پایش عملکرد گندم و چغندرقند در استان خراسان: 2- برآورد خلاء عملکرد

در این تحقیق عملکرد پتانسیل و خلاء عملکرد گندم آبی و چغندرقند در استان خراسان رضوی طی دوره‌ای 10 ساله (1393-1384) مورد بررسی قرار گرفته است. به این منظور بر اساس داده‌های درازمدت هواشناسی 17 شهرستان و با استفاده از آنالیز خوشه‌ای سه ناحیه اقلیمی کشاورزی در استان خراسان رضوی از یکدیگر تفکیک شدند. پیش‌بینی عملکرد پتانسیل با استفاده از مدل شبیه‌سازی lintul1 انجام شد و پیش از استفاده از آن بر مبنای داده‌های عملکرد در معرض تعیین اعتبار متقابل قرار گرفت. بر اساس نتایج شبیه‌سازی، عملکرد پتانسیل (yp) گندم آبی در نواحی اقلیمی کشاورزی 1 (نیمه‌خشک و معتدل)، 2 (خشک و گرم) و 3 (نیمه‌خشک و گرم) به‌ترتیب 7248، 6478 و 7852 و درکل استان 6936 کیلوگرم در هکتار برآورد شد. در حدود 74 درصد از تغییرات سالانه yp گندم آبی ناشی از تغییر در طول دوره پر شدن دانه به دلیل افزایش درجه حرارت می‌باشد. خلاء عملکرد گندم آبی در هر سه ناحیه در طی 5 سال ابتدای دوره به‌طور نسبی افزایش یافته و به حدود 4 تن در هکتار رسید ولی از سال 1390 خلاء عملکرد در حال کاهش بوده به‌طوری‌که میزان خلاء قابل مهار آن در سال 93 بین 0.48-0.50 عملکرد پتانسیل بوده است. میانگین عملکرد پتانسیل گندم دیم در نواحی اقلیمی بین 2800-2000 کیلوگرم در هکتار برآورد شد و بر این اساس میانگین خلاء نسبی استان در محدوده 0.75-0.8 به‌دست آمد. میانگین 10 ساله عملکرد پتانسیل چغندرقند در نواحی اقلیمی استان خراسان رضوی بین 77-88 t ha-1 پیش‌بینی شد.

Yield Monitoring for Wheat and Sugar beet in Khorasan Province: 2 Estimation of Yield Gap

<p > <strong >Introduction: </strong >To realize global food demand by 2050 world cereal production should be increased up to 49% compared to 2006. This level of production could be achieved by annual yield increment of 1.16%. However, the current rates are much lower. At the same time, there is a very restricted area to increase cultivated lands because of resource limitation, provided that increase in crop yields is the main option to sustain food security. Potential yield (YP) could be achieved when limiting and reducing factors are completely absent during crop growth. YP is an indicator for the yielding capacity of a given environment and management system and estimating the difference between YP and actual yield, known as yield gap, is crucial for improvement of crop production systems at regional or national scale. In this study yield gap and its temporal trend for sugar beet, irrigated and rainfed wheat are estimated over Khorasan Razavi province based on the method developed by Global Yield Gap Atlas. </p >; <p > <strong >Materials and Methods: </strong >Following the protocol provided by Global Yield Gap Atlas, Khorasan province was clustered into agroclimatic zones using the proposed indices (cumulative degree days above 0 ºC, aridity index and temperature seasonality) based on 10 years (13841393) weather data. YP of sugar beet and irrigated wheat for the study period in the climatic regions was first estimated for selected cities within each region using LINTUL model and finally the simulation results were up scaled from cities to region and from regions to the whole province. The model was crossvalidated against measured data using leaveoneout (LOO) method to increase accuracy of predictions. Potential yield of rainfed wheat (YW) was estimated from frontier production function which was fitted to yield data over a wide range of annual precipitation. Yield gap (YG) of the studied crops was estimated as the difference between potential (YP) and actual yields (YA) for each region and over the 10year period. In addition exploitable gap (YG85%=85%YPYA) was also calculated. </p >; <p > <strong >Results and Discussion: </strong >The accuracy of LINTUL model for simulation of sugar beet and irrigated wheat yields was considerably increased after cross validation and the prediction error was reduced by 6.5 7.8%. Mean YP of irrigated wheat in the climatic region 1 (temperate, semidry), 2 (hot, dry) and 3 (temperate, dry) was respectively, 7248, 6478 and 7852 and for the whole province 6936 kg ha1. Time trend of YP for irrigated wheat was not significant in 3 climatic regions however, high annual variation of YP was found over the studied period. Results indicated that up to 74% of this variation was accounted for by changes in the effective grain filling period in response to temperature. YG85% of irrigated wheat in all climatic regions was increased up to 4 t ha <sup >1 </sup > during 13841388 but decreased later on so that relative gap was 0.480.50 of YP in 1993. Average YW of rainfed wheat in the climatic regions of the province was estimated as 20002800 kg ha <sup >1 </sup > with a negative trend due to decreased precipitation, the highest negative slope in YW (59 kg ha <sup >1 </sup > y <sup >1 </sup >) was found in the hot dry region. Rainfed wheat showed an extremely high yield gap in all climatic regions and mean relative yield gap (YG/YW) was estimated as 0.750.80 over the province. Mean YP of sugar beet in different climatic regions of the province was estimated from 78 to 88 t ha1 with the lowest potential in hotdry region. However, declining trend was found in the yield gap of sugar beet in all studied regions with the highest gap filling rate of 1.44 t ha <sup >1 </sup > y <sup >1 </sup > in temperatedry region. </p >; <p > <strong >Conclusions: </strong >Simulated YP of sugar beet and irrigated wheat were higher in temperatesemi arid regions of the province and lower in hotdry regions. However, coldsemi arid regions had the highest YW of rainfed wheat. When upscaled over the province, YG85% was about 50% of YP for irrigated wheat and sugar beet and 25% for rainfed wheat. It was concluded that closing yield gap of sugar beet and irrigated wheat would be possible mainly by improving management practices however, for rainfed wheat breeding strategies should be considered as the first priority. </p >