Nutritional Values of Some Biowastes As Soil Amendments

Abstract

As a result of increased population, improved standards of living, and strict environmental laws, biowastes have been generated in huge quantities. Thus, land applications of these wastes are desirable, or even necessary, to keep the environment healthy and to conserve natural resources. Yet, the success of such uses requires knowledge of complex biochemical reactions when the wastes are applied to soils. To obtain this knowledge, we evaluated soil amendment properties, primarily nitrogen (N) mineralization/immobilization of six bio wastes when used as plant growth media. An immature yard trimmings compost, ground fresh corn stovers, a commercial peat moss, a chicken manure, and two biosolids were each mixed with a Mollisol at either 25 percent and 50 percent by volume for the plant based wastes, or at 2.5 percent and 5.0 percent by weight for the animal based wastes. Treatments with urea at 0, 70 and 210 mg N kg−1 were included for comparison. The treated soils were incubated moist for two weeks at which time they were sampled for chemical analysis, and planted to tomatoes. The results showed that those wastes, when added to soil, produced growth media with C/N < 15, and released inorganic N that increased dry matter yield of tomatoes many times over that of the unamended control. In contrast, a waste amended soil with a C/N > 20 immobilized some inorganic N, reduced plant growth, and caused N deficiency in tomatoes. Such a deficiency was characterized by low N concentrations in leaves (< 2.0 percent) and chlorosis, which corresponded to a color index of 0.25 or less. Biowaste amendments also affected soil P extractability differently: Chicken manure increased NaHCO3-extractable P many fold over the control, whereas corn stover, peat moss and raw biosolids did not. The yard trimmings compost and the anaerobically digested biosolids increased soil P moderately.