The hysteretic water content‐pressure head relationship and the hydraulic conductivity‐water content relationship for a porous material are needed in the solution of the water flow equation to predict behavior of a given flow system. These hydraulic properties were measured in an unsteady‐state manner using gamma ray attenuation for the water content and strain gauge pressure transducer tensiometery for the pressure head. Envelope curves and four to six primary wetting and drying scanning curves of the water content‐pressure relationship were determined. A convenient method of representation of the scanning curves by an empirical function was developed for use in computer solutions of the water flow equation.
The yield in any given field or management zone is a product of interaction between many soil properties and production inputs. Therefore, multi-year yield maps may give better insight into determining potential management zones. This research was conducted to develop a methodology to delineate yield response zones by using two-state frequency analysis conducted on yield maps for 3 years on two commercial corn fields near Wiggins, Colorado. A zone was identified by the number of years that yield was equal and greater than the average yield in a given year. Classes producing statistically similar yield were combined resulting in three potential yield zones. Results indicated that the variability of yield over time and space could successfully be assessed at the same time without the drawbacks of averaging data from different years. Frequency analysis of multi-year yield data could be an effective way to establish yield response zones. Seventeen percent of the field #1 consistently produced lower yield than the mean while 43% of the field produced yield over the mean. Corresponding values for field #2 were 6% and 42%. The remainder of the fields produced fluctuating yields between years. These spatially and temporally sound yield response maps could be used to identify the yield-limiting factors in zones where yield is either low or fluctuating. Yield response maps could also be helpful to delineate potential management zones with the help of resource zones such as electrical conductivity and soil maps, along with the directed soil sampling results.
scale too coarse to be effective. Franzen et al. (2002) compared Order 1 and Order 2 soil surveys with maps Variable rate fertilizer application technology (VRT) can provide from grid sampling and topography based zone maps. an opportunity to more efficiently utilize fertilizer inputs; however, accurate prescription maps are essential. Researchers and farmers Order 2 soil surveys were seldom useful in determining have understood the value of dividing whole fields into smaller, homo-zones for site specific management of NO 3 -N. Order 1 geneous regions or management zones for fertility management. Mansoil surveys were more highly related to soil NO 3 -N agement zones can be defined as spatially homogeneous subregions than Order 2 surveys, but their consistency was not as within a field that have similar crop input needs. Delineating managehigh as when topography based zones or maps from ment zones that characterize the spatial variability within a field may grid sampling were used. Landscape position also has provide effective prescription maps for VRT. The objective of this been used to divide fields (Fiez et al., 1994). They found research was to compare and evaluate management zones developed that landscape position alone was not effective in dividfrom soil color (SC) and farmer experience with management zones ing fields into units for variable rate N management. developed from apparent electrical conductivity (EC a ). These two However, Franzen et al. (2001) concluded that topogramethods of developing management zones were compared with soil nutrient levels, texture, and crop yields collected on two fields in 1997.
phy-based zone soil sampling may be useful in semiaridThe soil and yield parameters followed the trends indicated by both environments. Long et al. (1998) proposed using the spamanagement zone methods at Field 1 with the highest values found tial variation in grain protein levels to identify N manin the high productivity zones and the lowest the low productivity agement zones in spring wheat (Triticum aestivum L.).
zones. Significant differences were found among the managementCurrently, the procedure is applicable for dryland fields zones. However, at Field 2 the high and medium productivity zones that are cropped annually to wheat. Practical implemenwere generally not significantly different using the SC approach, tation of this procedure requires that an appropriate whereas the EC a approach was effective in identifying three distinct sensor be made available to producers that can continumanagement zones. Both methods of developing management zones ously read the protein concentration of grain from comseem to be identifying homogeneous subregions within fields. bine harvester. Ostergaard (1997) developed management zones for VRT N application based on soil type, yield, topography, aerial photos, and producer experi-Predicted SOM was highly correlated with measured Bldg.
A finite difference solution of the Richards equation was tested experimentally for hysteretic flow in a nonuniform medium. The space‐dependent hydraulic properties (water content‐pressure head and hydraulic conductivity‐water content) were determined experimentally on a laboratory column of sand and were represented in the numerical model by empirical equations.Boundary conditions resulting in hysteretic flow were applied to both the experimental column and the numerical model and the resulting water content and pressure head profiles were compared. Agreement was excellent between the measured and computed results. An additional simulation, in which the medium was considered to be nonhysteretic, gave good agreement between the measured and computed pressure head values but resulted in substantial error in the computed water content values.
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