Calcium and phosphorus play important roles in plant root growth. A greenhouse experiment was carried out to study the effect of three levels of Ca and four levels of P on soybean root growth, dry matter production and mineral nutrition. Two soybean plants cv. IAC 17 were grown for 35 days in 7 L pots containing a Dark Red Latosol (Acrortox, sandy loam). Lime was applied in amounts calculated to raise the soil base saturation to 45, 50 and 75%. Phosphorus was applied at 25, 50, 100 and 200 mg kg-1, using a Ca free compound. A calcium content of 8.5 mmol(c) dm-3 in the soil allowed for a normal growth of soybean roots. When the soil base saturation was low (46%), the low availability of P led to an increase in root length and surface, without a corresponding increase in root dry matter. Although these thin, long roots have an adequate geometry for P absorption, when the soil P contents were lower than 45 mg kg-1 this adjustment was not enough to maintain soybean P absorption at an adequate rate for plant growth.
Glycine max; root length; root radius; calcium; phosphorus; plant nutrition
