Growing Food with Garbage: Waste Amendments for Vegetable Production

Organic wastes are abundant sources of C to build soil organic matter and nutrients for crop production, yet over 50 million tons a year in the United States are not being put to beneficial use. Some, like gelatin waste and dehydrated food waste, remain relatively unstudied, whereas others, like biosolids and paper waste, have been extensively studied, but data about their effects on soil and crops are often conflicting. In a two-year field trial (2013 and 2014) on a silt loam in southern Rhode Island, I compared the effects of paper fiber sludge/chicken manure (PF), biosolids/yard waste co-compost (BS), multi-source compost (MS), yard waste compost (YW), dehydrated food waste (FW), gelatin waste (GW), and a mineral fertilizer (20-20-20) control on soil quality and the yield of sweet corn (Zea mays cv. Applause, Brocade, and Montauk), butternut squash (Cucurbita moschata cv. JWS 6823), and potatoes (Solanum tuberosum cv. Eva). The experiment was arranged in a randomized block design (n=4) and amendments were applied to supply 10,000 kg/ha of C over two seasons. Amendment with wastes did not negatively impact soil moisture, bulk density, electrical conductivity or the concentration of heavy metals in soil or plant tissue. Amendment with MS significantly (P < 0.05) increased soil pH and amendment with FW significantly decreased bulk density in comparison to the control. Amendment with YW and BS increased soil organic matter, although not consistently across all plots. Waste amendment application was not a reliable way to increase soil inorganic N later in the growing season, or potentially mineralizable N (PMN), a measure of the organic N mineralized to inorganic forms, in comparison to the control. Yields from plots amended with GW, BS, and FW were comparable to the control for all crops. While YW, PF, and MS underperformed for corn and/or squash production, they performed as well as the control for potatoes. Although potatoes from plots amended with PF showed inhibition of emergence and early growth, their quality in 2014 was significantly better than the control, possibly due to less disease and/or insect damage. While all crops and treatments had sufficient tissue concentrations of N, P, Ca, Mg, Mo, Cu, and Fe, some were deficient in K, Mn, B, and Zn. However, there was no clear connection between nutrient deficiencies and treatments with reduced yields. All waste amendments studied showed promise as effective replacements for mineral fertilizers for at least one of the crops grown.