U.S. flagAn official website of the United States government
                    Here's how you know **Official websites use .gov**
                            
                            A **.gov** website belongs to an official government organization in the United States.
 **Secure .gov websites use HTTPS**
                            
                            A **lock** (                            
                              A locked padlock                                                      
                            
                            ) or **https://** means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.


Menu Agricultural Research Service
						
                    U.S. DEPARTMENT OF AGRICULTURE
 close



Research
                Research Home
                            National Programs
                            Research Projects
                            Scientific Manuscripts
                            International Engagement
                            Scientific Software/Models
                            Databases and Datasets
                            Office of Scientific Quality Review
            Media
                News & Features
                            Multimedia
                            Briefing Room
                            Down on the Farm
                            Press Room
                            Science in Your Shopping Cart
                            Scientific Discoveries
                            Tellus
                            Under the Microscope
            About ARS
                About ARS Home
                            Staff Directory
                            Labs and Research Centers (Map)
                            Headquarter Offices
                            Organizational Chart
                            Employee Services (REE Employees Only)
                            Office of Outreach, Diversity, and Equal Opportunity
            Work With Us
                Work With Us Home
                            ARS Vacancies at USAJOBS
                            Careers at ARS Information
                            Scientific Collaborations
                            Extramural Agreements
                            1890 Faculty Research Sabbatical ProgramSearch small
                    Search
            
            ARS Home
                                About ARS
                                Contact Us




ARS Home Research Publications at this Location





- ARS National Programs
- Search for a scientific manuscript
- Search for a research project
- ARS Software
- Programs and Projects
- Collaborations
- Subjects of Investigation
- Publications

Title:   Author  item
                                            AGAM, NURIT - Gilat Research Centeritem
                                            Kustas, William

                                                         - *Bill*item
                                            Evett, Steven

                                                         - *Steve*item
                                            Colaizzi, Paulitem
                                            Cosh, Michaelitem
                                            McKee, Lynn
  Submitted to: Advances in Water Resources
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 7/6/2012
                                    Publication  Date: 11/29/2012
                                    Citation: Agam, N., Kustas, W.P., Evett, S.R., Colaizzi, P.D., Cosh, M.H., McKee, L.G. 2012. Soil heat flux variability influenced by row direction in irrigated cotton. Advances in Water Resources. 50:31-40.Interpretive Summary: In temperate humid climates, where 100% vegetation cover is common, soil heat flux (G) is a relatively small component of earth’s surface energy balance.  Since micro-meteorological techniques for estimating surface energy balance and evapotranspiration (ET) were initially developed in temperate regions, G was not considered to be a critical component.  However,  under partial vegetation cover conditions, particularly for row crops in arid environments, G may reach 50% of total net radiation and even for taller canopies, can account for 30-50% of net radiation.  Therefore, inaccurate estimates of G may lead to non-negligible errors in the surface energy balance and ET estimation, adversely affecting irrigation scheduling and water resource assessments in water-limited agricultural areas. In this study the effect of row orientation and sensor position on G magnitude and variability in an irrigated row crop of cotton is reported. In addition, the effect of errors in water content estimation on the heat storage at the uppermost soil layer is assessed. The research was conducted in the Southern High Plains of the USA, as part of the Bushland Evapotranspiration and Agricultural Remote Sensing Experiment of 2008 (BEAREX08).  Measurements were concentrated in two irrigated cotton fields, one with north-south (N-S) and the other with east-west (E-W) row orientations. It was found that using properly calibrated soil moisture sensors reduced errors from 27% to 9%.  In addition, row orientation had an effect on the temporal trace in G and when summed over the daytime period.  Important short-term (15-min average) variability in G at the various locations in the interrow was observed under partial canopy cover conditions for the N-S row orientation, while the daily sum of G () in both row orientations was similar.  In the beginning and the end of the growing season, was larger in the N-S orientation field.  In the E-W orientation field, a minimum of 3 sensor sets (as are often deployed at ET measurement installations) were found to adequately describe the G pattern of the 10-location average, with errors as small as 6% and with a transitory maximum error of 12%.  In the N-S row orientation field, however, no 3 sensor combination was adequate to represent the field average G. This suggests that reliable surface energy balance and ET estimation for row crops requires a more extensive array of soil heat flux measurements, particularly for N-S oriented row crops.
                                Technical Abstract: In applications of micrometeorological techniques for surface energy balance estimation, most often the least attention and effort has been devoted to determining the area-average soil heat flux (G).  Although spatial and temporal variability in G under sparse/clumped vegetation conditions is significant and has been studied, less attention has been devoted to evaluating the variability of G with respect to row crops, particularly with respect to row orientation.  The variation in G for row crops is related to the effect of differential shading of the soil surface, which is dependent on plant architecture, row spacing, and row orientation/direction.  The effect of the latter on G variability, to the authors’ knowledge has not been previously studied.  In this study the effect of row orientation and sensor position on G magnitude and variability in an irrigated row crop of cotton is reported. In addition, the effect of errors in water content estimation on the heat storage at the uppermost soil layer is assessed. The research was conducted in the Southern High Plains of the USA, as part of the Bushland Evapotranspiration and Agricultural Remote Sensing Experiment of 2008 (BEAREX08).  Measurements were concentrated in two irrigated cotton fields, one with north-south (N-S) and the other with east-west (E-W) row orientations.  In each field, 10 sets of sensors in two replicates at 5 locations across the interrow (76 cm row spacing) were used to quantify G positional variability.  In each location, a sensor set consisted of a soil heat flux plate installed at a depth of 80 mm, above which thermocouples were installed at 60, 20 and 0 mm depths.  Average field volumetric soil water content (W) was measured with Hydra Probe sensors (W_hp) and in the NE field conventional time domain reflectrometry was also used to assess soil water content (W_tdr). Correcting W_hp to the local soil improved G computations, and reduced the overestimation from 27% for the uncorrected to 9% when corrected W_hp was used.  Row orientation had an effect on the temporal trace in G and when summed over the daytime period.  Important short-term (15-min average) variability in G at the various locations in the interrow was observed under partial canopy cover conditions for the N-S row orientation, while the daily sum of G () in both row orientations was similar.  In the beginning and the end of the growing season, was larger in the N-S orientation field.  In the E-W orientation field, 3-replicate sensor sets (as are often deployed at flux tower installations) were found to adequately describe the G pattern of the 10-location average, with errors as small as 6% and with a transitory maximum error of 12%.  In the N-S row orientation field, however, no 3-replicate combination was adequate to represent the field average G.


Return to top


Connect with ARS Sign up


ARS Home
                            USDA.gov
                            Plain Writing
                            Policies & Links
                            Civil Rights Statements
                            FOIA
                            Accessibility Statement
                            Privacy Policy
                            Non-Discrimination Statement
                            Quality of Information
                            USA.gov
                            WhiteHouse.gov