Seed Corn Irrigation: Under Constant Attention
Although the profile of sensitivity to water stress during crop growth does not differ much between corn hybrids and their parental lines, there are certain characteristics that influence the plants’ behaviour and guide the irrigation of seed corn crops.
First of all, plantings done later – in order to synchronise the flowering of the male and female lines – require complementary irrigation (to enable emergence) more often than in grain corn crops. It is particularly done in years with prolonged spring droughts.
More often than not, the parental lines are pure lines that have neither the size, nor the root exploration ability of hybrids. The data – issued from trials carried out by the ARVALIS Institute under the Technical Action Programme for Seeds, of the F.N.P.S.M.S. – are taken into account in decision-assisting tools such as Irre-Lis®. Thus, the share of soil moisture (R.U.) that is readily available to the plant (R.F.U.) has been estimated at 50 percent, as against 66 percent for a corn hybrid.
Starting off irrigation during the plant’s elongation, beginning with the V10 (the ten leaf) stage has proven to be essential in seed corn. The LAI (Leaf Area Index) is strongly influenced by the water availability during that period. Any stressor that appears before flowering will limit the plant’s ability to attain its maximum LAI, either in the male or in the female lines. Careful early management will secure a balanced growth of both parental lines – and a homogeneous one for the female line (important as it facilitates detasseling operations).
During the flowering/pollination stage, the plant’s water needs and water stress sensitivity are at their peak. While the effects of stress on female reproductive organ development are well-known, recent studies have emphasized how well-managed irrigation during this period is important for pollen production. Regular and sufficient water supply – correlated to climate conditions – is indispensable for pollen potential achievement (the number of pollen grains per tassel) and more importantly, for pollen viability, which can be reduced by as much as 45 percent in case of stress during this period.
It is equally important to support the plant’s nutrition during the period that follows pollination, as the number of grains per square meter (preliminary indicator of the yield, as bags of seeds per hectare) and the quality of their filling (weight of grains) influence the final yield directly.
In quality terms, the effects of irrigation in these later stages can be decisive for the grain calibration and germination ability. However, in our trials, the water supply differences that were insignificant towards the end of the cycle produced no major differences among the water regimens. The 50-percent grain moisture remains the most reliable indicator of the end of irrigation, in seed production.
Trials Focused on Optimizing Irrigation in Seed Production
With SEMAE assistance, the F.N.P.S.M.S carried out open field trials, under various water stress conditions. Run by the ARVALIS teams, the trials were aimed at comparing the results of different levels of irrigation (meeting water needs at different levels), using a control plot described as “well irrigated” and various scenarios of restrictive irrigation.
First of all, the trials have enabled us to characterise the effects of water stress on the physiology of the plant, on the development of yield components, and finally, on quality. Secondly, the purpose of the trials has been to develop strategies of production under water stress conditions. At present, the trials focus on the relationships between irrigation and plant population structures.