Liming improves herbage yield, essential oil yield and nutrient uptake of rose-scented geranium (Pelargonium capitatum×P. radens) on acidic soils

Abstract

A field experiment was conducted on rose-scented geranium (Pelargonium sp.) in Pretoria, South Africa, to evaluate plant response to liming on acidic soils. Treatments were dolomitic limestone at 0 (control), 2, 4 and 6 t/ha, laid out as a randomized complete block design. Soil pH was not influenced by liming for any of the treatments at the first harvest, whereas at the second, third and fourth harvests an increase in pH was observed for all the limed treatments. At the time of the first harvest, plants did not respond significantly to 2 and 4 t/ha of liming, but responded positively to 6 t/ha, with higher herbage yield compared with the control and 2 t/ha lime treatments. At the second, third and fourth harvests fresh herbage and essential oil yield increased significantly due to liming. The differences among limed treatments were not significant for fresh herbage and essential oil yield. Cumulative fresh herbage and essential oil yields of all harvests were higher on the limed treatments than the control. Soil pH above 5.5 and soil base saturation above 55% increased fresh herbage and essential oil yield (per ha), which corresponded in this case with 2 to 6 t/ha of lime application. Oil content (%) was not affected by application of lime or an increase in soil pH but was more dependent on air temperature fluctuations. Similarly, no clear differences were observed in the composition of the essential oil throughout the experimental period due to liming. The ratio between citronellol and geraniol correlated with seasonal differences in maximum temperatures and not with liming. The implication of this study is that optimum growth of rose-scented geranium can be achieved by application of lime when plants are grown on acidic soils (pH (H2O) <5.5) but without any effect on oil content and essential oil composition.