Changes in water content in and under frozen soil in Iowa,U.S.A.

Water contents were measured in a soil profile during the winter from the time of harvest until soil temperatures were greater than 0°C through this profile in the spring. Water movement between successive layers was predicted using the Darcy flow law and changes in water flux. These values were then compared with the changes in soil water content observed in field measurements. Results showed that water content changes (accumulation or loss) below the frozen layer were greater than predicted but that the differences between predicted and measured contents were small, much smaller than the amounts reported in previous experiments.     

Plant Response to Air Pollution,edited by M. Yunus and M. Iqbal

Water, Air, &; Soil Pollution -     

Nutrient content of precipitation over Iowa

Nutrient content and pH of precipitation samples collected at six sites during 1971–1973 were studied to determine the fraction of rainfall and snowmelt and the amounts of N, S, and P added by precipitation over Iowa The amount of NH₄-N ha^?1 added by precipitation annually at each site was about equal to that added as N0₃-N. The amounts of inorganic N ha^?1 yr^?1 added ranged from 10 kg in north-central to 14 kg in west-central Iowa, and the annual amounts of S0₄-S ha^?1 added ranged from 13 kg in northeastern to 17 kg in north-central Iowa. It is estimated that, on average, precipitation adds about 0.6 kg of NH₄-N, 0.6 kg of N0₃-N, and 1.5 kg of S0₄ -S ha^?1 monthly in Iowa. However, the data indicated that, on an annual basis, the contribution of precipitation to P in soil is very small; at the most, about 0.1 kg of water-soluble P0₄-P ha^?1 was added annually in Iowa. No N0₂-N could be detected in any of the precipitation samples analyzed. Average pH value of the rainfall and snowmelt samples collected at each site during each year was about 6, individual samples seldom reached as low as pH 4. The data indicate that the concentration of S0₄-S in precipitation in this region is seasonal, high during fall and winter and low during spring and summer.     

Quasi-biennial corn yield cycles in Iowa

Quasi-biennial cycles are often reported in climate studies. The interannual El Niño Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) are two phenomena containing quasi-periodicities of approximately 2.5 and 2.2 years. It is known that ENSO affects corn yield through weather patterns, NAO affects surface temperature and cloudiness, and surface temperature, rainfall, and radiation affect corn yield. However, a quasi-biennial pattern in corn yield and the combined effect of several climate signals on long-term U.S. corn yield are not known. Here we show statistically significant 2–3 year periods in long-term corn yield from one of the world's most important corn producing regions. High (low) yields are due in part to high (low) surface radiation and low (high) temperature early in the corn growing season coupled with sufficient (insufficient) rainfall later in the growing season. A statistical model we developed using three climate indices accounts for 54% of the interannual variation in Iowa corn yield. The most significant periodicities found in the model's spectrum are similar to the quasi-biennial periodicities in observed corn yield. We classify Iowa corn yield from several regional datasets (1960–2006) for ‘low yield’ and ‘high yield’ conditions as predicted by the model. The difference between observed corn yields for ‘high’ and ‘low’ yielding years was 19% (p = 0.0001). The results demonstrate a quasi-biennial pattern in long-term Iowa corn yield related to large-scale climate variability. This knowledge could lead to models that help guide springtime agricultural management decisions that improve profitability and reduce nitrate flux to groundwater, streams, rivers, and coastal oceans.     

Phosphorus transformations in stream bank sediments in Iowa,USA, at varying redox potentials

Journal of Soils and Sediments - Stream bank erosion is one of the main sources of suspended sediments in stream water, and it often carries phosphorus with it. With a controlled laboratory study,...     

Fungal presence in paired cultivated and uncultivated soils in central Iowa, USA

 Amounts of fungal biomass in adjacent cultivated and uncultivated soils in central Iowa were estimated and compared by quantifying soil ergosterol concentrations and lengths of fungal hyphae present. Both indices of fungal biomass, with one exception, indicated that there was at least twice as much fungal biomass in uncultivated soil as in cultivated soil. Levels of microbial biomass carbon in uncultivated soils were also determined to be at least twice that in cultivated soils. Data collected in this study indicate that fungi may be more significantly affected by agricultural soil management practices than other components of the soil microbial community. For two of the soils examined, calculated estimates denote that fungal biomass carbon represented approximately 20% of the total microbial biomass carbon in cultivated soil and about 33% of the microbial biomass carbon in uncultivated soil. Results of this study indicate that conventional agricultural practices result in a significant reduction of fungal biomass production in soil. Implications of differences in fungal biomass between the soils are discussed. Received: 12 October 1997     

A preliminary watershed scale soil quality assessment in north central Iowa, USA

Soil quality assessment has been recognized as an important step toward understanding the long-term effects of conservation practices within agricultural watersheds. Our objective was to assess soil quality within the South Fork watershed of the Iowa River using various indicators and assessment approaches. Soil samples were collected during 2003 and 2004 from 29 areas of 32 ha (80 acres) each along two transects traversing the watershed. Soil pH, Mehlich III extractable P, K, Ca and Mg, electrical conductivity (EC), total organic carbon (TOC), and total N (TN) were measured. The Soil Management Assessment Framework (SMAF) was used to compute a soil quality index (SQI), while soil loss, the soil tillage intensity rating (STIR), N-leaching potential, and soil conditioning index (SCI) were determined for each sampling area using the 2003 version of the Revised Soil Loss Equation (RUSLE2). Overall, there were no soil fertility limitations within the watershed based on an average pH of 6.96 and extractable P and K levels of 36 and 162 mg kg⁻¹, respectively. Soil loss, STIR, N-leaching, and SCI averaged 1.13 Mg ha⁻¹, 68, 3, and 0.4, respectively. The SMAF analysis indicated soils within the watershed were functioning at 87% of their full potential. The lowest indicator score was associated with TOC (0.60) because the average value was only 28.4 g kg⁻¹. The SCI and SQI indices were positively correlated although since it used measured data, the SMAF appears to provide more information about the effects of management practices within the watershed. Soils in upper landscape positions had lower TOC and C:N ratios indicating an increased risks for both erosion and for nitrate leaching. Management of soils on hilltops may be the most effective way to minimize N and P losses within the watershed.     

Trace Element Concentrations of Iowa Surface Soils

Trace elements in the environment have received considerable attention in recent years. This study was carried out to assess the concentrations of 15 trace elements in 171 representative Iowa surface soils obtained from 30 counties, representing 41 major soil series in Iowa, which constitute 63.5% of the Iowa landscape. This was coupled with analysis of eight major elements. The trace metals were determined either by atomic absorption spectrophotometry or an argon plasma emission spectrometer in soil digests. The ranges, means, median, standard deviations, and frequency distribution of the elements studied are reported. Results showed that, in general, concentrations of the trace elements were significantly correlated (P < 0.01) with those of the major elements studied. With a few exceptions, the concentrations of trace elements were intercorrelated (P < 0.01), suggesting their presence in soils predominantly as mineral constituents.     

RZWQM simulation of long-term crop production, water and nitrogen balances in Northeast Iowa

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 from 29 of the 36 plots at the same research site (six were excluded). The dataset contains measured tile flow that varied considerably from plot to plot so we calibrated total tile flow amount by adjusting a lateral hydraulic gradient term for subsurface lateral flow below tiles for each plot. Keeping all other soil and plant parameters constant, RZWQM correctly simulated year to year variations in tile flow (r² = 0.74) and N loading in tile flow (r² = 0.71). Yearly crop yield variation was simulated with less satisfaction (r² = 0.52 for corn and r² = 0.37 for soybean) although the average yields were reasonably simulated. Root mean square errors (RMSE) for simulated soil water storage, water table, and annual tile flow were 3.0, 22.1, and 5.6 cm, respectively. These values were close to the average RMSE for the measured data between replicates (3.0, 22.4, and 5.7 cm, respectively). RMSE values for simulated annual N loading and residual soil N were 16.8 and 47.0 kg N ha⁻¹, respectively, which were much higher than the average RMSE for measurements among replicates (7.8 and 38.8 kg N ha⁻¹, respectively). The high RMSE for N simulation might be caused by high simulation errors in plant N uptake. Simulated corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yields had high RMSE (1386 and 674 kg ha⁻¹) with coefficient of variations (CV) of 0.19 and 0.25, respectively. Further improvements were needed for better simulating plant N uptake and yield, but overall, results for annual tile flow and annual N loading in tile flow were acceptable.     

Assessment of the condition of Iowa augers, auger-related injuries, and farmers' perceptions about auger-related injuries

This study provides an insight into auger-related injuries, Iowa farmers' perceptions of auger-related injuries and the condition of augers used in Iowa agriculture. Specific auger-related injury data (437 records) from the Iowa Department of Public Health (IDPH) was examined and interpreted. The most likely body part injured was the finger and 11:00 A.M., 3:00 P.M., and 5:00 P.M. were the times of the day with the highest number of injuries reported. In addition, a survey was administered to 400 farmers to ascertain their awareness of auger-related injuries and to determine the condition of their augers. Farmers' perceptions of what body part is most likely to be injured by an auger and the level of severity expected from those injuries coincided with injury records from 1993 to 1997. A total 34% of the primary and secondary augers reported were unshielded or without guarding. This assessment provides insight for development of intervention countermeasures to reduce auger-related injuries.