اثر دوره‌های تر و خشک‌شدن بر برخی شاخص‌های فیزیکی بسترهای رشد بر پایه بیوچار و پشم‌سنگ

نوع مقاله : مقالات پژوهشی

نویسندگان

1 دانش‌آموخته کارشناسی ارشد گروه علوم خاک، دانشکده کشاورزی، دانشگاه صنعتی اصفهان

2 استاد گروه علوم خاک، دانشکده کشاورزی، دانشگاه صنعتی اصفهان

3 استاد گروه علوم خاک، دانشکده کشاورزی، دانشگاه صنعتی اصفهان، اصفهان، ایران

چکیده

بررسی تغییرات ویژگی‌های فیزیکی و پایداری بسترها در حین کشت گیاه به دلیل تغییراتی که در اثر رشد ریشه و دوره‌های تر و خشک‌شدن رخ می­دهد، ضروری است. در این پژوهش 14 بستر رشد ترکیبی با نسبت­های مختلف حجمی از مواد جداگانه تهیه شدند. در ابتدا تخلخل کل (TP)، چگالی ظاهری (BD)، چگالی حقیقی (PD)، pH و رسانایی الکتریکی (EC) در بسترهای رشد اندازه‌گیری شده و در قالب طرح کاملاً تصادفی بررسی شد. به منظور بررسی تغییرات بسترهای رشد با گذشت زمان (آبیاری­های متوالی) در کشت­های گلخانه­ای، 10 دوره متوالی تر و خشک­شدن (حدود 80 روز) بر بسترهای رشد اعمال شد. پیش از اعمال دوره­های تر و خشک­شدن و پس از اعمال آخرین دوره، شاخص‌های متعدد فیزیکی و هیدرولیکی شامل آب به آسانی قابل دسترس (EAW)، گنجایش هوایی پس از آبیاری (AIR)، گنجایش بافری آب (WBC) و گنجایش نگهداشت آب (WHC) در بسترها تعیین شد. همچنین میزان نشست، درصد کاهش جرم و میزان تجزیه مواد آلی بسترها با گذشت زمان تعیین شد. این بخش آزمایش در قالب طرح کرت­های خردشده در زمان با طرح پایه کاملاً تصادفی تجزیه و تحلیل شد. مقادیر BD، TP، EAW و WHC در اکثر بسترهای رشد در دامنه­های مطلوب بود و حتی در برخی از موارد از بستر کوکوپیت-پرلیت (به عنوان شاهد) بهتر بودند. اعمال دوره­های تر و خشک­شدن بر بسترهای رشد سبب تجزیه مواد آلی، به­هم­خوردگی و تغییر آرایش ذرات، خرد شدن ذرات آلی و معدنی، انقباض، سخت­شدن و نشست آن­ها شد. نتایج نشان داد بسترهای با مقدار قابل توجه مواد آلی ناپایدارتر از بسترهای معدنی یا غالباً معدنی بودند. به طور کلی اعمال دوره­های تر و خشک­شدن سبب افزایش معنی­دار تخلخل و فراوانی منافذ ریز در بسترهای رشد شد. این دوره­ها اثر مثبتی بر ویژگی­های EAW، WHC، AIR و WBC اکثر بسترهای رشد داشته و سبب افزایش آن­ها شد. این یافته بیانگر بهبود بسترهای رشد با گذشت زمان (دوره­های تر و خشک­شدن) بر اساس متغیرهای مقداری مذکور بود اگرچه برای ارزیابی بهتر، بررسی اثر این دوره­ها بر متغیرهای شدتی مانند هدایت هیدرولیکی، پخشیدگی اکسیژن و اعوجاج منافذ در بسترهای رشد نیز ضروری است.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

The Effect of Wetting and Drying Cycles on Selected Physical Indicators of Biochar- and Rockwool-Based Growth Media

نویسندگان [English]

  • Sh. Shahmansouri 1
  • M.R. Mosaddeghi 2
  • H. Shariatmadari 3
1 Graduated M.Sc. Department of Soil Science, College of Agriculture, Isfahan University of Technology
2 Professor, Department of Soil Science, College of Agriculture, Isfahan University of Technology, Isfahan 84156-83111, Iran
3 Professor, Department of Soil Science, College of Agriculture, Isfahan University of Technology, Isfahan, Iran
چکیده [English]

Introduction
Monitoring the changes in physical and hydraulic properties and stability of growth media due to root growth effects and wetting and drying cycles is important. Wetting and drying cycles can probably change physical characteristics, availability of water, air and nutrients for the plant and, as a result, might affect the growth and yield of the greenhouse plants. The growth period greatly affects the physical characteristics of the growth substrates; therefore, the watering of growth substrates should be managed according to these changes to avoid improper irrigation.
Materials and Methods
In this study, 14 growth media were prepared from individual substrates with different volumetric ratios. In order to evaluate the changes of growth media over the time (i.e., during consecutive irrigation events) in the greenhouse, 10 wetting and drying cycles were applied on the growth media in the lab. Several physical indicators including easily available water (EAW), air after irrigation (AIR), water buffering capacity (WBC) and water holding capacity (WHC) of the growth media were determined before and after the wetting and drying cycles. Besides, the subsidence, decrease of mass and decomposition of the growth media were determined over the time. Total porosity (TP), bulk density (BD), particle density (PD), pH and electrical conductivity of the mixtures were measured as well.
Results and Discussion
The pH values in the growth media varied from 5.72 to 6.94. The maximum pH value was related to sawdust- sugarcane bagasse biochar produced at 300C vermiculite-zeolite, and wheat straw-vermiculite substrates, and the minimum value was related to the cocopeat-perlite substrate. The values of EC in the growth media varied from 0.21 to 1.43 dS m-1. The highest and lowest EC values among the growth substrates were related to date palm bunches-vermiculite-rockwool and rockwool (0.2)-perlite substrates, respectively. The bulk density (BD) values of the growth media varied in the range of 0.163-0.401 Mg m-3. The values ​​of total porosity (TP) of the growth media varied in the range of 64.8-82.8%v/v. The highest TP was related to the cocopeat-perlite substrate. The TP values ​​of most of the substrates were greater than 70%v/v. The average values of EAW in the growth substrates ranged from 0.123 to 0.272 cm3 cm-3. The highest EAW was related to the sawdust-sawdust biochar produced at 500 ◦C vermiculite-zeolite substrate. The application of wetting and drying cycles increased EAW in most of the growth media. Therefore, it can be stated that the time had a positive effect on the EAW in most of the growth media. The average values of AIR before and after the application of wetting and drying cycles for the growth media varied in the range of 0.063-0.240 cm-3 cm3. The highest value of this indicator was observed in the sawdust-date palm bunches biochar produced at 300C vermiculite substrate. In all substrates (with the exception of the sawdust-sawdust biochar produced at 500C vermiculite-zeolite), the AIR increased after wetting and drying cycles. The range of WHC values before and after applying wetting and drying cycles was 0.453-0.699 cm3 cm-3. The highest WHC belonged to the wheat straw-vermiculite substrate. The WHC values of five growth media, including cocopeat-perlite, decreased due to the application of wetting and drying cycles, and the WHC values of nine growth media decreased. The most stable substrate after the wetting and drying cycles was rockwool-sawdust-vermiculite. The effect of time on the quantity of WBC was positive, so that with the application of wetting and drying cycles, the WBC values of most of the substrates increased. In all substrates, subsidence and dry weight reduction were observed after the wetting and drying cycles. These changes were low for the substrates with a high volumetric ratio of inorganic materials. The least change among the growth substrates in terms of decomposition (dry weight reduction) was related to the completely inorganic substrate rockwool (0.1)-perlite (%0.17). The most stable substrate in terms of subsidence after wetting and drying cycles was the rockwool-sawdust-vermiculite, which has a large volumetric ratio of individual inorganic substrates. The highest subsidence was observed in the substrates containing wheat straw (wheat straw-vermiculite and date palm bunches biochar produced at 300◦C wheat straw-vermiculite). The organic matter content in all the growth substrates decreased over time (after wetting and drying cycles). The decrease of organic matter in the substrates can be related to the decomposition of organic materials as a result of wetting and drying cycles.
Conclusion
The BD, TP, EAW and WHC of the majority of growth media were in the optimal ranges and for some mixtures even better than cocopeat-perlite. Wetting and drying cycles could affect the growth media through several processes such as decomposition of organic compounds, displacement and rearrangement of particles, fragmentation of particles, shrinkage, hardening and subsidence. The growth media with a high percent of organic substrates were unstable as compared with those containing a high proportion of inorganic substrates. In general, the wetting and drying cycles increased the frequency of micropores in the growth media. The wetting and drying cycles positively affected EAW, WHC, AIR and WBC of most growth media. These findings imply that wetting and drying cycles may improve the growth media according to the studied extensive variables. However, it is necessary to study the intensive variables such as hydraulic conductivity, oxygen diffusion and pore tortuosity in the growth media for better evaluation of the impact of wetting and drying cycles as well.

کلیدواژه‌ها [English]

  • Air after irrigation
  • Easily available water
  • Growth medium
  • Water retention
  • Wetting and drying cycles
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