Farm Table says:
Long-term experiments (LTE) are useful to understand and compare long-term effects of organic and conventional systems on crop productivity and the environment. For this reason, we started the BIOSYST LTE in 1996, to compare an organic rotational system and a conventional low-input system in Central Italy.
The aim of this work, which is to evaluate the grain yield and apparent biomass and N balances of soft and durum wheat rotated to several arable and vegetable cash crops in a long-term experiment conceived to compare an organic and a conventional low-input system in an inland plain of Central Italy.
Soft wheat yielded more than durum wheat. For both species, grain yield and protein content were more variable across years and generally lower in the organic than in the conventional system. In both systems, grain yield of both species resulted negatively correlated with fall-winter rainfall, likely for its effect on soil N availability. Both species caused a lower return of biomass and a higher soil N depletion in the organic than in the conventional system.
In the experimental conditions, both soft wheat and durum wheat yielded less in the organic than in the conventional system and gave grains with lower protein content, used the supplied N more efficiently (on a marketable yield dry matter basis) and caused higher depletion of soil N.
The main limitation for organic crops was the low N availability, not counterbalanced by the supposed residual effect of green manuring carried out before the preceding summer vegetable. In the conventional system, the chance to split the rate by using mineral fertilizers allowed to prevent leaching in fall-winter and guaranteed some N availability in spring.
Our experiment confirmed that winter wheat can help exploit the soil N availability and reduce N leaching in fall-winter, especially after summer vegetables, but in stockless or stock-limited organic systems it needs to be included in rotations where soil fertility is restored by fall-winter green manures to be carried out before summer crops.