اثر مديريت علف‌هاي هرز و منابع كود نيتروژن بر عملكرد كمي و كيفي ذرت علوفه‌اي

Effect of weed management and sources of nitrogen fertilizer on quantitative and qualitative yields of forage maize

مديريت علف­هاي­ هرز و كود نيتروژن در توليد ذرت علوفه‌اي، دو مسئله حائز اهميت مي‌باشند. در اين مطالعه اثر روش‌هاي مختلف كنترل علف‌هاي‌هرز و منابع كود نيتروژن بر كنترل علف‌هاي‌هرز و خصوصيات كمي و كيفي ذرت علوفه­اي ارزيابي شد. آزمايش به‌صورت اسپليت پلات و در قالب طرح بلوك كامل تصادفي در دو سال زراعي 95-1394 در مزرعه تحقيقاتي دانشكده كشاورزي دانشگاه فردوسي مشهد انجام شد. روش مديريت علف‌هاي‌هرز در سه سطح (كنترل تلفيقي (شيميايي +مكانيكي)، كنترل شيميايي و شاهد علف‌هاي‌هرز) به­ عنوان عامل كرت اصلي و منبع كود نيتروژن در پنج سطح (اوره، آمونيوم سولفات، كلسيم نيترات، آمونيوم نيترات فسفات و شاهد بدون كود) به ­عنوان عامل كرت فرعي در نظر گرفته شدند.كارايي كنترل تلفيقي نسبت به كنترل شيميايي در كاهش وزن خشك علف‌هاي‌ هرز، در سال اول و دوم به ترتيب حدود 68 و 57 درصد بيشتر بود كه اين كارايي بيشتر منجر به افزايش عملكرد نهايي علوفه خشك ذرت حدود 17 و 14 درصد شد.ضمن اينكه مصرف علف‌كش در كنترل تلفيقي نسبت به كنترل شيميايي، 25 درصد كاهش يافت. بااين‌ وجود كنترل شيميايي علف‌هاي‌ هرز نيز موجب كاهش 71 و 79 درصدي وزن خشك علف‌هاي‌ هرز نسبت به شاهد علف‌هاي‌ هرز به ترتيب در سال اول و دوم شد. ب ه‌طوركلي بيشترين عملكرد كمي و كيفي علوفه ذرت شامل (عملكرد ماده خشك، عملكرد پروتئين خام و عملكرد ماده خشك قابل‌هضم) با اعمال كنترل تلفيقي علف‌هاي‌ هرز به همراه مصرف كودهاي آمونيوم نيترات فسفات و آمونيوم سولفات حاصل شد.

Two important factors in producing forage maize (Zea mays L.) are weed control and nitrogen fertilizer management. Low maize yields are typically attributed to low corn growth rate at the beginning of the growing season, wide spacing of plant rows and rapid establishment of weeds. Weeds are a major challenge to row crops and research has usually emphasized on the integrated weed management using chemicals and mechanical control (Chauhan, 2013). In modern agriculture, weed control is primarily done with herbicides due to the effectiveness and ease of use. However, environmental concerns about pollution of groundwater and surface water, have led researchers to focus on integrated weed management and reduced herbicide consumption. On the other, selection of nitrogen fertilizer source may be an important component of weed management. Some studies have investigated nitrogen fertilizer management in order to integrated weed management. The present study was carried out to investigate the effect of chemical control and mechanical + chemical control of weeds and different sources of nitrogen fertilizer on weeds control and quantitative and qualitative characteristics of forage maize. Materials and Methods This experiment was conducted with a factorial arrangement based on randomized complete block design with three replications at the experimental station of Ferdowsi University of Mashhad during the growing season of 2015 -2016. The treatments were control methods of weeds including chemical control, integrated control (mechanical+chemical) and weedy control, and the sources of nitrogen fertilizers including urea (U), ammonium sulfate (AS), calcium nitrate (CN), ammonium nitrate phosphate (ANP) and no fertilizer (NF). In this study, Kjeldahl method was used to measure nitrogen content of the forage. Crude protein (CP) of forage maize was calculated using the following equation (1). Measurements of acid detergent fiber (ADF) and neutral detergent fiber (NDF) was done based on Van Soest method (1967). The equation (2), proposed by Oddy et al (1983) was used to determine digestible dry matter (DMD). Equation 1: 6.25 × N (%) = CP (%) Equation 2: DMD (%) =83.58 – 0.82 ×ADF(%) + 2.262 × N(%) Results and Discussion The integrated control of weeds reduced dry matter of weeds compared to chemical control by 68% and 57% in the first and second year of the experiment, respectively (50 days after corn planting), leading to increased dry matter yield of maize by 17% and 14%, respectively. Furthermore, in the integrated control, herbicide consumption decreased 25% compared to chemical control. However chemical control of weeds reduced dry matter of weed compared to weedy control by 71% and 79% in the first and second year, respectively. The greatest dry matter yield (DM-Y), dry matter digestible yield (DMD-Y) and crude protein yield (CP-Y) were observed with the integrated control and ANP or AS application (there were no significant differences between ANP and AS fertilizers), while the lowest DM-Y, DMD-Y and CP-Y were obtained with weedy control (there were no significant differences between fertilizers treatment). Conclusion In the integrated control with proper implementation to reduce weed dry matter, not only did increased quantitative and qualitative yield of forage but also herbicide consumption decreased 25% compared to chemical control. Reducing herbicide consumption through integrated weed management will preserve the environment, improve human health and increase product quality and quantity. On the other hand, it seems that (ANP and AS) as nitrogen fertilizer sources are more effective in terms of increasing maize production compared to other nitrogen sources. It can be suggested, using ANP fertilizer that contains both nitrogen forms (nitrate and ammonium) leads to increasing maize yield. Also, assimilation of ammonium requires the low energy and occurs faster than nitrate in plants. This energy savings may lead to greater dry weight production for plants with an ammonium diet. In addition, the sulfur in AS fertilizer as an essential element for plants may improved plant growth and metabolism