Micronutrients in the Soil and Wheat Grain and Straw: Impact of 84 Years of Organic or Synthetic Fertilization and Crop Residue Management.

Although the micronutrients in soils are essential for crop production, the status of micronutrients in the long-term crop residue experiment (CR-LTE) at Pendleton were never examined. The assessment of micronutrients is crucial to design the future management policies for the sustainable crop production. The objective of this study was to assess the effect of management practices on the micronutrient availability in the soil at 4 depths (0-10 cm, 10-20 cm, 20-30 cm, and 30-60 cm) and in wheat grain and straw of the CR-LTE in 1995, 2005, and 2015 samples. The micronutrients tested were magnesium (Mg), manganese (Mn), copper (Cu), iron (Fe), boron (B), and zinc (Zn) and were extracted by Mehlich III solution. The treatments consisted of the incorporation of wheat straw; fall burn with 0 kg N ha^-1 (FB0); spring burn with 0 kg N ha^-1 (SB0), 45 kg ha^-1 (SB45), or 90 kg ha^-1 (SB90); no burn with 0 kg N ha^-1 (NB0), 45 kg ha^-1 (NB45) or 90 kg ha^-1 (NB90); and no burn with manure (FYM) or pea vine (PV) incorporation. Manure treatment had the highest available Mn (162 kg ha^-1) and Zn (3.79 kg ha^-1) followed by PV (for most of the nutrients) in the top soils (0-10, and 10-20 cm). Available Cu was highest in SB0 (7.01 kg ha^-1) and were lowest in the organic amendments (FYM :6.58 kg ha^-1; PV: 6.51 kg ha^-1). The availability of Mn and Zn decreased with the increase in soil depths whereas Cu availability was higher in deep profile. The concentration of Mn, Cu, and Zn in the grain and straw significantly declined over time since 1995. Changes in management are required to maintain micronutrients for a sustainable wheat production in the CR-LTE.