Chemical Composition and Weed Seed Viability in Co-composted Animal Waste and Farm Residue under the Desert Environment.

The increasing number and the size of confined animal feeding operation (CAFO) result in animal waste production much greater to be absorbed on the cropland surrounding CAFO. The annual manure production in Arizona is approaching 10 million tons, often hauled away if applied at the recommended rate. Hauling manure to the fields is cost prohibitive, limits its application to more lucrative vegetable crops. But manure becomes an alternative source of crop nutrients as fertilizer and hydrocarbon’s cost increases. However, the increasing public awareness about the pathogen contamination risk on produce receiving manure and the increasing consumer’s demand for organically grown crops result in more manure being composted. Growers see compost’s benefits as valuable nutrient source, free pathogens and  viable weed seed. Natural Resource Conservation Service (NRCS) provides technical and financial assistance to producers, under Environment Quality Incentive Program, interested in adequately managing animal waste including composting practices. An incentive that helps producers achieve simultaneously, their production objectives and environmental sustainability. Among producers’ objectives from co-composting include nutrients and free weed seed viability. Compost areas were laser leveled and packed to minimize the runoff. Co-composted manure and crop residues were arranged in windrows 50-100 m long, 5 m wide and 1.30 m high for 6 to 9 months. Seed were buried in the windrows and retrieved between windrow turnings. Windrows were watered and turned with a self propelled or tractor pulled composter two to three times a week during the first month and once a week afterward. Producers collected compost samples sent to the laboratory for chemical analysis. Temperature was monitored at different depths. N mineralization   was rapid before it was stabilized. Temperature was the highest at the center of the windrows reaching 70 ^oC. Seed viability was evaluated by seed staining with tetrazolium, ranged from 0 to less than 5%.