The effect of nitrogen fertilizer management and heat stress during quinoa anthesis

Background and objectives:
Chenopodium quinoa is a facultative halophyte plant which has been considered for cultivation in saline soils. Although most studies of the nutritional requirement of quinoa focus on nitrogen consumption management. Since the plant is considered for organic production in Peru and Bolivia and is also grown after crops such as potatoes, fertilizer is not recommended and the plant uses the fertilizer residues of the previous crop (19). Under these conditions, the optimal use of fertilizers, especially nitrogen fertilizers, to prevent lodging, mechanized harvesting and increase yield is very important. Climate conditions have a major impact on quinoa performance. The most important stress on the central plateau, in addition to salinity, is heat stress during the pollination and grain filling period, which causes a sharp decrease in yield (21). The purpose of this experiment is to optimize nitrogen fertilizer management in changing environmental conditions.

Materials and methods:
In order to determine quinoa fertilizer requirements under normal and heat stress during pollination period the experimental was conducted based on complete randomized block design in three replications, it was performed in Sadough Research Station of Yazd. Treatment consisted of nine treatments with different amounts of nitrogen (50, 100, 150 and 200 kg of urea ha-1) and splitting (two splitting at planting and early floral initiation and three splitting at planting, early floral initiation and flowering) plus a control treatment with three replications. Quinoa cultivation of Titicaca was carried out on September 1, 2017 and August 7, 2018. Applied irrigation water salinity after sowing was 8 dS/m and after emergence 14 dS/m saline water applied every two weeks. After harvesting, yield and yield components and nitrogen percentage of grain were measured. The efficiency of nitrogen consumption, partial efficiency, recycling of nitrogen consumption and the growing degree day for each growth stage were calculated. Data analysis was performed for each year separately due to the significance of the Bartlett test with SAS v9.1 software.
Results:
The results showed that the level of application of fertilizer treatment had a significant effect on yield and biomass production. In the first year, the maximum grain yield obtained at 200 kg ha-1 with seed yield of 2 t ha-1. At lower level of fertilizer application, the adsorption efficiency and the amount of nitrogen recycled were higher, and the treatments of the three splitting were better than the two. At higher levels of fertilizer, the effect of splitting was less than lower levels of fertilizer. The amount of harvested available nitrogen in the control treatment was 2.8 and at 200 kg ha-1 was 6.3 g m-2. The highest recycling efficiency was observed in 50 kg treatment with 3 splitting. The percentage of seed nitrogen in the control was significantly lower than the fertilizer treatments and there was no significant difference between the fertilizer treatments, which shows the plant's ability to remobilize nitrogen to seeds and maintain protein percentage in low-input systems under saline condition. In the second year with heat stress during the anthesis period, grain yield and nitrogen yield decreased by 62% and 59%, respectively. The effect of thermal stress during the quinoa pollination period reduced the efficiency of fertilizer use and severely reduced yield, but did not affect the percentage of grain nitrogen and the thousand kernel weight.
Conclusion:
The fertilizer requirement, the efficiency of fertilizer application and the recovery of quinoa seed nitrogen changed under different climatic conditions, although the percentage of nitrogen accumulated in the grain did not change significantly, so to achieve the desired result, fertilizer management would be altered in different climatic and soil conditions.