Field experiments were conducted on Kenansville lfs (Arenic Hapludult) in 1977 and on Rumford lfs (Typic Hapludult) in 1978 to compare two bulk-spread supplemental Ca sources with bagged landplaster. Bagged LP, 420 Landplaster Bulk (420-Bulk) and Texasgulf Gypsum (Tg Gypsum) were appplied on Florigiant peanuts (Arachis hypogaea L.) at rates equivalent to 260 kg/ha Ca broadcast and at three different dates: planting, early June just prior to flowering, and late June in early flowering stage. The relative effects of these Ca sources on changes in the contents of H₂O- and 1.0 N NH₄OAC-extractable soil Ca, Mg, and K in the 0- to 10-cm and 10- to 20-cm soil layers wre measured by analysis of periodic soil samplings taken during the peanut fruiting period.

All three Ca sources increased the contents of both H₂O- extractable Ca (H₂O-Ca) and NH₄OAc-extractable Ca (Ac-Ca) in both soil layers throughout the sampling period. In 1977, contents of H₂O-Ca in treated plots often were 100 to 125 μg/g of soil higher in the 0- to 10-cm layer and 50 μg/g higher in the 10- to 20-cm layer than in untreated plots. Increases in the contents of Ac-Ca in treated plots up to 150 μg/g of soil occurred in several cases in the 0- to 10-cm layer and up to 100 μg/g in the lower layer. The Ca applications in 1977 increased the initial extractable contents of H₂O-Ca and Ac-Ca more and the Ca persisted longer after Ca application than in 1978. Bagged-LP or Tg Gypsum generally increased the contents of H₂O-Ca and Ac-Ca in the 0- to 10-cm layer considerably more than 420-Bulk, particularly in 1977. Differences between Ca sources often diminished with time after application of the materials. This occurred to a greater extent in 1978. The contents of Ac-Ca, particularly, in plots amended with 420-Bulk usually increased considerably toward the end of the sampling period. The contents of H₂O-Ca and Ac-Ca in comparable samplings of the peanut fruiting layer generally were similar much of the time for all three times of applications.

Changes in NH₂OAc-extractable Mg contents extracted from the 0- to 10-cm and 10- to 20-cm layers following application of the Ca sources ranged from 10 to −25 and 28 to −22 μg/g of soil, respectively, in 1977. The ranges in 1978 were from 0 to −20 and 12 to −14 μg/g of soil, respectively. Similarly, changes in NH₄OAc-extractable K in the surface and lower layers ranged from 10 to −25 and 13 to −18 μg/g of soil, respectively, in 1977. The ranges in 1978 were from 11 to −20 and 14 to −24 μg/g of soil, respectively. These contents of Ac-Mg and Ac-K decreased more frequently than they increased after application of the Ca sources, particularly when applied at planting. Relatively more increases occurred after the later application.