The Effect of Nitrogen and Organic Fertilizers on Biological Activity of Soil Planted with Soybeans

Dima al-Saied
General Commission for Scientific Agricultural Research-
Homs Research Center
Faculty of Agriculture, al-Ba’ath University,


A field experiment was conducted on soybean (Sb44) for two years, included 16 treatments with three replicates : control without nitrogen or organic fertilizers, four levels of nitrogen fertilizer (kg N/ha)(N0(0), N1(50), N2(100), N3(150)), and four levels of organic fertilizer (kg N/ha) (O0(0), O1(50), O2(100), O3(150)), and the interference between these levels, noting that the quantity of nitrogen has been calculated as it is equal to both of nitrogen and organic fertilizers. Some biological properties of soil, nodulation on plant roots and  soybean yield were determined.
The results showed an increase the populations of heterotrophic bacteria in treatment N1 in the first season, while the populations of soil microorganisms physiological groups increased in treatment  N2 and heterotrophic bacteria increased in treatment N3 in the second season. The populations of most bacteria increased in treatments O2 and O3 in the first season. Besides,  most populations of treatment O2 increased  in the second season, while populations of heterotrophic bacteria and phosphate solubilizing bacteria raised at N1O2, and actinomycetes at N3O1, and azotobacter and fungi at N1O3.
The respiration of soil increased at treatments N1 and O1 in the first season, and in treatments amended with  nitrogen and organic fertilizers. Also, phosphates activity in soil raised in the second season more than  in the first season for most treatments,  and it was high (N1O1,N3O3). The numbers of root nodules decreased in both seasons with increasing the amount of mineral fertilizer, whereas the numbers of these nodules and their wet weight increased at treatment O3 in the first season and at O1 in the second season.
Soybean yield increased at treatment N1 and O2 in both seasons, meanwhile  it increased at treatment N2O3 in the first season and at N3O2 in the second season.
The results in the second season were better than those of the first season. Plant length in treatment N1O1 was superlative in the first season and treatment  N1O2 in the second season. Significant differences in dry weight were noticed in treatment N3O3 and N2O2 comparing to other treatments.  As for  soybean productivity, treatment N2O3 in the first season and treatment N3O2 in the second season were the best with insignificant differences.  Percent protein  was significantly increased in most treatments  comparing to control for two seasons, treatment N1O2 (first season) and  treatment N3 (second season) were the best.
For soil NPK,  significant differences in soil N for most treatments  comparing to control especially in the second season (the best treatment was N2), whereas the available P increasing was at introduction between mineral fertilizer and organic fertilizer especially in the first season  and treatment N1O1  was the best. Finally available potassium increased in most treatment comparing to control, and the best treatment was N1O3.
Key words: soil, organic fertilization,  microorganisms, soil respiration, soybean.