Effect of water and citrate solubility on agronomic effectiveness of acidulated phosphates in three consecutive corn crops

In the process of phosphate rock acidulation, several impure P compounds may be formed along with the desirable Ca and NH4 phosphates. Such compounds normally reduce the content of water-soluble P and thus the agronomic effectiveness of commercial fertilizers. In order to study this problem, a greenhouse experiment consisting of three consecutive corn crops was conducted in samples of a Red-Yellow Latosol (Typical Hapludox) in a completely randomized design (6 x 2 x 2), with four replicates. Six commercial fertilizers were added to 2 kg of soil at a rate of 70 mg kg-1 P, based on the content of soluble P in neutral ammonium citrate plus water (NAC + H2O) of the fertilizers. Fertilizer application occurred either in the original form or leached to remove the water-soluble fraction, either by mixing the fertilizer with the whole soil in the pots or with only 1 % of its volume. The corn plants were harvested 40 days after emergence to determine the shoot dry matter and accumulated P. For the first crop and localized application, the elimination of water-soluble P from the original fertilizers resulted in less bioavailable P for the plants. For the second and third crops, the effects of P source, leaching and application methods were not as evident as for the first, suggesting that the tested P sources may have similar efficiencies when considering successive cropping. The conclusion was drawn that the water-insoluble but NAC-soluble fractions of commercial P fertilizers are not necessarily inert because they can provide P in the long run.

Short and long-term effects of tillage systems and nutrient sources on soil physical properties of a Southern Brazilian Hapludox

Soil tillage promotes changes in soil structure. The magnitude of the changes varies with the nature of the soil, tillage system and soil water content and decreases over time after tillage. The objective of this study was to evaluate short-term (one year period) and long-term (nine year period) effects of soil tillage and nutrient sources on some physical properties of a very clayey Hapludox. Five tillage systems were evaluated: no-till (NT), chisel plow + one secondary disking (CP), primary + two (secondary) diskings (CT), CT with burning of crop residues (CTb), and CT with removal of crop residues from the field (CTr), in combination with five nutrient sources: control without nutrient application (C); mineral fertilizers, according to technical recommendations for each crop (MF); 5 Mg ha-1 yr-1 of poultry litter (wetmatter) (PL); 60 m³ ha-1 yr-1 of cattle slurry (CS) and; 40 m³ ha-1 yr-1 of swine slurry (SS). Bulk density (BD), total porosity (TP), and parameters related to the water retention curve (macroporosity, mesoporosity and microporosity) were determined after nine years and at five sampling dates during the tenth year of the experiment. Soil physical properties were tillage and time-dependent. Tilled treatments increased total porosity and macroporosity, and reduced bulk density in the surface layer (0.00-0.05 m), but this effect decreased over time after tillage operations due to natural soil reconsolidation, since no external stress was applied in this period. Changes in pore size distribution were more pronounced in larger and medium pore diameter classes. The bulk density was greatest in intermediate layers in all tillage treatments (0.05-0.10 and 0.12-0.17 m) and decreased down to the deepest layer (0.27-0.32 m), indicating a more compacted layer around 0.05-0.20 m. Nutrient sources did not significantly affect soil physical and hydraulic properties studied.

Aggregate stability as affected by short and long-term tillage systems and nutrient sources of a hapludox in southern Brazil

The ability of a soil to keep its structure under the erosive action of water is usually high in natural conditions and decreases under frequent and intensive cultivation. The effect of five tillage systems (NT = no-till; CP = chisel plowing and one secondary disking; CT = primary and two secondary distings; CTb = CT with crop residue burning; and CTr = CT with removal of crop residues from the field), combined with five nutrient sources (C = control, no nutrient application; MF = mineral fertilizers according to technical recommendations for each crop; PL = 5 Mg ha-1 y-1 fresh matter of poultry litter; CM = 60 m³ ha-1 y-1 slurry cattle manure; and SM = 40 m³ ha-1 y-1 slurry swine manure) on wet-aggregate stability was determined after nine years (four sampled soil layers) and on five sampling dates in the 10th year (two sampled soil layers) of the experiment. The size distribution of the air-dried aggregates was strongly affected by soil bulk density, and greater values of geometric mean diameter (GMD AD) found in some soil tillage or layer may be partly due to the higher compaction degree. After nine years, the GMD AD on the surface was greater in NT and CP compared to conventional tillage systems (CT, CTb and CTr), due to the higher organic matter content, as well as less soil mobilization. Aggregate stability in water, on the other hand, was affected by the low variation in previous gravimetric moisture of aggregates, which contributed to a high coefficient of variation of this attribute. The geometric mean diameter of water-stable aggregates (GMD WS) was highest in the 0.00-0.05 m layer in the NT system, in the layers 0.05-0.10 and 0.12-0.17 m in the CT, and values were intermediate in CP. The stability index (SI) in the surface layers was greater in treatments where crop residues were kept in the field (NT, CP and CT), which is associated with soil organic matter content. No differences were found in the layer 0.27-0.32 m. The effect of nutrient sources on GMD AD and GMD WS was small and did not affect SI.

Evaluation of Fly Ash Concrete Durability Containing Class II Durability Aggregates, July 1986

Fly ash was used in this evaluation study to replace 15% of the cement in Class C-3 concrete paving mixes. One Class "c" ash from Iowa approved sources was examined in each mix. Substitution rate was based on 1 to 1 basis, for each pound of cement removed 1.0 pound of ash was added. The freeze/thaw durability of the concrete studied was not adversely affected by the presence of fly ash. This study reveals that the durability of the concrete test specimens made with Class II durability aggregates was slightly increased in all cases by the substitution of cement with 15% Class "c" fly ash. In all cases durability factors either remained the same or slightly improved except for one case where the durability factor decreased from 36 to 34. The expansion decreased in all cases.

Interim Guide for Optimum Joint Performance of Concrete Pavements, September 2011

The purpose of this guide is to help practitioners understand how to optimize concrete pavement joint performance through the identification, mitigation, and prevention of joint deterioration. It summarizes current knowledge from research and practice to help practitioners access the latest knowledge and implement proven techniques. Emphasizing that water is the common factor in most premature joint deterioration, this guide describes various types of joint deterioration that can occur. Some distresses are caused by improper joint detailing or construction, and others can be attributed to inadequate materials or proportioning. D cracking is a form of joint distress that results from the use of poor-quality aggregates. A particular focus in this guide is joint distress due to freeze-thaw action. Numerous factors are at play in the occurrence of this distress, including the increased use of a variety of deicing chemicals and application strategies. Finally, this guide provides recommendations for minimizing the potential for joint deterioration, along with recommendations for mitigation practices to slow or stop the progress of joint deterioration.

Substitutable Concrete Pavements: A Manual of Practice, August 2011

Developed as a more detailed follow up at a 2009 briefing document,Building Sustainable Pavement with Concrete, this guide provides a clear, concise and cohesive discussion of pavement sustainability concepts and of recommended practices for maximizing the sustainability of concrete pavements. The intended audience includes decisions makers and practitioners in both owner-agencies and supply, manufacturing consulting and contractor businesses. Readers will find individual chapters with the most recent technical information and best practices related to concrete pavement deign, materials, construction, use/operations, renewal and recycling. In addition, they will find chapters addressing issues specific to pavement sustainability in the urban environment and to the evaluation of pavement sustainability.

Sustainable Concrete Pavements: A Manual of Practice, January 2012

Sustainable Concrete Pavements: A Manual of Practice is a product of the National Concrete Pavement Technology Center at Iowa State University’s Institute for Transportation, with funding from the Federal Highway Administration (DTFH61-06-H-00011, Work Plan 23). Developed as a more detailed follow-up to a 2009 briefing document, Building Sustainable Pavement with Concrete, this guide provides a clear, concise, and cohesive discussion of pavement sustainability concepts and of recommended practices for maximizing the sustainability of concrete pavements. The intended audience includes decision makers and practitioners in both owner-agencies and supply, manufacturing, consulting, and contractor businesses. Readers will find individual chapters with the most recent technical information and best practices related to concrete pavement design, materials, construction, use/operations, renewal, and recycling. In addition, they will find chapters addressing issues specific to pavement sustainability in the urban environment and to the evaluation of pavement sustainability. Development of this guide satisfies a critical need identified in the Sustainability Track (Track 12) of the Long-Term Plan for Concrete Pavement Research and Technology (CP Road Map). The CP Road Map is a national research plan jointly developed by the concrete pavement stakeholder community, including Federal Highway Administration, academic institutions, state departments of transportation, and concrete pavement–related industries. It outlines 12 tracks of priority research needs related to concrete pavements. CP Road Map publications and other operations support services are provided by the National Concrete Pavement Technology Center at Iowa State University. For details about the CP Road Map, see www.cproadmap. org/index.cfm.

Pedotransfer functions to estimate water retention parameters of soils in northeastern Brazil

Pedotransfer functions (PTF) were developed to estimate the parameters (α, n, θr and θs) of the van Genuchten model (1980) to describe soil water retention curves. The data came from various sources, mainly from studies conducted by universities in Northeast Brazil, by the Brazilian Agricultural Research Corporation (Embrapa) and by a corporation for the development of the São Francisco and Parnaíba river basins (Codevasf), totaling 786 retention curves, which were divided into two data sets: 85 % for the development of PTFs, and 15 % for testing and validation, considered independent data. Aside from the development of general PTFs for all soils together, specific PTFs were developed for the soil classes Ultisols, Oxisols, Entisols, and Alfisols by multiple regression techniques, using a stepwise procedure (forward and backward) to select the best predictors. Two types of PTFs were developed: the first included all predictors (soil density, proportions of sand, silt, clay, and organic matter), and the second only the proportions of sand, silt and clay. The evaluation of adequacy of the PTFs was based on the correlation coefficient (R) and Willmott index (d). To evaluate the PTF for the moisture content at specific pressure heads, we used the root mean square error (RMSE). The PTF-predicted retention curve is relatively poor, except for the residual water content. The inclusion of organic matter as a PTF predictor improved the prediction of parameter a of van Genuchten. The performance of soil-class-specific PTFs was not better than of the general PTF. Except for the water content of saturated soil estimated by particle size distribution, the tested models for water content prediction at specific pressure heads proved satisfactory. Predictions of water content at pressure heads more negative than -0.6 m, using a PTF considering particle size distribution, are only slightly lower than those obtained by PTFs including bulk density and organic matter content.

Hygroscopicity and ammonia volatilization losses from nitrogen sources in coated urea

Hygroscopic fertilizers tend to absorb moisture from the air and may have undesirable characteristics such as moistness, clumping and lower fluidity, hampering the application. The increasing use of urea is due to its numerous advantages, although this nitrogen (N) source is highly susceptible to volatilization losses, particularly when applied to the soil surface of management systems with conservation of crop residues. The volatilization losses can be minimized by slow or controlled-release fertilizers, with controlled water solubility of the urea-coating materials; and by stabilized fertilizers, which prolong the period during which N remains in the amide or ammonia forms by urease inhibitors. This study evaluated the hygroscopicity of and ammonia volatilization from urea coated with boric acid and copper sulfate or with sulfur. The hygroscopicity of the sources was evaluated over time after exposure to five levels of relative humidity (RH) and volatilization evaluated after application to the soil surface covered with sugarcane trash. Ammonium nitrate has a low potential for volatilization losses, but is highly hygroscopic. Although coating with boric acid and copper sulfate or elemental sulfur reduced the critical humidity level of urea, the delay in the volatilization process is a potential positive factor.

Concrete Pavement Construction Basics, June 2006

General principles • Everyone at the construction site, particularly foremen and supervisors, is responsible for recognizing and troubleshooting potential problems as they arise. • Batches of concrete should be consistent and uniformly mixed. • A major cause of pavement failure is unstable subgrade. The subgrade should consist of uniform material, and the subgrade system must drain well. • Dowel bars are important for load transfer at transverse joints on pavements with high truck volumes. Dowels must be carefully aligned, horizontally and vertically, to prevent pavement damage at the joints. • Stringlines control the slipform paver’s horizontal and vertical movement and ensure a smooth pavement profile. Once stringlines are set, they should be checked often and not disturbed. • Overfinishing the new pavement and/or adding water to the surface can lead to pavement surface problems. If the concrete isn’t sufficiently workable, crews should contact the project manager. Changes to the mixture or to paver equipment may reduce the problem. • Proper curing is critical to preventing pavement damage from rapid moisture loss at the pavement surface. • A well spaced and constructed system of joints is critical to prevent random cracking. • Joints are simply controlled cracks. They must be sawed during the brief time after the pavement has gained enough strength to prevent raveling but before it begins to crack randomly (the “sawing window”). • Seasonal and daily weather variations affect setting time and other variables in new concrete. Construction operations should be adjusted appropriately.

Soil Water Potentials and Capsicum annuum L. under Salinity

ABSTRACT Investigations into water potentials in the soil-plant system are of great relevance in environments with abiotic stresses, such as salinity and drought. An experiment was developed using bell pepper in a Neossolo Flúvico (Fluvent) irrigated with water of six levels of electrical conductivity (0, 1, 3, 5, 7 and 9 dS m-1) by using exclusively NaCl and by simulating the actual condition (using a mixture of salts). The treatments were arranged in a randomized block design, in a 6 × 2 factorial arrangement, with four replicates. Soil matric (Ψm) and osmotic (Ψo) potentials were determined 70 days after transplanting (DAT). Soil total potential was considered as the sum of Ψm and Ψo. Leaf water (obtained with the Scholander Chamber) and osmotic potentials were determined before sunrise (predawn) and at noon at 42 and 70 DAT. There were no significant differences between the salt sources used in the irrigation water for soil and plant water potentials. The supply of salts to the soil through irrigation water was the main factor responsible for the decrease in Ψo in the soil and in bell pepper leaves. The total potential of bell pepper at predawn reached values of -1.30 and -1.33 MPa at 42 and 70 DAT, respectively, when water of 9 dS m-1 was used in the irrigation. The total potential at noon reached -2.19 MPa. The soil subjected to the most saline treatment reached a water potential of -1.20 MPa at 70 DAT. There was no predawn equilibrium between the total water potentials of the soil and the plant, indicating that soil potential cannot be considered similar to that of the plant. The determination of the osmotic potential in the soil solution should not be neglected in saline soils, since it has strong influence on the calculation of the total potential.

Evauation of Recycled Asphalt Concrete Pavements: Final Report for Kossuth County, Iowa, HR-1888, February 1980

After some success with a small asphalt pavement recycling project in 1975, Kossuth County, Iowa programmed a much larger undertaking during the 1976 construction season. The work performed in 1975 indicated that a quality product could be produced with some modifications to conventional equipment. As anticipated , the major problem encountered was the excessive air pollution created during the heating and mixing process. As part of its 1976 road program, Kossuth County developed plans for recycling sixteen miles of existing asphalt pavements using the "hot mix" recycling process. One project, ten miles in length, was selected by the Federal Highway Authority as part of "Demonstration Project No. 39, Recycling Asphalt Pavements." The FHWA provided a $29,500 grant t o the project to be used for project testing and evaluation. Cooperation and input into the work proposed for 1976 was received from many sources. The people and organizations contributing were the Federal Highway Authority, the Iowa Department of Environmental Quality, the Federal Environmental Protection Agency, several contractors, and personnel from the Kossuth County Engineer's Office.

Task 4: Testing Iowa Portland Cement Concrete Mixtures for the AASHTO Mechanistic-Empirical Pavement Design Procedure, May 2008

The present research project was designed to identify the typical Iowa material input values that are required by the Mechanistic-Empirical Pavement Design Guide (MEPDG) for the Level 3 concrete pavement design. It was also designed to investigate the existing equations that might be used to predict Iowa pavement concrete for the Level 2 pavement design. In this project, over 20,000 data were collected from the Iowa Department of Transportation (DOT) and other sources. These data, most of which were concrete compressive strength, slump, air content, and unit weight data, were synthesized and their statistical parameters (such as the mean values and standard variations) were analyzed. Based on the analyses, the typical input values of Iowa pavement concrete, such as 28-day compressive strength (f’c), splitting tensile strength (fsp), elastic modulus (Ec), and modulus of rupture (MOR), were evaluated. The study indicates that the 28-day MOR of Iowa concrete is 646 + 51 psi, very close to the MEPDG default value (650 psi). The 28-day Ec of Iowa concrete (based only on two available data of the Iowa Curling and Warping project) is 4.82 + 0.28x106 psi, which is quite different from the MEPDG default value (3.93 x106 psi); therefore, the researchers recommend re-evaluating after more Iowa test data become available. The drying shrinkage (εc) of a typical Iowa concrete (C-3WR-C20 mix) was tested at Concrete Technology Laboratory (CTL). The test results show that the ultimate shrinkage of the concrete is about 454 microstrain and the time for the concrete to reach 50% of ultimate shrinkage is at 32 days; both of these values are very close to the MEPDG default values. The comparison of the Iowa test data and the MEPDG default values, as well as the recommendations on the input values to be used in MEPDG for Iowa PCC pavement design, are summarized in Table 20 of this report. The available equations for predicting the above-mentioned concrete properties were also assembled. The validity of these equations for Iowa concrete materials was examined. Multiple-parameters nonlinear regression analyses, along with the artificial neural network (ANN) method, were employed to investigate the relationships among Iowa concrete material properties and to modify the existing equations so as to be suitable for Iowa concrete materials. However, due to lack of necessary data sets, the relationships between Iowa concrete properties were established based on the limited data from CP Tech Center’s projects and ISU classes only. The researchers suggest that the resulting relationships be used by Iowa pavement design engineers as references only. The present study furthermore indicates that appropriately documenting concrete properties, including flexural strength, elastic modulus, and information on concrete mix design, is essential for updating the typical Iowa material input values and providing rational prediction equations for concrete pavement design in the future.

Evaluation of Fly Ash Concrete Durability Containing Class II Durability Aggregates, July 1986

Fly ash was used in this evaluation study to replace 15% of the cement in Class C-3 concrete paving mixes. One Class "c" ash from Iowa approved sources was examined in each mix. Substitution rate was based on 1 to 1 basis, for each pound of cement removed 1.0 pound of ash was added. The freeze/thaw durability of the concrete studied was not adversely affected by the presence of fly ash. This study reveals that the durability of the concrete test specimens made with Class II durability aggregates was slightly increased in all cases by the substitution of cement with 15% Class "c" fly ash. In all cases durability factors either remained the same or slightly improved except for one case where the durability factor decreased from 36 to 34. The expansion decreased in all cases.

Evaluation of Fly Ash in lean Portland Cement Concrete Base "Econocrete", August 1986

Fly ash was used in this evaluation study to replace 30, 50 and 70 percent of the 400 1bs. of cement currently used in each cu. yd. of portland cement econocrete base paving mix. Two Class "c" ashes and one Class "F" ash from Iowa approved sources were examined in each mix. When Class "c" ashes were used, they were substituted on the basis of 1.0 pound for each pound of cement removed. When Class "F" ash was used, it was substituted on the basis of 1.25 pounds of ash for each pound of cement removed. Compressive strengths with and without fly ash were determined at 7, 28 and 56 days of age. In most cases, strengths were adequate. The freeze/thaw durability of the econocrete mixes studied was not adversely affected by the presence of fly ash. The tests along with erodibility and absorption tests have demonstrated the feasibility of producing econocrete with satisfactory mechanical properties even when relatively low quality and/or locally available aggregate is being used at no sacrifice to strength and/or durability.