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Economic evaluation of alley cropping leucaena with Maize-Maize and Maize-Cowpea in Southern Nigeria
4gricultural Systems 17 (1985) 243-258
Economic Evaluation of Alley Cropping Leucaena with Maize-Maize and Maize-Cowpea in Southern Nigeria Dezi S. N g a m b e k i International Institute of Tropical Agriculture, Ibadan, Nigeria S UMMA R Y Alley cropping is an aspect of agroforestry being developed for small farmers in the tropics. It consists of establishing fast-growing leguminous shrubs or tree species in rows, then controlling the shading from the trees during cropping by pruning the branches which can be used as mulch or green manure to benefit the companion crops planted between the alleys. This paper attempts to assess the economic implications on labour utilization for the management of the leucaena hedgerows, on crop yields and the overall benefits from alley cropping with leucaena. The results show that although the management of leucaena trees increases labour requirements by about 50 %, the system can sustain and increase maize yields by over 60 %, reduce the use of nitrogenous fertilizers and give an attractive net income and marginal rate of return per unit cost. It gave a reasonable benefit-cost ratio of 1.23 to 1"32 and looks promising, especially for maize production in tropical areas.
INTRODUCTION Alley cropping is a land-use system in which arable crops are grown in the spaces between established rows of leguminous shrubs or tree species. The tops or branches of the trees can be periodically pruned during cropping to prevent shading and to minimize tree--crop competition for moisture and nutrients (Kang et al., 1981a). The prunings can be left on the soil surface as mulch or incorporated in the soil as green manure for the companion crops. Some agronomic research on alley cropping leucaena with maize has 243 Agricultural Systems 0308-521X/85/$03"30 ~c~Elsevier Applied Science Publishers Ltd, England, 1985. Printed in Great Britain
244
Dezi S. Ngarnbeki
shown that leucaena can contribute nitrogen of over 200 kg/ha/year and increase significantly the yields of the associated maize crop (IITA, 1980, 1981; Kang et al. 1981b). The alley cropping concept is an adaptation and a refinement of some forms of agroforestry being commonly practised by small farmers in Africa and Asia (Wilson & Kang, 1981; Kang et al., 1981a; Vergara, 1982), because some farmers in the tropics recognize the need to use certain plant species to maintain the soil fertility of their land. For example, in certain parts of Nigeria, farmers retain woody species such as Acioa baterii, Anthonata macrophylla and Glyricidia sepium after land clearing and encourage them in the bush fallow (Benneh, 1972; Okigbo, 1976). The Chinese use leguminous crops such as Sesbania cannabina, Astragalus sinicus and Vicia faba in their green manuring national programme in four different ways. Green manure crops are: (a) sown and ploughed under in the same field, (b) harvested and incorporated in other fields, (c) cut, mixed with grasses and mud and put in pits in corners of fields for compost making or (d) interplanted with summer rice crops (FAO, 1977). With increasing population pressure, frequent and extensive forest clearing for wood, cultivation, grazing and other human activities, the traditional fallow periods in the humid tropics have become progressively shorter, thus making their primary function of soil fertility restoration less effective, causing soil nutrient depletion and poor crop yields (Okigbo, 1974, 1982; Ruthenberg, 1976). Leucaena leucocephala is a fast-growing tree species and has a range of varieties that are either tall and slender (20 m) or are bushy (5 m) with deep roots of 2 to 5 m (Dijkman, 1950). Leucaena can fit a wide range of environments ranging from semi-arid with low rainfall to forest with high rainfall, heavy clay and alkaline soils. It has the ability to restore woody bushes in derived grassland (NAS, 1980). Once the leucaena is established in hedgerows, it has several advantages: for example the leucaena hedgerows can (a) help to maintain soil fertility which will allow continuous cultivation as they fix atmospheric nitrogen, (b) recycle leached nutrients from the subsoils, (c) protect against soil erosion, (d) provide an inexpensive source' of stakes to support yam vines, provide fuel, wood, fodder and (e) it is sometimes used for human food. Under these circumstances, the alley cropping system would seem attractive for farmers, especially in tropical Africa. It is therefore important to examine the economic implications regarding the amount of
Alley cropping leucaena in southern Nigeria
245
land occupied by leucaena stands, the extra demand for labour needed for cutting and pruning leucaena during the cropping season vis-gt-vis the question of profitability from continuous cultivation under alley cropping. OBJECTIVES A series of agro-economic experiments were carried out at the International Institute of Tropical Agriculture (IITA) in South Western Nigeria, on alley cropping leucaena with maize followed by maize in 1981 and with maize followed by cowpea in 1982, with the following objectives: (a) to monitor labour and other inputs, (b) to assess the effect of alley cropping with leucaena on maize and cowpea yields, and (c) to determine the economic viability of the maize and/or cowpea-leucaena alley cropping system as compared to that of herbicide and nitrogen application. METHODOLOGY To assess whether leucaena is compatible with nitrogen and herbicides, a 2 x 2 x 2 factorial design was used comprising leucaena and herbicides at two levels each. A piece of land of about 0.23 ha, which had been left under fallow in 1980, was planted to maize followed by maize in 1981 and the maize followed by cowpea in 1982. The trial had 4 replicates along the contours with each of the replicates subdivided into 8 treatments of 6 by 10metres, with the leucaena plots in a replicate already established. Leucaena, herbicides, leucaena-herbicides and a control were the main plot-randomized treatments in maize. Using split-plots, nitrogen treatment at 80 kg/ha was superimposed on these. The rainfall in South West Nigeria varies between 1250 and 1500 mm per year. The rainfall pattern is bimodal with peaks in May and August/September. According to the moisture cycle in this area, the first rains are expected by the third week of March, stabilizing around midApril. Then moisture usually cuts off in late July and re-stabilizes in the third week of August, cutting off again by mid-November. Critical periods for planting and harvesting of first-season crops are mid-April and the second week of August, respectively, and the planting of the second-season crop should not be later than last week of August.
246
Dezi S. Ngambeki
In the leucaena plots, leucaena trees were cut in April 1981, prunings left on the plots as mulch and the stems removed. During the cropping seasons at planting, weeding and flowering, leucaena tops were pruned, weighed and returned as mulch to the crop. Maize was planted at a spacing of 75 by 25 cm, cowpea at 60 by 25 cm, and weeding was done two weeks after planting. The herbicide plots were sprayed with paraquat at 3 litres/ha before planting and atrazine at 2.51itres/ha after planting for maize, and paraquat and dual at 2.5 litres/ha for cowpea. The cowpea crop received four insecticide applications to control thrips, aphids, maruca and pod bugs. The plots were planted to maize or cowpeas without tillage and were top-dressed with P and K fertilizers at 60 kg/ha and 30 kg/ha respectively for maize only. To obtain realistic labour input data, casual workers with some farming experience were hired on a daily task work basis. This resulted in more efficient labour inputs than with regular workers. Leucaena stands occupy 20 to 26 ~o of the land, which is regarded as a cost. Data on all inputs and crop yields based on whole plot areas were carefully recorded. For analysis of variance used in this paper to separate the main effect of each factor and the interaction effects between factors is as follows. If we designate the treatments thus: A =leucaena, B = herbicide, C = nitrogen, A B = leucaena-herbicide, A C = leucaenanitrogen and A B C = leucaena-herbicide-nitrogen, then the main effect of A is defined as: A = ¼ ( a b e ) - ( b e ) + ( a b ) - ( b ) + ( a c ) - (c) + (a) -
(1)
and the interaction of A with B is measured thus: A B = ¼(abe) - ( b e ) - ( a c ) + (c) + ( a b ) - ( b ) - (a) +
(1)
(Cochran & Cox, 1957). Other types of analyses used include plant tissue of maize ear leaf for nitrogen content and input-output budgeting to determine various economic indicators. RESULTS A N D DISCUSSION
Labour utilization in alley cropping with ieucaena Cutting leucaena, including shredding the leaflets, at about 15 000 trees/ha took 185 man-hours/ha or 30.8 man-days/ha (6 man-hours being equal to
Alley cropping leucaena in southern Nigeria
247
one man-day) in 1981 when the plots had been put under fallow during the previous year. The pruning of leucaena tops took 145.9 man-hours/ha or 24.23 man-days/ha for first season and 113-89 man-hours/ha or 19 mandays/ha for second season 1981. In first season 1982, cutting leucaena regrowth took 16-46 man-days/ha and two prunings took respectively 14-6 and 7.5 man-days/ha, making a total of 38.56 man-days/ha for the management of leucaena for that cropping season. In the second season of 1~82, cutting leucaena regrowth took 16.2 man-days/ha and two prunings took respectively 7.5 and 6.9 man-days/ha or a total of 30.6 man-days/ha for management of leucaena in second season. Considering the labour inputs for various treatments in the agroeconomic experiments on alley cropping leucaena with maize or cowpeas, the leucaena treatment doubled the labour inputs in 1981 firstseason maize, but increased them by 25 ~o (164 man-hours/ha) in 1981 second-season maize and 37 ~o (148 man-hours/ha) in 1982 first-season maize as compared to those of the control. The leucaena-nitrogen treatment which took the highest amount of labour, took (in manhours/ha) 921 and 895 in 1981 first- and second-season maize, and 565 in 1982 first-season maize compared to 424, 652 and 400 man-hours/ha used in the control plots for the respective seasons. Thus, labour inputs were increased by 117, 37 and 41 ~o in the respective seasons. The herbicide treatments, however, reduced the labour inputs by about 30 ~o per season. Table 1 shows average labour inputs per season by treatments for the production of maize or cowpeas. On average, the maize crop leucaena treatment increased labour inputs by 52 ~o, leucaena-nitrogen by 61 ~o, leucaena-herbicide by 31 ~o and leucaena-nitrogen-herbicide by 40 ~o. In comparison, herbicide reduced labour input by 35~o and herbicide-nitrogen reduced it by 26 ~o. With the cowpea crop, leucaena treatment increased labour inputs by 28 ~o and herbicide reduced them by 27~o. The main and interaction effects of leucaena, herbicides and nitrogen on crop yields
Table 2 shows the analysis of variance of treatments on maize and cowpea yields in 1981 and 1982. The treatments of nitrogen and leucaena had significant effects on both maize ear leaf nitrogen and maize yields at the 1 ~ level. The herbicide treatment had significant effect at the 1 ~o level on maize ear leaf
Dezi S. Ngambeki
248
TABLE 1 Average L a b o u r I n p u t s per Season by T r e a t m e n t s for Maize or C o w p e a (IITA, 1981/82)
Labour input Jor maize Manhours~ha
Increase over control Manhours/ha
Control Nitrogen Herbicide Herbicide-nitrogen Leucaena L e u c a e n a nitrogen L e u c a e n a herbicide Leucaena-nitrogen herbicide
492 538 319 365 751 794 644
-46 - 173 - 127 259 302 152
691
199
Labour input Jor cow,peas Manhours/ha
"o
9.3 35 - 26 52 61 31
Increase over control Matthours~ha
442 . . . . 321 - 121 . . . . . 565 123 505
63
"o
-27 . 28 14
40
nitrogen in 1982 and at the 5 °..o level on maize yield in the second season of 1981 and first season of 1982. The interaction effects between herbicide-nitrogen on maize yield were only significant at the 5 °.o level in first season 1982 and those between leucaena-herbicide only significant at the 1 '~o level in first season 1981. But the interaction effects between leucaena-nitrogen and those between leucaena-herbicide nitrogen tended not to be significant. For the cowpea crop, only the herbicide treatment had significant effect. Table 3 shows the main effects and interaction of the various treatments in 1981 and 1982. Calculations of maize effects and interactions were based on a statistical analysis of a 2 x 2 x 2 factorial experiment (Yates, 1937; Friedman & Savage, 1947: Cochran & Cox, 1957). The analysis shows that leucaena had additive main effects of about 1.6 t/ha maize grain yields and 30 to 60",, maize ear leaf nitrogen which were significant at the 1".o level and greater than those of nitrogen and herbicide in the two seasons of 1981 and in the 1982 first season. Nitrogen had additive main effects of about 0.8 t/ha on maize yields and 25 to 34 ° o of maize ear leaf N. They were also statistically significant except in the 1981 second season when they were insignificant. However, the herbicide treatment tended to have negative main effects on maize yields, except in
31
Total
** F ratio significant at 1 °.o. * F ratio significant at 5 °/ o .
3 1 1 1 1 1 1 1 21
Replication s Nitrogen Herbicide Herbicide n i t r o g e n Leucaena Leucaena-nitrogen Leucaena-herbicide Leucaena herbicide-nitrogen Error
Source o f variation
Tre~tmen t
0.33 9.04** 0.36 1.61 16,62"* 0-03 0.25 0-08 -
lst-season maize ear l e a r N ','o 0.67 0.36 0"71 0.42 8.45** 1.7 7.34"* 0.43
lst-season maize yield
1981
2.86 7.83** 7.34* 3.34 74.12"* 0.003 1.92 0.25
2nd-season maize yield
F ratio
--
0.94 14.56"* 20'41 ** 5.53* 55.78** 0.26 1.97 0.48 --
lst-season maize ear leaf N °,o
--
0.18 15.49"* 5" 11" 2.53 162.82"* 3.41 31.84"* 2.60 --
lst-season maize yield
1982
--
0.25 -0.24
8.60 * -14.04"*
2nd-season cowpea yield
TABLE 2 Analysis o f V a r i a n c e o f T r e a t m e n t s o n M a i z e a n d C o w p e a Yield in a n Alley C r o p p i n g E x p e r i m e n t ( I I T A , 1981; 1982)
t,~
~ ~.
~.
5"
5'
TABLE 3
0.25** -0.15 0" 17 0.64** 0.03 - 0"07 0.04
lst-season maize ear leaJ N ~o 807 1 279 - 215 1 760** - 303 - 629* 151
1st-season maize yield kg/ha
1981
240** - 142" - 1 319 1 610"* 70 - 717 - 149
2nd-season maize yield kg/ha 0-34** -0.15'* 0"08" 0.28** - 0.02 0"05 0.03
1st-season maize ear leaf N%
Main effects and interactions
729.57** 485* 340.6 1 183.37"* - 172.69 289"61 ** 150.8
1st-season maize yield kg/ha
1982
18.66 --
-140-09"* -- 19-03
2nd-season cowpea yield kg/ha
** F r a t i o significant at 1 ~o. * F r a t i o significant at 5 %, b u t t h e a c t u a l F r a t i o statistics a r e p r e s e n t e d in T a b l e 2. t T h e statistical a n a l y s i s u s e d a 3 x 2 f a c t o r i a l e x p e r i m e n t a n d figures in t h e table i n d i c a t e a d d i t i v e r e s p o n s e s r e s u l t i n g f r o m e i t h e r a single f a c t o r or c o m b i n a t i o n o f f a c t o r s in a t r e a t m e n t .
Nitrogen Herbicide Herbicide nitrogen Leucaena Leucaena-nitrogen Leucaena herbicide Leucaena-nitrogen herbicide
Treatment
T h e M a i n Effects a n d I n t e r a c t i o n s t o f T r e a t m e n t s o n M a i z e a n d C o w p e a Y i e l d s in a n A l l e y C r o p p i n g E x p e r i m e n t ( I I T A , 1981 ; 1982)
4.
e~
4.
251
Alley cropping leucaena in southern Nigeria TABLE 4
Nitrogen Content of Maize Ear Leaf from First-Season Maize Leucaena Alley Cropping (IITA, 1981; 1982) Treatment
Maize ear leaf % N 1981
1982
Control Nitrogen Herbicide Herbicide-nitrogen Leucaena Leucaena-nitrogen Leucaena-herbicide Leucaena-nitrogen-herbicide
2.11 2.36 1-96 2'48 2.74 2.97 2.31 3'03
2.67 2.97 2.41 2.82 2.95 3-16 2-74 3.16
Stand. dev. LSD
0.11 0.45
0.31 0.27
the 1982 first season when its effects were positive and significant at the 5 ~o level. The interaction effects between leucaena and nitrogen on maize ear leaf nitrogen and grain yield both tended to be negative but insignificant, reducing maize yield by 0.2 to 0.3 t/ha. The interaction effects between leucaena and herbicide on maize, were negative in 1981 but positive and significant in the 1982 first season. Whereas the interaction effects between leucaena, nitrogen and herbicide on both maize ear leaf nitrogen and grain yield, were mostly positive but insignificant except in 1981 when they gave negative though insignificant effects on maize yields. Maize ear leaf content for first season both in 1981 and 1982 (Table 4) suggests that the herbicides plots had less nitrogen uptake. While the leucaena treatment had a main effect of over 20 ~o on ear leaf nitrogen content, suggesting a more efficient uptake of N, there was a negative interaction between leucaena and herbicide in 1981, thus suggesting that herbicide application tends to depress N status in maize ear leaf. The negative interaction between leucaena and nitrogen, though not significant, and the significant negative interaction between leucaena and herbicides in 1981, suggest that applications of herbicides, together with a certain level of nitrogen to maize-leucaena alley cropping, reduces the effects of leucaena on maize grain yield, thus constituting an economic waste of resources.
TABLE
5
744.46 761.00
* 1981 second-season crop was badly hit by drought. t Hand-weeded and no fertilizers. ++ Hand-weeded.
211.50 575.07
Stand. dev. LSD
758 998 616 1 049 2486 2 496 1 685 2 153 662.78 564.71
2 159 2 872 1 929 3 021 3 141 3 206 3 660 4708 151.08 174.85
745 -576 -730
623
1st-season 2nd-season maize cowpeas kg/ha
1st-season 2nd-season* maize maize kg/ha
1 957 2 749 3 094 3 342 3 789 3 627 3 358 3 192
1982
1981
Controlt Nitrogen+'t" Herbicide Herbicide nitrogen Leucaenat Leucaena-nitrogent+ Leucaena-herbicide Leucaena nitrogen herbicide
Treatment
752 453 1 123 1 407 1 358 1 451 1 892
Maize kg/ha
36 22 45 68 66 70 90
°o
-47 -107 -
122
Cowpeas kg/ha
Average increases/decreases in yield
Maize and Cowpea Yield Response to Treatment in the Alley Cropping Experiment (IITA, 1981; 1982)
-
17.17
7.54
19.58
I
O, '"0 t~
e~
t'J
Alley cropping leucaena in southern Nigeria
253
It therefore appears that the negative interaction between leucaena and nitrogen on maize crop yield is due to the fact that application of the nitrogen supplied by leucaena leaflets increases the level of soil nitrogen content beyond the optimal level, thus reaching a point where any additional nitrogen brings about diminishing returns in the response of the maize crop yield to total soil nitrogen. As for the tendency to a negative effect between leucaena and herbicides, it appears that atrazine in particular depresses the growth of leucaena shoots, thus reducing the amount of leucaena prunings for mulch and nitrogen suppliable by it. In contrast with maize, herbicide was the only treatment that had statistically significant additive main effects on cowpea yields (Table 3). The main effect of leucaena treatment on cowpea yields was negative but insignificant, while the interaction effects between leucaena and herbicide on cowpea yield were not significant. Both the negative increase caused by leucaena treatment on cowpea yields (Table 5) and the negative main effect of leucaena on cowpea yields (Table 3) suggest that a leucaena alley cropping system alone does not benefit the cowpea crop as much as it does the maize crop, probably due to shading effects of leucaena shoots on cowpea and/or the additional nitrogen supplied by leucaena, especially considering that the interaction effect between leucaena and herbicides on cowpea is less than the main effects of herbicides on cowpea. Table 5 shows maize and cowpea yield response to treatment in an alley cropping experiment. The leucaena treatment increased maize grain yields by 95 ~o (1832 kg/ha) to 45 ~o (984 kg/ha) in the first seasons of 1981 and 1982 respectively. Leucaena-nitrogen increased maize yields by o~J ''/ /o (1670kg/ha) to 48~o (1048kg/ha), leucaena-herbicide by 70~o (1401kg/la) to 69°//o (1501kg/ha) and leucaena-nitrogen-herbicide increased them by 63 ~o 0235 kg/ha) to 118 ~o (2549 kg/ha) as compared to maize yields of 1957 and 2159 kg/ha obtained from the control plots in the respective seasons. The low values of LSD indicate that the means of the various treatments are statistically different. Using an average of three seasons for maize and one season for cowpeas, the leucaena treatment gave an average increase for maize yields of 68 ~o (1407 kg/ha), leucaena-nitrogen 66 ~o (1358 kg/ha), leucaenaherbicide 70~o (1451 kg/ha) and leucaena-nitrogen-herbicide 90~0 (1892 kg/ha). As for the cowpea crop, the treatment of herbicide and leucaena-herbicide respectively gave yields of 745 and 730 kg/ha which is an increase of 19.58 and 17.17% as compared to cowpea yields of
480 146 496 130 139 -58
Herbicide
Herbicide nitrogen
Leucaena
Leucaena-nitrogen
Leucaena herbicide
Leucaena nitrogen-herbicide
loss
1.97
1.56
2.33
loss
0-97
1.07
1.05
1-32
1-1
1-18
-0.79
Marginal Benefit rate o[ cost return/ ratio/ ha ha
1 108
765
302
396
992
650
491 669
Net returns US$/ha
1.30
0.43
-0.23
-0.21
10.0
2-23
8-60
subsidized
1.69 (2.90) 2-60 (1-25) 3.90 (3-10) -0.21 (1.58) 0.34 (1-16) 0.63 (2.81) 1.01 (2.80)
1.76
1.49
1.29
1-31
2.04
1.65
1.50 1.72
1.59
1.44
1.17
1.23
1.76
1.51
1.39 1.49
unsubsidized
Benefit cost ratio~ha
unsubsidized subsidized
Marginal rate* of return/ha
1982 maize cowpea
* Figures in parentheses represent marginal rate of return from 1982 first-season maize alone. In 1981/82 farmers in Nigeria received 75 "o subsidy on fertilizers and the price was 13-5 US$/50 kg of nitrogenous fertilizers.
- 438 371
Net returns US$/ha
1981 maize maize
Control Nitrogen
Treatment
TABLE 6 The Economic Contribution of Various Treatments in Agro-economic Alley Cropping Experiments (IITA, 1981; 1982)
4,
Alley cropping leucaena in southern Nigeria
255
623 kg/ha obtained from the control plots. But the leucaena treatment by itself lowered cowpea yields by 7.54 ~ (47 kg/ha). The economic contributions of leucaena vis-it-vis those of herbicide and nitrogen Three economic indicators, namely net return/ha, marginal rate of return and benefit-cost ratio (Table 6), were calculated to determine the economic contributions of each treatment for 1981 and 1982. In all the analyses for 1981, the leucaena treatment gave highest economic returns. Leucaena plots gave a net return of $496 (US)/ha, equivalent to a marginal rate of return of 2.33 per ha per additional unit cost and a benefit-cost ratio of 1.32. This was followed by the herbicide, which gave a net return of $480 ha, equivalent to a benefit-cost ratio of 1.18, then leucaena-herbicide which gave a net return of $139/ha, equivalent to a marginal rate of return of 1.97 per ha per additional unit cost and a benefit-cost ratio of 1.07. The leucaena-nitrogen treatment gave net returns of $130/ha, equivalent to a marginal rate of return of 1.56 per unit additional cost and a benefit-cost ratio of 1.05. In that year (1981), all treatments suffered a loss during the second season due to severe drought. But the leucaena treatment suffered only 6 ~ loss as compared to leucaena-nitrogen or leucaena-herbicide which suffered over 20 ~o loss each and compared to nitrogen or herbicide each of which had a loss of 60~o. In 1982, however, the treatment of leucaena-nitrogen-herbicide in absolute terms gave the highest net return of $1108/ha, followed by the treatment of herbicide-nitrogen at $992/ha, then the treatment of leucaena-herbicide at $765/ha. But the treatments of herbicide-nitrogen and herbicide alone gave highest marginal rates of return, being respectively 3.9 and 2-6 per additional unit cost. Considering the benefit-cost ratio, again the treatment of herbicide-nitrogen gave the highest ratio of 1.76, followed by that of leucaena-nitrogen-herbicide, then that of herbicide alone which was 1.59 and 1.51. The leucaena treatment gave a negative marginal rate of return of 0.21 units per additional unit cost per hectare based on maize and cowpea crops, but for maize alone it yielded a relatively higher marginal rate of return of 1.58 per unit additional cost. When costs of fertilizers are calculated at subsidized prices, the combination of herbicides-nitrogen gives the highest marginal rate of
256
Dezi S. N~ambeki
return of 10 per additional unit cost and benefit-cost ratio of 2, followed by nitrogen at 8 marginal rate of return per additional unit cost. Generally, the three economic indicators show that with a crop sequence of maize-maize, the treatment of leucaena gives the best economic returns, followed by herbicide-nitrogen and leucaena-herbicide. But with a crop sequence of maize-cowpea, the treatment of herbicidenitrogen gives the best economic returns followed by leucaena-nitrogenherbicide, nitrogen and leucaena-herbicide, in that order. In all cases, the treatment of leucaena gives better economic returns than that of leucaena-nitrogen. Also, leucaena stands produce about 9 to 15-5 t/ha fresh weight of leucaena wood or 5 to 8.6 t/ha dry weight and about 6 to 12 t/ha fresh weight of leucaena tops for mulch equivalent to between 60 and 70 N kg/ha at 3.2 ~o dry leaf N content.
CONCLUSIONS From the results of the agro-economic experiments, four conclusions can be drawn: (a) The consistently statistically significant increases in maize yields by leucaena and the small negative interactions between leucaena and nitrogen from three successive seasons (Tables 2, 3 and 5) suggest that the maize-leucaena alley cropping system can give high maize yields without nitrogenous fertilizers. The use of nitrogen fertilizers (at full rate) with leucaena (even at subsidized prices) seems to be an economic waste, but results from elsewhere showed that, with this system~ maximum yields of maize can be obtained when the leucaena tops are supplemented with nitrogenous fertilizers (Kang et al., 1981b). (b) Although leucaena stands occupy about 20 ~0 of the land and the cutting and pruning of leucaena increases labour costs by about 52 )o, the economic contributions of leucaena are greater than those from leucaena-nitrogen, from herbicide-nitrogen or from herbicide (Tables 1 and 6). (c) The highest level of technological input, leucaena-nitrogenherbicide, gave on average the highest physical increase of 90 ~o on maize yields followed by leucaena-herbicide and leucaena alone with respectively 70 and 69~o increases on maize yields (Table 5), its economic contributions are not necessarily better than those of herbicide-nitrogen, or those of leucaena-herbicide (Table 6).
Alley cropping leucaena in southern Nigeria
257
(d) With a crop sequence of maize-maize, leucaena gave the best economic returns followed by herbicide-nitrogen and leucaena-herbicide. But with a crop sequence of maize--cowpea, herbicide-nitrogen gave the best economic returns followed by leucaena-herbicide. However, leucaena was observed to have depressing effects on cowpea yields, unlike the case with maize. This needs to be investigated further. In all cases, the leucaena treatment gave better economic contributions than leucaena-nitrogen plots. Alley cropping, therefore, appears to be a good land-conserving system; but with availability of subsidies on fertilizers and herbicides the system may become less attractive. Nevertheless, the questions of determining economic returns from leucaena alley cropping over long-term periods, the economic rates of supplementary nitrogeneous fertilizers and that of designing suitable equipment for cutting and pruning the leucaena to ease labour use need further investigation. REFERENCES Benneh, G, (1972). Systems of agriculture in tropical Africa. Econ. Geog., 48, 244-57. Cochran, W. G. & Cox, G. M. (1957). Experimental Designs, John Wiley and Sons, New York. Dijkman, M. J. (1950). Leucaena, a promising soil-erosion control plot. Econ. Bot., 4, 337-49. FAO (1977) Soils Bulletin, 40. China: Recycling of Organic Wastes in Agriculture. FAO, Rome. Friedman, M. & Savage, L. J. (1947). Planning experiments seeking maxima. In Techniques of Statistical Analysis. McGraw-Hill, New York. IITA Annual Reports (1974), (1980), (1981). International Institute of Tropical Agriculture, Ibadan, Nigeria. Kang, B. T., Wilson, G. F. & Sipkens, L. (1981a). Alley cropping maize (Zea mays L.) and leucaena (Leucaena leucocephala) in Southern Nigeria. Plant and Soil, 53, 165-79. Kang, B. T., Sipkens, L., Wilson, G. F. & Nangju, D. (1981b). Leucaena (Leueaena leucocephala (Lam) de Wit) prunings as nitrogen source for maize (Zea mays L.), Fertilizer Research, 2, 279-87. NAS (1980). Firewood Crops: Shrub and Tree Species for Energy Production. National Academy of Sciences, Washington, DC. Okigbo, B. N. (1974). Fitting research to farming systems. In Proc. Second Int. Seminar on Change in Agriculture, Reading, England. Okigbo, B. N. (1976). Role of legumes in small holdings of the humid tropics of Africa. In Proc. of a Workshop on Exploiting the Legume-Rhizobium
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Symbiosis in Tropical Agriculture. University of Hawaii, College of Tropical Agriculture. Misc. Publications 145. Okigbo, B. N. (1982). Impact of agricultural systems and rural development of Nigerian forests. In Agro-forestry in the African Humid Tropics, ed. L. H. Macdonald, the United NationsiUniversity, Tokyo, Japan. Ruthenberg, N. (1976). Farming Systems in the Tropics. Oxford University Press, London. Vergara, N. T. (1982). New Directions in Agroforestry: The Potential Legume Trees Improving Agroforestry in the Asia-Pacific Tropics. East-west Center and United Nations University, Honolulu, Hawaii. Wilson, G. F. & Kang, B. T. (1981). Developing stable and productive biological cropping systems for the humid tropics. In Biological Husbandry: A Scientific Approach to Organic Farming. ed. B. Stonehouse. Butterworth, London. Yates, F. (1937). The design and analysis of factorial experiments. Imp. Bur. Soil Sci. Tech. Comm., No. 35, Harpenden, England, p. 95.
Economic Evaluation of Alley Cropping Leucaena with Maize-Maize and Maize-Cowpea in Southern Nigeria Dezi S. N g a m b e k i International Institute of Tropical Agriculture, Ibadan, Nigeria S UMMA R Y Alley cropping is an aspect of agroforestry being developed for small farmers in the tropics. It consists of establishing fast-growing leguminous shrubs or tree species in rows, then controlling the shading from the trees during cropping by pruning the branches which can be used as mulch or green manure to benefit the companion crops planted between the alleys. This paper attempts to assess the economic implications on labour utilization for the management of the leucaena hedgerows, on crop yields and the overall benefits from alley cropping with leucaena. The results show that although the management of leucaena trees increases labour requirements by about 50 %, the system can sustain and increase maize yields by over 60 %, reduce the use of nitrogenous fertilizers and give an attractive net income and marginal rate of return per unit cost. It gave a reasonable benefit-cost ratio of 1.23 to 1"32 and looks promising, especially for maize production in tropical areas.
INTRODUCTION Alley cropping is a land-use system in which arable crops are grown in the spaces between established rows of leguminous shrubs or tree species. The tops or branches of the trees can be periodically pruned during cropping to prevent shading and to minimize tree--crop competition for moisture and nutrients (Kang et al., 1981a). The prunings can be left on the soil surface as mulch or incorporated in the soil as green manure for the companion crops. Some agronomic research on alley cropping leucaena with maize has 243 Agricultural Systems 0308-521X/85/$03"30 ~c~Elsevier Applied Science Publishers Ltd, England, 1985. Printed in Great Britain
244
Dezi S. Ngarnbeki
shown that leucaena can contribute nitrogen of over 200 kg/ha/year and increase significantly the yields of the associated maize crop (IITA, 1980, 1981; Kang et al. 1981b). The alley cropping concept is an adaptation and a refinement of some forms of agroforestry being commonly practised by small farmers in Africa and Asia (Wilson & Kang, 1981; Kang et al., 1981a; Vergara, 1982), because some farmers in the tropics recognize the need to use certain plant species to maintain the soil fertility of their land. For example, in certain parts of Nigeria, farmers retain woody species such as Acioa baterii, Anthonata macrophylla and Glyricidia sepium after land clearing and encourage them in the bush fallow (Benneh, 1972; Okigbo, 1976). The Chinese use leguminous crops such as Sesbania cannabina, Astragalus sinicus and Vicia faba in their green manuring national programme in four different ways. Green manure crops are: (a) sown and ploughed under in the same field, (b) harvested and incorporated in other fields, (c) cut, mixed with grasses and mud and put in pits in corners of fields for compost making or (d) interplanted with summer rice crops (FAO, 1977). With increasing population pressure, frequent and extensive forest clearing for wood, cultivation, grazing and other human activities, the traditional fallow periods in the humid tropics have become progressively shorter, thus making their primary function of soil fertility restoration less effective, causing soil nutrient depletion and poor crop yields (Okigbo, 1974, 1982; Ruthenberg, 1976). Leucaena leucocephala is a fast-growing tree species and has a range of varieties that are either tall and slender (20 m) or are bushy (5 m) with deep roots of 2 to 5 m (Dijkman, 1950). Leucaena can fit a wide range of environments ranging from semi-arid with low rainfall to forest with high rainfall, heavy clay and alkaline soils. It has the ability to restore woody bushes in derived grassland (NAS, 1980). Once the leucaena is established in hedgerows, it has several advantages: for example the leucaena hedgerows can (a) help to maintain soil fertility which will allow continuous cultivation as they fix atmospheric nitrogen, (b) recycle leached nutrients from the subsoils, (c) protect against soil erosion, (d) provide an inexpensive source' of stakes to support yam vines, provide fuel, wood, fodder and (e) it is sometimes used for human food. Under these circumstances, the alley cropping system would seem attractive for farmers, especially in tropical Africa. It is therefore important to examine the economic implications regarding the amount of
Alley cropping leucaena in southern Nigeria
245
land occupied by leucaena stands, the extra demand for labour needed for cutting and pruning leucaena during the cropping season vis-gt-vis the question of profitability from continuous cultivation under alley cropping. OBJECTIVES A series of agro-economic experiments were carried out at the International Institute of Tropical Agriculture (IITA) in South Western Nigeria, on alley cropping leucaena with maize followed by maize in 1981 and with maize followed by cowpea in 1982, with the following objectives: (a) to monitor labour and other inputs, (b) to assess the effect of alley cropping with leucaena on maize and cowpea yields, and (c) to determine the economic viability of the maize and/or cowpea-leucaena alley cropping system as compared to that of herbicide and nitrogen application. METHODOLOGY To assess whether leucaena is compatible with nitrogen and herbicides, a 2 x 2 x 2 factorial design was used comprising leucaena and herbicides at two levels each. A piece of land of about 0.23 ha, which had been left under fallow in 1980, was planted to maize followed by maize in 1981 and the maize followed by cowpea in 1982. The trial had 4 replicates along the contours with each of the replicates subdivided into 8 treatments of 6 by 10metres, with the leucaena plots in a replicate already established. Leucaena, herbicides, leucaena-herbicides and a control were the main plot-randomized treatments in maize. Using split-plots, nitrogen treatment at 80 kg/ha was superimposed on these. The rainfall in South West Nigeria varies between 1250 and 1500 mm per year. The rainfall pattern is bimodal with peaks in May and August/September. According to the moisture cycle in this area, the first rains are expected by the third week of March, stabilizing around midApril. Then moisture usually cuts off in late July and re-stabilizes in the third week of August, cutting off again by mid-November. Critical periods for planting and harvesting of first-season crops are mid-April and the second week of August, respectively, and the planting of the second-season crop should not be later than last week of August.
246
Dezi S. Ngambeki
In the leucaena plots, leucaena trees were cut in April 1981, prunings left on the plots as mulch and the stems removed. During the cropping seasons at planting, weeding and flowering, leucaena tops were pruned, weighed and returned as mulch to the crop. Maize was planted at a spacing of 75 by 25 cm, cowpea at 60 by 25 cm, and weeding was done two weeks after planting. The herbicide plots were sprayed with paraquat at 3 litres/ha before planting and atrazine at 2.51itres/ha after planting for maize, and paraquat and dual at 2.5 litres/ha for cowpea. The cowpea crop received four insecticide applications to control thrips, aphids, maruca and pod bugs. The plots were planted to maize or cowpeas without tillage and were top-dressed with P and K fertilizers at 60 kg/ha and 30 kg/ha respectively for maize only. To obtain realistic labour input data, casual workers with some farming experience were hired on a daily task work basis. This resulted in more efficient labour inputs than with regular workers. Leucaena stands occupy 20 to 26 ~o of the land, which is regarded as a cost. Data on all inputs and crop yields based on whole plot areas were carefully recorded. For analysis of variance used in this paper to separate the main effect of each factor and the interaction effects between factors is as follows. If we designate the treatments thus: A =leucaena, B = herbicide, C = nitrogen, A B = leucaena-herbicide, A C = leucaenanitrogen and A B C = leucaena-herbicide-nitrogen, then the main effect of A is defined as: A = ¼ ( a b e ) - ( b e ) + ( a b ) - ( b ) + ( a c ) - (c) + (a) -
(1)
and the interaction of A with B is measured thus: A B = ¼(abe) - ( b e ) - ( a c ) + (c) + ( a b ) - ( b ) - (a) +
(1)
(Cochran & Cox, 1957). Other types of analyses used include plant tissue of maize ear leaf for nitrogen content and input-output budgeting to determine various economic indicators. RESULTS A N D DISCUSSION
Labour utilization in alley cropping with ieucaena Cutting leucaena, including shredding the leaflets, at about 15 000 trees/ha took 185 man-hours/ha or 30.8 man-days/ha (6 man-hours being equal to
Alley cropping leucaena in southern Nigeria
247
one man-day) in 1981 when the plots had been put under fallow during the previous year. The pruning of leucaena tops took 145.9 man-hours/ha or 24.23 man-days/ha for first season and 113-89 man-hours/ha or 19 mandays/ha for second season 1981. In first season 1982, cutting leucaena regrowth took 16-46 man-days/ha and two prunings took respectively 14-6 and 7.5 man-days/ha, making a total of 38.56 man-days/ha for the management of leucaena for that cropping season. In the second season of 1~82, cutting leucaena regrowth took 16.2 man-days/ha and two prunings took respectively 7.5 and 6.9 man-days/ha or a total of 30.6 man-days/ha for management of leucaena in second season. Considering the labour inputs for various treatments in the agroeconomic experiments on alley cropping leucaena with maize or cowpeas, the leucaena treatment doubled the labour inputs in 1981 firstseason maize, but increased them by 25 ~o (164 man-hours/ha) in 1981 second-season maize and 37 ~o (148 man-hours/ha) in 1982 first-season maize as compared to those of the control. The leucaena-nitrogen treatment which took the highest amount of labour, took (in manhours/ha) 921 and 895 in 1981 first- and second-season maize, and 565 in 1982 first-season maize compared to 424, 652 and 400 man-hours/ha used in the control plots for the respective seasons. Thus, labour inputs were increased by 117, 37 and 41 ~o in the respective seasons. The herbicide treatments, however, reduced the labour inputs by about 30 ~o per season. Table 1 shows average labour inputs per season by treatments for the production of maize or cowpeas. On average, the maize crop leucaena treatment increased labour inputs by 52 ~o, leucaena-nitrogen by 61 ~o, leucaena-herbicide by 31 ~o and leucaena-nitrogen-herbicide by 40 ~o. In comparison, herbicide reduced labour input by 35~o and herbicide-nitrogen reduced it by 26 ~o. With the cowpea crop, leucaena treatment increased labour inputs by 28 ~o and herbicide reduced them by 27~o. The main and interaction effects of leucaena, herbicides and nitrogen on crop yields
Table 2 shows the analysis of variance of treatments on maize and cowpea yields in 1981 and 1982. The treatments of nitrogen and leucaena had significant effects on both maize ear leaf nitrogen and maize yields at the 1 ~ level. The herbicide treatment had significant effect at the 1 ~o level on maize ear leaf
Dezi S. Ngambeki
248
TABLE 1 Average L a b o u r I n p u t s per Season by T r e a t m e n t s for Maize or C o w p e a (IITA, 1981/82)
Labour input Jor maize Manhours~ha
Increase over control Manhours/ha
Control Nitrogen Herbicide Herbicide-nitrogen Leucaena L e u c a e n a nitrogen L e u c a e n a herbicide Leucaena-nitrogen herbicide
492 538 319 365 751 794 644
-46 - 173 - 127 259 302 152
691
199
Labour input Jor cow,peas Manhours/ha
"o
9.3 35 - 26 52 61 31
Increase over control Matthours~ha
442 . . . . 321 - 121 . . . . . 565 123 505
63
"o
-27 . 28 14
40
nitrogen in 1982 and at the 5 °..o level on maize yield in the second season of 1981 and first season of 1982. The interaction effects between herbicide-nitrogen on maize yield were only significant at the 5 °.o level in first season 1982 and those between leucaena-herbicide only significant at the 1 '~o level in first season 1981. But the interaction effects between leucaena-nitrogen and those between leucaena-herbicide nitrogen tended not to be significant. For the cowpea crop, only the herbicide treatment had significant effect. Table 3 shows the main effects and interaction of the various treatments in 1981 and 1982. Calculations of maize effects and interactions were based on a statistical analysis of a 2 x 2 x 2 factorial experiment (Yates, 1937; Friedman & Savage, 1947: Cochran & Cox, 1957). The analysis shows that leucaena had additive main effects of about 1.6 t/ha maize grain yields and 30 to 60",, maize ear leaf nitrogen which were significant at the 1".o level and greater than those of nitrogen and herbicide in the two seasons of 1981 and in the 1982 first season. Nitrogen had additive main effects of about 0.8 t/ha on maize yields and 25 to 34 ° o of maize ear leaf N. They were also statistically significant except in the 1981 second season when they were insignificant. However, the herbicide treatment tended to have negative main effects on maize yields, except in
31
Total
** F ratio significant at 1 °.o. * F ratio significant at 5 °/ o .
3 1 1 1 1 1 1 1 21
Replication s Nitrogen Herbicide Herbicide n i t r o g e n Leucaena Leucaena-nitrogen Leucaena-herbicide Leucaena herbicide-nitrogen Error
Source o f variation
Tre~tmen t
0.33 9.04** 0.36 1.61 16,62"* 0-03 0.25 0-08 -
lst-season maize ear l e a r N ','o 0.67 0.36 0"71 0.42 8.45** 1.7 7.34"* 0.43
lst-season maize yield
1981
2.86 7.83** 7.34* 3.34 74.12"* 0.003 1.92 0.25
2nd-season maize yield
F ratio
--
0.94 14.56"* 20'41 ** 5.53* 55.78** 0.26 1.97 0.48 --
lst-season maize ear leaf N °,o
--
0.18 15.49"* 5" 11" 2.53 162.82"* 3.41 31.84"* 2.60 --
lst-season maize yield
1982
--
0.25 -0.24
8.60 * -14.04"*
2nd-season cowpea yield
TABLE 2 Analysis o f V a r i a n c e o f T r e a t m e n t s o n M a i z e a n d C o w p e a Yield in a n Alley C r o p p i n g E x p e r i m e n t ( I I T A , 1981; 1982)
t,~
~ ~.
~.
5"
5'
TABLE 3
0.25** -0.15 0" 17 0.64** 0.03 - 0"07 0.04
lst-season maize ear leaJ N ~o 807 1 279 - 215 1 760** - 303 - 629* 151
1st-season maize yield kg/ha
1981
240** - 142" - 1 319 1 610"* 70 - 717 - 149
2nd-season maize yield kg/ha 0-34** -0.15'* 0"08" 0.28** - 0.02 0"05 0.03
1st-season maize ear leaf N%
Main effects and interactions
729.57** 485* 340.6 1 183.37"* - 172.69 289"61 ** 150.8
1st-season maize yield kg/ha
1982
18.66 --
-140-09"* -- 19-03
2nd-season cowpea yield kg/ha
** F r a t i o significant at 1 ~o. * F r a t i o significant at 5 %, b u t t h e a c t u a l F r a t i o statistics a r e p r e s e n t e d in T a b l e 2. t T h e statistical a n a l y s i s u s e d a 3 x 2 f a c t o r i a l e x p e r i m e n t a n d figures in t h e table i n d i c a t e a d d i t i v e r e s p o n s e s r e s u l t i n g f r o m e i t h e r a single f a c t o r or c o m b i n a t i o n o f f a c t o r s in a t r e a t m e n t .
Nitrogen Herbicide Herbicide nitrogen Leucaena Leucaena-nitrogen Leucaena herbicide Leucaena-nitrogen herbicide
Treatment
T h e M a i n Effects a n d I n t e r a c t i o n s t o f T r e a t m e n t s o n M a i z e a n d C o w p e a Y i e l d s in a n A l l e y C r o p p i n g E x p e r i m e n t ( I I T A , 1981 ; 1982)
4.
e~
4.
251
Alley cropping leucaena in southern Nigeria TABLE 4
Nitrogen Content of Maize Ear Leaf from First-Season Maize Leucaena Alley Cropping (IITA, 1981; 1982) Treatment
Maize ear leaf % N 1981
1982
Control Nitrogen Herbicide Herbicide-nitrogen Leucaena Leucaena-nitrogen Leucaena-herbicide Leucaena-nitrogen-herbicide
2.11 2.36 1-96 2'48 2.74 2.97 2.31 3'03
2.67 2.97 2.41 2.82 2.95 3-16 2-74 3.16
Stand. dev. LSD
0.11 0.45
0.31 0.27
the 1982 first season when its effects were positive and significant at the 5 ~o level. The interaction effects between leucaena and nitrogen on maize ear leaf nitrogen and grain yield both tended to be negative but insignificant, reducing maize yield by 0.2 to 0.3 t/ha. The interaction effects between leucaena and herbicide on maize, were negative in 1981 but positive and significant in the 1982 first season. Whereas the interaction effects between leucaena, nitrogen and herbicide on both maize ear leaf nitrogen and grain yield, were mostly positive but insignificant except in 1981 when they gave negative though insignificant effects on maize yields. Maize ear leaf content for first season both in 1981 and 1982 (Table 4) suggests that the herbicides plots had less nitrogen uptake. While the leucaena treatment had a main effect of over 20 ~o on ear leaf nitrogen content, suggesting a more efficient uptake of N, there was a negative interaction between leucaena and herbicide in 1981, thus suggesting that herbicide application tends to depress N status in maize ear leaf. The negative interaction between leucaena and nitrogen, though not significant, and the significant negative interaction between leucaena and herbicides in 1981, suggest that applications of herbicides, together with a certain level of nitrogen to maize-leucaena alley cropping, reduces the effects of leucaena on maize grain yield, thus constituting an economic waste of resources.
TABLE
5
744.46 761.00
* 1981 second-season crop was badly hit by drought. t Hand-weeded and no fertilizers. ++ Hand-weeded.
211.50 575.07
Stand. dev. LSD
758 998 616 1 049 2486 2 496 1 685 2 153 662.78 564.71
2 159 2 872 1 929 3 021 3 141 3 206 3 660 4708 151.08 174.85
745 -576 -730
623
1st-season 2nd-season maize cowpeas kg/ha
1st-season 2nd-season* maize maize kg/ha
1 957 2 749 3 094 3 342 3 789 3 627 3 358 3 192
1982
1981
Controlt Nitrogen+'t" Herbicide Herbicide nitrogen Leucaenat Leucaena-nitrogent+ Leucaena-herbicide Leucaena nitrogen herbicide
Treatment
752 453 1 123 1 407 1 358 1 451 1 892
Maize kg/ha
36 22 45 68 66 70 90
°o
-47 -107 -
122
Cowpeas kg/ha
Average increases/decreases in yield
Maize and Cowpea Yield Response to Treatment in the Alley Cropping Experiment (IITA, 1981; 1982)
-
17.17
7.54
19.58
I
O, '"0 t~
e~
t'J
Alley cropping leucaena in southern Nigeria
253
It therefore appears that the negative interaction between leucaena and nitrogen on maize crop yield is due to the fact that application of the nitrogen supplied by leucaena leaflets increases the level of soil nitrogen content beyond the optimal level, thus reaching a point where any additional nitrogen brings about diminishing returns in the response of the maize crop yield to total soil nitrogen. As for the tendency to a negative effect between leucaena and herbicides, it appears that atrazine in particular depresses the growth of leucaena shoots, thus reducing the amount of leucaena prunings for mulch and nitrogen suppliable by it. In contrast with maize, herbicide was the only treatment that had statistically significant additive main effects on cowpea yields (Table 3). The main effect of leucaena treatment on cowpea yields was negative but insignificant, while the interaction effects between leucaena and herbicide on cowpea yield were not significant. Both the negative increase caused by leucaena treatment on cowpea yields (Table 5) and the negative main effect of leucaena on cowpea yields (Table 3) suggest that a leucaena alley cropping system alone does not benefit the cowpea crop as much as it does the maize crop, probably due to shading effects of leucaena shoots on cowpea and/or the additional nitrogen supplied by leucaena, especially considering that the interaction effect between leucaena and herbicides on cowpea is less than the main effects of herbicides on cowpea. Table 5 shows maize and cowpea yield response to treatment in an alley cropping experiment. The leucaena treatment increased maize grain yields by 95 ~o (1832 kg/ha) to 45 ~o (984 kg/ha) in the first seasons of 1981 and 1982 respectively. Leucaena-nitrogen increased maize yields by o~J ''/ /o (1670kg/ha) to 48~o (1048kg/ha), leucaena-herbicide by 70~o (1401kg/la) to 69°//o (1501kg/ha) and leucaena-nitrogen-herbicide increased them by 63 ~o 0235 kg/ha) to 118 ~o (2549 kg/ha) as compared to maize yields of 1957 and 2159 kg/ha obtained from the control plots in the respective seasons. The low values of LSD indicate that the means of the various treatments are statistically different. Using an average of three seasons for maize and one season for cowpeas, the leucaena treatment gave an average increase for maize yields of 68 ~o (1407 kg/ha), leucaena-nitrogen 66 ~o (1358 kg/ha), leucaenaherbicide 70~o (1451 kg/ha) and leucaena-nitrogen-herbicide 90~0 (1892 kg/ha). As for the cowpea crop, the treatment of herbicide and leucaena-herbicide respectively gave yields of 745 and 730 kg/ha which is an increase of 19.58 and 17.17% as compared to cowpea yields of
480 146 496 130 139 -58
Herbicide
Herbicide nitrogen
Leucaena
Leucaena-nitrogen
Leucaena herbicide
Leucaena nitrogen-herbicide
loss
1.97
1.56
2.33
loss
0-97
1.07
1.05
1-32
1-1
1-18
-0.79
Marginal Benefit rate o[ cost return/ ratio/ ha ha
1 108
765
302
396
992
650
491 669
Net returns US$/ha
1.30
0.43
-0.23
-0.21
10.0
2-23
8-60
subsidized
1.69 (2.90) 2-60 (1-25) 3.90 (3-10) -0.21 (1.58) 0.34 (1-16) 0.63 (2.81) 1.01 (2.80)
1.76
1.49
1.29
1-31
2.04
1.65
1.50 1.72
1.59
1.44
1.17
1.23
1.76
1.51
1.39 1.49
unsubsidized
Benefit cost ratio~ha
unsubsidized subsidized
Marginal rate* of return/ha
1982 maize cowpea
* Figures in parentheses represent marginal rate of return from 1982 first-season maize alone. In 1981/82 farmers in Nigeria received 75 "o subsidy on fertilizers and the price was 13-5 US$/50 kg of nitrogenous fertilizers.
- 438 371
Net returns US$/ha
1981 maize maize
Control Nitrogen
Treatment
TABLE 6 The Economic Contribution of Various Treatments in Agro-economic Alley Cropping Experiments (IITA, 1981; 1982)
4,
Alley cropping leucaena in southern Nigeria
255
623 kg/ha obtained from the control plots. But the leucaena treatment by itself lowered cowpea yields by 7.54 ~ (47 kg/ha). The economic contributions of leucaena vis-it-vis those of herbicide and nitrogen Three economic indicators, namely net return/ha, marginal rate of return and benefit-cost ratio (Table 6), were calculated to determine the economic contributions of each treatment for 1981 and 1982. In all the analyses for 1981, the leucaena treatment gave highest economic returns. Leucaena plots gave a net return of $496 (US)/ha, equivalent to a marginal rate of return of 2.33 per ha per additional unit cost and a benefit-cost ratio of 1.32. This was followed by the herbicide, which gave a net return of $480 ha, equivalent to a benefit-cost ratio of 1.18, then leucaena-herbicide which gave a net return of $139/ha, equivalent to a marginal rate of return of 1.97 per ha per additional unit cost and a benefit-cost ratio of 1.07. The leucaena-nitrogen treatment gave net returns of $130/ha, equivalent to a marginal rate of return of 1.56 per unit additional cost and a benefit-cost ratio of 1.05. In that year (1981), all treatments suffered a loss during the second season due to severe drought. But the leucaena treatment suffered only 6 ~ loss as compared to leucaena-nitrogen or leucaena-herbicide which suffered over 20 ~o loss each and compared to nitrogen or herbicide each of which had a loss of 60~o. In 1982, however, the treatment of leucaena-nitrogen-herbicide in absolute terms gave the highest net return of $1108/ha, followed by the treatment of herbicide-nitrogen at $992/ha, then the treatment of leucaena-herbicide at $765/ha. But the treatments of herbicide-nitrogen and herbicide alone gave highest marginal rates of return, being respectively 3.9 and 2-6 per additional unit cost. Considering the benefit-cost ratio, again the treatment of herbicide-nitrogen gave the highest ratio of 1.76, followed by that of leucaena-nitrogen-herbicide, then that of herbicide alone which was 1.59 and 1.51. The leucaena treatment gave a negative marginal rate of return of 0.21 units per additional unit cost per hectare based on maize and cowpea crops, but for maize alone it yielded a relatively higher marginal rate of return of 1.58 per unit additional cost. When costs of fertilizers are calculated at subsidized prices, the combination of herbicides-nitrogen gives the highest marginal rate of
256
Dezi S. N~ambeki
return of 10 per additional unit cost and benefit-cost ratio of 2, followed by nitrogen at 8 marginal rate of return per additional unit cost. Generally, the three economic indicators show that with a crop sequence of maize-maize, the treatment of leucaena gives the best economic returns, followed by herbicide-nitrogen and leucaena-herbicide. But with a crop sequence of maize-cowpea, the treatment of herbicidenitrogen gives the best economic returns followed by leucaena-nitrogenherbicide, nitrogen and leucaena-herbicide, in that order. In all cases, the treatment of leucaena gives better economic returns than that of leucaena-nitrogen. Also, leucaena stands produce about 9 to 15-5 t/ha fresh weight of leucaena wood or 5 to 8.6 t/ha dry weight and about 6 to 12 t/ha fresh weight of leucaena tops for mulch equivalent to between 60 and 70 N kg/ha at 3.2 ~o dry leaf N content.
CONCLUSIONS From the results of the agro-economic experiments, four conclusions can be drawn: (a) The consistently statistically significant increases in maize yields by leucaena and the small negative interactions between leucaena and nitrogen from three successive seasons (Tables 2, 3 and 5) suggest that the maize-leucaena alley cropping system can give high maize yields without nitrogenous fertilizers. The use of nitrogen fertilizers (at full rate) with leucaena (even at subsidized prices) seems to be an economic waste, but results from elsewhere showed that, with this system~ maximum yields of maize can be obtained when the leucaena tops are supplemented with nitrogenous fertilizers (Kang et al., 1981b). (b) Although leucaena stands occupy about 20 ~0 of the land and the cutting and pruning of leucaena increases labour costs by about 52 )o, the economic contributions of leucaena are greater than those from leucaena-nitrogen, from herbicide-nitrogen or from herbicide (Tables 1 and 6). (c) The highest level of technological input, leucaena-nitrogenherbicide, gave on average the highest physical increase of 90 ~o on maize yields followed by leucaena-herbicide and leucaena alone with respectively 70 and 69~o increases on maize yields (Table 5), its economic contributions are not necessarily better than those of herbicide-nitrogen, or those of leucaena-herbicide (Table 6).
Alley cropping leucaena in southern Nigeria
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(d) With a crop sequence of maize-maize, leucaena gave the best economic returns followed by herbicide-nitrogen and leucaena-herbicide. But with a crop sequence of maize--cowpea, herbicide-nitrogen gave the best economic returns followed by leucaena-herbicide. However, leucaena was observed to have depressing effects on cowpea yields, unlike the case with maize. This needs to be investigated further. In all cases, the leucaena treatment gave better economic contributions than leucaena-nitrogen plots. Alley cropping, therefore, appears to be a good land-conserving system; but with availability of subsidies on fertilizers and herbicides the system may become less attractive. Nevertheless, the questions of determining economic returns from leucaena alley cropping over long-term periods, the economic rates of supplementary nitrogeneous fertilizers and that of designing suitable equipment for cutting and pruning the leucaena to ease labour use need further investigation. REFERENCES Benneh, G, (1972). Systems of agriculture in tropical Africa. Econ. Geog., 48, 244-57. Cochran, W. G. & Cox, G. M. (1957). Experimental Designs, John Wiley and Sons, New York. Dijkman, M. J. (1950). Leucaena, a promising soil-erosion control plot. Econ. Bot., 4, 337-49. FAO (1977) Soils Bulletin, 40. China: Recycling of Organic Wastes in Agriculture. FAO, Rome. Friedman, M. & Savage, L. J. (1947). Planning experiments seeking maxima. In Techniques of Statistical Analysis. McGraw-Hill, New York. IITA Annual Reports (1974), (1980), (1981). International Institute of Tropical Agriculture, Ibadan, Nigeria. Kang, B. T., Wilson, G. F. & Sipkens, L. (1981a). Alley cropping maize (Zea mays L.) and leucaena (Leucaena leucocephala) in Southern Nigeria. Plant and Soil, 53, 165-79. Kang, B. T., Sipkens, L., Wilson, G. F. & Nangju, D. (1981b). Leucaena (Leueaena leucocephala (Lam) de Wit) prunings as nitrogen source for maize (Zea mays L.), Fertilizer Research, 2, 279-87. NAS (1980). Firewood Crops: Shrub and Tree Species for Energy Production. National Academy of Sciences, Washington, DC. Okigbo, B. N. (1974). Fitting research to farming systems. In Proc. Second Int. Seminar on Change in Agriculture, Reading, England. Okigbo, B. N. (1976). Role of legumes in small holdings of the humid tropics of Africa. In Proc. of a Workshop on Exploiting the Legume-Rhizobium
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Symbiosis in Tropical Agriculture. University of Hawaii, College of Tropical Agriculture. Misc. Publications 145. Okigbo, B. N. (1982). Impact of agricultural systems and rural development of Nigerian forests. In Agro-forestry in the African Humid Tropics, ed. L. H. Macdonald, the United NationsiUniversity, Tokyo, Japan. Ruthenberg, N. (1976). Farming Systems in the Tropics. Oxford University Press, London. Vergara, N. T. (1982). New Directions in Agroforestry: The Potential Legume Trees Improving Agroforestry in the Asia-Pacific Tropics. East-west Center and United Nations University, Honolulu, Hawaii. Wilson, G. F. & Kang, B. T. (1981). Developing stable and productive biological cropping systems for the humid tropics. In Biological Husbandry: A Scientific Approach to Organic Farming. ed. B. Stonehouse. Butterworth, London. Yates, F. (1937). The design and analysis of factorial experiments. Imp. Bur. Soil Sci. Tech. Comm., No. 35, Harpenden, England, p. 95.