Short-term sowing decisions based on individual crop rather than whole-rotation margins can damage profitability.
That is the warning from ProCam Agronomy, whose 4cast crop management calculations suggest growers might sacrifice £80/ha (£198/acre) a year by introducing too much oilseed rape.
Over four years’ recording the crop averaged 3.61t/ha at an average input cost of £238/ha, says the firm’s Nick Myers.
At the same time, the 4cast growers averaged 8.84t/ha from first wheats and 8.13t/ha from second wheats at costs of £258/ha and £263/ha, respectively.
Table 1 suggests many units would be better off growing rape instead of second wheat.
But would they?
Much depends on how well rape yields can be maintained and workloads balanced in tighter rotations, says Mr Myers.
Adding the gross margins and dividing by rotation length, as in table 2, takes account of every crop’s impact on its successors, he explains.
“If you assume you’ll maintain the same rape performance, of course you’ll be slightly better off with wheat/rape at £379/ha a year,” says Mr Myers.
But experience suggests rape yields fall and costs rise the more often it is grown.
“For this reason, we have to assume oilseed rape performance will fall.
“In our calculations I’ve used the level achieved by our bottom 25% growers over four years – 2.64t/ha at a cost of £263/ha – rather than the average.
“At the sort of performance many will find familiar, it leaves an annual rotation margin £83/ha less than wheat/wheat/rape.