Individual study: Mechanical weeding effects on soil structure under field carrots (Daucus carota L.) and beans (Vicia faba L.)
Ball B. C. & Crawford C. E. (2009) Mechanical weeding effects on soil structure under field carrots (Daucus carota L.) and beans (Vicia faba L.). Soil Use and Management, 25, 303-310
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Amend the soil with fresh plant material or crop remains
A before-and-after trial in 2003-2005 on loam/sandy loam soils in the UK (Ball & Crawford 2009) found that incorporating straw using reduced tillage (without ploughing) did not improve topsoil quality in compacted soils. Anaerobic growing conditions were found, shown by the high nitrous oxide flow to the air from below the straw layer (720 g N/ha/day) compared to above it (50 g N/ha/day). The carrot Daucus carota crop was part of a cereal/potato Solanum tuberosum/carrot/spring cereal rotation undersown with grass, clover Trifolium pratense and peas Pisum sativum. Carrot beds were roughly 2 m wide. Straw was incorporated into the soil before the carrot crop. Straw was incorporated using reduced tillage by discing to about 10 cm depth, without ploughing. Nitrous oxide and carbon dioxide fluxes were measured to determine whether soil conditions were anaerobic.
Change tillage practices
A before-and-after trial in 2003-2005 on a loam - sandy loam soil in Scotland, UK (Ball & Crawford, 2009), found that mechanical weeding caused structural deterioration and subsoil compaction under broad bean Vicia faba crops (17.5 kPa – 39 kPa with increasing depth) due to tractor wheeling. In the carrot Daucus carota crop, soil was >50 kPa for each soil type when wheeled, and <22 kPa for each soil type in unwheeled areas. Compaction control measures (controlled traffic and precision driving) are therefore important when using mechanical weeding. The broad bean crop was part of an eight year rotation of vegetables, potatoes, wheat Triticum aestivum, beans, barley Hordeum vulgare, peas Pisum sativum and red clover Trifolium pratense. The carrot crop was part of a cereal/potato/carrot/spring cereal rotation undersown with grass and clover and peas. Carrot beds were roughly 2 m wide. Soil strength and the soil density were measured. Weeds were controlled by several passes of a light spring-tine harrow in the broad bean crop, and by a steerage hoe between the rows of carrot.