اثر مقدار كود و زئوليت‌هاي كلسيمي، پتاسيمي و تركيبي بر كاهش آبشويي نيترات از خاك

Effect of Amount of Fertilizer and Calcic, Potasic and Soil Zeolite on Reducing Nitrate Leaching from Soil

آبشویی نیترات نه تنها باعث اتلاف هزینه‌های بسیار زیادی می‌شود بلكه تشدید آلودگی منابع آب را نیز به دنبال خواهد داشت. بدین منظور راه‌های بسیاری برای جلوگیری از آبشویی نیترات پیشنهاد شده است كه به دلیل مشكلاتی مانند هزینه بالا و كارایی كم مورد استقبال واقع نشده‌اند. استفاده از زئولیت‌ها یكی از راه‌هایی است كه به دلیل ارزانی و توانایی بالا مورد توجه قرار گرفته است. بدین منظور این تحقیق در سال 1392 با 21 تیمار و در 3 تكرار و مجموعاً 63 گلدان در مزرعه تحقیقاتی دانشكده كشاورزی دانشگاه بیرجند انجام شد. تیمار‌های مورد بررسی در این تحقیق شامل نوع زئولیت (كلسیمی: Zca، پتاسیمی: Zk و تركیبی: Zs) در سه سطح (M0، M2 و M6 به ترتیب شامل صفر، 2 و 6 درصد وزنی) و سه سطح كود اوره (F0، F2 و F4 به ترتیب شامل صفر، 200 و 400 میلی‌گرم در هر كیلوگرم خاك) بود. نتایج نشان داد كه نوع زئولیت، مقدار زئولیت، مقدار كود مصرفی، نوع زئولیت×مقدار زئولیت اثر معنی‌داری در سطح احتمال 1 درصد بر آبشویی نیترات داشتند. همچنین اثر متقابل مقدار زئولیت×مقدار كود نیز در سطح احتمال 5 درصد اثر معنی‌داری بر آبشویی نیترات نشان داد. سایر اثرات متقابل معنی‌دار نشدند. در این آزمایش، زئولیت پتاسیمی اثر بیشتری بر كاهش آبشویی نیترات نشان داد. با اعمال 200 و 400 میلی گرم كود اوره، كمترین میزان آبشویی در تیمار ZkM6 مشاهده شد كه نسبت به شاهد به ترتیب 47/3 و 61/4 برابر كاهش داشت. با توجه به معنی‌دار نبودن اختلاف تیمارهای ZkM6F2 و ZkM6F4 نسبت به ZcaM2F4، به منظور كاهش مصرف زئولیت، پیشنهاد می‌شود كه از تیمار ZcaM2F4 در كشت زعفران استفاده شود.

Introduction: Nitrogen is an essential element for plant nutrition. Urea is a common fertilizer that used by farmers due to high nitrogen content in its structure. This fertilizer transforms into nitrate in soil. Nitrate is leached below the rooting zoon of agricultural soil. Nitrate leaching is not only a waste of a great cost, but also causes the pollution of water resources. Methemoglobinemia and cancer are well known issues that caused by nitrate leaching. For this purpose, many methods have been proposed to prevent nitrate leaching but due to high cost and low efficiency are not accepted. Using of zeolites is one of the ways that is considered due to its low cost and ability. Zeolite is a mineral material that found in many regions in Iran. Although effect of zeolite on nitrate leaching reduction was studied by many researchers, but there was no study on common three types of Iranian zeolite. Materials and Methods: For this purpose, a study was conducted as factorial layout based on a CRD with 21 treatments and 3 replications (total of 63 pots) at the Agricultural Research Station (with longitude and latitude 59o 21’ E and 32o 78’ N, respectively, and elevation 1941m), University of Birjand during 2013. Treatments consisted of calcic zeolite (Zca), potasic (Zk) and z-mix (Zs) in three levels: 0 (M0), 2 (M2) and 6 (M6) as wt% and three nitrogen levels: zero (F0), 200 (F2) and 400 (F4) (as mg.kg-1 soil). Natural clinoptilolite zeolite (Zca, Zk and Zs) were collected from Semnan province (53o 15’ E, 35o 25’ N) and analyzed for its chemical composition by X-ray diffraction. Pots after saffron harvesting irrigated (in October) and urea treatment added to irrigation water (Iranian farmers called as Zaeech Ab). For prepared sufficient drain from all pots, due to different effect of type and amount of zeolite on soil water content, based on former experiments, leaching fraction was considered as 20%. Sample drain from each pot were transferred toa lab, immediately, and were measured by spectrophotometer. Data related to nitrate leaching were analyzed by ANOVA and Tukey’s test. In this study, SAS 9.1.3 software and Microsoft Excel 2013 were used. Results and Discussion: Results showed that type of zeolite, amount of zeolite, amount of nitrogen fertilizer, type of zeolite with amount of zeolite (interaction effect) had significant effect (P <0.01) on nitrate leaching. Also, type of zeolite and amount of fertilizer (interaction effect) had a significant effect (P-value <0.05) on nitrate leaching. Other interaction effects were not significant. Results showed that z-mix zeolite had less effect on nitrate leaching reduction compared to calcic and potasic zeolite. It might be due to its properties since z-mix zeolite were prepared as gross zeolite. Potasic and calcic zeolite reduced nitrate leaching about 15.4 and 21.8% compared to z-mix zeolite, respectively. By increasing the amount of zeolite, nitrate leaching reduced. These reductions were 32 and 34% by using M2 and M6 treatments compared to M0, respectively. Amount of urea had a significant effect on nitrate leaching reduction (P-value <0.05). Although no significant effect between F2 and F4 was observed, but these treatments had significant effects compared to F0 (P-value <0.05). The highest nitrate concentration in drain water was observed in ZkM0F4, ZsM0F4 and ZcaM0F4. It is well known that no zeolite was used in these treatments. Results showed a significant difference (P-value <0.05) between ZkM0F4 and ZkM0F0. There was not significant effect between ZkM0F0 and ZkM0F2 due to high bulk density and salinity. So, soil had no capability to maintain nitrate when 400 mg of urea were used. The Zca and Zs treatments showed similar results. When zeolite was not used in soil, it is necessary to apply urea in several times with low levels. It is recommended for both Zca and Zs treatmensts. In this experiment, potasic zeolite showed the greatest effect on reducing nitrate leaching. By applying 200 and 400 mg of urea, the lowest leaching was observed in ZkM6 treatment which compared to control it was reduced 3.47 and 4.61 times, respectively. As ZcaM2F4 showed a reduction about 45.75% in nitrate leaching, it can be recommended to use in saffron cultivation. This proposal was due to lack of significant effect among ZcaM2F4, ZkM6F2 and ZkM6F4. In addition, amount of zeolite is reduced enough by application of this treatment.