The use of cover crops is not without some potential problems. Many annual cover crops must be mowed before they produce viable seeds which could become a weed. Some cover crops have allelopathic properties that can have detrimental effects on the cash crops that follow. Large amounts of cover crop residues can cause significant problems during seeding of the next crop. Precision seeders are particularly sensitive to seedbed conditions with excessive crop residues. Nitrogen can be tied up during decomposition of incorporated fibrous plant material to the detriment of the cash crop. Poorly selected cover crops can attract, stimulate or harbour pests that can negatively impact the following cash crop.