Optimizing maize productivity in the Sahel region through the incorporation of exotic shrub species and reduced mineral fertilization

Description du sujet. La dégradation des terres agricoles et la surexploitation sont causées au Mali par la croissance démographique, les aléas climatiques, la sécheresse à répétition, la baisse de la fertilité des sols, la mauvaise répartition des précipitations et la réduction de l'utilisation des engrais minéraux et organiques. Cependant, la contrainte majeure desdits systèmes dans cette zone demeure la baisse de la fertilité des sols qui se traduit généralement par l’épuisement de la teneur en éléments organiques et minéraux du sol.Objectif. L’étude vise l’amélioration de la productivité du sorgho ainsi que la préservation de la fertilité du sol par l’identification des espèces ligneuses prometteuses pour l’usage de leurs émondes en compostage de surface.Méthodes. L’étude a été conduite sur un dispositif en blocs complets randomisés (Bloc de Fisher) en quatre répétitions. La formule de fertilisation a été le facteur étudié à cinq niveaux de variations qui sont : T0 (Témoin sans apport d’émondes) ; T1 (P. reticulatum 2,5 t d’émondes/ha) ; T2 (G. senegalensis 2,5 t d’émondes/ha) ; T3 (G. sepium 2,5 t d’émondes/ha) ; T4 (P. reticulatum 0,83 t d’émondes/ha + G. senegalensis 0,83 t d’émondes/ ha + G. sepium 0,83 t d’émondes/ha). La détermination du mode de décomposition des émondes de ligneux et leur impact comme engrais vert sur les performances agronomiques du sorgho ont été évaluées au cours de cette étude.Résultats. La vitesse de décomposition suit l’ordre décroissant suivant : Gliricidia sepium Jacq. Walp > Piliostigma reticulatum (DC.) Hochst > Guiera senegalensis J. L. Gmel. L’apport des émondes a permis une amélioration de l’activité biologique des sols, un meilleur contrôle de l’érosion et une augmentation du rendement du sorgho comparé au témoin sans apport.Conclusion. Ces résultats montrent que l’apport annuel de 2 t.ha-1 de biomasse sèche des émondes de Guiera senegalensis J. L. Gmel., Piliostigma reticulatum (DC.) Hochst, Gliricidia sepium Jacq. Walp, et la combinaison des émondes des trois espèces permettent une amélioration des rendements du sorgho (respectivement 4,5 % ; 66,5 % ; 100 % et 5,59 %), une baisse significative de la densité apparente avec respectivement 1,32 g/cm3, 1,30 g/cm3, 1,25 g/cm3 et 1,29 g/cm3 contre 1,59 g/cm3 de densité apparente pour le témoin et une augmentation significative de la porosité du sol. Description of the subject. Agricultural land degradation and overexploitation are caused in Mali by population growth, climatic hazards, repeated drought, declining soil fertility, poor rainfall distribution, and reduced use of mineral and organic fertilizers. However, the major constraint of these systems in this area remains declining soil fertility, which generally results in the depletion of the soil's organic and mineral content.Objective. The study aims to improve sorghum productivity and preserve soil fertility by identifying promising woody species for the use of their prunings in surface composting.Methods. The study was conducted using a randomized complete block design (Fisher Block) with four replicates. The fertilization formula was the factor studied at five levels of variation: T0 (Control without prunings); T1 (P. reticulatum 2.5 t of prunings/ha); T2 (G. senegalensis 2.5 t of prunings/ha); T3 (G. sepium 2.5 t of prunings/ha); T4 (P. reticulatum 0.83 t of prunings/ha + G. senegalensis 0.83 t of prunings/ha + G. sepium 0.83 t of prunings/ha). This study assessed the decomposition mode of woody prunings and their impact as green manure on the agronomic performance of sorghum.Results. The decomposition rate followed the decreasing order of Gs > Pr > Gu. The addition of prunings led to an improvement in soil biological activity, better erosion control, and an increase in sorghum yield compared to the control without addition.Conclusion. These results show that the annual application of 2 t.ha-1 of dry biomass from the prunings of Guiera senegalensis J. L. Gmel., Piliostigma reticulatum (DC.) Hochst, Gliricidia sepium Jacq. Walp, and the combination of prunings from the three species lead to an improvement in sorghum yields (4.5 %; 66.5 %; 100 % and 5.59 %, respectively), a significant decrease in bulk density with 1.32 g/cm3, 1.30 g/cm3, 1.25 g/cm3 and 1.29 g/cm3, respectively, compared to 1.59 g/cm3 of bulk density for the control, and a significant increase in soil porosity.

In the coming decades, rainfall in many Mediterranean‐type ecosystems is expected to decline overall, but also become more variable interannually. Historically plant communities in these regions have been dominated by native shrubs, but are becoming increasingly invaded by exotic annual species, making it important to evaluate how native versus exotic species will respond to shifting rainfall patterns associated with climate change. Exotic species are often found to possess a suite of traits associated with fast growth and resource uptake, as well as high plasticity in traits. Hence, we hypothesized that exotic species would benefit disproportionately over native species under high rainfall conditions, while native species with more conservative growth strategies would better tolerate drought. We evaluated these expectations by manipulating rainfall (five levels, from total exclusion to a doubling of ambient rainfall) over plots containing a mix of herbaceous exotic species, mature native shrubs, and planted shrub seedlings, and measured functional trait and growth responses of focal species. We found significant variation among groups in their response to variation in rainfall quantity: growth of exotic herbaceous species was higher in response to high rainfall, and lower in response to drought, compared with native adult shrubs, with juvenile shrubs having an intermediate response. In contrast with these growth responses, functional traits of native and exotic species responded similarly to experimental variation in rainfall. Further, although we found exotic species possessed thinner leaves and higher photosynthetic capacity, neither mean trait values nor trait plasticity were predictive of species‐level responses to altered rainfall in this system. We conclude that while some functional traits often predict community composition across large environmental gradients, traits may not predict species responses to environmental change at local scales with limited species pools.

Zinc fertilization influence on maize productivity and grain nutritional quality under integrated soil fertility management in Zimbabwe

Background: Continuous cultivation without fertilizer application and soil erosion are responsible for plant nutrient depletion and yield decline of major food crops in Sub-Saharan Africa.Methods: Nutrient status of Calliandra calothyrsus, Leucaena leucocephala, Acacia angustissima and Cassia spectabilis were characterized. Field experiments were conducted over two years in the Western Highlands of Cameroon to evaluate the effects of the application of leaf biomass of agroforestry tree species and mineral fertilizers on maize yield performance. The residual effects on soil physicochemical properties were also investigated for umbric Cambisols of Babungo and ustic Oxisols of Bansoa. Ten treatments encompassing; sole leaf biomass of Calliandra calothyrsus, Leucaena leucocephala, Acacia angustissima and Cassia spectabilis, leaf biomasses combined with NPK fertilizer, sole NPK fertilizer and absolute control were laid in a randomized complete block design and replicated three times. Data were subjected to analysis of variance and the Duncan Test (p < 0.05) used for mean separation.Results: All the species characterized had nitrogen, polyphenol and lignin contents greater than 2.5 %, 5 % and 15 % respectively. Significant differences (p < 0.05) were observed among treatments on maize growth, productivity parameters and soil chemical properties for both soil types. The highest maize grain yields were recorded in plots amended with 1 t/ha of biomass of Calliandra calothyrsus or Leucaena leucocephala as well as1.5 t/ha of biomass of Acacia angustissima and Cassia spectabilis plus mineral fertilizer (50 N+ 37.5 P2O5 + 45 K2O) on both soils compared to other treatments.on umbric Cambisols and ustic Oxisols respectively. The residual effects of treatments on soil chemical properties showed severe nutrient depletion in control plots and those amended with sole inorganic fertilizer.Conclusions: Combined application of agroforestry tree biomass and inorganic fertilizers remains an appropriate technology to enhance maize yield and sustain production of resource-limited farmers of acid tropical soils..

The introduction of alien species represents one of the greatest threats to biodiversity worldwide. Highway construction increases the dispersal and invasion of exotic plant species. This study examined the assembly process of the plant communities to determine whether the roadsides of the Patagonian steppe represent a reservoir and dispersal source of invasive exotic species. We analyzed the composition of exotic and native species and functional groups present in the established vegetation and seed banks of roadsides and reference areas nearby. The type of dispersal of exotic and native species at the roadsides was also evaluated. Total cover and that of exotic and native species was lower at the roadsides than in the reference areas; however, at the roadsides the cover and seed abundance of exotic species was higher than that of native species. In the roadsides vegetation, native shrubs such as Acaena splendens predominated, along with exotic perennial herbs and grasses which were mainly represented by Rumex acetosella. In the seed bank the predominant species were exotic perennial herbs, also represented by R. acetosella, annual exotic species such as Epilobium brachycarpum and Verbascum thapsus, and annual native species such as Heliotropium paronychioides. No exotic shrubs were found either at the roadsides or in the reference areas. The species at the roadsides did not present a dominant type of dispersal. The abundance of exotic species at the roadsides, both in the aboveground vegetation and the seed bank, may be due to the stressful environment and the characteristics of the species themselves, such as the ability to form seed banks. This work revealed that the roadsides of the Patagonian steppe constitute reservoirs of invasive exotic species, highlighting the importance of identifying them and controlling their spread, with a view to generating ecosystem management programs.

Climate change and soil fertility decline are major threats to smallholder farmers' food and nutrition security in southern Africa, and cropping systems that improve soil health are needed to address these challenges. Cropping systems that invest in soil organic matter, such as no-tillage (NT) with crop residue retention, have been proposed as potential solutions. However, a key challenge for assessing the sustainability of NT systems is that soil carbon (C) stocks develop over long timescales, and there is an urgent need to identify trajectory indicators of sustainability and crop productivity. Here we examined the effects of NT as compared with conventional tillage without residue retention on relationships between soil characteristics and maize (Zea maysL.) productivity in long-term on-farm and on-station trials in Zimbabwe. Our results show that relationships between soil characteristics and maize productivity, and the effects of management on these relationships, varied with soil type. Total soil nitrogen (N) and C were strong predictors of maize grain yield and above-ground biomass (i.e., stover) in the clayey soils, but not in the sandy soils, under both managements. This highlights context-specific benefits of management that fosters the accumulation of soil C and N stocks. Despite a strong effect of NT management on soil C and N in sandy soils, this accrual was not sufficient to support increased crop productivity in these soils. We suggest that sandy soils should be the priority target of NT with organic resource inputs interventions in southern Africa, as mineral fertilizer inputs alone will not halt the soil fertility decline. This will require a holistic management approach and input of C in various forms (e.g., biomass from cover crops and tree components, crop residues, in combination with mineral fertilizers). Clayey soils on the other hand have greater buffering capacity against detrimental effects of soil tillage and low C input.

Water use characteristics of native and exotic shrub species in the semi-arid Loess Plateau using an isotope technique

The colonization of an exotic species by native herbivores is more likely to occur if that herbivore is a generalist. There is little information on the life-history mechanisms used by native generalist insects to colonize exotic hosts and how these mechanisms are affected by host properties. We examined the ability of the generalist seed beetle Stator limbatus Horn to colonize an exotic species. We compared its host preference, acceptability, performance, and egg size when ovipositing and developing on two native (Pithecellobium dulce (Roxb.) Benth and Senegalia riparia (Kunth)) and one exotic legume species (Leucaena leucocephala (Lam.)). We also analyzed the seed chemistry. We found that females recognize the exotic species as an unfavorable host for larval development and that they delayed oviposition and laid fewer and larger eggs on the exotic species than on the native species. Survivorship on the exotic host was 0%. Additionally, seeds of the native species contain five chemical compounds that are absent in the exotic species, and the exotic species contains three sterols, which are absent in the native legumes. Genetically based differences between beetles adapted to different hosts, plastic responses toward new hosts, and chemical differences among seeds are important in host colonization and recognition of the exotic host. In conclusion, the generalist nature of S. limbatus does not influence its ability to colonize L. leucocephala. Explanations for the colonization of exotic hosts by generalist native species and for the success of invasive species must be complemented with studies measuring local adaptation and plasticity.

Previous studies of the invasion of two exotic plants – Berberis thunbergii and Microstegium vimineum – in hardwood forests of New Jersey have shown a significant increase of pH in soils under the invasive plants as compared with soils from under native shrubs (Vaccinium spp). We present a further investigation of soil properties under the exotic plants in question. We measured the densities of earthworms in the soil under the two exotics and the native shrubs in three parks in New Jersey. In the same populations we also measured the extractable ammonium and nitrate in the top 5 cm of the soil, as well as the respiration of the soils and the potential rates of mineralization (aerobic lab incubation). In addition, we measured the nitrate reductase activity in leaves of the two exotic plants and several native shrubs and trees. Although there were differences between parks, we observed significantly higher earthworm densities in the soil under the exotic species. The worms were all European species. Soil pH, available nitrate and net potential nitrification were significantly higher in soils under the two exotic species. In contrast, total soil C and N and net ammonification were significantly higher under native vegetation. Nitrate reductase activities were much higher in the leaves of exotic plants than in the leaves of native shrubs and trees. Changes in soil properties, especially the change in nitrogen cycling, associated with the invasion of these two plant species may permit the invasion of other weedy or exotic species. Our results also suggest that even if the two exotic species were removed, the restoration of the native flora might be inhibited by the high nitrate concentrations in the soil.

This study, conducted in Bazoulé, central Burkina Faso during the 2023/2024 seasons, evaluated the impact of three fertilizer trees – Albizia stipulata, Albizia lebbeck, and Gliricidia sepium – on soil quality and maize productivity, without the addition of organic or mineral fertilizers. Despite young trees and no complementary inputs or conservation practices, the results still showed promising improvements in yields and soils. A. stipulata consistently produced the highest maize grain yields (1.814 t/ha in 2023; 1.621 t/ha in 2024) and the greatest aboveground biomass (3.780 t/ha in 2023 and 3.264 t/ha in 2024). All fertilizer tree plots improved key soil properties, including organic carbon, nitrogen, available phosphorus, and cation exchange capacity. A. stipulata also enhanced soil pH (7.08) and water infiltration rates (1.21 cm/h versus 1.04 cm/h in the control). Meanwhile, G. sepium demonstrated strong hydrological performance, highlighting its complementary role. These results indicate that even young fertilizer trees can enhance soil fertility, crop productivity, and water retention under climate stress. The study recommends multiseason trials combining fertilizer trees and water conservation techniques, along with farmer training and localized climate monitoring. Overall, the findings promote fertilizer trees as a nature-based solution for food security and land restoration in the Sahel region.

There are abundant local legume trees and shrubs potentially suitable for alley cropping systems in the sub-Saharan Africa, which are yet to be studied. The nitrogen contribution of two years old Albizia lebbeck and S. corymbosato yield of maize grown in alley cropping was compared to that of Senna siamea, Gliricidia sepium and Leucaena leucocephala in four seasons at Ibadan. Maize shoot biomass and maize grain yield in A. lebbeck alley compared favourably with that in G. sepium and L. leucocephala. Maize biomass and grain yield in S. corymbosa alleys were the lowest. Within A. lebbeck, L. leucocpehala, and G. sepium alleys there were no significant differences in the maize yield in the alleys that received 0, 40 or 80 kg N/ha. Application of more than 40 kg N/ha in S. corymbosa alleys was not necessary as there was no significant increase in maize yield at the higher level of nitrogen. Maize yield and N uptake in A. lebbeck alleys were not significantly different from yield and N uptake in G. sepium, and L. leucocephala at the same fertilizer level. There was a significant correlation between hedgerow tree biomass and maize grain yield. At the end of twelve weeks after pruning application, the organic residues of the pruning applied in the alleys ranged from 5% in G. sepium and 44% in A. lebbeck in the first year compared with the original pruning applied which showed that the slow rate of A. lebbeck decomposition could have a beneficial effect on the soil. The maize N recovery from applied N fertilizer was low (10–22%). Percentage N recovery from the prunings was low in the non-N fixing trees (12–22%), while the recovery was high (49–59%) in A. lebbeck as well as in the other nitrogen fixing tree prunings. Thus A. lebbeck, apart from enhancing maize growth and grain yield like in L. leucocephala and G. sepium, had an added advantage because it remained longer as mulching material on the soil because of its slow rate of decomposition. It was able to survive pruning frequencies with no die-back. This indicates that A. lebbeck is a good potential candidate for alley cropping system in West Africa. S. corymbosa performed poorly compared with the other legume trees. Though it responded to N fertilizer showing a positive interaction between the hedgerow and fertilizer application, it had a high die back rate following pruning periods and termite attack.

Exotic shrub species (Caragana korshinskii) is more resistant to extreme natural drought than native species (Artemisia gmelinii) in a semiarid revegetated ecosystem

Decomposition and spatial microbial heterogeneity associated with native shrubs in soils of agroecosystems in semi-arid Senegal

Alteration of soil physical properties and processes after ten years of intercropping with native shrubs in the Sahel

The aim of this study was to evaluate the effect of soil cover with a combination of tree leguminous on increasing grain yield, grain protein content, and maize protein yield. The experiment was conducted with 10 treatments: Leucaena leucocephala + Clitoria fairchildiana + urea (L+C+U); L. leucocephala + Acacia mangium + urea (L+A+U); Gliricidia sepium + C. fairchildiana + urea (G+C+U); G. sepium + A. mangium + urea (G+A+U); L. leucocephala + C. fairchildiana (L+C); L. leucocephala + A. mangium (L+A); G. sepium + C. fairchildiana (G+C); G. sepium + A. mangium (G+A); bare soil with urea (B+U); and a control with bare soil without mineral fertiliser. Differences between G+C+U and B+U, in the agronomic efficiencies, increase in N contents, increase in grain yield. To increase the protein yields in humid regions, leguminous are used to provide nutrients and improve the root environment rather than interacting antagonistically with the crops.