Learning about the growing habits and reproductive strategy of Thinopyrum intermedium through the establishment of its critical nitrogen dilution curve

Abstract

The perennial grain crop Thinopyrum intermedium can provide various ecosystem services and a dual production of grains and forage. Yet, to improve crop management, better knowledges of its physiological behavior and growing habits are required. The goal of this study was to characterize Th. intermedium nitrogen (N) requirements through the evaluation of its response to N fertilization and the subsequent determination of its critical nitrogen dilution curve (CNDC). A field experiment was implemented in Belgium during three growing seasons with various N fertilization schemes. Biomass of the different organs and their N contents were measured at specific phenological stages. To estimate the CNDC, a Bayesian hierarchical model was applied on the assembled dataset. The validity of the curve was assessed on an independent dataset including contrasted N situations. Globally, N fertilization had a positive impact on the dry matter (DM) of leaves, stems and ears (p-value<0.05). The aboveground biomass and N uptake were found maximum with fertilization comprised between 100 and 150 kg N/ha applied over the entire growing year. At grain harvest, total DM ranged from 7.0 to 16.4 t DM/ha for a fertilization strategy of 100 kg N/ha, depending upon the growing season. The N amount of the aboveground biomass was found to decrease during the second phase of the growing cycle. As observed with the proposed CNDC, the aerial N content tended to decrease with the evolution of growing stages and biomass accumulation. Through the low a-coefficient determined for the CNDC, it was confirmed that the crop had reduced need in terms of N nutrition. The reduced N requirements can be linked to the high N use efficiency and a potential resource-conservative strategy of the crop. This, combined with the observed decrease of the N uptake by the aboveground biomass during the second phase of growth, can be related to the long-term survival strategy of the crop. The latter requires substantial investments in perennial belowground structures coupled with reduced resource allocations to seeds. Our study has highlighted that Th. intermedium is able to reach a high shoot DM production with low N needs. Our proposed CNDC will be highly helpful to help define N requirements in various pedo-climatic environments and adjust accordingly the soil-crop management, among which the N fertilization. Ultimately, the low N requirements of Th. intermedium coupled with a high N use efficiency demonstrated that it could enhance agronomic and environmental benefits.