Soil solarization and Dacthal: influence on weeds, growth, and root microflora of collards.
Field trials in Tuskegee revealed that the av. temperature of sandy loam covered by a 50-cm-thick clear polythene mulch in June 1985 exceeded nonsolarized soils by 12.3 and 6.6°C at 5 and 20 cm depth, resp., after 98 d. Soil solarization resulted in 91% reduction of weeds (mainly Cyperus rotundus, Digitaria ciliaris, Echinochloa crus-galli, Richardia scabra and Amaranthus retroflexus) at harvest in collards (Brassica oleracea var. acephala) cv. Vates (transplanted as 6-week-old seedlings in March 1986), compared to only 69% control by pre-em. application of 11.2 kg/ha chlorthal-dimethyl (Dacthal-75W). Solarization also enhanced collard yield (from 4.2 to 18.1 t/ha), root branches and FW (from 14 and 4.7 g to 30 and 16.2 g), and thermotolerant fungi and bacteria in the rhizosphere (from 1.8 × 104 and 1.8 × 107 to 8.7 × 104 and 4.0 × 107, resp.), and was markedly more effective than Dacthal. All of these parameters, although higher than untreated controls, were negatively correlated with Dacthal dose between 2.8 and 11.2 kg.