Organic mulches alter nematode communities, root growth and fluxes of phosphorus in the root zone of apple

Nematode community structure, root biomass and P availability indices (in situ incubation of anion-exchange resin strips, lab incubation of resin strips, extractable P) were assessed for root zone soil of Golden Delicious/M9 apple trees that were mulched with (1) shredded office paper, (2) a mixture of compost plus biosolids, (3) office paper applied over the compost + biosolids treatment, and (4) non-mulched control plots. Two-week long in situ incubations of anion-exchange resin strips indicated that shredded paper mulch reduced availability of P in root zone soil, probably as a result of microbial immobilization driven by C inputs from the paper mulch. Apple leaf-P was not reduced in paper mulch plots, however, indicating that other factors affected by the paper mulch may have allowed for adequate P uptake despite the apparent P immobilization. Paper mulch increased nematode indicators of enhanced nutrient cycling, indicating that fluxes of nutrients through the soil biota were increased under paper mulch; enhanced P fluxes could have compensated for the low P availability. Fine root biomass in the 0–15 cm horizon was doubled by shredded paper, and we speculate that increased root abundance allowed for adequate P acquisition despite the reduced availability of P. The number of root-lesion nematodes (Pratylenchus penetrans) per gram fine root was also reduced under paper mulch, and reduced nematode damage is one of several possible reasons for the enhanced root growth under paper mulch.