Morphological variables such as phytomass, plant height, leaf area, number of leaves, have been used to express the influence of mineral nutrients on plant growth patterns, since the vegetative development responds, in general, favorably to fertilizer applications. This work evaluates the effect of P on both, some morphological characteristics and total [P] in the shoot of eight grain sorghum (Sorghum bicolor L. Moench) genotypes. Genetic materials were grown in nutrient solution under three concentrations of P (0; 0.5 and 1.0 mmol L-1). Plants were harvested 41 days after sowing, and leaf area per plant (LA), number of leaves (NL) per plant, root volume (RV), plant height (PH), root dry matter (RDM), shoot dry matter (SDM), total dry matter (TDM), RDM/SDM ratio, and total P concentration in shoot were determined. RDM/SDM was high for treatment P(0) and diminished about twice when P was added. Lack of applied P decreased the final NL and LA. Shoot [P] was positively correlated with solution [P], but the increase in P concentration in the nutrient solution from 0.5 to 1.0 mmol L-1 had a negative effect on growth. Both under deficiency and sufficiency conditions of P, Himeca-101 showed the best behavior in terms of RDM, SDM, TDM, RV, LA and NL. LA and PH were identified as the best indicators to predict dry matter yield of sorghum plants under P supply conditions.

For alkali sodic soils (pH>8.5), the "hydrolysis of exchangeable sodium" has been used as a possible explanation for the alkalinity production and rise in pH of these soils. As an alternative to this hypothesis, a model was developed to simulate and to explain that the alkalinity production and rise in pH is possible in a soil that accumulates alkaline sodium salts and CaCO3. Several simulations were performed by using different combinations of CO2 partial pressures (P), presence or absence of MgCO3, along with experimental values of exchangeable sodium percentage (ESP) and ion concentrations in saturation extracts from an alkali sodic soil (named Pantanal). A hypothetical system with similar conditions to the Pantanal soil but with a Gapon selectivity coefficient (KG) of 0.01475 (mmol L-1)-1/2 was also considered. Good agreement was obtained between experimental and predicted values for pH and ion concentrations in the soil solution when the model (without MgCO3) was applied to the Pantanal soil. However, KG values calculated for the Pantanal soil were generally higher than 0.01475 (mmol L-1)-1/2. Moreover, high pH values and elevated ionic strength were obtained when a KG of 0.01475 (mmol L-1)-1/2 was used at high ESP (similar to those found in the Pantanal soil). KG values obtained for the Pantanal soil and the results obtained in the simulation of the hypothetical system are suggesting that a value higher than 0.01475 (mmol L-1)-1/2 should be used to adequately simulate the behavior of the Pantanal soil at low ionic strength and high ESP values.