Undersowing wheat with different living mulches in a no-till system. II. Competition for light and nitrogen

No-till wheat management systems with a living mulch is a possible means to improve agricultural sustainability. Nonetheless living mulches may affect wheat production by competition for light and nutrients. Therefore, here we studied competition for light and nitrogen between wheat and different living mulches under no-till. We grew wheat using three different practices: (1) conventionally-tilled wheat, (2) no-till wheat and (3) wheat undersown with various living mulches. Living mulches were: red fescue, sheep's fescue, alfalfa, bird's-foot-trefoil, black medic, and white clover. We measured: leaf area index and height of wheat and living mulch, and radiation partitioning between species; above-ground biomass of wheat and living mulch; nitrogen uptake of wheat and living mulch; and wheat nitrogen status using a nitrogen nutrition index. Our results showed that at flowering, competition for light between mixed species occurred in sixteen out of the eighteen situations, i.e. in three experiments times six no-till/living mulch treatments. Further, the biomass of wheat grown with living mulches was 24-84% lower than no-till wheat alone. At flowering, competition for nitrogen only occurred in seven out of the eighteen situations. Our findings showed that competition for light was due to light partitioning between mixed species. Furthermore, we found that the light competitive ability of wheat undersown with a living mulch was the highest when wheat was much taller than living mulch, and also when wheat leaf area in the mixed canopy layer was greater than that of living mulch. We conclude that the negative effects of living mulches on wheat yield should be solved by a careful choice of living mulch species and the control of living mulches by mechanical or chemical means.