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A Brief History of Growing Plants in Space.

Agricultural and biological engineering extends beyond terrestrial farming and plant research. Since the advent of the space age, there has been a desire to provide capabilities for plant growth in the unique environment of space, both to use reduced gravity as a new variable to elucidate plant physiological processes and to develop the foundation of plant-based regenerative life support systems mimicking the Earth's biosphere. In space, plants are subject to elevated levels of ionizing radiation and reduced gravity, both of which may affect plant response. Reduced gravity also affects the behavior of the fluids and gases necessary for plant growth and development. Over the years, hardware systems engineered to grow plants in micro-gravity have evolved to provide improved control of the root and shoot environment to enable long-duration testing, to support good plant growth, and to minimize confounding factors that can mask responses caused by the space environment.

The first successful in-orbit plant experiments were flown on Biosatellite II, a free-flying platform that was placed in orbit for three days in 1967 and returned to Earth by parachute. Since then, most plant growth systems have been engineered to grow plants in manned vehicles and are generally a single or double "middeck locker equivalent," a mid-deck locker equivalent being about 50 x 43 x 25 cm (20 x 17 x 10 in.). The precursor to modern space plant growth systems was the NASA Plant Growth Unit, which first flew on the STS-3 space shuttle mission in 1982.

Examples of plant growth units that have been used aboard the space shuttle or the International Space Station since that time include the Astroculture system, the Advanced Astroculture system, the Biomass Production System, the Plant Generic Bioprocessing Apparatus, the Advanced Biological Research System, and the European Modular Cultivation System. These systems were developed to conduct research primarily with seedlings or small species such as dwarf Brassica and Arabidopsis. A "quad middeck locker" sized plant research system, called the Plant Habitat, is currently in development for a 2016 flight and will be the largest in-orbit plant growth system to date. The Plant Habitat is designed to accommodate small to medium-sized plants or dwarf versions of larger plants and is being developed as a permanent in-orbit research facility.

Over time, from simple to complex

The evolution of plant growth systems from the inception of spaceflight to the space station era has been from simple, short-duration systems to more complex units with advanced environmental controls capable of supporting long-duration testing. These systems are the precursors a large-scale plant growing systems that may eventually support the long-term exploration of space. Diverging from these highly controlled research systems are the "space gardens" that began with the Svet plant growth unit on the Mir space station. followed later by the Lada unit on the International Space Station (ISS). Another space garden is the deployable vegetable production system (Veggie) that will launch to the ISS in 2014 with the goal of supplementing the ISS crew's diet with fresh vegetables. These space garden systems represent the transition from ground testing of plant-based life support to actual in-orbit demonstrations of plants that provide food as well as atmospheric and water revitalization.

The success of space-based plant growth systems relies. heavily on collaboration between plant scientists and engineers to develop technologies that overcome the constraints imposed by the space environment, including reduced gravity and restrictive limitations on power, mass, volume, and crew time. The capabilities provided by the most advanced plant growth chambers include control of light level, quality, and timing; control of root zone moisture and nutrients; and control of shoot zone temperature, humidity, and atmospheric composition (primarily carbon dioxide level).

Light level

Lighting systems for space-based plant growth initially used fluorescent lamps, which required compromises due to safety issues such as high voltages, glass envelopes, and the presence of mercury, a hazardous. contaminant in a space vehicle. Fluorescent technology has since been replaced by LED-based lighting. LED systems eliminate the hazards of gas discharge lamps and provide more functionality and higher efficiency. The development of LEDs for space-based photosynthetic lighting has provided much of the technological base for transitioning to LED lighting for horticultural applications, providing yet another example of how space technologies can be spun-off for terrestrial applications.

Water, always a necessity

The need to deliver water to .plants in a weightless environment while providing sufficient aeration of the root zone is a particular challenge. Early systems using sponges or gels were not adequate for long-term plant growth. To counter the lack of gravity, root modules have been designed to use capillary force. The plants are rooted in a particulate medium into which water is transferred using porous tubes that provide a capillary interface between the fluid reservoir and the root zone. These systems maintain precise control of root zone moisture while providing aeration and containment of water. Thin-film hydroponic and aeroponic systems could also function in reduced gravity, but they have not been used to date.

The APEX model evaluates various land management strategies by considering sustainability, erosion (wind, sheet, and channel), economics, water supply and quality, soil quality, plant competition, weather, and pests. It has components for routing water, sediment, nutrients, and pesticides across complex landscapes and channel systems to the watershed outlet, as well as groundwater and reservoir components. The integration of APEX into the NTT enhanced the NTT's capabilities for estimating phosphorus, nitrogen, and sediment losses, along with changes in yield under different management scenarios.

The NTT predicts changes in edge-of-field nutrient losses. It primarily tracks how nutrients move in and off the field, rather than generating tradable credits that can be sold or listed for sale in environmental markets. The NTT edge-of-field results need to be bundled with personal information and further adjusted by location-specific factors, such as uncertainty factors and trading ratios, to define tradable credits. Thus, the name of the NTT was further changed from Nutrient Trading Tool to Nutrient Tracking Tool to reflect its real function and capabilities. This version of the NTT is hosted on the TIAER server (

Components of the NTT

The NTT consists of the following components and processes:

* A user-interface including a GIS that allows the user to delineate an area of interest (AOI) and select and/or enter information related to that location.

* A set of databases that contain information including soils, climate, crops, management, and conservation practices needed to run the simulation model.

* A mechanism that processes the user-supplied/selected information along with site-specific information from different databases to generate input files to a linked simulation model such as APEX or NLEAR

* A model, such as APEX or NLEAR that simulates the baseline and alternative scenarios with the site-specific resource and crop management information using the generated input data files.

* Processing of the model outputs to generate and present reports to the user.

All of these components and processes are important successful implementation of the NTT. However, the development team at the USDA-NRCS West National Technology

Support Center (WNTSC) has primarily concentrated on the following components and processes:

* A user interface that is intuitive and easy to use for selecting and entering information.

* Design and implementation of databases with mechanisms to efficiently store, access, and process soil, climate, and crop data.

* Transformation of the user input and database information into a format that can be used by the simulation model.

* Making simulation calls to the model and running it for the baseline and alternative scenarios.

* Analysis of model outputs for producing and presenting reports that can be easily understood by the user.

When combined with other site-specific information, the NTT reports provide a foundation for generating the water quality credits that can be traded in environmental markets. It is important that the model linked to the NIT interface, such as NLEAP or APEX, is well parameterized and calibrated for the region. As the developer of the NTT interface and associated databases, we have relied on the authors of the models and the research community engaged in testing and validating these models for these services. We recognize the magnitude of this task for a tool like the NTT, with its national scope. Thus, we have proposed a "professional validation" process in which the NTT outputs are checked, verified, and blessed by regional experts for their validity and appropriateness for generating water quality credits for regional environmental markets.

Current configuration of the NTT

To date, all versions of the NTT have been implemented as web applications. In these implementations, all components of the NTT, including the user interface, the simulation model (NLEAP or APEX), and the databases and programming code, are hosted on a single server. The data on soils, climate, and crop management are downloaded from their original locations and duplicated on the NTT server, after preprocessing if necessary.

In the current NTT configuration, hosted on the TIAER website, the user interacts with the NTT through a web browser on a PC. The NTT application programming interface (API) within the web browser connects to the NTT web server, which hosts the NTT components, including the APEX model, the databases, and the programming code. Based on user input, the NTT API interacts with the NTT web server to access different databases (soils, crops, and climate) and generate the APEX input files. The NTT API then runs the APEX model, linking the input files with the APEX parameter files that are also stored on the web server. The APEX simulations produce a set of output files, which are then processed to produce NTT reports. These reports are displayed to the user for viewing and printing.

This configuration requires significant time and resources to process information from the national databases, which are duplicated on the NTT hosting server. In addition, the national databases change at their original locations, requiring regular updates of the in-house NTT data. This data transition process can lead to significant potential for error if not handled with a high level of quality control and quality assurance. It can also result in discrepancies between the data at the national sites and the data stored on the NTT website, leading to erroneous simulation results.

The next generation of the NTT

The next generation of the NTT is being designed to reduce or eliminate these data processing limitations. This new version of the NTT is being developed in collaboration with the NRCS Information Technology Center and the Soil Science and Resource Assessment Division of the Texas A&M AgriLife Research Center in Temple, Texas, using recent computer technologies. These technologies include cloud computing, web services, distributed corporate databases, and an enhanced integrated geo-spatial navigation system.

All components of the next-generation NTT are being restructured using web services to access corporate databases and models running in a distributed cloud environment. This allows accessing the soils, climate, and crop management data from the original databases, thereby eliminating the need to, duplicate the databases on the NTT hosting server. Several of the data-provisioning techniques, such as data mining and processing for the APEX model being developed for the NTT, will also be applicable to other models planned for the CDSI framework. This new configuration is in alignment with the NRCS streamlining effort and will enable seamless integration of the NTT into the CDSI desktop computing environment.

Similar to the current version, the user of the next-generation NTT will interact with the NTT API through a web browser. However, the new API will be greatly enhanced with improved menus that simplify the data entry and editing process as compared to the previous version. The enhanced API will also have an integrated GIS that will allow the user to delineate the area of interest (A01). Based on the A01, the system will automatically access the national databases for soil, weather, and crop information specific to the delineated site. These databases include the NRCS Web Soils Survey (WSS) for soils, the NRCS High-Resolution Climate Extractor (1-ICE) for weather, and a Land Management Operations Database (LMOD), which is under development by the NRCS. for crops and associated operation schedules.

The GIS interface of the NTT API will provide the centroid of the AOI along with the acreage of different parcels with individual soil map units. The centroid of the AOI is used to access historical weather data, such as daily rainfall and minimum/maximum temperatures, from the HCE database using the web services. The A01 centroid will also be used to identify the crop management zone (CMZ) for the A01 and to extract the most dominant cropping systems and associated operations for each crop. The information on soil properties and crop operations will be presented to the user for editing, if desired, a selected set of parameters. This will allow the user to customize the data for a specific location while maintaining the overall integrity of the corporate databases.

The historical climate data along with the customized crop operation and soil parameters will be transformed into APEX input data files. These files, along with APEX parameter files, will be used to run the APEX model in the cloud using the web services. The resulting output files will be processed to produce the NTT reports, which will be presented to the user for viewing, or printing, similar to earlier NTT implementations.

The distributed environment for storing and accessing the databases and for running the APEX model in the cloud using web services, coupled with improved system integration, is expected to reduce the run-time requirement for the NTT and enable multiple users to access the NTT simultaneously.

More work still needs to be done

Several of the components of the next-generation NTT, such as the improved user interface for selecting and entering data, the web services for accessing the national databases, and the programming code for transforming the user-supplied and database information into APEX input file format, have been developed and are available for testing. However, a considerable amount of work still needs to be done to complete the initial prototype and subsequently the production version of the next-generation NTT. Some of these tasks include:

* Further improvements of the user interface, with editing capabilities that let users customize the data accessed from the national databases specifically for their location.

* A GIS interface that lets users modify the AOI with multiple non-contiguous fields and provide their spatial and non-spatial attributes. These include the AOI centroid, the area of each field and of the mapping units within them, and the soil characteristics of all mapping units.

* Integration of the most recent version of the APEX model that has been parameterized and calibrated for the U.S. geographic regions where the next-generation NTT is planned to be introduced and that has the capability to generate the NTT reports.

* Integration of the different components of the next-generation NTT into a functioning prototype and then testing it for proper functioning.

Thanks to our partners and collaborators

Our team will continue to rely on the developers of the simulation models and other experts for the accuracy and usefulness of the NTT. In the first prototype of the NTT (known as the Nitrogen Trading Tool) using NLEAP, we collaborated with Dr. Jorge Delgado and Dr. Mary Shaffer at the USDA-ARS Natural Resources Research Center in Fort Collins, Colorado. For the current versions of the NTT (the Nutrient Trading Tool and the Nutrient Tracking Tool) using APEX, we collaborated with Dr. Ali Saleh at the Texas Institute for Applied Environmental Research (TIAER) at Tarleton State University in Stephenville, Texas. For the next generation of the NTT, we are collaborating with Dr. M. Lee Norfleet at the Soil Science and Resource Assessment Division of the Texas A&M AgriLife Research Center in Temple, Texas. Thanks to their efforts, as well as the comments we have received from NTT users, the next-generation NTT will provide many new benefits in comparison to its current and past implementations.

ASABE Member Harbans Lal. Environmental Engineer, USDA-NAGS West National Technology Support Center, Portland, Ore., USA.

Comparison of the current NTT and the next-generation NTT.

                      Current NTT               Next-Generation NTT

Hosting server        TIAER (http:              USDA-NRCS
                      //nn.tarleton. edu/

APEX version          CustomizedVersion         Version 0806 or
                      0604                      higher

NTT operation and     Changes and maintenance   Web services can be
maintenance           of NTT components,        modified
                      including the simulation  independently to
                      model, databases, or      accommodate changes
                      program code, can result  in the simulation
                      in disruptions of         model and data
                      service and require       structures with
                      re-building of the        minimum effect 011
                      servers.                  other components.

Soil, weather, and    Downloaded from           Accessed directly
crop databases        corporate data sources,   from the corporate
                      pre-processed and stored  data servers using
                      on the NTT server along   web services and
                      with the APEX model.      processed on the

Area of interest      Cut-and-paste from the    A GIS interface for
(AOI) selection       Web Soil Survey (WSS)     the AOI is an
                      interface.                integral part of the
                                                next-generation NTT

System configuration  The APEX model,           A distributed data
                      associated input files,   structure leads to
                      and other data files are  improved processing
                      stored on a single        time and allows
                      server, leading to        simultaneous access
                      slower processing         processing for
                      speed.                    multiple users.

System expansion      To meet increased system  Cloud-based service
                      demand, additional        implementation offers
                      servers with duplicate    the ability to expand
                      databases would be        the capacity as
                      required.                 demand increases.

NTT input data        User selection of state,  Accessing and
consistency           county, climate, crop,    processing of crop,
                      soils, etc.,              soil, and weather
                      individually from         information based on
                      different menu systems    the user-defined AOI
                      increases the             eliminates the
                      possibility of            possibility of
                      inconsistency among       mismatch of these
                      these data.               data elements.

Crop management and   Generated independently   Accessed from the CMZ
operation data        of the CMZ (crop          within the
                      management zone)          user-defined AOI and
                      operational file.         converted to the APEX
                                                input files.
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Author:Morrow, Robert
Publication:Resource: Engineering & Technology for a Sustainable World
Date:May 1, 2014
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