Agricultural methods to reduce the risk to birds from cereal seed treatments on fenlands in eastern England. I. Sowing depth manipulation

This study investigated whether the risk to birds from pesticide-treated ce real seed could be reduced by increasing sowing depth and hence reducing th e density of seed exposed on the soil surface. Results are presented from b oth commercially farmed fields and experimental field trials on light fenla nd soils in England. Farmers' intended sowing depth for winter wheat varied considerably (20-60 mm) and often exceeded the recommended depth. The dens ity of exposed seeds on commercial fields and in two experimental sowings w as inversely related to actual sowing depth. In the experimental trials, be tter incorporation was achieved on a fine seedbed than on a rough seedbed d rilled at similar depth. Results suggest that the manipulation of the depth of sowing provides satisfactory seed coverage in the centre of fields (mai nfield) with a fine seedbed, but it is less effective in rough seedbeds and in the margins (headlands). In trials, deep sowing (46-50 mm) gave better yields than shallower sowings (20-36mm), An estimated risk index to woodpig eons (Colmba palumbus) and house sparrows (Passer domesticus) showed that i ncreasing the depth from 25 to 40-55 mm reduced the risk by a factor of 3-1 5 in the mainfield but a lower reduction in risk was achieved in the headla nds. Potential risks to birds can therefore be significantly reduced by fea sible increases in sowing depth using standard seed drills, at least on lig ht fenland soils. Crown copyright (C) 1999 Published by Elsevier Science B. V. All rights reserved.