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Often perennial pastures have to tolerate soil water restriction during summer, which can affect the relative abundance of the most desired species. In the south of Chile, Bromus valdivianus and Lolium perenne are preferred species. The competitiveness of B. valdivianus and L. perenne was evaluated when sown in pots in a glasshouse as monocultures or a mix (50/50 %) with restricted water availability. The water restriction treatments were as follows: 80-85 % field capacity (FC), 45-50 % FC and 20-25 % FC, maintained for 1196 growing degree days. For both species, dry matter (DM) accumulated per plant and per pot decreased similarly with increasing water restriction, but at tiller level, resource allocation differed, for B. valdivianus root growth was accentuated over aerial development, but this was less so for L. perenne. The foliage mass per tiller for B. valdivianus decreased relatively more than that for L. perenne with increasing water restriction. As monocultures, B. valdivianus produced larger tillers than L. perenne, such that B. valdivianus tillers had 2.2 times greater lamina mass, 3.6 times more leaf area and 2.5 times greater root mass than those of L. perenne. However, L. perenne produced a larger number of smaller tillers that enabled foliage, root and total mass at plant level, to be similar to that of B. valdivianus. Within the mixed pasture, L. perenne tiller density increased compared with when grown as a monoculture, but not for B. valdivianus. The results of the study suggested that L. perenne and B. valdivianus have differences in growth strategies that allow them to survive under environmental stress and competition. Competitiveness increased for L. perenne aboveground without water restriction and that for B. valdivianus increased belowground as water restriction was increased.

Restricting plant available water in the soil can negatively affect pasture growth. Lolium perenne L. (Lp) and Bromus valdivianus Phil. (Bv) are important components of the permanent pastures in southern Chile. The aim of this study was to investigate the growth response of Lp and Bv when subjected to soil water restriction, contrasting soil structure conditions and growing as a single species pasture or in a mixture. The treatments were two soil physical conditions (undisturbed (US) and disturbed soil (DS)), two soil water restriction levels (optimum PAW and very-dry PAW), and three pastures (Bv, Lp and Bv+Lp). The US provided more water to plants regardless of the soil water restriction, and Bv and Lp presented more development (highest accumulated herbage mass) in US than in DS, under a similar soil water restriction. The soil structure and soil water restriction did not modify the tiller number of Bv, although Lp showed different tiller numbers under each condition, soil structure and soil water restriction. The conservation of the soil structure (undisturbed soil) has an important role in pasture productivity by providing a continuous pore system, which certainly improved the water accessibility for the growing species.

Short persistence of renovated pastures is a major problem for pastoral production systems. Pasture species establishment, species performance and persistency and their relationships with soil–water attributes following pasture improvement methods were evaluated over two years. Fertilised naturalised pasture (FNP), non‐fertilised naturalised pasture (NFNP), Lolium perenne–Trifolium repens cultivated pasture (CP), L. perenne–T. repens direct‐drilled pasture (DP), and Bromus valdivianus, Holcus lanatus, Dactylis glomerata, L. perenne and T. repens direct‐drilled pasture (DDP) were established as a randomised complete block design. Pastures were limed, fertilised and sheep‐grazed. Plant growth compensatory mechanisms, by decreasing tiller number and increasing tiller size, equalised pasture yield during the establishment. In both years, the improved pastures yield was greater than that of NFNP. In the second year, DDP and FNP reached the higher pasture growth rate, with a seasonality diminishment. During the second summer, soil matrix potential at 0–20 cm soil profile exceeded the permanent wilting point, resulting in the pasture growth rate of NFNP and the sown pastures ranging from 0.0 to 3.6 kg DM/ha per day, while for FNP, it was 17.8 kg DM/ha per day. Sown species, fast‐growing species spontaneous colonisation and growth were all stimulated in the improved pastures over species that tolerate stress, improving agronomical and ecological pasture features.

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