The Agricultural Value of Dredged Material: final report

An alternative for disposal of dredged sediment is to use them beneficially to amend marginal agricultural soils. To study the suitability of dredged material for corp. production, 10 dredged material samples and 10 marginal soil samples were collected from locations in the United States. The soils were marginal for crop production and were of such character that additions of dredged material might improve their physical and chemical properties. The soils and dredged material samples were dried, ground, and mixed for plant growth studies and laboratory analysis. The following treatments were prepared: (a) soil alone; (b) 1/3 soil and 2/3 dredged material; (c) 2/3 soil and 1/3 dredged material; and (d) dredged material alone. In addition, three productive soils were chosen from the St. Paul, Minn., area to serve as controls in the plant growth studies. In general, chemical properties of the dredged material samples did not differ greatly from the chemical properties of the three productive soils from Minnesota. Some of the dredged material samples were relatively high in organic matter, nitrogen, total sulfur, extractable zinc, copper, nickel, and cadmium contents. Samples high in total sulfur were also low in pH and thus had a high lime requirement. High oil and grease content of a few dredged material samples made them slower wetting than most of the soil samples. The clay fractions of many of the fine-textured dredged material samples were amorphous in nature. High organic mater content and the amorphous nature of the clay-size fraction partially explain the low bulk densities and high soil water retention capacities. Multiple regression relationships were developed which can be used for predicting water retention characteristics of dredged material, marginal soil, and their mixtures by considering the sand, silt, clay, and organic matter content and bulk density. Three cuttings of ryegrass and two crops of barley were harvested from each of the treatments. Yields by plants in the greenhouse were greater for all fine-textured dredged material samples as compared to the coarse-grained marginal soils. Elemental analysis of the plant samples showed that, with the possible exception of boron in Alabama dredged material, none of the elemental concentrations were high enough to be toxic to plants. Zinc and copper contents of plants fell within the normal range expected. Nickel and cadmium contents were above the normal ranges expected in plants. It is concluded that the dredged material used in this study would be beneficial for increasing agricultural production when mixed with marginal soils. Relationships between uptake and the availability of various soil elements were developed that can be used in setting the ratio of dredged material to marginal soil to be used in the field. Physical and chemical data, along with the plant growth data, were used to develop guidelines for the disposal of dredged material on marginal soils.