The first region is tipically flooded during the rain season and not used as an experimental area. The calcium levels would represent the natural content in the region. The second region has received fertilizers a while ago and is tipically occupied by rice fields. The third region has recieved fertilizers recently and is frequently used as an experimental area.
data(ca20)
Capeche, C.L.; Macedo, J.R.; Manzatto, H.R.H.; Silva, E.F. (1997) Caracteriza��o pedol�gica da fazenda Angra - PESAGRO/RIO - Esta��o experimental de Campos (RJ). (compact disc). In: Congresso BRASILEIRO de Ci�ncia do Solo. 26., Informa��o, globaliza��o, uso do solo; Rio de Janeiro, 1997. trabalhos. Rio de Janeiro: Embrapa/SBCS.