The Effect of Plant Extracts and Humic Acid on the Ammonium Content in the Soil and the Numbers of Nitrosomonas Bacteria in Soil Planted with Potatoes

An experiment was carried out according to the design of factorial experiments with a completely randomized block design (CRBD). The number of experimental treatments was (20), including the comparison treatment, with three replications. The first factor included the addition of plant extracts (garlic cloves, pomegranate peels and pulp, Eucalyptus and myrtle) at one level (4 ml kg −1 soil), which are symbolized by (P1, P2, P3, and P4), respectively. The second factor included adding urea fertilizer at two levels (50 and 100) kg N ha −1 , symbolized by (U1 and U2), respectively, and the third factor included adding humic acid (H) at one level (80) kg ha −1 , the results of the experiment showed that the added fertilizers significantly affected the ammonium content of the soil and the numbers of Nitrosomonas bacteria. In the flowering and full maturity stages, the combination of eucalyptus extract and the first level of urea fertilizer (P3U2) produced the highest average soil nutrient levels (36.54 and 33.95 mg kg −1 soil, respectively), compared to the comparison treatment (17.98 and 16.28 mg kg −1 soil, respectively). Additionally, in the U2 treatment, the average numbers of Nitrosomonas bacteria were highest, reaching (20.49 and 18.23)×105CFU g −1 dry soil in the two stages, respectively, compared to the comparison treatment (C), which had the lowest values (6.78 and 5.98) 105 cells g −1 dry soil, during the flowering and full maturity stages, respectively.