@article{crozier_naderman_tucker_sugg_1999, title={Nutrient and pH stratification with conventional and no-till management}, volume={30}, ISSN={["1532-2416"]}, DOI={10.1080/00103629909370184}, abstractNote={Abstract This study investigated changes in soil test results associated with sampling depths in fields managed with conventional tillage, no‐till for less than 3 years, no‐till for 3 to 6 years, and no‐till for more than 6 years. Soil samples from depths of 0–5, 0–10, 0–20, and 10–20 cm were collected from 59 fields with different tillage histories from several geologic regions, and analyzed by the North Carolina Department of Agriculture soil test laboratory. Some nutrient stratification was noted in all tillage categories. Soil test phosphorus (P), potassium (K), and zinc (Zn) concentrations were significantly higher in the 0–10 cm depth than in the 10–20 cm depth. Stratification probably results from the prevalence of tillage with disks, chisel plows or subsoilers, which do not mix the soil thoroughly. With the adoption of no‐till methods, stratification becomes even more pronounced. Our data suggest that stratification in pH, calcium (Ca), manganese (Mn), and sulfur (S) is more likely for fields in t...}, number={1-2}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Crozier, CR and Naderman, GC and Tucker, MR and Sugg, RE}, year={1999}, month={Jan}, pages={65–74} }
 @article{borkert_cox_tucker_1998, title={Zinc and copper toxicity in peanut, soybean, rice, and corn in soil mixtures}, volume={29}, ISSN={["0010-3624"]}, DOI={10.1080/00103629809370171}, abstractNote={Abstract Applications of zinc (Zn) and copper (Cu) at excessive rates may result in phytotoxicity. Experiments were conducted with mixtures of soils that were similar except for their Zn and Cu levels. The critical toxicity levels (CTL) in the soils and plants for these elements were determined. Peanut (Arachis hypogaea L.), soybean [Glycine max (L.) Merr.], corn (Zea mays L.), and rice (Oryza sativa L.) were the crops grown. One soil mixture had Mehlich 3‐extractable Zn concentrations up to 300 mg dm‐3 with no corresponding increase in soil Cu; two soil mixtures had soil Zn concentrations up to 400 and 800 mg dm‐3 with a corresponding increase in soil Cu up to 20 and 25 mg dm‐3, respectively; and four soil mixtures had no increase in soil Zn, but had Mehlich 1‐extractable Cu concentrations from 6 to 286 mg kg‐1. Under a given set of greenhouse conditions, the estimated Mehlich 3‐extractable Zn CTL was 36 mg dm‐3 for peanut, 70 mg dm‐3 for soybean, between 160 and 320 mg dm‐3 for rice, and >300 mg dm‐3 fo...}, number={19-20}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Borkert, CM and Cox, FR and Tucker, MR}, year={1998}, pages={2991–3005} }