Green manures are cover crops grown for mulching onto and into the topsoil. They protect the soil from the heat of the sun, thereby reducing burning of organic matter; they save work – farmers can sow into the plant residue rather than tilling the soil; they keep the excess nitrogen from acidifying the upper soil horizons; and they prevent soil erosion.
Green manure and cover crops (gm/cc's) can produce from 50 to 140 tons per hectare (22 to 62 tons/acre) (green weight) of organic matter with very little work: no transporting of material and no cutting up or layering or turning over of compost heaps. Sometimes, because of the gm/cc's control of weeds, net labor costs decrease and soil quality improves visibly each year.
Laki-laki Dennstaedtia glauca (Polypodiaceae) is used as a green manure in specific agricultural contexts in Puno, Peru. It is applied in conjunction with animal manure and prior to potato cultivation in the first year after a period of fallow. Fronds of D. glauca, while containing average or low amounts of micronutrients, are high in nitrogen, phosphorus, and potassium in comparison with other fern species and plant material in general. It is likely that this fern contributes to fertility of soil used for tuber crops. The plant grows in abundance along watercourses and may play an important role as a recycler of nutrients leached from terraced fields.