RUNOFF AND SEDIMENT YIELDS SIMULATION UNDER FIVE SOIL MANAGEMENT PRACTICES SIMULACIÓN DE ESCURRIMIENTO Y SALIDA DE SEDIMENTOS EN CINCO PRÁCTICAS DE MANEJO DE SUELO

Runoff containing sediment, nutrients, and pesticides originating from agricultural uplands are the main pollution agents for the Lake of Pátzcuaro, Mich., México. The purpose of this research was to simulate runoff (Q) and sediment yield (Sy) under natural rainfall, through model simulation which describes hydrologic processes for five agricultural management systems in the Pátzcuaro region. Five treatments were imposed on runoff plots measuring 25 m x 4 m on the Ajuno Experimental Station of the National Sustainability Production Center (CENAPROS-INIFAP). Plots were planted with corn (Zea mays L.) on June of 1996 and May of 1997. The treatments consisted of: 1) Bare soil (BS), 2) Traditional tillage (TT), 3) No till with 33 % residue cover (NT- 33), 4) No till with 100 % residue cover (NT-100), and 5) Conventional till (CT). TT and CT are the main regional production systems. The GLEAMS model (Groundwater Loading Effects of Agricultural Management Systems), was tested and calibrated for 1996 and validated on CT and NT-100 for 1997 to simulate the hydrologic and erosive response using the plot data. Results indicated that BS, CT and TT had higher runoff and sediment yields than both NT management treatments. GLEAMS simulated sediment yield better than discharge, with good precision (more than 80 %). Model proficiency was better than mean values in all cases for Sy, except for the BS. Model validation found underestimation in runoff and sediment for both treatments. These results demonstrated the feasibility of simulating Q and Sy from agricultural lands to locate the main Q and Sy sources and to provide information supporting changes to the prevalent soil management system.