Core Sampling For Nitrogen

Well its that time of year again when we go and test the amount of nitrogen left in the soil after the winter.  The nitrogen is measured after the winter so that we can take account of any nitrate that has leached (washed) out from the soil.  The nitrogen left in the soil has come form a few places.  There might be some that we applied, left over that the plants were unable to absorb in the previous crop.  Some has come from the breakdown of the plant material by soil microbes in the autumn, before the temperatures got too cold and the stopped working, and some has come form mineralisation of the soil, during cultivations.  It is important to have an idea of what nitrogen is available for the crop because it will affect how much we are allowed to add artificially and how much the crop needs to produce an optimal yield.  Artificial nitrogen is very expensive, has a huge carbon footprint, is potentially damaging to the environment so we need to be absolutely sure what we apply is used by the crop.  

The probe on the quad bike, is a service offered by Soil Quest through Agrii (first time we have used it), also logs the sample location with a GPS point, so that we can come back year on year to assess the variability between years.  There is some discussion as to the accuracy of the sampling (to a point) but over time it will show a trend of how much nitrogen is available to the plant and at what depth.  The probe samples soil between 0-30cm and between 30-60 cm, then the driver has to sample by hand the 60-90cm depth (if you have enough soil!)  

The results are back now and they are showing a range of between 48Kg/Ha on the sandy soil up to 61Kg/Ha on some of the brash soil.  These two I can understand but then I also have a heavy clay soil with a reading of 50kg/ha which seems odd.  I guess though all of these values are low, due to the heavy rainfall we've had all winter, so we will have to apply a greater amount of purchased nitrogen fertiliser this season if we are to produce out optimum, and not maximum yield.  Imagine if we were in an organic system, there would be very little nitrogen left over from previous clover leys to feed this crop.