Nutrient and heavy metal concentration and distribution in corn, soybean and wheat as affected by different tillage systems in the Argentine Pampas

Different tillage techniques affect the root absorption of macronutrients a nd trace elements. Our objective was to study the effect of conventional an d zero tillage on the concentration of macro- and micronutrients and specia lly heavy metals and their distribution in soybean, wheat and maize plants in a area located far from contamination sources. The study was performed i n a field experiment initiated in 1979 at the Agricultural Experimental Sta tion located at Pergamino (Buenos Aires province, Argentina). The soil is a Pergamino Series Typic Argiudoll. The crops were wheat-soybean/com in cont inuous sequence, in plots subjected to no tillage and conventional tillage. The experiment was a randomized block design, with four replications of ea ch tillage treatment, Fertilizers were applied annually, averaging 90 kg N/ ha/yr and 18 kg P/ha/yr. Wheat, corn and soybean were sampled in 1997 and s eparated into roots, aboveground material and grains. The three crops were analyzed for nitrogen (N), phosphorus (P), sulfur (S), potassium (K), boron (B), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), molybdenum (Mo), nickel (Ni) and zinc (Zn), Macronutrient concentration was higher in grain s than in roots (i.e. N in corn: grains, 11.5 g kg(-1); roots, 6.9 g k(-1)) . Micronutrients and heavy metals concentration were higher, with the excep tions of Mo and Cd, in roots than grains (i.e. Zn in soybean: grains, 44.85 mg kg(-1); roots, 64.73 mg kg(-1) or Cr in wheat: grains, 1.77 mg kg(-1); roots, 19.70 mg kg(-1)). The effects of tillage were limited for nutrient c oncentrations, but significant for heavy metals. Soybean appeared to be mor e sensitive than cereals to the apparent effect of soil tillage. Compared w ith early published data of soils at the same location, there was only a si gnificant relationship between Zn concentration in soils and its accumulati on in plant roots. (C) 2001 Published by Elsevier Science B.V.