Relationship of Geomorphology to Origin and Distribution of a High Charge Vermiculitie Soil Clay

Abstract

AbstractA large quantity, up to 560 kg/ha, of elemental K fertilizer was required to obtain optimum yields and quality of tomatoes (Lycopersicon esculentum Mill.) in a fertility trial. The fertility trial was on a low well‐drained terrace of the St. Joseph River at Sodus Horticultural Experiment Farm located in Berrien County, Michigan.The surface layer of the soil contained 15% clay with a Ca/Mg cation exchange capacity of 115 meq/100 g. This clay was capable of fixing about 94% of the applied K fertilizer.A study of the glacial geology and more recent geomorphology in the area was done in order to determine the distribution and possible origin of the vermicultic soil clay at the study site.The geomorphic study showed that the oldest land surface had acid leached soils with the surface layer containing considerable chloritized vermiculitic clays but little or no vermiculite. In contrast the younger well‐ and moderately well‐drained river terraces had soils that were higher in pH, and the surface layers contained vermiculitic clay but very little chloritized vermiculite.Analysis of the soils on the river terraces showed a relationship of vermiculitic clay content to soil pH. If the soil pH was > 7.5 or < about 6.3 the vermiculite content of the surface layer dropped sharply.The vermiculite in the river terrace soils is apparently derived from chloritized vermiculitic soil clays that were eroded from the older upland soils. The change in pH of the environment from acid to neutral or mildly alkaline plus abundant organic matter, under suitable conditions, evidently triggers a dechloritization reaction involving an aluminate or organic complexing mechanism.