Urban and agricultural wastes for use as mulches on avocado and citrus and for delivery of microbial biocontrol agents

Abstract

SummaryUrban and agricultural waste products generally available to avocado and citrus growers in southern California were analyzed for their suitability for use as bioenhanced mulches on citrus and avocado. Of the mulches tested only yard waste (consisting of wood chips, grass and leaves), rice hulls and rice hulls-and-paper were not harmful to any growth parameter of citrus or avocado and were also adequate substrates for the growth of three biocontrol agents: Trichoderma harzianum, Gliocladium virens, and Pseudomonas fluorescens. Several mulches such as milled peanut hulls, milled almond hulls, chicken manure, a horse/cow manure mixture, cow manure and alfalfa hay were poor substrates for growth of the biocontrol agents and were damaging to at least one growth parameter of avocado and citrus. These mulches released toxic amounts of ammonia upon degradation, some in excess of 1000 µg NH3−1 dry wt. The percentage of healthy citrus roots, percentage of healthy avocado roots and growth of T. harzianum and ...