بررسی شکل های شیمیایی فسفر برای مدیریت فسفر خاک در اراضی تحت کشت پسته

داشتن اطلاعات کافی و دقیق در مورد فسفر معدنی خاک برای توسعه کشاورزی پایدار در مناطق خشک بسیار مهم است. همچنین آگاهی از تغییر شکل فسفر در خاک‎های مختلف برای توصیه کود فسفره بسیار مهم است. هدف از این مطالعه یافتن اثرات استفاده طولانی مدت از مقادیر مختلف فسفر بر میزان فسفر قابل استفاده برای گیاهان و تعیین شکل‎های معدنی فسفر موجود در خاک بود.برای این منظور 84 نقطه نمونه برداری با فاصله منظم 2 کیلومتر از یکدیگر به کمک نرم افزار ایلویس تعیین گردید و 168 نمونه خاک از دو عمق 40 0 و 80 40 سانتی‎متری از اراضی زیر کشت پسته شهرستان سیرجان جمع آوری شد. به منظور جداسازی و تعیین شکل‎های معدنی فسفر در خاک از روش جیانگ و گو (عصاره گیری دنباله دار) استفاده ‎شد. این روش، فسفر را به شکل‎های دی کلسیم فسفات ، اکتاکلسیم فسفات، فسفات‎های آلومینیوم ، فسفات‎های آهن، فسفات‌های محبوس و آپاتیت جدا می‌کند. نتایج نشان داد که مقدار فسفر کل در این نمونه های خاک به طور میانگین بالای 460 میلی‎گرم در کیلوگرم خاک بود و فراوانی اشکال شیمیایی فسفر به ترتیب آپاتیتapatite> فسفات آلومینیومal p> دی‎کلسیم فسفاتca2 p> فسفر محبوسoc p≥ فسفات آهنfe p > اکتا کلسیم فسفاتca8 p بود. این نتایج نشان داد که مصرف مداوم فسفر منجر به تبدیل فسفر موجود در خاک به شکل‎های غیرقابل دسترس مانند آپاتیت می‎شود. مقادیر بالای فسفر کل نشان می‎دهد که با مدیریت بهینه مصرف کودهای فسفره و تغییر شرایط خاکی تا حد امکان مانند افزودن مواد آلی، می توان فسفر مورد نیاز را بدون منابع جدید تامین کرد.

investigation of chemical forms of phosphorus for soil phosphorus management in pistachio orchards

introduction phosphorus (p) is the second essential element and plays a key role in plant growth. the availability of p in the soil depends on the p fractions, which influence the primary productivity of agricultural ecosystems. having sufficient and accurate information about soil mineral phosphorus is very important for the development of sustainable agriculture in arid regions. awareness of phosphorus deformation in different soils is also very important for phosphorus fertilizer recommendation. when phosphorus is used in its soluble forms, it is rapidly converted into unusable forms for the plant. native soil phosphorus is often in unusable form for the plant. therefore, having enough information about phosphorus deformation in different soils is very important to recommend phosphorus fertilizer. the objective of this study was to find out the effects of long term use of different sources of phosphorus on available p for pistachio plants in southeast iran. materials and methods for this research were taken depths from 0 40 cm and 40 60cm in 63000 ha of sirjan pistachio orchards of kerman province. jiang and gu method was used to isolate and determine the mineral forms of phosphorus in the soil. each p fraction was extracted as follows: 1g (oven dry weight) of sample soil weighed out into a 50 ml polyethylene centrifuge tube. a volume of 40 ml of the first extractant, nahco3 (table 1) was added and placed in an automated mechanical shaker at 25° c with 110 rpm for 1 h to allow time for the solution top equilibrate. the tubes were then centrifuged at 6000 × g for 15 min and the supernatant was carefully filtered through whatman no. 42 with minimum loss of soil. reactive p in the supernatant was determined using the ascorbic acid method at 882 nm. this method separates phosphorus in the forms of di calcium phosphate, octa calcium phosphate, aluminum phosphates, iron phosphates, occluded phosphates and apatite. results and discussion results showed that the total p was high in these soil samples and the abundance of p fractions was in order to ca10 p type≥ al p >ca2 p type> occluded p ≥ fe p > ca8 p type in two depths. these results suggested that continuous p application leads to plant available p convert into unavailable p forms such as ca10 p. results indicate that naoh extractable p has resulted from active fe oxides. also, by comparing two depths of soil in the study area, it can be concluded that the occupied phosphorus in the surface layer is more than the deep layer. finally, it can be concluded that by increasing the stability of various forms of phosphorus, their contribution to other forms of phosphorus increases, so that the concentration of apatite is much higher than phosphate calcium phosphate. results showed the amount of available phosphorus (ca2 p) in the surface layer is more than the deep layer, which can be attributed to surface application of phosphorus fertilizers. however, there are sections where phosphorus in the surface layer and the bottom is almost equal. amount of this form of p is less than al p and fe p. it may be due to increase in al and fe contents in in calcareous soils. conclusion high amounts of total p clarifies that by optimally managing the use of phosphorus fertilizers and soil conditions, the required p of the plant can be provided without additional use. from the results, it appears that in the calcareous soils the abundance of different forms of p was in order ca10 p type≥ al p >ca2 p type> occluded p ≥ fe p > ca8 p. furthermore, it observed that fe p, al p and oc p are important forms of p and on average constitute 30% of the sum of inorganic p forms. these findings demonstrate that the ability of naoh to extract al p will be reduced with an increase in al p content and that naoh is