**7. Effects of organic matter application**

Soil organic matter is important for biological nitrogen fixation (BNF) because of its influence on soil physical, chemical and biological properties and processes. It helps to create a favourable medium for physical processes, chemical reactions, and biological activity. The multi-faceted role of soil organic matter (SOM) must therefore be taken into consideration in any assessment of `soil quality' and `sustainable land management. Low concentration of organic matter can have a deleterious effect on offsite environment because it is often associated with decreased soil fertility, water holding capacity and water infiltration, and increased erosion. Further, SOM turnover controls the fluxes of nutrients. Microbial biomass measurements combined with soil respiration have frequently been used as an index of soil development or degradation (Insam and Domsch, 1988) and to assess the quality of organic matter input (Anderson and Domsch, 1990). Interactions between soil microorganisms and soil microfauna, particularly Protozoa and Nematoda, largely control SOM turnover (Elliot et al., 1984).

Harvested crop residues and rotation has a major impact on the soil organic matter content. However, some features, such as the type and degree of decomposition of organic matter, affected BNF in different ways. Many field trials which were applied organic material by Gok et al. (2001) show that with the organic material application, organic matter content of soil increased in the short term but at the end of the trial, soil organic matter content decreased due to high rate of mineralization. To gain long-term soil organic matter, all kind of organic substrates should be regularly added to the soils which under the effect of semi-arid climate condition. Moreover, degradation resistant substrates such as lignin and cellulose should be preferred to dump mineralization. With this way nitrogen is temporarily immobilized in biomass that preventing (Asmus and Hubner 1985; Gok 1987). In a research, Limon-Ortega et al. (2002) studied to evaluate the effects of burning and natural wheat or maize stubble on some properties of soil. Results indicated that the positive effect of that substrates appeared after 2 or 3 year continuously stubble applications. The result obtained at 5th – 6th years were more expressive than those obtained in the 1st to 3rd years. When the stubble is burned almost all nutrients in organic substrates converted to available form for plants in seconds. Therefore, compared with burned or natural stubble applied plots, in the beginning years burned stubble seems to be more efficient, but in following years the effects of stubble become much more effective on the soil parameters.

A two year field experiment at soybean cultivation was undertaken for determining the effects of stubble burning, a widely performed practice in Cukurova Region, along with admixing 0, 5000 and 10000 kg ha-1 tobacco wastes on symbiotic nitrogen fixation, grain

Due to the fields where soil was taken is not previously introduced with the rhizobia that match with soybean; no nodule occurrence was observed in the pot which non-inoculated control variant. A few nodules observed in non-HFA applied pots however HFA application increased nodule occurrence considerably. Both "incorporation to soil" and "admixing by irrigation" applications were effective on formed nodule number; however because of the dilution effect in incorporation to soil application, admixing by irrigation application seems to be more effective than incorporation to soil. (dilution effect). Increasing doses of HFA increased the number of nodule, thus findings expressing the considerable positive effects of

Soil organic matter is important for biological nitrogen fixation (BNF) because of its influence on soil physical, chemical and biological properties and processes. It helps to create a favourable medium for physical processes, chemical reactions, and biological activity. The multi-faceted role of soil organic matter (SOM) must therefore be taken into consideration in any assessment of `soil quality' and `sustainable land management. Low concentration of organic matter can have a deleterious effect on offsite environment because it is often associated with decreased soil fertility, water holding capacity and water infiltration, and increased erosion. Further, SOM turnover controls the fluxes of nutrients. Microbial biomass measurements combined with soil respiration have frequently been used as an index of soil development or degradation (Insam and Domsch, 1988) and to assess the quality of organic matter input (Anderson and Domsch, 1990). Interactions between soil microorganisms and soil microfauna, particularly Protozoa and Nematoda, largely control

Harvested crop residues and rotation has a major impact on the soil organic matter content. However, some features, such as the type and degree of decomposition of organic matter, affected BNF in different ways. Many field trials which were applied organic material by Gok et al. (2001) show that with the organic material application, organic matter content of soil increased in the short term but at the end of the trial, soil organic matter content decreased due to high rate of mineralization. To gain long-term soil organic matter, all kind of organic substrates should be regularly added to the soils which under the effect of semi-arid climate condition. Moreover, degradation resistant substrates such as lignin and cellulose should be preferred to dump mineralization. With this way nitrogen is temporarily immobilized in biomass that preventing (Asmus and Hubner 1985; Gok 1987). In a research, Limon-Ortega et al. (2002) studied to evaluate the effects of burning and natural wheat or maize stubble on some properties of soil. Results indicated that the positive effect of that substrates appeared after 2 or 3 year continuously stubble applications. The result obtained at 5th – 6th years were more expressive than those obtained in the 1st to 3rd years. When the stubble is burned almost all nutrients in organic substrates converted to available form for plants in seconds. Therefore, compared with burned or natural stubble applied plots, in the beginning years burned stubble seems to be more efficient, but in following years the effects of stubble become much more effective

A two year field experiment at soybean cultivation was undertaken for determining the effects of stubble burning, a widely performed practice in Cukurova Region, along with admixing 0, 5000 and 10000 kg ha-1 tobacco wastes on symbiotic nitrogen fixation, grain

HFA on biological nitrogen fixation.

SOM turnover (Elliot et al., 1984).

on the soil parameters.

**7. Effects of organic matter application** 

yield and biomass production (Coskan et all, 2009). Results revealed that applications were significantly effective on nitrogen fixation, yield and biomass production. According to overall averages, the highest biomass production of root and shoot were observed at wheat burned and 10000 kg ha-1 tobacco waste applied plot as 830 and 4730 kg ha-1. The highest nitrogen contents at harvest stage were determined in the plot wheat and 5000 kg ha-1 tobacco waste applied (root, 0.87%; shoot, 0.95%). At the end of experiment determined grain yield amounts in first year were higher in the stubble burned plots. No statistical difference was determined between burned and non-burned stubble in the second year. When the variants of tobacco waste applications were compared according to their tobacco rates, the productivity was increased at plots of waste application in both years. The determined highest yield 4520 and 5280 kg ha-1 at stubble burned and nonburned plots in which 10000 kg ha-1 waste was applied in the first and second years, respectively
