Soil Fertility Problems Research Articles

Isotope‐Filtered 4D NMR Spectroscopy for Structure Determination of Humic Substances

AbstractHumic substances, the main component of soil organic matter, could form an integral part of green and sustainable solutions to the soil fertility problem. However, their global‐scale application is hindered from both scientific and regulatory perspectives by the lack of understanding of the molecular make‐up of these chromatographically inseparable mixtures containing thousands of molecules. Here we show how multidimensional NMR spectroscopy of isotopically tagged molecules enables structure characterization of humic compounds. We illustrate this approach by identifying major substitution patterns of phenolic aromatic moieties of a peat soil fulvic acid, an operational fraction of humic substances. Our methodology represents a paradigm shift in the use of NMR active tags in structure determination of small molecules in complex mixtures. Unlike previous tagging methodologies that focused on the signals of the tags, we utilize tags to directly probe the identity of the molecules they are attached to.

Isotope-Filtered 4D NMR Spectroscopy for Structure Determination of Humic Substances.

Humic substances, the main component of soil organic matter, could form an integral part of green and sustainable solutions to the soil fertility problem. However, their global-scale application is hindered from both scientific and regulatory perspectives by the lack of understanding of the molecular make-up of these chromatographically inseparable mixtures containing thousands of molecules. Here we show how multidimensional NMR spectroscopy of isotopically tagged molecules enables structure characterization of humic compounds. We illustrate this approach by identifying major substitution patterns of phenolic aromatic moieties of a peat soil fulvic acid, an operational fraction of humic substances. Our methodology represents a paradigm shift in the use of NMR active tags in structure determination of small molecules in complex mixtures. Unlike previous tagging methodologies that focused on the signals of the tags, we utilize tags to directly probe the identity of the molecules they are attached to.

A review of effects of nutrient elements on crop quality.

The problem of low soil fertility and poor plant nutrition does not only affect crop yields but also crop quality. A review of many refereed published journal articles and books sourced from internet and libraries was conducted with the aim of highlighting the effects of plant nutrition on crop quality. Emphasis was put on elucidating the functions through which various nutrient elements influence biochemical processes and eventually affect the overall quality of various crops and their products. Nutrients reviewed in this paper included elements such as nitrogen (N), phosphorus (P), potassium (K), sulphur (S), magnesium (Mg), calcium (Ca), zinc (Zn), iron (Fe), and cobalt (Co). The crop quality characteristics mostly reported t o be affected by plant nutrition include: proteins, carbohydrate, sucrose and fructose content in grains, root crops, tuber crops and fruits; vitamins like beta-carotene content in fruits and tubers; moisture content at storage in cereal grains, potato tuber density; and frying colours, and fruit weight. It has been noted that essential and beneficial nutrient elements contribute to crop quality through functioning as raw materials for the synthesis of various plant components that have food value to humans and animals. Nitrogen and S are raw materials for protein synthesis. Others like Ca, P, Zn and Fe are involved in enzyme synthesis, activation or as electron carriers while Mg, and K are mostly involved in enzyme activation and transportation of materials such as fructose and sucrose from points of synthesis to sites of loading and hence affect quality of fruits, and root and tuber crops greatly. It has been noted that crop quality is also greatly influenced by the synergistic and antagonistic interactions in various nutrients uptake and utilization. Therefore, balanced nutrition is noted to be o f paramount importance. From this review it can be concluded that crop quality is a very important area to consider advancing and putting up resources for research since it has a huge bearing on human health and socioeconomic effect on farmers through its in fluence on marketability of crops and crop products.

Morphology, Physicochemical Characteristics and Land Suitability in the Western Highlands of Cameroon

The aim of the study was to evaluate the morphology and physicochemical properties of soils and their suitability to potatoes, maize and beans, in order to contribute to stop rural migration, prevent conflicts between farmers and breeders and contribute to the increase of agricultural yields in the eastern slope of the Bambouto Mountain, Cameroon. Morphologically, the studied soil profiles are poorly or more developed, characterized respectively by AC or ABC horizon sequences. All the soil samples recorded acidic pH (4.8 to 5.5) except in the Bawa and in Zavion footslope where this pH is slightly acidic (6.0 to 6.2). Nitrogen contents are low to medium (0.04 to 0.225), except in midslope and footslope of Zavion site where these contents are very high (0.406 and 0.436% respectively). Organic matter contents increase from the Medji (1.42%) site to Zavion site (9.84%). High content of organic matter in Bawa located at the same altitude as Medji is related to the basaltic bedrock which glasses weathering might induce increase of organic matter content, while high content in Zavion might be mostly related to the increase in altitude and the decrease of Original Research Article Tsozue et al.; IJPSS, 7(1): 29-44, 2015; Article no.IJPSS.2015.128 30 temperature which slacks up microorganism activities. Phosphorous level is very low and largely under the critical limit (20 ppm) for all the study sites. Calcium is the dominant exchangeable cation, with contents ranging between 0.13 and 7.53 cmol(+)/kg of soil. The cation exchange capacity varied between 2.03 and 29.59 cmol(+)/kg of soil. Base saturation percentage fluctuates from 11.80 to 39.70%. The production of bean, maize and potatoes in the study sites is limited due to high rainfall and wetness, high slope gradient and soil fertility problems which could respectively be solved by promoting crops cultivation at the end of the raining season, terracing of arable land and fertilization and liming.

Soil Fertility Characterization in Vertisols of Southern Tigray, Ethiopia

A fresh soil profile pit was opened and representative soil samples were collected from the profile and surface (0-15 cm) soil of the experimental area to characterize the fertility status of the soils of the study area on the base of selected physicochemical properties. The soil textural class of the surface layer (0-25 cm) of the profile and the mean composite surface (0-15 cm) soil samples of the experimental field was clay loam while it was clay for the subsurface (25-150+ cm) layers of the profile. The bulk density values of the layers in the profile varied consistently with depth ranging from 1.18 g cm-3 at the surface layer to 1.32 g cm-3 at the bottom layer while the average bulk densities of experimental field. The bulk and particle density values increased consistently with depth of the profile ranging from 1.18 to 1.32 and 2.51 to 2.85 g cm-3, respectively. The organic matter (0.05 to 4.39%), available P (0.86 to 22.50 mg kg-1) and total N (0.03 to 0.23%) of the soil profile decreased consistently with depth. Both the profile and the composite surface soil sample indicated that the soil of the site was slightly acidic to moderately alkaline in reaction (6.5 to 8.20). The soil exchange complex was mainly dominated by Ca and Mg where the order of occurrence was Ca > Mg >K > Na. The CEC values were very high ranging from 41.42 to 50.37 c mol (+) kg-1. The results of the study revealed that the physical and chemical properties of the soils are highly variable to each other which disagrees the blanket rate of fertilizer recommendation throughout the country. The turning point to solve the problems should be restoring, maintaining and increasing the fertility status of the soils. These phenomena necessitate soil-crop specific fertilizer recommendation. Therefore, the existing soil fertility problems should be addressed sooner by introducing/developing resistant crop varieties, applying organic and inorganic fertilizers, and other soil fertility management options.

The Effect of Shocks: An Empirical Analysis of Ethiopia

Beside striving for the increase of production and development, it is also necessary to reduce the losses created by the shocks. The people of Ethiopia are exposed to the impact of shocks having natural and manmade origin. Following this, policy makers, governmental and nongovernmental organizations need to identify the important shocks and their effect and use as an input. This study was conducted to identify the food insecurity shocks and to estimate their effect based on the conceptual framework developed in Ethiopia, Amhara National Regional State of Libo Kemkem District. Descriptive statistical analysis, multiple regression, binary logistic regression, chi-square and independent sample T-test were used as a data analysis technique. The study shows eight shocks affecting households which are weather variability, weed, plant insect and pest infestation, soil fertility problem, animal disease and epidemics, human disease and epidemics, price fluctuation problem and conflict. Weather variability, plant insect and pest infestation, weed, animal disease and epidemics create a mean loss of 3,821.38, 886.06, 508.04 and 1,418.32 Birr respectively. In addition, human disease and epidemics, price fluctuation problem and conflict affect 68.11%, 88.11% and 14.59% of households respectively. Among the sample households 28.1 percent were not able to afford their food need throughout the year while 71.9 percent could. The result of the multiple regression models revealed that weed existence (? =-0.142, p<0.05), plant insect and pest infestation (? =-0.279, p<0.01) and soil fertility problem (? =-0.321, p<0.01) had significant effect on income. Asset was found significantly affected by plant insect and pest infestation (? =-0.229, p<0.01), human disease and epidemics (? =0.145, p<0.05), and soil fertility problem (? =-0.317, p<0.01) while food production was affected by soil fertility problem (? =-0.314, p<0.01). Binary logistic regression model reveals that food availability of the households was highly affected by the asset (Exp (B) = 1.00, p<0.1), and food production (Exp (B) = 1.379, p<0.01).

Soil fertility characterisation of teak (Tectona grandis L.f.) plantations in Central America

Teak (Tectona grandis L.f.) is an important species in the worldwide quality tropical hardwood sector, which has gained significance in Central America since the first large plantations were established in the 1980s. The present work is a descriptive study that aims to: (1) analyse and characterise the general soil patterns which may be influencing teak plantations in Central America; (2) assess differences between countries and sub-regions; (3) create a global framework to help contextualise the soil fertility analyses conducted at sub-regional or farm level, and (4) determine the main problems associated with soil fertility in the region. Soil fertility was measured at 684 sites in Costa Rica, Guatemala and Panama. Although teak is considered to be a species with high soil nutrient requirements, and high fertility is usually assumed in teak plantations, the results show that this species has been planted in a wide variety of soils, including many with serious fertility problems (e.g. Ultisols and perhaps Oxisols) or with added difficulties due to their physical properties (e.g. Vertisols). The present analysis reveals a general K deficiency in the Central American teak plantations, where P deficiency and acidity toxicity are also relatively common problems. These soil fertility problems probably stem from poor site selection by forest managers in the 80s and 90s. Hence, although soil fertility is carefully evaluated when most teak plantations are established today, managers have to deal with soil fertility deficiencies in many sites where teak was established some years ago.

Particles interaction forces and their effects on soil aggregates breakdown

Soil aggregates profoundly influence soil fertility and environmental problems, and usually improving soil aggregation is the central issue in soil management. Compared with external forces, the internal forces of soil, i.e., surface hydration force, electrostatic force and van der Waals force, may play a crucial role in aggregate formation and stability. However, there are few quantitative investigations on those fundamental issues. In the present work we aim to calculate surface hydration force, electrostatic force and van der Waals force of soil/clay particles in aqueous solution, and then quantitatively evaluate the effects of the three forces on soil/clay aggregates breakdown. There was critical surface potential in particles interaction pressure and aggregates breakdown, and if the surface potential exceeded this critical point, a further increase of the surface potential could not significantly increase particles interaction pressure and aggregate breakdown. The critical surface potentials for particle interaction pressure were 207.0 and 179.7mV for the soil and montmorillonite, respectively. Our study suggested two steps in aggregate breakdown when dried aggregates were re-wetted: (1) separating soil particles in aggregates to a distance of 1.2–1.4nm between two adjacent particle surfaces by the surface hydration forces (swelling process); (2) breaking soil aggregates in a way of explosion or dispersion under strong or weak electric field conditions. Surface hydration force played a crucial role in aggregate swelling, and without this repulsive pressure, a dried aggregate could not be dispersed again after re-wetting.

Land-use/land-cover (LULC) change and socioeconomic conditions of local community in the central highlands of Ethiopia

This paper presents a case study of land-use/land-cover (LULC) changes from 1975 to 2014 in the central highlands of Ethiopia and traces out its impact on socioeconomic conditions of the local community in the study area. We used four time series Landsat satellite images, that is, Landsat MSS (1975), Landsat Thematic Mapper (1986), Enhanced Thematic Mapper (2000), and Landsat 8 OLI scenes (2014), to investigate the changes in LULC. In addition, individual interviews with 51 randomly selected households, discussions with focus group and key informants, and field observations were also incorporated for the study. The image classification indicated four categories of LULC classes: Natural forest, eucalyptus plantations, cropland/settlements, and grasslands. Between 1975 and 2014, cropland/settlements and eucalyptus plantations considerably increased, whereas grassland cover drastically decreased. According to the results, the area under cropland/settlements and eucalyptus plantations increased by 62 and 335%, respectively, with 74% concomitant decrease in the area of grasslands in the same period. Survey results showed that deterioration of soil fertility (41.2%) followed by shortage of land (35.3%) is the major constraint for crop production for poor farmers in the study area. However, better-off farmers ranked deterioration of soil fertility (64.7%) followed by lack of credit (17.6%) as priority constraints for crop production. Interviews mainly focused on selected women group revealed that the expansion of eucalyptus in the area greatly curbed the burdens of collecting fuel woods from long distances in the past. The availability of too many religious holidays (on average 16 days/month) directly or indirectly contributes to the current seasonal food shortages of the community. Generally, our results show that the community in the study area is beset with a host of social, economic, and institutional challenges. As a result, majority of the farming households are destitute, unable to make a livelihood from their small plot of land and live in absolute poverty. Therefore, in light of these finding, it is imperative that timely interventions by government and other development stakeholders are needed to come to grips with problems of soil fertility, land-use change, and food insecurity in the study area.

Smallholder Farmers’ Responses to Rainfall Variability and Soil Fertility Problems by the Use of Indigenous Knowledge in Chipepo, Southern Zambia

The study conducted in Southern Zambia investigated smallholder farmers’ use of indigenous knowledge to respond to rainfall variations and soil fertility problems. Farmer and key informant interviews and observations were employed to collect data. A total of 60 smallholder farmers and 6 key informants were interviewed. Chipepo lies in the low rainfall region of Zambia. Its upland area faces moisture stress and soil fertility problems compared to its valley areas located along tributaries of the Zambezi River. The annual flooding of the tributaries of the Zambezi River along the valley fields results in loss of crop yields. Farmers have responded to problems of low moisture in the upland fields and too much moisture in the river valley fields through crop diversification concentrated on three main food crops namely; maize, sorghum and bulrush millet. These differ not only in their moisture requirements but also in maturity periods. Drought tolerant early maturing crop varieties and off-farm activities enhance their resilience. Maize was planted in river valley fields due to its high water requirements while drought tolerant sorghum and millet were planted on upland fields. The farmers’ knowledge of particular flowering plants helped forecast the onset of rains for purposes of early planting. Farmers with upland fields have adopted indigenous soil classification techniques based on vegetation types, soil colour, and texture and soil workability and utilize particular soils for specific crops. Integrating this indigenous knowledge into modern technologies will enhance smallholder farmers’ resilience when faced with impacts of climate change and variability.

REGESOL: a diagnostic tool for forest soil improvement by liming.

In the 1980s, the acid rain phenomenon and the risk of forest decline revived the problems of forest soil fertility. To understand the phenomenon and to rectify it, research scientists used old fertilizationimprovement trials installed in the 1970s and new calcium and/or magnesium trials were set-up. Today, these trials form the liming-fertilization network. In parallel, to study the biogeochemical cycles and the mineral element inputs and outputs of forest ecosystems in depth, these experimental sites have been highly instrumented and monitored intensively and at present are integrated into SOERE F-ORE-T. The liming-fertilization network, linked with studies of biogeochemical cycles, has resulted in great improvements in our knowledge about the restoration of mineral fertility by liming in deteriorated forest ecosystems.

Evaluation of rhizosphere, rhizoplane and phyllosphere bacteria and fungi isolated from rice in Kenya for plant growth promoters.

Rice (Oryza sativa L.) is the most important staple food crop in many developing countries, and is ranked third in Kenya after maize and wheat. Continuous cropping without replenishing soil nutrients is a major problem in Kenya resulting to declining soil fertility. The use of chemical fertilizers to avert the problem of low soil fertility is currently limited due to rising costs and environmental concerns. Many soil micro-organisms are able to solubilize the unavailable phosphorus, increase uptake of nitrogen and also synthesize growth promoting hormones including auxin. The aim of this study was to isolate and characterize phyllosphere, rhizoplane and rhizosphere micro-organisms from Kenyan rice with growth promoting habits. In this study whole plant rice samples were collected from different rice growing regions of Kenya. 76.2%, over 80% and 38.5% of the bacterial isolates were positive for phosphate solubilization, nitrogenase activity and IAA production whereas 17.5% and 5% of the fungal isolates were positive for phosphate solubilization and IAA production respectively. Hence these micro-organisms have potential for utilization as bio-fertilizers in rice production.

English

&nbsp; A study was conducted in Hai and Lushoto districts, Northern Tanzania to establish the farmers&rsquo; perception of soil fertility problems and their attitudes towards integrated soil fertility management (ISFM) for coffee, thereby identifying the appropriate intervention strategies. The study was based on a structured questionnaire involving 126 respondents. Both farmers&rsquo; awareness of the problem and their attitudes&nbsp;were highly significant (at p&lt;0.01). Age, household size, and adoption of improved coffee varieties, affected farmers&rsquo; awareness significantly (p&lt;0.05).&nbsp;As for farmers&rsquo; attitudes, six of the eight predictors were significant (p&lt;0.05). Age, household size, adoption of new varieties and total farm income were highly significant (p&lt;0.01). Age, total land under coffee and total off-farm income negatively affected farmers&rsquo; attitudes. As farmers get older, they tend to refrain from innovation. Larger farms are likely to exert more pressure on the available organic resources. With multiple farms, distant farms are likely to receive less attention. When off-farm income was considered, multiple ventures compete for the farmers&rsquo; time, resources and attention. For the two districts, ISFM interventions will make a better impact to younger and more energetic farmers with sufficient lands for commercial coffee production and to farmers who depend largely on this resource for their livelihood. &nbsp; Key words:&nbsp;Soil fertility, farmers&rsquo; perception, integrated soil fertility management (ISFM), coffee, Tanzania.

Soil Heterogeneity and Soil Fertility Gradients in Smallholder Farms of the East African Highlands

Heterogeneity in soil fertility in these smallholder systems is caused by both inherent soil-landscape and human-induced variability across farms differing in resources and practices. Interventions to address the problem of poor soil fertility in Africa must be designed to target such diversity and spatially heterogeneity. Data on soil management and soil fertility from six districts in Kenya and Uganda were gathered to understand the determinants of soil heterogeneity within farms. Analysis of the variance of soil fertility indicators across 250 randomly selected farms (i.e., 2607 fields), using a mixed model that considered site, sampling frame, farm type, and field as random terms, revealed that the variation in soil organic C (6.5–27.7 g kg−1), total N (0.6–3.0 g kg−1), and available P (0.9–27 mg kg−1) was mostly related to differences in the inherent properties of the soils across sites (50 to 60% of total variance). Exchangeable K+ (0.1–1.1 cmol(+) kg−1), Ca2+ (1.5–14.5 cmol(+) kg−1), Mg2+ (0.6–3.7 cmol(+) kg−1), and pH (5.1–6.9) exhibited larger residual variability associated with field-to-field differences within farms (30 to 50%). Soil fertility indicators decreased significantly with increasing distance from the homesteads. When this variable was included in the model, the unexplained residual variances—associated with soil heterogeneity within farms—were 38% for soil C; 32% for total N; 49% for available P; 56, 49, and 38% for exchangeable K+, Ca2+ and Mg2+, respectively; and 49% for the pH. In allocating nutrient resources, farmers prioritized fields they perceived as most fertile, reinforcing soil heterogeneity. Categorization of fields within a farm with respect to distance from the homestead, and soil fertility classes as perceived by farmers, were identified as entry points to target soil fertility recommendations to easily recognizable, distinct entities.

Economic Analysis of Adoption of Mulching Technology in Yam Production in Osun State, Nigeria

In addressing the problem of low soil fertility and land degradation occasioned by increased population growth, erosion of soil nutrients and extreme exposure of land to harsh weather conditions resulting in reduced yam yield, mulching technology was adopted by the farmers in Osun State, Nigeria. This study used a multi-stage sampling technique to select 105 farmers involving adopters and non-adopters of mulching technology. Data were analysed with the aid of descriptive statis- tics, budgetary techniques and probit model. The results of budgetary analysis showed that seed yam and labour costs con- stituted significant parts of the variable costs. The average revenue per hectare for adopters was N412,971.69 while that of non-adopters was N346,456.75. However, the average net incomes were N326,865.02 and N236,087.40 for the adopters and non-adopters, respectively. The benefit-cost ratios were 4.79 and 3.13 for adopters and non-adopters, respectively. The probit model revealed that household size and hired labour were significant factors determining the farmers' adoption decisions. There is therefore the need to encourage farmers on the importance of adopting this land protecting technology and a policy thrust that make seed yam available and affordable as well as reducing the costs incurred on labour will be in the right di- rection of boosting yam production.

Soils, science and the politics of knowledge: How African smallholder farmers are framed and situated in the global debates on integrated soil fertility management

The paper addresses an important and often overlooked cultural aspect of smallholder agriculture in sub-Saharan Africa (SSA). This relates to how different policy organisations conceptualise soil management problem, its causes and solutions and how these framings intersect with, and incorporate smallholders’ indigenous knowledge. The article provides a brief review of the positionality of modernists and post-modernists on knowledge production and the politics which the process entails. Considering the ideology of some continental and global initiatives on integrated soil fertility management (ISFM), the paper identifies and addresses institutional framings of soil fertility problem in SSA. It also analyses the political economy [and ecology] of soil management in SSA; and investigates how farmers’ knowledge are incorporated into ISFM in the sub-continent. Drawing from some empirical evidences, the paper suggests that there is need for an economically viable and socio-culturally acceptable framework for the integration of both western and local knowledge in ISFM.

Systematic Approach to Diagnosing Fertility Problems in Soils of Sri Lanka

Diagnosing soil fertility problems is essential to supply plant nutrients in a complete and a balanced manner. We evaluated and validated a systematic approach of diagnosing fertility problems based on optimum values established elsewhere for 32 cultivated soils representing different agroecological zones of Sri Lanka. Soils were analyzed for available ammonium nitrogen (NH4−N), phosphorus (P), potassium (K), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), calcium (Ca), magnesium (Mg), sulfate – sulfur (SO4−S), and boron (B) concentrations, and based upon these analyses we calculated nutrient application rates. Molybdenum (Mo) and calcium carbonate (CaCO3) application rates were calculated based on the active acidity of soils, while those of P, K, S, Cu, Mn, Zn, and B were adjusted considering their respective fixation capacities. An optimum treatment providing nutrients at “optimum” concentrations was validated in the greenhouse using sorghum as the indicator plant. The optimum treatment was compared with 13 other treatments of individual nutrients or CaCO3 consisting of either omissions (optimum treatment minus a particular nutrient) or additions (optimum treatment plus a particular nutrient). The treatments were replicated four times. All soils were deficient in N and B, while most (30 out of 32) were deficient in P, K, and S. Deficiencies of Ca, Mg, Cu, Zn, and Mn were less common (<75% of soils), while all soils had sufficient Fe. Fixation abilities for nutrients varied widely. Significant (P < 0.05) yield reductions in minus treatments were observed for N and P in 100% of soils; K, S, and CaCO3 in 50–60% of soils; Ca in 38% of soils; and Mg, Cu, Zn, B, and Mo in less than 20% of soils. Plus treatments gave significant yield reductions occasionally, probably due to toxicities and nutrient imbalances. In 11 soils identified as deficient in K, Ca, and B, dry-matter yields were significantly lower in the optimum treatment than the respective minus treatment, indicating that bringing the nutrient concentration up to the optimum level reduced the yields, signifying the need to validate the optimum levels used for these nutrients. This approach of combining soil analyses and fixation studies could be successfully used to diagnose fertility problems; however, the results indicate the need to adjust the “optimum” concentrations of K, Ca, and B before using them in a fertilizer recommendation program.

NORMS FOR MULTIVARIATE DIAGNOSIS OF NUTRIENT IMBALANCE IN THE EAST AFRICAN HIGHLAND BANANAS (MUSA SPP. AAA)

Despite low yields and soil fertility problems, fertilizer use in the East African Highland banana (AAA-EA) production is absent. High fertilizer costs increase the need for site-specific fertilizer recommendations that address deficiencies. This study aimed to derive and compare norms for AAA-EA bananas, using Compositional Nutrient Diagnosis (CND), Diagnosis and Recommendation Integrated System (DRIS), and a DRIS that includes a filling value (DRIS-Rd), and study nutrient interactions. Data on foliar nitrogen, phosphorus, potassium, calcium, and magnesium concentrations, and plant performance were obtained from 300 plots in Uganda. CND indices were closely related to DRIS and DRIS-Rd indices (R2 > 0.965). Four nutrient interactions were common in both low and high bunch weight subpopulations. Although the three approaches can be used to determine nutrient imbalances in AAA-EA bananas, we recommend CND for ease of use. Diagnosis of nutrient deficiencies should be based on methods that identify plant nutritional imbalances.

Biological nitrogen fixation and socioeconomic factors for legume production in sub-Saharan Africa: a review

Low crop productivity is a general problem facing most farming systems in sub-Saharan Africa (SSA). These low yields are pronounced in grain legumes and are often associated with declining soil fertility and reduced N2-fixation due to biological and environmental factors. Unfortunately, the majority of African small farmers are now unable to afford the high mineral fertilizer prices. More than 75% of the fertilizers used in Africa are imported, putting pressure on foreign exchange. Low cost and sustainable technical solutions compatible with the socioeconomic conditions of small farmers are needed to solve soil fertility problems. Biological nitrogen fixation (BNF), a key source of N for farmers using little or no fertilizer, constitutes one of the potential solutions and plays a key role in sustainable grain legumes (e.g., soybean) production. Given the high cost of fertilizer in Africa and the limited market infrastructure for farm inputs, current research and extension efforts have been directed to integrated nutrient management, in which legumes play a crucial role. Inoculation with compatible and appropriate rhizobia may be necessary where a low population of native rhizobial strains predominates and is one of the solutions which grain legume farmers can use to optimize yields. It is critical for sustained yield in farmlands deficient in native rhizobia and where N supply limits production. Research on use of Rhizobium inoculants for production of grain legumes showed it is a cheaper and usually more effective agronomic practice for ensuring adequate N nutrition of legumes, compared with the application of N fertilizer. Here, we review past and ongoing interventions in Rhizobium inoculation (with special reference to soybean) in the farming systems of SSA with a view to understanding the best way to effectively advise on future investments to enhance production and adoption of BNF and inoculant technologies in SSA. The major findings are: (1) complete absence of or very weak institutions, policy and budgetary support for biotechnology research and lack of its integration into wider agricultural and overall development objectives in SSA, (2) limited knowledge of inoculation responses of both promiscuous and specifically nodulating soybean varieties as well as the other factors that inhibit BNF, hence a weak basis for decision-making on biotechnology issues in SSA, (3) limited capacity and lack of sustainable investment, (4) poorly developed marketing channels and infrastructure, and limited involvement of the private sector in the distribution of inoculants, and (5) limited farmer awareness about and access to (much more than price) inoculants. The lessons learned include the need: (1) to increase investment in Rhizobium inoculation technology development, and strengthen policy and institutional support, (2) for public private partnership in the development, deployment and dissemination of BNF technologies, (3) to develop effective BNF dissemination strategies (including participatory approach) to reach farmers, (4) for greater emphasis on capacity building along the BNF value chain, and (5) for partnership between universities in SSA and those in the North on BNF research.

Evaluation participative &lt;em&gt;ex ante&lt;/em&gt; de propositions de la recherche. Cas d’application dans le sud du Togo

L’objectif de cette étude a été d’expérimenter une méthode d’évaluation participative d’options techniques au sud du Togo. Pour répondre aux besoins face aux problèmes de fertilité des sols dans un contexte de systèmes mixtes agriculture élevage, des chercheurs ont évalué avec les diverses catégories d’acteurs le potentiel d’adoption de l’association du maïs, plante à fonction mixte alimentaire (grain) et fourragère (paille), et du Mucuna pruriens, légumineuse à cycle long employée comme fourrage et pour améliorer la fertilité des sols. L’association fertilisée avec des engrais chimiques a été dénommée MME ci-après. La méthode utilisée a mobilisé des outils d’analyse de la méthode active de recherche participative (MARP) et a compris quatre phases. La première correspondait à la description générale de l’ensemble de la région d’étude pour identifier des sites représentatifs à partir de la littérature et d’entretiens exploratoires. La seconde phase a permis la caractérisation de la diversité des producteurs à partir d’entretiens auprès des personnes ressources des sites retenus. La troisième phase a concerné la sélection participative d’un éventail d’options techniques comprenant l’association MME mais aussi des pratiques locales présentant des similitudes avec l’association MME, ainsi que d’autres propositions alternatives de la recherche pour améliorer la fertilité des sols et assurer l’alimentation fourragère des animaux. Cette sélection a été réalisée par un échantillon de producteurs représentatifs de leur diversité. Il leur a été demandé de hiérarchiser les différentes options techniques présentées lors de visites de parcelles expérimentales ou à l’aide de supports visuels. Ils ont utilisé des notes ou des cailloux compte tenu de la forte proportion d’illettrisme. La quatrième phase a été celle de l’évaluation aux dires de producteurs des effets perçus des différentes options sur la gestion des ressources agropastorales (eau, sol, biodiversité), leur acceptabilité ou leur rentabilité en fonction du coût de la main d’oeuvre. Cette méthode a été appliquée dans trois villages du sud du Togo. Dans ces villages, six principales catégories de producteurs ont été identifiées : les propriétaires terriens, les locataires de terres, les membres d’organisations paysannes, les producteurs lettrés, les producteurs illettrés, et les femmes. En plus du MME, six options ont été retenues dont l’association MME avec des variantes issues de pratiques locales, soit l’association maïs et Mucuna à cycle long mais sans l’usage d’engrais (MM), l’association maïs et Mucuna à cycle court et à base d’engrais (MMCE), l’association maïs et Mucuna à cycle court sans l’usage d’engrais (MMC), et maïs en culture seul avec apport massif d’engrais (ME). Les deux autres options ont été proposées par la recherche : maïs entouré de haies vives de légumineuses fourragères destinées à du bétail en stabulation contrôlée et dont le fumier était ensuite épandu au champ (MHF), et culture en couloirs de maïs et de Cajanus cajan. L’association MME a été l’option préférée des propriétaires terriens, des lettrés et des membres d’organisations paysannes. Chez les femmes, l’option privilégiée a été l’association MM compte tenu de leurs faibles ressources financières mais aussi de leur insécurité foncière. Chez les locataires des terres et les producteurs illettrés, l’option favorite a été l’association MMCE qui permettait le maintien de la seconde saison de culture. L’évaluation des différentes options a montré que l’association MME et l’option MHF ont été jugées par la majorité des catégories de producteurs comme ayant les effets les plus positifs sur les ressources agropastorales. Les associations MME et MMCE ont été considérées comme étant les plus acceptables socialement, notamment chez les propriétaires terriens mais aussi chez les vulgarisateurs, les consommateurs et les commerçants également interrogés ; venait ensuite l’option MHF. La rentabilité a été la meilleure pour les associations MM et MME et la plus faible pour les deux autres alternatives proposées par la recherche. Cette méthode d’évaluation permet de valoriser l’expertise des producteurs. Elle repose sur la perception que les producteurs ont des effets des technologies. Une perception positive constitue un des premiers facteurs d’adoption d’une proposition de la recherche. Mais pour cela du temps et des outils appropriés doivent être consacrés à l’étape de formation des producteurs sur les différentes options pour que cette perception ne soit pas biaisée par la qualité de l’information donnée par le chercheur. Cette évaluation permet en outre d’identifier ou d’adapter des variantes locales aux options pré-identifiées par les chercheurs. Les efforts de recherche-développement doivent se concentrer sur les processus de ces adaptations participatives.