تغييرات زماني رواناب و هدررفت خاك تحت دبي‌هاي مختلف جريان در شيارهاي كشت گندم ديم

Temporal changes of runoff and soil loss under different flow discharges in furrows of rainfed wheat

ﮔﻮﻧﺎﮔﻮﻧﯽ ﻋﻮاﻣﻞ ﻣﺆﺛﺮ ﺑﺮ وﯾﮋﮔﯽﻫﺎي ﺧﺎك ﻣﻨﺠﺮ ﺑﻪ ﺗﻐﯿﯿﺮات زﻣﺎﻧﯽ در ﻓﺮاﯾﻨﺪ ﻓﺮﺳﺎﯾﺶ ﺧﺎك ﻣﯽ ﺷﻮد. اﯾﻦ ﭘﮋوﻫﺶ ﺑﺎ ﻫﺪف ارزﯾﺎﺑﯽ ﺗﻐﯿﯿﺮات زﻣﺎﻧﯽ ﺗﻮﻟﯿﺪ رواﻧﺎب و ﻫﺪررﻓﺖ ﺧﺎك در ﻧﻮارﻫﺎي ﮐﺸﺖ ﮔﻨﺪم دﯾﻢ اﻧﺠﺎم ﮔﺮﻓﺖ. ﺑﺮاي اﯾﻦ ﻣﻨﻈﻮر، ﺳﻪ ﮔﻨﺪمزار دﯾﻢ ﺑﺎ ﺷﯿﺐ ﻣﺘﻮﺳﻂ 15 درﺻﺪ و ﺗﺤﺖ آﯾﺶ در ﺟﻨﻮب ﻏﺮﺑﯽ اﺳﺘﺎن ﮐﺮﻣﺎﻧﺸﺎه اﻧﺘﺨﺎب و در ﻫﺮ زﻣﯿﻦ ﺷﯿﺎرﻫﺎﯾﯽ ﺑﻪ ﻃﻮل ﭘﻨﺞ ﻣﺘﺮ و ﻋﺮض 30 ﺳﺎﻧﺘﯽﻣﺘﺮ اﯾﺠﺎد ﺷﺪ. ﺑﺮاي ﺑﺮرﺳﯽ ﺗﻮﻟﯿﺪ رواﻧﺎب و ﻫﺪررﻓﺖ ﺧﺎك، از ﭼﻬﺎر دﺑﯽ ﺑﺮاﺑﺮ 0/5، ﯾﮏ، 1/5 و دو ﻟﯿﺘﺮ ﺑﺮ دﻗﯿﻘﻪ اﺳﺘﻔﺎده ﺷﺪ و ﻣﻘﺪار رواﻧﺎب و ﻫﺪررﻓﺖ ﺧﺎك از ﺷﯿﺎرﻫﺎ در ﺑﺎزهﻫﺎي زﻣﺎﻧﯽ ﭘﻨﺞ دﻗﯿﻘﻪ ﻃﯽ 60 دﻗﯿﻘﻪ در ﺳﻪ ﺗﮑﺮار اﻧﺪازهﮔﯿﺮي ﺷﺪ. ﺑﺮ اﺳﺎس ﻧﺘﺎﯾﺞ، ﺑﺎ اﻓﺰاﯾﺶ دﺑﯽ ﺟﺮﯾﺎن، ﺣﺠﻢ رواﻧﺎب و ﻫﺪررﻓﺖ ﺧﺎك در ﺷﯿﺎرﻫﺎي ﮐﺸﺖ اﻓﺰاﯾﺶ ﯾﺎﻓﺖ، ﺑﻪﻃﻮريﮐﻪ ﮐﻤﺘﺮﯾﻦ ﻣﻘﺪار ﻫﺪررﻓﺖ ﺧﺎك در دﺑﯽ 0/5 ﻟﯿﺘﺮ ﺑﺮ دﻗﯿﻘﻪ )2/66 ﮔﺮم ﺑﺮ ﻣﺘﺮ ﻣﺮﺑﻊ( و ﺑﯿﺸﺘﺮﯾﻦ ﻣﻘﺪار آن در دﺑﯽ دو ﻟﯿﺘﺮ ﺑﺮ دﻗﯿﻘﻪ )85/33 ﮔﺮم ﺑﺮ ﻣﺘﺮ ﻣﺮﺑﻊ( ﻣﺸﺎﻫﺪه ﺷﺪ. ﻫﻤﭽﻨﯿﻦ، ﺣﺠﻢ رواﻧﺎب در دﺑﯽ 0/5 ﻟﯿﺘﺮ ﺑﺮ دﻗﯿﻘﻪ ﮐﻤﺘﺮﯾﻦ ﻣﻘﺪار )0/47 ﻟﯿﺘﺮ( و در دﺑﯽ دو ﻟﯿﺘﺮ ﺑﺮ دﻗﯿﻘﻪ ﺑﯿﺸﺘﺮﯾﻦ ﻣﻘﺪار )7/65 ﻟﯿﺘﺮ( ﺑﻮد. ﻣﺠﻤﻮع ﮐﻞ رواﻧﺎب ﺗﻮﻟﯿﺪي ﭘﺲ از ﻣﺪت زﻣﺎن 60 دﻗﯿﻘﻪ و ﻫﻤﭽﻨﯿﻦ، ﻣﯿﺎﻧﮕﯿﻦ رواﻧﺎب ﺗﻮﻟﯿﺪي در دﺑﯽ 0/5 ﻟﯿﺘﺮ ﺑﺮ دﻗﯿﻘﻪ ﺑﻪ ﺗﺮﺗﯿﺐ 12/33 و 1/03 ﻟﯿﺘﺮ و در دﺑﯽ دو ﻟﯿﺘﺮ ﺑﺮ دﻗﯿﻘﻪ ﺑﻪ ﺗﺮﺗﯿﺐ 43/81 و 6/79 ﻟﯿﺘﺮ ﺑﻮد. ﺗﻔﺎوتﻫﺎي ﻣﻌﻨﯽدار در ﺗﻮﻟﯿﺪ رواﻧﺎب و ﻫﺪررﻓﺖ ﺧﺎك ﻃﯽ زﻣﺎن در دﺑﯽﻫﺎي ﻣﻮرد ﻣﻄﺎﻟﻌﻪ ﻣﺸﺎﻫﺪه ﺷﺪ )p<0/01(. ﺗﻮﻟﯿﺪ رواﻧﺎب در اﺑﺘﺪاي آزﻣﺎﯾﺶ اﻧﺪك ﺑﻮد و ﺑﺎ ﮔﺬﺷﺖ زﻣﺎن، ﺑﺮ ﻣﻘﺪار آن اﻓﺰوده ﺷﺪ. اﻟﮕﻮي ﺗﻐﯿﯿﺮات زﻣﺎﻧﯽ ﻫﺪررﻓﺖ ﺧﺎك ﻣﺘﻔﺎوت از ﺗﻮﻟﯿﺪ رواﻧﺎب ﺑﻮد، ﺑﻪﻃﻮريﮐﻪ ﻣﻘﺪار ﻫﺪررﻓﺖ ﺧﺎك در آﻏﺎز آزﻣﺎﯾﺶ ﻧﺴﺒﺖ ﺑﻪ زﻣﺎنﻫﺎي ﭘﺎﯾﺎﻧﯽ ﺑﯿﺸﺘﺮ ﺑﻮد ﮐﻪ ﻋﻠﺖ آن را ﻣﯽ ﺗﻮان ﺑﻪ ﻓﺮاﻫﻤﯽ زﯾﺎد ذرات ﺧﺎك ﻗﺎﺑﻞ اﻧﺘﻘﺎل در ﺷﯿﺎرﻫﺎ در اﺑﺘﺪاي آزﻣﺎﯾﺶ ﻧﺴﺒﺖ داد. ﻣﻘﺪار ﻫﺪررﻓﺖ ﺧﺎك از آﻏﺎز آزﻣﺎﯾﺶ ﺗﺎ زﻣﺎن 25 دﻗﯿﻘﻪ، ﮐﺎﻫﺸﯽ ﺷﺪﯾﺪي ﯾﺎﻓﺖ و ﺳﭙﺲ، از اﻟﮕﻮي ﮐﺎﻫﺸﯽ ﺗﺪرﯾﺠﯽ ﭘﯿﺮوي ﮐﺮد و در ﭘﺎﯾﺎن ﺑﻪ ﻣﻘﺪار ﺛﺎﺑﺘﯽ رﺳﯿﺪ. ﻧﺘﺎﯾﺞ ﻧﺸﺎن داد ﮐﻪ ﻓﺮﺳﺎﯾﺶ ﺷﯿﺎري ﺑﻪ ﺷﺪت ﺗﺤﺖ ﺗﺄﺛﯿﺮ ﺷﺪت ﺟﺮﯾﺎن ﻗﺮار دارد و ﻣﻘﺪار آن ﻃﯽ زﻣﺎن ﺗﻐﯿﯿﺮ ﻣﯽﮐﻨﺪ و اﯾﻦ ﺗﻐﯿﯿﺮات ﻣﺴﺘﻘﻞ از ﺗﻮﻟﯿﺪ ﺟﺮﯾﺎن ﺑﻮده، ﺑﻪ ﻓﺮاﻫﻤﯽ ذرات ﻗﺎﺑﻞ اﻧﺘﻘﺎل در ﺷﯿﺎر واﺑﺴﺘﻪ اﺳﺖ.

The variety of factors affecting soil properties leads to temporal changes in the soil erosion process. This research was conducted to assess short-term changes in runoff and soil loss in rainfed wheat furrows under fallow conditions. To this end, three rainfed lands with 15% slope gradient were selected in south west of Kermanshah Province. In each land, furrows with five m in length and 30 cm in width were created using sowing set. Runoff and soil loss were measured using simulated flows with a discharge of 0.5, 1, 1.5 and 2 L.min-1 at intervals of five minutes to 60 minutes 60 minutes in three replications. Results showed that the lowest soil loss was recorded in flow discharge of 0.5 L.min-1 (2.66 g.m-2) and the highest of soil loss was produced in flow discharge of 2 5 L.min-1 (85.33 g.m-2). Also, the lowest runoff was recorded in flow discharge of 0.5 L.min-1 (0.47 L) and the highest of soil loss was produced in flow discharge of 2 5 L.min-1 (7.65 L). The effect of time on runoff and sediment variables was significant in all flow discharge (p<0.01). Runoff production was low at the beginning of the experiment and increased over time. The pattern of temporal changes in soil loss was different from runoff production, amount of soil loss at the beginning of the experiment was higher values ​​than the final test times, which associated with to supply of erodible soil particles in the rills in the beginning of the experiment. With starting the experiment to 25 minutes, the rate of soil loss changes drastically and then until the end of the experiment, it followed a uniform reduction pattern and in the final stages, it is almost constant. The results showed that rill erosion is strongly influenced by flow intensity and its value changes over time and these changes are independent of flow production and depended on the transmittance of soil particles transferable in the rill.