We studied cultivar and drought effects on the water relations of a large set of cultivars of bread wheat (Triticum aestivum L.), durum wheat (T. turgidum), triticale (X Tritosecale Wittmack) and barley (Hordeum vulgare L.), grown in field plots in north-western Mexico in the presence and absence of simulated late drought. Leaf water potential (Ψ) and osmotic potential (π), and leaf permeability (LP) to viscous air flow were measured between 1000 and 1600 hours on many dates; leaf turgor potential (p) was calculated. Drought caused associated reductions in Ψ, π and LP. Cultivar effects on these variables were usually significant on given dates, and reasonably consistent between dates and drought intensities in the case of Ψ, but less so for π and LP. There were consistent positive phenotypic correlations between Ψ and LP, and Ψ and anthesis date, and a negative correlation between Ψ and stature in the absence of drought. The relationship of LP to Ψ for different cultivars differed significantly: in particular, tall bread wheats had lower LP than dwarf cultivars at high values of Ψ, whereas at low Ψ they had higher LP than the dwarf cultivars. There was general osmotic adjustment, and a tendency for the relationship of p to Ψ to vary between cultivars. Irrespective of statistical significance, the effects of cultivar were generally small relative to those of drought intensity.

Plant water potential and leaf diffusive conductance, key features of plant responses to water stress in field experiments, can be estimated, respectively, by xylem pressure potential measured with the pressure chamber apparatus, and leaf permeability measured with the air flow porometer. This paper describes modifications to these two techniques in order to increase the rapidity of measurements in wheat to 60/h with the pressure chamber, and 200/h with the porometer. Rapid measurements are needed because of the large within-and between-plot errors encountered with daytime measurements in typical field experiments, examples of which are presented.

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The nutrient use efficiency of perennial ryegrass (Lolium perenne L.) (PR) and white clover (Trifolium repens L.) (WC) cultivars can affect the grass-legume compatibility of different cultivar combinations, thus impacting the sustainability of animal production systems, especially on marginal soils. The objective of this work was to evaluate N, P, and K absorption efficiency (NAE, PAE, and KAE) and use efficiency (NUE, PUE, and KUE). This study included two experiments with the same full factorial treatment structure (4 PR cultivars × 3 WC cultivars) in a randomized complete block design under field conditions and a completely randomized pot design. The field cutting experiment was carried out on sites with two contrasting soil depths and the pot experiment was conducted under shade conditions. Results showed nonsignificant (P > 0.05) factor interactions for DM yield and both nutrient absorption and use efficiency. The NAE and PAE of PR 'Extreme' and 'Bealey' were higher under field conditions than pot conditions. In the field experiment, NAE of WC 'Will' (2.33 kg DM ha -1 /mg N kg -1 ) tended to be similar (P < 0.05) to other cultivars in deep soil, but was significantly higher (P < 0.001) than 'Ladino' and 'Bounty' in shallow soil (0.70 kg DM ha -1 /mg kg -1 ). The evaluation of NUE and PUE under field conditions and KUE under pot conditions showed that PR 'Bealey' and WC 'Ladino' reached higher values. In conclusion, results showed a cultivar effect on nutrient use efficiency in PR/WC mixtures, which had an impact on PR-WC compatibility, mainly due to the higher absorption efficiency of PR 'Bealey' and WC 'Will', both of which exhibited the highest degree of compatibility for total DM yield.

The effect of soil environment on cultivars compatibility was evaluated in a cutting field experiment during two growing seasons. A factorial combination of four perennial ryegrass (Lolium perenne L.; PR) and three white clover (Trifolium repens L.; WC) cultivars were grown on deep (DSS) and shallow (SSS) soils under irrigated conditions. Measurements included herbage accumulation (HA), root attributes, leaf chlorophyll content, and interception of photosynthetic radiation. The PR–WC compatibility was affected by soil environment. In both soil sites and growing seasons, the WC + PR herbage accumulations were similar but with different PR and WC partial accumulation. In DSS, the partial PR HA was 22% less than that observed in SSS; the partial WC HA was almost twice in DSS relative to SSS. In SSS, the WC stolon growing point numbers, stolon length, and stolon biomass increased 60, 88, and 94% relative to DSS, respectively. In the same way, the mixed sward increased root biomass and root length density, which was considered as a mechanism for improving plant resources capture from the soil. At cultivar level, the PR–WC compatibility was affected mainly by WC cultivar, and the effect of PR cultivar was fairly weak. The medium‐leaved WC cultivar ‘Will’ showed the greatest compatibility with PR, particularly with cultivar ‘Bealey’. These results are valuable when designing new management strategies for mixed sward production in marginal environments. Modern cultivars of PR have capacity for adapting to marginal environments; however, it is necessary to improve the competitive ability of WC to capture soil resources under marginal soil conditions.