How to model the effects of farming practices on weed emergence

Early weed emergence models directly relate the weed seedbank to emerged seedlings, with constant emergence rates for each tillage tool. These models compare cropping systems at long term in a given region. Other models relate emergence to rain and air temperature. They are useful in no-till systems with seeds close to soil surface. Recently, other authors split emergence into germination and pre-emergence growth, depending on soil climate. But seed survival and dormancy as well as tillage were not yet integrated. Models advising farmers for strategic farming decisions in a large range of situations must split emergence into mechanistic relationships distinguishing the various underlying biological subprocesses in order to correctly quantify the effect of cropping system. The model ALOMYSYS for Alopecurus myosuroides emergence follows this principle, based on submodels predicting (a) soil environment resulting from the cropping system, (b) vertical soil seed distribution after tillage, and (c) seed survival, germination and pre-emergence growth depending on soil environment, seed depth, characteristics and past history. This model can be used to determine the optimal tillage modes and sowing dates, depending on the preceding crop succession, the following crop and the work constraints of the farmer.