ORGANIC WASTE AMENDMENTS AS SOURCES OF CARBON AND FERTILITY FOR VEGETABLE

Waste amendments, such as food or yard waste, are abundant potential sources of C for soil organic matter and nutrients for crop production. A number of amendments, like gelatin waste and dehydrated food waste, remain relatively unstudied. For those amendments that have been extensively studied, like biosolids and paper waste, the conclusions about their effects on soil and crops are often conflicting, likely due to the varying experimental conditions. To address this gap in knowledge, I compared six waste amendments and their effects on soil quality and vegetable crop production to a mineral fertilizer control. In a two-year field trial (2013 and 2014) 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), and gelatin waste (GW) against a mineral fertilizer (20-20-20). Three crops were included in the study: sweet corn (Zea mays cv. Applause and Brocade (2013) and Applause and Montauk (2014)), butternut squash (Cucurbita moschata cv. JWS 6823), and potatoes (Solanum tuberosum cv. Eva) for their physiological diversity and importance to the local economy. The experiment was conducted at the University of Rhode Island’s Greene H. Gardiner Crop Science Field Laboratory in Kingston, RI, and was laid out in a randomized block design (n=4). Waste amendments were applied to supply 10,000 kg C/ha over two seasons. Amendments were analyzed for pH, electrical conductivity (EC), total C, N and P content, organic matter (OM) content, moisture, density and heavy metals. Amendment effects on soil quality were assessed based on soil OM levels, bulk density, pH, and moisture. Soil samples were also tested for EC and heavy metals, two of the potential limiting factors for the use of waste amendments. Levels of inorganic N and potentially mineralizable N (PMN) were used to assess effects on soil fertility. Crop quality was assessed based on emergence and early growth, nutrient and heavy metal concentrations of tissue samples, and yield quantity and quality. Waste amendment properties, including pH, moisture, density, and OM content, varied between wastes, and year-to-year for the same waste, however none had problematically high EC or heavy metal levels. The nutrient (N, P, K) density of amendments was generally low, although GW contained considerable amounts of both N and P. Unique characteristics, like the presence of seashells in MS, affect estimates of carbon inputs and effects on soil pH, and are therefore important to note. Amendments did not significantly alter soil moisture or heavy metal concentrations, or increase EC to potentially problematic levels. Only MS significantly increased pH compared to the control, likely due to the presence of CaCO3 from seashells. Only FW produced a significant decrease in bulk density, compared to the control. Amendment with YW and BS significantly increased OM compared to the control, although effects were not consistent across crops. The organic N in waste amendments must be converted to inorganic forms to be plant-available. Waste amendment application was not a reliable way to increase late season inorganic N, or potentially mineralizable N (PMN), a measure of the organic N mineralized to inorganic forms, in comparison to the control. Although PF was the only amendment with a C:N ratio above 25:1, the threshold above which N immobilization is likely; inorganic N levels in plots amended with PF were not always significantly lower than the control. Potatoes from plots amended with PF had significantly lower emergence (2014) and were significantly shorter (2013 and 2014) compared to the control, indicating inhibition of early growth, although the same was not observed for corn or squash. Nutrient levels in plant tissue varied among treatment, but not consistently with application rates. Tissue levels of N, P, Ca, Mg, Mo, Cu, and Fe were all adequate for plant growth although concentrations of K, Mn, B, and Zn were deficient for some or all crops and treatments. There were no significant differences in corn cob tissue heavy metal levels among treatments (2014), indicating that short-term application of waste amendments does not increase corn ear heavy metal concentrations. Gelatin waste, BS, and FW produced yields comparable to the control for all crops. While YW, PF, and MS underperformed the control for corn and/or squash production, they performed as well as the control for potatoes. Paper fiber/chicken manure enhanced potato quality significantly in 2014. All waste amendments studied showed promise as effective replacements for mineral fertilizers, although not consistently for all crops. Although benefits to soil quality from application of waste amendments were limited, their application did not appear to be harmful or contribute problematic levels of salinity or heavy metals. Lastly, some waste amendments provided unique benefits such as increasing pH (MS) or improving potato quality (PF)