If you travel to Saudi Arabia, do not miss a visit to the city of Hail, you can take a tour to Jubbah, one of the principal pre-islamic archeological sites in the country.  You will see petroglyphs that date back to 5500 BC, when the area was a great lake. The ancient inhabitants registered on stone the many aspects of their culture. Where there once was a lake, today there is a desert, but thanks to irrigation, the region of Hail remains one of the main agricultural areas of Saudi Arabia.  In fact, I travelled there to support the local farmers in growing their potato crops.  They explained that the harvest and the quality of the tubers was below the expected standard in spite of the use of a good fertilizer.  After examining the soil and the type of fertilizer that was used, we decided to change the percentage ratio between the sources of nitrogen, as well as the ratio between nitrogen and potassium.  In a few words, nitric nitrogen was incremented from 11% to 44% of the total N applied, and the ratio N:K was doubled from 1:0.7 to 1:1.4. The results? It was possible to see the benefits in both the size of potatoes and the quantity of tubers.  In the following harvest, productivity increased by 13.5%!