The important role that micronutrients play in nitrogen use efficiency has been highlighted by a grain ‘post-mortem' that enables growers to identify areas for future improvement in their crop nutrition programmes.
Agronomy firm Agrii is encouraging growers to adopt a holistic approach to include soil, tissue and grain analysis within their testing schedules to provide a full interpretation of nutrient requirements and an understanding of how certain nutrients can affect the uptake of others.
Throughout 2022, Agrii monitored six sites across northern England and Scotland to compare the grain nutrient level of winter oilseed rape and found that 33 out of 70 values across all sites were sub-optimal with all nutrients at lower levels in 2022 when compared with 2021 with a particular deficiency noted in boron across all sites. 
"We need to rethink our approach in terms of the amount of boron that we're applying and where it is targeted," says Jim Carswell, research and development manager for Agrii.
"We've had some fairly hefty yield responses when applying boron beyond the 450 grams per hectare which is often beyond the rate recommended," says Mr Carswell. 
Copper
Work based at Bishop Burton College in Yorkshire, reviewed post-harvest data of a winter oilseed rape crop. The analysis identified sub-optimal levels of copper in the harvested seed. 
"Oilseed rape is generally thought to be unresponsive to copper, but from our analysis over the last few years, we found sub-optimal levels of copper in the grain," says Mr Carswell. 
However, soil analysis indicated that levels of copper were normal to high, indicating a lock-up issue within the soil. In response to the previously low copper readings in the grain, in one trial Agrii scheduled three additional applications of copper at a rate of 415 grams per hectare. Post-harvest seed analysis showed the yield had increased by 0.21 tonnes per hectare when applying ten times the ‘standard' rate of copper of 40g/ha.
"You get a very positive effect on the value of the seed and we're getting a positive return on investment which just shows the magnitude of these micronutrients," says Mr Carswell. 
The analysis showed that additional copper not only increased the copper within the crop but also increased levels of other nutrients. 
"[The results] showed we increased the copper levels which was not unexpected, but we've increased the nitrogen level in the seed as well. 
"There's been more assimilation of nitrogen so we've got better nitrogen use efficiency. 
"Our potash, calcium, manganese, molybdenum and boron levels have all been elevated in the seed, which suggests that the crops had more access to these nutrients just by tweaking the copper levels," says Mr Carswell. 
Foliar calcium
A second trial looked at foliar calcium applied across winter wheat where the grain analysis indicated slightly low to low levels in the grain. Again, soil analysis suggested normal levels which posed questions around calcium availability for the crop. 
Mr Carswell says: "With the additional calcium and everything else the same during the season we got a 0.24t/ha yield increase and a slightly better bushel weight at 83.4 kilograms per hectolitre compared with 83kg/hl, so it's going in the right direction and we're not having any negative effects."
The grain nitrogen was also higher at 9.86 per cent against 9.32 per cent highlighting better utilisation in the crop. Foliar calcium did not increase the grain calcium levels at harvest.
"Initially I had to scratch my head on this one, as the calcium levels in the grain are lower where we put the product on. 
"But we've got higher nitrogen levels in the grain so by using that calcium we are getting better nitrogen use efficiency," says Mr Carswell. 
Nutrient analysis on the straw was also carried out to determine where the nutrients had been taken up. The crops with additional calcium had increased the calcium content to 0.50 per cent in the straw analysis as opposed to 0.36 per cent without additional calcium applied.
"This gives [growers] increased feed value as we've also got elevated levels of nitrogen, phosphate, potash and sulphur to give better quality straw," he adds. 
Mr Carswell believes growers cannot base a nutritional programme on plant tissue tests and seasons alone as many of the results will depend on external factors such as the time of day, crop stress and disease pressures, so a holistic approach concluding with a grain analysis will provide a broader picture.
