Compost for Management of Weed Seeds, Pathogen, and Early Blight on Brassicas in Organic Farmer Fields

Abstract

Low-input methods for addressing economic and management challenges of plant pathogens and weed seeds will advance sustainable farming practices. Objective 1 was to demonstrate that U.S. National Organic Standards (NOS) for compost are sufficient to kill plant pathogens and weed seed. Known quantities of early blight inoculum (Alternaria brassicinae) and giant crab grass (Digitaria sanguinalis) seed were enclosed in bags and inserted into manure-based compost containing different sources of C: 1) manure–silage, 2) hay, 3) softwood, and 4) hardwood. Except for the manure–silage control, treatments represented C:N ratios prescribed by NOS. Bags were removed at five times during the compost process. Both pathogenicity and seed germination were reduced to zero by following NOS guidelines. Patterns of microbial enzyme activity illustrated that labile substrates were abundant in manure–silage and hay, but limited in softwood and hardwood treatments. For Objective 2, field trials were conducted at two farms. Compost treatments were applied after the first cultivation as mulch as follows: 1) manure–silage, 2) hay, and 3) hardwood. Non-mulched plots were used as bare controls. When compost was applied at a rate of 54.8 ton/ha (20 ton/acre), compost made with hardwood bark suppressed severity of early blight disease more than compost made with softwood, hay or manure–silage.