Soil Weed Seed Bank Response to Crop Management Practices on Smallholder Farms Across an Agroclimatic Gradient in Zimbabwe

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.