An economic evaluation of a long-term experiment on phosphorus and manure amendments to sandy Sahelian soils: Using a stochastic dominance model

Poor fertility status of sandy Sahelian soils represents a major constraint to cereal and legume production. Soil amendment options were evaluated, using a stochastic efficiency framework. Dominance analyses showed that in the presence of annual applications of 30 kg N ha−1 and 30 kg K ha−1, efficient soil amendment options comprise of either the annual application of 8.7 kg P ha−1 in the form of single superphosphates in combination with 5 tonnes manure ha−1 applied every three years or the annual application of 17.5 kg P ha−1 in the form of single superphosphates. Choice between these two efficient options depends on the availability of manure, deficiencies in sandy soils and farmer resource endowments

Stochastic dominance analysis of soil fertility restoration options on sandy Sahelian soils in Southwest Niger

The poor fertility of sandy Sahelian soils remains one of the major constraints to pearl millet (Pennisetum glaucum) production in West Africa. On-farm trials under farmers' management were conducted in two rainfall zones of Niger in 1996 and 1997 to evaluate the risk characteristics of six soil fertility restoration options. Stochastic dominance analysis was used to compare the fertilizer treatments tested. Results showed that the farmers' traditional method (no fertilizer control), Tahoua phosphate rock (PRT) alone applied at 13 kg P ha-1 broadcast, and a combination of PRT broadcast at 13 kg P ha-1 and single super phosphate (SSP) hill-placed at 4 kg P ha-1 had the most desirable risk characteristics and were acceptable to risk averse decision-makers in both rainfall zones. At current input-output price ratios, most fertilizer-using farmers would choose the combination of PRT broadcast and SSP hill-placed. If the availability of SSP was limited, some farmers would use PRT alone. The demand for risk efficient alternatives could significantly increase if farmers could bear less than half the fertilizer costs at the current output price, although further research is required to say if a fertilizer subsidy could be justified on broader economic or social grounds

Effects of phosphorus on yield of cowpea cultivars intercropped with pearl millet on Psammentic paleustalf in Niger

Phosphorus (P) is the most limiting soil nutrient in the sandy soils of Niger and farmers rarely use chemical fertilizers in producing pearl millet and cowpea. A 3-yr study was conducted in farmer's fields at two locations in South Western Niger to investigate yield response of six cowpea cultivars to applied P-fertilizer (0, 8, 16 kg ha(-1)) when intercropped with millet. Significant yield differences were found between cultivars for their seed and dry fodder yield at all rates of applied P. Cultivars responded differently to the application of P. Millet grain was more than doubled with the addition of 8 to 16 kg P ha(-1). Cowpea cultivars did not have significant differential effect on millet yields. Cowpea cultivars differed significantly in the accumulation of P in fodder with the highest yielding cultivars taking up more P than the low yielding ones. The results have important implications for breeding and selection of cowpea cultivars that are adapted to a range of fertility levels

Effet de la combinaison des fumures organo-minérales et de la rotation niébé-mil sur la nutrition azotée et les rendements du mil au sahel

Peu de données existent sur la contribution en azote des légumineuses, et leurs impacts en présence des fumures sur la nutrition azotée des  céréales. Ainsi, pour évaluer les effets du niébé et des fumures organo-minérales sur la nutrition azotée et les rendements du mil subséquent, une expérimentation a été conduite de 2008 à 2009 à Sadoré au Niger. Dans un dispositif en split-plot, trois doses de résidus, de fumier et d’engrais minéraux ont été appliquées dans une rotation niébé-mil. La méthode isotopique de 15N a été utilisée pour déterminer le coefficient réel d’utilisation d’engrais azoté (CRU). En présence de résidus, le CRU a varié de 16 à 23%. Les doses du fumier ont entraîné sa variation de 16 à 22%. Le CRU du mil subséquent était de 30% contre 22% pour le mil en monoculture. Le mil subséquent a prélevé du sol 54 kg N ha-1 contre 38 kg N ha-1 pour le mil en continu. Les doses des fumures et leur  combinaison dans les systèmes de culture, ont augmenté les rendements du mil de 17 à 272%. La nutrition azotée et la productivité des systèmes peuvent donc être améliorées en combinant les fumures organo-minérales et les rotations avec légumineuses.Mots clés : Céréale, légumineuse, rotation, azote, dilution isotopique, Niger

Integrated Management of Soil Fertility and Land Resources in Sub-Saharan Africa: Involving Local Communities

The soils of sub-Saharan Africa are characterized by their poverty in nutrients along with low clay and organic carbon content and low exchange capacity. There is high pressure on land resources with the quick growth of population and demand for food. Maintaining the fertility of cultivated soils and land resources is a challenge. Since the paradigm of “external input” in the 1960s and 1970s, to the latest concept of integrated soil fertility management, most of the approaches remain crop oriented or livestock oriented with less attention to local communities (LC), which are at the heart of land resource management. This chapter suggests a new integrated and holistic approach involving LC for land resources management, including cultivated soils and rangelands. A global framework is proposed for development of management options of land resources with LC. It is a dynamic process of participative management of lands as providers of services for the entire community

Rotation and nitrogen fertilizer effects on pearl millet, cowpea and groundnut yield and soil chemical properties in a sandy soil in the semi-arid tropics, West Africa

A 5-year study was conducted from 1988 to 1992 at three sites in Niger to determine the effects of crop rotation of a cereal and legumes and nitrogen fertilizer on chemical properties of the soil (0-20 cm) and yield of pearl millet (Pennisetum glaucum), cowpea (Vigna unguiculata), and groundnut (Arachis hypogaea). Four N levels (0-45 kg N/ha) and rotation treatments including continuous fallow were investigated. Soil samples taken from the top 20 cm depth at the end of the experiment from treatments without nitrogen application which included continuous fallow, fallow-millet rotation, groundnut-millet rotation, cowpea-millet rotation, and continuous millet were analysed for soil pH, organic carbon, total nitrogen and exchangeable bases. Fertilizer N significantly increased yield of pearl millet, cowpea and groundnut. Continuous monocropping of pearl millet resulted in lower yields across N levels compared to legume-millet rotations. Legume yields were also consistently lower in monoculture than when rotated with millet. There was a decline in organic matter under continuous millet, cowpea-millet rotation and groundnut-millet rotation. The fallow-millet rotation supplied more mineral N than the legume-millet rotations. Nitrogen availability was greater in cowpea-millet rotation than continuous millet. Crop rotation was more productive than the continuous monoculture but did not differ in maintaining soil organic matter. The legume-millet rotation at 30 kg/ha N appears to be the most viable for millet production. Research should focus on understanding the effect of legume/cereal intercrops and rotations on soil productivity

Changes in a sandy sahelian soil following crop residue and fertilizer additions

The use of crop residues as surface mulches has been shown to have a beneficial effect on the growth of pearl millet [Pennisetum glaucum (L.) R.Br.] in the Sahelian zone of West Africa. This study was conducted to discern the mechanism(s) responsible for yield increases resulting from crop-residue additions in a field trial located on a sandy soil at the ICRISAT Sahelian Center near Niamey, Niger. Soil chemical and physical properties were examined to a depth of 120 cm after 5 yr of application of millet residue as a surface muich, P and N fertilizer, or a combination of fertilizer and residue. Annual residue application resulted in a higher exchangeable-base content, lower Al saturation, and slightly higher available-P values than the control. The use of fertilizer resulted in an increase in available P and exchangeable Ca. The combination of residue plus fertilizer resulted in greater enhancement of soil fertility parameters than the use of tbese inputs alone. Differences in soil chemistry were operative in only the top 20 cm of the soil profile, bowever, the surfaces of the plots receiving residues were 15 to 20 cm higher than the surfaces of the control and fertilizer-only plots. The surfaces of the residue plots also had lower clay contents than the surface soils in the nonresidue plots. The increase in soil fertility following the application of millet residue as a surface mulch was due to two mechanisms: (i) the recycling of nutrient elements to the soil following termite and microbial decomposition of the residue, and (ii) the entrapment of eolian materials, which generally have better fertility characteristics than the subsoil, or protection of the more fertile surface soil from the erosive effects of the strong winds that are common in the Sahe

Multi-site time-trend analysis of soil fertility management effects on crop production in sub-Saharan West Africa

Soil fertility constraints to crop production have been recognized widely as a major obstacle to food security and agro-ecosystem sustainability in sub-Saharan West Africa. As such, they have led to a multitude of research projects and policy debates on how best they should be overcome. Conclusions, based on long-term multi-site experiments, are lacking with respect to a regional assessment of phosphorus and nitrogen fertilizer effects, surface mulched crop residues, and legume rotations on total dry matter of cereals in this region. A mixed model time-trend analysis was used to investigate the effects of four nitrogen (0, 50, 90 or 150 kg/ha) and phosphorus (no fertilizer, 13 kg/ha single superphosphate, 39 kg/ha Tahouca rock phosphate, an additional annual placement of rock phosphate at 4 kg/ha, and as NPK) rates, annually applied crop residue dry matter at 500 and 2000 kg ha-1, and cereal-legume rotation versus continuous cereal cropping on the total dry matter of cereals and legumes. The multi-factorial experiment was conducted over four years (1995-98) at eight locations (Banizoumbou, Sadore, Kara Bedji, Goberi, Gaya, Fada-Kouare, Koukombo and Kaboli), with annual rainfall ranging from 510 to 1300 mm, in Niger, Burkina Faso, and Togo. With the exception of phosphorus, treatment effects on legume growth were marginal. At most locations, except for typical Sudanian sites with very low base saturation and high rainfall, phosphorus effects on cereal total dry matter were much lower with rock phosphate than with soluble phosphorus, unless the rock phosphate was combined with an annual seed-placement of 4 kg ha-1 phosphorus. Across all other treatments, nitrogen effects were negligible at 500 mm annual rainfall but at 900 mm, the highest nitrogen rate led to total dry matter increases of up to 77% and, at 1300 mm, to 183%. Mulch-induced increases in cereal total dry matter were larger with lower base saturation, reaching 45% on typical acid sandy Sahelian soils. Legume rotation effects tended to increase over time but were strongly species-dependen

Fertility status of selected millet producing soils of West Africa with emphasis on phosphorus

Millet (Pennisetum americanum) producing soils of West Africa were sampled at selected locations throughout the Sudano-Sahelian agroecological zone. The nutrient status of these soils was determined and related to P dynamics. Soils were neutral to acid in reaction, but few had any measurable amounts of exchangeable Al. Total P, Bray 1 extractable P, and P adsorption maxima were low which reflected their low levels of clay and organic matter. Phosphorus sorption characteristics were controlled by the poorly crystalline Al and Fe phases and the soil clay fraction. The poorly crystalline Al and Fe phases were highly correlated with the clay fraction. The P external requirement ranged from 11 to 40 mg P/kg soil. Given the low levels of total and labile P and the low fixation capacity of these soils, low to moderate levels of P amendments are necessary for sustained productivit