Written by James Warne from Soil First Farming
What an extraordinary growing season we seem to have had. In a nutshell, very low rainfall, low temperatures until June and good levels of solar radiation (sunshine) resulting in generally good yields with good specific weight and moderate protein. Especially so as most crops senesced approximately 2 weeks earlier than normal.
All the more extraordinary is where we have, once again, been trialing reduced nitrogen rates on production we have seen very little difference in final yield between standard N rates and reduced N rates (until we reach a critical level, then yield drops significantly). Where we have found yield difference this comes from lower grain weight as opposed to reduced plant counts or tiller numbers. So what can we draw from this wealth of variables? Firstly, autumn 2021 was the kindest drilling season we have had for a couple of years suggesting that most crops went into good soil conditions backing up the adage ‘well sown-half grown’! the autumn and winter that followed was certainly dryer and in some areas was probably below average on the rainfall scale suggesting that crops rooted well.
Winter was also very mild with very few days of frost and certainly no prolonged periods of cold weather. Wheat tends to be growing at around 5’C and above and I believe that the crops were growing most of the winter, albeit very slowly probably contributing to root mass development as much as above ground vegetative growth.
Temperature
One of the greatest contributing factors in this year’s yield-fest has been the temperature, or rather lack of if we cast our minds back to the early spring and summer. For the majority of us the temperatures were in the comfortable mid to high teens (celcius) occasionally reaching the low 20’s but never exceeding this until mid-June.
Contrary to popular belief high-temperatures can be one of the greatest yield reducing factors for wheat as it can be sensitive to high temperatures throughout its growth cycle. It is, however, particularly to heat during the period from booting, through ear-emergence and flowering. This sensitivity then reduces after flowering trough grain-fill and maturity. Research shows temperature effects can start from the mid-late 20’s and become significant once into the 30’s. This is particularly so during the period of pollen formation and fertilisation.
Typically wheat is in flower around the second wheat in June (assuming the midlands of the UK). This occurred 7-10 days earlier this around, early June. The first really warm temperatures occurred around the 15th June onwards this year. By which time wheat had passed through the temperature critical period of pollen formation and flowering. From then on the temperatures typically remained in the low 20’s throughout June and into July when the skies cleared and we had prolonged periods if high 20’s-30’s and clear skies. This warmth and sun, combined with large soil moisture deficits, lead to rapid senescence and ripening. But the critical period of reproductive growth (stem extension and ear formation through to flowering) occurred during steady consistent conditions.
The high temperatures came too late to have any potential to reduce yield. Although those in the very dry east of the country probably found the lack of moisture contributed to a drop in yield.
Nitrogen
It is generally accepted that the crop only receives half its nitrogen requirement from that we apply. The other 50% comes from or via the soil. With the majority of the nitrogen being taken up in the nitrate form which is very water soluble it is assumed that the plant takes up most of its nitrogen as nitrate in the soil water.
With the bulk of the uptake happening from stem extension through to ear emergence. As I have already mentioned above a large chunk of the UK was very dry during this period of April & May with some areas receiving zero rainfall, yet crops were still able to access the nitrogen they required for canopy and ear development. Although it seems perhaps not enough to assimilate into protein but that may also be attributed to sulphur availability.
What is really interesting though is where we had reduced the soil applied N by half, combined with a small amount of foliar applied N this gave a very similar yield to wheat which had received a typical nitrogen dose. Where we had dropped the soil applied N further we did start to see a yield drop. I must stress these results were consistent on farms which have been practicing carbon building practices as in a Conservation Agriculture strategy, where we believe there to be a greater supply of N available for mineralization by the soil biology.
Although another question must surely be if the soil was moisture deficient the biology must surely have been dormant and therefore unable to mineralise the nitrogen! It’s also worth noting that while it developed into another low disease year we saw a marked increase in mildew develop in the high N plots compared to lower total N plots. Never forget that nitrogen can help drive disease levels within the crop. Finally, one of the most perplexing outcomes of this year is if the crop is able to produce the yields we have had when its growing cycle was at least two weeks shorter than average, why do we spend so much time and effort in trying to keep the canopy green? If there is one thing we have been shown this year it’s the lifespan of the crop has no direct influence on the final yield…..