Growth of Field Crops in Soil Treated with Chemical Growth-Regulators

Abstract

1. In two field tests 2,4-dichlorophenoxyacetic acid (2,4-D) and isopropyl-N-phenyl carbamate (IPPC) were applied as top dressings in dry form at rates from 1 to 4 lb. per acre on neutral or alkaline loam soils at the start of the growing season. Successive plantings of Red Kidney beans, mustard, wheat, field corn, and sweet corn were made at intervals up to 52 days after the time of treatment of the soil. 2. Desirable control of weeds during the growing season resulted from treatment with 2,4-D, while IPPC did not influence dicotyledonous weeds and had only slight temporary inhibitory effect on weedy grasses. 3. Activity of the 4-lb. treatment of these growth-regulators, which was evaluated on test crops by means of the rate and amount of their emergence, number and condition of 30-day-old seedlings, survival of seedlings to maturity, and the amount of growth of tops, appeared to persist in the soil 7 weeks for 2,4-D and 5 weeks for IPPC. The growth of corn indicated that residual activity of the acid lasted longer than 7 weeks. 4. Growth-regulator treatments slightly prolonged the green condition of kidney beans; IPPC similarly influenced wheat. 5. Weights of shoots of mature bean or wheat plants grown in untreated soil and in soil treated with 4 lb. of 2,4-D per acre were equal when plantings were made 5-6 weeks after treatment. 6. The weights of shoots of kidney beans were generally slightly heavier than controls if plantings were made more than 4 weeks after treatment of the soil with 2,4-D. 7. Shoots of corn grew more rapidly and were heavier in soil pretreated with 2,4-D than in untreated soil. This stimulation was considered in relation to weed competition and residual activity of treatment.