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ABSTRACT
Soil samples from archives and newly collected groups were analyzed to examine changes in mineral nutrient availability and selected soil chemical factors under long-term management systems. Continuous corn (CC), corn-soybeans (CS), corn-soybean-wheat (CSW), and continuous soybeans (SS) were the rotations examined under moldboard plow (MP) and no-tillage (NT) conditions on a silty clay loam soil. Crop rotation had little effect on nutrient availability. Reduced soil pH by rotations containing corn was likely due to nitrogen fertilization with anhydrous ammonia. Reduced tillage resulted in reduced pH, increased cation exchange capacity (CEC), and increased calcium (Ca) and magnesium (Mg) availability. Sixteen years of cropping without added fertilizer [other than nitrogen (N)] did not alter the total extractable levels for phosphorus (P), potassium (K), Ca, Mg, manganese (Mn), zinc (Zn), copper (Cu), boron (B), or sodium (Na); however, iron (Fe) levels were reduced by NT. Average soil pH, available P, and available Mn declined over time while available Ca, available Mg, and CEC increased over time. Available K declined initially and then recovered to initial levels.
ACKNOWLEDGMENT
The author wishes to gratefully acknowledge the contributions of Dr. Marvin M. Schreiber for the establishment of the original experiment in 1980 and for his encouragement and editing skills.