Predicting Unsaturated Zone Nitrogen Mass Balances in Agricultural Settings of the United States

Abstract

Unsaturated zone N fate and transport were evaluated at four sites to identify the predominant pathways of N cycling: an almond [Prunus dulcis (Mill.) D.A. Webb] orchard and cornfield (Zea mays L.) in the lower Merced River study basin, California; and corn-soybean [Glycine max (L.) Merr.] rotations in study basins at Maple Creek, Nebraska, and at Morgan Creek, Maryland. We used inverse modeling with a new version of the Root Zone Water Quality Model (RZWQM2) to estimate soil hydraulic and nitrogen transformation parameters throughout the unsaturated zone; previous versions were limited to 3-m depth and relied on manual calibration. The overall goal of the modeling was to derive unsaturated zone N mass balances for the four sites. RZWQM2 showed promise for deeper simulation profiles. Relative root mean square error (RRMSE) values for predicted and observed nitrate concentrations in lysimeters were 0.40 and 0.52 for California (6.5 m depth) and Nebraska (10 m), respectively, and index of agreement (d) values were 0.60 and 0.71 (d varies between 0 and 1, with higher values indicating better agreement). For the shallow simulation profile (1 m) in Maryland, RRMSE and d for nitrate were 0.22 and 0.86, respectively. Except for Nebraska, predictions of average nitrate concentration at the bottom of the simulation profile agreed reasonably well with measured concentrations in monitoring wells. The largest additions of N were predicted to come from inorganic fertilizer (153-195 kg N ha(-1) yr(-1) in California) and N fixation (99 and 131 kg N ha(-1) yr(-1) in Maryland and Nebraska, respectively). Predicted N losses occurred primarily through plant uptake (144-237 kg N ha(-1) yr(-1)) and deep seepage out of the profile (56-102 kg N ha(-1) yr(-1)). Large reservoirs of organic N (up to 17,500 kg N ha(-1) m(-1) at Nebraska) were predicted to reside in the unsaturated zone, which has implications for potential future transfer of nitrate to groundwater.

Leaching losses from Kenyan maize cropland receiving different rates of nitrogen fertilizer

“…The model of our study area could be improved by accounting for dual porosity flow using for example the dual porosity flow model MACRO ? SOILN (e.g., Larsson and Jarvis 1999), or RZWQM2 (e.g., Nolan et al 2010), but would require additional field measurements to calibrate the Total precipitation is shown for each period additional transport process. Another model design limitation was caused by the disparity between model time step and the pattern of rainfall in the study area.…”

“…Noted weaknesses include typical omission of certain transport phenomena such as multi-phase flow, hysteresis, and difficulty predicting nutrient transport in low N fertilizer application settings. Advances in predictive nutrient flux modeling account for N transformations and uptake, organic matter mineralization, and crop yield (Endo et al 2009;Nolan et al 2010), though model input requirements are greater than for fluid flow models.…”

Sustainability and environmental assessment of fertigation in an intensive olive grove under Mediterranean conditions

“…Maximum LAI is also assumed to be in coordination with maximum daily N uptake. The Quicktree module was first used by Nolan et al (2010) to study N leaching in an almond orchard in California, USA, but it has not been applied for olive trees and under the Mediterranean environment. Changes were made to this module in order to adapt it to this situation.…”

Nitrate mass balance in agricultural areas of intensive fertilizer application: the North Maresme aquifer system case study (Spain)

“…Finally authors recommend integrating the proposed methodology with other N mass balance approaches, and furthermore, with N fate and transport modeling (Nolan et al, 2010) in order to improve management of fertilizers practices in agricultural areas.…”