تأثير برخي عمليات حفاظت خاك بر شاخص‌هاي كيفيت زيستي خاك در منطقه چهل‌چاي استان گلستان

Effect of Some Conservation Practices on Soil Biological Quality Indices in The Chehelchai Region, Golestan province

استان گلستان به دليل پستي و بلندي، اقليم متنوع، اراضي لسي و حساسيت اين اراضي به فرسايش، نياز به توجه بيش‌تري در خصوص حفاظت خاك دارد. روش ­هاي مختلف براي افزايش كيفيت خاك پيشنهاد شده ­است. مطالعه حاضر با هدف بررسي نقش عمليات­ حفاظتي بر بهبود كيفيت زيستي خاك طراحي شده است. عمليات‌ حفاظتي نها ل­كاري، تراس­بندي و باغ‌كاري انتخاب و كيفيت زيستي آن‌ها در مقايسه با اراضي زراعي، مرتعي و جنگلي بررسي شد. نتايج نشان داد كه تبديل اراضي جنگلي و مرتعي به كشاورزي موجب تخريب كيفيت خاك مي‌شوند؛ به نحوي كه شاخص­ هاي كيفيت خاك، مانند موادآلي تا 60 درصد و پايداري خاكدانه تا70 درصد كاهش نشان مي‌دهند. هم‌چنين در اين مطالعه شاخص ­هاي زيستي و شاخص ­هاي­ كيفيت زيستي خاك (QBS) و شاخص­ هاي اكومرفولوژيك (EMI) كاهش نشان دادند. در مقابل عمليات حفاظتي باعث بهبود اين شاخص ­ها شده بود. در شاخص ­هاي زيستي، عمليات نهال­ كاري و باغ‌كاري افزايشي حدود 40 درصد در EMI و كربن زي‌توده ميكروبي و تا 80 درصد در تنفس ميكروبي را موجب شدند و تراس­بندي نسبت به عمليات ديگر بهبودي كم‌تر، در حدود 11 درصد در EMI و تا 20 درصد در كربن زي‌توده ميكروبي موجب گرديد. در مجموع روند يكساني براي همه­ ي شاخص­ها و عمليات قابل مشاهده نبود. كمي افزايش در برخي شاخص­ ها مورد بررسي، مشاهده شد كه به آن نظرمي­رسد به دليل عمر كوتاه عمليات حفاظتي بوده و در آينده نتايج، بهبود بيش‌تر و بهتري را نشان خواهند داد.

Introduction Soil quality has been defined as a “The potential of soil to play a positive relationship with the other parts of ecosystem”. Soil biological indicators provide insight into the living component of the soil. Similar to physical and chemical indicators, biological indicators have a relationship to soil functions and can evaluate soil functions to assess soil quality. Between biological indicators, an index that can be measured quickly and easily is more useful to show the changes. In many studies an indicator of microbial respiration, microbial population, nitrogen mineralization and enzymes activity can be used. Special ability is required to measure quickly and show the quality of soil microorganisms and reaction to environmental changes. Soil health is defined by chemical and physical parameters such as soil texture, soil pH, electrical conductivity, etc., that are not quantifiable completely. Therefore, conservation practices planting and forestry may directly or indirectly affect a organism’s activities. The results of land-use systems without consideration of the consequences on soil quality have been environmental degradation. Agricultural management systems have been generally adopted without attending to soil conservation and soil quality, and this therefore causes significant decline in agricultural soil health worldwide. Different methods of soil conservation have been proposed to prevent erosion and improve soil quality destructive phenomena. In Golestan province due to topographical and climatic conditions and less soil sensitivity to erosion, more attention should be given to this issue. But it remains unclear how far this conservation practice can take to prevent damage. This study aimed to investigate the role of conservative practices to improve the soil quality indicators. Materials and Methods The watershed of Chehelchai is located between North latitudes 36° 59´ and 37° 13´ and Earth longitudes 55° 23´ and 55° 38´. The history of land use in the region shows that more than about 40 years ago, all the study area was covered by forest. Agricultural land use changes occurred on a large scale. With emphasis on conservation operation, parts of the agricultural land were changed to productive gardens, partly forested, partly pasture with native species. Different land uses were selected in loess formations, and slope of 41 %, with life operations was about 6 to 7 years. Protective Operations Garden species, terraces and forestry were selected and quality of soil was compared with agricultural land, pasture and natural forest. In this regard, 10 soil samples were taken. After preparation of the samples, physical, chemical and biological analysis were measured. Additionally, soil properties (pH, Electrical Conductivity, Calcium carbonate, organic matter, texture, bulk density, aggregate stability, microbial respiration, microbial biomass population count of micro- arthropods, biological soil quality) were analyzed. The data were analyzed using software SAS. Ver 9. and the results were compared in a randomized complete block design. Analysis of variance in the form of randomized complete block design was done using the LSD multiple comparison. Results and Discussion Our results showed that the dominant soil texture class in land uses was silty loam. It seems that soil texture is less affected by the land use changes. The results showed that the changes of forest and pasture to agricultural lands have destroyed the soil quality. Soil quality indicators such as organic matter and aggregate stability have declined by 60 and 70 percent respectively. Like wise, biological indicators such as microbial respiration, microbial biomass carbon and QBS (biological soil quality indicators based on the population of micro- arthropods) and EMI (index dependence of soil to soil organisms) showed a similar trend. In contrast, the Conservation practices improved the indices. Biological indicators in the forestry and gardening showed an increase of 40 percent in EMI Microbial biomass carbon and 80 percent in microbial respiration. Terracing had less improvement than other operations in about 11 to 20 percent in EMI and microbial biomass carbon.