West: How much nitrogen to apply and when?

Most oilseed rape crops, apart from those which were flooded, are looking remarkably green despite constant rainfall since New Year. Unseasonal mild winter weather appears to have provided a ‘free’ first nitrogen top dressing, very welcome with current wet ground conditions. Nitrogen plans need to be in place before any applications are made.

Our winter rape canopies are not massive compared to crops further east and most plant populations are on target – so much better than last year. We plan to split nitrogen/sulphur dressings three ways, with a bigger proportion applied later. The contrary view is that we should apply more nitrogen earlier to get it into the soil profile in case we  run into a drought. The few outstanding weed treatments may have to be missed as buds are starting to rise. Applications of growth regulator/fungicides and trace elements are being  planned for later.

The priority for wheat crops is to complete outstanding blackgrass herbicide treatments. Autumn residual treatments have worked quite well, but there are some fields which missed blackgrass and also barley yellow dwarf virus (BYDV) treatments. These are  causing concern. Blackgrass plants are now well tillered and will be difficult to control. Tank-mixes will be avoided if possible, but with the ever present threat of rust the addition of a low dose of triazole may be needed. Late drilled wheats will be the first to receive nitrogen applications as they need help with tillering.

Time has also been spent reviewing other major nutrient needs. These can easily be overlooked, especially during difficult growing seasons and when crop returns are under pressure. Potash leaches – just like nitrogen and sulphur – and so should be replenished. Phosphate should also not be forgotten. It is immobile and so is needed close to crop roots – especially when soil conditions are waterlogged, compacted or tight.

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