In Rio Grande do Sul, Brazil, irrigated rice fields use large amount of water and have the potential of contaminate surface water bodies when drainage is performed. The objective of this experiment was to quantify the amount of water in flooded rice fields under different cropping systems (Experiment I) and to measure the concentration of nutrients in the initial drainage water of pre-germinated, pre-germinated mix and seedling transplanting systems (Experiment II). The research was conducted during 2000/01 and 2001/02 (Experiment I) and during 1999/00, 2000/01 and 2001/02 (Experiment II) in a lowland area of a Planosoil located at the Federal University of Santa Maria-RS, Brazil. In the years 2000/01 and 2001/02 (Experiment I) five cropping systems (conventional, minimum tillage, pre-germinated, mix of pre-germinated and seedling transplanting) randomized block experimental design with four replications were used. The cropping systems did not influence the use of water by flooded rice, varying from 5,431 to 6,422 and 5,347 to 5,852m³ ha-1 for the years 2000/01 and 2001/02, respectively. The amount of water used for flooding the soil in the pre-germinated and seedling transplanting systems or form stablishing a layer of water in the mix pre-germinated was 1,285m³ ha-1. In Experiment II, three cropping systems (pre-germinated, mix of pre-germinated and seedling transplanting) were compared. Nitrate, phosphorus and magnesium concentrations in the initial drainage water were similar in the different cropping systems. In the mix of pre-germinated system, ammonium and potassium concentrations were higher when compared with the pre-germinated and seedling transplanting systems with averages of 3.85 and 7.70mg L-1, respectively. Recorded nutrient losses were within the range allowed by the currente legislation. The concentration of sediments in the drainage water was lower in the mix of pre-germinated system when compared to pre-germinated and seedling transplanting systems. These suggest that the maintenance of water in the rice field in these cropping systems is important to achieve the sustainability of the flooded rice fields and maintenance of high potential of crop yield.
Orysa sativa L.; crop systems; environment
