Charlie Flindt: The dilemma with seed rates

Of all the rows that I had with my Old Man (and believe me, there were some major ones), one of the biggest was about seed rates.

Back in the 1980s there was a very simple formula: Winter wheat at 1.5cwt per acre and spring barley at 1.25cwt. As far as he was concerned, it had worked perfectly well for decades.

When I suggested we should switch to aiming for a certain number of seeds per square metre, it did not go down well. I explained the concept of thousand-grain weights and how a sample of big, bold seeds would mean, in some years, a far higher seed rate that a sample of thin lightweight ones.

Ah, said the Old Man, but big bold berries have more vigour, so you need fewer seeds, and you end up back where you started.

I was reminded of this row last week when my spring beans arrived. Before ordering them, my agronomist and I had set aside a couple of hours to discuss the seed rate. No blanket annual rates here now; oh no, it’s a long and complicated calculation involving variety, soil type, rainfall, date of ploughing (not finished yet!), ley lines and conjunction of the planets – beware of Mars in Uranus.

The arguments go on for hours: He hates thick crops, I hate thin ones. Finally, after at least 10 packets of HobNobs, we agreed on 40 plants/sq m. So for 36ha, rounding up to 45plants/sq m (to allow for 90% germination), we ordered 16.2m beans. Not 16,199,999, not 16,200,001; we placed the order for 16,200,000.

You can imagine my surprise when 18,644,067 arrived, 11t of finest Fuego with a TGW of 590. “11t?” I thought to myself as I unloaded the last couple of bags from the lorry. “That seems a bit much.”

I used to be able to do that sort of sum in my head, but nowadays I have to resort to a calculator. That’s 305kg/ha. And I still go old-fashioned: that’s about 2.47cwt/acre.

Blimey, at that seed rate I’d hardly get up and back in Drier Field with my little packtop drill before I’d need to fill up again. I’d spend more time leaping in and out of the drill and loader tractors than I would actually drilling – not good with the state of my sacrum at the moment.

So I rang the agronomist, who was as surprised as I was. Now, despite being just re-cleaned, these beans aren’t cheap, so I thought an email to the seed company would be useful. Their man explained that he, too, considers it his job to adjust for germination rate and he, too, had assumed germination of 90%.

His final tally (once the TGW had been done) was just over 10.5t, so that was rounded up to 11t. That’s nearly 52 seeds/sq m – a 15% increase on a rate that my agronomist reckoned was a bit high in the first place. So much for precision seed rates. Anyway, after some fairly terse emails, they’re coming to take 1t away.

I’m just off to check the latest batch of spring barley. Let’s check the sums: We’ve ordered 325 seeds/sq m, and the TGW is 50, so that’s 162kg/ha which converts to about Oh blimey, don’t tell the Old Man.