The development of piatã grass fertilized with phosphorus sources with different solubilities in water was evaluated. The experiment was developed in the unit of Aquidauana of UEMS, MS, from February to August, 2012. Four treatments were evaluated: control (without phosphorus fertilization), slow solubility, fast solubility (readily available), and mixed solubility sources of phosphorus (FH Pasture(r)). It was adopted a randomized blocks design with four blocks and four replicates in a total of 16 pastures (0.5 ha each one). Measurements were performed weekly to evaluate structural characteristics and morphogenic variables of the plants. Data were submitted to a variance analysis according to the model. When necessary, the means of treatments with different phosphorus fertilizer sources were compared with the control using the Dunnett test and with other treatments by using student's t test. The significance level of 5% was adopted in all analysis. No significant effect was observed (P<0.05) in the evaluated traits in the first year of the experiment.

The development of piatã grass fertilized with phosphorus sources with different solubilities in water was evaluated. The experiment was developed in the unit of Aquidauana of UEMS, MS, from February to August, 2012. Four treatments were evaluated: control (without phosphorus fertilization), slow solubility, fast solubility (readily available), and mixed solubility sources of phosphorus (FH Pasture(r)). It was adopted a randomized blocks design with four blocks and four replicates in a total of 16 pastures (0.5 ha each one). Measurements were performed weekly to evaluate structural characteristics and morphogenic variables of the plants. Data were submitted to a variance analysis according to the model. When necessary, the means of treatments with different phosphorus fertilizer sources were compared with the control using the Dunnett test and with other treatments by using student's t test. The significance level of 5% was adopted in all analysis. No significant effect was observed (P<0.05) in the evaluated traits in the first year of the experiment.

In semi-arid irrigation areas, one of the most important water quality problems is nutrient pollution from agriculture through irrigation return flows. The element that most frequently limits the growth of aquatic vegetation is phosphorus (P) that may cause eutrophication above certain thresholds. Several management models for phosphorus diffuse pollution by agriculture are available currently, some of which resort to the use of indices. An index of phosphorus risk loss (PI) is a numerical value that weighs in a qualitative way the risk of water pollution by P associated to farming practices, soil and meteorological conditions. For these, a PI must account for and integrate the processes involved in P availability and P transport. In this thesis, a new PI (IPreg) has been developed for the irrigated area within "Las Filadas" gully watershed (Huesca), with a total 4,920 ha and included in the water users associations of Orillena, Lanaja and Lalueza