Although it was a mild winter on the Highveld, there was a rather cold period where some damage occurred. A post mortem of some of the damage will help us to prepare better for the future. A mistake that I saw plenty examples of was bad planning last summer for the winter plantings. After a final cold snap, few farmers think about winter plantings until it’s too late. Room must be made available for winter crops on higher ground. When the time came to plant them in late summer, many farmers had already planted the high ground and were forced to plant in the lower and cooler lands. Planning for this should start right now.
The Thursday night when the cold struck, was on neighbourhood watch duty in our village. At 3am the temperature at the top of the village was -3ºC and the lower section -6ºC. As we drove around, we watched how this pattern was maintained. By 7am the temperature in the lower section was -8ºC and the top -4ºC. difference of a few degrees can cause a lot more physical damage and stunting. One can clearly feel this difference when riding a bicycle at night in winter, going up and down hills. he next big, big mistake that many farmers made was to irrigate their lands in the teeth of the cold front. O n the a cold front in winter usually means dry, cold wind from the southwest. Dry air evaporates water much faster, and together with the wind causes a substantial cooling. By sprinkle irrigating a crop in these conditions, the wet soil and leaf area acts like a cooling wall in a greenhouse.
By nightfall, the land will be a few degrees cooler than an unirrigated land and this difference will be sustained until the coldest part of the morning. And, if the crop is under drought stress at the time of the big freeze, the damage can be worse. still don’t know how this aspect works but can vouch for the fact that it is so. If a scientist could explain the mechanisms of this event to me, I’d appreciate it. The ideal situation would be if the soil were moist underneath, but not on the surface. W e should learn to recognise approaching cold fronts, as I’ve never found the weather forecast to be accurate for predicting the degree of cold.
Their prediction on the internet the night of the cold front was -3ºC for us. We usually have a few days warning before the arrival of a front and although we may not know how far north it may reach or how cold it will be, we can still make the necessary preparations to take the sting out of its tail. – Bill Kerr ((016) 366 0616 or e-mail [email protected].) |fw
