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Published online 5 June 2006
Published in Agron J 98:883-889 (2006)
DOI: 10.2134/agronj2005.0025
© 2006 American Society of Agronomy
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Production Papers

Cover Cropping and Nutrient Management Strategies for Maize Production in Western Africa

J. M. Sogbedjia, H. M. van Esb,* and K. L. Agbekoa

a Univ. of Lome, Ecole Superieure d'Agronomie, Lome, Togo
b Dep. of Crop and Soil Sciences, Cornell Univ., Ithaca, NY 14853

* Corresponding author (hmv1{at}cornell.edu)

Received for publication January 25, 2005.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
Introduction of cover cropping systems may be important to a stable food supply in sub-Saharan Africa. We examined the effects of three cropping systems in a 2-yr, four growing season study in Togo: continuous maize (Zea mays L.), maize–mucuna [Mucuna pruriens (L.) D.C.], and maize–pigeon pea (Cajanus cajan L.). Mucuna and pigeon pea were grown in 1- or 2-yr cycles, and three N and two P fertilizer rates were factorially applied on maize. Use of mucuna and pigeon pea after maize in the first year reduced N and P fertilizer needs in the subsequent year. Cover crops increased maize grain yield by 37.5 and 32.1%, respectively, in the second year. Two-year cumulative economic returns on maize production were optimal when cover crops were grown every other year (every fourth season), compared to continuous maize or annual cover crops. The April 2002 to December 2003 soil N budgets showed a gain of N (>400 kg ha–1) under all cropping systems. Initial soil nitrate (NO3)–N was reduced by 57.8% under the continuous maize system, but increased by 39 and 3.6% under the mucuna-based and pigeon pea–based systems, respectively. Low (<20 kg ha–1) N losses occurred during the fallow period. Phosphorus losses occurred for all periods, but a mucuna-based cropping system has potential for soil P replenishment. The relay of a mucuna cover crop into maize in one out of 2 yr was most economical and improved soil N and P status without commercial fertilizers.

Abbreviations: MaMaMaMa, four seasons of continuous maize • MaMuMaMa, one season of maize followed by seasons of mucuna, maize, and maize • MaMuMaMu, one season of maize followed by seasons of mucuna, maize, and mucuna • MaPpMaMa, one season of maize followed by seasons of pigeon pea, maize, and maize • MaPpMaPp, one season of maize followed by seasons of pigeon pea, maize, and pigeon pea


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
DECLINING SOIL FERTILITY in sub-Saharan Africa has been documented by several studies (Stoorvogel etal., 1993; Smaling, 1993; Poss et al., 1997), and has occurred because traditional shifting cultivation has disappeared in most areas due to land pressure from increasing population and competing land-use demands. In the coastal region of West Africa, the Ferralsols on which maize, the primary staple food crop, is grown are fragile and need to support a dense population of >220 inhabitants km–2 (Poss et al., 1997; Manyong et al., 1999). The demand for high productivity on these soils has increased the need for replenishment of nutrients. Under the socio–economic conditions in Africa, such systems must focus on the maximum use of organically-derived nutrients and the minimal use of costly purchased inputs (Smaling et al., 1992). In West Africa, cropping systems involving grain legumes such as cowpea [Vigna unguiculata (L.) Walp.], pigeon pea, soybean [Glycine max (L.) Merr.], and groundnut (Arachis hypogaea L.) in rotation with maize improved soil fertility and increased maize yields by about 50% (Hulugalle and Lal, 1986; IFDC, 1990, 1992, 1993). Improved soil fertility and maize yields have also been obtained with cropping systems that include annual nonfood grain legumes such as lablab (Lablab purpureus L.) and mucuna as cover crops in rotation or intercropped with maize (Sanginga et al., 1996; Galiba et al., 1998; Sedga and Toe, 1998; Manyong et al., 1999). However, such cropping systems imply a loss of grain production from the second annual growing season, and therefore require considerable maize yield increases for the first season. Short-duration, planted tree fallows, using fast growing legume species, have also been identified as a means of restoring soil fertility and increasing maize yield. Research efforts in Africa (IFDC, 1993; Barrios et al., 1997; Bashir et al., 1998) indicated that short-duration improved fallows with pigeon pea, leucaena [Leucaena leucocephala (Lam.) de Wit], sesbania (Sesbania sesban Merr.) etc., resulted in soil fertility improvement and increased maize yields.

Although organic agricultural technology may result in improvement of soil fertility and maize yield in sub-Saharan Africa, questions remain about the potential of the technology alone to sustain high maize yields (Place et al., 2003; Sanchez and Jawa, 2002; Carsky et al., 1999). Several other studies (Pieri, 1989; van Reuler and Prins, 1993; Adetunji, 1997) concluded that the combined application of mineral and organic fertilizers, together with methods to conserve organic matter may be the most promising strategies for improving soil fertility and sustaining maize yields. However, some key questions still remain regarding (i) the frequency of the use of cover crops to sustain high maize yields and (ii) the quantity and timing of supplemental fertilizer applications.

The sustainability of a cropping system is primarily a function of crop yield and the associated fertility status of the soil. The harvested produce is the major avenue of nutrient removal, particularly in annual crops (Nair, 1993). On the average, 1 ha of harvested maize removes 100 to 150 kg of the major nutrients N, P, and K (FAO, 1990). The dynamics of plant nutrient uptake is quite complex and a time lag exists between when nutrients are available and when plant roots absorb them, during which the nutrients are vulnerable to losses (Zhang et al., 1996). Nutrient loss potential is a function of nutrient type, soil type, weather conditions, and cropping system (Pieri, 1989; Christianson and Vlek, 1991; Alva and Wang, 1996; Sogbedji et al., 2000). Nitrogen and P behave quite differently in the soil environment, where N is biologically very dynamic and, after conversion to NO3, very mobile, while P may quickly become inaccessible to crops due to chemical precipitation. These nutrient dynamics are still poorly understood in complex cropping systems that include organic inputs.

The objectives of this research were (i) to determine the effects of three cropping systems including various organic and inorganic nutrient inputs on maize grain yield and the profitability of each system and (ii) to establish and compare N and P budgets under the three systems. The ultimate aim was to identify appropriate cropping systems that have the potential to sustain maize production and minimize nutrient depletion from soils in coastal West Africa.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
Experimental Site
The study was conducted at the University of Lomé Research Farm near Lomé, Togo (6°22' N, 1°13' E; altitude = 50 m). The soil type was a rhodic Ferralsol locally called "Terres de Barre" that developed from a continental deposit (Saragoni et al., 1991). This soil type covers part of the arable lands in Togo, Bénin, Ghana, and Nigeria (Louette, 1988; Raunet, 1973) and is commonly used for maize production in coastal western Africa. It is a well-drained soil, very low in organic matter (<10 g kg–1) and K (<0.2 cmol kg–1), and has total P contents ranging from 250 to 300 mg kg–1, cation exchange capacity of 3 to 4 meq kg–1, and pH of 5.2 to 6.8 (Raunet, 1973; Tossah, 2000). Sand content is approximately 800 g kg–1 at the 0- to 0.20-m depth, and decreases to <600 g kg–1 at the 0.50- to 1.20-m depth (Lamouroux, 1969). The experimental site has a slope of <1%. Annual precipitation typically ranges from 800 to 1100 mm and allows for two maize growing seasons, one from April to July and another from September to December. At the onset of this experiment, the site, which has usually been used by farmers for unfertilized continuous maize cropping, was under a 1-yr grass fallow.

Crop and Soil Management
A 2-yr period (four growing seasons, 2002–2003) split-plot experiment was established with three replicates (Fig. 1 ). Three cropping systems were the main plot effects and four fertilizer levels were at the subplot level. The site was manually plowed and 12 main plots (16 by 16 m) and 48 subplots (4 by 4 m) were laid out in a spatially-balanced complete block design (van Es and van Es, 1993). Spatially-balanced complete block (SBCB) designs are a model-based approach that guarantees that the experiment is insensitive to trends, spatial correlation, or periodicity in the research domain (van Es et al., 2004). It aims to equalize variances among treatment contrasts and allows for conventional statistical analysis methods. The cropping system scenarios include: (i) maize monoculture for four growing seasons (MaMaMaMa), (ii) relay (interseeding) of a mucuna crop into the first maize crop so that it grew from June to December for the first year; in the second year, the first season was grown to maize but the plots were divided into two subplots, one of which was grown to mucuna (relay of mucuna into maize) from June to December and the other to a second maize crop (MaMuMaMa and MaMuMaMu), and (iii) relay of a pigeon pea crop into the first maize crop so that it grew from June to April for the first year; in the second year, the first season was grown to maize but the plots were split into two subplots, one of which was grown to pigeon pea (relay of pigeon pea into maize) and the other to a second maize crop (MaPpMaMa and MaPpMaPp). The maize cowpea-based cropping system (Fig. 1) is not discussed in this paper because cowpea growth was hampered by pests during the period of study.


Figure 1
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  		Fig. 1. Plot layout and experimental design.

 
Fertilizer treatments were applied to subplots only when maize was grown in all three cropping systems. Four subplots were treated with combinations of three levels of N (0, 40, and 80 kg ha–1) and two levels of P (0 and 30 kg ha–1): N0–P0, N40–P0, N40–P30, and N80–P30. All maize plots were fertilized with 60 kg P ha–1. Fertilizer P and K rates were manually broadcast as phosphate (P2O5) and potash (K2O), respectively, at maize planting while N rates were manually point-placed as urea 3 wk after planting at approximately 8-cm depth. Maize (IKENNE, the most commonly used improved variety) was planted in April and harvested in July during the first growing season, and was planted in September and harvested in December during the second season at a density of 50 000 plants ha–1. The crop was manually weeded three times during each growing season. Pigeon pea and mucuna were planted at a density of 42 000 and 35 000 plants ha–1, respectively. Crop residues from pigeon pea (after grain harvesting) and mucuna fallow (after seed harvesting) were incorporated into the soil during land preparation for the subsequent maize crop.

Data Collection
At maize planting, initial soil NO3–N and labile (soluble) P contents were measured on each main plot from 12 composite soil samples at depth intervals of 0 to 30 and 30 to 60 cm using the standard methods of the International Institute for Tropical Agriculture (IITA, 1982). During each growing season, composite soil samples were collected monthly during the first year and twice during the second year of the study from each plot or subplot at the above depth intervals to monitor soil NO3–N and labile P contents. Mass of soil NO3–N and labile P was estimated from their soil concentrations (mg kg–1) multiplied by the approximate mass of the soil layer from which the samples were taken, and converted to kg ha–1 units. Eighteen undisturbed soil cores were collected at each depth interval from the site to determine soil bulk density. Mass of soil was then estimated from the mean bulk density.

Maize grain yield was determined under each cropping system scenario from two 6-m long rows of maize from the center of each plot or subplot that were harvested and adjusted to 14% moisture content. Maize N and P uptake was determined from samples of three randomly selected whole plants. Each was chopped, mixed, and oven-dried at 60°C to determine moisture content. The sample was then ground, and a subsample of the dry matter was analyzed for total Kjeldahl-N and P contents using the standard methods of the International Institute for Tropical Agriculture (IITA, 1982). Maize grain yield data were analyzed using the general linear mixed model with rep and rep*cropping system as random, and fertilizer level and cropping system as fixed effects. Significant effects were followed by multiple comparisons adjusted with a Bonferoni correction. The MIXED procedure in Statistical Analytical System (SAS Institute, 2004) was used to run the analysis.

Economic Analysis
The profitability of the MaMaMaMa, MaMuMaMa, and MaPpMaMa treatments was estimated through a partial budget analysis. Output consisted of the amount of cash corresponding to the maize grain yield for the four growing seasons, which was assumed to be sold at 100 F CFA (US$0.22) kg–1, the average sale price in the country. For continuous maize cropping, grain yield under the N80P30 fertilization was used, and average yield values for the four mineral fertilization treatments were used for the cropping systems involving mucuna and pigeon pea. The inputs consisted of the costs associated with each cropping system, including those for soil preparation, seed, crop planting and related tasks, fertilizer purchase and application, crop weeding and crop harvesting and associated tasks. Mucuna and pigeon pea grain yield sale values and harvesting costs were not included in the budget because mucuna grain is a nonfood product and has no sale value as seed at the farmers' level in the country. Pigeon pea grain is used as food mainly in rural areas, but its sale value is not well established. No weeding costs were associated with the mucuna and pigeon pea crops as they were relayed into maize crops and because of their competitive growth and ability to provide soil cover. Labor costs were assumed to be 900 FCFA (US$2.0) on average per person day, and fertilizer costs were based on prices used by the Direction Régionale de l'Agriculture, de l'Elevage et de la Pêche (personal communication, 2002). Estimates of labor for maize, mucuna, and pigeon pea crops in a growing season as defined in the MaMaMaMa, MaMuMaMa, and MaPpMaMa systems are presented in Table 1, and are based on labor records from the experiment.


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  		Table 1. Estimated labor associated with continuous maize, maize mucuna-based, and maize pigeon pea–based cropping systems.

 
Nitrogen and Phosphorus Budgets
Nitrogen and P budgets were estimated for the 0- to 60-cm soil layer for each plot during the periods April to December 2002 (from the beginning of the first growing season to the end of the second growing season of the first year), December 2002 to April 2003 (the nongrowing or fallow period of 2003), and April 2002 to December 2003 (from the beginning to the end of the four growing seasons). For each period, the inputs of the budget consisted of the soil profile mass NO3–N and labile P at the beginning of the period (initial nutrient content) and the applied fertilizer N and P. Outputs consisted of maize N and P uptake and the soil profile mass NO3–N and labile P at the end of the period (residual nutrient content). The difference between inputs and outputs may be attributed to the balance of denitrification (for N), leaching and runoff losses, immobilization or mineralization of soil N and P, and atmospheric deposition, as none of these were explicitly measured.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSION
 REFERENCES
 
Maize Grain Production
Maize grain yield was not responsive to cropping system and fertilization pattern in the first year of the study (Table 2). Grain yield from all cropping system scenarios ranged from 6.1 to 6.5 and 3.7 to 4.0 Mg ha–1 during the first and the second growing seasons, respectively. The yield depression in the second growing season presumably resulted from lower rainfall (154.1 mm) compared with the first growing season (529.6 mm), similar to previous research (DRA, 1985; Sogbedji, 1986). The limited yield response to N and P occurred primarily as a result of the high initial soil NO3–N content (36.8–46.1 kg ha–1) and labile P content (345.2–368.9 kg ha–1, Table 4). In addition, the lack of yield response suggests that mucuna and pigeon pea crops that were relayed 50 to 60 d after maize planting did not significantly reduce maize nutrient use and growth. Traoré et al. (1999) found that relay of mucuna into maize 30 d after maize planting resulted in maize yield depression due to competition, and suggested a longer time period between the planting time of the two crops.


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  		Table 2. Mean maize grain yields (Mg ha–1) for each growing season, year and the entire period of the experiment.

 

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  		Table 4. Budget of measured N and P inputs (initial soil and applied NO3–N and labile P) and outputs (Maize N and P uptake and residual NO3–N and labile P) for the 0- to 0.6-m soil layer.

 
In the second year, the effects of fertilizer and cropping system and their interaction were significant. During the first growing season under continuous maize (MaMaMaMa), grain yield was significantly lower under N0P0 fertilization compared with those for others (N40P0, N40P30 and N80P30, Table 2). The lack of response to P fertilization and the interaction between N and P presumably resulted from the high (typically 100–140 kg P ha–1) April 2003 residual soil P contents (Table 4). Except for the N0P0 fertilization level under MaMaMaMa, grain yield was similar for all fertilization levels under the three cropping systems (Table 2). This demonstrates that the interaction of fertilizer rate with cropping system was significant and that nutrient restitution to soil through incorporation of the cover crops prevented the need for additional fertilizer. During the second growing season of the second year, grain yields for the highest fertilization level (N80P30) under MaMaMaMa and all fertilization levels under MaMuMaMa and MaPpMaMa were similar (3.7–4.6 Mg ha–1), but higher than the three other fertilization levels (N0P0, N40P0 and N40P30, 2.5–2.8 Mg ha–1) under MaMaMaMa. This, again, indicates that the effects of fertilization level on grain yield varied with cropping system. In each of the two growing seasons of the second year of the study, maize grain yields were similar or slightly higher for MaMuMaMa and MaPpMaMa and lower for MaMaMaMa compared to those in the corresponding seasons of the first year (Table 2). These results indicate that MaMuMaMa and MaPpMaMa sustained higher maize yields at minimal mineral fertilizer rates.

In the first year of the study, two-season cumulative grain yields for MaMaMaMa were higher (9.8–10.5 Mg ha–1, Table 2) than those for MaMuMaMa and MaPpMaMa (6.2–6.5 Mg ha–1) because the latter did not allow for a second maize crop. In the second year, however, yearly cumulative grain yields were higher (10.4–11.4 Mg ha–1) for MaMuMaMa and MaPpMaMa than those for MaMaMaMa (7.0–9.6 Mg ha–1). Our total annual yield results in the second year agreed with those of Galiba et al. (1998) in that a mucuna cover crop may allow for similar or higher yearly maize grain yield even if it causes the loss of the second maize crop of the year. The magnitude of the yield increases in this study (37.5 and 32.1% on average for MaMuMaMa and MaPpMaMa, respectively) was higher than the 25% reported by Lamboni (2000), but lower than the more than 100% increase published by Oséi-Bonsu et al. (1995). In the second year, the lowest cumulative annual grain yields were observed under MaMuMaMu and MaPpMaPp (6.6–7.0 Mg ha–1).

The 2-yr cumulative grain yield data showed that the highest fertilization level (N80P30) under MaMaMaMa resulted in higher yield (20.1 Mg ha–1) than the N0P0 (16.8 Mg ha–1) and all fertilization levels under MaPpMaMa (16.7–17.2 Mg ha–1, Table 2). Except for the N80P30 under MaMaMaMa, all fertilization levels under MaMaMaMa, MaMuMaMa, and MaPpMaMa provided similar 2-yr cumulative grain yields (16.7–18.6 Mg ha–1). Only significant additional fertilizer allowed for higher yields (20.1 Mg ha–1 under N80P30) for MaMaMaMa. The MaMuMaMu and MaPpMaPp systems resulted in the lowest 2-yr cumulative grain yields (12.9–13.5 Mg ha–1), mainly due to a loss of the second maize crop in each year.

Partial Budget Analysis
Results of the budget of inputs (seasonal costs associated with maize or mucuna and pigeon pea production) and output (maize grain yield for the four growing seasons) are presented in Table 3. The output from MaMaMaMa with high fertilization level (N80P30) was 12.4 and 14.9% higher than those for MaMuMaMa and MaPpMaMa, respectively. However, the input (labor, seeds, and fertilizer total cost) associated with MaMaMaMa was 86.8 and 91.2% higher than those for MaMuMaMa and MaPpMaMa, respectively. The balance was positive in all cases, but was on a per hectare basis 0.3% (6243 F CFA = US$13.87) higher and 1.7% (30757 F CFA = US$68.34) lower for MaMuMaMa and MaPpMaMa, respectively, compared to that of MaMaMaMa with N80P30 mineral fertilization. Although the differences in the balance for the three systems appear insignificant for a 2-yr period, MaMuMaMa and MaPpMaMa may be superior to MaMaMaMa if other benefits such as soil improvement and higher grain yields from MaMuMaMa and MaPpMaMa are accounted for.


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  		Table 3. Partial budget analysis for continuous maize, maize mucuna-based and maize pigeon pea–based cropping systems.

 
Nitrogen and Phosphorus Budgets
Estimates of the inputs and outputs of the N and P budgets are presented in Table 4. For the period from April 2002 to December 2002, maize N uptake during the two growing seasons exceeded fertilizer N application in all cases, typically ranging from 300 to 480 kg N ha–1 for the continuous maize system, and 195 to 280 kg N ha–1 for mucuna and pigeon pea–based systems. The greater N uptake under MaMaMaMa over MaMuMaMa and MaPpMaMa resulted from the presence of two vs. one maize crop. Under each of the three systems maize N uptake increased from the lowest to the highest N treatment rates. The greater N uptake under the 40 and 80 kg N ha–1 rates compared to 0 kg N ha–1 while yields were similar (Table 2) suggests that luxury consumption of N occurred. Maize N uptake in 2002 exceeded soil residual inorganic N (April 2002) and fertilizer N application rates by 300 to 330 kg ha–1 in the MaMaMaMa cropping system and by 200 to 250 kg ha–1 in the MaMuMaMa and MaPpMaMa cropping systems (Table 4).

For the fallow period (December 2002–April 2003), the N budget values were generally positive (≤20 kg ha–1, Table 4) under all cropping systems, with small losses presumably due to immobilization. These results suggest that much of the residual N at the end of the second growing season (on average 75% for continuous maize and pigeon pea–based systems and 95% for mucuna-based system for this study) may be carried over to the next year. Low losses may be attributed to the fact that the December to April period is generally dry and no leaching or denitrification occurs.

For the 2-yr period, maize N uptake exceeded mineral N fertilizer applications and the budget was negative under the three cropping systems. This suggests that in all cases a gain of N occurred presumably through mineralization of soil N and atmospheric deposition. Nitrogen gains were on average lowest (441.5 kg N ha–1) for MaMaMaMa, intermediate (484.7 kg N ha–1) for MaPpMaMa, and highest (534.3 kg N ha–1) for MaMuMaMa, which demonstrates that the presence of the cover crops increased potentially mineralizable soil N levels. The initial (April 2002) and residual (December 2003) soil NO3–N data (Table 4) showed that on average 57.8% of the initial soil NO3–N was depleted under MaMaMaMa, but 39 and 3.6% of the initial soil NO3–N was built up under MaMuMaMa and MaPpMaMa, respectively. This suggests that these legume cover cropping systems are promising in maintaining maize cropping while improving soil N status.

For the April to December 2002 period budget, maize P uptake exceeded fertilizer P applications in all cases, typically ranging from 30 to 70 kg P ha–1, but the results were strongly influenced by the initial (April 2002) soil labile P levels. In April 2002, 368.9, 345.2, and 360.5 kg ha–1 of labile P were measured under MaMaMaMa, MaMuMaMa, and MaPpMaMa, respectively (Table 4). As a result, the budget was positive under the three cropping systems, indicating that much of the P could not be accounted for and a portion was lost through chemical precipitation and/or uptake by mucuna or pigeon pea crops. The losses were lowest under MaMaMaMa (between 40 and 70 kg P ha–1), primarily as evidenced by its high residual P levels, intermediate for MaMuMaMa (between 95.7 and 103.3 kg P ha–1) and highest under MaPpMaMa (between 160.2 and 183.2 kg P ha–1). The greater loss under pigeon pea over the mucuna-based system presumably resulted from the higher P retrieving ability of pigeon pea from soil.

During the December 2002 to April 2003 period the P budget was positive, indicating that some fraction of soil P was lost during the fallow period primarily through the process of chemical precipitation. The losses were MaMaMaMa > MaMuMaMa > MaPpMaMa, primarily as a result of the trends of the initial (December 2002) and residual (April 2003) soil labile P contents under the three systems (Table 4).

For the April 2002 to December 2003 period, fertilizer P application exceeded maize P uptake under MaMaMaMa, indicating that a portion (6.1% on average) of the applied P was not used by the crop. Under MaMuMaMa and MaPpMaMa on the other hand, maize P uptake exceeded fertilizer P applications by 31.4 and 24.3% on average, respectively, indicating higher P fertilizer-use efficiency. In addition, residual soil P content under MaMuMaMa was on average 50.1 and 52.5% higher than for MaMaMaMa and MaPpMaMa, respectively, suggesting that MaMuMaMa has a greater soil P replenishment potential. Although the budget was positive for all systems (Table 4), indicating P losses, the average losses were much lower (113.9 kg P ha–1) under the mucuna-based system compared with the 239.2 and 219.4 kg P ha–1 values for the continuous maize and pigeon pea–based systems, respectively.


   CONCLUSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
REFERENCES
 
Initial soil N and P contents masked the cropping system effects in the first year of this study. Relaying mucuna and pigeon pea into a maize crop does not cause maize grain yield depression if appropriate time period, typically 50 to 60 d, is allowed between maize and the legume crop planting. Cropping systems with relay of mucuna and pigeon pea into maize in one out of the 2 yr sustained higher maize yields and required minimal mineral fertilizer rates compared to the continuous maize system. Continuous maize system can yield higher maize grain when using high levels of fertilization, but is less profitable than the maize–mucuna system when mucuna is grown during the second growing season in alternate years. The annual relay of mucuna and pigeon pea into maize is not recommended because it results in low total annual maize grain yields. Continuous maize cropping system, even with high levels of mineral fertilization, has the potential to result in soil mining, but the maize mucuna and pigeon pea–based systems proved to be capable of improving soil N and P status, with a greater benefit from the mucuna-based system.


   ACKNOWLEDGMENTS
 
The authors acknowledge the Rockefeller Foundation and the International Foundation for Science for financially supporting this research work, and recognize the contributions of Robert Carsky from IITA (deceased), Kagnissa Atafei from the University of Lomé, and Marco Wopereis from IFDC-Africa Division to this research.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 





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