Arkansas Soil Research Articles

Long-term residue and water management practice effects on particulate organic matter in a loessial soil in eastern Arkansas, USA

Long-term sustainability of soils with a prolonged history of crop production can be better understood by characterizing soil aggregation, particularly the distribution of carbon (C) and nitrogen (N) among particulate organic matter (POM) fractions within various soil aggregate-size fractions. The objective of this field study was to evaluate the effects of residue level, residue burning, tillage, and irrigation on macro-aggregate (>250 μm), micro-aggregate (53–250 μm), coarse (>250 μm) and fine POM (53–250 μm), and silt-clay fractions and their associated C and N in the top 10 cm of a highly erodible loessial soil (Glossaquic Fraglossudalf) after 13 years of consistent management in a wheat-soybean, double-crop (WSDC) system in the Lower Mississippi River Delta region of eastern Arkansas. The total aggregated soil fraction was 11.2% greater (P = 0.02) in the no-tillage (NT)-irrigated compared to the average of the other three tillage-irrigation combinations, which did not differ. Averaged over irrigation, burn, and residue-level treatments, the C concentration in the sand-free macro-aggregate fraction was 8.8% less (P < 0.05) under conventional tillage (15.6 g kg−1) than under NT (17.1 g kg−1). Fine POM C and N concentrations within sand-free-adjusted aggregates were 1.9 times greater (P ≤ 0.04) in the burn-low (2.59 and 0.21 g kg−1, respectively) compared to the burn-high treatment (1.35 and 0.11 g kg−1, respectively), while that in the no-burn under either residue level, which did not differ, were intermediate (2.43 and 0.23 g kg−1, respectively). Results showed that alternative management practices, such as NT and non-burning, can contribute to improved soil health and long-term sustainability and the mitigation of climate-change-related greenhouse gas concentrations in the atmosphere by reducing SOM oxidation, microbial respiration, and carbon dioxide emissions.

Water Management and Cultivar Effects on Methane Emissions from Direct-seeded, Delayed-flood Rice Production in Arkansas

Methane (CH4) emissions from rice (Oryza sativa L.) production are a source of concern in the environmental and agricultural communities. New and/or revised agronomic methodologies will be needed to identify production practice combinations that reduced CH4 emissions without decreasing yields or milling quality. The objective of this study was to evaluate the effects of water management (i.e., full-season flood and mid-season drain) and cultivar (i.e., pure-line cultivar LaKast and the RiceTec hybrid XL753) on CH4 fluxes and season-long emissions from rice grown in the direct-seeded, delayed-flood production system on a silt-loam soil in east-central Arkansas.

Long-term effects of residue and water management practices on plant parasitic nematode abundance and soybean root infection

Soil-borne, plant parasitic nematodes are potentially agronomically and economically damaging in the wheat (Triticum aestivum L.)-soybean (Glycine max L.), double-crop production system that is common in the mid-southern United States. Double-crop field studies with at least five years of consistent management are rare, but can provide a valuable setting to assess long-term, and potentially cumulative, management practice effects on nematode abundance and root damage. The objective of this study was to evaluate the effects of a combination of management practices including residue burning (burned and no burn)-irrigation (irrigated and non-irrigated), wheat residue level (high and low), and tillage (conventional tillage and no-tillage) practices on plant parasitic nematode soil abundance and reproduction on soybean 34 and 70 days after planting following 14 complete cropping cycles in a wheat-soybean, double-crop production system on a silt-loam soil in eastern Arkansas. Stunt and total nematode abundances were at least 8.2 and 4.2 times greater (P < 0.05), respectively, under the burn-non-irrigated-no-tillage than under the other three burn-irrigation-tillage treatment combinations 34 and 70 days after planting. Root-associated soybean cyst nematode egg concentrations were 16.2 and 4.5 times greater under the burn-non-irrigated-low-residue than under the no-burn-irrigated-low-residue and burn-non-irrigated-high-residue treatment combinations, respectively, which did not differ, 34 days after planting, but were unaffected by any field treatment 70 days after planting. Producers may consider avoiding the combination of residue burning, no-tillage, and dryland soybean production to help keep the parasitic nematode population low. Results of this long-term field support the notion that properly managed crop rotations contribute enough diversity of inputs and processes to limit the known negative effects of continuous monoculture.

Characterization of Methane Emissions From Rice Production on a Clay Soil in Arkansas

AbstractRice (Oryza sativa L.) production systems have a greater global warming potential than upland crops because of methane (CH4) emissions resulting from anaerobic conditions of the flooded soils. Differences in cultural practices, cultivar choice, previous crop/crop rotation, and in particular

Carbon dioxide emissions from switchgrass and cottonwood grown as bioenergy crops in the Lower Mississippi River Alluvial Valley

Marginal land of the Lower Mississippi Alluvial Valley (LMAV) has the potential to be utilized for substantial production of bioenergy feedstocks. However, resulting ecosystem services associated with dedicated bioenergy crop production, such as soil respiration and carbon dioxide (CO2) emissions, which play an important role in global carbon (C) cycling, are not well understood. The objective of this study was to evaluate the effects of land use [i.e., switchgrass (Panicum virgatum) and eastern cottonwood (Populus deltoides) grown as dedicated bioenergy crops and a soybean (Glycine max)-grain sorghum (Sorghum bicolor) agroecosystem rotation] on monthly respiration and estimated annual CO2 emissions for 2012 and 2013 from a silt -loam soil in east-central Arkansas. Peak monthly fluxes achieved each year differed (p < 0.05) somewhat among ecosystems. Annual CO2 emissions differed among ecosystems (p < 0.001), but not between years (p = 0.45). Cottonwood emitted less CO2 in both years (7.3 and 7.4 Mg ha−1 for 2012 and 2013, respectively) compared to the other two ecosystems, while emissions from the switchgrass did not differ from those from the soybean in 2012 (10.3 and 9.5 Mg ha−1, respectively) or grain sorghum in 2013 (9.7 and 9.2 Mg ha−1, respectively). Results showed established bioenergy feedstock cropping systems do not have greater soil CO2 emissions compared with a traditional soybean-grain sorghum crop rotation. Results also indicated that different bioenergy feedstocks can produce different quantities of CO2 emissions, which may be important to consider when converting marginal lands to bioenergy feedstock cropping systems.

Soybean Seed Quality: An Empirical Analysis on Clayey Soils in Arkansas

Soybean [Glycine max (L.) Merr.] seed quality is an important factor for seeding rate recommendations. Which seed quality measure to use for seeding rate recommendations and how seed treatment and planting date affect returns are assessed within. Results suggest that adding seed vigor information to seed labels would be beneficial in providing seeding rate recommendations. Seed treatment is profitable and more so at lower seeding rates. Seed survival impacts yields, but seed quality effects do not affect yield potential post–plant establishment. Planting season is an important determinant of seed survival and yield potential.

Chamber Size Effects on Methane Emissions from Rice Production

Quantifying methane (CH4) emissions from cultivated rice (Oryza sativa L.) production in the field has received increased attention recently due to methane’s importance as a greenhouse gas. The enclosed-headspace chamber technique is the standard methodology for field assessments of trace gas emissions. However, to our knowledge, no direct comparisons of measured CH4 fluxes and emissions from field-grown rice among differing chamber sizes have been reported. Therefore, the objective of this study was to evaluate the effect of chamber size [15.2- and 30.4-cm inside diameter (id)] on CH4 fluxes and season-long emissions from rice grown on a clay soil in Arkansas. Chamber size did not affect (P > 0.05) CH4 fluxes on 10 sampling dates during the flooded portion of the rice growing season and only affected fluxes on one of four sampling dates after flood release. Total season-long CH4 emissions from optimally N-fertilized rice were 32.6 and 35.6 kg CH4-C ha&#451&#183season&#451, which did not differ, and from bare clay soil were 0.74 and 1.75 kg CH4-C ha&#451&#183season&#451, which also did not differ, from the 15.2- and 30.4-cm chambers, respectively. Chamber size (i.e., 15.2- or 30.4-cm id) did not result in differences in cumulative CH4 emissions from this flooded-rice study that was conducted on a Sharkey clay soil in northeast Arkansas. Results indicate that both 15.2- and 30.4-cm diameter chambers were similarly adequate for measuring CH4 fluxes and emissions from the clay soil investigated. The similarity in emissions results between chamber sizes also indicates that the 15.2-cm diameter chambers adequately facilitated the quantification of CH4 emissions in this study.

Increased Effluent Dosage Effects on On-Site Wastewater Treatment Systems of Differing Architecture Type

Approximately 20% of homes nationwide use an on-site treatment system as a form of household wastewater management. However, approximately 10% to 20% of on-site treatment systems malfunction each year, many of which have either failed or exceeded the soil’s long-term acceptance rate (LTAR), causing environmental and human health risks. The objective of this field study was to evaluate the effects of soil condition (e.g., wet and dry) and product architecture type [i.e., chamber, gravel-less-pipe (GLP), polystyrene-aggregate, and pipe-and-aggregate] on in-product solution storage and biomat thickness in a profile-limited soil in northwest Arkansas under increased loading rates and to estimate the LTAR for each product. During Phase I of this study (March 13 to October 4, 2013), effluent loading rates were approximately doubled, while rates were approximately quadrupled during Phase II (October 8, 2013 to May 29, 2014), from the maximum allowable loading rate for each product. The pipe-and-tire-chip, 46-cm-wide trench pipe-and-gravel, and the 25-cm diameter GLP products had the greatest (p < 0.001), while the 31-cm-width and the 5.4-m-long chambers had the lowest (p < 0.001) in-product solution storage during wet-soil conditions of Phase I monitoring. The 25-cm diameter GLP product had the greatest (p < 0.001), while the 61-cm-width, 5.4-m-long chamber had the lowest (p < 0.001) in-product solution storage during Phase II. Results of this study indicate that some alternative products may be able to effectively handle effluent loading rates in excess of those currently allowed by the State of Arkansas. Further research will be required to confirm these interpretations.

Effect of understory management on phenological responses of eastern black walnut on an alluvial Arkansas soil

Black walnut (Juglans nigra L.) is commonly grown in agroforestry practices for nuts and/or timber with little knowledge of how understory herbage management might affect tree phenology. We compared black walnut plant type (variety and wild-type) for phenological response in date of budburst, leaf area index (LAI), quantum yield of photosystem II (Fv/Fm), radial stem growth, and total chlorophyll concentration in response to understory herbage N fertilization and herbage suppression in an agroforestry practice on an alluvial soil. Herbage treatments generally had little impact on phenological responses, although N fertilization increased herbage yield that delayed budburst. Radial stem growth commenced at about budburst (mid-April) and virtually ceased in late October, about 30 days before leaf drop. Early-season radial stem growth was greater for the wild-type than the variety, while the variety had more rapid late-season growth. The wild-type had consistently greater LAI than the variety at any given day-of-year (DOY), and usually had greater LAI than the variety regardless of herbage treatment. Leaves of both plant types maintained a high Fv/Fm during most of the growing season, but total chlorophyll concentration decreased across DOY regardless of plant type. N fertilizer should be applied with understory herbage suppression to avoid delay of budburst. Further study is needed of phenological responses during longer growth periods, or as affected by latitude, soil water, and soil fertility.

Rice Rotation and Tillage Effects on Water-Stable Soil Macroaggregates and Their Associated Carbon and Nitrogen Contents in a Silt-Loam Soil

Rice (Oryza sativa L.)-based cropping systems are different from other crop rotations because of the flood-irrigation scheme, which can influence the rate of soil organic matter decomposition, water-stable soil aggregation, and carbon (C) and nitrogen (N) sequestration over time. A study was conducted on a silt-loam soil (fine, smectitic, thermic, Typic Albaqualf) in eastern Arkansas to evaluate the effects of rice-based crop rotations (with maize (Zea mays L.), soybean (Glycine max L.), and winter wheat (Triticum aestivum L.)), tillage (conventional tillage and no-tillage (NT)), and soil depth (0–5 cm and 5–10 cm) after 10 years of management on water-stable macroaggregates (WSA) and their C and N concentrations (g kg−1), C:N ratios, and contents (g m−2). The total amount of WSA (WSATotal >0.25 mm in diameter) and the distribution of WSA among five different size classes (0.25–0.5, 0.5–1, 1–2, 2–4, and >4 mm in diameter) within each treatment combination were evaluated. The concentration of WSATotal was 1.2 to four times greater under NT/0- to 5-cm soil depth (9.2–16.0 g kg−1) than under other tillage-depth combinations. Macroaggregate concentration in the 0.25- to 0.5-mm size class was greater under continuous rice (9.3 g kg−1) and rice rotations with maize (7.6–8.0 g kg−1) than in rotations with wheat (4.9–6.5 g kg−1). The NT/0- to 5-cm combination had three to six times greater WSATotal C (235 g m−2) and N (20.6 g m−2) contents than all other tillage-depth combinations (C, 38.3–80.5 g m−2; N, 3.5–5.7 g m−2), which did not differ. Despite field management differences from using seasonal flood-irrigation in rice, this study demonstrates that the extent of tillage and crop rotation effects on soil macroaggregation and the associated macroaggregate-associated C and N contents were proportionate to trends commonly reported in dryland crop rotations.

Methane Emissions from Drill-Seeded, Delayed-Flood Rice Production on a Silt-Loam Soil in Arkansas

Rice ( L.) production is unique among staple food crops because the majority of the growing season typically occurs under flooded-soil conditions. Flooding the soil leads to anaerobic conditions, which are a precursor to methane (CH) production. However, no known research has investigated CH emissions from the drill-seeded, delayed-flood rice production system common in Arkansas, the leading rice-producing state in the United States. Therefore, research was conducted in 2011 to determine the effects of vegetation (rice and bare soil), chamber location (in- and between-rice rows), and nitrogen (N) fertilization (optimal and no N) on CH emissions from a silt-loam soil. Methane fluxes measured weekly from flooding until flood release were affected by vegetation, chamber location, and sample date ( < 0.05). In-row CH fluxes were <0.7 mg CH-C m h until 20 d after flooding (DAF) and <1.0 mg CH-C m h from between-row and bare soil until 41 DAF and were unaffected by fertilization over time. The largest weekly measured CH flux (31.9 mg CH-C m h) was observed from in-row rice at 41 DAF. Post-flood-release CH fluxes were affected by vegetation, fertilization, chamber placement, and sample date ( < 0.05) and accounted for approximately 3 to 7% of the season-long CH emissions. Methane emissions averaged 195 kg CH-C ha per growing season and were unaffected by fertilization. Direct measurement of CH emissions from drill-seeded, delayed-flood rice grown on a silt-loam soil will improve the accuracy of assessments of the carbon footprint and long-term sustainability of rice.

Field Validation of N-STaR for Rice Produced on Silt Loam Soils in Arkansas

To facilitate the incorporation and understanding of the Nitrogen Soil Test for Rice (N-STaR), field validation studies were implemented to evaluate the ability of N-STaR to predict the field-specific N rates required to maximize rice yield on silt loam soils in Arkansas. Before flooding, soil samples to a 45-cm depth were taken and analyzed by N-STaR, a direct steam distillation procedure. These field trials compared N rates from three calibration curves, developed to predict 90, 95, and 100% relative grain yield (RGY), with the standard recommendation for rice (Oryza sativa L.) grown on silt loam soils (168 kg N ha−1). Nitrogen fertilizer rates predicted from the three calibration curves ranged from 22 to 252 kg N ha−1. Rice grain yields fertilized with N rates from the N-STaR 90% RGY curve were equal to or greater than the standard recommendation for nine of the 14 sites. Grain yields for rice receiving the N-STaR 95% RGY N rates were equal to or greater than the standard recommendation for 13 of the 14 sites. Similarly, rice yields obtained from the N-STaR 100% RGY curve were equal to or greater than the standard N rate at all of the study sites. Despite visual differences in rice height and color, there were little to no differences in rice yield. These results indicate the importance of field-scale demonstration trials of the N-STaR technology to educate producers, consultants, and extension personnel before full release of this soil-based N test for rice grown on silt loam soils.

Soil Depth Coupled with Soil Nitrogen and Carbon can Improve Fertilization of Rice in Arkansas

Success of alkaline hydrolyzable nitrogen (AHN) to predict N fertilizer needs when soils were sampled over the effective rooting depth of the crop rekindled an interest in more traditional soil procedures including soil total nitrogen (STN) and total carbon (STC). The benefits of a N soil test that can accurately predict N fertilizer needs are not solely about optimizing economic or agronomic returns, but include making environmentally sound N fertilization decisions. This paper presents the results of a study assessing the ability of STN and STC to predict the N fertilizer needs of direct‐seeded, delayed‐flood rice (Oryza sativa L.) produced on silt loam soils in Arkansas. Twenty‐five N response trials were conducted from 2004 to 2008 to correlate STN and STC with rice response parameters such as total nitrogen uptake (TNU), check plot grain yield, and percent relative grain yield (RGY) and calibrate STN and STC to predict the fertilizer N rate required to achieve 95% RGY. Relationships with the selected parameters were evaluated for both methods over a series of soil depth increments using linear regression models. Soil TN was significantly and positively correlated with all rice response parameters except check plot grain yield at the 15‐ to 30‐ and 45‐ to 60‐cm depths. Coefficients of determination were greatest for percent RGY at the 0‐ to 45‐ cm depth for STN (r2 = 0.62) and STC (r2 = 0.33). Calibration of the fertilizer N rate to achieve 95% RGY mimicked correlation of rice response parameters with soil depth, but with higher r2 values. The highest coefficients of determination were observed in the 0‐ to 45‐cm depth where STN explained 74% and STC explained 54% of the variability in the fertilizer N rate required to achieve 95% RGY. These relationships indicate the importance of proper sampling depth for successful correlation and calibration of soil analytical methods.

Predicting Nitrogen Fertilizer Needs for Rice in Arkansas Using Alkaline Hydrolyzable-Nitrogen

The immediate profitability and long-term sustainability of domestic crop production have been threatened by increasing N fertilizer costs. Currently, there is no soil test which can accurately predict the N fertilizer needs of direct-seeded, delayed-flood rice (Oryza sativa L.) produced on silt loam soils in Arkansas. Fertilizer N recommendations could be improved substantially with a calibrated soil N test, while also lowering potential environmental impacts. Twenty-five N response trials were conducted between 2004 and 2008 to correlate alkaline-hydrolyzable N (AH-N), as quantified by the Illinois Soil N Test (ISNT) and direct steam distillation (DSD), with rice response parameters such as total N (TN) uptake, check plot grain yield, and percentage of relative grain yield (RGY) and calibrate AH-N to predict the fertilizer N rate required to achieve 95% RGY. Relationships with the selected parameters were evaluated for both methods over a series of soil depth increments that included 0 to 15, 15 to 30, 30 to 45, 45 to 60, 0 to 30, 0 to 45, and 0 to 60 cm using linear regression models. Alkaline hydrolyzable-N was significantly and positively correlated with all rice response parameters except check plot grain yield and percentage of RGY using AH-N at the 45- to 60-cm depth. Coefficients of determination were greatest for percentage of RGY at the 0- to 30- and 0- to 45-cm depth for the ISNT (r2 = 0.57) and DSD (r2 = 0.73), respectively. Calibration of the fertilizer N rate to achieve 95% RGY resulted in similar trends as the correlation of rice response parameters, but with higher r2 values. Alkaline hydrolyzable-N explained 68 and 89% of the RGY variability in calibration for the ISNT using the 0- to 30-cm depth and the DSD using the 0- to 45-cm depth, respectively. These successful calibrations can be attributed to the N dynamics that exist in direct-seeded, delayed-flood rice production systems and identification of the proper sampling depth.

Winter Wheat Yield Response to a Urea Amended with a Urease Inhibitor and Fertilization Time

Amending urea with a urease inhibitor may be of benefit in reducing NH losses and increasing winter wheat (Triticum aestivum L.) grain yield. Our primary objective was to evaluate wheat yield as affected by urea amended with and without the urease inhibitor Agrotain applied at four different times at a suboptimal N rate. A secondary objective was to evaluate wheat yield response to N rate across four N application times. Six trials were established on silt loam soils in eastern Arkansas with 75 lb N/acre as urea and Agrotain-treated urea applied from mid-February through early April. Five trials also included 125 lb N/acre as Agrotain-treated urea to evaluate wheat yield response to N fertilization rate and time. Averaged across 24 N applications, wheat fertilized with Agrotain-treated urea produced yields that were 3% greater than urea alone. Categorizing the N source yield differences for each fertilization event showed that Agrotain-treated urea increased wheat grain yields by 0%, 6.9%, 10.3%, and 27.1% above that of wheat fertilized with urea for 14, 5, 3, and 2 of the 24 fertilization events, respectively.. Wheat receiving 125 lb N/acre produced yields that were 7% to 15% greater than wheat receiving 75 lb N/acre at four of five sites. Wheat yield response to N application time depended on site-year and suggested that N should be applied before Feekes stage 6.

Phosphorus and trace metal dynamics in soils amended with poultry litter and granulates

AbstractEnvironmental sustainability of animal agriculture is strongly dependent upon development of approaches to minimize the potential environmental impacts of applying animal manures. The excess manure and its nutrients (primarily phosphorus) in intensive animal production regions may need to be exported to other areas to comply with increased regulations on manure management. In our previous study we generated a variety of granulated products from poultry litter to achieve export of excess litter from the southwestern Ozarks, AR, USA. Our objective in the present study was to determine the effect of the application of poultry litter and granulated litter products on phosphorus (P), arsenic (As), copper (Cu) and zinc (Zn) dynamics in two Arkansas soils (Dewitt silt loam and Hector sandy loam). Poultry litter and granulated products were mixed with the surface horizon (0–15 cm) of soils at two application rates: P‐based (100 kg total P per hectare) and N‐based (160 kg plant‐available N per hectare). Soil–litter mixtures were incubated at 25 °C for 21 days. Sub‐samples were removed at 1, 7 and 21 days to determine the solubility and availability of P, As, Cu and Zn in soils. Results suggest that when litter was applied at 100 kg total P per hectare, contents of P, As, Cu and Zn were significantly greater in the soils amended with litter and granulated products than in the control (soil alone). However, the contents of P, As, Cu and Zn did not significantly differ in the soils amended with either normal litter or granulated litter products at total P or plant‐available N‐based application rates. This suggests that poultry litter granulation is a sound management practice that can be used to reduce concerns with fresh litter transport and potentially improve P and trace element balances in intensive poultry production regions, especially when applied on a plant‐available N basis.

Effect of Loblolly Pine Root Pruning on Alley Cropped Herbage Production and Tree Growth

Tillage to disrupt (prune) tree roots is an intensive practice which could improve herbage productivity at the crop–tree interface by reducing competition for water. We compared tillage effects on 9‐ to 11‐yr‐old loblolly pine (Pinus taeda L.) growth and herbage yields of annual ryegrass (Lolium multiflorum Lam.) and pearl millet [Pennisetum glaucum (L.) R. Br.] on a fragipan soil in Arkansas. Alley crops were rotationally grown in a 9.7‐m wide alley (main plot) between bordering trees on one of three tillage treatments: control (surface tillage), rip followed by surface tillage, and trench plus root barrier followed by surface tillage. Topsoil water in May through September, herbage mass, and nutritive value were measured for each crop for 2 or 3 yr in three subplots systematically arrayed (north, middle, and south) across the alley. Diameter at breast height (DBH, measured 1.3 m above soil surface) and height of border trees were measured annually. Trenching resulted in a more uniform distribution of topsoil water among subplots compared to the other tillage treatments. Annual ryegrass yield did not show a tillage response, but pearl millet yielded more herbage in the rip (6760 kg ha−1 in 2003) and trench (3300 kg ha−1 in 2005) than the control treatment (4990 and 1260 kg ha−1 for 2003 and 2005, respectively). Ripping and trenching significantly reduced loblolly pine DBH and height compared to the control. Similarly configured alley cropping practices probably have little potential for annual herbage production even with root pruning.

Land Use Effects on Runoff and Water Quality on an Eastern Arkansas Soil Under Simulated Rainfall

ABSTRACT Over the past century, a significant proportion of the native grasslands that once occupied much of the middle third of the United States have been converted to cultivated agriculture, causing short- and long-term variations in soil physical and hydraulic properties that influence runoff-infiltration partitioning and runoff water quality. Eastern Arkansas is highly agriculturally productive when irrigated. However, the long history of irrigated agriculture and more recent shifts in rainfall patterns during the growing season have resulted in regional groundwater aquifer depletion with minimal regional recharge. The objective of this study was to evaluate the effects of land use on soil physical properties, runoff-infiltration partitioning, and runoff water quality on a typical agricultural soil in the Mississippi River Delta region of eastern Arkansas. Small-plot rainfall simulations were conducted on an Immanuel silt loam, (fine-silty, mixed, active, thermic, Oxyaquic Glossudalf) in plots (1.5 × 2 m) under native tallgrass prairie (PR) and two cultivated agroecosystems, ridge-tillage (RT), and conventional-tillage (CN). Residue cover was greatest in the PR and lowest in the CN system and differed significantly (p < 0.05) among all three land uses. However, runoff from the two agroecosystems did not differ, averaging 87% of the total amount of water applied, but both were significantly greater (p < 0.05) than that from the PR system, which averaged 62% of the total amount of water applied. Runoff turbidity and suspended solid concentration and load were greater (p < 0.05) from the CN than from the RT or PR systems. The CN system also had the greatest (p < 0.05) total P concentration and load, but the RT system produced runoff with the greatest (p < 0.05) soluble reactive P concentration and load of the three systems. Results indicate that land use and the degree of soil disturbance significantly affects runoff-infiltration partitioning and runoff water quality on this typical eastern Arkansas agricultural soil. Should results prove consistent on other regional soils, further depletion of local aquifers and degradation of surface water quality will likely continue if more sustainable agricultural practices are not increased.

Bermudagrass Yield Response to Nitrogen and Potassium Fertilization in Northwest Arkansas

Potassium performs a vital role in maintaining yield potential and stand persistence of bermudagrass (Cynodon dactylon L.) making proper fertilization critical for sustainable hay production. Our primary objective was to demonstrate how N and K fertilizer rates influence bermudagrass yield and soil-test K across a four-year period. Each year, N was applied at 180 and 300 lb/acre in three equal split applications in combination with K2O at 0 and 180 lb/acre. Potassium fertilization maintained soil-test K between 157 to 160 ppm (optimum). When no K was applied, soil-test K declined to 62 ppm (low) in fall 2007 following the fourth year of study. On average, forage yields were increased 25% by increasing N rate from 180 to 300 lb of N per acre/year and 12% by increasing K rate from 0 to 180 lb of K2O per acre/year, respectively. Forage yield per unit of N fertilizer also decreased from 42 to 36 lb of forage per pound of N when no K was applied. Proper K fertilization is essential for maximizing forage utilization of N fertilizer and maintaining soil K fertility on low cation exchange capacity soils in northwestern Arkansas.

Relationship between major soil properties and culturable microorganisms affecting CH4 and N2O dynamics in rice soils

Microorganisms associated with methane (CH4) and nitrous oxide (N2O) dynamics were studied in eight rice (Oryza sativa L.) soils by culture-dependent most probable number (MPN) methods. Enumeration of methanogens showed that acetoclastic methanogens (104 to 109 cells g−1) outnumbered lithotrophic methanogens (103 cells g−1). Serological analysis indicated that type II methanotrophs belonging to Methylosinus and Methylocystis genera are probably the dominant CH4-oxidizing communities. For chemolithotrophic nitrifiers, nitrite oxidizers outnumbered ammonium oxidizers in most of the studied soils. The populations of both the acetoclastic methanogens (p = 0.05) and methanotrophs (p = 0.06) exponentially increased with the soil pH. Soil denitrifier populations (in a range of 103 to 106 cells g−1) exponentially decreased as soil C content increased (p = 0.03). Nitrifier and denitrifier populations generally showed a similar trend of variation with soil C/N ratio. The largest nitrifier populations were found in the Texas soil (C/N = 13.9), and largest denitrifier population in the Arkansas soil (C/N = 13.1). The relationships between the studied microbial groups and major soil properties help to understand the dynamics of CH4 and N2O production and consumption in soils.