Search

Thirteen states associated with the Southern Extension and Research Activities Information Exchange Group-6 (SERA-IEG-6) agreed to share their soil test based P and K rate recommendations for nine major crops. The objectives were to compare fertilizer P and K rate recommendations, to look for opportunities to rationalize similar recommendations across state lines, and to examine challenges to the development of a cooperative regional approach to P and K recommendations. Mehlich-3 (eight states), Mehlich-1 (five states), or Lancaster (one state) extractions were the basis of plant available soil P (STP) and K (STK) assessment. Fertilizer recommendation philosophies (sufficiency, build and maintain, and/or hybrid) variation among the states might be the main reason behind such discrepancies. Although a few similarities in P and K rate recommendations were found, the different philosophies, numerical presentations, and extraction procedures drove important recommendation differences. Widespread adoption of the Mehlich-3 extraction procedure has not reduced variation in fertilizer P and K rate recommendations among the states. Instead, for states using Mehlich 3, soil test critical concentrations ranged from 30 to 75 mg P kg(-1) and 60 to 175 mg K kg(-1) for corn (Zea mays L.) grain and warm-season grass hay production. The adoption of uniform soil testing terminology, sample collection guidelines, extraction methods, and interpretations across common physiographic regions, soils, and state lines remains a challenge. Differences arise because of the different soil orders and properties, climate conditions, and resulting crop responses to added P and K fertilizers. Such differences in soil-test-based fertilizer P and K recommendations are state specific and highlight needs to examine the soil testing and recommendation process, make soil test results end-user friendly, and, when appropriate, standardize fundamental information used in the soil testing guidelines. USDA-NRCSUnited States Department of Agriculture (USDA) [69-3A75-17-45]; USDA-ARS Award [58-8070-8-016] Published version The authors are thankful for the partial funding provided by USDA-NRCS Grants 69-3A75-17-45 (CIG), as well as USDA-ARS Award 58-8070-8-016.

While phytosiderophores (PS) are known to chelate Fe, the role that microbial siderophores play in iron and zinc transport in graminaceous plants has not been sufficiently investigated. The aim of ...

Potential carbon mineralization (Cmin) is a commonly used indicator of soil health, with greater Cmin values interpreted as healthier soil. While Cmin values are typically greater in agricultural soils managed with minimal physical disturbance, the mechanisms driving the increases remain poorly understood. This study assessed bacterial and archaeal community structure and potential microbial drivers of Cmin in soils maintained under various degrees of physical disturbance. Potential carbon mineralization, 16S rRNA sequences, and soil characterization data were collected as part of the North American Project to Evaluate Soil Health Measurements (NAPESHM). Results showed that type of cropping system, intensity of physical disturbance, and soil pH influenced microbial sensitivity to physical disturbance. Furthermore, 28% of amplicon sequence variants (ASVs), which were important in modeling Cmin, were enriched under soils managed with minimal physical disturbance. Sequences identified as enriched under minimal disturbance and important for modeling Cmin, were linked to organisms which could produce extracellular polymeric substances and contained metabolic strategies suited for tolerating environmental stressors. Understanding how physical disturbance shapes microbial communities across climates and inherent soil properties and drives changes in Cmin provides the context necessary to evaluate management impacts on standardized measures of soil microbial activity. Foundation for Food and Agricultural Research [523926]; Samuel Roberts Noble Foundation; General Mills Published version Foundation for Food and Agricultural Research (grant ID 523926), General Mills, and The Samuel Roberts Noble Foundation.

Nitrogenous fertilizers have nearly doubled global grain yields, but have also increased losses of reactive N to the environment. Current public investments to improve soil health seek to balance productivity and environmental considerations. However, data integrating soil biological health and crop N response to date is insufficient to reliably drive conservation policy and inform management. Here we used multilevel structural equation modeling and N fertilizer rate trials to show that biologically healthier soils produce greater corn yields per unit of fertilizer. We found the effect of soil biological health on corn yield was 18% the magnitude of N fertilization, Moreover, we found this effect was consistent for edaphic and climatic conditions representative of 52% of the rainfed acreage in the Corn Belt (as determined using technological extrapolation domains). While N fertilization also plays a role in building or maintaining soil biological health, soil biological health metrics offer limited a priori information on a site’s responsiveness to N fertilizer applications. Thus, increases in soil biological health can increase corn yields for a given unit of N fertilizer, but cannot completely replace mineral N fertilization in these systems. Our results illustrate the potential for gains in productivity through investment in soil biological health, independent of increases in mineral N fertilizer use.

No-tillage (NT) has been touted as one of several climate-smart agriculture (CSA) management practices that improve food security and enhance agroecosystem resilience to climate change. However, the sustainable effectiveness of NT greatly depends on trade-offs between NT-induced changes in crop yield and greenhouse gas (GHG, i.e. CH4, CO2, and N2O) emissions. Such trade-offs are regulated by climate fluctuations and heterogeneous soil conditions and have not been well addressed. Supporting CSA management decisions requires advancing our understanding of how NT affects crop yield and GHG emissions in different agroecological regions. In this study, a meta-analysis was conducted using 740 paired measurements from 90 peer-reviewed articles to assess the effects of NT on crop yield, GHG emissions, and the global warming potential (GWP) of major cereal cropping systems. Compared to conventional tillage (CT), NT reduced in GHG emissions and increased crop yield in dry, but not humid, climates, and reduced in the GWP at sites with acidic soils. Across different cropping systems, NT enhanced barley yield by 49%, particularly in dry climates, and it decreased the GWP of rice fields through a 22% reduction in both CO2 and CH4 emissions. Our synthesis suggests that NT is an effective CSA management practice because of its potential for climate change mitigation and crop yield improvement. However, the net effect of NT (relative to CT) was influenced by several environmental and agronomic factors (climatic conditions, tillage duration, soil texture, pH, crop species). Therefore, agroecological setting must be taken into consideration when conducting a comparative evaluation of different tillage practices.

Nitrification is the biological oxidation of NH3 to NO2− and NO3− for which ammonia-oxidizing bacteria (AOB) are the functionally dominant group in cropland responsible for the rate-limiting step of NH3 oxidation. Different AOB species have functional differentiation and do not equally contribute to nitrification. This investigation explored if long-term N fertilization and tillage influenced AOB community structure. The study site was a long-term (>40 years) continuous maize (Zea mays L.) experiment with three N fertilization rates (0, 168, and 336 kg ha−1) and either no-tillage (NT) or moldboard plow tillage (PT). We used denaturing gradient gel electrophoresis (DGGE) to analyze PCR-amplified bacterial ammonia monooxygenase genes and detect changes among NH3-oxidizing bacteria. Tillage, fertilization, and sample season all significantly influenced the AOB community. The AOB were more diverse in NT than PT. The AOB became more diverse with increasing N input and were more diverse in summer than winter samples. Nitrosomonas-like and Nitrosospira-like groups were identified based on gel migration patterns. Unique bands occurred in different treatments, manifesting environmental selection. The long-term field trial showed soil management consistently influenced AOB communities. Significantly, AOB diversity differed at a small scale within a relatively uniform landscape, even in the presence of long-term management practices.

Measuring biological net soil nitrogen mineralization (NSNM) can assist nitrogen (N) fertility management in agroecosystems, but the time and apparatus required for this assessment limits measurement frequency. Stable NSNM predictors that could be rapidly measured to compare systems would be extremely useful. We compared the effects of crop and soil management on NSNM from 2011 to 2013 and evaluated several carbon (C) and N indices including particulate organic carbon (POC), particulate organic nitrogen (PON), permanganate oxidizable carbon (POXC), soil organic carbon (SOC), and soil total nitrogen (STN) as NSNM indicators. Soil (0 to 10 and 10 to 20 cm depths) was collected from six long-term burley tobacco (Nicotiana tobacum L.) tillage and rotation systems. Net soil nitrogen mineralization was estimated by a 120-d laboratory incubation. The relative effects of management on NSNM among these systems were stable across 3 yr, which suggested NSNM measurement can be reduced to that frequency when NSNM is used to compare different crop and soil management. The soil C and N fractions contributed variably to predicting soil N mineralization in the different rotation systems, but SOC (which can be calculated from soil organic matter, a common index in the routine test package of many soil testing laboratories) was the best overall NSNM predictor in this study.

No-till management is a proven practice for increasing soil organic matter in many environments. By increasing soil organic matter, no-till may increase soil N mineralization, potentially reducing crop demand for N fertilizer relative to inversion tillage. In this study, we hypothesized that, relative to inversion tillage (moldboard plowing), long-term no-till would: i) increase total N stocks, ii) increase mineralized N during the growing season, iii) increase grain yield and N uptake, and iv) reduce reliance of corn (Zea mays L.) on N fertilizer inputs. We tested these hypotheses in a long-term, continuous corn tillage and fertilizer N rate study located in Lexington, KY. We measured the total soil N and potentially mineralizable N after 48 years, the in situ mineralized N and N uptake during two corn seasons (2018–2019), and the corn grain yield for five seasons (2015–2019). We evaluated the effect of no-till on N fertilizer reliance in two ways – the first was by measuring the agronomic optimum N rate of corn in the two tillage systems, and the second was by measuring the corn yield response to late N fertilization timing in the two tillage systems. We found that the no-till system had 1000 kg N ha−1 greater total soil N stocks in the top 20 cm, mineralized 65 kg ha−1 more N during corn growth, and resulted in 22−71 kg N ha−1 and 780−1800 kg ha−1 greater N uptake and grain yield across N rates, respectively, than the plowed system. The agronomic optimum N rate (AONR) did not differ among tillage treatments, potentially because the no-till treatment yielded more and thus demanded more N. Although corn yield responded to the late N fertilization treatment, the response was similar in both the no-till and plowed treatments. We conclude that long-term no-till increases soil N mineralization and corn yield relative to inversion tillage, with minimal effect on the AONR or optimal timing of N fertilizer application.

Nitrification is the biological oxidation of NH3 to NO2− and then NO3−. Understanding soil management consequences for nitrifier ecology could improve nitrogen (N) fertilizer use, decrease NO3− leaching, and minimize NO and N2O emissions. This study examined how long-term N fertilization and tillage influenced nitrifier density, ratios, and nitrification rate. The study site had > 40 years of continuous maize (Zea mays L.) with three nitrogen fertilization rates (0, 168, and 336 kg ha−1) and either no-tillage or plow tillage. The Most Probable Number (MPN) method was used to estimate the cell density of ammonia-oxidizing (AOB) and nitrite-oxidizing (NOB) bacteria and the shaken slurry method was used to measure potential nitrification rates. Tillage, fertilization, and their interaction significantly influenced the ammonia oxidizer and nitrite oxidizer cell densities and the potential nitrification rate. Nitrifier cell densities increased with increased nitrogen fertilization; nitrite oxidizer density increased more than ammonia oxidizer density leading to a decreasing AOB:NOB ratio. There were positive correlations between ammonia oxidizer and nitrite oxidizer cell densities, especial in plow tillage. The trends for nitrifier cell density and potential nitrification rate were not consistent. Fertilization increased ammonia oxidizer and nitrite oxidizer densities and potential nitrification rate, but the influence of tillage differed for different fertilization rates. This long-term field trial demonstrated that specific soil management practices differentially influence not only the cell density of nitrifiers, but their relative ratios and their response to increased inorganic nitrogen in the environment.

SUMMARYFew studies have investigated nitrogen (N) fertilizer management in no-tillage (NT) tobacco (Nicotiana tobacumL.) production systems, even though N fertilization is known to influence tobacco cured leaf yield and quality. The present study evaluated how tillage practice and N fertilizer rate affected burley tobacco agronomic performance, plant available nitrogen (PAN) supply, and leaf chemical constituents. In 2012 and 2013, three N fertilizer rates (0, 140 and 280 kg N/ha) were introduced as split-plots within a long-term NT and conventional tillage (CT) (mouldboard plough) comparison study. Results (2007–2013) showed that the effect of tillage on tobacco yield depended on seasonal weather; NT tobacco appeared to have lower yield than CT tobacco in seasons with 500 mm. In 2012 (432 mm rainfall; 84% of the long-term seasonal mean), leaf SPAD reading, leaf nitrate concentration, total nitrogen concentration at the topping day (i.e. removal of flowers/buds at the tops of the plants) and cured leaf nicotine and alkaloid content suggested that N deficiency was more pronounced in NT than CT at the lowest N fertilizer rate. The PAN supply, as measured by a modifiedin situresin core method, was similar in 2012 between NT and CT, suggesting that plant factors may have had a role in N uptake efficiency. This scenario did not repeat in 2013 (706 mm rainfall; 137% of the long-term seasonal mean). Even though N fertilization rates were identical for both tillage practices in 2012 and 2013, PAN was lower, on average, in 2012. Because N uptake is largely the result of mass flow, the impact of reduced root density in NT tobacco would be expected to be more pronounced in a season such as 2012, when water was limited. Banding N close to the tobacco root system and/or side-dressing some portion of N may be recommended strategies to improve N use efficiency in NT burley tobacco production.

Additions of nitrogen (N) fertilizer to surface soil can trigger a wide array of complex effects, including changes in soil chemical, physical, and microbial properties which impact both the nitrogen and carbon cycles. While abundant literature exists regarding the influence of N amendments on processes and properties influencing the soil carbon cycle, there is little recognition given to potential changes in soil mineralogy. We collected surface soil (Maury silt loam, Typic Paleudalf) from a long-term agroecosystem under no-tillage management which has received annual inorganic N additions (0, 168, 336 kg N ha − 1 ) for 34 years and characterized the soil mineralogy and other relevant properties. With recent liming, N fertilizer addition was associated with only slight changes in soil pH and the suite of exchangeable cations. Silt mineralogy was not influenced by N, but x-ray diffraction found changes in the clay fraction. The clay mineral assemblage in the control (0 kg N ha − 1 ) is complex, comprised of layers of pedogenic chlorite, vermiculite, hydroxy-interlayered vermiculite, mixed-layer chlorite–vermiculite, illite, kaolinite, and quartz. Fertilizer N additions resulted in a 3- and 3.3-fold decrease in the 1.4 nm/1.0 nm peak area ratios for Mg-clay slides in the 168 and 336 kg N ha − 1 treatments. This decrease is likely due in part to fixation of NH 4 + in vermiculite layers, corroborated by increases in the intensity of the infrared (IR) band at 1430 cm − 1 (assigned to the N H bending mode of NH 4 + ) with added N. The role of biota emerged as shown by a negative relationship between water-soluble oxalate concentrations and the 1.4 nm/1.0 nm peak area ratios (r = 0.56, P = 0.06). Past acidification due to nitrification of added NH 4 + which occurred prior to liming might have played a role in weathering of pH-sensitive minerals such as chlorite. Our findings raise questions about the capacity of reactive 2:1 mineral layers to fix NH 4 + and how this is moderated by biota in no-till agroecosystems.

Climate-smart agriculture management practices such as no-tillage (NT) and cover crops (CCs) have been widely applied and are expected to offer multiple environmental benefits (e.g., soil carbon sequestration, yield stability, and climate resilience). However, the long-term effects of these management practices, especially their synergistic interaction, have not been well addressed. This study used an improved agroecosystem model (DLEM-Ag) to explore the synergistic effects of NT and CCs on soil carbon dynamics in a continuous maize system in the middle south of the United States for 1970–2099. Simulation results for 1970–2018 show that NT, relative to conventional tillage (CT), led to carbon gains (0.22 Mg C ha−1 yr−1) in the topsoil in a CC-inclusive continuing maize system; however, NT per se brought minor net carbon gains. This well captures the field observations. Model factorial analyses reveal that soil carbon sequestration was highly correlated with biomass carbon inputs from both the winter cereal CC and the summer maize. Elevated CO2 and warming effects were the main contributors to soil carbon gains, as these promote CC growth. Further model projections suggest that soil organic carbon would increase in the RCP 8.5 future scenarios (2019–2099), with greater gains under NT-CCs than under CT-CCs (0.089 vs. 0.058 Mg C ha−1 yr−1), largely due to enhanced CC biomass production. Moreover, NT-CCs would reduce carbon loss compared to CT-CCs (-0.002 vs. -0.017 Mg C ha−1 yr−1) in the RCP 2.6 scenarios. Our study highlights the importance of CCs in enhancing cropland carbon sequestration and indicates that NT and CCs, taken together, can serve as a viable strategy to ensure crop production through promoting soil health in similar maize cropping systems.

Ammonia-oxidizing archaea (AOA) catalyze a rate-limiting step in nitrification - ammonia (NH3) oxidation. There are more AOA than ammonia-oxidizing bacteria (AOB) in many soil systems, including cropland, and AOA dominate in unfavorable environmental conditions, such as soils with low NH4-N. The ecological role of the ubiquitously distributed AOA is unclear, as are the factors regulating AOA community dynamics. This study investigated how long-term N fertilization and tillage management influenced the AOA community in cropland. The study site was a long-term (>40 years) field experiment with either no-tillage (NT) or plow tillage (PT) at three N fertilizer rates (0, 168, and 336 kg ha−1) and continuous maize (Zea mays L.). We used PCR-denaturing gradient gel electrophoresis (DGGE) to assess the archaeal amoA gene as a measure of the changing AOA community. Tillage rather than N fertilizer played the dominant role affecting the AOA community. Fertilizer rate did not significantly influence AOA diversity, but sample season and N fertilization had selection function on AOA composition. In winter, AOA were more diverse in NT than PT. Unique groups were discovered in different treatments, demonstrating selection by tillage, fertilization, season, and/or their interactions. The significant tillage regulation of AOA provides new clues to investigate which environmental factors influence the AOA community and to explore its ecological significance in agricultural land.

Burley tobacco (Nicotiana tobacum L.) production in Kentucky is typically tillage intensive and is often mono-cropped. Intensive tillage has been reported to degrade soil structure and deplete soil organic carbon (SOC) and total soil nitrogen (TSN) stocks. This study assessed the effect of tillage, crop rotation, and N fertilizer application on soil structure, water-stable aggregation, and aggregate-associated SOC and TSN concentrations and stocks for rotations including burley tobacco. Four burley tobacco production systems (main plots) were established in 2007 on a Bluegrass-Maury (fine, mixed, active, mesic Typic Paleudalf) silt loam soil including: (i) no-tillage continuous tobacco (NT-Tobacco); (ii) conventional tillage continuous tobacco (CT-Tobacco); (iii) 2-yr sod (Festuca arundinacea Schreb.) 1-yr no-tillage tobacco (NT-Rotation); (iv) 2-yr sod and 1-yr conventional tillage tobacco (CT-Rotation). In 2012, two N rates (0 and 280 kg N ha⁻¹) were applied to split plots. Soil samples were taken in Spring 2013 to determine water-stable aggregate-size distributions and associated SOC and TSN concentrations and stocks. Compared with conventional tillage and tobacco monoculture, no-tillage and rotation with sod significantly increased macroaggregate fractions (>250 μm), and associated SOC and TSN stocks at the expense of the silt-clay size class (

Many sensors require algorithms/mathematical functions to translate measurements into practical outcomes. In arrays (sensor groups), the agronomic consequences of variations in individual unit performance, while driving an algorithm, remains uncharacterized. Our objective was to study the performance of individual active canopy reflectance sensors outputting normalized difference vegetative index (NDVI) data, used to prescribe the corrective N fertilization rate for winter wheat (Triticum aestivum L.). We hypothesized that sensor output differences would influence corrective N prescriptions when the NDVI data were interpreted with the usual discontinuous, “stair-step”, algorithms. The NDVI data from an eight-sensor GreenSeeker array (Trimble Navigation Limited, Westminster, CO) were obtained at growth stage Feekes 6 for four wheat fields. Individual sensors were coupled with individual liquid N application nozzle sets, and operational settings make possible the independent fertilization of each 0.56 m² of field area. Two algorithms (A and B) were evaluated. We observed large differences in individual sensor corrective N prescriptions, despite little short range (

Manure and bedding material (litter) generated by the broiler industry (Gallus gallus domesticus) often contain high levels of arsenic (As) when organoarsenical roxarsone and p-arsanilic acid are included in feed to combat disease and improve weight gain of the birds. This study was conducted to determine As levels and species in litter from three major broiler producing companies, and As levels in soils, corn tissue (Zea mays L.), and groundwater in fields where litter was applied. Total As in litter from the three different integrators ranged between

A reusable catalytic reductor consisting of 96 copperized-cadmium pins attached to a microplate lid was developed to simultaneously reduce nitrate (NO3–) to nitrite (NO2–) in all wells of a standard microplate. The resulting NO2– is analyzed colorimetrically by the Griess reaction using a microplate reader. Nitrate data from groundwater samples analyzed using the new device correlated well with data obtained by ion chromatography (r2 = 0.9959). Soil and plant tissue samples previously analyzed for NO3– in an interlaboratory validation study sponsored by the Soil Science Society of America were also analyzed using the new technique. For the soil sample set, the data are shown to correlate well with the other methods used (r2 = 0.9976). Plant data correlated less well, especially for samples containing low concentrations of NO3–. Reasons for these discrepancies are discussed, and new techniques to increase the accuracy of the analysis are explored. In addition, a method is presented for analyzing NO3– in physiological fluids (blood serum and urine) after matrix modification with Somogyi's reagent. A protocol for statistical validation of data when analyzing samples with complex matrixes is also established. The simplicity, adaptability, and low cost of the device indicate its potential for widespread application.

Abandoned feedlots have been found to enhance nitrate (NO3−) production and subsequent contamination of nearby groundwater. Site remediation depends on a thorough understanding of existing manure deposits, knowledge often lacking when dealing with abandoned feedlots. The main objective of this work

Adenosine triphosphate (ATP) measurement by bioluminescence is used in microbial adsorption studies for which colony-forming units (CFU) may underestimate true microbial numbers. We observed that citric acid profoundly affected ATP measurement by luciferin-luciferase assay, and we assessed the effect of citric acid on ATP detection in water and buffer systems in the pH range 4.9 to 7.4. Bioluminescence depended on the buffer system, increasing as pH increased in each buffer system and decreasing as the buffer system changed from Na-phosphate to citrate-phosphate. Citrate-phosphate buffer decreased bioluminescence by 82% relative to water at the same pH. Consequences of poor buffer selection are potentially reduced luciferase activity in the bioassay system and underestimation of microbial numbers.

Soil conditions at sampling and the dimensions of the sample are critical factors when soil aggregation is indirectly characterized by determining the distribution of soil fragments. Our objective was to determine the effects of gravimetric soil water content and core sampler diameter (16, 54, and 84 mm) at sampling on the dry‐fragment‐size distribution of two soils (Typic Paleudalf and Typic Hapludalf) under undisturbed Festuca arundinacea L. sod and recently rototilled treatments. The 16‐mm core diameter sampler compressed the rototilled soil, and it was not appropriate for soil aggregation studies. The fragmentation of samples taken with core diameters greater than 54 mm decreased with decreasing soil water content. A greater probability of discriminating between undisturbed and fragmented silt loam or clay loam soils was observed when sampling with a 54‐mm‐diameter probe and when the soil had a mean soil water content of 237g kg−1 or at a potential of −0.61MPa.

Tillage, cropping system, and cover crops have seasonal and long‐term effects on the nitrogen (N) cycle and total soil organic carbon (C), which in turn affects soil quality. This study evaluated the effects of crop, cover crop, and tillage practices on inorganic N levels and total soil N, the timing of inorganic N release from hairy vetch and soybean, and the capacity for C sequestration. Cropping systems included continuous corn (Zea mays L.) and stalk residue, continuous corn and hairy vetch (Vicia villosa Roth), continuous soybeans (Glycine max L.) plus residue, and two corn/soybean rotations in corn alternate years with hairy vetch and ammonium nitrate (0, 85, and 170 kg N ha−1). Subplot treatments were moldboard plow and no tillage. Legumes coupled with no tillage reduced the N fertilizer requirement of corn, increased plant‐available N, and augmented total soil C and N stores.

Efficient use of real-time canopy sensors requires knowledge of the scale (resolution) of variation in the measured canopy property. Knowing the amount of needed optical data requires estimation of the optimal combination of physical sensor density (number of sensors along the applicator boom) and sensor output density (sensor readings per unit distance along the travel path). The objective of this study was to determine the sampling grid size that would adequately describe field variation in canopy normalized difference vegetative index (NDVI) by varying either physical sensor density or sensor output density. Wheat (Triticum aestivum L.) canopy NDVI data were collected at Feekes growth stage 3 in five fields in central and western Kentucky in February of 2004 or 2005. Spatial structure of NDVI was characterized by variogram analysis across grid sizes ranging from 0.56 (high-density) to 5.1 m 2 and both semivariance and spatial structure parameters for high-density data sets were compared to those obtained with decreasing numbers of sampling points (greater grid size). Nugget, range, and sill values were maintained across evaluated grid sizes in four of five site-years. Correlations between each field's high-density semivariance values and those for the "low-density" data sets were generally high (1.0 < R 2 < 0.8) for all site-years, but there were many cases where intercepts deviated significantly from 0.0 and slopes deviated significantly from 1.0. Observed differences in individual sensor performance did not influence the pattern of NDVI spatial structure. Grid size could be increased from 0.56 to 5.1 m 2 without significantly affecting the measured spatial structure of canopy NDVI in most fields. Wheat growers might achieve spatially optimal N applications with lower data resolution and less capital intense machinery.

Measurement of the soil fragment size distribution has been found to be related to erosion processes, water retention, temperature, porosity and other soil properties that can affect crop growth and productivity. However, there is little agreement about the procedure to follow to determine dry soil fragment size distributions using flat sieves. Our objective was to determine the effects of dry-sieving duration and loading on the resulting fragment size distributions of 2 soils [Maury silt loam (Typic Paleudalf) and McAfee clay loam (Typic Hapludalf)] under contrasting management practices (undisturbed sod and recently roto-tilled). After air drying, the samples were dry-sieved with a vertical vibratory sieve shaker and the mass of soil retained on each sieve in a nest of 13 sieves, with aperture sizes ranging from 16.00 to 0.85 mm, was determined. The ability to discriminate between undisturbed and tilled soil samples varied with the mass fraction of fragments examined. In general, there was a greater probability of discriminating between sod and tilled soils, with a lower coefficient of variation, when the sieving duration was at least 30 s. Loading the uppermost sieve up to 30% of its volume did not significantly affect the results, and allowed for processing, in a single operation, composite samples taken with a probe of 5.4 cm diameter and 10.0 cm length.

Tillage impacts many components and functions of the soil ecosystem. Thus, the prediction of soil structures produced by tillage may be regarded as a major objective in soil science. Brittle fracture is the desired mode of failure in most tillage operations. Mechanistic or phenomenological models based on the probabilistic Weibull "weakest link" theory are commonly applied to model brittle fracture of air-dry aggregates. The overall objective of this study was to develop a Weibull model to describe the strength of different-sized soil aggregates across a wide range of water contents. Rupture energy data were obtained for aggregates sampled in three field experiments. These included two soil compaction experiments (Bygholm I and II, sandy loam) and a long-term tillage and fertilization experiment (Maury, silt loam). Aggregates were subjected to a crushing test after having been adjusted to matric potentials ranging from -10 kPa to -163 MPa (air dry). Water content strongly affected the characteristic rupture energy (Weibull α parameter), and this relationship was successfully modeled with a power law function. In contrast, water content had little or no effect on the spread of aggregate strengths (Weibull β parameter). Based on these results, we proposed a three-parameter Weibull brittle fracture model for the tested sandy loam and silt loam soils that takes account of the effect of water content for a single aggregate size fraction. This model, in which only α depends on water content, explained on average 89% of the total variation in rupture energy. Further research is needed to fully investigate the influence of water content on the rupture energy of different-sized aggregates.

Soil–landscape modeling techniques have been developed as a quantitative method to predict patterns of soil properties from observed patterns in soil-forming factors. However, transportability of these models to unsampled landscapes is unknown. Our objective was to develop quantitative soil–landscape models for multiple study sites and examine the similarity of these quantitative models, and therefore the similarity of soil–landscape relationships among areas with similar soils. We collected high-resolution digital elevation models (DEM) for six study sites across the Pennyroyal physiographic region of Kentucky, and for each study site used terrain attributes derived from the DEM to collect discrete soil samples using a stratified random sampling design for morphological, physical, and chemical characterization. For three of these sites we examined the inherent differences in terrain attributes among sites, and developed quantitative soil–landscape models that predict the spatial patterns in A-horizon depth, surface soil organic carbon content, and surface sand and silt content. The other three sites were used to test the transportability of these models. Terrain attribute distributions differ significantly among study sites, with regional terrain attributes (upslope contributing area, topographic wetness index) being more similar among fields than local terrain attributes (slope gradient, slope curvature). Predictive models explained from 28% to 67% of the variation in soil properties. The terrain attributes that best predicted soil variability were similar across all three fields used for model development, with slope gradient, elevation, slope curvature, and upslope contributing area appearing in most of the models. However, applying models from one field to other fields within the same physiographic region produced inconsistent results. In general, prediction quality decreased with distance from the site of model development. Further sampling, modeling, and validation at additional field sites are required to properly establish model transportability.

Few studies have examined the water quality impact of manure use in no-tillage systems. A lysimeter study in continuous corn (Zea mays L.) was performed on Maury silt loam (fine, mixed, semiactive, mesic Typic Paleudalf) to evaluate the effect(s) of tillage (no-till [NT] and chisel-disk [CD]), nitrogen fertilizer rate (0 and 168 kg N ha -1 ), and dairy manure application timing (none, spring, fall, or fall plus spring) on NO 3 -N, atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), and alachlor [2-chloro-2'-6'-diethyl-N-(methoxymethyl) acetanilide] concentrations in leachate collected at a 90-cm depth. Herbicides were highest immediately after application, declining to less than 4 μg L -1 in about two months. Manure and manure timing by tillage interactions had little effect on leachate herbicides; rather, the data suggest that macropores rapidly transmitted atrazine and alachlor through the soil. Tillage usually did not significantly affect leachate NO 3 -N, but no-tillage tended to cause higher NO 3 -N. Manuring caused higher NOj-N concentrations; spring manuring had more impact than fall, but fall manure contained about 78% of the N found in spring manure. Nitrate under spring only fertilizer treatment exceeded 10 mg L -1 38% of the time, compared with 15% for spring only manure treatment. After three years, manured soil leachate NO 3 -N exceeded that for soil receiving only N fertilizer. Soil profile (90 cm) NO 3 -N after corn harvest exceeding 22 kg N ha ' was associated with winter leachate NO 3 -N greater than 10 mg N L -1 . Manure can be used effectively in conservation tillage systems on this and similar soils. Accounting for all N inputs, including previous manure applications, will be important.

it is not clearly understood which distribution model parameters the rootsarerespondingtowhenwaterimbibitionandnutrientavailability availability of oxygen, water, and the resistance to peneare not limiting factors. The objective of this study was to determine tration by shoots and roots in seedbeds created by tillage the effect(s) of variation in geometric mean diameter (GMD) and (Hadas and Russo, 1974; Taylor, 1974; Schneider and log of the geometric standard deviation (LogGSD) taken from a log- Gupta, 1985; Nasr and Selles, 1995). Braunack (1995) normal model of soil fragment size distribution on maize (Zea mays described an earlier and greater emergence of maize L.) root elongation over a range of soil bulk density (b) and air-filled or soybean [Glycine max (L.) Merr.] seedlings when porosity (AFP) levels. Root growth, determined 48 h after seedling planted in fine (aggregate size between 1 and 2 mm) vs. emergence, was evaluated in a greenhouse experiment with artificially coarse (aggregate size between 5 and 15 mm) seedbeds. packed soil fragments sieved from a Maury silt loam (fine, mixed, Soybean emergence was delayed in the presence of semiactive, mesic Typic Paleudalf) under sod. Two experiments were structural units 1 mm and 4 mm (Nash and Baligar, conducted. The first consisted of a complete factorial combination of 1974). In the same experiment, these authors concluded

The development of well-structured soils is a goal for achieving sustainable and productive agricultural systems. Nevertheless, the maintenance of soil structure in continuous no-till (NT) soils has sometimes been thought to induce soil conditions that are detrimental to crop yields. The objectives of this research were to characterize the effects of periodic tillage disruption in otherwise NT systems on soil properties and the yields of winter wheat (Triticum aestivum L.), double-cropped soybean [Glycine max (L.) Merr.], and maize (Zea mays L.) in rotation and to determine if soil structural changes occurring in tilled soils are independent of changes in other soil properties. A field experiment was established in 1992 on a Huntington silt loam soil (Fluventic Hapludoll) at the University of Kentucky Research and Education Center in Princeton (KY) under a NT crop sequence with two seedbed preparation methods for winter wheat, (a) NT or (b) chisel plus disk tillage (Till). In fall 2000, similar soil chemical properties were observed between disrupted and continuous NT systems over the 0- to 20-cm layer. The geometric mean diameter of dry fragments and the soil water content retained between 0.0003 and 0.03 MPa water potential was greater in NT soils than in soils tilled for winter wheat. Tillage for winter wheat enhanced winter wheat yields (4.2% increase), mostly under low-yielding conditions, but it resulted in a reduction of subsequent summer crop yields (i.e., 3.7% for soybean and 7.0% for maize). The yields obtained in our study translate to an economic benefit for the continuous NT system. Net returns per hectare were estimated to be $73 higher for the winter wheat/double-crop soybean-maize rotation under NT than under Till treatments. The differences in maize yields between NT and tilled treatments were attributed to a better water supply in NT soil due to the maintenance of a larger number of mesopores and a great hydraulic conductivity. In the absence of significant changes in other physicochemical properties, periodic tillage appears to disrupt soil structure, which negatively affects crop productivity.

Phenol oxidase is associated with the carbon cycle and its presence in soil environments is important to the formation of humic substances. Little effort has been made to integrate the response of phenol oxidases with soil management. We investigated phenol oxidase activity on a Maury silt loam (fin

We combined water activity meters and fractal modeling to facilitate rapid, physically based characterization of the soil water retention curve. Desorption data (6 points per sample) were collected in the tension (h) range 2.0 x 10 2 to 1.5 × 10 5 kPa using the gravimetric method to measure water content (w) and water activity meters to measure h. Thirty-two disturbed samples from a long-term nitrogen fertilization and tillage comparison study on a silt loam soil were analyzed. A new form of an established fractal equation was derived: w = ah D-3 - ρ n /ρ s , where a is a compound parameter including the bulk density (ρ b ) and air entry tension (h a ), D is the mass fractal dimension, ρ w is the density of water, and ρ s is the particle density. This model was fitted to the measured water retention curves by nonlinear regression analysis. The a and D parameters were estimated, while ρ w and p, were fixed at 1.00 and 2.65 Mg m -3 , respectively. Convergence was always achieved and the equation fitted the data extremely well; residual sums of squares ranged from 1.2 × 10 -6 to 6.7 x 10 -5 , with a median value of 2.2 X 10 -5 . Estimates of a (0.62-0.74) and D (2.948-2.963) were physically reasonable, and sensitive to soil management practices. The a parameter increased, r = 0.80 (P < 0.01), (signifying decreasing ρ b and/or h a ) whereas D decreased, r = -0.75 (P < 0.01), (signifying more rapid capillary drainage) with increasing soil carbon content. Additional research is needed to test this approach on other soil types, and to assess the influence of soil disturbance and variations in p, on the model's performance.

Surface accumulation of soil organic carbon (SOC) under conservation tillage has significant effects on stratification of other nutrients, on crop productivity and in ameliorating the greenhouse effect via atmospheric CO 2 sequestration. A measure of SOC stratification relative to deeper soil layers has been proposed as a soil quality index. Our objective was to determine the effects of the duration of tillage practices upon the SOC and extractable P distribution with depth in Maury silt loams (Typic Paleudalfs) at similar levels of corn ( Zea mays L.) productivity without P fertilization. Soil samples (0–20.0 cm in 2.5 cm increments) were collected under moldboard tillage (MT), chisel tillage (CT) and no-tillage (NT) and in surrounding tall fescue ( Festuca arundinacea L.) sods selected from three tillage experiments (1–2-, 8- and 29-year durations) in Kentucky. SOC stratification was greater under conservation tillage (CT and NT) and sods than under MT. SOC and soil-test-extractable P stratification were positively related. Increasing the duration under NT caused the thickness of C stratification to increase. In NT soils, C stratification ratio (CSR) approached CSR in the nearby long-term sods with time. Conservation tillage rapidly promoted the occurrence of CSR greater than 2 while MT always resulted in values lower than 2. The rapid initial change in CSR suggests characterization of thin soil layers (i.e. 2.5 cm depth increments) is desirable under conservation tillage.

The western part of the Argentine Pampas is a subhumid and semiarid region consisting of extensive plain with deep sandy and sandy-loam soils. The agricultural system includes pastures in rotation with annual grain crops and grazed crops or continuous annual row cropping. The objective of this review was to present and discuss changes in soil properties due to different soil management systems, mainly no-tillage practices, in the western part of the Argentine Pampas. The effects of tillage, crop sequences under no-till, and grazing on soil properties and crop productivity have been studied since 1990 on loamy and sandy Haplic Phaeozem (Typic Hapludolls and Entic Hapludolls) and Haplic Kastanozem (Typic Haplustolls). A database developed from the yield and soil test records of growers affiliated with Regional Consortium for Agricultural Experimentation (CREA) were also utilized in the study. The results showed that soil organic C (SOC) content depends both on soil texture and soil management. SOC decreases when the length of the row crop cycle increases and also in moldboard plow and chisel-tillage systems. Pastures and no-till row crop sequences with more years of maize ( Zea mays L.) and wheat ( Triticum aestivum L.), than sunflower ( Helianthus annus L.) or soybean ( Glycine max (L.) Merrill) tended to increase the SOC content in the 0–20 cm layer. Deep tillage of no-till soils with compacted layers improved maize dry matter production but, in the same experiment, yield was increased more by nitrogen fertilization than by subsoil tillage. The grazing of crop residues increases the soil bulk density only in the 0–5 cm layer of tilled soils, but did not significantly change bulk density on soils under continuous no-till. Crop productivity was related to SOC content of the 0–20 cm layer of the soils. Due to the positive effect of SOC on crop yields, no-till soil management and pasture–annual row crop rotations are two practices that permit the development of sustainable production systems in the western part of the Argentine Pampas.

Slaking experiments were conducted of fragipan clods immersed in solutions of poultry manure, aerobically digested biosolid waste (ADB), fluidized bed combustion byproduct (FBC), D-H2O, CaCO3, NaF, Na-hexa-metaphosphate, and ryegrass root biomass. The fragipan clods were sampled from the Btx horizon of an Oxyaquic Fragiudalf in Kentucky. Wet sieving aggregate analysis showed significantly better fragmentation in the NaF, Na-hexa-metaphosphate, and ryegrass root solutions with a mean weight diameter range of 15.5–18.8 mm compared to the 44.2–47.9 mm of the poultry manure, ADB, and FBC treatments. Dissolved Si, Al, Fe, and Mn levels released in solution were ambiguous. The poor efficiency of the poultry manure, ADB, and FBC treatments was attributed to their high ionic strength, while the high efficiency of the NaF, Na-hexa-metaphosphate, and rye grass root solutions to their high sodium soluble ratio (SSR). A slaking mechanism is proposed suggesting that aqueous solutions with high SSR penetrate faster into the fragipan capillaries and generate the critical swelling pressure and shearing stress required to rupture the fragipan into several fragments. Additional fragmentation occurs in a followup stage during which potential Si, Al, Fe, and Mn binding agents may be released into solution. Field experiments testing these findings are in progress.

The compactability of a soil can be determined from parameters derived from laboratory compaction curves generated using the Proctor test. However, this is a destructive, time-consuming, and labor-expensive procedure. Our objective was to evaluate a new more rapid test to determine the maximum dry bulk density (ρ Max b and soil water content at ρ Max b (SWC Max ) from laboratory compaction curves using a mold with smaller dimensions than established for the standard procedure. Laboratory compaction curves were developed for nine soils with clay contents ranging from 232 to 385 g kg -1 using the standard Proctor test procedure and the proposed procedure, which uses a 54-mm diam. mold and a 24.4 N rammer dropped from a height of 305 mm to produce a compactive effort (CE) of 109 kJ m -3 drop -1 . At a CE of 545 kJ m -3 , which is similar to the 540 kJ m -3 produced by the standard test, the ρ Max b and SWC Max parameters derived from the proposed procedure were positively and significantly correlated with those derived from the standard Proctor test. With both procedures, ρ Max b decreased and SWC Max increased as the soil clay content increased. The small mold method did not affect the linear relationship between soil clay content and ρ Max b , However, different relationships between SWC Max and clay content were observed, depending on the compaction procedure. Use of the small mold procedure requires less dry sieved soil, saves time, and labor in evaluating soil compactability. Based only on the reduction in rammer drops, use of the small mold procedure involves 15 times less labor requirements than the standard Proctor test.

Wild and domesticated animals can harbor a pathogenic Escherichia coli strain designated as O157:H7. Potential health problems could occur if strain O157:H7 is a more robust survivor in defecated waste than commonly used indicator bacteria. A laboratory study was conducted to assess E. coli O157:H7 survival relative to a nonpathogenic E. coli strain in two soils with different physical and chemical characteristics. Bacteria in the inoculated soils were enumerated on a weekly basis for 8 wk using a most probable number (MPN) technique. First-order decay models were used to describe bacteria mortality in the soils. Decay series were described slightly better by a two-stage function than by a single-stage function. Strain O157:H7 exhibited similar mortality patterns to the nonpathogenic E. coli in the same soil environment. Both E. coli strains had greater mortality rates in Pope silt loam (coarse-loamy, mixed, active, mesic Fluventic Dystrudept) than Zanesville silt loam (fine-silty, mixed, active, mesic Oxyaquic Fragiudalf). Differences in available soil water probably were the overriding factor in E. coli survival. Escherichia coli O157:H7 survival could be modeled in the same way as nonpathogenic E. coli and appears to have a slightly higher mortality rate.

Fragipans are impermeable layers in soil that affect more than 950,000 ha of land in Kentucky and create seasonally perched water tables that may promote denitrifier growth and activity. We used denitrification enzyme activity assays and Most Probable Number (MPN) estimates of soil and water samples