تاثیر مدیریت بقایای گیاهی و نیتروژن بر تغییرات وزن خشک و عملکرد گیاه پنبه (gossypium hirsutum l.) در دو سامانه خاک ورزی

اجتناب از شخم مکرر زمین به‌همراه حفظ بقایای گیاهی و مدیریت تغذیه گیاه می تواند به حفاظت و بهبود شرایط خاک و گیاه کمک نماید. در این راستا جهت بررسی تاثیر کاربرد مقادیر مختلف بقایای گیاهی و کود نیتروژن در دو سامانه مختلف خاک ورزی بر عملکرد و اجزاء عملکرد پنبه، آزمایشی در دانشکده کشاورزی دانشگاه بیرجند در قالب طرح اسپلیت فاکتوریل با سه تکرار در سال 1392 انجام شد. عامل اصلی دو سطح خاک‌ورزی معمول (شخم برگردان‏دار) و کم خاک‌ورزی (دیسک) بود. عامل فرعی نیز شامل دو سطح نیتروژن (50 و 150 کیلو‏گرم در هکتار) و پنج سطح بقایای جو (معادل صفر، 77، 154، 231 و 308 گرم در مترمربع) بود که به‌صورت فاکتوریل در کرت‏های فرعی به‌صورت تصادفی توزیع شدند. صفات مورد بررسی شامل درصد سبز شدن، وزن خشک گیاه و عملکرد و اجزای عملکرد بودند. نتایج نشان داد که کاربرد بقایا سبب کاهش سبز شدن پنبه شد. کاربرد مقادیر اندک بقایا سبب کاهش وزن خشک و عملکرد پنبه نسبت به عدم کاربرد شد، ولی با افزایش بقایا مقادیر این صفات به‌ویژه در شرایط کاربرد بیشتر نیتروژن و شخم برگردان دار، افزایش زیادی را نشان دادند، به‌نحوی‌که بالاترین میزان عملکرد الیاف به‌میزان 1.04 تن در هکتار در سطح 308 گرم بقایا همراه با 150 کیلوگرم نیتروژن و کاربرد شخم برگردان دار حاصل شد. بر مبنای یافته ها، در صورت افزودن 100 درصد بقایای محصول قبل به خاک، باید میزان نیتروژن به‌کار برده شده نیز به‌طور متناسب افزایش یابد، در غیر این صورت کاهش معنی‌داری در عملکرد و اجزاء آن به‌ویژه در سطوح بالای بقایا رخ می دهد. هم‌چنین به نظر می رسد حداقل در کوتاه‏مدت اجرای سامانه‏های کم‏خاک‏ورزی تاثیری بر عملکرد نداشته و یا حتی سبب کاهش آن شوند و به مطالعات درازمدت برای تعیین اثربخشی سامانه‏های خاک‏ورزی حفاظتی نیاز است.

Effect of Crop Residue Management and Nitrogen on Variations of Dry Matter and Yield of Cotton (Gossypium hirsutum L.) under two Cultivation Systems

Introduction;Avoidance of repeated soil tillage in conjunction with maintaining crop residues and plant nutrition management may help to conserve and improve the soil and plant conditions. Primary goals of conservational systems consist of eliminating some cultivation practices and increasing surface crop residues in the planting system. In such residue conserving systems, nitrogen fertilizers are considered as important elements in crop production and influence the pattern of soil organic carbon storage as well as crop growth and yield. Currently, cotton is mainly cultivating in many farms of the country, and in particular in the Southern Khorasan province, after removal of the residues of the previous crop, and few studies have been conducted on the importance of plant residues in this plant in Iran. Therefore, this research was carried out with the aim of investigating the interaction of barley plant residues and different levels of nitrogen on yield and yield components of cotton in two different tillage systems (conventional tillage with moldboard plowing and reduced tillage with disk).;Materials and Methods;To study the effect of application of different residue amounts and nitrogen fertilizer under two different cultivation systems on dry matter accumulation, yield and yield components of cotton, an experiment was conducted as splitplot factorial design with three replications at the Faculty of Agriculture, University of Birjand, Birjand, Iran. The main plot consisted of two cultivation levels including conventional tillage (mould board plowing) and reduced tillage (disking). The subplot included two nitrogen levels (50 and 150 kg.ha1) and five levels of barley residues (0, 77, 154, 231 and 301 g.m2) which were factorial arranged in sub plots. Cotton, Khordad cultivar, was planted on 20th June 2013. Plant dry weight was measured at three stages over the growing season and cotton bolls were collected at two stages and the lint, seed cotton and cottonseed yields was recorded.;Results and Discussion;Results showed that the cotton emergence in moldboard plowing (46.8%) was significantly higher than disk (38.1%), and seedling emergence in both tillage systems decreased with increasing amount of residues on the soil surface. The highest percentage of emergence was related to zero residues in moldboard plowing and the lowest emergence was observed in low tillage (disc) with residues of 308 g.m2. The residue application also reduced the plant dry weight early in the growing period. Although application of low amounts of residues reduced plant dry weight and cotton seed and lint yields compared to nonresidue application at the end of the growing season, increased levels of residues, especially where high rates of nitrogen application and moldboard plow were practiced, remarkably increased these traits, so that the greatest lint yield (1.04 ton.ha1) was observed with 308 g.ha1 of residue in conjunction with application of 150 kg.ha1 nitrogen and practicing moldboard plowing. Moldboard plow system caused a greater dry matter accumulation and crop yield and it seems that initiation of crop residue conservation and reduced tillage requires more time.; ; ;Conclusion;The research clearly demonstrated the beneficial effects of not removing plant residues and mixing them with soil even for a single crop season, which, in turn, emphasizes the avoidance of incorrect burning of the residues of the previous crop. According to this study findings, where 100% of previous crop residues are added to the soil, the application of nitrogen should be increased proportionally. Otherwise, a significant reduction in crop yield and yield components would be observed especially at high rates of crop residues. Moreover, it appears that reduced cultivation systems might not influence crop yield and even reduce it in short term and requires long term research studies to determine the efficacy of conservational cultivation systems.