Rubén asks: Hello Gustavo. For logistical reasons, I could not take soil samples before sowing, so I made an estimated fertilization according to the potential of yield and fertility of the soils of the last 3 years. I wanted to know if now that the crop has emerged, I can do a soil sample for both nitrogen and phosphorus, on the one hand to see what dose of N to apply, and on the other hand to see if the applied P was correct. The idea is to take the samples in the middle as far as possible to get away from the line. It is right?
Answer from Gustavo Ferraris: Hello Ruben. Regarding phosphorus, it is valid to do the sampling now. You will have to make sure not to “chop” on the fertilization line at all times, in which case the sampling will be invalidated because it will directly be introducing fertilizer and it will give a very high value.
In the case of nitrogen, the reasoning is different. It is a mobile nutrient, very soluble. Considering that there is good moisture in the soils, it has surely diffused into the solution.
But there has been no uptake by the crop. So you are going to analyze a sample recharged by the nitrogen pool from the fertilizer. In this case, it is convenient to wait until the end of the tillering, where you can measure the absorption of the crop, immobilization together with carbon and an eventual dilution or leaching if significant rainfall occurs. If it seems most practical to concentrate both analyzes in a single sample, it would make the determinations at the end of tillering, with the precautions already described for the case of phosphorus. Thank you very much for writing me and many successes with wheat! I leave you a very cordial greeting.
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