Integrated natural resource management (INRM) is considered in the context of evolving crop-livestock systems in West Africa and recent developments in approaches for INRM research. The major crop-livestock systems, ranging from extensive grazing, through integrated crop-livestock farming to intensive peri-urban 'industrial' type production are considered. Relationships between these systems and key INRM issues facing farmers in each are highlighted. Results of research aimed at improving and understanding crop-livestock production systems, followed by two examples of on-going INRM strategies from mixed farming systems in the region are discussed. Challenges and opportunities for research on INRM are discussed in relation to the evolving production systems. It is argued that by taking an INRM approach to research, institutions are beginning to address issues confronted and managed by farmers. With such an approach, interventions will be increasingly relevant and more readily adapted and widely adopted by smallholder farmers in the region.

Although crucial for assessing the functioning of alley cropping systems, quantitative information related to the hedgerow tree root distribution remains scarce. Soil mapping and destructive soil sampling was used to assess the impact of soil profile features on selected root characteristics of Senna siamea hedgerows, growing in alley cropping systems in three sites (Glidji, Amoutchou, and Sarakawa) representative for the derived savanna of Togo, West Africa. While the soil profiles in Glidji and Sarakawa contained a clay accumulation horizon, the Amoutchou profile was sandy up to 1 m. The number of small roots (diameter < 2 mm), quantified on a soil profile wall, decreased with depth in all sites. For most soil depths, the abundance of small roots tended to be higher near the tree base, e.g., ranging from 5.3 dm−2 in Amoutchou to 21.4 dm−2 in Glidji for the 0–20 cm layer, than in the middle of the alley, e.g., ranging from 3.1 dm−2 in Amoutchou to 13.8 dm−2 in Glidji for the 0–20 cm layer. Root length density (RLD) of the 0–10 cm and 10–20 cm layers was significantly higher in Glidji than in Amoutchou (P < 0.05) and in Sarakawa (P = 0.08). Differences in RLD between sites were not significant for layers below 30 cm. For each layer, root weight densities (RWD) were similar in all sites, e.g., ranging from 0.44 mg cm−3 in Amoutchou to 0.64 mg cm−3 in Glidji in the 0–10 cm layer, indicating that the roots in the Glidji topsoil had a smaller overall diameter than in Amoutchou. In Amoutchou, the relative RLD was lower than in Glidji or Sarakawa for the top 40 cm of soil, while the inverse was observed for the layers between 50 and 100 cm deep and this was related to the sandy soil profile in Amoutchou. Another consequence of the sandy profile was the larger tap root diameter below 50 cm in Amoutchou compared to Sarakawa. For all sites, significant (P < 0.001) linear regressions were observedbetween RLD's, RWD's, and the abundance of small roots, although the variation explained by the regression equations was highest for the relationship between RLD and RWD. The potential of the hedgerows to recover nutrients leached beyond the reach of food crops or the safety-net efficiency was evaluated for the tree sites.

Sustainable resource management is the critical agricultural research and development challenge in sub-Saharan Africa. The accumulated knowledge on soil management gathered over the last 10 years, combined with solid crop improvement and plant health research at farmers' level, has brought us to a stage where we can now address with confidence the intensification of cereal-grain-legume-based cropping systems in the dry savanna of West Africa in a sustainable and environmentally positive manner.Two sustainable farming systems that greatly enhance the productivity and sustainability of integrated livestock systems have been developed and implemented in the dry savanna of Nigeria. These are: (i) maize (Zea mays L.)-promiscuous soybean [Glycine max (L.) Merr.] rotations that combine high nitrogen fixation and the ability to kill large numbers of Striga hennonthica seeds in the soil; and (ii) miflet [Eleusine coracana (L.) Gaerth] and dual-purpose cowpea [Vigna unguiculata (L.) Walp.]. Improvement of the cropping systems in the dry savanna has been driven by the adoption of promiscuously nodulating soybean varieties (in particular TGx 1448-2E) and dual-purpose cowpea. The rate of adoption is very high, even in the absence of an efficient seed distribution system. The number of farmers cultivating the improved varieties increased by 228% during the last 3 years. Increased production of promiscuous soybean has been stimulated by increased demand from industries and home utilization. Production in Nigeria was estimated at 405,000 t in 1999 compared to less than 60,000 t in 1984. Economic analysis of these systems shows already an increase of 50-70% in the gross incomes of adopting farmers compared to those still following the current practices, mainly continuous maize cultivation. Furthermore, increases in legume areas of 10% in Nigeria (about 30,000 ha in the northern Guinea savanna) and increases of 20% in yield have translated into additional fixed nitrogen valued annually at US$ 44 million. This reflects, at the same time, an equivalent increase in land-use productivity, and with further spread of the improved crops, there are excellent prospects for additional economic and environmental benefits from a very large recommendation domain across West Africa. (C) 2003 Elsevier B.V. All rights reserved.

Although the fertility status of soils in the West African moist savanna is generally believed to be low, crop yields on farmers' fields vary widely from virtually nil to values near the potential production. The soil fertility status was evaluated for a number of farmers' fields selected at random in 2 villages (Zouzouvou and Eglimé) representative for the derived savanna (DS) benchmark area and in 2 villages (Danayamaka and Kayawa) representative for the Northern Guinea savanna (NGS) benchmark area. The relation between soil fertility status and soil type characteristics and fertilizer use was explored. In an accompanying missing nutrient greenhouse trial, the most limiting nutrients for maize growth were determined. While soils in the DS villages were formed on different geological units, soils in the NGS villages could be differentiated according to their position on the landscape. Generally, soils in the DS contained a smaller amount of silt (104 vs. 288 g kg −1 ), a larger amount of sand (785 vs. 584 g kg −1 ), C (9.3 vs. 6.3 g kg −1 ), N (0.7 vs. 0.5 g kg −1 ), Olsen-P (10.7 vs. 5.4 mg kg −1 ), and had a higher CEC (7.0 vs. 4.8 cmolc kg −1 ) than soils in the NGS villages. The large silt content of the soils in the NGS is a reflection of the aeolian origin of the parent material. Within the benchmark areas, general soil fertility characteristics were similar in the villages in the NGS, except for a larger amount of particulate organic matter in Kayawa than in Danayamaka. This may also have led to a significantly larger amount of ammonium-N content in the 0–20 and 20–40 cm soil layers in Kayawa compared to Danayamaka (42 vs 24 kg N ha −1 in the 0–20 cm soil layer). Differences in topsoil soil characteristics between the DS villages were a reflection of differences in clay quality (kaolinitic vs. 2:1 clay minerals) of the parent material and past fertilizer use. The Olsen-P and exchangeable K contents were observed to increase with increased fertilizer application rate in both benchmarks, while fertilizer application rate had no significant effect on the organic C or total N content of the soil nor on its ECEC. The response of maize shoot biomass production to applied N was similar for both benchmarks (biomass accumulation in the treatment without N was, on average, 55% of the biomass production in the treatment which received all nutrients), while soils in the NGS responded more strongly to applied P than soils in the DS (37% vs 66% of biomass production in the treatment which received all nutrients). The more favourable P status of soils in Eglimé (DS) was attributed to the more intense use of P fertilizers, as a result of government-supported cotton production schemes. Response to cations, S or micronutrients were neglegible. A significant linear relationship was found between the soil Olsen-P content and the response to applied P up to levels of 12 mg kg −1 in the topsoil. Above this level, a plateau was reached.

Nutrient depletion is a major constraint to crop production for moist savanna soils, and inputs of nutrients are required to overcome this constraint. The impact of sole and combined applications of organic inputs (OIs) [fresh tree prunings, Pueraria phaseoloides (Roxb.) Benth. residues, and manure] and urea [(NH 2 ) 2 CO] on maize ( Zea mays L.) performance was investigated at four sites in West Africa. Interactions between OIs and urea resulting in added benefits from their mixed rather than sole application were quantified, and likely causes were evaluated. Maize in the mixed treatments, receiving 45 kg ha −1 urea N and 45 kg ha −1 N as OIs, produced 1.6 and 3.7 Mg ha −1 grain in Sékou and Glidji, respectively. Based on the yields from sole application of either OIs or urea, added benefits from the mixture were 0.49 Mg ha −1 grain ( P < 0.001) in Sékou and 0.58 Mg ha −1 ( P < 0.15) in Glidji. These benefits were generated during grain filling, which was characterized by drought, and they were likely caused by improved soil water conditions with mixed applications compared with sole applications. Nitrogen recovery from urea was higher in the combined treatments (44% in Sékou and 32% in Glidji) relative to the sole urea treatments (22% in Sékou and 15% in Glidji). Positive interactions between OIs and urea occurred at two of four sites and were likely caused by improved soil water conditions after applying OIs. Organic inputs can alleviate constraints to crop growth other than N depletion and, as such, improve the use efficiency of N fertilizer.

The study was conducted in research villages in the derived savannah (DS) and northern Guinea savannah (NGS) benchmark areas of the Ecoregional Programme for the humid and sub-humid tropics in Sub-Saharan Africa to investigate the possible benefits of combining organic matter with urea under a range of on-farm conditions. Biophysical and socioeconomic characteristics of the area are discussed. The maize response to combined applications of organic matter and urea in on-station field trials at four locations (Bouaké, central Côte d'Ivoire; Glidji, southern Togo; Sékou, southern Benin and Zaria, northern Nigeria) and the maize grain yield in a researcher-managed on-farm trial in two villages (Eglimé and Zouzouvou) in the DS benchmark area, southern Benin, and in two other villages (Kayawa and Danayamaka) in the NGS benchmark area, northern Nigeria, are presented and discussed. In the DS, a 2-year farmer-managed trial was initiated in 1999 by the Research and Development branch of INRAB in southern Benin, wherein cowpea was used as an in-situ source of organic matter. In the NGS, demonstration trials were initiated at seven states of the northwestern and northeastern Nigeria. Preliminary yield data support observations made earlier under on-station and researcher-managed on-farm conditions: maize grain yields in the sole fertilizer treatment were similar to yields in the mixture treatment in which approximately 40% of the fertilizer N was substituted by manure.

The question of how increased soil organic carbon (SOC) levels, through increased buffering for water, cations, and against pH-changes, translate into maize yields and increased efficiency of inorganic fertilizers is addressed. The study investigates how much organic matter needs to be applied to the soil to achieve a certain SOC increase for West African conditions. This will give a more realistic view on the magnitude of the achievable SOC increase, and facilitate the discussion on potential benefits of the SOC increase. This study is mainly limited to the savanna zone in West Africa, and considers the situation where the land is cultivated continuously or almost continuously.

Differences in growth, nodulation and arbuscular mycorrhizal fungi (AMF) root infection among recent cowpea breeding lines from IITA were examined at low and high P levels in pot (94 lines) and field experiments (43 lines) at Fashola in the derived savanna zone of Nigeria. Based on their growth performance, these lines were subdivided into 5 groups: (i) poor performance under low and high P conditions; (ii) good performance under low P and poor performance under high P; (iii) intermediate performance under high and low P; (iv) good performance under high and low P conditions; and (v) good performance under high P and poor performance under low P. About 42% of the breeding lines (18 out of 43 lines tested) had the same grouping for the field and pot experiments. Eight cowpea lines (4 P-responders and 4 non-P-responders) were selected from the first experiment for subsequent studies on the effect of P supply (0, 20, 40 and 60 kg P ha -1 ) on P uptake, P use efficiency, dry matter production, N-fixation, AMF infection and N balance. Dry matter production, shoot/root ratio, total shoot N, and total N-fixed of the non-P-responder line, IT81D-715, were strongly related to P uptake efficiency. The P-responder IT81D-849 had a significant (95%) correlation between AMF and P-use efficiency. The cowpea lines fixed on average 22 kg N ha -1 , which was 70% of the plant total N. The N balance based on the difference between the amount of N 2 fixed and N exported through the harvest, ranged between −10.6 kg N ha -1 and +7.7 kg N ha -1 . Based on its adaptability to grow in low P soils and overall positive N balance, the cowpea line IT81D-715 should be recommended for cultivation when P is the limiting factor.

The impact of land use (unfertilized continuous maize cropping, unfertilized and fertilized alley cropping with maize, Gliricidia sepium tree fallow, natural fallow) on the soil organic matter (SOM) status and general soil fertility characteristics were investigated for a series of soils representative for the West African moist savanna zone. Three soils from the humid forest zone were also included. In an associated pot experiment, relationships between maize N and P uptake and SOM and general soil characteristics were developed. Soils under natural fallow contained the highest amount of organic C (1.72%), total N (0.158%), and had the highest effective cation exchange capacity (ECEC) [8.9 mEq 100 g–1 dry soil], while the Olsen P content was highest in the fertilized alley cropping plots (13.7 mg kg–1) and lowest under natural fallow (6.3 mg kg–1). The N concentration of the particulate organic matter (POM) was highest in the unfertilized alley cropping plots (2.4%), while the total POM N content was highest under natural fallow (370 mg N kg–1) and lowest in continuously cropped plots (107 mg N kg–1). After addition of all nutrients except N, a highly significant linear relationship (R2=0.91) was observed between the total N uptake in the shoots and roots of 7-week-old maize and the POM N content for the savanna soils. POM in the humid forest soils was presumably protected from decomposition due to its higher silt and clay content. After addition of all nutrients except P, the total maize P uptake was linearly related to the Olsen P content. R2 increased from 0.56 to 0.67 in a multiple linear regression analysis including the Olsen P content and clay content (which explained 11% of the variation in P uptake). Both the SOM status and N availability were shown to be improved in land-use systems with organic matter additions, while only the addition of P fertilizer could improve P availability.

The moist savanna of West-Africa is characterized by a wide range of climates and soil types. The impact of the biophysical environment on hedgerow N uptake, wood production and maize grain yield was assessed for three years in three alley cropping trials with a selected number of hedgerow species in Glidji (Southern Togo), Amoutchou (Central Togo), and Sarakawa (Northern Togo). Senna siamea hedgerows accumulated significantly more N in the first pruning in Glidji (129−138 kg N ha−1) and Sarakawa (102−185 kg N ha−1) than in Amoutchou (17–26 kg N ha−1). This difference in N uptake was attributed to the infertile subsoil in Amoutchou, which was sandy up to 1 m and had a shallow groundwater-table. The amount of N accumulated in the Gliricidia sepium biomass varied between 38 kg N ha−1 in Glidji and 142 kg N ha−1 in Amoutchou. Averaged over all species and sites, 9 to 29% and 9 to 39% of the annual N accumulation in the hedgerow biomass is incorporated in the second, respectively third pruning. The Gliricidia trees produced between 12 and 26 ton fresh matter ha−1 of wood and the Senna trees between 4 and 38 ton fresh matter ha−1. Maize grain yield in Glidji was not affected by treatments (3196 kg ha−1, on average). In Amoutchou, the highest grain production was observed in the Gliricidia treatment (2774 kg ha−1 vs 1007 kg ha−1 in the control), while in Sarakawa, the Gliricidia (3786 kg ha−1) and Senna (3842 kg ha−1) plots produced a greater grain yield than the control plots (2123 kg ha−1). Maize yield increase in the alley cropping systems relative to the control plots was related to the soil total N content. Top and sub-soil characteristics were shown to be an important modifier of the functioning of alley cropping systems and should be taken into account when deciding on whether to use alley cropping and when selecting the hedgerow species.

The potential of alley cropping systems supplied with a limited amount of fertilizer to restore crop productivity on a degraded site and to maintain crop productivity on a recently cleared, non-degraded site on ‘terre de barre‘ soils in Southern Bénin was investigated from 1994 to 1996. Leucaena leucocephala, Senna siamea and Gliricidia sepium were used as hedgerow species. Maize yields of the no-tree control plots dropped from the initial (1990) 401 kg ha−1 and 2181 kg ha−1 on the degraded and non-degraded sites, respectively, to 109 kg ha−1 and 1346 kg ha−1 in 1996, even with application of a minimal amount of mineral fertilizer. The alley cropping systems produced on average (mean of three treatments and three years) 107% more grain than the initial 1990 values on the degraded site and 11% less grain than the initial 1990 values on the non-degraded site. Especially the Senna and to a lesser degree the Leucaena treatment yielded consistently more grain than the control. The Senna trees contained a larger amount of N and produced more wood during the first pruning on the degraded site (155 kg N ha−1 and 14.0 ton fresh wood ha−1) than on the non-degraded site (49 kg N ha−1 and 6.6 ton fresh wood ha−1) most likely because of differences in subsoil fertility, as indicated by the higher clay, exchangeable bases, and N content between 60 and 125 cm cm. N accumulation and wood production by the Leucaena and Gliricidia trees was similar in both sites (82 and 36 kg N ha−1 and 4.6 and 9.3 ton fresh wood ha−1, respectively). When a limited amount of fertilizer is available, Senna appears to be the best choice as hedgerow species on sites with a relatively fertile subsoil. For other soils, a N2-fixing species may be a better choice.

In cropping systems with limited amounts of external inputs, the soil organic matter pool (SOM) may contribute significantly to plant nutrition. The impact of organic inputs on total SOM and particulate organic matter (POM) N contents as affected by soil type and the relationships between sources of N and maize N uptake were assessed for a set of alley cropping trials in the West- African moist savanna. The trials were established in Niaouli (Bénin Republic), in Glidji, Amoutchou, and Sarakawa (Togo), and in Bouaké and Ferkessédougou (Côte d‘ Ivoire). The total soil N content, averaged over all treatments and years, varied between 324 and 1140 mg N kg−1 soil. The POM-N content varied between 50 and 160 mg N kg−1 soil. The average proportion of soil N belonging to the POM pool ranged between 9% and 29%. This was significantly related to the annual N inputs from maize stover and prunings, when averaged over the different alley cropping treatments. The trial ‘age‘ also appeared to be related to the impact of the different treatments on the POM-N content. The Ferkessédougou soil contained a relatively higher proportion of total soil N in the POM pool because of its relatively high silt and clay content, compared to the other sites. The relative change in POM-N content between 1996 and the initial sampling was about twice the relative change in total soil N content. This suggests that N incorporated in the POM is relatively labile, compared to N incorporated in the other SOM fractions. Maize N uptake was related to the amount of add pruning-N (partial r2 of 27%), the rainfall during the growing season (partial r2 of 17%), the POM-N content (partial r2 of 14%), and to a lesser degree to the POM N concentration (partial r2 of 5%), the fertilizer N addition rate (partial r2 of 3%), and the silt and clay content of the soil (partial r2 of 3%). The POM-N content was shown to be influenced by organic matter additions and soil characteristics and to contribute significantly to maize N supply. This pool may be an important indicator for the soil fertility status of savanna soils.

A synthesis of results from the savanna zone of West Africa suggests that cowpea rotation can be considered to be an effective resource management technology in cereal-based systems. Part of the N requirement of cereal crops can be satisfi ed by cowpea crop rotation. Furthermore, benefi ts of cowpea rotation are sometimes higher than expected based on the N content of the cowpea crop alone. Reasons for this include substantial root biomass and N, substantial N-sparing by the legume, and other benefi ts such as reduction in Striga hermonthica, or pests and often diseases, and possibly access to sparingly soluble P. The characteristics to be encouraged to maximize the N benefi t are the amount of nitrogen derived from the atmosphere and the amount of N returned in the residues. In addition the data sug- gest that (1) the maturity class of the cowpea variety should be as late as possible, (2) the cereal should be planted as soon as possible after cowpea has been harvested, and (3) minimum soil requirements for optimum cowpea growth should be respected. These can be considered as recommendations to be followed if appropri- ate for local agroecological and socioeconomic circumstances.