Portal de Periódicos da CAPES

LEACHING FROM A TROPICAL ANDEPT DURING BIG STORMS

1985; Lippincott Williams & Wilkins; Volume: 139; Issue: 2 Linguagem: Inglês

10.1097/00010694-198502000-00012

1538-9243

Ann E. Russell, John J. Ewel,

Soil Moisture and Remote Sensing

We measured water and nutrient (Ca, Mg, K, and NO3) leaching in the field using three methods: (1) estimates of flux using the Darcy flow equation, (2) a water balance, and (3) zero-tension lysimeters. The methods were compared in an Andept near Turrialba, Costa Rica, during two large storms (33 and 22 cm wk-1), at two soil depths (25 and 110 cm), and in four kinds of 1− to 2.5-yr-old vegetation. The water balance was the most accurate method, because the other two techniques sample only parts of the flow. Zero-tension lysimeters were evaluated for use in measuring channeled flow under certain conditions. Mean water flows calculated by the flux and water balance methods were signifi cantly different: 28.5 and 31.5 cm, respec tively, at 110 cm during the 33-cm storm. The lux method overestimated water flow during the 22-cm storm: 51.7 cm compared with 21.7 cm determined by the water bal ance. Mean water flow determined from zero-tension lysimeter data during both storms was substantially lower than that estimated by the other two methods: 2.1 cm for the 33-cm storm and 2.5 cm during the 22-cm storm. Nutrient leaching was determined two ways. First, nutrient concentrations measured using porous cup samplers were multiplied by water flows derived from water balance data. Second, nutrient concentrations of leachate collected by zero-tension lysimeters were multiplied by water flows from the lysimeters. In general, nutrient losses determined by the first method were greater than those measured by zero-tension lysimeters, but in some of the vegetations, nutrient losses were so low that there was no difference between the two methods. A few zero-tension lysimeters collected large amounts of leachate even though the soil did not reach saturation during the storms. Solution collection in the lysimeters was mostly a large-storm phenomenon; of the solution caught annually by the lysimeters at 110 cm, 84% was collected during two, week-long storms. One lysimeter (of 96 monitored) consistently collected leachate in excess of the rainfall and low in nutrient concentrations. It is likely that this lysimeter sampled channeled flow. In this soil, where lateral flow is relatively unimportant and impeding layers do not occur, the lysimeters provide a measure of the occurrence and quality of rapid channelized flow.