پديد آورندگان :
شفيعي، سعيد دانشگاه زنجان - دانشكده كشاورزي - گروه خاك , گلچين، احمد دانشگاه زنجان - دانشكده كشاورزي - گروه خاك , دلاور، محمدامير دانشگاه زنجان - دانشكده كشاورزي - گروه خاك
كليدواژه :
سرعت تجزيه بقايا , شرايط آب و هوايي , هدررفت كربن , گياه يونجه
چكيده فارسي :
توازن كربن در بوم نظام هاي زميني از اختلاف بين كربن ورودي از طريق بقاياي گياهي و برگشت كربن به اتمسفر از طريق تجزيه مواد آلي تعيين مي گردد و تجزيه مواد آلي خود توسط عوامل زنده و غيرزنده مانند كيفيت بقايا و شرايط اقليمي كنترل مي شود. بر اين اساس هدف اين پژوهش بررسي معدني شدن كربن بقاياي گياه يونجه (Medicago sativa L.) در شرايط آب و هوايي مختلف مي باشد. براي اين منظور آزمايشي به صورت اسپليت پلات در زمان بر پايه طرح كاملاً تصادفي در سه شرايط آب و هوايي اجرا گرديد و اثر شرايط آب و هوايي از طريق تجزيه مركب آناليز شد. فاكتورهاي مورد بررسي شامل منطقه در سه سطح (جيرفت، نراب و ساردوئيه)، غلظت نيتروژن بقايا در سه سطح (كم، متوسط و زياد) و زمان نمونه برداري در چهار سطح (دو، چهار، شش و هشت ماه پس از شروع آزمايش) بود. تعيين اقليم به روش تحليل خوشه اي و آزمايش به روش كيسه لاشبرگ انجام گرديد و كيف هاي كلش در سطح خاك قرار داده شدند. نتايج نشان داد كه منطقه، غلظت نيتروژن بقايا و زمان نمونه برداري تأثير معني داري بر مقدار كربن باقيمانده، هدررفت و ثابت سرعت تجزيه كربن داشت. اثرات متقابل مناطق و گذشت زمان تأثير معني داري بر كربن باقيمانده و ثابت سرعت تجزيه كربن داشت. به طوري كه بيشترين كربن باقيمانده در منطقه جيرفت و بيشترين ثابت سرعت تجزيه كربن در منطقه ساردوئيه اندازه گيري شد. در منطقه جيرفت علي رغم بالاتر بودن دما هدررفت و ثابت سرعت تجزيه كربن كمتر از منطقه ساردوئيه بود، به دليل مناسب بودن دما در ماه هاي فروردين تا آبان ماه در مناطق مورد مطالعه به نظر مي رسد رطوبت در طي اين ماه ها فاكتور مهمي براي تجزيه بقاياي گياهي است و در منطقه ساردوئيه در طي هشت ماه 6 / 30 درصد هدررفت كربن وجود داشت. در هر سه منطقه بيشترين ثابت سرعت تجزيه كربن در ماه هاي فروردين و ارديبهشت مشاهده شد. افزون بر اين، با افزايش غلظت نيتروژن بقايا، كربن باقيمانده كاهش و هدررفت و ثابت سرعت تجزيه كربن افزايش يافت.
چكيده لاتين :
Introduction
Various factors like climatic conditions, vegetation, soil properties, topography, time, plant residue quality
and crop management strategies affect the decomposition rate of organic carbon (OC) and its residence time in
soil. Plant residue management concerns nutrients recycling, carbon recycling in ecosystems and the increasing
CO2 concentration in the atmosphere. Plant residue decomposition is a fundamental process in recycling of
organic matter and elements in most ecosystems. Soil management, particularly plant residue management,
changes soil organic matter both qualitatively and quantitatively. Soil respiration and carbon loss are affected by
soil temperature, soil moisture, air temperature, solar radiation and precipitation. In natural agro-ecosystems,
residue contains different concentrations of nitrogen. It is important to understand the rate and processes
involved in plant residue decomposition, as these residues continue to be added to the soil under different
weather conditions, especially in arid and semi-arid climates.
Material and methods
Organic carbon mineralization of alfalfa residue with different nitrogen concentrations was assessed in
different climatic conditions using split-plot experiments over time and the effects of climate was determined
using composite analysis. The climatic conditions were classified as warm-arid (Jiroft), temperate arid (Narab)
and cold semi-arid (Sardouiyeh) using cluster analysis and the nitrogen (N) concentrations of alfalfa residue
were low, medium and high. The alfalfa residue incubated for four different time periods (2, 4, 6 and 8 months).
The dynamics of organic carbon in different regions measured using litter bags (20×10 cm) containing 20 g
alfalfa residue of 2-10 mm length which were placed on the soil surface.
Results and discussion
The results of this study showed that in a warm-arid (Jiroft), carbon loss and the carbon decomposition rate
constant were low in a cold semi-arid (Sardouiyeh). The most suitable temperatures occurred from April to
October in arid and semiarid climates and soil moisture is probably the key contributor to the rate of
decomposition. The highest carbon loss in alfalfa in the cold, semiarid climate for a period of 8 months was
32.64%. The highest carbon decomposition rate constant was observed in the first 2 months of the incubation
time. These results indicate that higher nitrogen residue resulted in greater decomposition of plant residue and
lower carbon remaining in all tested climates. The higher nitrogen content of plant residue potentially increases
the concentration of nitrogen in crop residue and may increase the decomposition rate.
The strong relation between decomposition and climate has led to the belief that favorable climatic
conditions can increase the decomposition rate on a global scale and positively decrease and distribute
greenhouse gases in the atmosphere. In arid and semi-arid ecosystems, it is difficult to assess the decomposition
rate based on climatic data; it seems to be related to temperature and available humidity. Furthermore, Austin &
Vivanco (2006) reported that, in semi-arid climates, the litter decomposition rate decreased by 60 % when solar
radiation was attenuated; they concluded that photodegradation exerts dominant control over litter
decomposition in a dry ecosystem.
Conclusions The results showed that, precipitation of the study area and soil moisture played a key role in the plant
residue decomposition rate. In the cold semi-arid climate which moisture was available for decomposition of
plant residues for a longer period of time, OC loss and decomposition rate constant were higher than those
obtained for warm-arid and temperate-arid climatic conditions. It may be concluded that crop fertilization, which
increases P and N concentrations of plant residue, increases decomposition rate of plant residue but decrease its
mean residence time in soils.
