Evaluation of the Association and Rotation of Maize with Legumes, in Direct Sowing in the Democratic Republic of Congo ()
1. Introduction
Intercropping was defined as an agricultural practice of growing two or more crops in the same space at the same time. Increasing productivity per unit area can be an important reason for growing two or more crops together [1]. It can be seen as practices application of diversification, competition and facilitation of species in cropping systems [2]. Cereal-legume intercropping plays an important role in food production worldwide. Crop intercropping is commonly practiced because of various advantages such as greater yield stability [3] [4], when one crop fails, the other can still give a reasonable yield [5], a higher efficient land occupation, a high capacity for competition against weeds; legumes can cover their need for atmospheric nitrogen (N2) [6] and thus is less competitive for soil nitrogen [4] [7] [8] [9].
In the Democratic Republic of Congo, in general, and in the Province of Central Kongo in particular, the production of legume residues remains low as a result of the export of organic matter out of the field and the practice of waste incineration. According to [10], research that had been carried out for more than 30 years [11] [12] had shown the causes and factors of the physical and chemical degradation of new land; Their findings had suggested a number of locally capable methods of delaying degradation, limiting losses, and even restoring acceptable fertility potential. In the current cropping system, a crop rotation system with the integration of cover crops has also been proposed in addition to the combination of crops, In order to solve the problems of depletion of cultivated soil [13] [14]. Studies conducted in the world have shown that the direct seeding mulch-based cropping system (DMC) ensures a good productivity of the cultivated surfaces and gives many advantages in the soil management [15] [16] [17]. To be successful, these cropping systems must produce high biomass, particularly in the first years of direct seeding.
Although the effects of mulch on the soil are well known [18] [19], but with a low protection, one may wonder what the real impact of this technique on rainfed maize yield and on the evolution of long-term fertility in our fields. Information on the associations and rotations of the different varieties of maize and pulses is very poor and does not allow sufficient information on these crops.
This study aims to acquire knowledge on the response of maize crops in association and rotation with food legumes used as cover crops in order to determine the type of cover to be used in order to better evaluate their effects on maize yield.
2. Material and Method
2.1. Experimental Site, Description and Characterization of Soil
This study was conducted at the Mvuazi Research Station during the 2011-2012 cropping season. Mvuazi is in the Kongo Central province of DRC with longitude 14˚54'E, latitude 5˚21'S and altitude 470 m. The soil of Mvuazi belongs to the Sudano-Guinean climate zone of the AW4 type [20]. This soil is characterized by low organic matter content and low water holding capacity resulting in low nitrogen availability. This soil valley develops a humiferous horizon 15 - 25 cm thick, black (fresh) or brownish (dry) with a well-pronounced subangular or grumulous structure. And this horizon is often overhauled by crops.
Mean annual temperatures vary between 24˚C and 30˚C with rainfall ranging from 800 to 1200 mm. The climatic data recorded during the experimental period are presented in Figure 1.
In this study, soil samples were collected and were analyzed to determine the NPK content and pH. These analyzes were made at the laboratory of Crop Nutrition Laboratory Services on July 20, 2011, and gave as contents: 0.21% for nitrogen N, 14 ppm for phosphorus P, 105 ppm for potassium K and a pH 5.76. The selected chemical and physical parameters for soils at experimental site are presented in Table 1.
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Figure 1. Temperature variation and precipitation amount during the study period.
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Table 1. Selected chemical and physical parameters for soils at experimental site.
2.2. Experimental Design and Plant Material
The trial was conducted under the split-plot design with 4 replications and the main factor consisted to intercropping and rotation treatments and the second factor was maize variety. Eight maize varieties (Mudishi-1, Mudishi-3, 07 SADVE, 08 SADVE1, 09 SADVE-F2, ZM523, VP0538 and Samaru) From CIMMYT/IITA and INERA were sown at a spacing of 1 m × 0.25 m in sole crop and intercrop with a density of 80,000 plants∙ha−1, according to [21], in the main plots of 6 m × 4 m of sizes. Soybean (Vuangi variety) and Cowpea (Diamand variety) were simultaneously planted with maize, at a spacing of 0.33 m × 0.055 m in sole crop and intercrop with a density of 360,000 plants∙ha−1. The pure culture for each variety was used as a control treatment. At the end of the first season (2011-2012), all the plots were mown and the residue was used as mulch: corn only, corn + cowpea and corn + soybeans. At the beginning of the second season (2012), corn was planted on a 5 cm thick mulch [22], without till. So, the experiment was installed in the same plots with a weed mulch plots control.
The parameters observed for this experiment are: maize and legumes yield, number of plants per plot, marketable ears biomass of and unmarketable ears biomass for all maize varieties, edible seed biomass, inedible seed biomass, empty pod biomass for two legume species studied. All of these parameters were observed at the maturity of maize and legume varieties, harvest and post-harvest.
2.3. Statistical Analyzes
Data collected were submitted to analysis of variance following the linear model (aov(y~Trait sec*Trait princ + error (replication/Trait princ)) using agricolae package of R 3.1.3 and least significant difference (LSD) test at 5% probability level was used to compare the treatment means. An economic analysis was carried out to show the profitability of DMC systems.
3. Results and Discussion
3.1. Intercropping Effect on Number of Plants, Biomass and Maize Yield in First Season
The number of plants varied from 56.21 for the maize sole crop to 38.6 for intercrop with cowpea. The sole crops of Mudishi1, Mudishi 3 and Samaru proved to be more effective with more than 60 plants per plot. This analysis of variance revealed significant differences (p < 0.05) between treatments and varieties (Table 2).
As for the marketable biomass, the difference was significant (p < 0.05) between treatments, but highly significant among varieties (p < 0.001), a peculiarity for Mudishi-3 variety which produced more than 73% of marketable biomass in all treatments. For unmarketable biomass, the difference was not significant between treatments. More losses were observed in sole crop than in intercrop (Table 2).
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Table 2. Intercropping and sole crop effects on the different maize varieties for number of plants, marketable ears biomass, unmarketable ears biomass and yield in first season.
Signification statistique: 0 “***” 0.001 “**” 0.01 “*” 0.05 “†” 0.1 “ns” 1.
About grain yield, a significant difference was observed (p < 0.001) between treatments (Table 1). Sole crop was greater (2350.2 kg∙ha−1) than the respective yield in mixture: 1342.9 kg∙ha−1 for cowpea and 2081.9 kg.ha−1 for soybeans. Therefore, the highest maize yield was from sole crop of Samaru with 2849.44 kg∙ha−1. The performance results corroborate those of the number of plants and the biomass of the ears. These results was be similar that obtained by [23] in trials at the SUWAN farm in Thailand, where the yield of maize grown in sole crop was 31.9% higher than maize-soybean. A low density of plants per unit area leads to a decrease in yield [4] [24]. The rate of sowing of each crop in the combination is adjusted below its maximum rate to optimize plant density. If the maximum rate of each crop was used, the yield would not be good due to overpopulation. By reducing the rates of each seedling, the crops have a chance to produce well within intercropping [25]. The challenge is how much can be reduced seeding rates. According to [26] and [27], the spatial arrangement of maize and legumes (intercropping or maize cropping after legume harvesting) does not affect maize yield. A reasonable leaf area index (LAI) is essential to maintain high photosynthesis and yield [28]. Prasad and Brook [29] reported that the increase in corn plant density had a significant effect on LAI in corn-soya intercropping.
3.2. Intercropping Effect on Number of Plants, Biomass and Legumes Yield in First Season
Sole crop yield of soybean was higher (1802.23 kg∙ha−1) than that observed in intercrop with maize (809.31 kg∙ha−1) in general, with the association 08SADVE1-soya (932.37 kg∙ha−1) in particular. However, sole crop yield of cowpea produced less (17.82 kg∙ha−1) than the intercrop with maize (48.39 kg∙ha−1), although the highest yield was obtained in the intercrop with Samaru (96.14 kg∙ha−1). Variance analyzes of legume seed yield showed very significant differences (p < 0.01) between varieties and interactions, and highly significant differences (p < 0.001) between treatments (Table 2). This reduction in soybean and cowpea yields under intercropping could be due to interspecific competition between the intercrop components for water, light, air and nutrients, and also the aggressive effects maize (C4 species) on soybean and cowpea, a C3 species [30] [31]. According to Heibsch et al. [32], crops with C4 photosynthetic pathways have been known to be dominant when intercropped with C3 species like soybean and cowpea. The shading of legumes by the maize plants (taller) may also have contributed to the reduction of the yields of intercropped soybean and cowpea. Olufajo [33] and Matusso [34] reported that shading by the taller plants in mixture could reduce the photosynthetic rate of the lower growing plants and thereby reduce their yields. As for biomass, highly significant differences (p < 0.001) were observed between treatment for empty pods and edible seeds (Table 3). The cowpea monoculture yielded 5.5% compared to 4.41% in combination for edible seeds. The soybean monoculture yielded 47.44% edible seed biomass, compared to the association with 46.13%. Analysis of mean numbers of seedlings and inedible biomass showed no differences between treatments, varieties, and interactions (Table 3). The reduction of yield of the legumes components observed in this study was also reported by other researchers [35].
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Table 3. Effect of the combination of crops on the number of plants per plot and the biomass of legumes in the first season.
Signification statistique: 0 “***” 0.001 “**” 0.01 “*” 0.05 “†” 0.1 “ns” 1.
Matusso [34] reported that the reduction was mainly due to maize shading effects on soybean, which caused the legume component to allocate its photosynthates to vegetative growth and height increasing for competing with taller maize.
3.3. Mulch Effect on Yield, Number of Plants and Maize Biomass in Second Season
Mean for the number of plants varied between 58.12 (maize mulch + cowpea) and 60.09 (maize mulch), and for the biomass of salable spikes varied between 49.30 (maize + Cowpea mulch) and 50.77 (maize mulch). For example, maize yield were higher on maize + cowpea mulch (2974.82 kg∙ha−1) followed by maize mulch (2686.77 kg∙ha−1) and maize + soybean mulch (2624.50 kg∙ha−1). Analysis of the variance of all parameters showed no significant differences (p > 0.1) between varieties, treatments and interactions (Table 4). The observations from the present study indicated that crop rotation and residue management practices can affect maize performance significantly. Edmeades [36] reported similar results from multilocals field experiments in Ghana, which showed that in the
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Table 4. Mulch effects on different maize varieties for number of plant, marketable ears biomass, unmarketable ears biomass and yield in second season.
Signification statistique: 0 “***” 0.001 “**” 0.01 “*” 0.05 “†” 0.1 “ns” 1.
absence of fertilizer, maize yields following maize sole crop fell significantly, but that this yield drop could be completely compensated by fertilizers or by a cowpea crop. Cowpeas improve maize yield by the nitrogen they fix and by unspecified improvements in soil conditions. Higher yields under maize-legume rotation would have been expected as legumes are known to fix nitrogen, thereby improving the soil nitrogen economy and enhancing the growth of subsequent crops [37]. The differences in maize response to the different rotations could also be attributed to the differences in biomass additions to the soil. Increased residue returned to the soil generally led to increased yields, whereas complete residue removal was very detrimental to maize growth and yield [38].
3.4. Variation in Maize Yield in Intercropping and on Mulch
These variations are of the order of 14.32% on maize mulch in sole crop, 121.52% on maize + cowpea mulch and 26.06% on maize + soybean mulch. Maize was seeded on maize + cowpea mulch doubled, tripled or quadrupled its yield compared to those obtained in intercropping during the first season. Analysis of the variance on the mean variation in yield of maize in combination and on mulch revealed highly significant differences between varieties, treatments and interactions (p < 0.001) (Table 5). These strong variations would be due to the improvement of the fertility of the soil by the effect of crop rotation. Many studies have reported the highly beneficial effects of seed pulses on soil nitrogen content and cereal grain yields [39] [40]. CIPEA’s work in Mali showed that the introduction of cowpea into the rotation resulted in a 60% increase in millet grain yields compared with results obtained in the first year of cultivation [41]. This situation has already been reported by Hardter et al. [42], although the maize-cowpea crop had yields lower than in rotation, continuous sole crop have lower productivities. Carsky et al. [43] showed higher grain yield of cereal following legume than continuous cropping of cereal in the Nigerian savanna. The increases in the cereal yield were attributed to the biologically fixed N from the legumes. But for such a positive effect to occur, it is expected that the amount of fixed N returned by the legumes to the soil must be greater than the amount of soil N in the harvested grain [44] [45].
According to Bandyopadhyay and De [46], this soil fertility can be explained by residual effects on cereals succeeding legumes in the rotation and by the underground transfers of nutrients in the rhizosphere during intercropping. It appears that the use of the cropping system under cover crop (or mulch) increases the maize yield as demonstrated by Scopel [47]. It turned out that most varieties behaved in the same way in each of the treatments. The Mudishi1 variety increased its yield by more than 250% when it was planted on cowpea and maize mulch (Table 6). Compared to the results presented in intercropping system, the presence of the mulch significantly influenced the grain yield. This situation shows that even at low doses of mulch (5 cm of residue thickness), a considerable effect can be observed on the behavior of the plants. These results are similar to those reported by Van Asten et al. [22]. These results could be explained that sowing under cover crop (or mulch) improves the fertility of the cultivated soils and, in particular, Productivity of the cultivated areas. Mckenney et al. [48], Mary et al. [49], Abiven [50], Schroth et al. [51] showed increased nitrogen availability due to degradation and mineralization of legume mulch compared to bare soil.
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Table 5. Intercrops and mulches effects on performance in the first and second seasons.
Signification statistique: 0 “***” 0.001 “**” 0.01 “*” 0.05 “†” 0.1 “ns” 1.
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Table 6. Economic analysis of maize varieties in combination with legumes.
Signification statistique: 0 “***” 0.001 “**” 0.01 “*” 0.05 “†” 0.1 “ns” 1. Average procurement price per kg of maize = $0.67; cowpea = $1; soybean = $1.
An organic matter and minerals enrichment through residual recycling was studied by Owens and Edwards [52] and Uzoh et al. [53] on maize-soybean-cowpea rotation, highlighting the recycling of carbon and nitrogen through the production of Vegetable biomass of legume.
3.5. Economic Analysis of Maize Varieties in a Combination and Rotation System on Legume Mulch
The economic analysis of different crops indicated gains for maize-cowpea ($1088.43) and maize-soybean ($3554.62) intercrops, losses for maize sole crops except for 07SADVE and Samaru varieties for which we observed gains in order of $121.09 and $140.62 respectively. On the different intercropping systems, the maximum net return were $USD 3919.12 (Mudishi 3-soya) and minimum were $712.70 (VPO538-cowpea). The greatest cost/benefit ratio of the Mudishi 3-soybean intercrop (4.04) indicates the low investment cost in operating expenses, while highest deficit observed in Mudishi 1 variety sole crop ($713.82) showing the high investment cost in operating expenses. Analysis of the variance of gross return, benefit, and benefit/cost ratio in intercropping economic analysis revealed highly significant differences (p < 0.001) between treatments (Table 6).
Maize varieties with soybeans in intercropping system produced higher values gross return and net return than maize-cowpea associations and the different sole crop, probably due to yields obtained in each crops. The large benefit produced in the maize/soybean intercrop compared to other systems could probably be the result of the high yield and price of legumes compared to maize [27]. Similar observations were made by Egbe [54] in pigeon pea-sorghum and pigeon pea-maize, and Banik (1996) in wheat-gram, wheat-pea and wheat-lentil intercrops. Njoroge et al. [55] estimated the net profit of coffee associated with food products by subtracting all variable costs from gross profits. Similarly, Egbe [54] had estimated the total profit and the marginal benefit/cost ratio from investment on different farm inputs used in pigeon pea/sorghum intercropping system by computing returns per naira invested. In an innovative, improved intercropping system, named MBILI (kiswahili for ‘‘two’’, and an acronym for ‘‘Managing Beneficial Interactions in Legume Intercrops’’), also known as a two-by-two staggered arrangement [56], the MBILI system resulted in robust increases in crop yields and net benefits, in comparison with the conventional intercropping system. The MBILI system did not entail larger labour costs and Woomer [57] showed that the MBILI system was profitable across a wide range of smallholders’ croplands in western Kenya, and that, when combined with a fertilizer application at a modest rate; the benefit-cost ratio was higher relative to other recommended technologies in the area.
In contrast, analysis of the variance of gross return, benefit, and benefit/cost ratio in mulch crops system revealed no significant differences (p > 0.1) between varieties, treatments and interactions (Table 7). On the different mulch cropping systems, maximum net return were $USD 1234.03 (07SADVE-cowpea) with a cost/benefit ratio of 2.01 and the minimum benefits were $USD 268.95 (VPO538 sole crop).
Residue production by preceding crop is an important factor in defining the magnitude of rotation benefit conferred to subsequent crop [58]. This is because
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Table 7. Economic analysis of corn varieties on legume mulch.
Signification statistique: 0 “***” 0.001 “**” 0.01 “*” 0.05 “†” 0.1 “ns” 1. Average procurement price per kg of maize = $0.67; cowpea = $1; soybean = $1.
Legume crop residues contain organic N and other nutrients, which are released after decomposition by soil microbes for the subsequent crop through mineralization [59]. And the quality of residue is very important in determining mineralization and nutrient release and then yield. Some of the residue parameters include C/N ratio, nutrient content etc. Uzoh et al. [53] reported that maize residues contained more carbon and less nitrogen than legumes residues and mineralization and release of nutrients were higher in plots amended with legumes residue as velvet-bean.
4. Conclusion
This study was to acquire knowledge on the profitability and response of maize crop in intercrop and rotation with legumes based on DMC to determine the optimum combination of yield grain and total grain biomass. The residual effects of cowpea crops have been shown to have considerably increased maize yield. As for the production of pulses in combination with maize, soybeans were more efficient than cowpeas. All maize varieties each presented a combination that maximized productivity. The varieties 09SADVE F2, Mudishi1, Mudishi3, VPO538 and Zm523 have doubled, tripled or quadrupled their yields when rotated with cowpea. Maize sole crop, which produces poor mulch, resulted in low yields in the second season, resulting in losses of more than 5%. The high yields observed in this study resulted in significant benefits in increasing their ratios whether in combination or in rotation.
Acknowledgements
We would like to thank the staff of The National Institute of Study and Research Agronomy (INERA) and The International Institute of Tropical Agriculture (IITA) for this financial support.