برآورد محصول ذرت (Zea mays L.) و نيتروژن خاك از طريق اندازه‌گيري هدايت الكتريكي خاك تحت تأثير كودهاي آلي، شيميايي و بيولوژيك

Estimation of Corn Yield and Soil Nitrogen via Soil Electrical Conductivity Measurement Treated with Organic, Chemical and Biological Fertilizers

برآورد میزان عملكرد محصول و تخمین میزان نیتروژن خاك در طول فصل رشد، ازجمله عواملی است كه می‌تواند به مدیریت مزرعه كمك نماید. به‌منظور بررسی امكان برآورد عملكرد دانه ذرت از طریق اندازه‌گیری خصوصیات خاك و میزان نیتروژن خاك به روش ساده، آزمایشی در قالب طرح بلوك‌های كامل تصادفی با سه تكرار در طی سال زراعی 89-1388 در مزرعه تحقیقاتی دانشگاه فردوسی مشهد اجرا شد. تیمارها شامل 1- كود دامی (30 تن در هكتار)، 2- ورمی‌كمپوست (10 تن در هكتار)، 3- كود بیولوژیك نیتروكسین، 4-كود اوره (400 كیلوگرم در هكتار) و 5- شاهد (عدم مصرف كود) بود. نتایج نشان داد كه خاك‌های تحت تیمار ورمی‌كمپوست و كود دامی با اختلاف معنی‌داری نسبت به سایر تیمارها، درصد نیتروژن بالاتری داشتند. در طول فصل رشد، تنفس میكروبی در خاك‌های تحت تیمار كود بیولوژیك و سپس كود آلی دارای بیشترین مقدار بود. روند تغییرات نیتروژن و هدایت الكتریكی خاك عكس یكدیگر بودند و بررسی نتایج همبستگی خصوصیات خاك نشان داد كه می‌توان از طریق اندازه‌گیری هدایت الكتریكی خاك به‌وسیله یك ECمتر ساده، میزان نیتروژن خاك را در این منطقه تخمین زد. روند تغییرات pH و درصد نیتروژن خاك تا حد زیادی مشابه هم بودند و بین آن‌ها همبستگی معنی‌داری وجود داشت. همچنین بین هدایت الكتریكی خاك و عملكرد دانه (**72/0-r=) و بین pH خاك و عملكرد دانه (**74/0-r= ) همبستگی منفی و معنی‌دار وجود داشت. بنابراین می‌توان نتیجه گرفت كه با اندازه‌گیری هدایت الكتریكی خاك در این منطقه، می¬توان عملكرد دانه ذرت را برآورد كرد.

Introduction Around the world maize is the second crop with the most cultivated areas and amount of production, so as the most important strategic crop, have a special situation in policies, decision making, resources and inputs allocation. On the other side, negative environmental consequences of intensive consumption of agrochemicals resulted to change view concerning food production. One of the most important visions is sustainable production of enough food plus attention to social, economic and environmental aspects. Many researchers stated that the first step to achieve this goal is optimization and improvement of resources use efficiencies. According to little knowledge on relation between soil electrical conductivity and yield of maize, beside the environmental concerns about nitrogen consumption and need to replace chemical nitrogen by ecological inputs, this study designed and aimed to evaluate agroecological characteristics of corn and some soil characteristics as affected by application of organic and biological fertilizers under field conditions. Materials and Methods In order to probing the possibility of grain yield and soil nitrogen estimation via measurement of soil properties, a field experiment was conducted during growing season 2010 at Research Station, Ferdowsi University of Mashhad, Iran. A randomized complete block design (RCBD) with three replications was used. Treatments included: 1- manure (30 ton ha-1), 2-vermicompost (10 ton ha-1), 3- nitroxin (containing Azotobacter sp. and Azospirillum sp., inoculation was done according to Kennedy et al.), 4- nitrogen as urea (400 kg ha-1) and 5- control (without fertilizer). Studied traits were soil pH, soil EC, soil respiration rate, N content of soil and maize yield. Soil respiration rate was measured using equation 1: CO2= (V0- V)× N×22 Equation 1 In which V0 is the volume of consumed acid for control treatment titration, V is of the volume of consumed acid for sample treatment titration, N is acid normality. The microbial respiration (mgCO2/g(dry soil).day1 calculated by dividing the record CO2 volume to number of days that sample have been placed on container plus dry weight of soil sample. Results and Discussion Results showed that soils treated with vermicompost and manure had the highest level of nitrogen during the growing season. Higher microbial respiration was recorded in soils treated with biological fertilizer. Changes in soil nitrogen and electrical conductivity was against each other and correlation results showed that soil nitrogen could be estimated via measurement of soil electrical conductivity. Changes of pH and soil nitrogen were similar and there was a significant correlation between them. Eigenberg et al. (8) suggested that the pattern of changes of soil electrical conductivity is highly dependent on soil conditions; also soil water and nutrient content are of the most important factors in determining soil EC. There is a significant and negative correlation between soil electrical conductivity and grain yield and it seems that in this region grain yield of maize can be estimated via measurement of soil electrical conductivity. Conclusions In general, the results indicated that there was a strong and negative relation between EC and soil N content. Also, soil EC showed a negative correlation with maize yield which suggested that it is possible to estimate soil N and maize yield through soil EC measurement during of the growing season in the study area.