My the rain fall soft upon your fields

Dear William,

Evaporation 8th to 14th November, 10,11,11,10,10,15,12 which I think is the highest weekly total I have ever recorded.

I have switched my pivot to a 13mm a day nozzle pack. Even with this, I should not (in theory) be able to keep up with this evaporation, given the frequency of power cuts, but I think two things have happened, that is making the tobacco ‘perform’ differently from the theoretical model. Firstly, it has been growing more slowly than ideal (because of a shortage of water) and secondly, it has shut down somewhat, so that the Et/Eo is again lower than it should be. This is a ‘safe’ position to be in, because the tobacco is not too soft and so not too prone to scorching. How long I can keep it like this before it rains is anybody’s guess.

I have learned a few other things too. Firstly, my nozzles on the pivot (which are now 10 years old) do not appear to have worn out very much. I have been meaning to do it for sometime, but, I finally got around to measuring the flow-rate into a bucket at three places along the length of the pivot. All three were bang on their spec – which is a relief. The second thing is that I am definitely losing 20% of the water through evaporation. What I measure in my rain-gauge is constantly 20% less than the measured output of the nozzles. That is no surprise, but one has to make sure one budgets for it. What is surprising is there doesn’t seem to be much difference between day and night time evaporation. (Sometimes the pivot passes over the gauge at night, but the loss is the same as during the day.)

Doug Watt (from Kabwe) attended the ZESCO/ZNFU meeting. Although Zambia has used up our allocation of water (and so must pay a penalty on any further use) there is still some water left in Kariba for generation. His other news was that some people had installed PF correcting equipment in Lusaka area – which didn’t work. I have heard of at least three different suppliers in Choma, so make sure your system works before you pay.




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