Viability of Weed Seeds Following Manure Windrow Composting

Abstract

Introduction of weed seeds is a concern when using animal manure as a nutrient source on croplands. The viability of weed seeds can be reduced through composting. Experiments were conducted in 1996 and 1997 to determine the effects of manure windrow composting on seed viability of eight weed species. Weed seeds were placed in nylon bags and buried at 25 and 75-cm within the composting windrows of dairy manure and beef cattle feedlot manure with or without water addition. After one turning a week later, the seeds of most weed species survived the composting conditions in the dairy cattle manure. Following the four to five month dairy manure composting process, all weed seeds lost viability except for 14% of the velvetleaf (Abutilon theophrasti) seeds. This occurred even though the temperature within the composting dairy manure windrow never reached 60°C, which is considered necessary for weed seed destruction. In the watered beef feedlot manure, all weed seeds lost viability after one turning. However, seeds of most species survived after the first turning of the unwatered beef feedlot manure. The temperature in the feedlot manure windrows with water addition was higher and stayed high longer than other manure windrows. Composting process that generates high temperature (≥60°C) can destroy seed viability after only one turning. When the composting materials are moist for most of the composting period, the viability of weed seeds can be reduced even though the critical temperature is not achieved possibly because of compost phytotoxins.