PEANUT GROWTH AS AFFECTED BY LIMING, CA-MN INTERACTIONS, AND CU PLUS ZN APPLICATIONS TO OXIDIC SAMOAN SOILS

Effects of coralline lime, in combination with 3 kg Cu ha(-1) plus 3 k g Zn ha(-1), on yield and nutrient uptake by peanut (Arachis hypogea) were studied at three locations in Western Samoa. Coarse (0-10 mm) cor alline lime material containing 31.1% Ca and 1.7% Mg was used as lime at 0, 555, 2222 and 5000 kg ha(-1). In the Togitogiga soil, which had the lowest level of exchangeable Ca, peanut yield increased by 6 fold after liming with 555 kg ha(-1), relative to the unamended control. Th is yield increase was associated with reduced Mn toxicity as well as r educed Ca deficiency. The alleviation of Mn toxicity was not likely du e to decreased Mn solubility because the lime application (555 kg ha(- 1)) increased soil pH by < 0.1 unit. Rather it was the increased Ca av ailability which reduced the Mn toxicity through a Ca/Mn antagonism. T he critical range of exchangeable Ca for peanut growth was found to be about 1.5-1.6 cmol 1/2 Ca2+ kg(-1). A Ca/Mn-ratio >80 was required fo r a desirable Ca/Mn balance in peanut tissue. On the other two locatio ns (with exchangeable Ca levels of 1.5-1.6 cmol 1/2 Ca2+ kg(-1)), limi ng increased peanut yields by 15-20%. Additions of Cu plus Zn also inc reased the yields, although the increases were small (7%) and not sign ificant at the 95% probability level.