CIRCULAR 171 OCTOBER 1969 The RHIZOTRON at AUBURN, ALABAMA -A PLANT ROOT OBSERVATION LABORATORY Agricultural Experiment Station AUBURN E. V. Smith, Director UNIVERSITY ALIuun, Alab ama CONTENTS Page CONSTRUCTION DETAILS 4 EQUIPMENT 6 PHILOSOPHY LEADING OF THE TO THE CONSTRUCTION RHIZOTRON7 FIRST PRINTING 3M, OCTOBER 1969 The RHIZOTRON at AUBURN, ALABAMA- A PLANT ROOT OBSERVATION LABORATORY HOWARD M. TAYLOR2 at Auburn is an underground walkway fitted on either side with windows to observe plant root growth in soil. It is designed to study growth and development of root systems in relation to the aerial parts of different plant species under controlled-rooting environments. The aerial parts of the plants are exposed to field environmental conditions. The rhizotron is located 2.3 miles southwest of Auburn on U.S. Highway 29. The Auburn rhizotron is one of four major root observation laboratories in the world. It is the only one devoted primarily to the study of annual plant root systems. The root observation laboratory at East Malling, England is used to study root systems of perennial fruit and berry plants. One located at Guelph, Ontario, Canada is used to study the root systems of fruit and ornamental trees. A fourth located at Mount Edgecombe, Republic of South Africa, is used to study effects of soil conditions on growth rate and yield of sugarcane. RHIZOTRON 3 THE 1 Contribution from the Soil and Water Conservation Research Division, Agricultural Research Service, USDA, and the Agronomy and Soils Department, Auburn University Agricultural Experiment Station, Auburn, Alabama. 2 Research Soil Scientist, USDA, Auburn, Alabama. 3 The word "rhizotron" is coined from the Greek word for root (rhizo) and the suffix for instrument (tron). FIG. 1. Inrerior view of the rhizotron. Compartments 1 through 10 are located on the right side and 11 through 20 are on the left side. Two technicians ore measuring root lengths through the sloping gloss panels of compartment 19. 'LII Ii)t tt! ulul' I thl i\ rINA t l liiiliii s1(hits ( tiscNt uJ~) t i i t tlt pc \t 11 ir cm -( il (IN ts c i tit t ifnN Si i 'I t VI 111 li t. I I ti Icrisi I.tiu t I Ii I s u tii I s11 it Ii -t (il I\ it ttit flit (s iu l t111 1 ii tst cI N\I, tti~IIif stIit ttt - it I I r i t t Nir ItII 1nli u Ii 2 oItN ot! CONSTRUCTION Thei t*itt/ttrtl is DETAILS I,'it I 7) ftfi 2 S ft. iltc il t. I inch( N \\icll liiiutu,li t \N iinu IN 't I it I ht (1(1.u tlli< li I NN I Ii SttionNi 1) W. tl f 41 trance to the rhizotron. Roof slopes are sufficient to ensure that rainfall will not concentrate and flow into any of the soil compartments. There are 20 soil compartments, 10 on each side of the tunnel. Each compartment has a glass side facing the walkway within the tunnel. The rear side of each compartment is the outer retainer wall of concrete. The bottom of each compartment is a concrete slab shelf 4 inches thick. Utility lines and water drains are located under the slab. All concrete surfaces are treated with epoxy paint to reduce soil contamination by the concrete material. Compartments are separated from each other by side panels of steel or aluminum plate between two stainless steel sheets. Silicone caulking seals all joints and cracks within each compartment. Each compartment is about 74 inches high and 48 inches wide. Compartments 1 through 10 are 24 inches from front to rear, both top and bottom. Compartments 11 through 20 are inclined 10 degrees from the vertical so that taproots will stay in the soil along the glass windows. The compartments are 24 inches at the top from front to rear, but 12 inches at the bottom from front to rear. Two 6 x 6 x 1/2-in rectangular porous plates with drainage tubes are located in the bottom of each compartment. In compartments 1 through 10, diatomaceous earth (about 2 inches thick) is placed over the porous plate drains. Except for compartments 7 through 10, each compartment has a window that contains 32 panes of glass, each about 10 inches wide and 1/4-inch thick. A 1/2-inch square grid wire mesh is embedded in each pane of glass. This wire provides a convenient measuring grid and also reduces shattering if the glass breaks. Vertical stainless steel bars, 1/2 x 2 inches, provide support for the window panes. Each pane is caulked to the support bar with silicone caulking compound and is supported by a stainless steel clip at each corner. Acrylic plastic sheets, each about 10 inches wide and 74 inches long, and from 1/4 to 1/2-inch thick, form the viewing area of compartments 7 through 10. Various measuring instruments are inserted into these compartments through holes drilled in the plastic sheets. A tunnel anteroom, located at the end opposite the entrance, provides space for recording instruments and equipment storage. The anteroom space is dehumidified for instrument longevity. [5] A FIG. 2. A rsearch scientist examining cotton ro~ots through a binocular microscopc. The microscope support stand can be moved to examine roots behind any part of the transparent panel. EQUIPMENT Bs osots I~csid i tilcir' iutiionui ro h, cils f tl ut ii and1 iiiit llllcitl li IaI Iiij dl i itIrt, IiIN cii 1 t1 sii Im d4iict l dli-i \ (i llC tI h iii 1111 i lsclitillc ts to ulInn /i li 1)1 I i tlitil [i itil i( tli all cord~~~~~~~~~~~~~ (c n i~ IdccncisiIIarto FIG. 3. An exterior view of the rhizotron. The research scientist is adjusting an instrument that measures plant stem shrinkage during periods of high evapotranspiration. sandy1 siils blmin tr(1)11 Tllalssee(. and( or thic A,, hoi ou of \mo )k l loa11 s TI II 1104( soil ('0! dition s. smuileI the pr('s'!nt soils w5i l of a (Onl parll i t, thll loss cr' p('5 of Mass5 ( tle i(' 5Il( f the 'Intranc('I 1en5 w cd(. c ill 1~ dumI 1o0ttd( 1 ) steps. IThis lh' 110)? PHILOSOPHY LEADING TO THE CONSTRUCTION OF THE RHIZOTRON 'mil plant to l((i t'5 osilieo'ui iiainil foh ircoh lfiirts' pro5 i - ~ -A p A t 4s ~ ti. 4*~*~*-~ a FIG. 4. A close-up view of corn roots 12 inches below the soil surface. Estimates of rooting length and intensity arc made by measuring the number of roots that intersect horizontal grid lines at 6-inch increments to 72 inches, or by measuring root lengths within sample squares. S tlii s itt ittto Y ',,t m t arc t' li Cii i it( t Iillicik tI iiiii, t thI all ie( of iftctt' c ci) hit mot Ciin Is'it tIttt/ici i-A on lii tilit it',ii toi)U rn it ) t 1 it4itttt I ',iiii l I iii ii~ i T hisI ( l lit ti i', oldi itl I dl l c\ct lica l i t ih t noti ' Sil tktili it', ai hidto(ni i S itt e I ii It. Iic- ltsi cis liito( iji ](, s 1ii. , h e s o r tcll r 1r c ic "It iti 1i t t Ii t I i Ia i t I i i to ,ti< i 1cr I 111 i t itN ciii I, [iitt tt I p ill~t (4 ii I irii t \s 'I11 1(1_ iI tcr1)1 I i it ~I i C I I- : il exam ierootl b l av beind use t clou togah is c;I FIG. 5.I Timn las pho~I tallo photgraphy of an th lasspaels The c!l~iaera uppot can be moe , !tl I rul~ l system.'i~i rotIn! pavro th v!u~iisibl AGRICULTURAL EXPERIMENT STATION SYSTEM OF ALABAMA'S LAND-GRANT UNIVERSITY WXith an agriclituoral research unit in ever N mjor soil area, AubrnI Uiversity serves tihl needs of field (lop, live-1 stock, forestry, and hoi ticoltoral producers in legion 1ll Ala-~ (each hama. Every citizeni otf the State has a stake in this resear ch prlogrami sinice frloml al-I laantage' and~ Ilnore Nvavs ofI 10 ®0 ® neNN - econom1~lilcal far p~roduicts dire ctX ben1efits the Ici siiii ii p bl ic. L Research Unit Identification 1. Tennessee Valley Substotion, Belle Mina. 2. Sand Mountain Substation, Crossville. 3. North Alabamo Horticulture Substation, Cullman. 4. Upper Coastal Plain Substation, Winfield. 5. Forestry Unit, Fayette County. 6. Thorsby Foundation Seed Stocks Farm, Thorsby. 7. Chilton Area Horticulture Substation, Clanton. 8. Forestry Unit, Coosa County. 9. Piedmont Substation, Camp Hill. 10. Plant Breeding Unit, Tallassee. 11. Forestry Unit, Autauga County. 12. Prattville Experiment Field, Prattville. 13. Black Belt Substation, Marion Junction. 14. Tuskegee Experiment Field, Tuskegee. 15. Lower Coastal Plain Substation, Camden. 16. Forestry Unit, Barbour County. 17. Monroeville Experiment Field, Monroeville. 1 8. Wiregross Substation, Headland. 19. Brewton Experiment Field, Brewton 20. Ornamental Horticulture Field Station, Spring Hill. 21. Gulf Coast Substation, Fairhope.