The Nutritional Effects of Digested and Undigested Organic Wastes Combined with Wood Ash Amendments on Carrot Plants

The impact of digestate and fresh animal manure (with and without ash) on soil fertility, carrot productivity, and metal uptake from soil to carrot was studied. Ash might contain high concentrations of metals. Since the impact of fiber and whole digestate with ash, on plant growth and metal uptake, remains unclear, their suitability as alternatives to inorganic fertilizer was assessed. Soil treatments included animal manure (AM), whole digestate (WD), fiber digestate (FD), animal manure with ash (AM+A), whole digestate with ash (WD+A), fiber digestate with ash (FD+A), inorganic fertilizer (positive control), and unamended (negative control). Impacts on soil properties were assessed initially and after a 6-week incubation, with plant morphometry and elemental composition, including nutrient and potential toxic element (PTE) uptake, determined. Performance of WD on carrot productivity was better than FD and AM. There was an overall positive effect of wood ash on the soil resulting in higher concentrations of all major elements. However, ash treatments had lower uptake and transfer factors of the metals while IF treatment had the highest transfer factors for Cr (16.3) and Ni (12.2). Also, based on carrot productivity, addition of wood ash mainly improved the performance of FD, having a slightly negative effect on AM. Despite the higher concentrations of trace metals in wood ash, it did not significantly increase the uptake of PTEs. The digestates and wood ash mixture had a positive effect on bioavailability of heavy metals in carrot plant and therefore can be a sustainable alternative amendment for root crops.