Effects of Variable Diuron on the Sugar Production and Enzyme Activity of Sugarcane Grown on Clay and Sandy Loam Soils in Puerto Rico

Abstract

Sugarcane was grown on Diuron-treated clay and sandy loam soils over a period of 16 months. There were three objectives: 1, To evaluate Diuron effects upon sugar production; 2, to determine Diuron effects upon enzymes over a prolonged period; 3, to measure residual effects of Diuron on sugar production with variable soil types. The cane, grown in greenhouse soil-benches, was given water equivalent to about 75 inches per year. Diuron was applied to the soil as a pre-emergence spray at rates of 0, 2, 6, and 18 pounds per acre. The following results were obtained: 1. Diuron severely suppressed sugar production by 2-month-old plants. At 6 months the Diuron effect had lessened and it was no longer evident at 12 and 16 months. 2. Leaf analyses showed that Diuron absorption declined greatly after 2 months. By 16 months only traces of the herbicide were entering leaf tissues. 3. Diuron was far more readily absorbed from loam than from clay at 2 months. At 16 months there was no detectable Diuron in leaf samples from loam, indicating a total exhaustion of the applied herbicide. 4. High Diuron absorption from loam was accompanied by a greater suppression of sugar in loam-produced samples than was evident with those from clay. 5. Soil type greatly affected the behavior of phosphatase, ATP-ase, amylase, invertase, peroxidase, and starch phosphorylase. None of the enzyme changes were consistent throughout the study, suggesting that the soil effects were indirect. 6. Diuron caused abnormal enzyme behavior throughout the study, but again the changes were inconsistent. It is theorized that the response of plants to initial Diuron action includes abnormal enzyme synthesis and synthesis of substances which block the sites of the herbicide's activity. 7. Enzyme activity generally declined as the plants grew older. First ratoon samples, representing 4 months of new growth, did not reveal activity comparable to the original 4-month-old material.