THE EFFECTS OF DAZOMET AND NITROGEN-FERTILIZER ON SUCCESSIVE CROPS OF MAIZE (ZEA-MAYS-L) GROWN FOR EITHER GRAIN OR FORAGE

Maize was grown for grain or forage on the same site at Woburn [UK] for 7 consecutive years. Yields were satisfactory and there were no serious pest or disease problems, provided the small plots were netted until young plants were established. Different rates of N fertilizer were tested with and without annual applications of a soil sterilant, dazomet. Average yields of grain (85% dry matter) and forage (dry matter) were, respectively, 4.5 and 8.8 t[tons]/ha with 50 kg N/ha and 5.0 and 9.5 t/ha with 100 kg N/ha. Without dazomet there was a further increase with 150 kg N/ha. Weather influenced the response to N, and the response to a split dressing of the highest rate was variable. Except for plots receiving the split dressing of N in 1973 and 1974 dazomet always increased yields: grain yields were increased on average by 1 t/ha and forage by 1.6 t/ha. Dazomet-treated plots had taller and heavier plants with more stems, leaves and nodal roots, but fewer seminal roots than untreated plots. Dazomet-treated plots also had fewer migratory nematodes and smaller and less varied root mycofloras. Most of these differences were greatest in the young crop. Possible reasons for this early boost are discussed.