Regis Chikowo

Soil organic carbon (SOC) and soil total nitrogen (STN) are critical indicators of soil health and vital sinks in agroecosystems. However, knowledge gaps remain regarding how long‐term crop‐livestock integration impacts coupled SOC and STN stocks on commercial versus communal smallholder farms in Africa. This study quantified whole profile SOC and STN stocks under two land‐use types (croplands and grazing lands) and two livestock management facilities (congregation points and corrals), across two adjacent, distinct mixed crop‐livestock farming systems, while evaluating how these land uses influence δ ¹³ C and δ ¹⁵ N isotopic signatures. A commercial farm and an adjacent communal smallholder farm with similar soil types were selected. Soil samples were collected from six depth increments (0–5, 5–10, 10–20, 20–40, 40–70, 70–100 cm) to determine profile‐wide SOC and STN stocks alongside their δ ¹³ C and δ ¹⁵ N signatures. Land‐use and management type impacted SOC and STN stocks more significantly in the communal system ( p < 0.001) than on the commercial farm ( p < 0.05). On the commercial farm, whole‐profile SOC (Mg C ha ⁻¹ ± SE) and STN (Mg N ha ⁻¹ ± SE) stocks peaked in grazing lands (129.7 ± 12.8; 10.32 ± 1.14) and reached minimums at livestock congregation points (68.1 ± 2.7; 7.04 ± 1.16). Conversely, in the communal smallholder system, both stocks peaked sharply at livestock congregation points (150.0 ± 4.6; 12.26 ± 0.27) and were lowest in croplands (56.5 ± 1.5; 5.20 ± 0.20). Deep subsoil layers (40–100 cm) stored a greater relative proportion of total stocks on the commercial farm (36%–43% SOC; 39%–45% STN) than on the smallholder farm (28%–39% SOC; 29%–39% STN). Soil δ ¹⁵ N values increased with depth across all land‐use and management types. Lower δ ¹⁵ N values in commercial croplands compared with smallholder croplands likely reflect higher synthetic fertilizer use, while the highest δ ¹⁵ N values occurred in cattle corrals. Contrary to typical microbial fractionation—where preferential loss of ¹² C during respiration enriches δ ¹³ C at depth—no consistent vertical increase in δ ¹³ C was observed; all land‐use types were enriched, averaging −17‰. Our results demonstrate that, within the narrow range of soil textures evaluated, land‐use and management serve as the primary determinants of SOC and STN stocks and their isotopic signatures. While livestock congregation points create intense, localized nutrient hotspots, their small spatial extent limits their landscape‐scale sequestration. Consequently, adopting conservation practices in commercial croplands as a proactive intervention, and optimizing the management of extensive communal grazing lands and croplands are collectively essential for enhancing regional biogeochemical storage and ecosystem resilience.

Maize ( Zea mays L.) is an important crop in Zimbabwe, but the grain yields achieved are often only one tenth of their estimated potential. Low grain protein content and low biomass yields further constrain food quality and livestock feed availability on smallholder farms. To assess whether integrating legumes into maize-based cropping systems could improve yields, yield stability, and biomass, calorie and protein production, we tested six cropping systems in rainfed conditions under conservation agriculture in central Zimbabwe in two identical field experiments on soils with contrasting textures. The cropping systems included maize monoculture, maize rotated with pigeon pea ( Cajanus cajan L. Millsp.) or cowpea ( Vigna unguiculata L. Walp.), maize-pigeon pea intercropping, and double-row strip crops of maize with pigeon pea or cowpea. Each system was tested with and without fertilizer (basal application 12 kg ha ⁻¹ N, 14 kg ha ⁻¹ P, 8 kg ha ⁻¹ K, plus two topdressings, each 26 kg N ha ⁻¹ ). Mean grain yields were highest in rotations (maize = 2855 kg ha ⁻¹ , pigeon pea = 752 kg ha ⁻¹ , cowpea = 567 kg ha ⁻¹ ). Rotations also had a high maize yield stability, comparable with the monoculture. However, total biomass, calories, and protein per hectare were highest in maize-pigeon pea strip cropping (5945 kg ha ⁻¹ , 9.14million kcal ha ⁻¹ , and 308 kg ha ⁻¹ , respectively). Across all cropping systems, fertilizer enhanced system productivity, increasing maize yields by 88% on average. Overall, maize-pigeon pea strip cropping produced the most food and feed per unit land area, in both fertilized and unfertilized conditions.

Phytopathogens are the major yield-reducing factors for groundnut, an important crop for food and nutrition for smallholder farmers in Zimbabwe. A disease survey was conducted during the 2023-24 farming season on farmers’ fields along an aridity gradient in Zimbabwe. Symptomatic leaves and stems of unknown aetiology with an incidence of more than 70% were observed. The symptoms appeared as large necrotic tissue, causing leaf defoliation. The pathogen was isolated on potato dextrose agar and was identified as Nigrospora sphaerica (Sacc.) Mason. To our knowledge, this is the first report of N. sphaerica causing leaf blight disease on groundnut in Zimbabwe.

Climate change is projected to exacerbate food insecurity in sub‐Saharan Africa (SSA) by reducing crop yields and soil fertility. Many climate change impact studies in SSA have overlooked long‐term effects of soil fertility on crop yield. We evaluated maize yields under different scenarios of soil fertility (using soil organic carbon as a proxy) and climate change (considering changes in temperature, rainfall, and CO ₂ ) at four sites in SSA. Using an ensemble of 15 calibrated soil‐crop models, we found a strong consensus that, without fertilization, soil fertility declines over time, impacting maize yields more strongly than changes in temperature, rainfall, or CO ₂ . The model ensemble indicated that when accounting for soil fertility changes, the yield benefits of combined application of organic and mineral inputs increase over time, even under climate change. These findings highlight the importance of considering long‐term change in soil fertility when assessing impacts of climate change and integrated nutrient management on crop production in SSA.

Weed seed banks function as subterranean reserves that continuously replenish weed populations, driving future infestations on farms. This study examined how various crop management practices on smallholder farms influence the size and composition of weed seed banks, analyzing farmer‐managed fields across an agroclimatic gradient in Zimbabwe. Tillage intensity, soil fertility management, crop rotation, intercropping, mulching, timing of first weeding, and weeding frequency were monitored across 75 smallholder principal maize fields, spanning three agroecological regions (AERs) (2, 3, and 4) during the 2022/23 and 2023/24 cropping seasons. At the end of the 2023/24 season, soil samples were collected at depths of 0–10, 10–20, and 20–30 cm using a 10 cm diameter bucket auger, pooling nine core samples per field into a composite sample. To determine weed seed bank size and composition, a glasshouse soil incubation experiment was established using the seedling emergence method. The trial followed a 3 × 3 factorial arrangement structured within a randomized complete block design (RCBD), evaluating AER and soil depth as the primary factors, while individual farmer fields nested within AERs served as replicates. Across the studied farms, diverse seed banks were recorded, comprising 25 distinct weed species belonging to 14 families, with community diversity and density varying significantly by both soil depth and AER. Seven species ( Richardia scabra L., Cyperus esculentus L., Galinsoga parviflora Cav, Leucas martinicensis L., Digitaria ternata (A. Rich) Roem, Eleusine indica (L.) Gaertn, and Acanthospermum hispidum D.C.) dominated the community, contributing 90.4% of the relative density. The largest seed bank of 316 weed seedlings was recorded in the wetter AER 2 compared to AER 3 (141) and AER 4 (194). Agronomic practices significantly drove seed bank dynamics. Conservation tillage using planting basins reduced seed density by 31% compared to conventional tillage. Cattle manure application showed divergent regional effects, suppressing emergence in AER 2 and 4, but increasing it in AER 3. Finally, early weeding at 2 weeks post‐crop emergence and a high weeding frequency ≥ 3 times significantly minimized seed bank density and diversity. Ultimately, weed seed bank communities proved highly responsive to management choices. Integrating planting basins with early, frequent weeding, and region‐specific fertilizer management offers a robust strategy for suppressing long‐term weed pressure on smallholder farms.

High weed infestation remains a major constraint on crop productivity for smallholder farmers practising Conservation Agriculture (CA). Fewer, more diverse weeds are desirable to reduce competition and provide ecosystem services. Crop diversification can help, but it is not yet clear which species combinations and layouts are most effective for smallholder CA. Here, we conducted an experiment in sub‐humid Zimbabwe at two research stations with contrasting soils, and over two growing seasons (2021–2022 and 2022–2023). We evaluated weed community responses to maize monoculture, maize rotated with cowpea or pigeon pea, maize‐pigeon pea intercropping and maize‐cowpea and maize‐pigeon pea strip cropping under moderately fertilised versus unfertilised conditions. Data were collected on weed abundance (number and biomass), diversity (species richness, Pielou evenness and Shannon diversity) and community composition. There were significant differences between sites and, to a lesser extent, between growing seasons. More substantial impacts of cropping systems on weeds were observed at the more fertile site. On average across both sites, seasons and fertiliser levels, maize‐pigeon pea strip cropping performed best, resulting in the lowest weed number (23.2 weeds m ⁻² ) and biomass (99.2 g m ⁻² ) and the highest weed species diversity (Shannon index = 1.35), while the maize‐cowpea rotation performed worst (number = 31.3 weeds m ⁻² , biomass = 179.3 g m ⁻² and Shannon index = 1.12). Cropping system biomass was associated with lower weed biomass, but had no consistent effect on weed numbers or diversity. Fertilisation had weak and inconsistent effects. Overall, our results suggest that high biomass cropping systems, such as maize‐pigeon pea strip cropping, could contribute to sustainable weed management in Zimbabwe. However, more research is needed to develop strategies for less fertile sites, where weeds seem less susceptible to crop competition.

Sub-Saharan Africa (SSA) has the world’s largest projected increase in demand for food. Increased dependence on imports makes SSA vulnerable to geopolitical and economic risks, while further expansion of agricultural land is environmentally harmful. Cereals, in particular, maize, millet, rice, sorghum, and wheat, take nearly 50% of the cropland and 43% of the calories and proteins consumed in the region. Demand is projected to double until 2050. Here, we assess recent developments in cereal self-sufficiency and provide outlooks until 2050 under different intensification, area expansion, and climate change scenarios. We use detailed data for ten countries. Cereal self-sufficiency increased between 2010 and 2020 from 84 to 92% despite the 29% population increase. The production increase was achieved by increased yields per hectare (44%), area expansion (34%), and a shift from millet to the higher yielding maize (22%). Outlooks for 2050 are less pessimistic than earlier assessments because of the larger 2020 baseline area, higher shares of maize and somewhat less steep projected population increase. Yet, to halt further area expansion, a drastic trend change in annual yield increase from the present 20 to 58 kg ha ⁻¹ y ⁻¹ is needed to achieve cereal self-sufficiency. While such yield increases have been achieved elsewhere and are feasible given the yield potentials in SSA, they require structural changes and substantial agronomic, socioeconomic, and political investments. We estimate that amounts of added nitrogen need to at least triple to achieve such yield improvements, but it is essential that this comes with improved context-specific agronomy.

Weed species composition is significantly affected by crop management practices. Intensive cropping is often associated with a reduction in weed species diversity. This study was conducted to assess the effect of intercropping and mulching on weed flora in three agroecological regions in eastern Zimbabwe. Two replicated on‐farm trials were laid out in three agroecological regions. Treatments included sole maize, sole maize with 4 or 8 Mg ha ⁻¹ mulch, sole cowpea, maize + cowpea intercrop and maize + cowpea intercrop with 4 or 8 Mg ha ⁻¹ mulch. Maize stover was used as mulch. Different weeds were identified and sampled at five positions within plots using 0.5 m × 0.5 m quadrats. Among the 34 weed species identified across sites, Richardia scabra and Cynodon dactylon were the most dominant weed species and were mostly associated with sole maize cropping. Maize stover as mulch contributed to a reduction in weed species density. Maize + cowpea intercropping systems proved effective particularly in suppressing the prevalence of R. scabra and C. dactylon . Cowpea grown as a sole crop was found to be effective in reducing the infestation of weeds. Maize intercropped with cowpea along with mulching resulted in a significant reduction of weed species, especially in arid agroecological zones.