LEACHM

Hutson JL, Wagenet R (1989) 'LEACHM: Leaching Estimation and Chemistry Model; a process-based model of water and solute movement, transformations, plant uptake and chemical reactions in the unsaturated zone, Version 2'.

The objectives of this paper deal with (1) to explore the transport and fate characteristics of N[O.sub.3]-N within the soil profile and the leaching loss from continuously typical intensive agriculture farmland, (2) to estimate the LEACHM model against the data in terms of its ability to simulate the process of N[O.sub.3]-N leaching loss in field conditions, and (3) to determine the overall N[O.sub.3]-N leached from the irrigation and natural rainfall and the leaching potential of nitrates under current traditional irrigation methods and suggest the best possible irrigation methods that can reduce nitrogen leaching.

Several models were reviewed before selecting LEACHM for simulating N[O.sub.3]-N concentration in field conditions.

The 4 models are: LEACHM (Hutson and Wagenet 1992), a deterministic, process-based model that simulates water transport using Richards' equation; GLEAMS (Leonard et al.

For cases in which a more detailed simulation and/or field study are needed, research models such as RZWQM, LEACHM, or ecosys, and research plots or farms can be used to establish refined values for NLI.

Some of these models are NLEAP, LEACHM, CERES, EPIC, NTRM, RZWQM, and GPFARM.

LEACHM: Leaching Estimation and Chemistry Model: A process-based model of water and solute movement, transformations, plant uptake, and chemical reactions in the unsaturated zone.

For LEACHM, soil hydraulic properties (K-[theta]-h relationship) were obtained by fitting the soil retention data for the all layers of soil (0-1.00m) to Campbell's equation to obtain the values for constants a (air-entry) and b (Campbell's exponent).

able 1 Rate coefficients for nitrification and denitrification from LEACHM calibrations (Sogbedji et al.

Webb TH, Lilburne LR (1999) Use of the LEACHM model and the DRASTIC index to map relative risk of groundwater contamination by pesticide leaching.

Simulations using a subsurface, field-scale simulation model (LEACHM) then were performed for the final six groups to assess water and pesticide movement (Petach et al.

In principle, the fate of cations such as [K.sup.+] and N[H.sub.4.sup.+] in solutions absorbed by soils can be predicted using models based on reaction chemistry and chromatographic theory such as LEACHM (Hutson and Wagenet 1992) and UNSATCHEM (Suarez and Simunek 1997; Suarez 2001).