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United States Department of Agriculture

Agricultural Research Service

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Ahuja, Lajpat R
Supervisory Soil Scientist
(970) 492-7315
Fort Collins CO 80526


Provide leadership in systems research for developing sustainable and adaptive integrated agricultural systems.


Enhance economic and environmental sustainability of agricultural production systems by:

  • Synthesizing and quantifying biological, chemical and physical processes at the whole-system level.
  • Conducting cooperative field research to fill knowledge gaps, especially for plant response to stress conditions & global change, and scaling up from plots to fields and larger areas.
  • Developing computer models of agricultural systems to support field research and analysis of major issues, emphasizing water quality and water conservation, production, precision farming, and climate change.
  • Providing farm-level computerized decision support technology and information system packages to farmers, ranchers, agricultural consultants and action agencies for evaluating sustainability of alternative farming/ranching options.
  • Creating an Object Modeling System with a library of science and related tools to assemble customized modular models.
  • Collaborating nationally and internationally to evaluate and improve knowledge and products.



The Agricultural Systems Research (ASR) Unit was originally called the Great Plains Systems Research (GPSR) Unit. The name change occurred in 2007. The GPSR Unit was created in 1985 by merging two units, Soil-Plant-Water Research Unit and Forage & Range Research Unit, with Dr. Al Grable as the Research Leader (RL). The driving force was the realization that the solution of real-world problems in the Great Plains and elsewhere requires whole-system approaches. The new GPSR Unit was charged with the mission to develop such approaches, and then transfer the technologies to users. Following Dr. Grable’s retirement in 1988, Dr. Charles Townsend became Acting RL, and Dr. Jim Welch became RL in 1990. In 1991, the GPSR and other natural resources research units in Colorado and Wyoming were reorganized into a Natural Resources Research Center (NRRC) with Dr. Jim Welch as the Director of NRRC and RL of GPSR. The GPSR Unit was reorganized by combining some members of the former GPSR and Hydro-Ecosystems Research Units. Dr. Laj Ahuja became RL in 1991.

For the first few years after the establishment of the Unit in 1985, its research primarily dealt with rangelands. Charles Townsend was working on breeding Cicer Milkvetch as a potential legume for rangelands. Marv Shoop was studying grazing management in short grass prairie at the CPER (Central Plains Experimental Range) in Northern Colorado. Bill McGinnis did range work and revegetation of minelands. Jon Hanson worked on extending the SPUR (Simulating Production and Utilization of Rangelands) model by adding the cow-calf model, application of the model to study potential global change effects on the livestock production, and on remote sensing of rangelands. Jack Morgan conducted physiological studies on winter wheat under drought, and modeling of these effects. He also started the studies on the effects of increased carbon dioxide and temperature on photosynthesis and transpiration responses of some range species. Vern Cole worked on soil phosphorous as well as participated with Colorado State University on dryland cropping system project and in the enhancement of the Century model for evaluating changes in soil organic matter in agricultural systems. Rudy Bowman was working on soil organic matter in cropping systems. Marv Shaffer was hired to initiate crop modeling and take a major part in developing the NLEAP model. Greg McMaster developed the SHOOTGRO model for wheat. In honor of Al Grable’s retirement, a symposium was held on “Sustainable Agriculture for the Great Plains” in 1989. Subsequent to the conference, a report entitled Great Plains Agrosystem Project outlined the basic components and key institutions needed in a regional project that would tie together the research across the Plains. The Project incorporated the conceptual basis and recognized the need for a systems approach and networking of scientists for agricultural research and technology development.

After its reorganization in 1991, the GPSR Unit inherited the development of the ARS Root Zone Water Quality Model from the Hydro-Ecosystem Unit. Four of the seven CAT-1 scientists in the Unit, Donn DeCoursey, Laj Ahuja, Marv Shaffer, and Jon Hanson, were already members of the RZWQM team. Work on other projects also continued. Dave Hartley and Carlos Alonso were working on SWAM, a small watershed model, Vern Cole on the dryland cropping systems and the Century model, Marv Shaffer on NLEAP, and Jon Hanson on SPUR2. In 1992, Donn, Carlos, and Dave left the Unit for other positions, and in 1993 Vern Cole retired. Over time, these positions were filled by current scientists of the Unit, Greg McMaster, Jim Ascough, Tim Green, and Liwang Ma. In 1993, the Unit started work on the development of GPFARM, a decision support system for farmers and ranchers in the Great Plains. All CAT-1 scientists participated in the development of RZWQM and GPFARM as team members. The tested and improved RZWQM version 2.0 was released in 2000 and GPFARM version 2.0 completed in 2002, and we are still supporting the users of these models. Over this time period, the Unit also refined and enhanced its Vision and Mission, in concert with our Customer Focus Group, stakeholders, and collaborators. The current CRIS projects described in the next section were the natural successors to the above major model development projects to meet the needs of our customers. Jon Hanson moved to Mandan, ND in 1999; Mark Weltz replaced him in 2000, then became a National Program Leader in 2002; and Marv Shaffer retired in 2003. We took this opportunity to create a new novel position of a Technology Transfer Coordinator for the Unit that was filled by Gale Dunn. Gale functioned as the Project Manager for the GPFARM and its successor the iFARM project. He now leads the development of simpler decision support tools for managing limited water range and crop systems. The ASR Unit usually has 3 to 4 ARS or cooperative postdoctoral or visiting scientists working on application of models. We brought Olaf David, a computer scientist, from Jena, Germany to work with us as a CSU Collaborator to help with building the Object Modeling System (OMS).

The Unit’s accomplishments thus far are summarized below:

A. Contributions to New Knowledge:

   Quantification, modeling, and evaluation of the effects of agricultural management practices on soil physical properties and processes that affect water, water quality, and plant growth—tillage and reconsolidation effects on bulk density, porosity, and soil water properties; wheel track effects; preferential flow of water and chemicals into the soil through macropores created in no-tillage soils; residue cover effects on infiltration, evaporation, soil temperature, and crop emergence, development and yield; how long-term no-tillage cropping and residue systems change surface organic matter, aggregation and soil water properties, and how surface aggregates hold back an agricultural chemical near the surface, reduce leaching through the soil, but increase transport in macropores; and how grazing intensity and micro-topography affect rangeland rain infiltration and production in the long run.


   Quantification, modeling, and field evaluation of the effects of soil properties on two-dimensional root growth; effects of two-dimensional root growth on water and chemical movement; two-dimensional infiltration of water from furrows-every furrow versus alternate furrows; effects of banding nitrogen in crop rows on its movement and availability to plants with furrow irrigation; leaching of chemicals in crop rows versus interrows.


       A cooperative research agreement with Colorado State University: contributed to the development of new dryland cropping systems for the Great Plains under no-tillage that improves the capture and retention of incident precipitation; established that 3 or 4 year rotations (wheat-corn-fallow, wheat-corn-millet-fallow) give higher annualized yields than the common 2 year rotation (wheat-fallow); and established that increased crop residues at the surface lead to increased soil organic matter, and improved aggregation and physical properties. The area under new rotations in the Central Great Plans has increased more than 20 fold in the last 20 years.


   Sequences were developed for simulating crop phenology under optimal and water-stressed conditions for winter wheat, barley, and corn; phytomers, phyllochrons, phenology, and temperate cereal development, and field evaluation of the simulations.


   The Unit developed and evaluated new simpler techniques to estimate model parameters--saturated hydraulic conductivity (Ksat) and water retention curve of soils and their spatial variability, from soil bulk density and 1/3-bar water content; new intrinsic scaling relationships, based on the pore-size distribution index or saturated hydraulic conductivity, for soil hydraulic properties across different soil textural classes, and extended to relate infiltration, soil water storage, evaporation, and transpiration in different soils. This scaling is a major breakthrough for site-specific management and estimating parameters and results for large scales. The scaling relations have been recently used to derive effective average soil hydrologic parameters for a spatially variable field for modeling as one unit.


   Numerous processes in our computer models were evaluated and improved with national and international collaborations.


   Through our research, we identified common patterns of crop yield, soil water content, and certain topographic attributes, where all of these variables can be characterized using fractal geometry; developed relationships between yield and topographic attributes.



B. Computer Models Delivered to Enhance and Extend Field Research, Problem Evaluation, Policy Assessments and Management Decision Aids:

   NLEAP model for assessment of nitrate leaching, 1991.

   SPUR2 model for rangeland-livestock systems, 1992.

   SHOOTGRO model for winter wheat, 1993.

   Contributed to Daily Version of the Century Model—Day Century, 1993.

   2-DROOT--A two-dimensional model of root growth, 1995.

   RZWQM for simulating management effects on water quality and crop production, Version 1.0 1992; Version 4.0 2000; Version 5.0 2004.

   GPFARM, a farm/ranch decision support system for strategic planning, Version 1.0 1998; Version 2.0 2002; Version 2.5 2003; Version 2.6 2004.

   Enhanced GPFARM-Range model for helping with grazing and drought management. 2008.

   RZWQM2, an enhancement of RZWQM in several areas and linkage with crop models from DSSAT group for improved simulation of crop and management systems. 2008.

   Completing the development of RZWQM2-GIS, a spatial modeling prototype for spatially variable fields and farms to assist with development of site-specific management (precision agriculture) and minimizing water quality impacts.

   A prototype OMS-based modular watershed model AgES for assessing effects of soil-water conservation practices was developed. 2010.


C. Technology Transfers and Outreach Accomplished:

   Conducted workshops and provided training on using the ARS Root Zone Water Quality Model (RZWQM) to 20+ groups composed of scientists, students, NRCS professionals and private industry in the U.S., Portugal, China, India, Switzerland and Canada.  In addition, we answer more than 100 questions from RZWQM users each year.  The Unit took extra steps to transfer ARS research results to customers. When the RZWQM model was developed in 1992, the Unit actively worked with scientists of the MSEA project to synthesize the multimillion-dollar-MSEA data. The RZWQM application results were published as a package of 8 papers in Agronomy J. (91:169-227) and in a Special Issue of Geoderma International journal. The RZWQM book and software were commercialized through Water Resources Publications who sold 500+ copies worldwide. Using a systems approach, the Unit also helped several ARS scientists to design the right type of experiments to fill knowledge gaps and collect the right type of data. Mentored over 80+ visiting scientists, students, post-doctorals, and young scientists in the development and application of models.


   The U.S. Geological Survey has selected RZWQM for process-based analysis of the water quality data from agricultural areas of their National Water Quality Assessment (NAWQA) Project 2004-present.


   The U.S. EPA has selected this model for future use in assessing environmental impacts of new pesticide candidates for registration by the industry in 2004.

Because of the above technology transfers of RZWQM-RZWQM2, the RZWQM team received an ARS award for Superior Efforts in Technology Transfer in 2006 and Outstanding Technology Transfer Award of the Federal Laboratories Consortium in 2007.

   GPFARM was officially released to central Great Plains farmers and ranchers in 2002. The GPSR/GPFARM team has made numerous presentations on GPFARM to various farm and ranch organizations over the last three years.  In particular, the Colorado Conservation Tillage Association asked the team to use GPFARM to answer specific questions and provide the results at their annual meeting.  The team made several presentations to the group over the last three years with attendance at sessions going from 5 producers to over 40.


   Successes with the Colorado Conservation Tillage Association lead to an agreement (MOU) with the Colorado Association of Wheat Growers (CAWG) to provide GPFARM in its membership packet. Approximately 600 copies of GPFARM have been distributed by CAWG. The team facilitated this activity and conducted several training sessions for the membership. As a result of the team's success with CAWG, the Kansas Association of Wheat Growers asked if they could develop a similar agreement with ARS. The agreement will result in distribution of over 2000 copies of GPFARM. The team is planning to conduct several training sessions to support this distribution.


In recognition of the GPFARM technology transfer achievements GPSR was awarded the “Outstanding Laboratory Award” by the Federal Laboratory Consortium Mid-Continent Region in 2005. The award was accepted by Gale Dunn, our Technology Transfer Coordinator, and Laj Ahuja, Research Leader.


   In 2002, the GPSR team gave demonstrations of RZWQM and GPFARM to 60 scientists in China.


   In 2004, Dr. Gale Dunn, the GPSR Technology Transfer Coordinator, was invited to Tunisia where he made several presentations on the use of GPFARM.


   Tim Green – Integrative Land Use Modeling cooperative agreement with ETHZ, 2005. The Institute of Terrestrial Ecology at the Swiss Federal Institute of Technology (ETH) in Zürich, Switzerland has invited and funded Dr. Green to be a visiting scientist for six months in 2005.  The purpose of this visit was to further our collaboration on agricultural hydrology, scaling, and landscape modeling.  Research ideas from our GPSR CRIS project plan (Scaling and Modeling Space-Time Variabilities of Landscape Processes to Enhance Management) were the basis for ETH’s interest and financial support (approx. $24,000).


   August-December 2004, Dr. Liwang Ma conducted collaborative research with CSIRO-APSRU in Toowoomba, Australia, under an OECD fellowship. The tile subsurface drainage component of RZWQM was incorporated into the APSIM model and tested using data from Nashua, Iowa. This new feature was released in APSIM version 4.0. He also incorporated transpiration efficiency approach into RZWQM to improve water stress on photosynthesis. The APSIM model was further tested for water and fertilizer management, and crop rotation effects on water use efficiency under Colorado conditions.


   Dr. Greg McMaster visited the CSIRO_APSRU group.  Jointly they developed a new plant component modeling approach.


   The GPSR/ASR Unit’s program has been the subject of the following articles written in popular magazines/press: Nitrates can leach, but they can’t hide—High levels of nitrate-nitrogen have plagued ground water in Weld County for some years. Now computer maps peg how it  ties to farming. Colorado Rancher and Farmer, November 1992, p. 6-8; Forecasting Livestock Production - Climate change in the Great Plains. Agricultural Research, p. 12-13, Feb. 1993; Computing Pollution. Agricultural Research, April, 1996; RZWQM - Modeling effects of farm decisions. Agricultural Research, p. 18-19, July 1997; Computer Model will help farmers project yields and water quality. ARS News Service, July 18, 1997; New software could help on farm and ranch decisions. ARS News Service, Jan. 28, 1998; Farmers get high-tech help: Software helps out plans for planting. Fort Collins Coloradoan (Daily Newspaper), Feb. 7, 1998; Fractals - a bridge to future for soil science.  Agricultural Research, p. 10-13, April, 1998; New computer model aims to keep farms and ranches productive. ARS Press Release, September 1998; Farm analysis and comparison tool - designed for world-wide web. AGRIFACTS, USDA-ARS, Akron, CO, Oct., 1998; GPFARM software foresees the future.  Agricultural Research, p. 22, Nov. 1998; User-Friendly farm Planning—Software helps you find the best option for your operation. Western Farmer-Stockman, July 2002, p. M6/10; More proof of the effectiveness of no-till farming. ARS News Service. May 2003; Moving away from wheat-fallow in the Great Plains, models are playing a role. Agricultural Research, p. 14-17, June 2005; Conservation: Are we getting the money’s worth? GPSR research and development of Object Modeling System will be key to nationwide computer modeling effort that forms CEAP’s backbone. Agricultural Research, p. 4-5, Dec. 2005; Non-risky business:  new technology improves ranch management.  ARS News.  January 2006. Evaluating nitrogen and water management in a double-cropping system using RZWQM. Science in Action. ASA-CSSA-SSSA. 2006. Get into the Zone…the Root Zone. Agricultural Research. P. 8-9, March 2007; Climate change and groundwater recharge.  ARS News, August 2007; iFARM:  Two high-tech tools for farm management.  ARS News, October 2007; Squeezing more corn and wheat out of each scarce drop of water.  Agricultural Research, p. 16-17, 2009; Squeezing more crop out of each drop of water. ARS News, October 2009; High Plains Journal, November 2009; Wisconsin Agriculture Connection, 2010; Good to the last drop. Vegetable Grower, p. 20, November 2009.     

Current State:

Currently, the ASR Unit is very well positioned for applying agricultural system models to solve problems of the 21st Century. It is a leading ARS Unit working on the synthesis and modeling of the whole agricultural system. During the next 5 years, the Unit aims to integrate system modeling  with field research to: enhance understanding and quantification of the complex field data, extend field research to multiple years of climate and other soils, and utilize the results to create simple decision support tools,  for use by farmers, ranchers, and action agencies in planning and management. The focus will be on water limited agricultural systems, both crops and range. This will be accomplished through collaboration with several ARS and university field experimental research units in the Great Plains and US west:  Central Great Plains Research Station at Akron, CO; Water Management Research Unit, Fort Collins, CO; Agricultural Systems Research Unit, Sidney, MT; Water Management Research Unit at Bushland, TX; Colorado State University and the University of Nebraska; Rangeland Resources Research Unit at Fort Collins, CO/Cheyenne, WY; and range research units at Miles City, MT and Woodward, OK.

The Unit’s RZWQM model has been or is also being used extensively in the U.S. Midwest (National Soil Tilth Laboratory< Ames, IA) and other countries—Canada, Portugal, Germany, China, India, Pakistan, Thailand, Uzbekistan, Italy, and more (see chart). The Unit has also developed collaborations with other leading systems modeling groups in ARS and internationally, including the Crop Systems and Global Climate Change Lab in Beltsville; the DSSAT crop modeling groups at the universities of Georgia and Florida; the N modeling groups at Taastrup, Denmark; APSIM modeling group at Toowoomba, Australia; the range-livestock modeling group at Canberra, Australia; and the Century Modeling group at Colorado State University. We are now developing collaborations with INRA, Toulouse, France.  The Unit has a dedicated group of farmer/rancher collaborators in the Great Plains who participated in the development and evaluation of GPFARM and who are helping us define a tactical planning and management decision tool, iFARM. The Unit is leading the ARS-NRCS-USGS efforts in developing an Object Modeling System for generating and updating customized system models of the future more easily and quickly.

Another cutting edge project the ASR Unit is working on is the “Object modeling and scaling of landscape processes and conservation effects in agricultural systems.”  The aim of this project is to produce next generation field to watershed scale models for NRCS’ Conservation Effects Assessment Project (CEAP). In collaborative efforts with Colorado State University, the Unit scientists have developed and released OMS3, a new framework for developing component-based modular models.  The OMS3 is a flexible model development system which allows the use of best available scale and problem specific science components, that are easier to understand, maintain, and update as new knowledge becomes available.  The OMS3 also supports the NRCS infrastructure for delivery of information technology tools for conservation planning and assessment.  We have developed an OMS-based prototype watershed model.  An initial version of this Java-based prototype watershed model (containing verified modular components for water balance, infiltration, groundwater recharge, runoff and stream flow dynamics, erosion, nutrient cycling, and plant growth) was developed and applied for simulation of runoff and stream flow between land units and stream reaches.  The model is now ready for evaluation of nitrogen and sediment transport, and has the potential (due to fully-distributed simulation capability) to better quantify conservation impacts on water quality at field to watershed scales.

This program of the ARS needs to be strengthened to fully realize the great potentials of the agricultural system models in research and technology transfer.



Last Modified: 7/28/2010
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