Technical report: Modeling nitrate leaching risk from specialty crop fields during on-farm managed floodwater recharge in the Kings Groundwater Basin and the potential for its management

This project has focused on better understanding the potential impact of On-Farm Flood Capture and Recharge (OFFCR) on groundwater quality pertaining to salts and nitrate and on assessing potential management opportunities. To achieve these goals, we used a combination of field and modeling studies. For the field study, soil cores were taken to a depth of 30 feet in replicate across fields with three different specialty crops identified as important to the San Joaquin Valley (tomatoes, almonds, vineyards) and with potential suitability for OFFCR. A prime goal of the field study was to provide data for parameterizing two models developed to assess nitrate, salt and water transport through the vadose zone, prior to percolating into the groundwater aquifer.However, the field study also resulted in key findings that show its value as a stand-alone study: 1) Nitrate concentrations are highest in the upper vadose zone and affected by texture. Those effects are not evident in the deeper vadose zone. 2) Vadose zone nitrate concentrations are affected by the crop grown. These results suggest an opportunity for lower legacy mass transport for grapes and higher legacy mass transport for both tomatoes and almonds.3) Variability in individual farmers’ past and present fertilizer and water management practices contributes to different legacy salt and nitrate loads in the vadose zone.Data from the field study and other related and concurrent OFFCR field efforts were used during model development. The overall modeling approach was designed to model nitrate and salt transport for lands under OFFCR operation for different crop types, vadose zone characteristics and groundwater characteristics. The defined goals of this design and modeling approach were to: 1) model nitrate and salt movement through the vadose zone and into groundwater; 2) test the model against scenarios that consider different recharge rates, cultural practices, soil types, and depths to groundwater, assessing the timing and magnitude of loading through the vadose zone and the effects on underlying groundwater; and 3) recommend management practices to mitigate potential groundwater impacts. To achieve these goals, two models were integrated to simulate nitrate and salt transport through the vadose zone to groundwater under different scenarios: a 1D Hydrus model and an analytical groundwater model (AGM).

Bibliographic Details

Main Authors:	Bachand, P.A.M., Bachand, S.M., Waterhouse, H., Rath, J., Ung, M., Roy, S., Kretsinger, V., Dalgish, B., Horwath, W., Dahlke, H., Creamer, C., Choperena, J., Mountjoy, D.
Format:	monograph biblioteca
Language:	English
Published:	Sustainable Conservation 2017-07-31
Subjects:	Agriculture, Chemistry, Earth Sciences, Engineering, Environment, Management, Planning, Pollution, on-farm recharge, floodmar, groundwater, management, agriculture, water quality, vadose zone, nitrate, BMPs, Kings Groundwater Basin,
Online Access:	http://hdl.handle.net/1834/41189
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