Abstract :
[en] Thinopyrum intermedium (Host) Barkworth & D.R. Dewey is a C3 grass currently proposed as a dual-use perennial cereal, producing both forage and grains for human consumption. Its integration into agricultural systems offers various environmental benefits such as the soil protection or the regulation of the water quality, thanks to its permanent soil cover and its extented belowground activity. The species is in the nascent stages of domestication and its grain yield potential is still low compared to annual counterparts. Forage valorization could be a way of generating additional agricultural production. In order to optimize yields, a good description of its functional traits as well as a better understanding of its resource allocation strategies are essential. Within the experimental farm of the faculty of Uliège - Gembloux AgroBio- Tech, Th. intermedium was tested in field from 2017 to 2023 under two different valorizations : dual-use for grain and forage and simple use for forage production. To develop an adapted agronomic management to this new species, multiple practices were conducted (i.e., N fertilization, establishment conditions, association with legumes or mowing regimes). The species was also grown in a growth chamber during its first days of development and compared with winter wheat (Triticum aestivum). Th. intermedium showed some environmental benefits compared with annual cereals, which may be associated with a significant investment in its long-lived organs such as its root system and stem bases. Relatively high amounts of biomass were produced with little N, as evidenced by its critical N dilution curve. In addition, low N export at the end of the growing season was observed (i.e., on average 60 kg of N ha−1). The plant also showed some resource conservation traits, with a higher root tissue density
and a preferential investment in root construction in the establishment phase. This latter
trait may explain its relatively lower growth rate compared with annual cereals such as winter wheat. Finally, its cespiteous form, producing closely spaced ramets, induces a slow and radial spread. This development strategy may provide to the species a good tolerance to stressful conditions and an efficient use of local resources (i.e., monopolization strategy). However, its slow establishment phase requires new solutions to limit competition from desired or undesired plants within the field. A certain compromise between vegetative growth, implying sufficient investment in long-lived organs, and grain production was observed. In fact, excessive biomass production and tiller density at the beginning of the growing season had a negative impact on the yield per spike. Although grain production is currently low (i.e., with a mean of 1 t ha−1), a major finding was that it remained constant over four years of cultivation, which was never observed in other studies.Within our pedoclimatic conditions (relatively favourable to its crop development), this grain yield was explained by stable tiller and spike fertility. The optimal time for tiller initiation has yet to be determined, but it should be early. Relatively dense sowing in late summer maximized tiller fertility. In regrowing years, overproduction of tillers and spikes should be avoided by a shredding of the post-harvest crop residues at ground level and a defoliation in autumn. This can also prevent light obstruction at the stem bases. Finally, an autumn fertilization of 50 kg of N ha−1 combined with an early spring fertilization of 50 kg of N ha−1 were effective in supporting tiller fertility while limiting the risk of excessive biomass. The species was not suited to intensive forage management. In fact, the initiation of regrowth was weak when the apical meristems were cut during the stem elongation phase. Forage management seemed only relevant in a context of a dual grain-forage valorization. Spring and autumn mowing were characterized by low forage yields (i.e., maximum of 2 t of DM ha−1), but with a good forage quality close to that of a fresh grass. Crop residue harvested at the time of grain maturity was characterized by good forage yields (i.e., 5 to 15 t of DM ha−1), but with a low forage quality, close to that of straws. In the context of a dual valorization, spring mowing should be avoided, as it reduced grain yield, while autumn regrowth was generally too weak to justify a mowing. The association with a forage legume could therefore be interesting in order to increase production during the autumn period. Integrating perennial cereals into agroecosystems therefore requires a rethinking of management strategies, and genetic selection remains crucial to achieve that goal. The latter should help to create new cultivars adapted to the different production contexts of farmers interested in establishing this new type of crop.
