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Trace elements distribution between the solid and soil solution phases is a key issue in assessing the mobility and retention of trace elements in soils. In a competitive system where soils are contaminated with several trace elements metal adsorption reactions become important. This study was conducted to assess the competitive sorption of cadmium (Cd), copper (Cu), zinc (Zn), nickel (Ni) and mangenese...
Geometric mean diameter (GMD), erodible fraction (EF), and dry aggregate stability (DASt) are soil parameters deduced by dry sieving that are used to identify soil susceptibility to wind erosion. Values of GMD, EF, and DASt have been calculated for different soil types but limited information is available on the effects of tillage on these parameters. In order to asses this influence we analyzed their...
For spatial prediction of soil variables where the local mean can be expressed as a local trend, or a linear function of some auxiliary (external drift) variable, the state-of-the-art is to estimate the spatial covariance parameters of the residual variation by residual maximum likelihood (REML). Method of moments estimators, as used to compute point estimates of the variogram in most geostatistical...
To explore the hypothesis that enrichment of decomposition-resistant compounds might vary in humic acid (HA) that is associated with silt and clay-size microaggregates, we used infrared spectroscopy, thermal analyses, nuclear magnetic resonance spectroscopy, and pyrolysis techniques to characterize the functional groups and structures of HA isolated from coarse silt and clay fractions of two Iowa...
Management of agricultural fields based on yield patterns may help farmers adopt environmentally friendly farming practices. Our objective was to investigate landscape and hydrologic attributes that affect spatial clusters of corn (Zea mays L.)–soybean (Glycine max L.) yields. The study was conducted at Iowa State University's northeastern research center near Nashua, Iowa, from 1993 to 1998. The...
Process-based agricultural system models require detailed description of soil hydraulic properties that are usually not available. The objectives of this study were to evaluate the sensitivity of model simulation results to variability in measured soil hydraulic properties and to compare simulation results using measured and default soil parameters. To do so, we measured soil water retention curves...
An accurate and management sensitive simulation model for tile-drained Midwestern soils is needed to optimize the use of agricultural management practices (e.g., winter cover crops) to reduce nitrate leaching without adversely affecting corn yield. Our objectives were to enhance the Agricultural Production Systems Simulator (APSIM) for tile drainage, test the modified model for several management...
The objective of this study was to explore if more crop-specific plant growth modules can improve simulations of crop yields, and N in tile flow under different management practices compared with a generic plant growth module. We calibrated and evaluated the Root Zone Water Quality Model (RZWQM) with the Decision Support for Agrotechnology Transfer (DSSAT v3.5) plant growth modules (RZWQM–DSSAT) for...
Agricultural system models are tools to represent and understand major processes and their interactions in agricultural systems. We used the Root Zone Water Quality Model (RZWQM) with 26 years of data from a study near Nashua, IA to evaluate year to year crop yield, water, and N balances. The model was calibrated using data from one 0.4 ha plot and evaluated by comparing simulated values with data...
Nitrate nitrogen losses through subsurface drainage and crop yield are determined by multiple climatic and management variables. The combined and interactive effects of these variables, however, are poorly understood. Our objective is to predict crop yield, nitrate concentration, drainage volume, and nitrate loss in subsurface drainage from a corn (Zea mays L.) and soybean (Glycine max (L.) Merr.)...
Accurate simulation of agricultural management effects on N loss in tile drainage is vitally important for understanding hypoxia in the Gulf of Mexico. An experimental study was initiated in 1978 at Nashua, Iowa of the USA to study long-term effects of tillage, crop rotation, and N management practices on subsurface drainage flow and associated N losses. The Root Zone Water Quality Model (RZWQM) was...
Thoroughly tested simulation models are needed to help quantify the long-term effects of agriculture. We evaluated the Root Zone Water Quality Model (RZWQM) response to different N management strategies and then used the tested model with observed weather data from 1961–2003 to quantify long-term effects on corn (Zea mays L.) yield and flow weighted nitrate-N concentration in subsurface “tile” drainage...
Spatial heterogeneity in fields may affect the outcome of experiments. The conventional randomized allocation of treatments to plots may cause bias and variable precision in the presence of trends (including periodicity) and spatial autocorrelation. Agricultural scientists appear to mostly use conventional experimental designs that are susceptible to adverse affects from field variability. The objectives...
The Matérn variogram model has been advocated because it is flexible and can represent varied behaviour at small lags. We show how the constraints on the spherical and exponential variogram at short lags ignore a possible source of uncertainty in the variogram and so in kriging surveys, that the Matérn model can describe. Matérn, spherical and exponential variogram models were fitted by maximum likelihood...
Combining global soil-spectral libraries with local calibration samples has the potential to provide improved visible and near-infrared (VNIR, 400–2500 nm) diffuse reflectance spectroscopy (DRS) soil characterization predictions than with either global or local calibrations alone. In this study, a geographically diverse “global” soil-spectral library with 4184 samples was augmented with up to 418...
The paper compares semi-automated interpolation methods to produce soil-class maps from profile observations and by using multiple auxiliary predictors such as terrain parameters, remote sensing indices and similar. The Soil Profile Database of Iran, consisting of 4250 profiles, was used to test different soil-class interpolators. The target variables were soil texture classes and World Reference...
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