Impact of dry-wet cycles on carbon mineralization of tropical soils. [P43]

In the context of climate change, the increase of dry-wet cycles could cause large losses of soil carbon stock. Located in the Sudano-Sahelian region, soils of North Cameroon experience dry periods followed by erratic rains at the beginning of the cropping season. This study was conducted during the dry season in North Cameroon and aimed to assess the impact of dry-wet cycles on carbon mineralization of soil. These soils were subjected to two differentiated managements of soil cover, mulch of straw residues and without mulch. For each soil, four water supply schemes were applied: permanently dry soil as a reference, permanently moist soil, soils subjected to five and to ten dry-wet cycles. Soil respiration, soil temperature and moisture were measured using four repetitions per plot during fifty days with an infrared gas analyzer and probes. The frequency of dry-wet cycles moderately increased the total soil carbon mineralization on a cultivated soil and mulched regularly. On this soil, ten dry-wet cycles caused a cumulated C mineralization of 1.32 tC.ha-1 on 50 days against respectively 1.17 and 1.15 tC.ha-1 on soils with five dry-wet cycles and permanently moist soils. In the absence of mulch, frequency of dry-wet cycles moderately decreased the total soil carbon mineralization. Ten dry-wet cycles caused a cumulated C mineralization of 0.74 tC.ha-1 on 50 days against respectively 0.93 and 0.94 tC.ha-1 on soils with five dry-wet cycles and permanently moist soils. Our results indicated that in tropical agro-ecosystems, the frequency of dry-wet cycles and management of soil might induce changes in the dynamics of soil carbon and should be considered into the simulation models of soil carbon. (Texte intégral

No-tillage and intercropping improve the yield and profitability of maize-cotton rotations in Northern Benin

This study investigated the effect of conservation agriculture (CA) practices (e.g. no-tillage (NT) and maize-soybean (MS) intercrops) on the yield and profitability of maize and cotton within the first two years of a crop rotation system. A factorial design that compared two tillage practices (conventional tillage, CT and NT) and two cropping systems (sole maize, M and MS) was implemented on an experimental station in Northern Benin. All treatments were replicated thrice in 2022 and 2023. Soybean yield, maize grain yield and yield components, and seed-cotton yield and yield components were measured. Gross margin, labour productivity, and benefit:cost ratio were calculated, and a sensitivity analysis was done on the economic indicators under five scenarios (S0: gross margin calculation based on actual costs; S1: 30% higher fertiliser price; S2: 30% lower fertiliser price; S3 and S4, respectively: considering +/−1 standard deviation to the maize grain + soybean and seed-cotton yield). Tillage options and cropping systems significantly affected maize and cotton performance, but effects tended to vary between seasons. Treatment NT+MS produced the highest grain yield (4487 kg ha–1) and rain use efficiency (4.12 kg mm–1) in 2022, while CT+M produced the highest grain yield (3195 kg ha–1) and rain use efficiency (2.84 kg mm–1) in 2023. In the case of cotton, NT produced higher seed-cotton yield (1720 kg ha–1), boll number (7.38 bolls/plant), and rainfall use efficiency (1.56 kg mm–1) compared to CT in 2022. In 2023, cotton preceded by maize-soybean intercrops (NT+MS and CT+MS) produced significantly higher yield, aboveground and belowground biomass than cotton preceded by sole maize (NT+M and CT+M). For maize plus soybean, treatment NT+MS resulted in a significant increase in the gross margin, with an average of 582 US$ ha–1 with respect to CT+M under all scenarios in 2022, whereas CT+M and NT+MS attained a significantly higher maize/ soybean gross margin in 2023. In the case of cotton, NT increased gross margin by 90-314% compared to CT across the sensitivity analysis scenarios in 2022. In 2023, cotton preceded by MS intercrops (NT+MS and CT+MS) showed a higher gross margin than preceded by sole crops (NT+M and CT+M) across all scenarios. To the well-documented effects of diversification on crop productivity, this study adds evidence on its positive impact on economic performance in a West African context. On-farm research and rural extension are necessary to further fine-tune these practices to fit the reality of smallholder cotton-based cropping systems of Benin.</p

No-tillage and intercropping improve the yield and profitability of maize-cotton rotations in Northern Benin

This study investigated the effect of conservation agriculture (CA) practices (e.g. no-tillage (NT) and maize-soybean (MS) intercrops) on the yield and profitability of maize and cotton within the first two years of a crop rotation system. A factorial design that compared two tillage practices (conventional tillage, CT and NT) and two cropping systems (sole maize, M and MS) was implemented on an experimental station in Northern Benin. All treatments were replicated thrice in 2022 and 2023. Soybean yield, maize grain yield and yield components, and seed-cotton yield and yield components were measured. Gross margin, labour productivity, and benefit:cost ratio were calculated, and a sensitivity analysis was done on the economic indicators under five scenarios (S0: gross margin calculation based on actual costs; S1: 30% higher fertiliser price; S2: 30% lower fertiliser price; S3 and S4, respectively: considering +/−1 standard deviation to the maize grain + soybean and seed-cotton yield). Tillage options and cropping systems significantly affected maize and cotton performance, but effects tended to vary between seasons. Treatment NT+MS produced the highest grain yield (4487 kg ha–1) and rain use efficiency (4.12 kg mm–1) in 2022, while CT+M produced the highest grain yield (3195 kg ha–1) and rain use efficiency (2.84 kg mm–1) in 2023. In the case of cotton, NT produced higher seed-cotton yield (1720 kg ha–1), boll number (7.38 bolls/plant), and rainfall use efficiency (1.56 kg mm–1) compared to CT in 2022. In 2023, cotton preceded by maize-soybean intercrops (NT+MS and CT+MS) produced significantly higher yield, aboveground and belowground biomass than cotton preceded by sole maize (NT+M and CT+M). For maize plus soybean, treatment NT+MS resulted in a significant increase in the gross margin, with an average of 582 US$ ha–1 with respect to CT+M under all scenarios in 2022, whereas CT+M and NT+MS attained a significantly higher maize/soybean gross margin in 2023. In the case of cotton, NT increased gross margin by 90-314% compared to CT across the sensitivity analysis scenarios in 2022. In 2023, cotton preceded by MS intercrops (NT+MS and CT+MS) showed a higher gross margin than preceded by sole crops (NT+M and CT+M) across all scenarios. To the well-documented effects of diversification on crop productivity, this study adds evidence on its positive impact on economic performance in a West African context. On-farm research and rural extension are necessary to further fine-tune these practices to fit the reality of smallholder cotton-based cropping systems of Benin

Limited yield penalties in an early transition to conservation agriculture in cotton-based cropping systems of Benin

Transitioning toward minimum or no tillage is challenging for smallholder farmers in sub-Saharan Africa (SSA), due to the possible yield penalties during the initial years of a transition. Understanding the early impacts of such transitions is crucial in a cash crop such as cotton, on which farmers rely for their income, and is necessary to inform agroecological strategies to cope with both these challenges. This study explores the combined impact of minimum or no tillage and fertilizer regimes on agronomic parameters of cotton–cereal rotations, as practiced by smallholder farmers in Benin. A multilocation experiment was set up in three different agroclimatic zones, namely, Savalou (7°55′41″, 1°58′32″), Okpara (2°48′15″, 7°72′07″), and Soaodou (10°28′33″, 1°98′33″). In each area, the experiment was laid out as a split-plot design with four replications (main plot = soil preparation; subplot = fertilizers regimes). The treatments consisted of three different forms of soil preparation, namely, tillage, strip tillage, and no tillage or direct seeding, and four fertilization regimes, namely, basal mineral fertilizers (BMF, 200 kg ha1 of N14P18K18S6B1 + 50 kg ha1 of urea), BMF + A (200 kg ha1 of calcium phosphate amendment, 22P2O5-43CaO−4S), BMF + C (400 kg ha1 of compost), and BMF + A + C. At all sites, direct seeding led to lower below-ground biomass growth and seed cotton yields compared with conventional tillage in an early transition to conservation agriculture starting from degraded soils (2% to 25%). Weak rooting under direct seeding resulted in lower cotton yields compared with that under tillage (−12%) and strip tillage (−15%). At 45 and 90 days after emergence, cotton plants were shorter under direct seeding compared with tillage (−9% and −13%, respectively) and strip tillage (−23% and −6%, respectively). Fertilizer regimes affected seed cotton yields differently across sites and treatments, with marginal responses within soil preparation methods, but they contributed to increase yield differences between conventional and no tillage. Considering the need for sustainable practices, in the context of degraded soils and poor productivity, such limited yield penalties under CA appear to be a reasonable trade-off in the first year of a transition. Alternatively, the results from the first year of this experiment, which is meant to continue for another 5 years, suggest that strip tillage could be a sensible way to initialize a transition, without initial yield penalties, toward more sustainable soil management

Understanding farm-level diversity to guide soil fertility management in West African cotton systems:Evidence from Benin

Although cotton cultivation grants farmers access to annual inputs of mineral fertilisers, there is a generalised tendency of soil fertility decline in Benin's cotton-growing area. This study aimed to understand the link between farm socioeconomic diversity, soil management practices, and soil fertility status in cotton-based farming system of Benin. Socio-demographic and farm management data were collected from 242 farms on three sites in southern-central and northern Benin. Principal component analysis and a hierarchical clustering were used to construct a farm typology. Soil management practices were analysed in the light of this typology. Composite soil samples 20 cm deep were then taken from 40 plots representing the farm/soil types identified, to assess variability in soil fertility as influenced by farm types and management practices. Four farm types emerged, differing in resource endowments and soil management practices. Practices such as manure application (92 %) and rotational herd corralling (42 %) were adopted more often by livestock owners. Farms without livestock implemented practices such as crop rotation (90 %) and intercropping (41 %). Soil fertility status was low to very low in all farms sampled across the three sites (extractable phosphorus &lt;10 mg P/kg soil, soil organic matter &lt; 20 g kg−1 soil). Although a link between farms’ soil management practices and soil fertility status was expected, no statistical differences were detected across farm types (p &gt; 0.05). Cotton yields, as declared by farmers, were also not statistically associated with soil fertility levels. The generalized poor fertility status of soils that receive annual fertilizer inputs suggests that this practice is not enough to maintain long-term soil productivity in the climatic and soil conditions of Benin cotton zones studied here. This was also the case in fields that received combinations of mineral fertiliser and animal manure, which is probably not used in sufficient quantity and quality. Low organic matter inputs, crop residue removal and conventional tillage, as practiced by the majority of farmers in our study sites (100 %), may contribute to explain the low levels of SOM and organically-held nutrients in the soil. Alternative measures to maintain soil fertility should be further investigated locally for their capacity to restore and maintain soil fertility in the long term and to improve crop yields, considering the socioeconomic diversity of farms and their environment.</p

Conservation agriculture compared to conventional tillage improves the trade-off between ground-dwelling arthropod trophic groups for natural pest regulation in cotton cropping systems

Conservation agriculture is an innovative approach based on minimal soil disturbance, soil cover with crop residues, and crop rotation, which increases the biodiversity of soil macrofauna thus contributing to nutrient cycling and soil aggregation. In addition, macrofaunal abundance may play a role at regulating insect pest populations. The study aims to predict the effects of soil management practices (conventional tillage and conservation agriculture) on the abundance of soil macrofauna and herbivore predation in cotton (Gossypium hirsutum L.) based cropping systems. We conducted a field experiment with a randomized complete block comprising two treatments, Conventional Tillage (CT) and Conservation Agriculture (CA), and six replications in a cotton-maize rotation system from 2020 to 2023. Soil monoliths and pitfall traps were installed in both treatments to collect ground-dwelling arthropods, to analyse the influence of soil management practices on their abundance, their trophic groups, and the rate of pest predation by generalist predators. Pest predation rates were assessed using artificial caterpillars made from plasticine. The results showed significant positive effects of soil management practices on herbivory rate, herbivore abundance, predator abundance, omnivore-predator abundance and pest predation rate. The average herbivory rate was 9.8 % in the conservation agriculture plots and 11.6 % in the conventional tillage plots. Overall, the predation rate was 58.9 % in the conservation agriculture plots and 21.8 % in the conventional tillage plots. The abundance of predators and of omnivore-predators were significantly higher in conservation agriculture than in conventional tillage. These findings suggest that conservation agriculture practices improve soil macrofauna and pest regulation, with potential benefits on soil quality and sustainability in cotton cropping systems.</p

Influence of cover crops and their traits on the yield of main annual crops grown in tropical and subtropical environments - A meta-analysis

Context or problem: The sustainability of agriculture in tropical regions is threatened by climate change, soil degradation, and food insecurity. Crop diversification through growing cover crops is a promising strategy to mitigate these problems. However, their effects in rotation and as intercrops has not been comprehensibly assessed in the tropics, considering cultural practices, edapho-climatic conditions, and the functional traits of these cover crops. This study aims to conduct a comprehensive meta-analysis to simultaneously analyze, in rotation and intercropping systems, the effect of cover crops and their traits on the yield of main annual crops grown in tropical and subtropical regions. Methods: A meta-analysis was conducted based on 1788 field observations from 191 articles covering 29 tropical and subtropical countries and regions. The analysis accounted for both rotation and intercropping systems, while considering the variability in cultural practices, edapho-climatic conditions, and traits of cover crops. Results: The results showed that the cover crops increased yields of cereals, legumes, and fiber crops by 25 % in rotation and by 7 % in intercrops compared to monocrops. These effects varied greatly depending on the context. In rotation, yield gains were enhanced by crop residue incorporation, nitrogen application, bimodal tropical climates compared to unimodal ones, and altitude. In intercrops, positive effects were associated with the use of Fabaceae as cover crops, staggered sowing, altitude, temperature, and subtropical climates and volcanic soils (Andosols). Yield responses varied depending on the annual crop: in rotation, maize (290 %), soybeans (300 %), and cotton (240 %), relative yield gains were observed in low-yielding environments, while in intercrops only maize (360 %) showed gains under these conditions, and rice (- 30 %) suffered a decline. Analysis of cover crop traits revealed that in rotation systems, aboveground cover crops biomass, root diameter and root density explained part of the relative yield variability and were positively associated with relative yield. In intercrops, cover crops aboveground nitrogen mass was explanatory of annual crop yield. Conclusions: Fabaceae cover crops tend to perform better in intercropping, particularly in subtropical climates and in Andosols. In tropical crop rotations, conserving cover crop residues improves yields, further enhanced by nitrogen fertilization. Cover crops are particularly beneficial in low-yield contexts. Furthermore, the traits of cover crops are insufficiently documented, and their explanatory power remains limited, making the effects of cover crops on annual crop yields unclear. This highlights the importance of conducting further research in this area to gather additional evidence