LEACHN Simulations of Nitrogen Dynamics and Water Drainage in an Ultisol

Abstract

Jabro et al., 1993; Jemison et al., 1994; Lengnick and Fox, 1994). Most of the evaluation studies have cali-Nitrate leached from soils can contaminate drinking water and brated a model with an individual data set and then pose a health risk at concentrations Ͼ 10 mg N L Ϫ1 . Computer models conducted a validation with additional independent data may be useful management tools for estimating NO 3 leaching, but they need to be calibrated and validated before use. The objective sets. Calibration of the model has been typically accomof this work was to calibrate and validate LEACHN to simulate soil plished by adjusting input parameters and rate constants NO 3 , soil NH 4 , water drainage, and NO 3 leaching in a Cecil sandy so that output values are as close as possible to measured loam (fine, kaolinitic, thermic Typic Kanhapludults). The calibration values in the calibration data set. This approach to testwas done by determining rate constants and parameters under laboraing a model has the disadvantage of requiring a calibratory conditions. The validation data was obtained from a two-year tion data set. In addition, the approach can be very timestudy with conventionally tilled corn (Zea mays L.) during summer consuming, especially if the range of values explored for and either a rye (Secale cereale L.) cover crop or fallow conditions each input parameter and rate constant is relatively during winter. Water drainage collected by tiles was automatically large. Furthermore, since this process adjusts several measured, subsampled, and analyzed for inorganic N concentrations.input parameters and rate constants at the same time, During the cold season, LEACHN underestimated soil NH 4 and NO 3 in at least half of the cases. During the warm season, the model

Management implications of conservation tillage and poultry litter use for Southern Piedmont USA cropping systems

“…The data can also be coupled with other studies investigating temporal and spatial ecosystem dynamics across regions. Data generated from the Watkinsville facility were used to evaluate the LEACHN (Johnson et al 1999) and RZWQM (Abrahamson et al 2006) models for estimating tile drainage and nitrate leaching from Cecil soils.…”

“…Soil C, N Initial C and N contents for the 0-15 cm depth in 1991 prior to the initiation of the conservation tillage treatments were 8.4 and 0.80 g kg -1 , respectively, (Johnson et al 1999). In winter 2005, soil C had increased to 13.3 and 16.2 g kg -1 and N had increased to 1.24 and 1.45 g kg -1 for the conventional tillage and no-toll treatments, respectively, for plots receiving poultry litter (Schomberg et al 2009b).…”

Calibration of LEACHN model using LH-OAT sensitivity analysis

“…If the NSEF value is closer to one, the efficiency of a model is higher. Sumner (2000) Air entry value (kPa) AVE -17 -0.149 Ramos and Carbonell (1991), Schmied et al (2000) Exponent for Campbell's equation BCAM 0.14 31.5 Lesikar et al (1997), Schmied et al (2000) Conductivity (mm day -1 ) K 264 13400 Ramos and Carbonell (1991), Schmied et al (2000) Dispersivity (mm) D 1 300 Ramos and Carbonell (1991) Crop data Maximum ratio of actual to potential RT 1 1.55 Acutis et al (2000), Schmied et al (2000) Relative root depth Denitrification rate (day -1 ) Kdenitr 2 9 10 -5 0.12 Johnson et al (1999), Schmied et al (2000) Residue rate (day -1 ) Kres 1.5 9 10 -3 0.01 Acutis et al (2000), Borah and Kalita (1999) Manure rate (day -1 ) Kman 8 9 10 -3 0.04 Sogbedji et al (2006), Acutis et al (2000) Humus rate (day -1 ) Khum 1.1 9 10 -5 7.5 9 10 -5 Acutis et al (2000), Schmied et al (2000) Nutr Cycl Agroecosyst (2010) Drained water at deeper soil depth is less, but the change of drainage was also smaller at deeper soil depth. Therefore they became more sensitive at deeper soil depth.…”

“…They need to be calibrated and validated for the conditions under which they will be applied (Ramos and Carbonell 1991). Calibration and validation of a model is typically accomplished by adjusting input parameter values so that model output values are as close as possible to measured values (Johnson et al 1999). Most of these models, however, require quite a few parameter values that cannot be easily obtained from simple field measurements.…”

“…In some studies, it was used to estimate the change of both water content and nitrate concentration at different soil depth, soil texture, and weather conditions (Ramos and Carbonell 1991;Johnson et al 1999;Schmied et al 2000;Roy et al 2000;Mahmood 2005). In other studies, nitrate leaching was simulated with the model at different fertilizer levels and crops, and then the simulation results were compared to the measured field data (Jemison et al 1994;Acutis et al 2000;Ng et al 2000;Singh and Sondhi 2001;Mahmood et al 2002).…”