SURVEY OF CALCIUM, MAGNESIUM, POTASSIUM AND MICRONUTRIENTS IN ZONES WITH DIFFERENT SOYBEAN PRODUCTIVITY

Abstract

The concentration of calcium (Ca), magnesium (Mg), potassium (K) and micronutrients could
limit soybean production (Glycine max L.) differentially according to areas of the Pampas region
(RP). The objective of the present work was to survey the concentration of Ca, Mg, K, boron (B),
copper (Cu), zinc (Zn), iron (Fe) and manganese (Mn) in soil, leaf and soybean grain. Seventynine
commercial fields were surveyed in the RP, divided into Northern Zone and Southern Zone
according to productivity. Nutrient concentration in soil at planting, foliar at flowering, and in
grain (Southern Zone only), and yield at maturity were quantified. Significant differences (P
<0.001) in the concentration of nutrients in soil (except K and Mn) and leaf between zones were
determined. Only the concentration of B and Zn in soil was below the critical level (NC)
reported in the literature. In the Northern Zone, 75% of the samples for B and 50% for Zn
showed values lower to the NC, while in the Southern Zone it was of 25% for B and less than 25%
for Zn. To Zn in both zones and Mn in Northern Zone, a significant association (p <0.05) was obtained between the concentration of nutrients in soil and leaf (r = 0.64 and 0.83,
respectively). The accumulation of nutrients in grain was mainly explained by the yield (p
<0.05) and not by concentration (p>0.05), with averages of 2.2, 2.4, 19.4, 44, 33, 9.4, 65 and 24
g per ton of grain for Ca, Mg, K, Zn, B, Cu, Fe and Mn, respectively. In summary, the
concentration of B and Zn could limit soybean yield differentially depending on the area of the
RP. Nutrient removal values in grain could be used as a national reference for estimating
soybean nutrient balances.