Abstract
Soil fertility management of smallholder farms in the humid tropics is a major issue as a result of inherently low fertility with nitrogen being the most limiting plant nutrient. Use of grain legume fallows could improve soil quality through nitrogen fixation and ensure food and nutritional security in developing countries. This field trial was laid out in a Randomized Complete Block Design (RCBD) to evaluate the short-term benefits of grain legume fallows (common bean, groundnut, cowpea, and soybean) on soil fertility improvement and income generation in relation to a natural weed fallow system. The results showed that total soil nitrogen content ranged from 0.19–0.24%, and differed (P < 0.001) significantly with the highest in common bean plots as compared to the others. The soil organic carbon (SOC) content was highest in cowpea plots (3.36 %) and lowest in the natural weed fallow (2.77 %). However, the SOC were not significantly different among the fallow systems but were higher than the SOC of the soil before sowing (2.41 %). Grain yield ranged from 1.0–1.9 t/ha and differed (P < 0.001) significantly. The highest profitability of integrating grain legumes in farming systems was recorded in the groundnut fallow, followed by soybean, and bean. Cowpea generated a negative return, while the natural fallow system had no effect. Integrating grain legumes fallow into agricultural systems in the humid tropics enhance the value of the fallow lands and may serve as viable short-term economic incentives for smallholder farmers.
Keywords: Fallow systems, Grain legumes, Nitrogen, Organic carbon, Profitability, Smallholder farmers.
Received: 12 August 2019 / Revised: 16 September 2019 / Accepted: 18 October 2019/ Published: 22 November 2019
Contribution/ Originality
This study contributes to the existing literature that reports the benefits of grain legumes on soil fertility improvement and also showed that the integration of grain legume fallows into agricultural systems in the humid tropics generate income for smallholder farmers and could serve as motivation for their adoption.
1. INTRODUCTION
Soil fertility decline in the tropics constitutes one of the major crop production constraints that threaten food and nutrition security (Dikand Kadiata and Lumpungu, 2003; Ngosong et al., 2018) with nitrogen (N) as the most limiting plant nutrient (Massawe et al., 2016). Managing soil fertility on smallholder farms has become a major issue as a result of degradation (Fritzpatrick, 1986). This is attributed to inherently low fertility, which could decrease rapidly when natural forest or fallow lands are converted to agricultural systems (Serrao et al., 1979; Koutika et al., 2005). In the case of the humid tropics, this rapid decline of soil fertility is due among other factors to the low buffering capacity, low activity clay content and small nutrient reserves of most of the soils and their vulnerability to erosion and compaction (Koutika et al., 2005). To improve soil fertility and optimize crop productivity, farmers often apply different fertilizers (Nottidge et al., 2005; Saha et al., 2008; Hepperly et al., 2009) including higher amount of nitrogenous fertilizers (Ngosong et al., 2019). However, fertilizers are expensive and are not easily affordable by most farmers in developing countries (Ngwu, 2008). As a result, soil degradation processes have intensified with soil nutrient mining as the most common form of soil degradation (Vanlauwe et al., 2015). Farmers have however turned to other sustainable alternative soil fertility management strategies such as crop rotation, intercropping with legumes, and fallow systems to improve soil quality.
Traditionally, fields are left fallow for a number of years, so that the natural vegetation can regrow for soil fertility to be restored (Vanlauwe et al., 2015). But nowadays, natural fallow is no longer an option due to the increasing demand for arable land while the available land area has remained constant (Vanlauwe et al., 2015) (Koutika et al., 2005). Cultivation of grain legumes has always been a part of crop rotations or intercropping systems as they play an important role in sustainable farming (Reem, 2017). Legumes are considered as "soil building" crops as they improve soil quality through their beneficial effects on soil biological, chemical and physical properties (Anikwe et al., 2016). Legumes have high litter quality that decompose quickly and accelerate nutrient cycling. They fix atmospheric-Nitrogen through symbiosis, increase soil carbon content, and stimulate the productivity of the ensuing crops with positive impact on the environment through reduction in the use of N fertilizers and Nitrogen losses in agricultural fields (Anikwe et al., 2016; Meena and Lal, 2018). Therefore, legumes, either as monocrops or in a cropping sequence, have great potential to enhance soil functions capable of sustaining productivity in agricultural systems (Meena and Lal, 2018).
Grain legumes are also used as an option for improving the nutritional composition of foods in developing countries due to growing demands for healthy and nutritious food (Meena et al., 2015). In most of the developing countries, grain legumes are the major sources of protein and other essential minerals and amino acids for the poor sector of the population (Leterme and Carmenza, 2002). Hence grain legumes have huge ecological benefits as nitrogen suppliers to arable soils and their adoption in farming systems is widely recommended, especially for smallholder farming systems in Africa. These grain legume fallow systems have other benefits such as provision of food and income to smallholder farmers (Muoni et al., 2019). From 2013 - 2016 in the Southwest Region of Cameroon, grain yield ranged from 6.926 - 29.907 tons for groundnuts, 9.242 - 10.973 tons for common beans, 142.1 - 258 tons for soybean and 534.7 - 797 tons for cowpea. Though these figures show a rise in growing of grain legumes (especially groundnuts) in the study area, their production remain however low thus justifying the low adoption of grain legumes in the farming system as compared to other agro-ecological zones in Cameroon (Cameroon annual statistics, 2017 edition).
This study evaluated short-term benefits of grain legumes on soil fertility improvement and their associated economic returns. Therefore, we tested the hypothesis of differential improvement of total soil nitrogen and organic carbon contents under short-term grain legume fallows and the related grain yield and income as compared to natural weed fallow system.
2. MATERIALS AND METHODS
2.1. Site Location
This field experiment was conducted from April to September 2018 at the farm of the Institute of Agricultural Research for Development (IRAD) located at Ekona (its geographical coordinates are 4º14' 0" north, 9º20' 4" east ), in Muyuka subdivision of Fako Division, Southwest Region, Cameroon. Ekona is situated on the Northeastern slopes of Mount Cameroon at 450 meters above sea level (Price, 1994) with humid tropical climatic conditions. It has two distinct seasons; a long rainy season from mid-March to mid-November and a short four-months dry season expanding from mid-November to mid-March. The mean temperature ranges between 23.70ºC in the rainy season and 24.40ºC in the dry season, with high annual humidity of 76 - 90% (Etchu et al., 2012) and average annual rainfall of 2284 mm. These rich volcanic soils belong to the Ekona series which was formed on older mudflows and have a well-developed argillic horizon (FAO-UNDP/ONAREST, 1980; Nanganoa et al., 2019).
2.2. Experimental Setup
The experimental site (759 m2) was cleared with a cutlass and plots measuring 5 x 4 m each were demarcated in a randomized complete block design (RCBD) with 5 treatments (1 natural-weed fallow and 4 different grain legume fallow systems) and 4 replications, giving a total of 20 experimental plots. The experimental plots (raised beds, 30 cm high) were prepared manually using conventional tillage with hoes. 1 m alleys separated the experimental plots and blocks, while 2 m buffer strips surrounded the entire experimental field. The fallow systems included natural-weed fallow (control), groundnut (cultivar ‘JL24’), common bean (cultivar ‘DOR-701’), soybean (cultivar ‘TGX14F’) and cowpea (cultivar ‘FEKEM’). Three seeds of each legume (obtained from the Institute of Agricultural Research for Development) were sown per hole on the 30th of April 2018. Groundnut, common bean, and soybean were planted at 40 x 20 cm spacing and cowpea at 75 x 25 cm spacing based on local recommendations. The seedlings were later thinned to two plants per stand at two weeks after planting (WAP), giving a plant population density of 250,000 plants per ha for groundnut, common bean, and soybean, and a plant population density of 106,667 plants per ha for cowpea. Weeds were controlled manually by weeding at 2, 4 and 6 WAP and each plot was fertilized with 0.1 kg N-P-K (20:10:10) fertilizer (Yara, Cameroon) at 2 WAP. Systemic and contact insecticide Paraster 40EC (Active ingredient: 20gr/l imidachlopride + 20gr/l lambdacyhalothrine) was applied at the rate of 40 ml in 16L knapsack sprayer at 2, 4, and 6 WAP to control insect pests. The soil moisture during the entire experimental period depended on the local rainfall regime.
2.3. Data Collection
2.3.1. Soil Physicochemical Properties
After clearing the experimental site in April 2018, pre-planting soil samples were randomly collected in a zigzag pattern at 0–20 cm depth with an auger and thoroughly mixed to form a composite sample. The soil was air-dried and sieved through 2 mm screen to remove stones and plant debris and then analysed as described below. The physicochemical properties of the pre-planting soil of the experimental site are presented in Table 1. On the 8th of September 2018, post-harvest soil samples were randomly collected (0 – 20 cm depth) from each fallow replicate and bulked to form a composite sample, giving a total of 20 composite post experimental soil samples. The soils were also air-dried and sieved through 2 mm screen. Soil pH was determined in the ratio of 1:2.5 soil/water suspensions using a digital pH meter. Available phosphorus was determined by Bray II method (Van Reeuwijk, 1992) organic carbon by the Walkley and Black wet digestion method (Kalra and Maynard, 1991) and total nitrogen by the Kjeldahl digestion method (Bremner and Mulvaney, 1982). Soil exchangeable bases were determined after extraction with 1 N ammonium acetate (NH4OAc) solution at pH 7. Calcium and magnesium were analysed with atomic absorption spectrometer (AAS), while sodium and potassium by flame photometer (Rowell, 1994). Exchangeable acidity was determined by 1N KCl extraction method, and titrated with 0.01 N NaOH using phenolphthalein indicators (Van Reeuwijk, 1992). The Effective Cation Exchange Capacity (ECEC) was determined by sum of exchangeable bases and acidity, while particle size distribution was determined by the pipette method and the textural class assigned according to the USDA textural triangle (Van Reeuwijk, 1992).
2.3.2. Senescent Leaf Nutrients Analysis
Senescent leaves were also harvested from each legume fallow replicate on the 8th of September 2018. At this stage of the legume crop maturity, most leaves had fallen and decomposing. The legume leaf samples were oven-dried at 80 °C and their nutrient (N, P, K, Ca, and Mg) contents analysed after extraction by dry ashing – dilute HNO3 method (Jones, 2001) following the elemental procedures described above for soil nutrient analyses. Several specimens of major plants in the natural weed fallow including foliage, stem, flowers and roots were taken to the laboratory, examined and identified by visible characteristics vis-à-vis photographs and written description of similar-looking weeds in the laboratory manual.
2.3.3. Grain Yield
The plants were harvested in August at physiological maturity when about 85% of the pods had turned brown. The entire plants from a net plot area of 1m x 1m in the center row were harvested by uprooting the whole plant. The pods were manually separated from the plants, sun-dried for one week, threshed and weighed to obtain the yield.
2.3.4. Economic Benefits of Legume Fallow
Cost-benefit analysis was performed to determine the economic benefit of the grain legume fallow systems in relation to natural fallow, and the profitability index was employed to estimate the land value during fallow. Gross income was determined in relation to the average local market prices (local currency – FCFA) recorded from two towns (Buea and Douala) in Cameroon, and reported in US dollars. The average market price per kg was $1.2 (588 FCFA) for groundnut, $1.2 (575 FCFA) for bean, $1.1 (550 FCFA) for soybean, and $0.8 (400 FCFA) for cowpea. Expenses for all farm related activities (e.g. clearing, weeding, raised beds, planting, thinning, fertilization, pest control, harvesting, drying, and shelling) were calculated for each fallow system to determine the total production cost. The net income and profitability index (benefit-cost ratio) were calculated as: Where NI = net income, GI = gross income from total sales, PC = total production cost, and BCR = benefit-cost ratio with values greater than one (>1) indicating profitability of the fallow system.
2.4. Statistical Analyses
All data sets were analyzed using the statistical software package STATISTICA 13.2 for Windows (StatSoft, 2016). One-way analysis of variance (ANOVA) was used to compare the effects of different fallow systems on soil physicochemical properties, senescent leaf nutrients, grain yields and economic benefits. Significant data means were compared by post hoc Tukey’s HSD test (P < 0.05).
3. RESULTS AND DISCUSSION
3.1. Major Plants in the Natural Weed Fallow
Weeds in this study were defined as all “invading species” that were present in the fallow plot, that were not specifically planted (Ngobo et al., 2004). These weeds were identified and grouped into invasive (Alternanthera brasiliana, Chromolaena odorata, Sorghum halepense, Macroptilium atropurpureum and Pueraria phaseoloides)and non-invasive plants (Nutsedges, Phyllanthus spp, Galinsoga parviflora, Desmodium spp.). Among the weeds, Chromolaena odorata, Macroptilium atropurpureum, Pueraria phaseoloides and Desmodium spp have been reported to possibly improve soil nitrogen (Ojeniyi et al., 2012; Franke et al., 2018).
3.2. Effect of Fallow Systems on Soil Physicochemical Properties
The textural class of the pre-planting soil of the experimental site is clay and was moderately acidic Table 1. According to Landon (1991) the soil organic carbon (2.41 %) and total nitrogen (0.18 %) were low, exchangeable potassium (0.85 cmol/kg) was high while available phosphorus (62 mg/kg) was very high.
Table-1. Pre-planting soil analysis.
| Soil parameters | Value |
| Particle size distribution | |
| Clay % | 60.06 |
| Silt % | 29.58 |
| Sand % | 10.37 |
| Soil texture | Clay |
| Moist. (105°c) % | 13.6 |
| Org. Carb. % | 2.41 |
| Total N% | 0.18 |
| C/N | 12.68 |
| Av. P (mg/kg) | 62 |
| pH(H20) 1:2.5 | 5.63 |
| pH(KCl) 1:2.5 | 4.93 |
| Na+ (cmol/kg) | 0.19 |
| K+ (cmol/kg) | 0.85 |
| Mg2+ (cmol/kg) | 4.69 |
| Ca2+ (cmol/kg) | 9.01 |
| Al +H (cmol/Kg) | 0.08 |
| ECEC (cmol/kg) | 14.82 |
Moist. – Moisture content, Org. Carb. – Organic carbon, Av. P – available phosphorus, ECEC – effective cation exchange capacity.
The different fallow systems had varying effects on the soil physicochemical properties. The most notable effect was the total nitrogen content that ranged from 0.19–0.24%, and differed (P < 0.001) significantly with the highest in common bean fallow system followed by cowpea, groundnuts, soybean and natural weed fallow Figure 1. Grain legumes improved soil physicochemical properties by fixing the atmospheric nitrogen converting it from an inert form to forms that are available for plants uptake. This biological fixed nitrogen can replace nitrogen fertilization wholly or in part (Dwivedi et al., 2015). Although the natural weed fallow system recorded the lowest total soil nitrogen, it was not significantly different from the groundnut, soybean and cowpea fallow systems. This might be as a result of Chromolaena odorata, Macroptilium atropurpureum, Pueraria phaseoloides and Desmodium spp. in the weed fallow plots. Their influence on total soil nitrogen contents had been widely reported (Fageria et al., 2005; Ojeniyi et al., 2012; Franke et al., 2018). Muhr et al. (1999) reported that green manure legumes such as Pueraria phaseoloides can contribute large quantities of residual biomass and nitrogen (N) to soil and Fening et al. (2009) showed that Chromolaena odorata contains appreciable quantities of plant nutrients. Hence, the natural weed fallow system that comprises some soil N-improving weeds would be a recommended sustainable soil regeneration option when only soil fertility improvement benefits are considered.
Figure-1. Effect of five fallow systems (Natural, soybean, groundnut, cowpea, and bean) on total soil nitrogen content (% ± SD) after nineteen weeks of crop cultivation. Data with different letters are significantly different(P < 0.05).
The soil organic carbon (SOC) content was highest in cowpea (3.36 %) and lowest in the natural weed fallow (2.77 %). However, the SOC were not significantly different among the fallow systems Table 2 but were higher than the SOC of the pre-planting soil 2.41 %, Table 1. This can be attributed to the conversion of biomass to organic matter, which increased the levels of SOC (Ojeniyi et al., 2012). Legume cultivation has also been associated with organic carbon dynamics in the rhizosphere (Hajduk et al., 2015; Bichel et al., 2016). The quantity of organic carbon buildup depends on the soil, climatic condition, and species of grain legume (Gogoi et al., 2018) and is essential to all soil processes that impact crop production and the environment. The C/N ratio ranged from 12.7–16.1, and differed (P < 0.05) significantly across fallow systems with the lowest in common bean as compared to the other treatments Table 2. The C/N ratios indicate the rate of decomposition of organic matter and these results in the mineralization or immobilization of soil nitrogen (Swangjang, 2015). Usually it is accepted that the optimal C/N ratio is around 10 while ratio over 30 is considered extremely high and can result in some soil nitrogen deficiencies. C/N ratio in cultivated lands commonly ranges from 8 – 15 (Brady and Wail, 2010).
Though not statistically significant, soil available phosphorus in the groundnut plot was higher (16.12 mg/kg) compared to the other fallow systems Table 2. However, available phosphorus in all the post-harvest soils was lower compared to soil phosphorus before sowing 62 mg/kg, Table 1. Among many environmental factors (temperature, water content, pH and N concentration), biological nitrogen fixation process in legume crops is also affected by plant nutritional status such as phosphorus level which controls nodule growth and nitrogenase activity (Liu et al., 2011; Sallaku et al., 2016) thus a high use of phosphorus was expected. The other soil parameters did not differ significantly across fallow systems. However potassium and calcium was highest in the natural weed fallow and magnesium in cowpea Table 2.
Table-2. Effect of five different fallow systems (Natural, soybean, groundnut, cowpea, and common bean) on soil physicochemical properties (Mean ± SD) after nineteen weeks of crop cultivation.
| Soil physicochemical parameters | Fallow systems |
||||
Natural |
Soybean |
Groundnut |
Cowpea |
Common bean |
|
| pH | 5.53 ± 0.54a |
4.99 ± 0.22a |
4.98 ± 0.25a |
5.24 ± 0.29a |
4.97 ± 0.16a |
| Organic carbon (%) | 2.77 ± 0.12a |
3.04 ± 0.28a |
3.27 ± 0.37a |
3.36 ± 0.23a |
3.08 ± 0.24a |
| Carbon/Nitrogen | 14.45 ± 0.99a |
15.17 ± 1.59a |
16.10 ± 1.62a |
15.66 ± 1.57a |
12.68 ± 0.69b |
| Phosphorus (mg/kg) | 14.12 ± 5.77a |
12.50 ± 1.90a |
16.12 ± 2.62a |
13.82 ± 2.36a |
14.26 ± 2.31a |
| Sodium (cmol/kg) | 0.21 ± 0.00a |
0.21 ± 0.01ab |
0.20 ± 0.01ab |
0.20 ± 0.01ab |
0.18 ± 0.02b |
| Potassium (cmol/kg) | 0.94 ± 0.04a |
0.69 ± 0.24a |
0.77 ± 0.14a |
0.75 ± 0.22a |
0.70 ± 0.05a |
| Calcium (cmol/kg) | 9.99 ± 0.06a |
9.52 ± 0.99a |
9.50 ± 0.79a |
9.61 ± 0.64a |
8.99 ± 1.18a |
| Magnessium (cmol/kg) | 3.40 ± 0.08a |
3.38 ± 0.23a |
3.28 ± 0.11a |
3.51 ± 0.33a |
3.28 ± 0.26a |
| Acidity (cmol/kg) | 0.06 ± 0.02a |
0.05 ± 0.01a |
0.05 ± 0.01a |
0.06 ± 0.01a |
0.07 ± 0.02a |
| ECEC (cmol/kg) | 14.60 ± 0.17a |
13.85 ± 1.28a |
13.79 ± 0.90a |
14.12 ± 0.36a |
13.20 ± 1.42a |
3.3. Nutrient Accumulation in Senescent Leaf Biomass
The release of nutrients, from litters and crop residues, is an important potential source of nutrients for subsequent crops (Blair and Boland, 1978; McLaughlin et al., 1988; Nanganoa and Njukeng, 2018). So the nutrient contents of the senescent leaves of different grain legume fallow systems were studied. The results showed that leaf nitrogen ranged from 1.5–2.6 % and differed (P < 0.01) significantly with the highest in groundnut, followed by cowpea, soybean, and common bean Figure 2. Flint and Roberts (1988) and Clark et al. (1998) also showed that the amount of nitrogen in legume crops varies among species. Leaf phosphorus varied from 0.25–0.41 % and differed (P < 0.001) significantly, with the highest in common bean, followed by cowpea, groundnut and soybean Table 3. Leaf potassium ranged from 5.0–8.4 % and also differed (P < 0.001) significantly, with the highest in common bean, followed by cowpea, groundnut, and soybean Table 3. The calcium content varied between 0.28–0.48 % and differed (P < 0.001) significantly, with the highest in soybean, followed by cowpea, common bean and groundnut Table 3. Magnesium content ranged from 0.16–0.20 % that differed (P < 0.01) significantly, with the highest in soybean, followed by cowpea, groundnut and common bean Table 3. Much of the soil nutrients including the Nitrogen (N) fixed by the legume crops is removed at harvest in seed and thus the net residual contributions of fixed N and other nutrients in the senescent leaves to agricultural soils after the harvest of legumes plays an important role in enriching the soil nutrients pool for the ensuing crops grown after the legumes.
Figure-2. Total leaf nitrogen content (% ± SD) of four different fallow legumes (Soybean, groundnut, cowpea, and bean) after nineteen weeks of cultivation. Data with different letters are significantly different(P < 0.05).
Table-3. Elemental composition (Mean ± SD) of four different fallow legumes leaves (Soybean, groundnut, cowpea, and bean) after nineteen weeks.
Fallow systems |
Phosphorus (%) |
Potassium (%) |
Calcium (%) |
Magnesium (%) |
Soybean |
0.25 ± 0.01c |
5.02 ± 0.30b |
0.48 ± 0.02a |
0.20 ± 0.01a |
Groundnut |
0.34 ± 0.02b |
6.77 ± 0.69a |
0.28 ± 0.01b |
0.16 ± 0.01b |
Cowpea |
0.39 ± 0.01a |
7.9 ± 0.35a |
0.33 ± 0.05b |
0.18 ± 0.02ab |
Bean |
0.41 ± 0.02a |
8.35 ± 0.93a |
0.28 ± 0.03b |
0.16 ± 0.01b |
Values within columns with different letters are significantly different (P < 0.05).
3.4. Yield and Profitability of Grain Legume Fallow Systems
The different legume fallow systems had varying grain yield and economic benefits that increased the economic value of the fallow land. Grain yield ranged from 1.0–1.9 t/ha that differed (P < 0.001) significantly, with the highest in groundnut (1.9 t/ha), followed by soybean (1.6 t/ha), common bean (1.3 t/ha), and cowpea (1.0 t/ha) Figure 3. The grain yields of the legumes used in this study are within the yield range of legumes grown as sole crops elsewhere in Sub Saharan Africa (Franke et al., 2018). Considering the fact that farm management practices were the same for the four different grain legume fallow systems, yield variations between them is likely due to crop specific nutrient acquisition potentials and adaptation to environmental variables. This yield variation is reflected in the differential net income generated by the four grain legume fallow systems that differed (P < 0.001) significantly.
Figure-3. Yield (t ha-1 ± SD) of four different fallow grain legumes (Soybean, groundnut, cowpea, and bean). Data with different letters are significantly different(P < 0.05).
Accordingly, the highest profitability of integrating grain legumes in farming systems was recorded in the groundnut fallow, followed by soybean, and common bean, whereas cowpea generated a negative return, while the natural fallow system had no effect Table 4. The high profitability index recorded for groundnut fallow as compared to the other fallow systems justifies the dominance of groundnut cultivation in this study area (Cameroon’s Annual Statistics, 2017). The negative return for cowpea could be attributed to brown rust (Uromyces spp) disease observed in the cowpea plots. Sulphur and potassium carbonate usually used to manage the disease were not readily available in the local markets. However, despite the negative returns, smallholder farmers rely almost exclusively on family labour thus the grain produced is consumed by the households that produce it.
Although the green manure legumes in the weed fallow improved soil nitrogen and organic carbon as compared to soil before sowing, their adoption by farmers has remained limited. All efforts to promote them among farmers and evidence of their beneficial effects on soil fertility and cereal yields have been futile (Muhr et al., 1999; Carsky et al., 2001). This is likely related to a general reluctance of farmers to invest land, labour and seed in a technology that does not provide a quick economic return on investments (Schulz et al., 2001).
Table-4. Net income (Mean ± SD) and profitability of five different fallow systems (Natural, soybean, groundnut, cowpea, and common bean).
| Fallow systems | Net income ($/ha) |
Profitability index |
| Groundnut | 1401 ± 394a |
2.7 |
| Soybean | 923 ± 229ab |
2.1 |
| Bean | 657 ± 221b |
1.8 |
| Cowpea | −44 ± 40c |
0.9 |
| Natural | 0.0 ± 0.0d |
0.0 |
Values within columns with different letters are significantly different (P < 0.05).
4. CONCLUSION
The grain legume fallow systems enhanced the soil nitrogen and organic carbon contents while providing food and income for smallholder farmers as compared to the short natural weed fallow. The highest profitability index recorded for groundnut fallow justifies the dominance of groundnut cultivation in the study area, while the high value recorded for soybean and common bean fallows is indicative of the potential for adoption of these grain legumes in the local cropping systems. Therefore, besides the potential agronomic and environmental benefits of integrating grain legumes into fallow systems, income generation from the sale of grain legumes enhances the value of fallow lands and may serve as viable short-term economic incentive for the smallholder farmers.
| Funding: The study was supported by the Agriculture Investment and Market Development Project (PIDMA), Cameroon. |
| Competing Interests: The authors declare that they have no competing interests. |
| Acknowledgement: All authors contributed significantly to this study and are grateful to the Soil, Plant and Water Analysis Laboratory, Ekona Regional Centre, Institute of Agricultural Research for Development (IRAD) for providing the analytical facility. |
REFERENCES
Anikwe, M.A.N., J.C. Eze, C.G. Chikelu and E.E. Ikenganyia, 2016. Quantifying short-term effects of soil improving legumes on soil properties and carbon sequestration in a degraded Paleustult in Agbani, Enugu Southeast Nigeria. International Journal of Plant & Soil Science, 13(3): 1-9.Available at: https://doi.org/10.9734/ijpss/2016/30001.
Bichel, A., M. Oelbermann, P. Voroney and L. Echarte, 2016. Sequestration of native soil organic carbon and residue carbon in complex agroecosystems. Carbon Management, 7(5-6): 261-270.
Blair, G. and O. Boland, 1978. The release of phosphorus from plant material added to soil. Soil Research, 16(1): 101-111.Available at: https://doi.org/10.1071/sr9780101.
Brady, N.C. and R.R. Wail, 2010. Elements of the nature and properties of soils. Pearson Education, New Jersey: Prentice Hall. pp: 361 –395.
Bremner, J.M. and C.S. Mulvaney, 1982. Nitrogen-total. In: Methods of soil analysis. Part 2. Chemical and microbiological properties, Page, A. L., Miller, R. H. and Keeney, D. R. (Eds.), American Society of Agronomy, Madison, Wisconsin: Soil Science Society of America. pp: 595 –624.
Cameroon’s Annual Statistics, 2017. National institute of statistics. Available from http://www.statistics-cameroon.org/news.php?id=513 [Accessed 20th September 2019].
Carsky, R.J., M. Becker and S. Hauser, 2001. Mucuna cover crop fallow systems: Potential and limitations. Sustaining Soil Fertility in West Africa, 58: 111-135.Available at: https://doi.org/10.2136/sssaspecpub58.c6.
Clark, M.S., W.R. Horwath, C. Shennan and K.M. Scow, 1998. Changes in soil chemical properties resulting from organic and low-input farming practices. Agronomy Journal, 90(5): 662-671.Available at: https://doi.org/10.2134/agronj1998.00021962009000050016x.
Dikand Kadiata, B. and K. Lumpungu, 2003. Differential phosphorus uptake and use efficiency among selected nitrogen-fixing tree legumes over time. Journal of Plant Nutrition, 26(5): 1009-1022.Available at: https://doi.org/10.1081/pln-120020072.
Dwivedi, A., I. Dev, V. Kumar, R.S. Yadav, M. Yadav, D. Gupta, A. Singh and S. Tomar, 2015. Potential role of maize-legume intercropping systems to improve soil fertility status under smallholder farming systems for sustainable agriculture in India. International Journal of Life Sciences Biotechnology and Pharma Research, 4(3): 145-157.
Etchu, K., V. Ndzi, K. Ndamukong and B. Oben, 2012. Comparative performance of grasscutters (Thryonomys swinderianus) fed maize and rodent pellets as concentrate supplement under intensive management system in Cameroon. African Journal of Agricultural Research, 7(6): 883-891.Available at: https://doi.org/10.5897/ajar10.677.
Fageria, N., V. Baligar and B. Bailey, 2005. Role of cover crops in improving soil and row crop productivity. Communications in Soil Science and Plant Analysis, 36(19-20): 2733-2757.Available at: https://doi.org/10.1080/00103620500303939.
FAO-UNDP/ONAREST, 1980. Soils and soil fertility management of lands of the Ekona Banana Estate,” Technical Report no. 11, Ekona, Cameroon: Cameroon Development Corporation.
Fening, J.O., E. Yeboah, T. Adjei-Gyapong and E. Gaizie, 2009. On farm evaluation of the contribution of three green manures to maize yield in the semi-deciduous forest zone of Ghana. African Journal of Environmental Science and Technology, 3(9): 234–238.
Flint, M.L. and P.A. Roberts, 1988. Using crop diversity to manage pest problems: Some California examples. American Journal of Alternative Agriculture, 3(4): 163-167.Available at: https://doi.org/10.1017/s0889189300002447.
Franke, A., G. Van den Brand, B. Vanlauwe and K. Giller, 2018. Sustainable intensification through rotations with grain legumes in Sub-Saharan Africa: A review. Agriculture, Ecosystems & Environment, 261: 172-185.Available at: https://doi.org/10.1016/j.agee.2017.09.029.
Fritzpatrick, E.A., 1986. An introduction to soil science. 2nd ed. New York, USA: John Wiley and Sons Inc. pp: 255.
Gogoi, N., K.K. Baruah and R.S. Meena, 2018. Grain legumes: Impact on soil health and agroecosystem. In: Meena, R., Das, A., Yadav, G., Lal, R. (Eds.), Legumes for soil health and sustainable management. Singapore: Springer.
Hajduk, E., S. Właśniewski and E. Szpunar-Krok, 2015. Influence of legume crops on content of organic carbon in sandy soil. Soil Science Annual, 66(2): 52-56.Available at: https://doi.org/10.1515/ssa-2015-0019.
Hepperly, P., D. Lotter, C.Z. Ulsh, R. Seidel and C. Reider, 2009. Compost, manure and synthetic fertilizer influences crop yields, soil properties, nitrate leaching and crop nutrient content. Compost Science & Utilization, 17(2): 117-126.Available at: https://doi.org/10.1080/1065657x.2009.10702410.
Jones, B.J.J., 2001. Laboratory guide for conducting soil tests and plant analysis. CRC Press, LLC.
Kalra, Y.P. and D.G. Maynard, 1991. Methods manual for forest soil and plant analysis. Information Report NOR-X-319, Forestry Canada, Edmonton, Alberta: Northwest Region, Northern Forestry Centre, pp: 116.
Koutika, L.-S., S. Hauser, J.M. Kamga and B. Yerima, 2005. Comparative study of soil properties under Chromolaena odorata, Pueraria phaseoloides and Calliandra calothyrsus. Plant and Soil, 266(1-2): 315-323.Available at: https://doi.org/10.1007/s11104-005-2279-3.
Landon, J.R., 1991. Booker tropical soil manual. UK: Longman Scientific and Technical Essex.
Leterme, P. and M.L. Carmenza, 2002. Factors influencing pulse consumption in Latin America. British journal of Nutrition, 88(S3): 251-254.Available at: https://doi.org/10.1079/bjn/2002714.
Liu, Y., L. Wu, J.A. Baddeley and C.A. Watson, 2011. Models of biological nitrogen fixation of legumes. A review. Agronomy for Sustainable Development, 31(1): 155-172.Available at: https://doi.org/10.1051/agro/2010008.
Massawe, P.I., K.M. Mtei, L.K. Munishi and P.A. Ndakidemi, 2016. Effect of rhizobium and intercropping systems on soil nutrients and biological nitrogen fixation as influenced by legumes (Phaseolus vulgaris and Dolichos lablab). International Journal of Current Microbiology and Applied Sciences, 5(10): 135-149.
McLaughlin, M.J., A. Alston and J. Martin, 1988. Phosphorus cycling in wheat-pasture rotations. Iii. Organic phosphorus turnover and phosphorus cycling. Soil Research, 26(2): 343-353.Available at: https://doi.org/10.1071/sr9880343.
Meena, R.S. and R. Lal, 2018. Legumes and sustainable use of soils. In: Meena R., Das A., Yadav G., Lal R. (Eds.), Legumes for soil health and sustainable management. Singapore: Springer. pp: 1 - 31.
Meena, R.S., R.S. Yadav, H. Meena, S. Kumar, Y.K. Meena and A. Singh, 2015. Towards the current need to enhance legume productivity and soil sustainability worldwide: A book review. Journal of Cleaner Production, 104: 513–515.Available at: https://doi.org/10.1016/j.jclepro.2015.05.002.
Muhr, L., M. Peters, S.A. Tarawali and R. Schultze-Kraft, 1999. Forage legumes for improved fallows in agropastoral systems of subhumid West Africa: II. Green manure production and decomposition after incorporation into the soil. Tropical Grasslands, 33(4): 234–244.
Muoni, T., A.P. Barnes, I. Öborn, C.A. Watson, G. Bergkvist, M. Shiluli and A.J. Duncan, 2019. Farmer perceptions of legumes and their functions in smallholder farming systems in east Africa. International Journal of Agricultural Sustainability, 17(3): 205-218.
Nanganoa, L.T. and J.N. Njukeng, 2018. Phosphorus speciation by 31P NMR spectroscopy in leaf litters and crop residues from para rubber, cocoa, oil palm, and banana plantations in the humid forest zone of Cameroon. Journal of Applied Chemistry, 2018(2): 1 – 8.Available at: https:// doi.org/10.1155/2018/6290236.
Nanganoa, L.T., J.N. Okolle, V. Missi, J.R. Tueche, L.D. Levai and J.N. Njukeng, 2019. Impact of different land-use systems on soil physicochemical properties and macrofauna abundance in the humid tropics of Cameroon. Applied and Environmental Soil Science, 2019(2): 1-9.Available at: https://doi.org/10.1155/2019/5701278.
Ngobo, M., M. McDonald and S. Weise, 2004. Impacts of type of fallow and invasion by Chromolaena odorata on weed communities in crop fields in Cameroon. Ecology and Society, 9(2): 1-15.Available at: https://doi.org/10.5751/es-00653-090201.
Ngosong, C., V. Bongkisheri, C.B. Tanyi, L.T. Nanganoa and A.S. Tening, 2019. Optimizing nitrogen fertilization regimes for sustainable maize (Zea mays L.) production on the volcanic soils of Buea Cameroon. Advances in Agriculture, 2019(7): 1 – 8.Available at: https://doi.org/10.1155/2019/4681825.
Ngosong, C., B.N. Nkiambuo, C.B. Tanyi, R.N. Nkongho, J.N. Okolle, A.E. Egbe and A.S. Tening, 2018. Comparative study of soil and foliar NPK fertilizers on the yield and income of cucumber (Cucumis sativus L.). Asian Journal of Advances in Agricultural Research, 8(3): 1-9.Available at: https://doi.org/10.9734/ajaar/2018/45721.
Ngwu, O.E., 2008. Nodulation and nitrogen fixation potentials of three wild legumes in an Utisol in South Eastern Nigeria. International Journal of Agriculture and Rural Development, 11(1): 171 – 174.
Nottidge, D., S. Ojeniyi and D. Asawalam, 2005. Comparative effects of plant residues and NPK fertilizer on soil properties in a humid Ultisol. Nigerian Journal of Soil Science, 15(1): 9-13.
Ojeniyi, S.O., S.A. Odedina and T.M. Agbede, 2012. Soil productivity improving attributes of Mexican sunflower (Tithonia diversifolia) and siam weed (Chromolaena odorata). Emirate Journal of Food and Agriculture, 24(3): 243-247.
Price, N., 1994. Alternate cropping in the management of radopholus similis and cosmopolites sordidus two important pests of banana and plantain. International Journal of Pest Management, 40(3): 237-244.Available at: https://doi.org/10.1080/09670879409371890.
Reem, M.H., 2017. The effect of phosphorus in nitrogen fixation in legumes. Agricultural Research & Technology: Open Access Journal, 5(1): 555652.Available at: https://doi.org/10.19080/artoaj.2017.05.555654.
Rowell, D.L., 1994. Soil science: Methods and applications. England, UK: Addison Wesley Longman Singapore Publishers (Pte) Ltd. pp: 350.
Saha, S., B. Mina, K. Gopinath, S. Kundu and H. Gupta, 2008. Organic amendments affect biochemical properties of a subtemperate soil of the Indian Himalayas. Nutrient Cycling in Agroecosystems, 80(3): 233-242.Available at: https://doi.org/10.1007/s10705-007-9139-x.
Sallaku, G., J. Liko, Z. Rada and A. Balliu, 2016. The effects of legume crops (pea and faba bean) on soil nutrients availability and yield parameters of subsequent cabbage crops under organic production conditions. Journal of Environmental Science and Engineering, 5(12): 619-625.Available at: https://doi.org/10.17265/2162-5298/2016.12a.004.
Schulz, S., R.J. Carsky and S. Tarawali, 2001. Herbaceous legumes: The panacea for West African soil fertility problems? Sustaining soil fertility in West Africa. SSSA Special Publication, 58: 179–196.
Serrao, E.A.S., I.C. Falesi, J.B. Da Veiga and F. Texeira Neto, 1979. Productivity of cultivated pastures on low fertility soils of the Amazon region of Brazil. In: Pasture production on acid soils of the tropics. Sanchez, P. A., Tergas, T. E. (Eds.), Cali, Colombia: CIAT. pp: 195–225.
StatSoft, 2016. STATISTICA version 13.2 for windows, Tusla, Okla, USA.
Swangjang, K., 2015. Soil carbon and nitrogen ratio in different land use. In International Conference on Advances in Environment Research, 87: 36–40.
Van Reeuwijk, L.P., 1992. Procedures for soil analysis. 3rd Edn., Wageningen: International Soil Reference and Information Centre (ISRIC).
Vanlauwe, B., J. Six, N. Sanginga and A. Adesina, 2015. Soil fertility decline at the base of rural poverty in sub-Saharan Africa. Nature Plants, 1(7): 15101.Available at: https://doi.org/10.1038/nplants.2015.101.
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