Quantifying yield gap of wheat in water and nitrogen limit conditions in Shirvan region: (Aqua crop & CERES-Wheat) and field experiment

Tavassoli, Abolfazl (2014) Quantifying yield gap of wheat in water and nitrogen limit conditions in Shirvan region: (Aqua crop & CERES-Wheat) and field experiment. Doctoral thesis, University of Zabol.

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This research is carried out for simulation of wheat yield in water and nitrogen limit conditions in Shirvan region, using models of Aqua crop & CERES Wheat. The goal of this research is to evaluate these two models for simulating different parameters of growth and development, by manner of comparison of simulated parameters with field results, and evaluation of model accuracy in predicting phonologic stages and crop yield; and quantifying effective factors in decrease of wheat potential yield (yield gap) in region. In order to obtain necessary data for calibrating and validating model, a field experiment was conducted as split plot using randomized complete block design with three replications in 2009-10 and 2010-11 on winter wheat (Sayonz cultivar). Irrigation treatments are composed of I1: optimum irrigation (field capacity (FC)), I2: 80% FC, I3: 60% FC and I4: no irrigation as the main plots. Nitrogen fertilizer was composed of N1: zero, N2: 100, N3: 175 and N4: 250 kg N/ha as the sub plots. The results obtained from simulation of phonological stages by CERES-Wheat model in experiments of the first year and the second year showed that normalized root means squares error (RMSEn) of flowering, milking seed and physiological ripening stages in both years is less than 10%, that indicates the model accuracy in simulation of phonological stages is very high. Although LAI development in both experiments was simulated well, but between observed LAI and simulated LAI there was a flagrant different. Seed yield RMSEn for the first year and the second year equals to 8.95% and 9.11%, respectively. Biomass RMSEn for the first year and the second year equals to 5.03% and 5.30%, respectively. These results show that seed yield and biomass was simulated well. The results of simulation by Aqua Crop model showed that the model has a good simulation in cover crop (CC), seed yield, biomass and water use efficiency (WUE), especially in treatment of optimum irrigation and consumption of complete nitrogen fertilizer. Comparison and evaluation of two models based on R2 and RMSEn indicators showed that CERES-Wheat model has simulated wheat yield (Sayonz cultivar) well and simulation accuracy of CERES-Wheat is better than Aqua Crop model in Shirvan region. The final goal of this research is to quantify yield gap of wheat in region. For reaching to the goal, a study was carried out as survey (in 20 farms selected in region) and field experiments. In this experiment, the most important reduced and limited factors of yield were water, nitrogen and management factors. The results of the first year of research showed that potential yield (yield simulated by model in optimum condition), attainable yield (yield obtained in field experiments in optimum condition of management) and actual yield (yield average obtained by region farmers) was equal to 11075, 6647 and 5025 kg/ha, respectively. Yield gap (potential yield – actual yield) created for wheat in region (Sayonz cultivar) about 5985 kg/ha, approximately. From this amount, water and nutrients as two limited factors has led to decrease 72.84% of potential yield. The thrice-reduced factor of yield was introduced as a management factor, so that this factor led to decreasing 27.16% of wheat yield. The results of the second year of experiment showed that potential yield, attainable yield and actual yield (yield average obtained by region farmers) equal to 10439, 6579 and 4960 kg/ha, respectively. Yield gap created for wheat in region about 5479 kg/ha, approximately. In addition, yield gap was estimated for a long time (2002-2011) in region. The simulation results showed that the potential yield is variable from 5973.34 to 8850.49 kg/ha. Wheat actual yield because of annual yield average was variable from 2511.09 kg/ha at 2002 to 4629.14 kg/ha at 2011 in Shirvan region. Yield gap average for a duration of 10 years showed that the gap between actual yield average (3524.15 kg/ha) and potential yield (7223.69) is high (near to 48.78%). Researchers stated that water, nitrogen, unsuitable sowing date, pests, diseases and weeds are of the most important factors created yield gap between actual yield and potential yield in region. Finally, we can conclude that with recognizing effective factors in yield gap, and optimizing them, wheat yield would increase exceedingly in region.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Wheat, CERES-Wheat, Aqua Crop, Potential yield, Actual yield, Yield gap
Subjects: S Agriculture > SB Plant culture
Depositing User: admin admin1 admin2
Date Deposited: 05 Apr 2016 09:20
Last Modified: 05 Apr 2016 09:20
URI: http://eprints.uoz.ac.ir/id/eprint/258

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