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Project Title:  Variability of Soil Chemical and Physical Properties and Their Influence On Soybean Yield In Mississippi
Investigators: Michael S. Cox, Department of Plant and Soil Sciences, MAFES, David R. Shaw, Department of Plant and Soil Sciences, MAFES; M. Alan Blaine, Department of Plant and Soil Sciences, MSU-MAFES, and David H. Laughlin, Department of Agricultural Economics, MAFES
Overview and Objectives: 

Mississippi has a broad spectrum of soils making up its landscape. It is one of the few states that contains as many as eight of the twelve soil orders.  This contributes to the high amount of variability seen throughout its soils.  Many studies have shown the importance of soil physical and chemical properties on the variation in soil characteristics and that found that soil physical and chemical properties have the potential to vary significantly with landscape position. However, a lack of consistent correlation between soil variables and yield is not uncommon.   The soil factor that may affect yield in one area within a field is subject to change throughout the field hence, its influence on yield can change. As new precision agricultural technologies reach the public, there is a great deal of question as to the abilities of these technologies. Without a thorough understanding of the factors affecting soybean production, it is impossible to determine the benefits of these technologies. This study attempts to define the benefits of precision agriculture to soybean production in Mississippi. Specific objectives are:

  1. To determine the amount of variability in selected soil physical and chemical properties.

  2. To determine the effect soil variability on soybean yield.

  3. To determine if soil variability could be described by soil series.

  4. To determine if apparent soil electrical conductivity could be related to soil properties.

  5. To determine if changes in apparent soil electrical conductivity could be related to changes in soybean yield. 

Results To Date: 

Delta and Hill (Producer) Fields: Variability of the measured soil parameters range from low (pH) to quite high (P) within the three fields used in this study. However, the variability of chemical factors tend to follow the same order among the fields suggesting that this order was somewhat common. Linearity among the soil parameters made their correlation with yield difficult to interpret. Principle component analysis coupled with stepwise regression allowed us to speculate that general fertility, clay content, and topography had important influences on crop yield with topography and clay content having an influence in all three fields. Although the influence of these factors are not always straightforward, the specific influence of the topographic features and clay content appeared to vary between fields and years and seemed to indicate water flow in the fields. While the topographic factors and clay content helped explain yield variation, they would be of questionable value in planning SSSM prior to the growing season. The principle component analysis also revealed some factor, possibly associated with P and K, that reduced crop yield. This factor requires more investigation as to its identity. As these three fields were considered representative of common Mississippi fields, the topographical and soil texture features of production fields should be considered when defining soil management. 

In addition to using the soil properties and topography to delineate management zones, comparisons of soil properties to soil series were also attempted. Only one field showed relationships between soil series and topography. There was no relation between yield and soil series for any of the three fields. These results indicate that using soil series as a delineating factor for soil management zones will lead to erroneous results.             

Black Belt (Experiment Station) Fields: The three fields chosen for this study possessed different histories and yield and soil characteristics despite a close proximity to each other. Two of the three fields had medium to high P and K values but low yields while the third field had low P and K values but relatively higher yields. These relationships suggest that soil factors other than fertility were yield-affecting. Soil variability, with the exception of pH, was highest in the North field. Potassium in this field exhibited evidence of high amounts of small-scale variability with CVs increasing approximately 66% despite soil samples being collected from the same areas. A lack of correlation between elevation and other soil properties indicated that negligible amounts of erosion had taken place in this field. The South and East fields used in this study had evidence of erosion processes taking place, however, this evidence was strongest for the East field. In the other measured soil factors, variability in these two fields were similar. Principle component analysis coupled with stepwise regression revealed that soil pedogenic factors (parent material, topography, and texture) influenced soybean yield more consistently across all three fields than any of the other measured soil properties. However, the effects of topography and texture appear to change based on the climatic conditions experienced by the crop during the growing season. This is interpreted to mean that these two factors were more indicative of the water holding characteristics of these fields. Soil fertility parameters did not appear to have much effect on soybean yield in these three fields. These results suggest that using pedogenic soil factors to determine soil management zones would be more beneficial than using anthropogenic factors such as soil fertility.

As many factors influence yield, and the objective of this project is to determine if EC can be used to define soil management zones, EC was also related to soil properties using the same methods as with. In the north field, shallow EC (0 to 1 ft) appeared to be related negatively to silt content and positively to elevation and slope while the deep EC appeared to be negatively related to silt and positively to slope. In the south field, shallow EC appeared related to P and K, and negatively related to clay content. Deep EC appeared to be related to Mg and elevation.  In the east field, the relationship between EC and soil properties appeared to be much more involved. Shallow EC appeared to be related to texture, Ca, K, and Mg. Deep EC appeared to be related to silt, K, and Mg. 

Conclusions To Date: 

Research indicates that many factors are influencing soybean yield in these fields. It appears that soil management zones cannot be strictly determined using any one soil parameter across all three fields. In these fields, it appears that topography and soil texture, most likely as they relate to plant available water, would be parameters that could be used on all fields. However, these parameters would not meet all of the needs on any of the fields used in this study. Main management zones based on these soil properties could then be further defined, possibly based on soil test values. 

It also appears that soil series difference will not adequately serve to delineate soil management zones. This could be due to many factors influencing soil mapping decisions.  Differences in soil series within fields may be due to subsoil characteristics that do not influence surface soil or yield parameters, or to differences in surface soil characteristics being removed due to anthropogenic reasons as the cropping histories of fields lengthen. 

Future Research: 
  1. Continue studying soil EC as a method for delineating soil management zones.

  2.  Possibly include hydrologic modeling moisture patterns in the field.

  3.  Study remote sensing as method for delineating management zones.


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Last Modified: 01/06/2004