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L. Carrasco-Letelier, and A. Beretta-Blanco. 2017. Soil erosion by water estimated for 99 Uruguayan basins. Cien. Inv. Agr. 44(2): 184-194. Soil erosion can be accelerated by agricultural intensification, and the soil loss can alter the quality of water bodies. Sustainable agricultural production therefore requires the management of erosion and potential water pollution. In Uruguay, where there is heavy use of soil for agriculture, there is a need to continually develop and update erosion management policies. In this framework, we estimated the erosion in 99 drainage basins by analyzing and managing the information required (K, L, S, C and R-factors) in the universal soil loss equation (USLE) and the revised universal soil loss equation (RUSLE) in a geographical information system (GIS). The studied drainage basins encompass 73% of the area of Uruguay. The results include the following values: the K-factor range from 0.0073 to 0.088 (t ha h)(ha MJ mm) -1 , the R-factor range from 3,547 to 9,342 (MJ mm)(ha h yr) -1 , the C-factor range from 0 to 0.155, the slope gradients are less than 4.3% in 78% of the soils, and the multiplicative products of L and S are less than 0.73 in 75% of the cases. The drainage basin characteristics allowed the identification of 4 homogeneous regions based on their erosion behavior. The northern-western-southern basins cluster and Sierras del Este basins clusters indicate the possibility of managing their erosion through control of vegetation cover, which is represented by the C-factor. In general, this forecast of soil erosion by water (92.9% of the soil polygons and 99.9% of the drainage basins) indicates a mean soil loss of less than 7 t (ha yr) -1 corresponding to the land cover surveyed in 2011.

A. Beretta-Blanco, L. Carrasco-Letelier. 2017. USLE/RUSLE K-factors allocated through a linear mixed model for uruguayan soils. Cien. Inv. Agr. 44(1): 100-112. Soil erosion by rainfall is a process that demands management, both for the prevention of excessive soil erosion and for the protection of the quality of freshwater bodies. Erosion coefficients (K-factors) of the universal soil loss equation (USLE)/revised USLE (RUSLE) model were assigned to 99 mapped Uruguayan soil types at 1:1,000,000 scale. This work developed a linear mixed model (LMM) with 79 soils with assigned K-factors, in which the following variables were considered: soil taxonomy, chemical composition, and parent material. The developed LMM had an R 2 =0.86, in which the soil taxonomy (p<0.0001), parent material (p=0.0174), clay (p=0.0005) and sand (p=0.017) contents had significant statistical effects. The prediction capacity of this model was assessed with 10 soils not previously used in development of the LMM with assigned K-factors. The prediction assessment had an R 2 =0.84 and a mean error of 9.08% of the mean K-factor value. The LMM developed was used for the allocation of K-factors to soils mapped at a 1:20,000-resolution. Thus, the use of LMM increased the soil area with assigned K-factors from 111,822 km 2 (at a scale of 1:1,000,000) to 174,132 km 2 (1:20,000).

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.