ارزیابی شاخص‌های کیفیت خاک تک‌متغیره و چندمتغیره مبنا در بخشی از اراضی کشاورزی دشت سراب (استان آذربایجان شرقی)

شاخص کیفیت خاک (sqi) موضوع تحقیق بسیاری از پژوهشگران در سه دهه اخیر بوده اما اغلب جنبه کلی داشته یا محصول مبنا نبوده‌است. هدف پژوهش حاضر، بررسی و ارزیابی کارایی روش‌های مختلف تعیین شاخص کیفیت خاک بر مبنای عملکرد محصول گندم آبی پاییزه در بخشی از اراضی دشت سراب بود. برای این کار، از توابع رتبه‌دهی خطی و غیرخطی و شیوه تلفیق رتبه افزودنی ساده (sa)، افزودنی وزنی (wa)، نمرو (n) و مقیاس‌شده (sc) استفاده شد و شاخص‌های کیفیت با عنوان چندمتغیره مبنا به‌ترتیب sqisc, sqin, sqiwa, sqisa هم برای مجموعه کل داده‌ها (tds) و هم مجموعه حداقل داده‌ها (mds) و شاخص کیفیت فیزیکی خاک دکستر (s-index)، جرم مخصوص ظاهری نسبی (rbd) و دامنه رطوبتی با حداقل محدودیت (llwr) با عنوان شاخص‌های کیفیت تک‌متغیره مبنا محاسبه شدند. برای مجموعه tds هر یک از توابع رتبه‌دهی (خطی و غیرخطی) منجر به sqiهای بین 0.280 تا 0.425 با تفاوت معنادار (p<0.05)  شد. برای مجموعه mds نوع رتبه‌دهی بر sqi اثر معنادار نداشت. شیوه تلفیق رتبه‌ها نیز منجر به مقادیر متفاوت sqi شد. برای مجموعه tds، شاخص کیفیت مقیاس‌شده (sqisc) و برای مجموعه حداقل داده‌ها، sqiwa بیشترین مقدار را داشتند (به‌ترتیب 0.45 و 0.53). همبستگی قوی و معنادار (r=0.74, p<0.01) بین شاخص‌های کیفیت حاصل از دو مجموعه داده، نشانگر پتانسیل مجموعه mds در برآورد شاخص کیفیت با صرفه‌جویی در هزینه و وقت، حداقل برای خاک‌های منطقه بود. بر مبنای درجه‌بندی sqiwa-mds، خاک بیش از 70 درصد مکان‌های مطالعه شده درجه کیفیت چهار (پایین یا فقیر) داشتند و در بیش از 65 درصد مکان‌ها نیز عملکرد گندم آبی پاییزه کمتر از میانگین منطقه مورد بررسی (4.3 تن بر هکتار) بود و بیانگر هماهنگی شاخص کیفیت مذکور با عملکرد گندم و کارایی آن در بیان کیفیت خاک‌های منطقه بود. همبستگی معنادار (p<0.01) بین شاخص‌های تک‌متغیره مبنا (llwr, rbd, s-index) باsqi  بیانگر این بود که به‌جای به‌کارگیری مجموعه‌ای از ویژگی‌ها برای ارزیابی کیفیت خاک‌ها، می‌توان از یک یا دو شاخص تک‌متغیره استفاده کرد. در بین سه شاخص مذکور، llwr بیشترین ضریب همبستگی (r = 0.55**) را با عملکرد محصول داشت وrbd  در مرتبه بعدی قرار گرفت که نشانگر توان بالقوه دو شاخص مذکور در ارزیابی وضعیت کیفیت خاک‌های منطقه با هدف عملکرد محصول گندم بود.

assessment of single and multivariate soil quality indices in the part of sarab plain agricultural lands (east azerbaijan province)

background and objectivessoil quality concept was initiated for the realization and strengthening of soil sustainable management particularly for sustained yield production as early as 1990 decade. at the time it was a qualitative concept but later evolved and expressed in quantitative term as soil quality index (sqi). briefly, it is based on selecting soil properties (referred as indicators) that attribute to general soil wellness or particular soil function (e.g. yield production, nutrient cycling, carbon sequestration etc.), assigning an appropriate score (0 to 1) for each indicator and integrating (averaging) the scores and expressing the outcome as sqi. substantial researches have been carried out on various aspects of the issue including indicators selection, their scoring, and score integration. however most of them have been generally-oriented or generally-purposed meaning that no particular or specific goal(s) has been in mind of the investigator. the sqi has often been determined by using the total available data (tds) or a minimum set of data (mds), hear after would be referred as multivariate based sqi. in the present study, we also investigated s-index, relative bulk density (rbd) and least limiting water range (llwr) by referring to them as a single variable quality index. the assessment of those multi and single variable based sqi in relation to winter wheat yield production was the major goal of the present research. methodologyin this research two types of indicator scoring functions (linear and non-linear) were applied to both tds and mds (identified by principle component analysis) to determine each selected indicator score. the scores were integrated as their simple average, weighed average, nemero and scaled average methods. the corresponding quality indices were designated as sqisa, sqiwa, sqin, and sqic, respectively. considering the single based quality indices, sd was determined using s-index proposed by dexter, rbd according to jones and llwr according to da silva et al. the pertinent parameters were obtained from soil water release and soil penetration resistance curves determined at 173 sites and wheat grain yield was recorded at all sites as well. resultslinear and non-linear indicator scorings led to sqis ranging from 0.28 to 0.53 being significantly different at 5% probability level. the four applied score integration methods also yielded statistically significant (p<0.05) sqis. for tds, sqisc showed the highest quality index of 0.45 while for mds, sqiwa was the highest (0.45). the results clearly indicated significant interaction between scoring (linear and non-linear) and score integration methods for both tds and mds. on the basis of sqiwa, at about 70% of the 173 studied locations, soil quality was graded as low or poor which is in accordance with low grain yield obtained at nearly 65% of those locations. this implies the potential applicability of sqiwa for wheat yield assessment at the studied area. single variable based quality indices (sd, rbd, llwr) were significantly (p<0.01) correlated to sqis, meaning that instead of set of variables (tds or mds), a single variable (e.g. rbd) may be adequate for soil quality assessment. among the single variable indices, the llwr showed the highest correlation (r = 0.55**) with wheat yield. the rbd stood at the second place indicating its high adequacy for the soil quality assessment in relation to wheat yield. conclusionstrongly significant (p<0.005) correlation between mds-based sqis with those tds-based ones along with low cost and less time needed for obtaining mds (%clay, awc, ph, pav., and mnav. in the present study) in comparison to tds (17 variables) indicated that the sqis based on mds may be preferred especially if periodic sqi assessment in the studied area is desired. among the single variable based quality indices, the llwr showed the highest correlation with grain yield indicating its potential applicability for soil quality assessment in relation to yield. generalization of this finding needs more investigations. in the present study, accessibility to the biological soil variables which may attribute to sqis was unfortunately impossible; their inclusion in sqis assessment for the area would be much valuable. it was also implicitly assumed that no water stress has been occurred during the active growth period for the crop in the studied area which again needs to be considered in future investigations.author contributionsconceptualization, m. r. n. and s. r. g.; methodology, m. r. n. and s. r. g.; software, r. h. and d. z.; validation, s. r. g. and r.  h.; formal analysis, s. r. g. and m. r. n.; investigation, s. r. g.; resources, s. r. g. and r. h.; data curation, s. r. g. and r. h.; writing- original data preparation, s. r. g.; writing-review and editing, m. r. n. and d. z.; visualization, s. r. g.; supervision, m. r. n.; project administration, m. r. n. and d. z.; funding acquisition, m. r. n. and s. r. g.  all authors have read and agreed to the published version of the manuscript. data availability statementdata is available on reasonable request from the authors. acknowledgementsthe authors are thankful to the university of tabriz for financial supports. conflict of interestthe authors declare no conflict of interest. ethical considerations the authors avoided data fabrication, falsification, plagiarism, and misconduct.