Arable News

  • Written by: Farmers Guide
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First results show soil nitrogen levels very variable

GrowHows arable agronomist, Allison Grundy.
Dont assume anything, thats the advice from the results from the first 200 or so samples to go through the GrowHow N-Min analysis this year. The patented GrowHow N-Min service measures the amount of Nitrogen that the crop can expect to get from the soil over the entire growing season, including Soil Mineral Nitrogen and, importantly, the Additionally Available Nitrogen which will mineralise from the soil.


Analysing the results, GrowHows arable agronomist, Allison Grundy says: With such a wet end to 2012 I think that farmers are generally thinking that nitrogen levels are going to be very low this year but so far its turning out to be a right mixed bag. The average N-Min to date is 86kg N/ha but that hides huge variability. The maximum we have measured is 219kg N/ha and the minimum 26kg N/ha.


Soil type


Maximum kgN/ha


Sandy clay loam




Clay loam




Silty clay loam




Looking at the table, we can see the variation in the amount of N for three widespread soil types sandy clay loam, clay loam and silty clay loam and again the spread is pretty wide. Overall 34% of fields are measuring over 100kg N/ha compared to 19.5% measuring less than 50kg N/ha. 


The take home message is that making assumptions about N fertiliser requirements based on previous cropping and soil type is going to be difficult this year. The cost of getting fertiliser recommendations wrong can be significant so spending around 100 on an N-Min test makes sense. If you dont measure N how can you manage it, she adds.


Farmacy has worked closely with GrowHow for a number of years, as Farmacys Services Leader Matt Ward explains: Since the launch of our Rootplanner nutrient management service more than 10 years ago, we have been advocates of appropriate Nitrogen planning for individual circumstances to optimise farmers margins. With support from the GrowHow N-Min service we have been better placed to offer our clients the best Nitrogen fertiliser advice field-by-field, season-by-season.


Mr Ward continues: We are definitely finding plenty of variation and it appears that the heavier the soil the more variation there is. Unexpectedly, the lighter soils are showing greater consistency with low readings. However, anything that has had manures applied within the last three years is also extremely inconsistent. What we are reporting back to clients is to be careful jumping to conclusions about low SNS. This year more than any other requires individual crop needs to be carefully assessed.

Allison concludes: All the results from the past 20 years of the GrowHow N-Min service clearly demonstrate that soil N levels can be surprisingly variable. However, this does not mean that every field needs to be sampled, concentrate on the main soil types and previous crops. Use GrowHow N-Min on barometer fields to check base levels and target fields that are likely to have low or high SNS as these will benefit the most from the analysis.

  • Written by: Farmers Guide
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