Bouyoucos (1936) proposed a more rapid and simpler procedure called the hydrometer method. Both analytical techniques are sedimentation procedures accepted as standard techniques for particle-size analysis. The sand, silt, and clay contents of several soil samples were determined using the Pipette method as a control and compared with the Bouyoucus, the Bouyoucos Modified (Bouyoucos_M) and the Bouyoucos Modified with gravimetric determination of the sand content (Bouyoucos_M-T) methods. Data obtained from these procedures was used to assess soil textural class, the soil erodibility coefficient (K), the water retained at field capacity (FC) and the permanent wilting point (PWP). In the Bouyoucos_M method, the soil organic matter (SOM) was destroyed and the dispersingagent concentration was increased. In the Bouyoucos_M-T method, the sand was quantified gravimetrically by sieving samples through a 53 µm mesh. The hydrometer and Pipette methods measurements correlated well. The Bouyoucos and the Bouyoucus-M methods overestimated the sand content. The performance of the Bouyoucos_M-T method did not differ from that of the Pipette method. Compared with the Pipette method, the Bouyoucus method underestimated the clay content, and the Bouyoucos_M method did not differ from the Pipette method. The values obtained with the Bouyoucos_M and the Bouyoucos methods underestimated the FC and the PWP, and Bouyoucos_M-T method did not differ from estimations based on the Pipette method data. The assessed K value was underestimated with the Bouyoucos_M method. The Bouyoucos and the Bouyoucos_M-T methods estimated the K values similar to the Pipette method. The Bouyucus_M-T method is suitable for determining the soil texture and inferring soil properties but is unacceptable for assessing the class texture for soil taxonomic classification.

El valor de acidez titulable a pH = 7 en suelo (AT_pH7) se utiliza con fines taxonómicos y para estimar la necesidad de encalado. Es posible predecir AT_pH7 por el valor de pH de la mezcla suelo:solución buffer (pH_equilibrio). A cada muestra se le agregó acetato de calcio buffereado a pH = 7, se midió el pH_equilibrio y el álcali necesario para llegar a pH=7. Con pH_equilibrio se estimó AT_pH7 por regresión (AT_eq) o por la cantidad de álcali neutralizado para alcanzar el pH_equilibrio (AT_OH). Existió un ajuste aceptable entre AT_pH7, AT_eq y AT_OH, pero sus diferencias no tuvieron distribución normal. Con AT_OH y AT_eq, se subestimó el promedio de AT_pH7. El valor de pH_equilibrio fue más preciso que AT_pH7, en tanto que las medidas AT_eq y AT_OH tuvieron menor precisión. Al utilizar AT_eq y AT_OH, no se introdujeron errores significativos al clasificar los suelos por su saturación en bases. Ambas mediciones se realizaron en menor tiempo que AT_pH7.

The increase in global demand for food and biofuels, has led to an high demand for agricultural products. That situation implies an intensification of production systems, and develop strategies to ensure stability against drought, and moreover a better levels of productivity. Objectives that could be achieved with the irrigation of crops; however, it can promote negative impacts due to cumulative effects on soil quality, which depend on the chemical composition of the water used. This paper show the results of a national study of freshwater quality, on 100 river watersheds (up to 100,000 ha), which correspond to a cumulative drainage area of 70% of country surface. In these freshwaters the following parameters was evaluated: electrical conductivity, concentration of major cations (Na, K, Ca, Mg), alkalinity, and pH. The results showed Ca, Mg, K, and Na concentrations in ranges of 0.0-45.1, 0.0-14.1, 0.019-16.8, and 0.78 -139 mg L-1, respectively. The alkalinity was in range of 32 to 420 CaCO3 mg L-1, and this variable was the most important contribution to get the different values of electrical conductivity of water, which had values between 71.6 and 1047 micro Siemens cm-1. These features allow propose at least 3 freshwater ecoregions (coastal and central-south; basalt; Northeast and southeast) at Uruguay, based on the chemical composition of studied freshwaters. Moreover, SAR values (([Na] / [(Ca + Mg) / 2] 1/2) of these waters shown a 99% of them has good quality characteristics for the development of irrigation, because they have a SAR below 10.

Los papeles reactivos al pH (tirillas) podrían ser útiles para medir pH del suelo. El objetivo fue evaluar la precisión y exactitud de estas medidas. Se comparó la medición de pH (suelo:agua 1:2,5) en 51 muestras de suelo, por tres métodos: con electrodo (pH_electrodo); con tirilla inmediatamente de ser sumergida en el sobrenadante luego de 20 minutos de reposo (pH_T); y con la misma tirilla luego de dos horas de secada, rehumedecida y lavada (pH_T_RL). Se utilizaron tirillas Millipore®, graduadas por unidad de pH, estimándose los valores intermedios. Se analizó carbono orgánico del suelo (COS) y conductividad eléctrica (CE) en cada muestra. Los valores pH_electrodo fueron tomados como referencia. Las lecturas pH_T y pH_T_RL tuvieron una relación aceptable (R2 de 0,50 y 0,48, respectivamente) con pH_electrodo, aunque subestima-ron en promedio 0,44 y 0,21 unidades de pH, respectivamente. Con el contenido de carbono orgánico y pH_T o pH_T_RL, se estimó satisfactoriamente el valor de pH_electrodo y la diferencia promedio fue de -0,02 y 0,24 unidades de pH, respectiva-mente. Hubo concordancia aceptable al clasificar la acidez del suelo por pH_electrodo, por pH_T_RL o por pH estimado a partir de pH_T y carbono orgánico. Al realizar una calibración entre lecturas de pH con tirillas en función del contenido de COS y las mediciones de pH con electrodo, es posible utilizar las lecturas de pH con tirilla como una medida orientativa para clasificar la acidez del suelo.