Simulation of the yield and biomass of quinoa under different agricultural management using the AquaCrop model

Quinoa (Chenopodium quinoa wild) is a dicotyledonous plant with about 95% purity. Quinoa is one-year, broad-leaved and has a height of one to two meters. This plant is native to South America, which is generally cultivated for its seeds, but its biomass is also popular as leafy vegetables. The seed of this plant is small in size and is a rich source of many vitamins and proteins. For this reason, its cultivation is expanding in Iran. For this reason, it is very important to know the effects of various factors such as planting method, planting time and cultivar used on its yield and biomass. Due to the high cost of field experiments, the AquaCrop model was used to simulate this crop plant in this research.

The current research was conducted in Khuzestan Agriculture and Natural Resources Research and Training Center located at 31° 20’ N latitude and 48° 40’ E longitude with a height of 18 meters above sea level during the years 2017-2018 and 2018-2019. The ten-year average rainfall leading to the time of the experiment is 240 mm and the average annual temperature is 25.3 degrees Celsius. The experimental treatments include planting dates at four times (T1: October 30, T2: November 10, T3: November 20, and T4: November 30), cultivation methods in two ways (R1: transplanting and R2: seed planting) and three cultivars (C1: Giza, C2: Q26 and C3: Titicaca). Tillage operation was done at the end of May for all treatments.

The sensitivity of the AquaCrop model to changes in base temperature, high temperature and initial canopy cover parameters was in the low category. Due to the low sensitivity of these parameters, the base and high temperature values remained as default. The initial canopy cover was also dependent on plant density, that's why its value was changed compared to the default state. The sensitivity of the AquaCrop model to changes in two parameters of normalized water productivity and the maximum crop coefficient for transpiration was in the high category. The sensitivity of other parameters was in the medium category and therefore these parameters were recalibrated. The average observed and simulated yield differences for T1, T2, T3 and T4 treatments were 198, 153, 97 and 97 kg.ha-1, respectively. The minimum difference between observed and simulated yield values was 93, 78, 62 and 66 kg.ha-1, respectively, and the maximum difference was 303, 210, 172 and 151 kg.ha-1 respectively. Therefore, the accuracy of the AquaCrop model was higher compared to the planting dates in the middle and end of November. The average difference between simulated and observed biomass for planting dates T1, T2, T3 and T4 was 870, 542, 533 and 635 kg.ha-1, respectively. The lowest difference for these treatments was 529, 401, 417 and 324 kg.ha-1 respectively and the highest difference was 1072, 871, 609 and 793 kg.ha-1 respectively. The average observed and simulated yield differences in the two cultivation methods R1 and R2 were 171 and 102 kg.ha-1, respectively. The lowest and the highest difference between the observed and simulated yield was 62 and 303 kg.ha-1 in the germination method and 66 and 194 kg.ha-1 in the direct method. Based on these results, the accuracy of the AquaCrop model in the direct method was about 40% higher than the seed planting. The average difference between the observed and simulated biomass in two germination and direct methods was 723 and 566 kg.ha-1, respectively. The minimum and maximum yield differences in the germination method were 567 and 979 kg.ha-1, respectively, and in the direct method, 324 and 1072 kg.ha-1. The average observed and simulated yield difference for this cultivar was 128, 158 and 123 kg.ha-1, respectively. The lowest observed and simulated yield differences for these three cultivars were 62, 96, and 67 kg.ha-1, respectively, and the highest yield differences were 303, 298, and 291 kg.ha-1, respectively. The average difference between observed and simulated biomass for three varieties of Giza, Q26 and Titicaca was 581, 662 and 691 kg.ha-1, respectively.

Based on all the results, the use of this plant model is suggested for simulating quinoa, although its error is less for direct cultivation in the middle and end of November than other conditions.