Peanut crops grown in the upland area of northeastern Thailand frequently have the problem of unfilled pods. The element calcium(Ca) plays a major role in seed formation and nutrient assimilation, and consequently, unfilled pod formation in peanut is thought to be caused by a Ca deficiency (Cox et al., 1982). From soil analysis, it was found that soil from the peanut growing areas contained less than 120 ppm of exchangeable Ca, whereas an adequate amount of Ca for peanut growth is suggested to be at 120 ppm (Adams and Hartzog,1980). In order to find out an effective and economical rate of Ca application for reducing unfilled pods in peanut, experiments were conducted in Ubon Ratchathani Field Crops Research Centre and farmers’ fields in Yasothon province during 1996-1998 using limestone (CaCo₃). Other nutrients were also included in the studies. The results can be concluded as follow:

1. The percentage of unfilled pod of peanut plants grown in soils containing less than adequate amounts, different amounts of exchangeable Ca (43-111 ppm) were not significantly different. Data also showed that unfilled pods were higher than 70%. An application of limestone at 100 kg/rai, given just prior to sowing peanut in the first year, can decrease the amount of unfilled pods of peanut to less than 20% for at least 3 years.
2. Ca application increase dry pod yield as the number of unfilled pods is reduced, and shelling percentage as well as seed size increase.
3. Other nutrients, applied into the soil in the form of Nutrifertilizer (consisting of 20%Mg, 7%S, 6%Mn, 6%Zn, 2%Fe, 2%Cu, 0.5%B, and 0.005%Mo) have no effect on unfilled pods formation, but increase shelling percentage and seed size.

For a recommendation, peanut grown in soils containing less than 120 ppm of exchangeable Ca, should be given an application of limestone (CaCo₃) as a source of calcium. A rate of 100 kg/rai (625 kg/ha) is recommended. Limestone is an economical calcium source as it costs only 1.00-1.20 baht/kg. In addition, the properties of limestone such as a weak reaction, slow release and a long-term residual effect, make it suitable for use in sandy soils. A limestone application, such as this, costs only 30-40 baht/rai/year.

Adams,F., and Hartzog, D. 1980. The nature of yield response of florunner peanuts to lime. Peanut Sci. 7:120-123.

Cox,F.R., Adams,F., and Tucker, B.B. 1982. Liming, fertilization and nutrition. In Peanut Science and Technology. Patter,H.E. and Young, C.T. (eds) American peanut Research and Education Society, Inc, Yaokum, Texas, U.S.A.

Peanut1-1