EFFECT OF LIME RATES ON NUTRIENT AVAILABILITY, MOBILITY, AND UPTAKE DURING THE SOYBEAN GROWING SEASON: 2. CALClUM, MAGNESIUM, POTASSIUM, IRON, COPPER, AND ZINC1

Liming is necessary in much of the southeast because of the aCld nature of the soils, which results from a humid climate, intensive farming, and the use of NH4-N fertilizers. Liming neutralizes soil aCldity, reduces toxic levels of Al and Mn, and enhances soil fertility. Considerable research has been done to ascertain the effect of limestone on soil aCldity and fertility, but the impact of liming on plant growth and nutrient uptake by determinate soybean varieties during the entire growing season awaits a deeper scrutiny.Three rates of dolomitic limestone were applied in triplicate to a field-grown Bragg soybean cultivar on a CeCll sandy loam soil (Typic Hapludult). Results showed that in the limed plots, the extractable Ca and Mg in the A horizon sharply increased with time and remained high, though the extractable K increased by week 2 and then progressively declined. The A horizon extractable Fe, Cu, and Zn in the limed plots were lower than in the unlimed plots and decreased with time.Shoot nutrient concentrations generally decreased with time, due to dilution by plant growth, despite increasing soil nutrient levels as in the cases of Ca, Mg, and K. Total shoot nutrient contents rapidly increased after week 4 with the onset of exponential plant growth, in spite of decreasing shoot nutrient concentrations. The daily nutrient accumulation rate increased after week 4 and peaked between weeks 8 and 12 or 8 and 16 for Ca, Mg, K, and Fe or continued to increase up to week 20, as in the cases of Cu and Zn. Although the rate of nutrient accumulation in the shoots generally decreased toward the end of the growing season, total nutrient uptake continued to increase at least up to week 20. Fifty percent of the total nutrient content of the shoots was present by week 12 or by the end of the vegetative stage of the plant life cycle.Based on the nutrient uptake data, we concluded that the best time for soybean tissue sampling is 8 wk after shoot emergence, or about flowering time, when nutrient concentrations are relatively constant and uptake rates are high.