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

Abstract

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.