The success of hot beds led to the use of huge amounts of animal manures to be employed in greenhouses, and many historical reports relate successful cucumber culture under this system. As much as 448 t/ha (200 tons/ac) of manure has been reportedly applied for the culture of greenhouse cucumbers, and as much as 5000 ppm of CO2 have been measured in closed greenhouses in Denmark in midwinter that evolved from the manure, peat, or straw used.