Spatial Analysis of NO 3 -N Concentration in Glacial Till

Analysis of the spatial variability of groundwater NO3 –N concentration is a logical step for a meaningful groundwater quality assessment, for mapping out areas of environmental concern, and for developing appropriate management schemes in a glacial till aquitard. This study was conducted to characterize the spatial variability of NO3 –N concentration in shallow (\u3c6.0 m) and deep (\u3e6.0 m) groundwater in a 12–ha. glacial till aquitard and to estimate NO3 –N concentration in unsampled locations. Omnidirectional and directional semivariogram analysis, statistical anisotropy analysis, and model fitting were performed for average and extreme monthly groundwater NO3 –N data. Results indicated a weak spatial structure of NO3 –N concentration for both shallow and deep well data. However, the best–fitted variogram models generally performed satisfactorily during cross validation, yielding a mean reduced error of –0.01 to –0.074 and reduced variance of 0.6 to 2.18. Untransformed shallow–well NO3 –N exhibited a lower range of correlation than deep–well data. Statistical anisotropy was found to coincide with the general groundwater flow directions for the average and maximum observed NO3 –N concentrations in shallow wells. Geostatistical estimation using ordinary kriging indicated relatively higher NO3 –N concentrations at the down–gradient areas for shallow wells and at regions close to nitrogen fertilizer application sites for the deep wells. With satisfactory cross–validation performance of the variogram models, the geostatistical results of this study may be used as basis for estimating spatially variable NO3 –N loading rates in the glacial till aquitard

Comparison of Saturated Hydraulic Conductivity Measurement Methods for a Glacial-Till Soil

Hydraulic conductivity is the single most important hydraulic parameter for flow and transport-related phenomena in soil, but the results from different measuring methods vary under different field conditions. To evaluate the performance of four in situ saturated hydraulic conductivity (Ks) measuring methods, Ks measurements were made at four depths (15, 30, 60, and 90 cm) and five locations on a glacial-till soil of Nicollet (fine-loamy, mixed, mesic Aquic Hapludoll)-Clarion (fine-loamy, mixed, mesic Typic Hapludoll) association. The four in situ methods were: (i) Guelph permeameter, (ii) velocity permeameter, (iii) disk permeameter, and (iv) double-tube method. The Ks was also determined in the laboratory on undisturbed soil cores collected from all the five sites and four depths. The Guelph permeameter method gave the lowest Ks values, possibly because of small sample size, whereas the disk permeameter and double-tube methods gave maximum values for Ks with minimum variability, possibly because of large sample size. Maximum variability in Ks values for soil cores at shallow depths may have occurred because of the presence or absence of open-ended macropores. Estimates of Ks, however, are most comparable for the velocity permeameter and the laboratory method using a constant-head permeameter

The Wnt/β-catenin pathway regulates growth and maintenance of colonospheres

<p>Abstract</p> <p>Background</p> <p>Recent evidence suggests that epithelial cancers, including colorectal cancer are driven by a small sub-population of self-renewing, multi-potent cells termed cancer stem cells (CSCs) which are thought to be responsible for recurrence of cancer. One of the characteristics of CSCs is their ability to form floating spheroids under anchorage-independent conditions in a serum-free defined media. The current investigation was undertaken to examine the role of Wnt/β-catenin pathway in regulating the growth and maintenance of colonospheres. Human colon cancer cells HCT-116 (p53 wild type; <it>K-ras </it>mutant), HCT-116 (p53 null; <it>K-ras </it>mutant) and HT-29 (p53 mutant) were used.</p> <p>Results</p> <p>Colonospheres formed <it>in vitro </it>exhibited higher expression of colon CSCs markers LGR5, CD44, CD166 and Musashi-1 along with putative CSC marker EpCAM, compared to the corresponding parental cancer cells and also exhibit the ability to form spheroids under extreme limiting dilution, indicating the predominance of CSCs in colonospheres. Colonospheres formed by HCT-116 cells show over 80% of the cells to be CD44 positive, compared to ≤ 1% in the corresponding parental cells. Additionally, colonospheres showed reduced membrane bound β-catenin but had increased levels of total β-catenin, cyclin-D1 and c-myc and down regulation of axin-1 and phosphorylated β-catenin. Increased expression of β-catenin was associated with a marked transcriptional activation of TCF/LEF. The latter was greatly decreased following down regulation of β-catenin by the corresponding siRNA, leading to a marked reduction in CD44 positive cells as well as colonospheres formation. In contrast, upregulation of c-myc, a down-stream effector of TCF/LEF greatly augmented the formation of colonospheres.</p> <p>Conclusion</p> <p>Our data suggest that colonospheres formed by colon cancer cell lines are highly enriched in CSCs and that Wnt/β-catenin pathway plays a critical role in growth and maintenance of colonospheres.</p

Effects of Laying Hen Manure Application Rate on Water Quality

Excessive use of animal manure on agricultural lands can impact the quality of surface and groundwater resources. A three–year study (1998–2000) was conducted on nine 0.4–ha plots and on six 2.1–m 2 lysimeters to investigate the effect of two nitrogen (N) application rates from laying hen manure and one N application rate from urea ammonium nitrate (UAN) fertilizer on surface and groundwater quality. Experimental treatments included N application rates of 168 kg–N/ha from UAN fertilizer, and 168 kg–N/ha and 336 kg–N/ha from laying hen manure to corn plots. Subsurface drain and runoff water samples were collected and analyzed for nitrate–nitrogen (NO3–N) and orthophosphate (PO4–P). Results of this study indicate that application of hen manure at 336 kg–N/ha resulted in the highest average NO3–N and PO4–P concentrations in subsurface drain water in comparison with the application of 168 kg–N/hafrom either hen manure or UAN fertilizer. Application of manure at 168 kg–N/ha resulted in significantly lower NO3–N loss with subsurface drain water in comparison with NO3–N loss from the other two N treatments. Manure application at a rate of 336 kg–N/ha resulted in a higher concentration of PO4–P in surface runoff in comparison with manure application rate of 168 kg–N/ha. Application rate of manure had no significant effect on NO3–N concentration in surface runoff water. In addition, higher PO4–P losses were observed with surface runoff water in comparison with subsurface drain water. The use of manure at both low and high application rates in field plots resulted in significantly higher corn and soybean yields in comparison with the use of UAN fertilizer. Results of this study led to the conclusions that application of hen manure at a lower rate of 168 kg–N/ha can result in higher crop yields and minimal water pollution in comparison with same amount of UAN fertilizer or higher manure application rate

Using Soil Attributes and GIS for Interpretation of Spatial Variability in Yield

Precision farming application requires better understanding of variability in yield patterns in order to determine the cause-effect relationships. This field study was conducted to investigate the relationship between soil attributes and corn (Zea mays L.)-soybean (Glycine max L.) yield variability using four years (1995-98) yield data from a 22-ha field located in central Iowa. Corn was grown in this field during 1995, 1996, and 1998, and soybean was grown in 1997. Yield data were collected on nine east-west transects, consisting of 25-yield blocks per transect. To compare yield variability among crops and years, yield data were normalized based on N-fertilizer treatments. The soil attributes of bulk density, cone index, organic matter, aggregate uniformity coefficient, and plasticity index were determined from data collected at 42 soil sampling sites in the field. Correlation and stepwise regression analyses over all soil types in the field revealed that Tilth Index, based upon soil attributes, did not show a significant relationship with the yield data for any year and may need modifications. The regression analysis showed a significant relationship of soil attributes to yield data for areas of the field with Harps and Ottosen soils. From a geographic information system (GIS) analysis performed with ARC/INFO, it was concluded that yield may be influenced partly by management practices and partly by topography for Okoboji and Ottosen soils. Map overlay analysis showed that areas of lower yield for corn, at higher elevation, in the vicinity of Ottosen and Okoboji soils were consistent from year to year; whereas, areas of higher yield were variable. From GIS and statistical analyses, it was concluded that interaction of soil type and topography influenced yield variability of this field. These results suggest that map overlay analysis of yield data and soil attributes over longer duration can be a useful approach to delineate subareas within a field for site specific agricultural inputs by defining the appropriate yield classes

Temporal Dynamics of Preferential Flow to a Field Tile

We conducted a sequential tracer leaching study on a field plot to investigate the temporal behavior of preferential flow to a field tile during an irrigation and subsequent rainfall events over a 14-d period. Two herbicides, along with the conservative tracer Br, were applied to a strip adjacent to a tile drain immediately before a 4.2-mm hr-1 irrigation. Three additional conservative fluoridated benzoates (PF, TF, and PF) were applied to the strip at 2-hr intervals during the irrigation. Breakthrough of the conservative tracer Br and the two herbicides occurred within the first 2-hr of irrigation, indicating that a small fraction of the solute moved through preferential flow paths. The last tracer (PF), applied 6 hr after the start of irrigation, took only 15 min and 1 mm of irrigation water to travel the 1.2-m distance between the soil surface and the tile. Thus, flow along preferential flow paths was faster during later stages of the irrigation. This study demonstrates that solute transport rates in preferential flow pathways is not a constant during a leaching event