تغییرات ویژگی‌های فیزیکی خاک مزارع دیم دشت مراغه در اثر اعمال تیمارهای خاک ورزی حفاظتی و سنتی

به‌منظور مطالعه اثرات خاک‌ورزی سنتی و حفاظتی بر خصوصیات فیزیکی خاک در اراضی کشاورزی دیم، تحقیقی به مدت 5 سال زراعی در موسسه تحقیقات دیم کشور در قالب طرح بلوک‌های کامل تصادفی با 5 تیمار خاک‌ورزی شامل: کاشت مستقیم در ته ساقه‌ها (nt1)، کاشت مستقیم در کلیه بقایا (nt2)، شخم قلمی + دیسک (ch)، کم خاک‌ورزی (mt) و شخم مرسوم (ct) در 4 تکرار به اجرا در آمد. نمونه‌برداری‌های خاک در انتهای سال پنجم برداشته شدند که این نمونه جهت آنالیز پارامترهای فیزیکی ازجمله پایداری خاکدانه‌ها (was)، میانگین وزنی و هندسی قطر خاکدانه ها به روش الک تر (gmdwet و mwdwet) و الک خشک (gmddry و mwddry)، بعد فرکتال جرمی خاکدانه‌ها (dm)، کربن آلی کل (toc)، کربن آلی محلول (doc) و جرم مخصوص ظاهری خاک استفاده شدند. نتایج نشان داد که اثر تیمارهای خاک‌ورزی بر پارامترهای mwddry و gmddry معنی‌دار بود. اثر متقابل روش‌های مختلف خاک‌ورزی و مکان بر روی doc و اثر متقابل عمق و مکان بر روی جرم مخصوص ظاهری معنی‌دار بود. میزان کربن آلی محلول در تیمار خاک‌ورزی سنتی با مقدار mg g^-1 3.74 در مکان اول به‌طور معنی‌داری بیشتر از سایر تیمارها (با مقادیر کمتر از mg g^-1 3.20) بود. همچنین در تیمار nt1 و nt2 میانگین وزنی (به ترتیب با 1.25 و 1.17 میلی متر) و هندسی (1.04 میلی متر برای هر دو) قطر خاکدانه ها اختلاف معنی‌داری با سایر تیمارها داشت. بر اساس نتایج به‌دست‌آمده توصیه می‌شود، به‌جای استفاده مداوم از خاک‌ورزی سنتی از خاک‌ورزی حفاظتی استفاده شود.

Changes in Physical Properties of Soils after Five Years of Application of Conventional and Conservation Tillage Practices

Introduction: Soil is one of the nonrenewable resources (in human being life time scale) that is important to be protected. Tillage operations are carried out in a variety of ways, which in general can be divided into two comprehensive classes of conventional and conservation tillage practices. The tillage has a very important impact on soil physical, chemical and biological properties. Different tillage systems can have conflicting effects on soil physical properties, which is thought to reflect the impact of different weather conditions. Therefore, it seems necessary to study the effects of different tillage practices on the soil attributes in different climatic conditions.;Materials and Methods: This experiment was conducted for five years from 2011 to 2016 in a randomized complete block design (RCBD) with repeated measurements in two different locations and four replications. The applied tillage practices included notill in standing residue (NT1), notill in entire residue (NT2), chisel plow plus disc harrow (CH), minimum tillage with mulch cultivator (MT) and conventional plowing with moldboard plowing (CT). The experiment was carried out at Dryland Agricultural Research Institute (DARI) in Maragheh. Soil samples were taken at the end of fifth year and then soil texture were determined by hydrometer method, weight and geometric means of aggregates diameters by wetsieving (MWDwetو GMDwet) and drysieving (MWDdry GMDdry) procedures, the stability of 1 to 2 mm aggregates (WAS) by wetsieving, total soil organic carbon (TOC) by wet oxidizing method, dissolved soil organic carbon (DOC) using carbon analyzer and mass fractal dimension aggregates using Tyler and Wheatcraft model. The soil bulk density (Db) was also measured by intact samples (from two depths of 015 cm and 1530 cm) prepared from the study area using sampling cylinders with a diameter of 5 and a height of 4 cm.;Results and Discussion: In general, the results showed that the interaction of depth and location on Db was significant at 5% probability level. The measured Db in 1530 cm was greater than the measured Db in a depth of 015 cm. Also, in spite of the significance of the main effects of location and tillage and the interaction of tillagelocation on soil dissolved organic carbon (DOC), tillage treatments and their interaction effects on total organic carbon (TOC) were not significant. The results showed that conventional tillage, CT, had the highest amount of DOC. However, notill in entre residue (NT2) and minimum tillage (MT) showed the lowest amount of DOC. Further, the main effects of tillage practices on MWDdry and GMDdry were significant at 5% probability level. Notill (NT1 and NT2) practices had the highest MWDdry with values of 1.17 and 1.25 mm. Tillage practices and location had no significant effect on WAS, Dm, and MWDwet and GMDwet.;Conclusion: It seems that the reason that DOC content of CT was higher than conservation tillage practices is due to the preservation of crop residues on the soil surface in conservation and notill systems and less mixing of them with soil and consequently their less decomposition. While in conventional tillage, plant residues were mixed with soil, and the effect of biological degradation increased soil DOC. The greater MWDdry in NT1 and NT2 practices suggests that tillage, even at a minimum or reduced state, breaks down the aggregates and produces smaller particles or aggregates. It also seems that the main reason for GMDdry reduction in minimum tillage is due to the further degradation of aggregates by the tillage agent. Therefore, to better and more accurately observe the effects of different types of tillage, sampling should be done at the end of each growing season.