslha.

*Seems high but verified against the original data.



67



CEREAL-LEGUME INTERCROPPING SYSTEMS



of 1.30 and 1.23 whereas earlier sowing of beans gave LER values of 1.36

and 1.27, respectively.

In Nigeria, Remison (1982) did not find any advantage of staggered over

simultaneous sowing of maize and cowpea. Intercropping reduced cowpea

yield by 57% and maize yield by 35% when sown simultaneously. Sowing

cowpea 14 days earlier than maize gave a LER value of 0.88 whereas maize

sown 14 days earlier gave a LER value of 1.20. LER values were higher

when maize was sown earlier than cowpea but results of this study do not

demonstrate consistent LER trends relative to yields of either of the component crops.

In Western Australia, Ofori and Stern (1987) concluded from a

maize-cowpea intercrop system that staggered sowing of component crops

at intervals of 10 or 21 days were of no advantage over sowing them

simultaneously. However, they found that the LER followed the trends in

cowpea yield rather than maize (Fig. 2)

Cowpea sowing relative to maize (days)



'2 1

10



-



w



I,.,



c



ooc -



'10

I



I



0



-10



I



I



-2 1

I



Sole maize



-0-



Intercrop maize



eooa



Y

Q)

v



.-*



'



600C



D

0)



4000



C



2000



-A-



I



.



J 1.0



Sole cowpea



'



-/intercrop cowpea

-2 1



-10



0



'10



+21



Maize sowing relative to cowpea (days]



FIG. 2. Seed yields of maize and cowpea and LER of the intercrop system when component crops are sown differentially. Sole crops were established only at simultaneous sowing,

i.e., 0 days. I, Least significant difference (LSD) @ < 0.05) to compare sole crops and intercrops of maize (M) and cowpea (C). (From Ofori and Stern, 1987.)



68



FRANCIS OFORI AND W.R. STERN



Manipulating the time intervals between growth durations of component

crops influences efficiency of cereal-legume intercrop systems. In an 85-day

bean and 120-day maize combination, a yield advantage of 20% was removed

by sowing beans 28 days after maize (Osiru and Willey, 1976). In another

study, May (1982) found that a yield advantage of 32% completely disappeared when greengram was sown one week after bulrush millet (Table VII).

From these studies, it may be concluded that staggered or differential sowing of component crops is of no advantage over simultaneous sowing. In

staggered sowing, the earlier sown component has an initial advantage over

the later sown component. Component crops are unable to compensate fully

for yield loss due to earlier or later association with the other component.

However, the efficiencies of cereal-legume intercrop systems measured in

terms of LER follow trends in the legume yields. It also appears that light is

an important factor in determining the magnitude of the LER.

D. EFFECTOF APPLIED NITROGEN

The responses to applied nitrogen of component crops differ in different

cereal-legume combinations 'thus affecting the efficiencies of various intercrop systems (Ahmed and Rao, 1982; Boucher, 1986).

I . Maize as the Cereal Component

Most studies on the effects of applied N on intercropping systems are based

on maize, and these indicate similar grain yield responses to applied N for

sole and intercrop maize (Dallal, 1977; Rao et al., 1979; Searle et al., 1981;

Chui and Shibles, 1984; Ofori and Stern, 1986).

In a maize-soybean intercrop system, Dallal(l977) reported that intercropping drastically reduced the seed yield of soybean, and seed yield showed no

response to applied nitrogen (Table VIII). The yields of intercrop soybeans

relative to the sole crops were reduced by 80% either with or without applied

nitrogen. The efficiency of intercropping measured by the LER was 1.15

without applied nitrogen and 1.09 with 100 kg N/ha.

In a maize-groundnut combination with N applied at 0, 25, 50, and 100

kg/ha, Searle et al. (1981) found significant yield reductions ranging from 70

to 88% for intercrop groundnut compared to the sole groundnut. The LER

values were 1.36 at nil N, 1.20 at 50 kg N/ha, and 1.24 at 100 kg N/ha (Table

VIII).

From the United States, Chui and Shibles (1984) reported that maize grain

yield responded to applied nitrogen at 135 kg N/ha both as a sole crop and as

an intercrop of soybean. Seed yield of the sole soybean at 135 kg N/ha was



69



CEREAL-LEGUME INTERCROPPING SYSTEMS

Table VIII

Yields (kg/ha) and LER of Various Cereal-Legume Intercrop Systems as

Influenced by Applied Nitrogen

N rate (To of maximum applied)

Source of data

and treatments

Dallal (1977)

Maize

Sole

Intercrop

Soybean

Sole

Intercrop

LER

Searle et al. (1981)

Maize

Sole

Intercrop

Groundnut

Sole

Intercrop

LER

Rego (1981)

Sorghum

Sole

Intercrop

Pigeonpea

Sole

Intercrop

LER

Chui and Shibles (1984)"

Maize

Sole

Intercrop

Soybean

Sole

Intercrop

LER



0



50



5082

4666



-



1478

334

1.15



-



6680

7080

1741

530

1.36



930

1240

1390

800

1.91



6160

6120

3400

570

1.16



-



-



8604

8237



418

1.20



2890

2410



820

1.42



-



100



5623

5099

1789

326

1.09



8941

9178



378

1.24



4590

3710



870

1.43



-



9160

8550



-



3410

420

1.05



"Data for 1981 experiment.



13% more than the yield obtained without nitrogen, but intercrop soybean

yield was 585 kg/ha compared to 730 kg/ha without N (Table VIII). The

LER value at nil N was 1.28 and 1.13 at 135 kg N/ha.

A multilocation appraisal of various maize-legume intercrop systems was

conducted under the 5-year INPUTS (Increased Productivity Under Tight



70



FRANCIS OFORI AND W.R. STERN



Supplies) program coordinated in Hawaii, with locations in the tropics and

temperate regions (Ahmed et al., 1979). Maize-cowpea and maize-groundnut

systems were studied at three locations, maize-mungbean in four locations,

and maize-soybeans in seven locations. Levels of applied N in the experimental treatments at each location were specified as 0,25,50, and 100%

of the local recommended rate. Table IX shows fitted regression models for

sole and intercrop maize grain yields and the intercrop legume seed yields,

averaged over all locations for each crop combination in response to applied

N. For the maize-groundnut system, only the data from Australia are shown

because data from the other locations were incomplete. From these studies,

maize grain yield responses to applied nitrogen were positive and behaved

similarly to those of cowpea, groundnut, mungbean, or soybean (Fig. 3).

However, in the sole maize, there was a lack of response to applied N in the



Table IX

Fitted Regression Equations for Component Crop Yields in Response to Applied Nitrogen in

Various Maize-Legume Intercrop Systems'

Cropping system



Number of

locations



Maize-cowpea

Sole maize

Intercrop maize

Intercrop cowpea



3



Maize-groundnutc

Sole maize

Intercrop maize

Intercrop groundnut



1



Maize-mungbean

Sole maize

Intercrop maize

Intercrop mungbean



4



Maize-soybean

Sole maize

Intercrop maize

Intercrop soybean



7



Equationb



R'



y = 2066

y = 1605

y = 1499



+ 29.6~



y = 6830

y = 6964

y = 526



+ 6 2 . 4 ~- 0 . 4 2 ~ '

+ 22.3~

+ 3 . 2 ~+ 0.02~'



0.91

0.96

0.98



y



= 2257

y = 2044

y = 418



+

+

+



19.2~

15.2~

4 . 7 ~- 0.04~'



0.95

0.83

0.99



y = 3019

y = 2835

y = 954



+

+

+



1806X

11.7~

5.3x - 0.04xI



0.88

0.96

0.90



+ 22.9~



+



6 . b - 0.04~~



'From the data of Rao eta/. (1979), data averaged over all locations for each system.

by is grain or seed yield (kglha); x is N as percentage of recommended dose in kg/ha.

'Data from Australia only.



0.91

0.89

0.99



71



CEREAL-LEGUME INTERCROPPING SYSTEMS



L

0



I



25



I

50



I

100



0



I



I



25



50



I

100



d



------.)--



It--



.



‘.



J1.40



looo



t



RG.3. Mean responses of component crops and land equivalent ratio to applied nitrogen in

various maize-legume intercrop systems. ( 0 ), Intercrop maize; (m), intercrop legume; (A), LER

estimated from the fitted yield curves. (Drawn from the data of Rao et al., 1979.)



maize-groundnut system that was attributed to high soil N status from

previous cropping (Searle et al., 1981). The LER values estimated from the

regression models at each nitrogen level ranged from 1.30 to 1.36 in the

maize-cowpea system, 1.43-1.55 in the maize-mungbean system, 1.21-1.25

in the maize-groundnut system, and 1.42-1.47 in the maize-soybean

system. Intercrop maize increased progressively in response to applied N,

heavy applications of N reducing yields of the associated legumes.

In a recent study of maize-cowpea intercrop systems, Ofori and Stern

(1986) also found declining trends in LER in response to applied nitrogen.

They used two maize cultivars of contrasting heights; LER values declined

from 1.67 to 1.42 with the short maize XL66 and from 1.40 to 1.32 with the

tall maize SR99 as applied N was varied from 0 to 100 kg N/ha.



72



FRANCIS OFORI AND W. R. STERN



The results of these studies show that LER varies with nitrogen status of

the soil and in general, where the inherent fertility of the soil is low, there

appears to be a greater advantage of intercropping maize with legumes.

2.



Other Cereal Components



Using a 45-cm alternate row arrangement in a sorghum-pigeonpea system

with N applied at 0, 60,and 120 kg N/ha at ICRISAT, India, Rego (1981)

obtained a progressive increase in grain yields of both sole and intercrop

sorghum (Table VIII). At nil N, intercrop sorghum yield was 33% higher

than sole sorghum. At 60 kg N/ha, intercropping reduced sorghum yields

by 17% and at 120 kg N/ha, the yield reduction was 20%. Applied N did

not significantly affect the yield of intercrop pigeonpea, and yield reductions from intercropping ranged from 37 to 42% compared to sole

pigeonpea. The LER value without applied N was 1.91 and declined to 1.42

at 120 kg N/ha.

These studies show that the intercrop cereal grain yields increase progressively with applied N, while seed yields of companion legumes decrease

or are less affected. It would appear that applying nitrogen does not improve the land equivalent ratio and therefore the efficiency of

cereal-legume intercrop systems.



V.



NITROGEN ECONOMY OF THE SYSTEM



In fixing atmospheric N,, legumes contribute to the N content of soil

either as sole crops in rotation, or as intercrops (LaRue and Patterson,

1981; Heichel and Vance, 1984). In such systems, legumes may either increase the soil N status through fixation and excretion, or in the absence of

an effective N-fixing system, compete for N (Trenbath, 1976). In the

literature on cereal-legume intercropping, there are surprisingly few data

concerning different parts of the system. In the sections following, the existing literature is reviewed on N, fixation, N transfer, losses, and

budgeting. Many of the examples cited are derived from agricultural

systems other than cereal-legume intercrop systems because the necessary

measurements to understand the processes involved are not always available

from intercropping studies.

A. NITROGEN

FIXATION

BY THE LEGUMECOMPONENT



The quantity of N, fixed by the legume component in cereal-legume intercropping depends on the species, morphology, density of legume in the



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