CROP SEQUENCE AFFECTS NUTRIENT COMPOSITION OF CORN AND SOYBEAN GROWN UNDER HIGH FERTILITY

Although crop rotation may change soil mineral status, particularly N, there may also be a rotation effect beyond that which can be explained by soil mineral status alone. Research has shown that leaf mineral-composition can vary between crop sequences at high fertilizer levels. We hypothesized that the rotation effect observed in long-term sequences of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] might be due to an increased nutrient concentration, not just an increased accumulation. A corn-soybean rotation study in Minnesota managed at high nutrient fertility was used to test our hypothesis. The high management level was appraised by soil test levels. Corn and soybean sequences evaluated were monoculture, first year, second year, and annually-alternated. These crop sequences were evaluated for their effects on plant nutrient concentration, accumulation, or both. The growth stage at which differences in plant nutrient concentration or accumulation might affect final yield was also evaluated. A positive effect of rotation on yield was observed in both crops. Shoot concentrations and total accumulations of N, P, and K were higher in first year corn compared to monoculture, suggesting that the increased corn yield associated with rotation may have been due to a general improvement in plant nutrition. Cropping sequence had less of an effect on soybean nutrient concentration than corn. Nutrient accumulation in soybean was not generally affected by crop sequence.