Don't be thrown by early Easter
04 March 2008 | Mark Britton
Maize planting time has a direct correlation to harvest time: the sooner the seed is in the ground, the sooner the crop will be in the clamp. True or false?
The Maize Growers Association (MGA) put the theory to the test in trials featuring three varieties planted on 14 April and with the same varieties planted one month later on 12 May. The MGA reported that the earlier drilled varieties were ready to harvest by mid-September, while those planted later would be ready closer to mid-October.
NK, the Syngenta Seeds brand for maize, agrees in principle with the trial findings, however we urge farmers to bear in mind some fundamental guidelines when considering sowing maize early: wait until the soil is warm enough before starting drilling and if you want an early harvest then you need to choose an early maturing variety.
We advise farmers to get out and measure soil temperature as it is the critical factor affecting safe sowing date. As soon as soil temperatures reach a consistent 5oC to 7oC without the risk of severe frost, then it will be safe to drill - but not before. The seed requires warmth plus moisture, and you simply cannot afford to risk drilling into a cold, wet seed bed. Nor can you risk maize seed emerging into cold temperatures, otherwise the plant will receive a check in its early growth stages. This will leave it extremely vulnerable in the longer term to pests and diseases and competition from weeds, all of which will impact on the final plant population and, ultimately, yield.
The 2008 drilling season has already raised a couple of issues for maize growers. Easter, the traditional time by which farmers aim to have their maize seed in the ground, has a very early calendar date towards the end of March. We continue to recommend the traditional optimum target drilling date of 20 April unless earlier drilling offers clear benefits and does not pose a threat to the crop. Furthermore, in February we experienced some unusual extremes of temperature from -9oC to 18oC; it’s those daytime highs that could encourage farmers to get the drill out early and attempt to offset the delays they experienced during the 2007 harvest.
Drill maize at the optimum temperature and its clock starts ticking immediately. That’s why we encourage farmers to decide carefully which variety to grow based on its maturity rating, a major factor in determining harvest date. Maize varieties vary in the number of Maize Heat Units (MHUs) required to reach maturity and subsequent optimum dry matter content. A MHU is the average of the maximum and minimum temperatures above 6oC on a cumulative basis from 1 May to 30 September.
For example, areas with a longer growing season will automatically rack up a higher number of MHUs and be suited to high yielding varieties such as NK Bull, which can make full use of the longer growing season. On the other hand, if you live further north, then you need to choose an earlier maturing variety, for example, Avenir, which requires less MHUs to reach its true potential.
Last year’s unusual summer conditions slowed down the accumulation of Maize Heat Units. The crop matured later, yield difference between the early and later maturing varieties was more exaggerated and the climate took its toll on starch content. In fact, the national maize crop harvest was down by an average 20% on the year to 16t/acre freshweight, however, it continued to remain a very cost effective crop to grow in terms of dry matter. For example, a maize crop harvesting 16t/acre freshweight can cost £21/t freshweight, equating to £63/t DM compared with cereals at approximately £180/t DM.
If by August, conditions are looking good and it looks as though we’re to have an early harvest, remember not to go too early or else sugar accumulated in the leaves and undeveloped cob will be lost in the ensiling process. On the other hand, if we are to have another wet year, then there is no alternative but to plan for a late harvest. How late can you go? We’d say around 20 October, after which day temperatures fall to an average maximum of 13oC or less, the plant stops growing and dry matter is redistributed from the leaf to the cob and stem.
