EFFECT OF LIMING ON THE YIELD, NUTRITION AND COPPER STATUS OF POTATOES, CARROTS AND ONIONS GROWN SEQUENTIALLY IN TWO PEAT SOILS

Abstract

In a greenhouse study, two Mesisols, a woody and a sedge peat, were enriched with calcitic agricultural limestone at rates of 0.5–30 t/ha to increase their pH from 3.0 to 5.8. The general fertilization included 50 ppm (20 kg/ha) of Cu (wt/wt). Maximum yields of potatoes were obtained at a soil pH of 3.4–3.6 (4–6 t lime/ha rate) but harvest index of potato tubers (mass of tubers as percent of total dry matter produced) indicated that the 10-t/ha rate would be more suitable. The Cu concentration of potato leaves and tubers did not exceed 16 ppm, and was thus less than phytotoxic level (20 or 30 ppm), even at soil pH lower than 3.4. After further addition of other fertilizers and 25 ppm of Cu, carrots gave maximum yields at the 30-t/ha rate. Copper concentrations in carrot tops and roots were below 16 ppm even at the 10-t-lime/ha rate (soil pH 3.8 or 4.0). Onions, grown after repetition of the fertilization for carrots, gave highest yield, particularly of bulbs, at the 30-t-lime/ha rate but this corresponded to an undesirably high soil pH of 5.7 or 5.8. The Cu concentration in bulbs exceeded 16 ppm only when yields were unacceptably low at the 6-t/ha and lower rates of liming. In all crops, Cu concentrations generally decreased sharply as soil pH rose above 4.0. The Ca:Mg ratio in plants usually increased with liming but, within the range observed here, did not closely parallel increases in yield. Plant concentrations of N, P and K generally decreased with liming at the highest rates (20 or 30 t/ha). Key words: Liming, peat, potatoes, onions, carrots, copper