Viticulture adaptation to global warming: Modelling gas exchange, water status and leaf temperature to probe for practices manipulating water supply, canopy reflectance and radiation load

Associated with climate change, the frequency, duration, and intensity of heatwaves are increasing in most of the key wine regions worldwide. Depending on timing, intensity, and duration, heatwaves can impact grapevine yield and berry composition, with implications for wine quality. To overcome these negative effects, two types of mitigation practices have been proposed (i) to enhance transpiration and (ii) to reduce the radiation load on the canopy. Here we use a biophysical model to quantify the impact of these practices on canopy gas exchange, vine water status, and leaf temperature (Tl). Model validation was performed in a commercial vineyard. Modelled Tl from 14 to 43 °C, and transpiration, from 0.1 to 5.4 mm d−1, aligned around the identity line with measurements in field-grown vines; the RMSD was 2.6 ºC for temperature and 0.96 mm day−1 for transpiration. Trellis system and row orientation modulate Tl. A sprawling single wire trellis with an EW orientation maintained the canopy around 1ºC cooler than a Vertical Shoot Positioned canopy with NS for the same range of total fraction of soil available water (TFAW). Although irrigation before a heatwave is a recommended practice, maximum transpiration can be sustained even when TFAW is reduced, limiting the heat dampening effect of irrigation. Alternatively, canopy cooling can be achieved through Kaolin application, the installation of shade cloth placement, or canopy trimming. Shade cloth produced a greater cooling than Kaolin in all the simulated scenarios; however, Tl differences between them varied. Trimming reduced Tl from 2 ºC to almost 8 ºC compared to its non-trimmed counterpart. Our analysis presents new insights to design heat wave mitigation strategies and supports agronomically meaningful definitions of heat waves that include not only temperature, but also wind, VPD, and radiation load as these factors influence crop physiology under heat stress.info:eu-repo/semantics/publishedVersio

Modelling the nitrogen-driven trade-off between nitrogen utilisation efficiency and water use efficiency of wheat in eastern Australia.

The nitrogen-driven trade-off between nitrogen utilisation efficiency (yield per unit nitrogen uptake) and water use efficiency (yield per unit evapotranspiration) is widespread and results from well established, multiple effects of nitrogen availability on the water, carbon and nitrogen economy of crops. Here we used a crop model (APSIM) to simulate the yield, evapotranspiration, soil evaporation and nitrogen uptake of wheat, and analysed yield responses to water, nitrogen and climate using a framework analogous to the rate-duration model of determinate growth. The relationship between modelled grain yield (Y) and evapotranspiration (ET) was fitted to a linear-plateau function to derive three parameters: maximum yield (Ymax), the ET break-point when yield reaches its maximum (ET#), and the rate of yield response in the linear phase ([Delta]Y/[Delta]ET). Against this framework, we tested the hypothesis that nitrogen deficit reduces maximum yield by reducing both the rate ([Delta]Y/[Delta]ET) and the range of yield response to evapotranspiration, i.e. ET# - Es, where Es is modelled median soil evaporation. Modelled data reproduced the nitrogen-driven trade-off between nitrogen utilisation efficiency and water use efficiency in a transect from Horsham (36°S) to Emerald (23°S) in eastern Australia. Increasing nitrogen supply from 50 to 250 kg N ha-1 reduced yield per unit nitrogen uptake from 29 to 12 kg grain kg-1 N and increased yield per unit evapotranspiration from 6 to 15 kg grain ha-1 mm-1 at Emerald. The same increment in nitrogen supply reduced yield per unit nitrogen uptake from 30 to 25 kg grain kg-1 N and increased yield per unit evapotranspiration from 6 to 25 kg grain ha-1 mm-1 at Horsham. Maximum yield ranged from 0.9 to 6.4 t ha-1. Consistent with our working hypothesis, reductions in maximum yield with nitrogen deficit were associated with both reduction in the rate of yield response to ET and compression of the range of yield response to ET. Against the notion of managing crops to maximise water use efficiency in low rainfall environments, we emphasise the trade-off between water use efficiency and nitrogen utilisation efficiency, particularly under conditions of high nitrogen-to-grain price ratio. The rate-range framework to characterise the relationship between yield and evapotranspiration is useful to capture this trade-off as the parameters were responsive to both nitrogen supply and climatic factors

Soil-water thresholds for the responses of leaf expansion and gas exchange: A review

Typical responses of leaf expansion and gas exchange rate to plant available soil water (PAW) can be described with two straight lines that intersect at PAWt, i.e., the PAW threshold for which the rate of the process in stressed plants starts to diverge from a reference value. PAWt is a parameter widely used in modelling plant responses to water deficits. It also reflects some apparent physiological mechanism because plants appear to be able to sense soil water status or related variable(s). In this paper comparisons are made between PAWt for various species (monocots and dicots) and plant processes (leaf expansion and gas exchange) in order to: (i) point out methodological sources of variation in published values of PAWt; and (ii) analyse variations in PAWt in relation to plant and environmental factors. Reported values of PAWt vary over almost the whole possible range of PAW (i.e., 0 to 1). Average thresholds reflect the greater responsiveness to water deficits of tissue expansion (average PAWt = 0.56) relative to gas exchange (0.40). Average PAWt for leaf water potential (0.61) and stomatal conductance (0.37) are very close to the average thresholds for expansion and gas exchange, respectively. Soil water thresholds for leaf expansion are also shown to discriminate between plant types (0.50 for monocots vs. 0.66 for dicots) and soils (0.72 for coarse- vs. 0.43 for fine-textured soils). The simplicity of characterising plant responses to water stress in terms of PAWt is attractive. In agreement with known physiological relationships, however, our analysis highlights how, for given processes and species, the measured value of PAWt can be affected by evaporative demand, root distribution, soil texture and soil bulk density, among other factors, thus making explicit some of the assumptions underlying the use of fixed soil-water thresholds in simulation models

Defining upper limits of nitrogen uptake and nitrogen use efficiency of potato in response to crop N supply

Sound nitrogen management seeks to ensure crop yield, quality and profit, while avoiding over-fertilization lead to excess reactive nitrogen entering the agro- ecosystem or under-fertilization leading to mining of soil organic matter. Here we advance a framework to compare crop nitrogen use efficiency (NUE) across genotypes, environments and management practices that accounts for the non-linearity between N supply and N uptake, and between N uptake and crop dry matter or yield. We used published data of potato dry matter production, yield, N uptake and N inputs to demonstrate the efficacy of simple frontier analysis to describe the upper limits of the first order components of nitrogen use efficiency. Using quantile regression, frontier curves were derived for the response of apparent nitrogen recovery to the rate of applied N and for the responses of crop dry matter and tuber yield (dry matter) to crop N uptake. The analysis captured the known higher NUE for tuber production of late relative to early maturing potato varieties. The maximum achievable apparent nitrogen recovery did not differ between N fertilization methods. Simple frontier analysis provides a practical approach to benchmark the nitrogen use efficiency of crops. This then allows valid comparison of treatments or commercial crops when there are differences in the amount of N applied or differences in crop dry matter accumulation

Intraspecific competition in oat varieties selected for grain yield and milling

Intraspecific competition in oat varieties selected for grain yield and milling Oats likely emerged as part of the weedy grass assemblage in early wheat and barley crops. Some Avena species, such as A. fatua and A. sterilis, evolved into aggressive weeds, and the high interspecific competitive ability of cultivated oats (A. sativa) is valued agronomically to facilitate weed control in rotations. We tested the hypothesis, verified in many crops, that high yield of oats is related to low intraspecific competitive ability. Ten contemporary oat varieties, selected for grain yield and milling attributes, where grown in three environments. Response to competition was calculated as 100 × (Yb – Yc)/Yc, where Y is yield measured in border (b) and centre (c) rows. The same definition was used to calculate response to competition of yield components (biomass, harvest index, grain number, grain weight) and the components of grain number (panicle number and grains per panicle). Yield response to competition was affected by all three sources of variation, i.e. environment, variety and variety × environment interaction. The interaction demonstrates the plasticity of yield response to intraspecific competition; for example, the response to competition of variety Mortlock varied from 9% to 71% among environments. This plasticity in yield response to competition was partially related to variety-dependent responses to competition for biomass and harvest index, number of panicles and number of grains per panicle. We did not find the expected negative association between yield and variety-dependent response to competition. We discuss how this lack of correlation could relate to sampling issues, i.e. a limitation in the range of environments and varieties explored in this study, or reflect a legitimate feature of oat crops arising from early and contemporary selective pressures.Victor O. Sadras, M. Mahadevan, and Pamela K. Zwe

Special issue on water management in grapevines

Ortega-Farias, S (reprint author), Univ Talca, Ctr Irrigat & Agroclimatol CITRA, Fac Agr Sci Res & Extens, Ave Lircay S-N, Talca, Chile.Editorial Material. Population growth, economic development, environmental demands, and climate change converge into a scenario of water scarcity worldwide (Fereres and Gonzalez-Dugo 2009). Water supply may therefore constraint grape production for quality wine. In this context, deficit irrigation (DI) strategies to stabilize yield and maintain or improve wine quality are critical