Avoid feedlot manures which are typically high in salts. Dairy cattle manure is generally a better quality, but poultry manures can also be used. Horse or sheep manures may carry weed seeds, spreading their growth. Compost is perhaps the best organic amendment. It can be purchased or made at home by recycling yard prunings and clippings.
Compost promotes microbiological activity in soils necessary for plant growth.
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