East: Soil nitrogen levels variable

Standard deep nitrogen coring, to measure soil mineral nitrogen (SMN), is producing some highly variable results. This is not surprising if you consider the factors that influence SMN levels in January/February. This year the most variable factor is the performance of the previous crop and its utilisation of nitrogen applied in spring 2011.

In many cases in East Anglia, SMN levels are lower than we would expect in a low rainfall winter. In some cases this can partly be explained by the fact that large crop canopies have trapped considerable amounts of nitrogen. Nevertheless, the indications are that total Soil Nitrogen Supply (SNS) figures are atypically low. Second wheats seem to buck this trend with higher SNS levels, which may reflect the often poorer performance of first wheats in 2011.

If soils dry over the next couple of weeks, top dressing nitrogen fertiliser will be the priority. With the threat of another dry spring even the forward crops, especially if they are sitting on low SMN levels, will receive a dose of N. Careful PGR management of large cereal crop canopies will be needed, with robust split applications at T0 and T1 in the highest risk situations.

The cold snap in February, including a -12C measured in mid-Suffolk, seems to have slowed active foliar disease in wheat and barley. However, septoria lesions are very evident and there are areas of leaf tissue which look as though they could soon erupt into active sporulating rust when the weather warms up. At the moment, plans for T0 remain robust and assume that rust and mildew will be very active again by leaf 4 emergence.

Oilseed rape canopies have generally shrunk back and become more prostrate, but many still contain considerable amounts of nitrogen. The forward crops were starting to think about stem extension prior to the cold weather and are likely to get going as soon as warmer weather arrives. Lodging risk is likely to be higher this year, especially where plant populations are too high, necessitating a robust PGR fungicide program. Metconazole-based fungicides will play an important part in this strategy, with first treatments during stem extension to maximise the stem shortening and root development benefits.

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