REGION-ADAPTED EARLINESS TRAITS
Region-adapted earliness traits
Grain maize is grown on a large share of the global area, due to its wide range of earliness traits that are adapted to a great variety of local temperature sums. The interest that grain maize presents economically is linked to its yield potential – which in turn depends on the available water resource. Producers may consider choosing a specific earliness category when they need to save on drying costs and they face water stress, whether in irrigated or rainfed systems. Choosing to plant earlier hybrids is a question that should be weighed in light of the yield losses that one may incur as a result of shorter growing cycles, as well as other aspects such as drying cost and irrigation savings, timing one’s crop so as to avoid water deficits, and the ability to harvest earlier. Early harvests allow one to free up the land sooner for the next crop, create mulch covers, or plant catch crops.
Corn research has helped to widen the range of earliness options and improve hybrid performance. Thus, early hybrids have come to be more and more productive. Moreover, breeders have been able to obtain faster grain dry-down rates over the past thirty years, through line crosses with late-flowering, early-maturing parents. This criterion has now become key when choosing one’s hybrids. The latest hybrid profiles cover all earliness groups of grain maize. For an equal length of the growth cycle (from planting to physiological maturity – at around 32 percent kernel moisture), the hybrids present later flowering (due to a higher number of leaves), which improves light interception.
The hybrids also present higher potential numbers of kernels per ear, as well as shorter kernel growth and dry-down rates, along with very good standing plant dry-downs. The progress made in terms of dry-down speed has largely contributed to drying cost savings as well as environmental benefits.
DROUGHT ESCAPE AND AVOIDANCE: PUTTING EARLINESS TO THE TEST
While choosing hybrids of a specific earliness group is less of an issue in favourable conditions, things are different in water stress environments. Historical weather data indicate a significant temperature increase at the time of corn development, over the past three decades. In the face of these climate changes, growing corn is about adjusting one’s strategy, namely:
- Planting earlier, without changing the hybrid earliness group. The crop will start its growth cycle earlier and will reach grain fill stage faster. The question of saving irrigation water remains highly variable, depending on the summer rainfall pattern and temperatures.
- Choosing earlier hybrids in a way that will allow the crop to attain its most sensitive growth stages earlier. Depending on the years, water reserve requirements are estimated to range between 0 and 30 mm of water. This type of strategy also allows one to harvest the grains at lower water contents and thus reduce drying costs. However, it also means giving up the higher yields one would get with later varieties, in good rainfall conditions or in a year with early water stress, followed by a return of rainfalls in August.
While the “escape” strategy allows one to manage growing corn in rainfed systems and to control water stress risks, it is important not to sow the seeds too close to the soil surface. Ensuring a soil water reserve of more than 100 mm is crucial. How early one can push the sowing date will still depend on how cold it is at the beginning of the cycle. In the coldest areas, one must monitor for the last frost days, since maize remains sensitive to frost until as late as 6-8 leaves. It is basically at that stage that the number of kernel rows is set. Any significant frost at that point will impact the yield. Another aspect to remember is that maize growth takes place from 6°C on. It is therefore recommended to wait for a temperature rise first, in order to plant maize in the best conditions. Any cold spell early in the plant’s cycle will limit its growth and will expose it to potential pests (especially wireworms) for a longer period of time.