03262nam a2200229 a 450000100080000000500110000800800410001910000180006024501230007826000160020130000110021750001020022852025600033065000150289065000160290565000100292165000330293165000090296465000130297365300100298665300360299612432912011-01-13       2000    bl uuuu  m   00u1 u    #d1 aCOELHO, A. M.  aIrrigated corn yeld as related to spatial variability of selected soilproperties in a silty clay loam and sandy soils.  a2000.c2000  a175 f.  aDissertation (Doctoral of Philosophy - Soil and Water Science) - University of Nebraska, Lincoln.  aSpatial variability of soil physical and chemical properties and its relationships with corn growth and development was assessed in a sandy soil cultivated with corn in central Nebraska. Field studies involved extensive soil sampling, measurement of plant population, leaf tissue composition, and grain yields during the 1997 and 1998 growing seasons. Classical statistics, geostatistics, factor analysis, and multiple linear regressions were used as the principal techniques to explore soil and crop variability, the nature of interactions that might affect crop yield, and to classify and map status of soil properties in the field. Spatial distribuion of grain yields was similar in both years. Grain yields ranged from 11 to 14 Mg ha-1 and averaged 12,5 Mg ha-1. Plant populations varied from 62 to 73 thousand plants per hectare across the field but were not consistently related to grain yield. Factor analysis was found a useful tool in analyzing associations of systematic soil variation within the experimental field. Most of the soil variation as related to crop growth was describe by five factors, which collectively explained 85% of the total soil variability. Regression models based on these factors were associated with 50% of the corn yield variation. The results suggest that soil physical-chemical factor, as related to organic matter, texture, bulk density, and pH has a large effect on the variation of corn yield. Soil inherent fertility and fertilizers factors had little relationship with grain yield mainly due to high levels of measured nutrients in the field and fertilizers applied by the farmer. Contour maps based on the score of each factor were useful in displaying the pattern of soil variation in the experimental field. The beginning of soil degradation associated with corn production was assessed by comparing field soil properties under corn managementto those under perennial grass. Loss of organic matter, due mainly to intensive tillage and input of fertilizers, mainly nitrogen, acidificaiton associated with application of ammoniacal fertilizer, and subsoilcompaction were some indicators of this degradation. As indicated by some soil properties measured in field, the actual systems of soil and crop management used by the farmer resulted in reduced soil quality and increased environmental degradation. Additional inputs of fossil fuel derived energy in irrigation and fertilizers will be necessary to sustain the high levels of corn production which likely lead to further soil and environmental degradation.  airrigation  aIrrigação  aMilho  aPropriedade Físico-Química  aSolo  aZea Mays  aMaize  aSoil chemicophysical properties