Seed rates: have I been underestimating field losses?
As we shut the gate on another autumn drilling campaign I do ask myself what lessons have we learnt now that we have completed our 3rd season strip-till drilling. Well, sitting down last week reviewing the year’s cashflow, one figure stood out in our fixed cost heading; just how much our fuel usage had dropped – a direct translation from a change of farming practice to the P& L account and something that’s hard to achieve these days with such clarity. It’s unequivocally a direct impact of reduced tillage. On a practical note we tackled our historic issues of trash management head-on this year. We have been drilling successfully into all crop residues other than when drilling 2nd cereals (when damp chopped straw blocks the drill), so this year I took the decision to bale all 1st wheats purely to circumvent this problem. At the expense of removing potential organic matter, it worked and I suppose exercising this option 1 year in 5 isn’t the end of the world. Timing applications of sewage cake, as we have done this year, to this ground entering a 2nd wheat, goes a long way toward mitigating the removal of crop residue. When you move to a one pass establishment system you have to do everything to promote the success of that operation. Our combining practices have changed to reflect this too, more attention to stubble height, more frequent changes of chopper blades and a reluctance to combine into the early hours all assist to make subsequent drilling easier.
On the back of the drilling plots trialled this autumn rose a related issue too commonly overlooked I think. Whilst the primary objective was to ascertain the pro’s and con’s of strip till drills v direct drills, subsequent plant counts concentrated the mind on just how accurate are we in forecasting plant density when deciding on drilling rates?
Figure 1. Is your plant number/m2 sub-optimal?
I believe I have been underestimating field losses when calculating seed rates. AHDB benchmarking data suggests 70% overwinter survival for September sowings falling to 50% for November sowings, so that’s an ‘average’ of 60% for cereals sown in October. And being an ‘average’ means heavier soils will be below that. We typically base September sowings on 300 seeds/m2 and October sowings on 350 seeds/m2 – that could well be too low to attain the 260 plants/m2 going into spring. Ground truthing is certainly a scientific approach to quantifying in-field variations in soils types and if you’ve ever undertaken the task yourself get a qualified geologist to do the same field – you’ll be surprised at just how different the zones look – I was, and you can see the potential degree for variation in the example below; the soils ranged from heavy silty clay loam (60% establishment) to sandy clam loam (90% establishment).
Figure 2. Newberry farm % establishment
Our January meeting will be looking at our current precision farming applications, including ground truthing, and asking what is the cost / gain scenario.