Productivity of a shortgrass prairie steppe was monitored at the Central Plains Experimental Reserve (CPER), also known as the Pawnee Grassland study site, from 1939 to the present. Measurement of monthly dynamics of above-ground plant biomass were made from 1970 to 1975, for untreated and treated plots with irrigation, fertilisation, and both irrigation and fertilisation together. Annual ... above-ground net primary production (NPP) was estimated by summing peak total biomass for different functional groups of vegetation between 1970 and 1975, and long-term annual above-ground NPP between 1939 and 1990 was estimated by correlation with records of forage production. Above and below ground NPP estimates, using (i) biomass increment methods and (ii) 14-C turnover methods, are available for 1985-88. Work was originally carried out by the US Agricultural Research Service, and later under the US Long-Term Ecological Research (LTER) programme. Data on soil dynamics at CPER were used in the development of the CENTURY plant/soil organic matter model. Climate data for this site are also available: see Any Other Relevant Information in section 11 of this document. More information on the entire Net Primary Production Project can be found at the NPP homepage.