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outputs in time. Prescription maps of fertilizer rates are usually derived from one or more condition maps, Zone sampling for site-specific N application has been shown to modified perhaps by performance maps. The four condibe effective in North Dakota and other areas of the Great Plains. Printed and sometimes digitized soil surveys are presently available tion-map categories for nutrient management are (i) for most agricultural counties in the USA. Order 2 soil surveys gener-soil surveys, (ii) interpolation of a network of point ally have scales that range from 1:12 000 to 1:31 680. These surveys samples (i.e., grid sampling), (iii) yield monitor data or were developed for general planning purposes. There is interest in remotely sensed images, and (iv) modeling to estimate using Order 2 soil surveys as a basis for delineating N management spatial nutrient patterns. zone patterns, especially where the soil-mapping units have been Soil surveys are compendiums of soils in a region. digitized. This study was conducted to evaluate soil survey scales at Compendiums contain information on boundaries of the Order 1 (scale Ͼ1:15 840) and Order 2 level against grid-and soil series, types, associations, or complexes that are topography-based zone sampling to determine whether soil surveys usually traced on aerial photographs of the region. Most at these scales could be used to delineate N management zones for soil surveys in the USA are designated second order site-specific fertilizer application. Fields mapped at a finer scale (Order 1 survey) showed some similarity between mapping units and N man-

A physico‐empirical model proposed by L.M. Arya and J.F. Paris in 1981 for predicting the soil moisture characteristic curve using particle size and bulk density data was compared with a commonly used laboratory method using undisturbed core samples and a pressure plate extractor, for precision in estimating in situ water retention measured with paired neutron probe and tensiometer installations. An empirical factor for the Arya and Paris (A&P) model was found to average close to the value (α = 1.38) proposed by its authors. Values for this experiment were different between texture classes. Loam and silt loam values were constant, while values for soils of sand, loamy sand, and sandy loam texture were nonconstant. The empirical factor was calibrated for (i) loam and coarse loam; (ii) silt loam; and (iii) sand, loamy sand, and sandy loam texture groups. The sandy soil values required linear calibration as a function of soil water potential. Results for the calibrated A&P model compared well, overall, with laboratory determinations on soils ranging in texture from sand to loam and silt loam. Laboratory estimates were slightly better for A and B horizon materials, while A&P estimates were better for C horizons. Error for estimation of field volumetric water content using A&P and lab methods was approximately twice the error for estimation of θ using a second field neutron‐tensiometer installation within one meter of the first field apparatus.

Wind erosion is a serious problem in the Red River Valley of North Dakota. Wind erosion sediments were characterized to evaluate their potential as nonpoint source pollutants for surface water and shallow groundwater. Thirty‐four sites from the South Dakota border to the Canadian border were sampled to measure physical and chemical characteristics of displaced sediment and field soils. Collected sediments originated from fields with soils having silt loam, silty clay loam or silty clay textures. Sediments had >98% water‐stable aggregates and average NO−3‐N levels of 105 mg kg−1. Calcareous sediments (22 samples) were significantly higher in pH, NO−3‐N and electrical conductivity (EC), while noncalcareous sediments (12 samples) were higher in P and K. Soils from sugar beet (Beta vulgaris L.) and small grain fields tended to have higher NO−3‐N levels than fields with other crops or cropping practices. Agricultural chemical residues were detected and identified at two sample sites. A comparison of displaced sediments with field soils showed significant increases in NO−3‐N, P, K and EC in the sediments and a significant reduction in pH. Nearly 96% of the NO−3‐N could be leached out of the sediments in an initial leaching. Wind erosion sediments have the potential to be nonpoint sources of NO−3‐N and salinity for surface and groundwater.

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