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

Publisher Website
Google Scholar
Abstract
Urban 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 P. fluorescens were negatively correlated with both ammonia evolved and total nitrogen content of the mulches. Citrus grew better with mulches having lower carbon/nitrogen ratios than did avocado; organic matter and organic matter/nitrogen ratio were negatively correlated with citrus shoot weight and the percentage of healthy citrus roots but were not negatively correlated with avocado growth parameters. Growth of all three biocontrol agents was positively correlated with the organic matter/nitrogen ratio and negatively correlated with the pH of the mulches. Growth of G. virens was negatively affected by the sodium concentration of the mulches. For the various mulches, the percentage of healthy citrus roots, percentage of healthy avocado roots, avocado root weight, avocado height increase and avocado shoot weight were positively correlated with the growth of P. fluorescens. In addition, the growth of T. harzianum on mulches was correlated positively with the percentage of healthy avocado roots mulched with the same material. This indicates that mulch characteristics which favour healthy roots of citrus and avocado also favour the growth of P. fluorescens and T. harzianum.

This publication has 1 reference indexed in Scilit: