Dennis L. McCallister

Organic carbon quantity and forms as influenced by tillage and cropping sequence

Abstract Soil organic matter and its chemical fractions have a profound impact on soil chemical and physical properties. In turn, the effect of management (cropping and tillage) on the quantity and chemical properties of soil organic matter can be substantial. The objective of this study was to compare the effects of specific tillage regimes and crop sequences commonly used in the central Great Plains of the United States on the quantity, quality, and distribution with depth of soil organic carbon (SOC). Soils were sampled in 1 cm or 2 cm increments to a depth of 10 cm from experimental field plots on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll). The plots had been under 6 continuous tillage regimes since 1978 and cropped to continuous corn, continuous soybean, or corn‐soybean in rotation since 1985. Soils were analyzed for total SOC, fulvic acid (FA) carbon, and humic acid (HA) carbon. No‐till and continuous corn (Zea mays L.) management generally had the highest SOC, with a sharp reduction in SOC below 2 cm. Only no‐till increased FA, which also decreased with depth, especially between 2 and 4 cm. Humic acid concentration was highest under continuous corn but was unaffected by tillage. Humic acid also was highest in the 1‐ to 2‐cm increment of continuous corn. Two ratios which are used as indices of degree of humification, HA/FA and (HA+FA)/SOC, gave different estimates of the effect of management. Only continuous com increased HA/FA, suggesting increased humification. No treatment affected (HA+FA)/SOC. Overall, continuous corn and no‐till contributed the greatest amounts of residue and maintained a soil environment conducive to preserving the resulting organic matter. These management options increase not only total SOC, but also alter the quality of that SOC as measured by HA and FA. These changes in SOC characteristics may have implications for long‐term soil quality and soil productivity.

Availability and fractionation of phosphorus in sewage sludge-amended soils

A laboratory incubation study was conducted with the objective of determining the effects of time, temperature, and soil properties on availability and chemical fractions of phosphorus (P) in sewage sludge-amended soils. Anaerobically digested sewage sludge was mixed with three soils (Crofton silty clay loam, Moody silty clay loam, and Thurman sandy loam) at a rate equivalent to 80 Mg sludge ha−1. The mixtures were incubated at 25 and 37°C for up to 120 days. Phosphorus in sewage sludge-treated soils was extracted with iron-oxide impregnated filter paper strips (strip-P). Phosphorus also was fractionated chemically into four components by sequential extraction. Phosphorus concentration in all fractions increased with sludge application. Strip-P concentration was higher at 25°C in all soils than at 37°C over the entire period of incubation. Soluble-P was greatest in sandy Thurman soil at both temperatures over all incubation times. A sharp increase in non-occluded P (NOC-P) concentration occurred in all soils with time at both temperatures. Occluded P (OC-P) in all soils decreased more rapidly with time at 37°C than at 25°C. Calcium-P (Ca-P) concentration was unaffected by time and was highest in calcareous Crofton soil. Soil texture and the presence of carbonates strongly influence the fate of P from applied sewage sludge. It was concluded, based on time trends that sludge as a P source on a P-limited soil should be applied well before the period of maximum plant demand. Elevated temperature (37°C) typical of mid-summer, promotes depletion of more available (strip-P and soluble P) fractions compared with lower temperature (25°C). *Contribution of the University of Nebraska Agric. Res. Div., Lincoln, NE as paper no. 13093.

Fly ash as a liming material for corn production

Fly ash produced as a by-product of subbituminous coal combustion can potentially serve as an alternative liming material without negatively affecting corn (Zea mays L.) production in areas where use of conventional liming materials can be uneconomical due to transportation costs. A study was conducted to determine if fly ash produced from the Nebraska Public Power District Gerald Gentleman Power Station located in Sutherland, NE could be used as an alternative liming material. This study had the following objectives: 1) compare the effects of fly ash on soil pH with other common agricultural lime materials; 2) determine the effects of fly ash on percent Al saturation in selected soils; and 3) determine the effects of fly ash on corn grain yields. Combinations of dry fly ash (DFA), wet fly ash (WFA), beet lime (by-product of sugar beet [Beta vulgaris L.] processing) (BL), and agricultural lime (AGL) were applied at rates ranging from 0.43 to 1.62 times the recommended lime rate to plots on four acidic soils (Anselmo fine sandy loam, Hord fine sandy loam, Holdrege sandy loam, and Valentine fine sand). Soil samples were collected to a depth of 0.2 m from plots and analyzed for pH before lime applications and twice periodically after lime application. The Hord and Valentine soils were analyzed for exchangeable Ca, Mg, K, Na, and Al for determination of percent Al saturation on selected treatments and sampling dates. Corn grain yields were determined annually. Depending on the lime source, soil pH increased in the upper 0.2 m of soil the year after application compared with the pre-application soil pH values for some sites and years, whereas in others there were no significant increases in pH. However, all lime materials at each site failed to raise the soil pH in the upper 0.2 m of all the treatments and soil types to the target pH of 6.5. Fly ash and AGL treatments did not significantly increase corn grain yields compared with the control on the Anselmo, Hord, and Holdrege soils. At the Hord site, AGL and DFA significantly reduced percent Al saturation by 3.1% and 3.7% compared with the control 5 years after application, respectively. Fly ash did not negatively affect corn grain yields compared with AGL. Yields were 12,472, 12,233, and 12,177 kg ha−1 for the Anselmo, Holdrege, and Hord sites averaged over all treatments and years. The lack of yield response to lime additions was potentially a result of lime materials not raising the soil pH to sufficient levels, higher subsoil pH values, or the exchangeable Al not being high enough prior to lime material application to reduce grain yields in these soils. We conclude that the fly ash utilized in this study and applied at rates in this study, increases soil pH comparable to agricultural lime and is an appropriate alternative liming material.

Manure source effects on soil phosphorus fractions and their distribution

Manure can be applied to soils as a major source of nutrients such as phosphorus (P). The environmental chemistry and plant availability of applied soil P are influenced by the chemical forms of P in the solid phase. The objectives of this study were to determine the amounts, availability, and chemical forms of P in a Hord silt loam soil (fine-silty, mixed, mesic Pachic Haplustoll) amended with beef and sheep feedlot, turkey house, and composted paunch manures. Manures were applied in alternate years from 1991 to 1997. In 1996, after three manure applications, total P in the manured 0-15-cm soil depth increased up to 14%and inorganic P up to 25% compared with nonmanured. Bray and Kurtz 1-P in 0-15-cm soil depth was almost 4 times greater in manured soil than in nonmanured (47.2 mg P kg−1 soil versus 12.7 mg P kg−1 soil).Soluble P was more than 4 times higher in the 0-15-cm depth of manured soils (13.9 mg P kg−1 soil) compared with nonmanured soil (3.2 mg P kg−1 soil). Nonoccluded P was more than 1.5 times higher in manure-amended soils (78.4 mg P kg−1 soil) than in nonmanured (46.8 mg P kg−1 soil) in the 0-15-cm soil depth. Occluded P in 0-15-cm soil depth was greatest in turkey manure-amended soil (45.2 mg P kg−1 soil), followed by beef manure-amended soil (36.7 mg P kg−1 soil). In 1997, all P fractions were higher in 0-7.5-cm depth than any other amended soil depth, and the same general trends among fractions held as in 1996. Although animal source of applied manure does have some influence on P fractionation and depth distribution, most P remains in the zone of application, emphasizing the need for conservation of the surface soil.

Delineating site-specific management zones for pH-induced iron chlorosis

Iron chlorosis can limit crop yield, especially on calcareous soil. Typical management for iron chlorosis includes the use of iron fertilizers or chlorosis tolerant cultivars. Calcareous and non-calcareous soil can be interspersed within fields. If chlorosis-prone areas within fields can be predicted accurately, site-specific use of iron fertilizers and chlorosis-tolerant cultivars might be more profitable than uniform management. In this study, the use of vegetation indices (VI) derived from aerial imagery, on-the-go measurement of soil pH and apparent soil electrical conductivity (ECa) were evaluated for their potential to delineate chlorosis management zones. The study was conducted at six sites in 2004 and 2005. There was a significant statistical relationship between grain yield and selected properties at two sites (sites 1 (2005) and 3), moderate relationships at sites 2 and 4, and weak relationships at site 5. For sites 1 (2005) and 3, and generally across all sites, yield was predicted best with the combination of NDVI and deep ECa. These two properties were used to delineate chlorosis management zones for all sites. Sites 1 and 3 showed a good relationship between delineated zones and the selected properties, and would be good candidates for site-specific chlorosis management. For site 5, differences in the properties between mapped zones were small, and the zones had weak relationships to yield. This site would be a poor candidate for site-specific chlorosis management. Based on this study, the delineation of chlorosis management zones from aerial imagery combined with soil ECa appears to be a useful tool for the site-specific management of iron chlorosis.

COAL FLY ASH AS AN ACID-REDUCING SOIL AMENDMENT AND ITS SIDE-EFFECTS

Coal combustion by-products may offer significant benefits if used properly to neutralize soil acidity, but unintended release of trace components must be considered. A study was conducted with two objectives: (i) To compare the efficacy of two different preparations of fly ash with that of conventional ag lime for their ability to raise soil pH and reduce exchangeable Al; and (ii) to determine if the Al applied in fly ash produces detrimental changes in soil properties following subsequent acidification. Either fly ash in one of two forms, or conventional ag lime, was applied to three acid soils (Anselmo loam, Valentine sandy loam, and Holdrege sandy loam) in a pot study at rates equal to 0.5, 1.0, and 1.5 times the soils’ lime requirements. Soils were equilibrated in triplicate at approximately 33 kPa water potential in the greenhouse for 315 days (liming phase), during which pH and exchangeable aluminum (Al) were measured. The soils were then acidified under similar conditions for 439 days (acidification phase) by adding dilute acid solution to simulate management-induced acidification, and pH and exchangeable Al were then measured again. Both fly ashes and ag lime were effective in raising soil pH by up to 1.2 units and in reducing exchangeable Al by up to 5.6 mg kg−1. Two-way interactions involving soil, liming material, and rate of application produced different results for combinations of these factors. All amendments helped the soils resist subsequent acidification compared with zero-rate treatments but differed based on the 3-way combinations of soil, liming material, and rate of application. We concluded that overliming (as indicated by exceeding the target pH of 6.5) is a problem with all liming materials on the coarsest soils, suggesting that lime calibration should be re-examined. The fly ash materials seem to contribute to soil exchangeable Al after acidification, but this contribution is inconsequential if soil pH values are maintained at agronomic optima.

Mobility of aniline, benzoic acid, and toluene in four soils and correlation with soil properties.

Soil properties and retention mechanisms affecting the relative mobility of aniline, benzoic acid, and toluene in Cecil sandy loam (clayey, kaolinitic, thermic Typic Hapludults), Holdredge silt loam (fine-silty, mixed, mesic Typic Argiustolls), Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudolls), and Valentine fine sand (mixed, mesic Typic Ustipsamments) were delineated in laboratory studies. The effect of the synthetic organic compounds (SOCs) was also determined on effective organic campounds (SOCs) was also determined on effective cation exchange capacity (ECEC) of the soils. Benzoic acid was most mobile of the SOCs but was retained in the Cecil soil by hydrogen bonds to Fe oxides. Toluene was least mobile and probably was hydrophobically sorbed to all soils. Aniline was electrostatically retained in protonated form to organic and inorganic exchange sites of the soils and reduced the ECEC of aniline-treated Holdredge and Sharpsburg soils.

Effect of potassium salts on alleviation of lime-induced chlorosis in soybean

Abstract Studies were conducted to determine the efficacy of K salts in alleviating lime‐induced chlorosis. Greenhouse studies using a Gibbon silt loam [fine‐silty, mixed (calcareous), mesic Typic Haplaquoll] and a 1: 1 mixture of Gibbon soil and washed sand were conducted with KCl, KNO3, K2SO4, K2HPO4, or KHCO3 applied at rates of 0, 250, and 500 mg K/kg soil. An FeEDDHA treatment was included for comparison. Similar studies were conducted at two field sites known to produce lime‐induced chlorosis. Potassium salts were applied at 0, 20, and 40 g K/m of row. In the greenhouse, plants treated with KCl, KNO3, and K2SO4 on Gibbon soil were less chlorotic than controls or plants treated with K2HPO4, or KHCO3. No K treatment totally alleviated chlorosis except FeEDDHA. Chlorophyll correlated positively with chlorosis rating. No relationship was found between leaf Fe uptake and chlorosis. Plants grown in soil/sand exhibited no chlorosis and had lower Fe uptake than plants grown in Gibbon soil. Thus chlorosis wa...

Soil temperature and fumigation effects on plant phosphorus uptake and related microbial properties

Abstract Early season problems with growth of corn (Zea mays L.) under cool, wet conditions prompted a study of the effects of soil and environmental conditions on mineralization and plant uptake of phosphorus (P). Our objective was to determine the effect of soil test P, temperature, and soil fumigation on soil P availability and uptake during early corn growth. Corn was grown in growth chambers at temperatures of 14°C or 25°C. Soils were a high‐P Hastings silty clay loam (fine, montmorillonitic, mesic Udic Argiustoll) and a low‐P Sharpsburg clay loam (fine, montmorillonitic, mesic Typic Argiudoll). Plants grew for up to 42 d either in soil which had been fumigated with methyl bromide to reduce microbial populations or left unfumigated. We harvested whole pots for soil and plant analysis at 1, 14, 28, and 42 d after planting. Biomass carbon (C) and biomass P were lower in fumigated soils and biomass C increased with time. Fumigation increased Bray Pl‐extractable P at all times. Phosphatase activity and m...

SOIL CHROMATOGRAPHIC COLUMNS TO ASSESS THE MOBILITY OF SYNTHETIC ORGANIC COMPOUNDS

Soil thin-layer chromatography (TLC) is useful for rapid determination of the relative mobility (RF) of herbicides and other synthetic organic compounds (SOC) in soil but fails for volatile compounds. An alternate method using small soil chromatographic columns was developed to minimize SOC volatilization while maintaining the essential characteristics of soil TLC. The column method utilizes soil contained in narrow diameter (4 mm I.D.) glass tubes. Soil TLC and soil chromatographic columns were used to determine the relative mobility of aniline and benzoic acid in unaltered and organic-free Cecil, Holdrege, Sharpsburg, and Valentine soils. Both methods indicated that benzoic acid was more mobile than aniline in most of the soils. Variations in RF values between methods generally were small and suggested that either method was acceptable for laboratory estimation of the relative mobility of SOC with low vapor pressures. Differences in RF values may be attributed to differences in soil preparation, as TLC plates were prepared by drying thinly spread soil slurries while soil chromatographic columns contained powdered soil. Soil chromatographic columns allowed determination of RF values for toluene, which is too volatile for soil TLC. Toluene was less mobile than benzoic acid in all soils, and less mobile than aniline in the unaltered Valentine soil and in the organic-free soils.