Lakeland Sand Research Articles

Carbon dioxide enrichment and nitrogen fertilization effects on cotton (Gossypium hirsutum L.) plant residue chemistry and decomposition

Increased atmospheric carbon dioxide (CO2) concentration will likely cause changes in plant productivity and composition that might affect soil decomposition processes. The objective of this study was to test to what extent elevated CO2 and N fertility-induced changes in residue quality controlled decomposition rates. Cotton (Gossypium hirsutum L.) was grown in 8-l pots and exposed to two concentrations of CO2 (390 or 722 μmol mol-1) and two levels of N fertilization (1.0 or 0.25 g l-1 soil) within greenhouse chambers for 8 wks. Plants were then chemically defoliated and air-dried. Leaf, stem and root residues were assayed for total non-structural carbohydrates (TNC), lignin (LTGA), proanthocyanidins (PA), C and N. Respiration rates of an unsterilized sandy soil (Lakeland Sand) mixed with residues from the various treatments were determined using a soda lime trap to measure CO2 release. At harvest, TNC and PA concentrations were 17 to 45% higher in residues previously treated with elevated CO2 compared with controls. Leaf and stem residue LTGA concentrations were not significantly affected by either the elevated CO2 or N fertilization treatments, although root residue LTGA concentration was 30% greater in plants treated with elevated CO2. The concentration of TNC in leaf residues from the low N fertilization treatment was 2.3 times greater than that in the high N fertilization treatment, although TNC concentration in root and stem residues was suppressed 13 to 23% by the low soil N treatment. PA and LTGA concentrations in leaf, root and stem residues were affected by less than 10% by the low N fertilization treatment. N concentration was 14 to 44% lower in residues obtained from the elevated CO2 and low N fertilization treatments. In the soil microbial respiration assay, cumulative CO2 release was 10 to 14% lower in soils amended with residues from the elevated CO2 and low N fertility treatments, although treatment differences diminished as the experiment progressed. Treatment effects on residue N concentration and C:N ratios appeared to be the most important factors affecting soil microbial respiration. The results of our study strongly suggest that, although elevated CO2 and N fertility may have significant impact on post-harvest plant residue quality of cotton, neither factor is likely to substantially affect decomposition. Thus, C cycling might not be affected in this way, but via simple increases in plant biomass production.

PEACH TREE SHORT LIFE NOT INFLUENCED BY PREPLANT HYDRATED LIME TREATMENTS

`Redhaven' peach trees were planted on a nonfumigated peach tree short life (PTSL) site in Pontiac, S.C. The experimental design was a split plot with 12 replicates. Preplant subplot treatments were 0, 3, and 6 kg of hydrated lime mixed with 1.9 cubic meters of native soil (Lakeland sand) per planting hole. Main plot treatments consisted of mixing in the planting holes 0 or 5 liters of soil taken from a nearby orchard site that had shown “suppressive” tendencies towards ring nematode reproduction. Hydrated lime treatments increased soil pH by 0.6 to 1.4 units. Boron deficiency occurred in the 6-kg plots. Hydrated lime did not significantly reduce PTSL as 88%, 79%, and 92% of the trees in the 0-, 3-, and 6-kg plots, respectively, died from PTSL by the fifth year. No differences in survival were found between the nonsuppressive and suppressive soil treatments, as both had 86% tree death from PTSL. No trends in ring nematode populations were found among treatments.

Provision of mid‐season potassium requirements in cotton with slow release potassium applied pre‐plant

Abstract Mid‐season development of potassium (K) deficiency in cotton is related to the high K demand during flowering and high rainfall, particularly on sandy soils, removing available K prior to peak demand. Slow‐release K sources have potential for supplying mid‐season K requirements of cotton without having to expend additional labor and fuel applying sidedress or foliar K in mid‐season. The objective of this study was to determine the potential for slow‐release K applied preplant in combination with muriate of potash (KCl) for meeting mid‐season K requirements of cotton. Tests were conducted on ‘Georgia King’ cotton grown on three soil types in the Coastal Plain region of Georgia: 1992–1993 on a Greenville sandy clay loam (Rhodic Kandiudults), 1994 on a Tifton sandy loam (Plinthic Kandiudults), and 1993 on a Lakeland sand (Typic Quartzipsamments). Three K rates were applied (0, 55, and 110 kg K2O/ha), and two K sources were utilized, KCl (muriate of potash; 0–0‐60) and Multi‐cote 4 slow‐release ferti...

INTERSTEM LENGTH AND ETHEPHON DO NOT ENHANCE TA TAO BLOOM DELAY

`Juneprince' peach was budded to Ta Tao 24 peach interstems on virus-free Lovell rootstock in June 1990. Trees were planted December 1990 in a fumigated Lakeland sand near Columbia, SC. The experimental design was a randomized complete block with 9 replicates each having 6 treatments plus a control. Four treatments were 20 and 40 cm interstem segments of Ta Tao 24 with and without an interstem branch. Two other treatments were 40 cm Ta Tao 24 interstems with no branches but receiving a single November spray of either 200 ppm ethephon or water. The control was `Juneprince' on Lovell rootstock. After 3 years, control trees were significantly larger in TCSA (cm2) than all treatment trees. Full bloom date was not significantly different among the 6 treatments, hut was significantly later (7 days) than the control trees. In March 1993, cold temperatures killed all open flowers on control trees. Fruit yields in 1993 were significantly higher in interstem trees (10.2 kg/tree) compared to the control trees (6.8 kg/tree). Fruit maturity date did not differ among treatments, hut was significantly later (10 days) than the control trees. `Juneprince' on Ta Tao 24 interstems were smaller in TCSA and had delayed bloom and fruit maturity. Ta Tao 24 interstem length presence of branches, and ethephon application did not enhance the differences observed in this study.

318 FIELD PERFORMANCE OF 28 PRUNUS ROOTSTOCKS AND INTERSTEMS IN SOUTH CAROLINA

A `Redglobe' peach orchard budded to 22 rootstock cultivars was planted in 198X on a Lakeland sand near Columbia, SC. Six of the 22 cultivars were also used as interstems on Nemaguard. The rootstocks tested were Lovell, Halford, Nemaguard, Bailey, Tennessee Natural, Tzim Pee Tao, Rutgers Redleaf, Higama, Rubira, Montclar, GF 305, Juseito, Myran, Ishtara, S.2729. St. Julian A, Citation, Marianna 2624, GF 557, GF 677, (S×R 185)6 and `Redglobe' own-rooted. Trees on Marianna 2624 grew poorly and eventually died from incompatibility. Plum hybrid rootstocks St. Julian A. Ishtara and Myran were susceptible to Pseudomonas syringae. Some peach X almond (S×R 185)6 trees died from unknown causes. Tzim Pee Tao was the only rootstock to delay bloom significantly later (1.5 days) than Lovell. All Nemaguard interstem combinations and Tzim Pee Tao had significantly more-rootstock suckers. Nemaguard, Myran and Higama trees were 25 to 43% larger in TCSA than Lovell. Ishtara trees were only 61% of Lovell in TCSA. St. Julian A and Citation trees were small, weak and unproductive. The highest yielding rootstocks were Nemaguard (Myran interstem), GF 305, Nemaguard (Ishtara interstem), Montclar and Rubira which averaged 69, 65, 64, 62 and 60 kg/tree, respectively in years 4 through 6.

Seeding Depth and Packing Wheel Pressure Effects on Oilseed Rape Emergence

Oilseed rape (Brassica napus L.), including industrial (rapeseed) and canola quality cultivars, offers potential for doublecropping in the southeastern USA. Early attempts at commercialization of this crop in the Southeast have frequently encountered difficulties in establishing stands. This 3-yr project (1986-1989) was undertaken to evaluate the effects of seeding depth and planter configuration (i.e., packing wheel pressure) on emergence of oilseed rape. The two field sites used for this study contained Lakeland sand (thermic, coated Typic Quartzipsamment) and Tifton loamy sand (fine, loamy, siliceous Plinthic Paleudult) soil types, respectively. Treatment factors were planter configuration, seeding depth, and cultivar [...]

Measurement of Density and Water Content in Soils with X-ray Linescan and X-ray Computed Tomography

Potentials for using X-ray computed tomography for determining soil bulk density and water content were investigated using Cecil sandy clay and Lakeland sand soils. Soils were moistened and samples were compacted to several levels. These samples were sequentially dried and scanned using tomography reconstructions as well as the linescan mode available on a CT scanner. Mean X-ray absorption and pixel standard deviation data were collected for each soil sample at scanning in both modes. For each soil-mode combination, relationships between mean X-ray absorption and soil bulk density and water content were determined as were relations between pixel standard deviation and soil density and water content. The experiment was then repeated to provide validation data. In the tomographic reconstruction mode with validation data, optimal water content and bulk density values for samples were determined for each corresponding mean absorption and pixel standard deviation measurements which minimized the error sum of squares. Density was predicted in both soils to within 2%. Predicted water content was within 50% of observed values. Using known values of density, water content was predicted to within 5%. In the linescan mode, density was usually predicted to within 5%. Water content was not significant (P < 0.15%) thus a prediction for water was not attempted in the linescan mode.

Zinc toxicity symptom development and partitioning of biomass and zinc in peanut plants1

Abstract High soil zinc (Zn) concentrations can cause Zn toxicity in peanuts (Arachis hypogaea L.), which decreases productivity and can be fatal to the plants. The objectives of this study were 1) to determine the optimal sampling time and plant part for diagnosis of Zn toxicity in peanuts, 2) to relate toxicity symptoms to plant Zn concentrations and calcium:zinc (Ca:Zn) ratios, and 3) to model the distribution of Zn and biomass into plant parts in relation to Zn concentration in the whole plant. A greenhouse study utilized four soils (Lakeland sand, Tifton loamy sand, Greenville sandy clay loam, and Greenville sandy clay) with Zn applications of 0, 10, 20, and 40 mg Zn/kg soil. Plants were sampled for analysis of nutrient concentrations, and Zn toxicity ratings were recorded biweekly. Toxicity symptoms became visible 4–8 weeks after planting, with stunting appearing at four weeks, horizontal leaf growth and leaflet folding at six weeks, and stem splitting at eight weeks. Optimal sampling time for diagn...

Measurement of Water Table Fluctuations in a Sandy Soil Using Ground Penetrating Radar

A study was conducted to assess the impacts of ground-penetrating radar (GPR) calibration techniques on the water table depths calculated from the GPR graphical output. A Geophysical Survey Systems, Inc., SIR-8 impulse radar with a 120 Mhz antenna operating at a scanning rate of 100 ns was used to produce GPR images along seven, 130 m transects of a field site. The study site is located near Tifton, Georgia, in the Coastal Plain physiographic region of southeastern U.S. The soil on the study site is classified as a Lakeland sand with profile depths from 1.9 to 4.4 m. Underlying the sand is a restricting layer consisting of tight clays.

EFFECTS OF PESTICIDE, SOIL, AND RAINFALL CHARACTERISTICS ON POTENTIAL PESTICIDE LOSS BY PERCOLATION -A GLEAMS SIMULATION

ABSTRACT Potential pesticide loss in soil percolate is influenced by pesticide persistence and sorption by soil constituents (organic matter). Pesticide persistence, expressed as half-life (ti/2), changes with soil depth as microbial activity and soil properties change. Little is known, however, how these changes influence potential pesticide transport out of the root zone. Objectives of this study were to investigate relative differences in potential pesticide losses from the root zone by percolation due to 1) different soil surface and subsurface textures and pesticide ti/2 and 2) interactions between pesticide ti/2 and timing of rainfall after pesticide application. The GLEAMS (Groundwater Loading Effects of Agricultural Management Systems) model and a 50-year historical rainfall record at Tifton, Georgia, were used to simulate pesticide losses by percolation from three soils ranging in surface texture from sand to sandy clay loam. Hypothetical pesticides had surface ti/2 of 5, 15, 30, and 60 d and a range of subsurface ti/2 (2.5-360 d), and were applied to continuous com {Zea maize, L.) at 2 kg ha~ ^ as surface spray at planting each year on 1 April. Simulated pesticide losses by percolation increased with increased surface and subsuiface t|/2 and decreased with increased KQC (adsorption constant based on soil organic matter) values. Potential pesticide leaching was greatest for Lakeland sand and least for Greenville sandy clay loam. Rainfall timing affected simulated pesticide loss by percolation, especially for nonpersistent pesticides. For short pesticide ti/2 (0-5 d), excessive rainfall events within 1 ti/2 were largely responsible for simulated pesticide loss by percolation. Results indicate that changes in pesticide t|/2 in surface and subsurface horizons of different soils influence potential pesticide leaching from the root zone, and models (i.e., GLEAMS) can be used to provide comparative analysis of soil-pesticide-climate interactions. For example, depending on soil type and pesticide K^^ and surface Xyp^ values, potential leaching losses increased two to seven times as subsurface tiy2 increased six times.

Gypsum material effects on peanut and soil calcium

Abstract Adequate availability of calcium (Ca) in the upper 7–10 cm of soil is extremely important for pod development and therefore for production of quality peanut (Arachis hypogaea L.). Supplemental Ca is usually applied as gypsum, however, availability of Ca may depend on the type of gypsum. The objective of a laboratory study was to evaluate recovery of Ca in Mehlich I, 0.01 M NaNO3 and deionized water extractants from seven gypsum materials which varied physically from fine and coarse powders to crystals, granules and pellets. Overall, recovery of Ca was much greater in Mehlich I (89.5–99.6% of total Ca) than in either 0.01 M NaNO3 (81.0–98.4%) or deionized water (78.7–97.5%). However, for 3 sources, recovery of Ca was very similar in NaNO3 solution and deionized water. Field experiments were conducted on Lakeland sand (Mehlich I Ca = 127 kg/ha, 0–15 cm) and Tifton loamy sand (Mehlich I Ca = 665 kg/ha) soils to study the effects of the gypsum materials on Florunner peanut grade and yield. Effects of...

Heterosis for Embryo Size and Source and Sink Components of Maize

Assimilate source and sink components controlled by genotype and environment determine grain yield of maize (Zea mays L.). Field experiments were conducted in 1986 and 1987 at Gainesville, FL (29° 38′ N) on a Lakeland sand (hyperthermicoated Thermic Quartzipsamment) to assess heterosis for vegetative and yield components. In order to equalize leaf area index and light interception, parent inbred lines B73, MO17, MS71, and VA22 were planted at normal plant populations density (PPD) of 55 000 and also at 110 000 plants ha‐1, while three F1 hybrids from these inbreds were planted at 55000 and 27 500 PPD. In hybrid seeds, embryo size was associated with seed size. At common seed size (8 ram), lengths embryo and embryo axis of hybrids were greater than those of midparent and inbred line means, manifesting heterosis for embryo size. At common PPD, all biomass and grain yield source and sink components were significantly greater for hybrids than for inbreds. At common LAI and light interception achieved by doubling inbred PPD, hybrids produced significantly more biomass and kernel yield, kernel growth rate and weight, and grain‐filling duration, but kernel number for hybrids and inbreds was similar at common LAI. We conclude that hybrids as compared with their parent inbreds express heterosis in source components, including embryo size, as well as sink components, all contributing to higher biomass and grain yields of maize.

Potassium, magnesium, and irrigation effects on peanuts grown on two soils

Abstract Research data are limited on K and Wg requirements of peanuts (Arachis hypogaea L.) grown on sandy soils either with or without irrigation. Purposes of this study were (1) to determine Mg, K, and irrigation effects on yield, sound mature kernels (SMK's), and diseases of ‘Florunner’ peanuts grown on two sandy soils and (2) to determine sufficient amounts of Mg and K in peanut leaves and soils. Field experiments were conducted for three years on a Lakeland sand (thermic, coated Typic Quartzipsainments) and a Fuquay loamy sand (siliceous, thermic, Arenic Plinthic Paleudults). Both soils initially tested low in Mehlich 1 extractable K and Mg, but Lakeland was lower than Fuquay in both K and Mg. Factorial treatments were 0, 67, 67 (split into three applications), and 134 kg Mg/ha as MgS04 and 0, 56, 112, and 224 kg K/ha as KC1. Neither irrigation, K, nor Mg treatment affected number of diseased plants. (Sclerotium rolfsii) or pod rot on either soil. Also, yield and % SMK's were not affected by any tre...

In Situ Nuclear Magnetic Resonance Imaging of Roots: Influence of Soil Type, Ferromagnetic Particle Content, and Soil Water1

AbstractThe paucity of root information combined with the difficulty in obtaining it make new approaches imperative. The observation of roots is essential to the understanding of plant growth and productivity. Proton (1H) nuclear magnetic resonance (NMR) imaging offers a noninvasive method for the study of both root morphology and function in situ. Herein, NMR imaging of plant root systems was evaluated for southeastern U.S. agricultural soil series from 30 different sites, and eight common artificial soil substrates, as a function of soil type, ferromagnetic particle content, and soil water, using a 1.5‐tesla medical research NMR imaging system and Vicia faba L. seedlings grown in the soils. Roots of about 1 mm in diameter and 1‐mm‐diam capillaries of water were undetectable by NMR imaging and conventional NMR in soils with ferromagnetic particle contents of greater than about 4% by weight. Below 4%, ferromagnetic particle content did not correlate well with NMR image quality, but the presence or absence of NMR signals from water‐containing capillaries embedded in soil samples in a conventional NMR experiment reliably reflected soil suitability for NMR root imaging. Images of seedlings in four of the artificial soils (perlite, Ottawa sand, peatlite, and peat) and seven of the native soils (Wynnville fine sandy loam, Lucy loamy sand, Dothan sandy loam, Lakeland sand, Kinston loamy sand, Blanton loamy sand, and Eustis fine sandy loam) showed excellent spatial resolution and accurate reproduction of the root systems when they were extricated from the soils. However, the results from three of the artificial soils (perlite, Ottawa sand, and peat) were significantly compromised by background NMR signals that derived from soil water. In the seven native soils, soil water to near saturation was rendered essentially invisible by the NMR imaging sequence employed, thereby demonstrating excellent root‐to‐soil image contrast. Several root pathologies apparent in the images were identified. The results reveal that 1H NMR imaging is a practical tool for the nondestructive, noninvasive investigation of plant root systems in many natural agricultural soils at virtually any stage of a water stress cycle.

Response of Nodulating and Non-Nodulating Peanuts to Foliarly Applied Nitrogen1

Abstract Field experiments were conducted on Lakeland sand (Thermic, coated Typic Quartz-ipsaments) during 1981-82 to determine the effect of foliarly applied N on yield, grade, and N, P, K, Ca, and Mg concentration of leaves and seed of nodulating and non-nodulating peanut (Arachis hypogaea L.). Nodulating cultivars; Florunner, Early Bunch, and Tifrun, and three non-nodulating experimental lines were sprayed 0, 1, 2 or 4 times at 13.5 kg N/ha beginning 28 days after emergence. Foliar application of N increased the yield of Florunner, Tifrun, and all non-nodulating lines, but had no effect on Early Bunch. The addition of N to non-nodulating peanut increased the percent fancy pods, extra large kernels, and weight of seed. Seed N concentration of non-nodulating lines increased with higher rates of N, but was higher in the nodulating cultivars. Seed of non-nodulating lines contained higher levels of P, K, and Mg than seed of nodulating lines. Nodulating lines had higher concentration of leaf N than did non-nodulating lines. The leaves of the non-nodulating lines contained higher levels of P, Ca, and Mg than those of the nodulating cultivars; whereas levels of K were higher for nodulating lines.

Effects of nitrogen fertilization method and tillage system on squash growth, nutrient uptake and fruit yield

Abstract Squash, cv Dixie, grown on a Lakeland sand was subjected to factorial combinations of 3 tillage systems and 2 N application methods during 1979 and 1980. Fruit yield was greatest with a combination of moldboard plow tillage and application of 22 kg N/ha preplant and 18 kg/ha increments of N by fertigation 2, 3, 4, 5 and 6 weeks after planting. Plant growth and nutrient uptake were greatest and N available for potential contamination of the ground‐water was least with subsoil‐bed tillage and N application by fertigation. Disc harrow tillage with 67 kg N/ha preplant and 45 kg N/ha 4 weeks after planting resulted in 42% less yield, 61% less plant growth, 29 to 64% less nutrient uptake and more than 5 times as much N available for potential contamination of the groundwater as the best practices.

Computer Model for Moisture Distribution in Stratified Soils Under a Trickle Source

ABSTRACT THIS research was conducted to: (1) develop a computer simulation modelor use an existing oneto simulate irrigation in stratified soils, (2) study the moisture distribution under a trickle source in a Lakeland sand, and (3) compare results of the computer model with field measurements. Field tests were conducted at various application rates and volumes, a CSMP model was modified for use in stratified soils, and this modified program was used to simulate irrigation in the Lakeland soil. The neutron scattering method was used to measure the moisture distribution to a depth of 150 cm and to a radius of 105 cm from the trickle emitter. For each test, measurements were made before and after irrigation and again after some redistribution period. Also, tensiometers were placed at specified depths at a radius of 45 cm to help locate the wetting front during application and redistribution. Input data for the CSMP simulation model (in-situ tension vs. water content and hydraulic conductivity vs. water content for each soil horizon) were obtained using the instantaneous profile method. Field measurements showed that the shape and size of the wetted zone is more a function of the volume of water applied than of the rate of application. When more than 32 L were applied, the additional water did not greatly increase the horizontal dimension of the wetted zone, but moved vertically through the profile. The CSMP simulation compared favorably with the field measurements in the Lakeland sand.

Response of Squash to Irrigation, Nitrogen Fertilization, and Tillage Systems1,2

Abstract ‘Dixie’ squash (Cucurbita pepo L. var. condensa) were subjected to factorial combinations of 2 irrigation levels, 4 N treatments, and 3 tillage methods on a Lakeland sand soil during 1978, 1979, and 1980. The greatest marketable fruit yield resulted from a combination of applying irrigation at 0.3 bar soil water tension, applying 22.5 kg N/ha through the irrigation system at 2, 3, 4, 5, and 6 weeks after planting, and preparing the seedbed by moldboard plow tillage. Yields were reduced 3 to 16% by either reducing the N rate, allowing a greater soil water tension before irrigating, or by the use of subsoil-bed or disk-harrow tillage system. A combination of subsoil-bed tillage and application of irrigation at 0.6 bar soil water tension resulted in the greatest yield when squash received a single N application after planting.

Adsorption and Reduction in Bioactivity of Polychlorinated Biphenyl (Aroclor 1254) to Redroot Pigweed by Soil Organic Matter and Montmorillonite Clay

AbstractAroclor 1254 polychlorinated biphenyl (PCB) applied to untreated (1.4% organic matter) and H2O2‐treated (0.2% organic matter) Lakeland sand at rates of 0, 50, 100, 150, and 200 ppm caused significant reductions in redroot pigweed (Amaranthus retroflexus L.) growth at the high rates of application. Polychlorinated biphenyl decreased plant height in the H2O2‐treated soil much more than in the untreated soil. A greater decrease in dry weight also resulted in the H2O2‐treated soil, but only at the 200 ppm rate. In one study, soil was amended with montmorillonite clay and organic matter (peaty muck) at rates of 0, 2.5, 5.0, and 10.0% by weight and treated with 200 ppm PCB. The organic matter proved to be much more effective than montmorillonite in reducing PCB toxicity to pigweed at the lower rates of addition (2.5 and 5.0%), but no differences were noted between the two adsorbents at the 10% rate. Adsorption of 14C‐labeled PCB closely resembling Aroclor 1254 by the untreated and H2O2‐treated soils, montmorillonite clay, organic matter, and activated carbon was measured. The order of highest to lowest adsorption was as follows: activated carbon ≫ organic matter &gt; montmorillonite clay &gt; Lakeland sand &gt; H2O2‐treated Lakeland sand. These experiments suggest that organic matter content of a soil, and clay content to a lesser extent, are involved in reducing the availability of soil‐applied PCB to pigweed. Differences in reduction of PCB toxicity to pigweed are explained by differences in adsorption by the adsorbents.

The Influence of Irrigation and Rhizobium japonicum Strains on Yields of Soybeans Grown in a Lakeland Sand1

AbstractUnder existing management technology, Lakeland sands (Typic Quartzipsamments) produce low yields of soybeans [Glycine max (L.)Merr.] in North Carolina. These soils have an available water holding capacity of only 4.0% on a weight basis and as a result require about 2.5 cm of water every 5 to 6 days during the growing season to produce acceptable crop yields. In addition, Lakeland sands usually have extremely low or a totally nonexistent indigenous population of Rhizobium japonicum. Information on irrigation and nodulation effects is needed to make these soils more productive.The objectives of this study were to investigate the influence of irrigation and inoculation with different R. japonicum strains on yields of soybeans grown in a Lakeland sand. The study was conducted at the Sandhills Research Station at Jackson Springs, North Carolina. Additional nonirrigated plots inoculated with strains 31, 110, and 122 were initiated on finer textured North Carolina soils for comparative purposes to the Lakeland sand.Soil moisture treatments included plots not irrigated and plots irrigated each week with 2.5 cm of water. The five inoculation treatments consisted of a set of noninoculated plots and plots inoculated with strains of R. japonicum representing serogroups 31, 76, 110, and 122 at the rate of 50 ✕ 104 cells per cm of soybean row. Numbers of soil rhizobia were monitored throughout the study using a plant infection and MPN technique.Irrigated soybean seed yields were significantly greater when inoculated with rhizobia of either serogroup 110 or 122 than yields from noninoculated but irrigated plots. Inoculation without irrigation did not increase soybean yields. It was also observed that inoculated, irrigated soybeans had greater nodule mass and numbers of nodules than the nonirrigated and/or noninoculated plots. All four serogroups used in the study adequately nodulated soybean roots under irrigation and produced fewer nodules on soybean roots in the nonirrigated plots. On the basis of seed yield, strain ranking from best to worst was: 122&gt;110&gt;31&gt;76. The noninoculated controls yielded higher than serogroup 76 but less than those soybeans in plots inoculated with serogroup isolate 31.