Nathan A. Slaton

Carbon and Nitrogen Storage in a Typic Albaqualf as Affected by Assessment Method

Accurate quantification of soil organic carbon (OC) and nitrogen (N) concentrations are necessary to ascertain the effects of land use, crop rotation systems, and management practices on soil C and N sequestration potential. Soil OC and total N were determined by various methods in a Typic Albaqualf under native tallgrass prairie and agricultural soil cropped to a rice (Oryza sativa L.)–soybean (Glycine max L.)–wheat (Triticum aestivum L.)/soybean rotation that has been annually cultivated for 15, 26, and 44 years. Two wet-oxidation methods, the Walkley-Black (WB) and modified Walkley-Black (mod WB), and high-temperature combustion using a Carlo-Erba and LECO analyzer were used to determine the effects of assessment method on soil OC concentration, while the high-temperature combustion method using the Carlo-Erba and LECO analyzer were used to determine the effects of assessment method on total soil N concentration. Soil OC and total N concentrations determined by high-temperature dry combustion using the Carlo-Erba and LECO analyzers did not differ significantly. Soil OC concentrations determined by the modWB method were generally significantly higher than those from the WB or high-temperature combustion methods. Despite significant linear correlation (r>0.74;p<0.001) between soil OC concentrations by wet-oxidation and dry-combustion methods, assessment methodology significantly affected interpretations regarding changes in soil OC storage over time. The results of this study indicate that the choice of assessment methodology is a critical decision for the accurate quantification of soil OC concentration, content, and change over time.

Root growth and distribution of two short-season rice genotypes

Root growth dynamics of lowland rice (Oryza sativa L.) throughout the growing season are poorly understood. A field experiment was conducted in 1987 to compare root growth and distribution of two rice genotypes at two Arkansas locations on soils with different physical and chemical properties. Two genotypes, ‘Bond’ and an experimental line (RU8701084), were grown on a Captina silt loam (Typic Fragiudults) at Fayetteville, AR, and on a Crowley silt loam (Typic Albaqualfs) near Stuttgart, Ar. Plots contained minirhizotrons oriented at a 45° angle and extended 55 cm (Captina) and 40 cm (Crowley) vertical to the soil surface. Root measurements were taken several times during the season at specific growth stages. Plant height and tiller number were taken at 9 dates at Fayetteville up to physiological maturity. In general, root length (RL) and root length density (RLD) were greater on the Captina soil. Genotypes at both locations reached maximum root growth rates between active tillering and panicle initiation (PI) and maximum RL by early reproduction. Total RL were similar between genotypes on the Captina. However on the Crowley, the mean RL for Bond between the period of early booting and flood removal was an average of 54% greater than for RU8701084. During early reproductive growth at both locations RL plateaued, but then declined during the grain filling process. There was a trend for RU8701084 to contain a greater percentage of its total RL in the top 20 and 10 cm of soil on the Captina and Crowley, respectively, while Bond tended to be a deeper rooted genotype. Bond had a greater RLD at the 20–30 cm depth increment on the Crowley, which contributed to the greater RL. Less than 15% of the total RL of either genotype was measured below 30 cm on the Crowley. In contrast, nearly 25% of the total RL was found at the 30–40 cm depth increment on the Captina. Results showed that rice root growth varied between soils, that root distribution patterns differed between genotypes, and that patterns of root growth changed with changes in plant development.

FIELD AND LABORATORY STUDIES COMPARING NUTRISPHERE-NITROGEN UREA WITH UREA IN NORTH DAKOTA, ARKANSAS, AND MISSISSIPPI

Nitrification and ammonia volatility are two important impediments to nitrogen (N) use efficiency and crop uptake around the world. Nutrisphere® is a relatively new product whose manufacturer claims both nitrification and urea volatilization inhibiting properties. Urea coated with Nutrisphere is and the resulting fertilizer is called Nutrisphere®-N urea, or Nutrisphere-N (NSN). Eight field studies on spring (Triticum aestivum L.) or durum [T. turgidum L. subsp duram (Desf.) Husn.] wheat in North Dakota, three field studies in Mississippi/Arkansas on rice (Oryza sativa L.), four laboratory experiments in North Dakota and one in Arkansas were conducted to determine the nitrification and urea volatilization inhibiting ability of NSN compared with urea alone. Results of field and laboratory experiments revealed that the product has no nitrification or urea volatilization inhibiting properties at the recommended rates and spring wheat and rice did not benefit from the application of NSN to urea.

Evaluation of Several Indices of Potentially Mineralizable Soil Nitrogen

Abstract A routine soil test that accurately predicts soil nitrogen (N) mineralization has long eluded researchers. Soil incubations, which are not practical for routine soil testing, are the only methods that have proven successful. Although several quick analytical methods have been proposed, no one method has correlated consistently enough to be implemented into a soil‐testing program. The objective of this study was to compare proposed quick analytical procedures with the amount of ammonium (NH4)‐N mineralized after a 14‐d anaerobic incubation. The analytical methods of interest were i. applying a mild acid oxidation to the soil using acidified permanganate; ii. analyzing a 1 M potassium chloride (KCl) soil extract in the ultraviolet (UV) spectrophotometric range before and after nitrate (NO3) removal with Devardas alloy; and iii. quantifying soil amino sugar‐N content using the Illinois soil N test (ISNT) diffusion method. Fifty agricultural soils with different physical and chemical properties were utilized in this study. All methods displayed significant relationships with the anaerobic incubation procedure; however, some methods displayed higher, more acceptable, coefficients of determination. The ISNT and UV spectrophotometry measurement at 210 nm after NO3 removal failed to accurately estimate N mineralization (R2=0.45 and 0.31, respectively). The acid oxidation procedure and UV measurement at 260 nm of soil extracts before NO3 removal produced better results with coefficients of determination of 0.58 and 0.56, respectively. We suspect the ability of some methods to predict N mineralization was hindered because of the wide variety of geographic locations from which the soils were collected. Additional analyses were conducted on a subset of 16 silt‐loam soils from Arkansas. The coefficient of determinations increased for each method: acid oxidation procedure increased to 0.83, the ISNT increased to 0.71, and the UV method (at 260 nm before NO3 removal) increased to 0.63. If anaerobic incubation is a true indication of N mineralization in the field, the aforementioned methods display promise to correlate with N uptake by field‐grown plant studies when adapted to a specific geographic location and/or soil series.

Short-term Effects of Poultry Litter Form and Rate on Soil Bulk Density and Water Content

Abstract Poultry litter is an organic amendment that has been used successfully as an alternative nutrient source to inorganic, commercial fertilizers. Poultry litter also has the potential to improve other aspects of soil quality. However, few field studies have been conducted to ascertain the effects of poultry litter on soil physical properties. The objectives of this study were to evaluate the short-term effects of poultry litter form (i.e., fresh vs. pelletized) and rate on soil bulk density and water content and early-season stand development in three fine-textured soils of the Mississippi River Delta region of eastern Arkansas that are commonly cropped to rice (Oryza sativa L.). Six litter rates were used representing a range of total nitrogen (N) rates. Soil samples were collected from the 0- to 10-cm depth between four and six weeks after litter application and incorporation for bulk density and volumetric water content determination. Leaf area index was measured as an indicator of early-season stand development. Litter form did not affect soil bulk density, water content, or leaf area index in two silt loams, and a silty-clay soil. In contrast, soil bulk density decreased significantly (p < 0.01) as litter rate increased and leaf area index decreased as bulk density increased in one silt-loam soil, but was unaffected by litter rate in the other silt-loam and silty-clay soil. Litter rate generally did not affect soil volumetric water content, but results indicate that the effects of litter rate may be manifested more at relatively low soil water contents. The results of this study demonstrate that poultry litter has positive short-term effects on physical properties of fine-textured soils. These results are agronomically significant for many crops in terms of the potential for creating a less compacted seedbed for seedling emergence, improved stand development, and ultimately increased crop yields.

Effects of common aerially applied rice herbicides on the plankton communities of aquaculture ponds

Abstract Ten common aerially applied herbicides for rice were tested for possible adverse impacts on pond phytoplankton and zooplankton and critical water quality variables. Treatments simulated direct spraying of ponds and amounts of drift judged able to reach the pond at 1/10 and 1/100 direct rates. The study was conducted in 12, 500-l outdoor pool mesocosms. Pond water from an adjacent baitfish rearing pond was used. Water quality measurements were made prior to application and at 24 and 48 h after application. Commercial compounds tested and direct rates in kg active ingredient ha −1 were clomazone (0.6), thiobencarb (3.4), pendamethalin (1.1), propanil-dry, flowable (4.5), quinclorac (0.6), halosulfuron (0.07), bensulfuron methyl (0.07), triclopyr (0.4), 2,4- d -amine (1.7), and molinate (5.6). In addition, propanil was evaluated in a second application scenario at the same rates and to the same pond water sample as the initial application. Except for propanil, the rice herbicides produced no measurable effect on pond plankton or associated water quality. Following the first application at full rate for propanil, morning oxygen levels were reduced to critical levels (below 3 mg/l) for 2 days. After a second application of propanil at the full and 1/10 rates, oxygen levels were not decreased, although there were significant increases in chlorophyll a and zooplankton concentrations.

Nitrogen Release from Environmentally Smart Nitrogen Fertilizer as Influenced by Soil Series, Temperature, Moisture, and Incubation Method

Environmentally Smart Nitrogen (ESN) is a polymer-coated urea fertilizer with potential to increase crop recovery of fertilizer nitrogen (N). Our research objectives were to characterize ESN N retention across time as affected by soil series, temperature, moisture, and incubation method. A rumen bag containing 38 to 44 mg ESN N was placed in 400 g soil, and the amount of ESN N remaining in prills was measured every 5 d for 40 d. Soil was incubated at 25 °C and 250 g H2O kg−1 soil, except in experiments where soil temperature or moisture was varied. Nitrogen retention in ESN was linear for three silt and sandy loams and curvilinear in two clayey soils with retention declining more rapidly in clayey soils. Soil temperature had the greatest effect on N retention with the rate of ESN N release increasing as soil temperature increased. Near complete release of ESN N was achieved by 40 d with temperatures ≥ 20 °C.

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.

DEVELOPMENT OF A CRITICAL MEHLICH 3 SOIL ZINC CONCENTRATION FOR RICE IN ARKANSAS

Zinc (Zn) fertilizer recommendations for rice (Oryza sativa L.) in Arkansas have been based on soil pH since the 1970s and have not accounted for the residual carryover of previous Zn fertilizer applications. Continuous application of Zn fertilizer to soil in some fields cropped to rice has resulted in very high Mehlich 3 extractable Zn (M3Zn) concentrations in soil and illustrates the need to develop improved recommendations. The objective of this research was to develop a critical M3Zn soil concentration for making Zn fertilizer recommendations to rice. The relationship between relative yield (RY), soil pH, and soil M3Zn concentration was determined from 36 Zn fertilizer studies conducted on silt loam soils between 1992 and 2000. Multiple regression analysis showed that soil pH, M3Zn concentration, and their interaction best described rice yield response to Zn fertilization. When soil pH was >5.5, a yield response to Zn fertilization was possible, but depended on the soils M3Zn concentration. The critical M3Zn concentration required to produce 90% RY, without Zn fertilizer application, for soils with pH values of 6.2, 7.0, and 7.8 was 1.3, 3.5, and 4.2 mg M3Zn kg soil−1, respectively. Results suggest that soil pH and M3Zn concentration should be used together when making Zn fertilizer recommendations for rice to prevent yield loss from Zn deficiency and economic loss from needless Zn fertilizer applications. Zinc fertilization is not needed on soils high in M3Zn concentration, regardless of soil pH, and rice yields could possibly be reduced by application of Zn fertilizer in these fields.

Near-Infrared Reflectance Spectroscopy as a Method for Determining Organic Carbon Concentrations in Soil

Near-infrared reflectance spectroscopy (NIRS) has the potential to be a reliable method for accurately quantifying soil organic carbon (SOC). The objective of this study was to evaluate NIRS as a method for predicting SOC. Partial least squares (PLS) regression was used to predict SOC from soil reflectance values or the first derivative of the reflectance values. Two model validation techniques were evaluated: One was a full cross-validation and in the other 30 percent of the samples were removed from the calibration data set and then tested using the calibrated model. Significant relationships were observed for predicted SOC when compared to laboratory-measured SOC for all models evaluated, regardless of validation technique. The prediction models using the first derivative of the reflectance values outperformed prediction models using the reflectance values alone. In conclusion, NIRS can be used as a quick and accurate method for measuring SOC.