C. E. Wilson

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.

Chemical estimation of nitrogen mineralization in paddy rice soils: II. Comparison to greenhouse availability indices

Abstract A simple nitrogen (N) availability index is needed to improve fertilizer recommendations and, thus, reduce the opportunity for over‐ or under‐fertilization of rice (Oryza sativa L.). Consequently, a study was conducted to develop a chemical extraction procedure that will estimate the potentially mineralizable N made available to rice during the growing season. The ammonium‐nitrogen (NH4+‐N) extracted with 0.05M KMnO4 (potassium permanganate) + 0.5M H2SO4 (sulfuric acid) (acidified KMnO4), 0.05M K2Cr2O7 (potassium dichromate) + 0.5M H2SO4 (acidified K2Cr2O7), 1.0M HC1 (hydrochloric acid), and 0.5M C2H2O4 (oxalic acid) was compared to total N uptake (TNU) by ‘Newbonnet’ rice grown under greenhouse conditions. Comparisons were also made between distillation of the entire soil‐extractant suspension (TOT) and distillation of the supernatant after centrifugation (SUP). Anaerobic incubation for 7, 14, and 21 d was also included for comparison. The indices evaluated decreased in ability to predict TNU in...

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.

Chemical estimation of nitrogen mineralization in paddy rice soils. I: comparison to laboratory indices

Abstract A reliable, rapid procedure for estimating native soil nitrogen (N) mineralization potential in paddy rice (Orysa sativa L.) has eluded researchers. While several have been proposed, no technique has been sufficiently reproducible to be implemented in any soil testing program. Therefore, the objective was to develop a chemical extraction procedure as an index to estimate N mineralization in silt.loam rice soils of the Southern United States Rice Belt. Samples of silt loam soils were collected from strategic locations throughout the rice‐growing region of Arkansas during 1990 and 1991. Anaerobic incubations were performed as an index of potentially mineralisable N. Extraction with acidified potassium permanganate (KMnO4), acidified potassium dichromate (K2Cr2O7), hydrochloric acid (HCl), and oxalic acid [(COOH)2], were evaluated at extractant:soil ratios ranging from 5:1 to 1:1. Also, distillation of centrifuged extracts (SUP) was compared to distilling the entire soil‐solution suspension (TOT). T...

Measurement of Technical, Allocative, Economic, and Scale Efficiency of Rice Production in Arkansas Using Data Envelopment Analysis

Data envelopment analysis is used to calculate technical, allocative, economic, and scale efficiencies for fields enrolled in the University of Arkansas Rice Research Verification Program. The results reveal most fields have high technical and scale efficiencies, implying inputs are used in minimum levels necessary to achieve given output levels and fields are close to optimal in size. However, most fields exhibit allocative and economic inefficiencies and do not use inputs in the right combinations necessary to achieve cost minimization. Tobit analysis indicated allocative and economic efficiencies could be improved with better variety selection and better irrigation management.

Differentiation between osmotic injury and chloride toxicity of rice seedlings grown under saline conditions

Abstract Rice (Oryza sativa, L.) is most sensitive to salinity injury as a seedling. Information describing the effects of salinity on the seedling rice plant is limited. Therefore, the current study was conducted to determine if salinity injury to rice seedlings is the result of toxic levels of chloride, or if a change in osmotic potential interferes with the plants ability to absorb water and nutrients. Rice was grown in controlled environmental conditions through the seedling growth stage. In hydroponic culture with a 50% Hoaglands solution, the rice was exposed to osmotic tensions of 0, 50, 100, 200, 400, 800, or 1,600 kPa imposed by either CaCl2 or polyethylene glycol (PEG). The rice was grown for 1 wk following imposition of the osmotic treatments. Visual ratings were then obtained and plants were harvested for dry matter determination and Cl‐ concentration. Shoot weights were lowered for PEG treatments compared to CaCl2. Root weights differed little between CaCl2 and PEG treatments. Root weights ...