Abstract: This study was conducted to investigate the effect of soil salinity on nitrogen mineralization in the presence and absence of wheat straw in three soils with textural classes of clay, loam and loamy sand under laboratory conditions as a factorial arrangement based on a completely randomized design with 3 replications. The studied factors were salinity (1, 10, 20 and 30 dS/m), wheat straw (0 and 2% by weight with C/N=89.5) and time (2, 5, 12, 20, 28, 37, 46, 53, 64, 73, 85 and 90 days). After investigation of different Iranian agricultural soils, three soils with low salinity (0.84-1.1 dS/m) and low organic carbon (0.22-0.98%) were selected. Considering the results, in the three soils, the amount of ammonium and nitrate in the treatment without straw was higher than those in the treatment with straw. In straw treatment, there was an initial descending trend in the amount of ammonium and nitrate for the three soils, but after a period of time, ammonium and nitrate content of the soil showed an ascending trend and returned to the initial value. With increasing soil salinity, the amount of soil ammonium increased in clay and loamy sand soils but decreased in the loamy soil. Nitrate content showed a descending trend for the three soils with increasing salinity. In general it is concluded that the presence of wheat straw in the soil can mitigate the negative effects of high concentrations of salt on nitrogen mineralization and reduce nitrogen losses. Introduction Soil salinity is one of the main factors of land degradation and decrease the yield of agricultural crops, affecting the population of soil microorganisms and soil dissolved organic carbon, plays an important role in soil nitrogen mineralization. Application of organic matter is often suggested as a solution to stimulate soil microbial activities in the soils affected by salt. Objective The present study was performed to investigate the effect of soil salinity on nitrogen mineralization in the presence and absence of wheat straw in three soils with textural classes of clay, loam and loamy sand under laboratory conditions. Materials and methods For this purpose, agricultural soil samples from different regions of Iran were investigated and three soils with low salinity (0.84-1.1 dS/m) and organic carbon (0.22-0.98%) were selected. The experiment was conducted as a factorial in a completely randomized design with the factors of salinity (initial salinity about 1, 10, 20 and 30 dS/m), wheat straw (two levels of 0 and 2% by weight with C/N=89.5) and time (2, 5, 12, 20, 28, 37, 46, 53, 64, 73, 85 and 90 days) by applying three repetitions for each sample. Results In addition to wheat straw, soil texture also has an effect on nitrogen mineralization, so that in clay and sandy loam soil without wheat straw, the ammonium content of the soil increased with increasing salt concentration, while in loamy soil without wheat straw, with increase soil salinity the amount of ammonium produced decreased. In all three soils, the amount of ammonium and nitrate in the treatment without straw was higher than in the treatment with straw. In the treatment with straw, there was an initial downward trend in the amount of ammonium and nitrate for all three soils, but after a period of time, the amount of ammonium and nitrate in the soil showed an upward trend and returned to the initial value. With the increase in soil salinity, the amount of soil ammonium increased in clay and loamy sand but decreased in loam soil, but the amount of soil nitrate showed a decreasing trend for all three soils with increasing salinity. Conclusion The results showed that soil salinity can lead to a decrease in soil mineral nitrogen by affecting the process of nitrogen mineralization, and the presence of wheat straw, although in a certain period of time, leads to a decrease in soil mineral nitrogen, but with the positive characteristics it gives to the soil, it can adjust the negative effects of high salt concentrations in the processes of ammonium and nitrate production in all of the three types of soil texture and on the other hand, reduce its losses by controlling the rate of nitrogen mineralization. Therefore, based on the results of this research, it is recommended to return wheat straw in saline soils along with calculating the nitrogen factor. The presence of wheat straw in saline soils can moderate the negative effects of high salt concentrations on nitrogen mineralization and reduce its losses. [ABSTRACT FROM AUTHOR]
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