مطالعه تغييرات جمعيت و بانك بذر علف هاي هرز و عملكرد سويا تحت تاثير روش هاي مختلف خاك ورزي

The Study of Weed Population and Seed Bank Dynamic and Soybean Yield under Different Tillage Methods

به منظور بررسي اثر روش هاي مختلف خاك ورزي (متداول، كم خاك ورزي و بدون خاك ورزي) بر جمعيت علف هاي هرز و بانك بذر آن ها، آزمايشي در سال زراعي 94-1393 در سه قطعه زمين تحت كشت سويا (Glycin max L.) (رقم دي پي ايكس) هر يك به مساحت 2500 متر مربع در شهرستان علي آباد كتول اجرا گرديد. نمونه برداري از فلور علف هاي هرز در ابتداي فصل رشد سويا (قبل ازكنترل علف هاي هرز)، به روي شبكه هاي مربعي شكل به ابعاد 5×5 متر و دركادري به ابعاد 50×50 سانتي متر انجام گرفت. جهت مطالعه بانك بذر نيز از سه عمق 5-0 و 15-5 و 30-15 سانتي متر نمونهبرداري گرديد. نتايج آزمايش اين قسمت حاكي از فراواني بالاي بذر علف هرز خرفه (Portulaca oleraceae L.) در بانك بذر بود. از اين رو در مرحله بعد به بررسي روند جوانه زني و قدرت حيات بذرهاي خرفه مستخرج از اعماق مختلف خاك، تحت تاثير روش هاي مختلف خاك ورزي پرداخته شد. به طوركلي تعداد گونه هاي مشاهده شده در تيمارهاي خاك ورزي متداول، كم خاك ورزي و بدون خاك ورزي به ترتيب 3، 5 و 5 گونه بود. در هر سه تيمار نيز، گونه غالب جگن (Cyperus sp.) بود. ميانگين تراكم و درصد نقاط عاري از اين گياه در تيمار خاك ورزي متداول 191/2 بوته در مترمربع و 13/4 درصد، در تيمار كم خاك ورزي 385/9 بوته در متر مربع و 10/3 درصد و در تيمار بدون خاك ورزي191/7 بوته در متر مربع و 3/29 درصد بود. تراكم بذر علف هاي هرز در روش خاك‪ورزي متداول در هر سه عمق نمونه برداري كمتر از دو روش ديگر بود. همچنين در هر سه روش خاك ورزي، تعداد بذرهاي مشاهده شده در لايه 5-0 سانتي متري خاك بيشتر از دو لايه ديگر بود. بيشترين مقدار شاخص تنوع شانون در تيمار بدون خاك ورزي و در اعماق نمونه برداري 5-0 و 15-5 سانتي متر مشاهده شد. كمترين مقدار اين شاخص نيز در همين تيمار و در عمق 30-15 سانتي متري خاك مشاهده شد. ميزان متوسط جوانه زني بذور خرفه جدا شده از خاك در تيمارهاي خاك وري متداول، كم خاك ورزي و بدون خاك ورزي به ترتيب 43، 59 و 43 درصد بود. نتايج تست تترازوليوم نشان داد كه تمامي بذور جوانه نزده مرده بودند. در هر سه روش خاك ورزي ، بيشترين درصد جوانه زني در بذور مستخرج از لايه 15-5 سانتي متري خاك مشاهده شد. اما كمترين مقدار اين فاكتور در تيمار خاك ورزي متداول و بدون خاك ورزي در لايه 30-15 سانتي متر و در تيمار كم خاك ورزي در عمق 5-0 سانتي متري خاك ديده شد. عملكرد دانه نيز نشان داد كه بيشترين عملكرد در شرايط بدون خاك ورزي به دست آمد. با توجه به نكات اشاره شده، در اين تحقيق كارايي روش بدون خاك ورزي در مقايسه با تيمار كم خاك ورزي و متداول بالاتر بود.

Introduction An integrated weed management approach requires alternative management practices for herbicide use, tillage, crop rotations and cultural controls to reduce soil weed seed banks. Tillage is often used as a weed control system, but the effects of tillage on weed dynamics go far beyond the physical removal of growing weeds. Changes in tillage practices can cause shifts in weed species and densities. Tillage operations can have a major impact on the distribution of weed seeds in the soil and on seed survival. Seed depth in the soil profile has an impact on soil environmental conditions that influence secondary dormancy. The aim of this study was to investigate the effect of tillage systems on weed and seed bank populations. Material and Methods A survey was conducted to study the effects of different tillage methods (Conventional tillage, Minimum tillage and no tillage) on the population and seed bank of weeds. An experiment was conducted in three fields of soybean (DPX Cultivar) in Ali_Abad Katool County at 2015. Sampling from weed populations (seedling) and seed bank was carried out at the beginning of soybean growth (before exerting control operation). Weeds were identified and counted at 126 points of field based on a 5× 5 m grid in 0.5×0.5m fixed micro plots. Sampling of soil seed bank was conducted based on W method in 0.5×0.5m quadrates at 0-5 and 5-15 and 15-30 cm depths, respectively. The results are shown as the high frequency of Portulaca oleracea in soil seed bank, so in the next stage investigated the germination and viability of Portulaca oleracea seeds from different depths of soil under the different tillage methods. Results and Discussion Generally, the observed species in the conventional, minimum and no tillage treatments were 3, 5 and 5 respectively. In every treatment, the Cyperus sp is the most importance observed species. The average of density of this herb in the conventional, Minimum and no tillage treatments were 191.23, 385.96 and 191.74 plant/m2, respectively. Weed free aria percent of Cyperus sp in the conventional, Minimum and no tillage treatments were 13/49%, 10.31% and 29.36%, respectively. Weeds seed density in the conventional tillage method (in three sampling depths) was lowest than the other two methods. The highest seed density was obtained in 0-5 cm depth in every three tillage methods. The maximum shanon diversity index was observed in no tillage treatment and in samples was taken in 0-5 and 5-15cm depth. The minimum shanon diversity index has seen in this treatment and in depth of 15-30 cm. There were different maximum germination percent of Portulaca oleracea seeds that it’s extracted from different tillage methods and depths. In average, maximum germination percent of this herb in the conventional, minimum and no tillage treatments were 43, 59 and 43%, respectively. In three tillage methods, the maximum germination percent was seen in the extracted seeds from 5-15 cm depth. But the minimum germination percent were observed in 15-30 cm depth in the conventional tillage and no tillage treatments, and 0-5 cm depth in no tillage treatment. Results showed highest grain yield of soybean was obtained in no tillage method. Conclusion We studied the influence of different tillage methods on weed seedling population, distribution of seed bank in soil profile, diversity and germination of seeds that extracted from different depths of soil. Result of this study showed the tillage, played a significant role in weeds and soil seed bank populations. Weeds seed density in the conventional tillage method was lowest than the other two methods. The highest seed density observed in 0-5 cm depth in every three tillage methods. Results showed death seeds percent in conventional and no tillage methods were lower than minimum tillage. The maximum shanon diversity index was observed in no tillage treatment. As one of the main goals in weed management is to prevent the domination of the weed flora by only a few species, thus the no tillage method seemed better than the minimum and conventional methods.