Crop rotation diversity and tillage effects on soil and wheat grain nutrient concentration in an organically-managed system

Consumer demand for high quality organic produce in Canada has in recent years contributed to the development of a more sustainable organic agriculture system that increased productivity without decreasing soil fertility. The objective of this 4-yr field study was to determine if an organic system with diversified crop rotations under reduced tillage would produce high quality spring wheat (Triticum aestivum L.) grain and improve soil fertility. A simplified rotation (SR) consisting of a forage pea (Pisum sativum L.) green manure (GM)-spring wheat sequence and a diversified rotation (DR, forage pea GM-oilseed-pulse crop-spring wheat sequence) were compared under two tillage intensities (high tillage [HT] and low tillage [LT]). The oilseed alternated between mustard (Sinapis alba L.) and flax (Linum usitatissimum L.), and the pulse alternated between field pea and lentil (Lens culinaris L.). Generally, nutrient concentrations in wheat grain were mostly significantly higher under LT than HT and in the DR compared with the SR. In addition, tillage-rotation system influenced soil zinc, calcium, magnesium, and sodium concentrations. However, grain Cd concentration was higher in the LT treatment under the DR sequence relative to other treatments. Our results indicate that organically managed diversified crop rotations under reduced tillage can produce wheat grains with high nutritional value for humans and livestock but may not increase soil micronutrient concentrations.