"All About Taxonomy"

mhmmd_ml@yahoo.comAbstract/ Amal Muhammad/ Unversity of Baghdad
This study was conducted on some soils of agricultural projects in the middle of Mesopotamian plain representing two physiographic units, river and irrigation canal levees. The aims of the study can be summarized as to:
(1) Descriping the studied soils.
(2) Classifying the studied soil pedons by using numerical methods.
(3) Comparing numerical classes with those of USDA (2003); and
Al-agidi (1976).
Semi-detail survey maps for nine agricultural projects in the middle of Mesopotamian plain were used as a basic maps to select the most dominant and frequent soil series in each project.
Nine sites were selected within three strip transects:
(1) Strip
1.     Ishaqi2.     Kassawiy
3.     Saqlawiya
 (2) Strip
1.     Baghdad
2.      Field of the college of Agriculture (Abu-Ghraib)
3.     Radhwania
 (3) Strip
1.     Suwaira
2.     Latifiyah
3.     Great Mussaib
The pedons were described and samples from each horizon were taken for some physical, chemical, and mineralogical analysis. The studied soils were classified down to family level according to USDA (2003); and down to series level according to Al-agidi (1976). Some morphological, chemical, physical and mineralogical properties were selected for hierarchical grouping methods which were:
(1) Single linkage (NN): where the distance between two clusters was determined by the distance of the two closest objects in the different clusters.
(2) Complete linkage (FN): where the distance between two clusters was determined by the greatest distance between any two objects in the different clusters.
(3) Unweighted pair-group average (UPGMA): where the distance between two clusters was calculated as the average distance between all pairs of objects in the two different clusters.
(4) Weighted pair-group average (WPGMA): this method was identical to the (UPGMA) method except that the size of the respective clusters was used as a weight in the computations.
(5) Unweighted pair-group centroid (UPGMC): where the distance between two clusters was determined as the difference between centroids.
(6) Weighted pair-group centroid (WPGMC): this method was identical to the (UPGMC) method; except that weighting was introduced into the computations to take into consideration differences in cluster sizes.
(7) Ward’s method (M.V.): this method attempted to minimize the sum of squares (SS) of any two clusters that could be formed at each step.
The results indicated that soil textures were ranged between moderately fine to moderately coarse; while the values of bulk density were low in the surface horizons for most soil pedons. The electrolytic conductivity values for all pedons in the study areas ranged between none to moderately saline soils, while the pH values ranged between slightly to moderately alkaline. The results also indicated that gypsum content was low for all pedons due to the effect of the nature of parent material and the agricultural activities in relation to physiographical location causing some effect of degypsification process specially during irrigation processes. The results showed a homogenous distribution of lime in all pedons due to the origin of the soils from calcareous parent material.
Cation exchange capacity varied in it’s values mainly due to the variation in clay content. The results of heavy minerals indicated that the opaque minerals did not show specific pattren of distribution within all studied pedons mainly due to the effect of geomorphological processes specially deposition process. The Amphibole minerals were the dominant in the pedons of Suwaira, Latifiyah and Mussaib, while Chlorite minerals were domenant in the pedons of Ishaqi and Baghdad. The resistant minerals were found in rare quantities which indicated the effect of mineralogical composition of parent material.
The results of light minerals indicated that Quartz mineral was dominant in all pedons due to it’s resistance to weathering and could be inherited from parent material. While Mica minerals were found in low amount as they were least resistance minerals and due to lower content of parent material for these minerals.
The results indicated that the Smectite minerals group was dominant in all pedons due to the presence of environmental conditions for their formation as well as they were inherited from parent material, while Chlorite minerals group was recognized as a second group in dominance in all pedons.
According to the morphological, physical, chemical and mineralogical data; all pedons were classified to Entisols order and to subgroup Typic Torrifluvents which consisted of seven families and nine soil series according to soil series classification (Al-agidi, 1976).
The results of numerical classification indicated that the upper fusions of the dendrogram showed higher dissimilarity indices towards the top of the dendrogram. The classification indicated that pedons of Ishaqi and Baghdad resulted in the highest similarity index in hierarchical clustering methods. This means that these pedons represented the closest objects in the dissimilarity matrix, and the major character of these pedons was the declining in electrolytical conductivity values. Pedons of Suwaira and Latifiyah showed high similarity index at the dendrogram which means that the two objects were highly homogeneous; and the major character of these pedons was the increasing of electrolytical conductivity values with homogeneity of mineralogical composition of fine sand fraction.
Comparison results of numerical classification with the soil taxonomy USDA (2003) at the family level indicated that the results of numerical classification methods of FN, WPGMA and M.V. were convenient with USDA system; while the numerical methods of FN, WPGMA and M.V. were in agreement with Al-agidi proposed system.
Using the criteria for hierarchical classification (Chaining, Stratification, Descriptive accuracy); the results indicated that the Ward’s method M.V. was the best numerical method because it was able to form obvious groups with most homogeneity in it’s fusions.