The role ofcrop managements farm technologies

tte adaptation of the crop calendar also involves potential changes in the sowing dates. For centuries the proper setting of the sowing date within a particular season has remained as extremely difficult task in practice. In some seasons it is also impossible to keep the recommended sowing dates because of constraints imposed either by weather conditions (e.g. high soil wetness / low soil workability) or other factors (e.g. machinery not adapted to wet soil conditions), ^e experimental data show that even small shifts in sowing dates can result in extreme differences in the final yields because vulnerable stages are exposed to different environmental stresses.

In many cases crop models can be used either to find the most appropriate sowing "window" or to calculate the penalty for premature /late sowing (Trnka et al., 2004; Zalud and Dubrovsky, 2002). ^e sowing date optimization procedure for a central European site is demonstrated in Figure 10.9a-b where two crop models were used to evaluate the effect of changing sowing dates. In the case of spring barley (Fig. 10.9a) it is clear that the overall mean yield is relatively insensitive to small changes in sowing date. Specifically, the median of the yields remains nearly constant if sowing varies within 20 days, ^erefore there would not be any severe penalty in most seasons if the sowing were moved. A simple rule based on the crop model results suggests that an earlier sowing date results in higher/more stable yields, which farmers in this region are already well aware of. ^e model we used also shows that the possibility of even earlier sowing is restricted by the soil workability in most of the seasons (grey box). On the other hand, if the planting

Spring barley - sowing date optimization

Spring barley - sowing date optimization

4000 8000 12000 grain yield (kg.ha'1)

16000

Fig. 10.9 a, b. Optimization of changing sowing dates for spring barley (a) and grain maize (b) for present climatic conditions as modelled by CERES-Barley and CERES-Maize. ^e shift is shown in terms of the deviation (in days) from the representative year's planting date (26 March-spring barley and 6 May), ^e bars represent quantiles (5th, 25th, median, 75th, 95th) of the model yields obtained in the 99-year crop model simulations for present and changed climate, ^e changed climate is represented by the AVG scenario, ^e shaded bars relate to the actual planting date, ^e shaded area in the case of spring barley marks unworkable soil conditions at the site.

4000 8000 12000 grain yield (kg.ha'1)

16000

Fig. 10.9 a, b. Optimization of changing sowing dates for spring barley (a) and grain maize (b) for present climatic conditions as modelled by CERES-Barley and CERES-Maize. ^e shift is shown in terms of the deviation (in days) from the representative year's planting date (26 March-spring barley and 6 May), ^e bars represent quantiles (5th, 25th, median, 75th, 95th) of the model yields obtained in the 99-year crop model simulations for present and changed climate, ^e changed climate is represented by the AVG scenario, ^e shaded bars relate to the actual planting date, ^e shaded area in the case of spring barley marks unworkable soil conditions at the site.

date is delayed, the grain yields tend to decrease because of the shift of the vegetation period to months with higher temperatures and lower precipitation causing higher water stress during the grain-filling phase and a shortening of this phase. An examination of grain maize yields at the same site (Fig. 10.9b) shows that they are also fairly insensitive to small changes in sowing date, but that in the case of the earlier sowing date, the probability that the yield will be damaged by a spring frost increases. On the other hand, if the sowing date is delayed, the grain yields tend to decrease because of the occurrence of autumn low temperatures, which terminate the grain filling phase.

Under changed climatic conditions the appropriate sowing times will have to be assessed again, but this adaptation measure is quite straightforward in the case of annual crops. For perennials (e.g. vineyards or orchards) the onset of phenological stages and the higher chance of frost damage are very threatening (Chemielevsky et al. 2006) especially under changed climatic conditions, and for this reason frost protection measures should be introduced (see below).

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