ارزيابي كارايي نيتروژن در ارقام ذرت (Zea mays L) تحت شرايط اقليمي كرمانشاه

Evaluation of Nitrogen Uptake and Productivity of Maize Cultivars (Zea mays L.) under Kermanshah Climate Conditions

كشت ارقام مختلف محصولات زراعي با كارايي جذب و مصرف بالاتر نهاده ها از جمله راهكارهاي كشاورزي پايدار است كه ضمن استفاده موثر گياهان از نهاده هاي شيميايي و طبيعي، مخاطرات زيست محيطي مصرف نادرست نهاده ها را نيز به طور چشم گيري كاهش مي دهد. بر اين اساس به منظور ارزيابي كارايي جذب، تبديل و مصرف نيتروژن ارقام ذرت (Zea mays L)، آزمايشي به صورت كرتهاي خرد شده در قالب طرح پايه بلوكهاي كامل تصادفي با چهار تكرار در مزرعه تحقيقاتي پرديس كشاورزي و منابع طبيعي دانشگاه رازي اجرا شد. تيمارهاي آزمايش شامل چهار سطح كود نيتروژن (40، 70، 100 و 140 درصد نياز گياهي ذرت به عنصر نيتروژن كه مقدار توصيه شده بر اساس آزمون خاك معادل 138، 238، 350 و 483 كيلوگرم اوره در هكتار در نظر گرفته شد) در قالب كرتهاي اصلي و سه رقم ذرت 704، سيمون و 678 BC در قالب كرتهاي فرعي بود. نتايج نشان داد كاربرد كود نيتروژن باعث بهبود عملكرد دانه (63 درصد) و عملكرد ماده خشك كل (58 درصد) شد. رقم سيمون نسبت به ارقام ديگر از عملكرد دانه بيشتري (19 درصد) برخوردار بود. بيشترين كارايي جذب نيتروژن مربوط به رقم 704 بود. رقم سيمون داراي بيشترين كارايي تبديل نيتروژن (38/1 كيلوگرم دانه بر كيلوگرم نيتروژن جذب شده) و كارايي مصرف نيتروژن (31/3 كيلوگرم دانه بر كيلوگرم نيتروژن فراهم خاك و مصرف شده) بود. همچنين كمترين كارايي تبديل نيتروژن (32/6 كيلوگرم دانه بر كيلوگرم نيتروژن جذب شده) و كارايي مصرف نيتروژن (26/8 كيلوگرم دانه بر كيلوگرم نيتروژن فراهم خاك و مصرف شده) نيز مربوط به رقم 678 BC بود. كاربرد كود نيتروژن به شدت بر صفات مربوط به كارايي جذب و مصرف نيتروژن تاثيرگذار بود. به طوري كه با افزايش ميزان كاربرد كود نيتروژن از 40 به 70 درصد نياز گياهي ذرت، كارايي جذب و مصرف نيتروژن افزايش يافت، ابن در حالي بود كه افزايش بيشتر كود نيتروژن از 70 به 140 درصد منجر به كاهش ويژگي هاي مذكور شد. با افزايش ميزان كاربرد كود نيتروژن كارايي تبديل نيتروژن حدود 22 درصد كاهش يافت. بيشترين كارايي تبديل نيتروژن در سطح كودي 40 درصد (30/2 كيلوگرم دانه بر كيلوگرم نيتروژن جذب شده) و كمترين آن در سطح كودي 140 درصد (17/6 كيلوگرم دانه بر كيلوگرم نيتروژن جذب شده) مربوط به رقم 704 بود. به طور كلي، مصرف بيش از حد كود نيتروژن نه تنها منجر به بهبود كارايي مصرف نيتروژن در سيستم توليد ذرت نشده است، بلكه افزايش مخاطرات زيست محيطي را به همراه خواهد داشت.

Introduction Nitrogen (N) is one of the main limiting factors in agroecosystems all around the world. However, high application rates of N fertilizers would led to strong environmental consequences. Reduction of N fertilizers consumption decreases production costs and environmental pollution. Therefore, we need to be enhance N efficiency due to the high N fertilizer cost and required measures to prevent the waste of N. Cultivation of diverse crop cultivars with higher resources absorption and utilization efficiency is one of the major approach in the sustainable agriculture that would led to effective use of natural and chemical inputs and reduce significantly the environmental risks. Kermanshah province is one of the maize production poles in Iran. In this province large amounts of N fertilizers annually consumes in the maize agroecosystem. Therefore, the aims of the present study were evaluating N uptake and utilization efficiency, and finally N use efficiency in the maize agroecosystem of Kermanshah Materials and Methods A split plot experiment was carried out based on randomized complete block design (RCBD) with four replications at the Campus of Agriculture and Natural Resources Field at Razi University at 2014. Treatments were four levels of N fertilizer rate (40, 70, 100 and 140 percent of the maize demand to N which were 138, 238, 350 and 483 kg.ha-1 urea) as main plots and three maize cultivars including SC-704, BC-678 and Simon as sub plots. Biomass of nitrogen at anthesis and maturity phases was measured by Kjeldahl method. Then, N uptake and utilization efficiency, and nitrogen use efficiency were calculated. Data analysis was done by SAS software (Ver 9.4) and means comparison were tested by LSD at 5% level. Results and Discussion The results showed that by increasing of N fertilizer rate from 40 to 140 percent of maize demand, amount of biomass N at anthesis and maturity phases changed from 1.2 to 1.1 percent, and 1.1 to 1.5 percent, respectively. By rising of N fertilizer rate from 40 to 140 percent of maize demand, total dry matter yield and grain yield improved about 58 and 63 percent, respectively. Grain yield of Simon cv was higher than other cultivars. Simon cv. had maximum grain yield in the N fertilizer level of 140 % and this increase was observed in 100% N in SC-704 and BC-678 cultivars %. The N utilization efficiency and N use efficiency were also different among maize cultivars. The highest N uptake efficiency was related to SC-704 cv. Moreover, Simon cultivar had the highest N utilization efficiency (38.1 g.kg-1) and N use efficiency (31.3 g kg-1). The lowest N utilization efficiency (32.6 g kg-1) and N use efficiency (26.8 g kg-1) were related to BC-678 cv. Our results also indicated that N fertilizer rate significantly had been affected on N uptake efficiency, N utilization efficiency, and N use efficiency. Increased N fertilizer rate from 40 to 70 percent of maize demand, improved N uptake efficiency and N use efficiency while these measured features decreased by more rising of N fertilizer rate from 70 to 140 percent. N utilization efficiency decreased about 22 percent (from 38.8 to 30.2 g kg-1) with increased N fertilizer rate from 70% to 140% of maize demand. The highest N utilization efficiency was 30.2 g kg-1 that was due to the fertilizer level of 40 percent and the lowest N utilization efficiency was 17.6 g kg-1 which was gained through fertilizer level of 140 percent for SC-704 cv. Conclusion The results of this study indicated that more traits in different maize cultivars such as grain yield have been improved by increased N fertilizer rate. But, evaluation of traits related to resources use efficiency showed that N use efficiency reduced by rising of N fertilizer rate for all maize cultivars. Therefore, from ecological viewpoint it can be concluded that excessive N fertilizer consumption not only did not improve productivity in the maize agroecosystems but also increased environmental hazard dramatically.