Tải bản đầy đủ - 0 (trang)
III. Competitive Relationships between Component Crops

III. Competitive Relationships between Component Crops

Tải bản đầy đủ - 0trang

CEREAL-LEGUME INTERCROPPING SYSTEMS



53



growth factor, which is below their combined demands (Clements et al.,

1929; Donald, 1963).

Willey (1979) pointed out that the efficiency of production in

cereal-legume intercrop systems could be improved by minimizing interspecific competition between the component crops for growth-limiting

factors. Growing component crops with contrasting maturities so that they

complement rather than compete for the same resources at the same time is

one way of achieving this. It is substantiated by the yield advantages

reported from various studies: 85-day bean and 120-day sorghum gave a

55% total yield increase (Willey and Osiru, 1972; Reddy et al., 1980) obtained a 31% yield advantage with 82-day millet and 105-day groundnut; and

Natarajar) and Willey (1980a) found a 62% yield advantage with 82-day

sorghum and 173-day pigeonpea. In contrast, lesser advantages have been

reported in crop combinations in which interspecific competition is evident

due to similar or almost overlapping growth durations. In this category,

Wahua and Miller (1978a) obtained an 11Vo advantage with a sorghum-soybean combination; 11Yo was obtained with 112-day maize and 116-day soybean (Dallal, 1977); and 8% with a maize-cowpea system (Wanki et al.,

1982). No yield advantages were found in maize-cowpea (Haizel, 1974) and

sorghum-cowpea (Andrews, 1972; Rees, 1986) intercrop systems in which

components were of similar growth durations.

Competition between component crops for growth-limiting factors is

regulated by basic morpho-physiological differences and agronomic factors

such as the proportion of crops in the mixture, fertilizer applications, and

relative time of sowing (Harper, 1961; Trenbath, 1976). Where component

crops are arranged in defined rows, the degree of competition is determined

by the relative growth rates, growth durations, and proximity of roots of

the different crops. The cereal component, with relatively higher growth

rate, height advantage, and a more extensive rooting system, is favored in

the competition with the associated legume. The cereal is described as the

dominant component and the legume as the dominated component (Huxley

and Maingu, 1978). In considering the relative yields of cereals and legumes

in intercropping systems, a survey of 40 published papers shows that the

yield of the legume component declined, on average, by about 52% of the

sole crop yield, whereas the cereal yield was reduced by only 11% (Table

111). Thus the general observation is that yields of legume components are

significantly depressed by cereal components in intercropping.

A. THELIGHTFACTOR

The rate of dry matter production in crops depends on the efficiency of

the interception of photosynthetically active radiation (PAR) (Biscoe and

Gallagher, 1977; Monteith, 1977).



54



FRANCIS OFORl AND W. R. STERN



Table I11

Yields of Component Crops and Relative Yield Loss Due to Intercropping in Various

Cereal-Legume Intercrop Systems

Sole crop yield

(kglha)

Crop combination

Maize-beans



Maize-cowpea



Maize-soybean



Maize-groundnut

Maize-calopo

Maize-greengram

Maize-pigeonpea

Sorghum-cowpea



Sorghum-soybean

Sorghum-groundnut

Sorghum-greengram

Sorghum-pigeonpea



Sorghum-blackgram

Sorghum-chickpea

Millet-groundnut

Millet-pigeonpea



Cereal



Legume



7320

7290

4126

5591

2080

1004

3860

6500

2678

7408

8455

9800

5353

8189

41 14

3467

7200

1987

8189

2080

2080

3170

2891

2579

3568

4860

3340

3680

4670

2794

8255

4467

3208

2853

3603

4325

2302

2407

2795

2354



1620

1958

1493

2986

1159

130



1176

2035

584

1500

3430

2100

1634

2677

1824

2290

3278

2441

1742

1159

I210

1195

997

584

676

2741

986

889

1430

704

2304

1017



Cereal



7

10



8

30

+I1

31

+ 45

33

25

18

12

46

9

13



14

4

2



Legume



Fisher (1977)

Cordero and McCollum (1979)

Francis et a/. (1982b)

Davis and Garcia (1983)



40



Agboola and Fayemi (1971)

Haizel (1974)

Remison (1978)

Wanki et a/. (1982)

Faris et a/. (1983)

Ofori and Stern (1986)



83

12

49

41

46

59

44

80

80

46

72

87



1



18



74



3



16

+5



17

6



1446



11



14

9

0

+2



52

48

7



Reference



60

69

39

74



3

+4

+9

4

31

35

+2

47

4



1380

1084



852

849

2463

1235

1244



“Percentage of sole crop yield.



Yield loss due to

intercropping ( V O ) ~



43

48

68

72

33

40



Betse (1976)

Beets (1977)

Dallal (1977)

Searle et a/. (1981)

Ahmed and Rao (1982)

Chetty and Reddy (1984)

Chui and Shibles (1984)

Baker (1978)

Searle el a/. (1981)

Agboola and Fayemi (1971)

Agboola and Fayemi (1971)

Yadav (1982)

Andrews (1972)

Faris et a/. (1983)

Singh and Jain (1984)



42

47

65

77

44

39

32

43

40

36



Wahua and Miller (1978a)

Singh and Jain (1984)



60

87

17

73

22



Singh and Jain (1984)



Singh and Jain (1984)

Chetty and Reddy (1984)

Singh and Jain (1984)

Freyman and Venkateswarlu (1977)

Natarajan and Willey (1980a)

Rao and Willey (1980)

Rego (1981)

Singh and Jain (1984)

Chowdhury and Misangu (1981)

Reddy et a/. (1980)

Willey and Reddy (1981)

Rao and Willey (1983)



CEREAL-LEGUME INTERCROPPING SYSTEMS



55



1. Light Interception



The amount of light intercepted by the component crops in an intercrop

system depends on the geometry of the crops and foliage architecture (Trenbath, 1982; Tsay, 1985). The generally taller cereal shades the legume, and

at high densities causes reduced growth and yield of the companion legume.

Gardiner and Cracker (1981), maintaining a constant bean density of

220,000 plantdha, found that varying maize density from 18,000 to 55,000

plantdha progressively reduced the amount of light available to the

beans. At the low maize density (18,000 plantdha), bean received 50% of

the incident light, compared to 20% at the highest maize density (55,000

plantdha). At the highest maize density, yield of the intercrop bean was only

30% that of the sole bean.

Several studies at the International Crops Research Institute for the SemiArid Tropics (ICRISAT), India, have measured percentage light intercepted

using short-duration cereal (e.g., maize, sorghum, or millet) and longduration legume (e.g., pigeonpea or groundnut) both as sole crops and as

intercropping mixtures (Reddy and Willey, 1981; Sivakumar and Virmani,

1980, 1984; Marshall and Willey, 1983).

In a sorghum-pigeonpea combination, the amount of light intercepted

relative to incoming incident radiation at 55 days was 84% in sole sorghum,

65% in sole pigeonpea, and 80% in the intercropping mixture (Natarajan

and Willey, 1980b). The data of Sivakumar and Virmani (1980) from a

maize-pigeonpea intercrop system shows that light interception was low

with the initial slow increase in leaf area index (LAI), and above 80% when

LA1 reached about 3. Although light interception in the sole crops and the

intercrops were almost similar, the foliage canopy of the intercrop was more

effective in capturing the light. The intercrop system attained an LA1 of 3 in

45 days, compared to 50 days in the sole maize and 115 days in the sole

pigeonpea.

Although the ICRISAT studies do not report the quantity of light

reaching the top of the associated legume canopy, the light intercepted by

the similarly spaced sole cereal crops suggests significant reductions in light

available to the companion legume. Assuming a peak LA1 of 2 for the intercrop cereal in these studies, the amount of light incident on the companion

legume canopy would be 30% or less of the total incoming radiation.

The reduction in light reaching the legume canopy when intercropped

with a taller component crop has been clearly demonstrated in a

cassava-soybean intercrop system in southern Queensland by Tsay (1985).

He found that PAR transmission was closely related to the distribution of

leaf area in the cassava canopy, and isopleths of PAR relative to full sunlight decreased towards the top of the legume canopy (Fig. 1). When intercropped soybean rows were 45-90 cm from cassava rows with an LA1 of about



56



FRANCIS OFORI AND W. R. STERN



3, the amount of light reaching the soybean canopy was about 25% of the

total incoming radiation.

2. Efficiency of Conversion of PAR into Dry Matter



The higher productivity of intercrop systems compared to the sole crops

may be attributed to better light utilization by a crop canopy composed of

plants with different foliage distributions (Willey and Roberts, 1976;

Willey, 1979). In a study of maize and pigeonpea, Sivakumar and Virmani

(1980) found that dry matter production per unit of PAR absorbed was

higher in the mixture than in the sole crops (Table IV).

The higher PAR conversion efficiencies of these systems relative to the

sole crops may be due to spread of light over greater leaf area, and more efficient distribution of light in the intercrop canopies during early stages of

growth. For example, using a pearl millet-groundnut system, Reddy and

Willey (1981) obtained energy conversion efficiencies at 68 days of 1.70

g/MJ in sole millet, 1.07 g/MJ in sole groundnut, and 1.95 g/MJ in the

mixture.

At maximum green leaf area index (61 days after sowing), Marshall and

Willey (1983) observed energy conversion efficiencies of 4.1 g/MJ in sole

millet, 2.5 g/MJ in sole groundnut, and 4.3 g/MJ in the intercropping mixture. The similarity in efficiency of dry matter production in the sole millet

and the mixture was attributed to the greater proportion (60%) of intercrop

millet in the total intercrop.

90cm x 90cm



180cm x 45cm



. = 0.15



LA1



LA1 = 3.69



LA1 = 2.8 1



3535d

. . ... ..



I: - I.:



.-



.:



I.:.



I



I . . .



..



:.



,



I



-



I"



0



45



0



1



0



I



I



1



45



90



45



J



0



Distance from cassava row (cm)



FIG. 1. Isopleths of relative percentages of available radiation (75%, m-m;

A-A;



50%,



of full sunlight) within intercrop cassava canopies in the density of 1.23

plants/m* with interrow spacings of 90 and 180 cm at 98 days after cassava planting. (From

Tsay, 1985.)

25%, 0-



0



57



CEREAL-LEGUME INTERCROPPING SYSTEMS



Table IV

Total Dry Matter, Grain Yield, Leaf Area Index, Light Interception (@lo), and Efficiency of

Dry Matter Production of a Maize-Pigeonpea Intercrop System"



Cropping

system



Total dry

matter yield

(kg/ha)



Grain

yield

(kglha)



Peak

LA1



Sole maize

Sole pigeonpea

Intercrop total



8,130

7,870

15,290



3,500

1,833

5,038



3.5

3.2

6.1



Light

interception

at peak LA1



VO)



Dry matter

production

efficiency

WMJ)



90

85

83



3.1

1.2

4.3



%om data of Sivakumar and Virmani (1980).



B. THESIGNIFICANCE O F WATER

Water is a most important soil factor in semiarid and subtropical regions,

where intercropping is extensively practiced in dryland farming systems and

inadequate rainfall may frequently limit crop production (Baker and Norman, 1975).

The differences in root systems, depth of rooting, lateral root spread, and

root density are factors that affect competition for water between component crops (Babalola, 1980; Haynes, 1980). The use of different parts of the

soil profile by root systems of different crop species minimizes the degree of

competition for water (Haynes, 1980). When component crops compete for

available water, the cereal, with its higher growth rate and more extensive

root system, is generally favored.

In India, Natarajan and Willey (1980b) found that the amount of water

transpired in a sorghum-pigeonpea intercrop system depended on growth

durations of the crops. The total water use by sole pigeonpea at the end of

the growing period (173 days after sowing) was 584 mm and in the mixture

585 mm; in sole sorghum at the final harvest (82 days after sowing) it was

434 mm. Using 82-day millet intercropped with 105-day groundnut, Reddy

and Willey (1981) obtained a total water use of 406 mm in the mixture, compared to 303 mm in sole millet and 368 mm in sole groundnut.

Shackel and Hall (1984) in the United States, studying plant water deficits

in sorghum intercropped with cowpea in terms of xylem pressure potential,

and osmotic potential under irrigated and water-limited conditions, found

that they were not substantially affected by intercropping. However,

shading by the associated sorghum slightly increased midday xylem pressure

potential and osmotic potential of intercropped cowpea leaves. The patterns

of cumulative water depletion from the top 195 cm of soil in the intercropped treatments were similar to values obtained in the sole crops. Sorghum



58



FRANCIS OFORI AND W. R. STERN



and cowpea appeared to be competing equally for soil water as evidenced by

absence of substantial effects of intercropping on the water relation of these

crops.

From the humid tropics of Nigeria, Hulugalle and Lal (1986) reported

that water use efficiency (WUE) in maize-cowpea intercrop was higher than

in the sole crops when soil water was not limiting; however, under drought

conditions, WUE in the intercrop was lower compared to the sole maize.

For the favorable moisture regimes, WUE (kg grain per mm per ha) of the

intercrop (alternate row arrangement) was 3.6 compared to 2.1 in either of

the sole crops, and for the droughty conditions, 1.6 for the intercrop, 2.2

for the sole maize, and 0.5 for the sole cowpea.

From the above, it may be concluded that cereal and legume intercrops

use water equally, and that competition for water may not be an important

factor in determining the efficiency of intercrop systems, except under

favorable soil moisture conditions.



c.



THEROLEOF SOIL NUTRIENTS



The major soil nutrients for which component crops compete when in

limited supply are nitrogen, phosphorus, and potassium. The cereal component, with a faster-growing or more extensive root system, generally has a

competitive advantage over the associated legume (Trenbath, 1976). The inability of the legume to compete for these nutrients are attributed to lesser

ramification of their root systems (Rabotnov, 1977). Competition for

nutrients is important and could begin early in the growth of the component

crops in cereal-legume intercropping systems (Wahua, 1983).



I. Nitrogen

The mobility and high demand for nitrogen by most crops, particularly

nonlegume, leads to severe competition for it in nonlegume-legume associations (Allison, 1973; Beets, 1982). In these associations, Evans (1977)

pointed out that the absorption of nitrogen is controlled by the roots of

component crops.

In cereal-legume intercropping, the legume component is capable of fixing atmospheric N,under favorable conditions and this is thought to reduce

competition for N with the cereal component (Trenbath, 1976). In the

absence of an effective N-fixing system, both cereal and intercrop legume

compete for available soil N (Ofori et al., 1987).

Ibrahim and Kabesh (1971) found that horsebean reduced N uptake of

wheat by 26% whereas wheat reduced that of horsebean by 44%. It is apparent that dry matter yield and N uptake of the component crops were



CEREAL-LEGUME INTERCROPPING SYSTEMS



59



severely affected in the mixed stands, as shown by the partial LER values:



Dry matter yield

N uptake



Wheat



Horsebean



0.63

0.74



0.63

0.56



In a maize-cowpea intercrop system, Wahua (1983) found that at 105 kg

N/ha, the crops were in competition for N and that this occurred before anthesis or flowering. The severity of the competition for N was greater for

cowpea and occurred at 40 days and was evident in the associated maize 10

days later. Nitrogen uptake by intercrop cowpea was 64 kg/ha compared to

88 kg/ha in the sole cowpea. Nitrogen uptake of intercrop maize was reduced by

17% compared to sole maize.

Without applied N, Chang and Shibles (1985a) and Ofori and Stern

(1986) reported strong competition for soil N by intercrop maize and

cowpea. This was particularly evident between 49 and 63 days when both

crop species were at the reproductive stage and required substantial

amounts of N.

2. Phosphorus

Phosphorus is a major nutrient that determines the production potential

of most grain legumes usually intercropped with cereals (Williams, 1936).

Legumes are poorer competitors for P when intercropped with grasses or

cereals, this being attributed to differences in root morphology (Donald,

1963; Jackman and Mouat, 1972; Evans, 1977).

Lai and Lawton (1962) evaluated root competition for P between corn

and intercrop field because using 32P-labeledfertilizer placed at different

depths. They found that corn was more vigorous in the uptake of P than

beans as a result of its more extensive roots.

Using a replacement series design, Dallal (1974) observed that intercropped maize and pigeonpea were competing for P from 28 days onward right

up to the maize final harvest (112 days after sowing) and that maize was

more competitive. At 112 days, intercropping reduced dry matter yield of

maize by 32% and pigeonpea by 66% compared to the sole crops; total P

uptake was reduced by 25% in maize and 70% in pigeonpea.

Wahua (1983) found that maize and cowpea were competing for P and

this was evident at anthesis or flowering (Table V). In the absence of applied

P, maize was more competitive than cowpea in the initial stages. However,

at high rates of applied P, P uptake of intercrop maize was reduced by 30%,

indicating competition for P from cowpea. Competition was clearly expressed in the observation that intercrop cowpea took up only 50% of the

sole cowpea P uptake in the absence of applied P, while at a high level of P,



60



FRANCIS OFORI AND W. R. STERN

Table V

Yield and P Uptake of Maize Intercropped with Pigeonpea or Cowpea

~~~~



P uptake

(kg/ha)



Dry matter yield

(kg/ha)

Source of reference

and cropping system



28 DAY



112 DAS"



28 DAY



112 DAY

~



Dallal (1974)

Sole maize

Intercrop maize

Sole pigeonpea

Intercrop pigeonpea



880

449

197

44



6408

4361

822

28 1



3.6

2.0

1.1

0.2



13.2

10.0

1 .o

0.3



Grain yield (kg/ha)

P rate (kg/ha)



Remision (1978)

Sole maize

Intercrop maize

Sole cowpea

Intercrop cowpea



3243

5591

1254

1060



3544

5042

1206

1138



P uptake at 50 DAS

P rate (kg/ha)



Wahua (1983)

Sole maize

Intercrop maize

Sole cowpea

Intercrop cowpea



3.5

4.6

1.4

0.7



5 .O

3.5

1.7

1.1



uDAS, Days after sowing.



65% was taken up. Remison (1978) concluded, however, from grain yield

data that intercropped maize and cowpea grown at two levels of P did not

compete for P, because there were no significant differences in yields of the

sole crops and the intercrops (Table V).



3. Potassium

Studies by Drake et al. (1951) showed that cation exchange capacities

(CECs) of roots of legumes are approximately double those of cereals. The

relatively high CEC of legumes indicates that on soils with low levels



CEREAL-LEGUME INTERCROPPING SYSTEMS



61



of exchangeable K, the legume would be deficient in K because larger

amounts of divalent cations would be adsorbed by the roots. The level of K

in many soils decreases as the growing season progresses; consequently K

uptake in competition with cereal becomes increasingly difficult for the

legume (Drake et al., 1951).

Dallal (1 974) found that intercropped maize and pigeonpea were competing for K at different stages of growth:

Reduction of K uptake due to

companion crop (Olo)

42 days



Maize

Pigeonpea



112 days



33



16



52



63



In an 82-day sorghum and 173-day pigeonpea intercrop system, Natarajan and Willey (1980b) found sorghum to be more aggressive for K than

pigeonpea, and this severely affected the early growth of pigeonpea. At 74

days, intercropping markedly affected K uptake of sorghum; the sole

sorghum absorbed 45 kg/ha of K and the intercrop 165 kg/ha. In

pigeonpea, K uptake was 28.6 kg/ha in the sole crop and 3 kg/ha in the intercrop, a reduction of 87.5070. In a maize-cowpea combination, Wahua

(1983) found maize to be more competitive for K than cowpea, particularly

when N was high. At 50 days, application of 115 kg/ha of N caused reductions of 3 1070 in uptake of K in the intercrop maize, and 50% in the intercrop cowpea, compared to the respective sole crops.



IV.



SOME AGRONOMIC FACTORS INFLUENCING

PRODUCTIVITY AND EFFICIENCY



The productivity and efficiency of cereal-legume intercrop systems are

affected by various agronomic variables that affect crop yields. In this section, the influence of variables such as component crop density, plant spacing and arrangement, relative time of sowing of component crops, and the

effect of applied nitrogen will be discussed.

A.



COMPONENT CROP DENSITY



The overall mixture densities and the relative proportions of component

crops are important in determining yields and production efficiency of

cereal-legume intercrop systems (Willey and Osiru, 1972; Lakhani, 1976).

When the components are present in approximately equal numbers, productivity and efficiency appear to be determined by the more aggressive



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



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

III. Competitive Relationships between Component Crops

Tải bản đầy đủ ngay(0 tr)

×