تاثیر توالی و فاصله زمانی افزودن ماده افزودنی و سولفوسولفورون به آب سخت در کنترل یولاف وحشی زمستانه (Avena Sterilis Ssp. Ludoviciana Durieu.)

اینکه آیا توالی و فاصله زمانی افزودن ماده افزودنی و علف کش به آب سخت می تواند کارایی علف کش را تحت تاثیر قرار دهد یا خیر تاکنون بدون پاسخ مانده بود. در آزمایش دُزپاسخ که در گلخانه تحقیقاتی دانشگاه بوعلی سینا اجرا شد، شش مقدار از سولفوسولفورون با آب مقطر و آب سخت حاوی کاتیون های na+، ca++ و fe+++ (600 میلی گرم در لیتر از نمک کربناتی) با و بدون افزودن اسیدسیتریک (500 میلی گرم در لیتر) یا سولفات‌آمونیوم (20 گرم در لیتر) نیم ساعت قبل، همزمان و نیم ساعت بعد از افزودن علف کش به حامل های پاشش بر روی یولاف وحشی زمستانه در مرحله چهار برگی پاشیده شد. نتایج تجزیه و تحلیل رگرسیون غیرخطی نشان داد که برعکس سولفات آمونیوم که بر کارایی سولفوسولفورون بی تاثیر بود، افزودن اسید سیتریک به آب مقطر با هر توالی و فاصله زمانی نسبت به سولفوسولفورون باعث بهبود کارایی سولفوسولفورون شد. حضور کاتیون های na+، ca++ و fe+++ در حامل پاشش مقدار سولفوسولفورون لازم برای کاهش 90 درصدی وزن خشک یولاف وحشی زمستانه را به ترتیب از 9.80 به 27.60، 47.48 و 50.32 گرم در هکتار افزایش داد. بین شدت ناسازگاری کاتیون های ca++ و fe+++ اختلاف معنی داری مشاهده نشد. افزودن هر دو ماده افزودنی نیم ساعت بعد از افزودن سولفوسولفورون به آب مقطر حاوی کاتیون ها هیچ تاثیری در رفع اثر ناسازگار کاتیون ها بر کارایی سولفوسولفورون نداشت. برعکس، افزودن سولفوسولفورون نیم ساعت بعد از افزودن مواد افزودنی به آب مقطر حاوی کاتیون ها بهترین کارایی سولفوسولفورون را رقم زد. بنابراین، موضوع توالی صحیح افزودن ماده افزودنی و علف کش به آب سخت حایز اهمیت است. عدم اطلاع از این موضوع، نه تنها سبب عدم کنترل علف هرز بلکه هزینه های اضافی به کشاورز تحمیل خواهد کرد.

The Effect of Sequence and Time Interval of Adding Adjuvant and Sulfosulfuron to Hard Water in the Control of Winter Wild Oat (Avena sterilis ssp. ludoviciana Durieu.)

Introduction: In arid regions such as Iran, water hardness, as a result of existence of calcium and magnesiumcontaining minerals, is a serious challenge for irrigation practice. The irrigation systems are often applied to spray herbicides. Therefore, using hard water having high cations for herbicide application is inevitable. Such water can adversely affect the activity of some herbicides particularly weak acid ones. A solution for overcoming this problem is the addition of an adjuvant to the tank. It is well established that the addition of (NH4)2SO4 (43) and C6H8O7 (45) will efficiently remove the cations of hard water from the spray solution of weak acid herbicides. However, there is no report on whether the efficacy of sulfosulfuron (a weak acid herbicide, pKa = 3.5) is affected by the cations of hard water. Furthermore, it is observed in literature and practice that the addition of herbicide to the tank is immediately done after adding the adjuvant to the tank. Thus, there is no report on whether the sequence and time interval of adding adjuvant and herbicide to hard water could be affected by the efficacy of weak acid herbicide.Materials and Methods: The seeds of winter wild oat (Avena sterilis ssp. ludoviciana Durieu.) were primed in the same method which was already described (3). Then, eight seedlings with a 1cm radicle and 0.5cm coleoptile were transplanted at a 1cm depth within each 3liter pot filled with a 1:1:4 ratio of sand: animal manure: clay loam soil, respectively. The experiment was carried out as a doseresponse study in a completely randomized design with three factorial (6×4×7) and four replications. The 1st factor was the dose of sulfosulfuron(0, 1.25, 2.5, 5, 10, and 20 g a.i. ha1). The 2nd factor included the type of spray carrier (distilled water, hard water containing sodium chloride (NaCl), calcium chloride (CaCl2) and iron chloride (CaFe3) at 600 mg L1). The 3rd factor was also the sequence and time interval of adding adjuvant and herbicide to the spray carrier (with and without adding 500 mg citric acid (C6H8O7) L1 or 20 g ammonium sulfate ((NH4)2SO4) L1 at 30 min before, simultaneous, and 30 min after adding sulfosulfuron to the spray carrier). Five weeks after spraying, the response of individual dry weight of winter wild oat to treatments was analyzed as a nonlinear regression. This was carried out by using a four parametric logistic model (36) to estimate the values of ED50 and ED90 which are the doses of sulfosulfuroncausing a 50 and 90% reduction in the dry weight as compared to the control, respectively. Results and Discussion: In contrast to ammonium sulfate which was ineffective, the addition of citric acid to distilled water under each sequence and time interval improved the efficacy of sulfosulfuron. Decreasing the pH can permit the weak acidic herbicides to pass through the cuticle and then cell membrane during the ionic trap process. The presence of Na+, Ca++ and Fe+++ cations in the spray carrier increased the amount of sulfosulfuron required for 90% reduction in the dry weight of winter wild oat from 9.80 to 27.60, 47.48, and 50.32 g ha1, respectively. There was no significant difference between the intensity of the incompatibility of Ca++ and Fe+++ cations. Similar to other weak acid herbicides, sulfosulfuron can also be ionized into anionic (a negatively charged form) and cationic (H+) fragments under alkaline conditions. The anionic part of sulfosulfuron bonds with the cations in hard water. As a result, a crystalline herbicidecation salt is formed which is not able to pass through the cuticle due to its low solubility in water. The addition of both adjuvants 30 min after the addition of sulfosulfuron to distilled water containing the cations had no effect on removing the adverse effect of cations on the efficacy of sulfosulfuron. Conversely, adding sulfosulfuron 30 min after the addition of both adjuvants to the distilled water containing the cations provided the best efficacy of sulfosulfuron. When the adjuvants are added to hard water before herbicide, the cations of hard water can receive the cation of H+ from citric acid or NH4+ from ammonium sulfate. Then, the formation and sediment of the cationanion salt turns hard water into soft water, having no problem with the efficacy of sulfosulfuron.Conclusion: The issue of correct sequence for adding adjuvant and herbicide to hard water is important. Lack of knowledge about this issue can lead to not only the lack of weed control but also the imposition of additional costs on the farmer.