Above-soil and in-soil degradation of oxo- and bio-degradable mulches: a qualitative approach

Degradable materials have been suggested to overcome accumulation in the field of persistent plastic residues associated with the increasing use of polyethylene mulches. New degradable materials have been proven successful for increasing crop productivity; however, their degradation in the field has been hardly addressed. A qualitative scale was used in the present study to assess the above-soil and in-soil degradation of degradable mulches during the cropping season. Degradation was determined in three biodegradable plastic mulches (Biofilm, BF; Mater-Bi, MB; Bioflex, BFx), two paper sheet mulches (Saikraft, PSA; MimGreen, PMG) and one oxo-degradable plastic mulch (Enviroplast, EvP). Polyethylene (PE) mulch was used as control. Mulches were tested in five Spanish locations (Castilla-La Mancha, La Rioja, Navarra, Aragón and Catalunya), with three crop seasons of processing tomato. Biodegradable plastic mulches BF and MB degraded more and faster above-soil than paper mulches; among biodegradable mulches BF degraded more than MB, and MB more than BFx. The above-soil degradation of the oxo-degradable mulch EvP was highly dependent on location and crop season, and it degraded more than PE. Main environmental factors triggering above-soil degradation were radiation, rainfall and crop cover. In-soil, paper mulches and BF degraded more and faster than MB, whereas BFx and EvP barely degraded. Environmental factors triggering in-soil degradation during the crop season were rainfall and irrigation water. The effect of soil parameters (organic matter, nutrient availability) on degradation during the cropping season was not evidenced. The qualitative scale used proved convenient for determining mulch field degradation. A visual scale for supporting the qualitative evaluation is provided. In order to standardise parameters and criteria for future studies on field mulching degradation evaluation, a unified degradation qualitative scale is suggested.