R.C. Abaidoo

Farmers' Adoption of Soil Conservation Technologies: A Case Study from Osun State, Nigeria

Abstract The main objective of this study was to determine the attitude of farmers towards erosion and the adoption of appropriate soil conservation technologies (SCTs). For the survey, farmers were selected from the communities Esa Oke, Elwure and Owode-Ede and Akoda in Osun State in Nigeria. In the first three communities farmers did receive training on soil conservation, in the fourth not. About 60 farmers were interviewed to obtain information on personal and socio-economic characteristics, awareness of environmental problems, attitude towards erosion control and experiences with SCTs. Statistical data analyses (analyses of frequencies, correlation, t-test, χ2-test) were made to examine possible relationships among parameters and the influence of factors on adoption. Most respondents were advanced in years, responsible for large households and characterized by low levels of income and literacy. Soil erosion was seen as a problem confronting agricultural production only to a small extent. The adoption rate of SCTs was low, as only mulching, cover cropping, contour tillage and cut-off drainage were practised and often rejected. Low labour-demand, the availability of common equipment, low costs of application, ease of practice and compatibility with the existing farming system influenced adoption. The observed positive correlation between level of education, knowledge of appropriate technologies, farming experience and the number of SCTs adopted emphasizes the importance for farmers of education and training. Strengthening agricultural extension agencies for capacity building is an important tool for improving soil conservation in Nigeria. The paper clarifies with specific examples the causes of the low rates of adoption of available technologies, with a reduced impact of research and of efforts to achieve food security and sustainable production at village level.

MINERAL NUTRIENT UPTAKE AND REMOVAL BY COWPEA, SOYBEAN AND MAIZE CULTIVARS IN WEST AFRICA, AND IMPLICATIONS FOR CARBON CYCLE EFFECTS ON SOIL ACIDIFICATION

A field study of cowpea, soybean and maize was made at Ibadan, Nigeria, to determine the uptake of mineral nutrients and quantities removed in crop residues and seed. Concentrations of N, the major cations (K, Ca, Mg and Na) and major anions (P, S and Cl), and the micronutrients (Fe, Mn, Zn and Cu) were determined in shoots harvested at flowering and maturity. Concentrations of excess cations in shoots at flowering were 135 cmol c kg −1 for soybean, 158 cmol c kg −1 for cowpea and 58 cmol c kg −1 for maize. In crop residues and seed at maturity, the values decreased to 75 and 56 cmol c kg −1 respectively for soybean, 68 and 27 cmol c kg −1 respectively for cowpea, and 52 and 10 cmol c kg −1 respectively for maize. Nutrient and excess cation concentrations were also measured in 13 soybean and eight cowpea lines grown in replicated field trials at Fashola in the derived savanna zone and Shika in the northern Guinea savanna zone of Nigeria to assess the variation within these species. Maize, mucuna and lablab were included at these sites. The results are discussed in the context of soil nutrient depletion due to removal of nutrient elements in harvested seed and stover. The contribution of seed and stover removal to the proton (H + ) budget and acidification of the soil is also discussed. It is estimated that the quantity of lime required to neutralize the acidity resulting from the removal of 1 t seed is 28 kg for soybean, 14 kg for cowpea and 5 kg for maize. The corresponding values for stover were soybean 35, cowpea 24 and maize 26 kg lime t −1 stover. Given the soil pH buffer capacity at the Ibadan site for the surface 16 cm, the yields obtained and assuming that seed and crop residues are removed, carbon cycle acidification would lead to a fall of 1 pH unit after 75 crops for soybean, 114 crops for cowpea and 68 crops for maize. The inclusion of legumes in cropping systems to increase N supply, and the use of P fertilizer to maximize N-fixation by legumes will raise production, but will inevitably accelerate removal of alkalinity and nutrients in harvested products, and the consequent decline in soil fertility. The data presented in this paper can be used in estimating the lime and fertilizer nutrients needed to maintain soil fertility and sustain yields.

Integrated soil fertility management involving promiscuous dual-purpose soybean and upland NERICA enhanced rice productivity in the savannas

Integrated soil fertility management (ISFM) involving a nitrogen-fixing grain legume, limited chemical fertilizer, and a resilient rice variety may reduce the rate of soil fertility loss and enhance rice productivity in fragile upland rice ecosystems. A 2-year, on-farm study was carried out at Eglimé in the southern Guinea savanna (SGS) and Ouake in the northern Guinea savanna (NGS) of the Republic of Benin to evaluate the contribution of dual-purpose soybean cultivars (Glycine max) to grain yield of upland NERICA® rice receiving low fertilizer N. In 2005, four dual-purpose, promiscuous soybean varieties (cv. TGX 1440-IE, TGX 1448-2E, TGX 1019-2EB, and TGX 1844-18E), a popular soybean variety (cv. Jupiter), and a popular rice (control) were sown in ten farmers’ fields. In 2006, resilient upland interspecific rice (NERICA1) and popular rice (IRAT-136) were sown in all plots with only 15 kg N ha−1. Soybean cv. TGX 1440-1E (late-maturing) ranked highest in nodulation, dry matter, shoot- and grain-N accumulation, and N-balance (21 kg ha−1) in NGS, while TGX 1448-2E (medium-maturing) surpassed other varieties in the SGS. Nitrogen fertilizer replacement value for growing cv. TGX 1440-1E in NGS prior to rice ranged from 17 to 45 kg N ha−1 depending on the reference rice. Grain yield of NERICA1 following 1-year rotation with soybean cv. TGX 1440-1E or TGX 1019-2EB was 1.5 Mg ha−1 greater than the yield obtained from farmers’ control of 2-year continuous IRAT 136 rice cropping. Results indicate that integrating appropriate dual-purpose soybean in an ISFM package can enhance rice productivity in resource-limited smallholder production systems.

Evaluation of microbial inoculants as biofertilizers for the improvement of growth and yield of soybean and maize crops in savanna soils

Certain rhizobacteria exert considerable influence on plant growth and development, particularly under limiting conditions. The effects of some indigenous soil microbial isolates and commercially produced microbial inoculants, referred to as bio-inoculants, on the growth and dry matter yield (DMY) of maize (Zea mays ) and soybean ( Glycine max ) crops were assessed under greenhouse conditions. In two sets of experiments, one set comprised of free-living nitrogen-fixing microorganisms (Azospirillum spp.), three soils from Ibadan, Mokwa and Shanono located in different agro-ecological zones, and maize as the test crop. The other set consisted of microbial inoculants that can act as biocontrol agents applied to sterilized and non-sterilized soils; soybean was the test crop. The bio-inoculants were applied separately and also in combination. The treatments included a reference termed ‘mineral N’ where macro- and micro-nutrients were supplied at optimal rates, a control where bio-inoculants were not applied, and four replicates. All treatments, excluding the reference, received only macro-nutrients at suboptimal rates. The crops were grown for eight weeks and growth parameters were measured. The shoot DMY of maize was relatively large (42 to 63 g plant -1 ) and differed significantly among the soils but the bio-inoculants did not improve the shoot DMY significantly (P > 0.05) in any of the soils when compared with the control. However, sole inoculation of Mazospiriflo-2 enhanced nitrogen uptake significantly in maize grown in Shanono soil. For soybean, the shoot DMY was also not improved by the inoculation or the addition of the microbial products compared with the control.

Use of remote sensing and GIS for improved natural resources management: case study from different agroecological zones of West Africa

Historical and recent aerial photograph and satellite images were analysed to study the change of land use/land cover and soil degradation in different agroecological zones of Nigeria and Benin. The sites were characterized by an expansion of farmland at the expense of forest and shrub, fallow and uncultivated land, at an increasing rate due to population growth, food demand and land scarcity. Sheet and gully erosion were the consequences of the land use intensification and have destroyed extensive areas of farmland and grazing land. Reduced agricultural and livestock production, declining revenue, as well as increased conflict from resource competition between farmers and pastoralists are expected for the future. To combat these problems, improved land use management through continuing land inventory, generating an environmental database, developing land use plans and controlling erosion through adequate soil conservation measures are recommended.

Influence of phosphorus application on growth and yield of soybean genotypes in the tropical savannas of northeast Nigeria

Abstract The cultivation of soybean is increasing in the savannas of Nigeria due to its widespread use in the food and feed industry. Production is, however, constrained by low soil phosphorus (P) levels in northeast Nigeria. This study evaluated four soybean varieties for their response to three rates of P in two agro-ecozones in 2004 and 2005. Experimental design was a split-plot arrangement of treatments with three replications. The main plots were assigned the P treatments and subplots were soybean cultivars randomised within the main plots. The studies found that soybean responds to P application but differences between 20 and 40 kg P/ha were not significant, despite low test P levels. This may be due to limitations in other nutrients. More studies are needed to determine the synergistic effect of P and other nutrients on soybean growth and yield. Soybean growth and seed yield were lower in 2004 than in 2005 because trials were established comparatively late in 2004 and crops were therefore affected by late season moisture stress. There is, therefore, a need to establish the appropriate time for planting soybean in these zones. Late maturing varieties produced higher yields than early maturing varieties in 2005 probably due to early planting which allowed full use of the growing season.

Evaluation of cowpea genotypes for variations in their contribution of N and P to subsequent maize crop in three agro-ecological zones of West Africa

Cowpea is an important source of food, cash, and fodder in West Africa. It is perceived to be tolerant to low available soil phosphorus (P) conditions and nodulates promiscuously contributing to soil fertility through its high nitrogen (N)-fixing capacity. Cowpea can contribute substantial amounts of N to a subsequent cereal crop but little is known of the effect of cowpea on P nutrition of a cereal crop grown in rotation. This study, therefore evaluated eight cowpea genotypes for N2 fixation, tolerance to low soil P (0P), and response to P fertilizer application (90 kg P ha-1 as Rock Phosphate (RP) or 30 kg P ha-1 as Triple Superphosphate (TSP)), and their potential contribution of N and P to a subsequent maize crop in three agroecological zones (at Shika, northern Guinea savanna; at Fashola, derived savanna; and Davie, coastal savanna). Grain yield and P uptake of cowpea genotypes were influenced by location. Relative response of cowpea genotypes to P application was highest at Shika where soil resin P content was lowest. The responses to RP application across locations ranged from –14 to 94%; and 194 to 358% for TSP application. Variation between genotypes was minimal within the 0P and RP treatments but more pronounced within the TSP treatment at all the locations. The results showed that N2 fixation, N exported in grain, and N balances of cowpea genotypes were different depending on P nutrition conditions. Grain yield of maize following cowpea was influenced largely by the previous cowpea genotype through its N and P dynamics, location, and VAM colonization of roots. There was, however, no consistent evidence of a significant effect of P applied to the legume, on the residual value to the subsequent maize crop.

ABUNDANCE AND DISTRIBUTION OF ARBUSCULAR MYCORRHIZAL FUNGI SPECIES IN LONG-TERM SOIL FERTILITY MANAGEMENT SYSTEMS IN NORTHERN NIGERIA

Soil fertility management systems (SFMS) can influence the community structure of arbuscular mycorrhizal fungi (AMF). Hence, long-term SFMS was studied. The SFMS comprised three legume combinations, urea application and solely maize as control. Spores were extracted by wet sieving, characterized and identified using their morphology. Interrelationships between cropping systems and occurrence of AMF species were analyzed with genotype by environment (GGE) biplot. Seventeen species were identified with Glomus species (47.05%) having highest value while Gigaspora species had the least (11.76%). Legume residues significantly (P < 0.05) increased spore population with the highest spore count (120 spores/100 g soil) obtained in plot under cowpea residue. Shannon Weiner index (H′) of maize/Lablab purpureus plot was highest (1.996) while that of sole maize system was the least (1.550). The GGE indicated Glomus intraradices as a stable species across all the SFMS. Community structure of AMF and function can be preserved using appropriate SFMS.

Effects of Arbuscular Mycorrhizal Inoculation and Phosphorus Application on Yield and Nutrient Uptake of Yam

To be sustainable, production in the traditional yam cropping system, faced with declining soil fertility, could benefit from yam–arbuscular mycorrhizal (AM) symbiosis, which can improve nutrient uptake, disease resistance, and drought tolerance in plants. However, only limited information exists about AM colonization of yam. A pot experiment was conducted to collect information on the response of two genotypes (Dioscorea rotundata accession TDr 97/00903 and D. alata accession TDa 297) to AM inoculation (with and without) and phosphorus (P) (0, 0.05, 0.5, and 5 mg P kg–1 soil). Factorial combinations of the treatments were arranged in a completely randomized design with four replicates. The percentage of AM colonization was significantly lowered at 5 mg P kg–1 soil rate in mycorrhizal plants of both genotypes. TDr 97/00903 showed more responsiveness to AM inoculation than TDa 297. The greatest AM responsiveness for tuber yield (52%) was obtained at 0.5 mg P kg–1 soil rate for TDr 97/00903. Mycorrhizal inoculation significantly increased root dry weight and tuber yield of TDr 97/00903 with the greatest values obtained at the 0.5 mg P kg–1 soil rate. Arbuscular mycorrhizal inoculation did not lead to significant (P < 0.05) changes in root length and area. Phosphorus application significantly increased the shoot dry weight and root diameter of TDa 297. Uptake of P was greatest at 0.5 mg P kg–1 soil in both genotypes and was significantly influenced by AM inoculation. Nitrogen (N) and potassium (K) uptake were greatest in mycorrhizal plants at 0.05 mg P kg–1 soil for TDr 97/00903 but at 0.5 mg P kg–1 soil of nonmycorrhizal plants of TDa 297. The increased tuber yield and nutrient uptake observed in the mycorrhizal plants indicate the potential for the improvement of nutrient acquisition and tuber yield through AM symbiosis.

Diversity of arbuscular mycorrhizal fungi in soils of yam (Dioscorea spp.) cropping systems in four agroecologies of Nigeria

The diversity of arbuscular mycorrhizal (AM) fungi in soils under a yam cropping system in four agroecologies of Nigeria was investigated. Soil samples were collected from yam fields at Onne (humid forest, high rainfall area), Ibadan (derived savanna), Abuja (Guinea savanna) and Ubiaja (humid forest, medium rainfall area). Soil characteristics, AM fungi species, spore abundance, Shannon diversity index, species richness and evenness were determined. A total of 31 AM fungi species was isolated from the four agroecologies with a range of 14–20 species found in a single location. Glomus species were the most abundant among AM fungi species with G. geosporum, G. intraradices and G. mosseae occurring in large populations in all locations. Ubiaja, which had a cassava/natural vegetation sequence before yam, had significantly higher spore abundance and species richness than the other locations, which had a yam/legumes or a maize/legume sequence before yam. However, diversity was significantly higher at Abuja, which had a maize/legume sequence with yam, than Ibadan, which had only a yam/legume sequence. The study revealed significant diversity in AM fungal species across agroecologies in yam-growing regions. Further research on the functional consequences of changing composition of AM fungi species across the region is recommended.