Non-limiting Water Research Articles

Evaluating the ability of four crop models to predict different environmental impacts on spring wheat grown in open-top chambers

We used the modeling package Expert-N to investigate the ability of four generic-mechanistic crop models that were originally developed under field conditions to simulate the plant growth of spring wheat grown in open-top chambers (OTC) under different environmental conditions. We focus on the impacts of water limitation and elevated atmospheric CO 2 concentration on biomass production. Expert-N facilitates the comparison of the components of agro-ecosystem models because it allows the exchange of single modules while leaving the rest of the model unchanged. The crop growth part of the models SPASS, CERES-Wheat, SUCROS and GECROS were combined with the Penman–Monteith equation for potential evapotranspiration, the HYDRUS-1D model for water transport and the LEACHN model for nitrogen transport and turnover simulation. The models were applied to a data set provided by OTC experiments with spring wheat ( Triticum aestivum L. cv. ‘Minaret’) that was grown under two atmospheric CO 2 concentrations (ambient/elevated), two irrigation schemes (non-limited water supply/water limitation) and two soil types (Cambisol/Chernosem) in two subsequent vegetation periods (1998/1999). Based on the model calibration using experimental and literature data, the best simulation results describing the impact of the considered environmental conditions were obtained using the SUCROS model followed by the SPASS, GECROS and CERES models. The study depicts the shortcomings of the underlying processes in all of the models. These shortcomings need to be addressed when models are applied on regional scales or for prediction under climate change conditions.

Endophyte infection of Festuca eskia enhances seedling survival to drought and cutting at the expense of clonal expansion

Symbiotic relationships between fungal endophytes and grass species are known to increase stress resistance in the grass host; however, there is little evidence to suggest that the positive effects occur early in the grass life cycle. In this study, we explored the effects of the endophyte Epichloë festucae on the growth and survival of Festuca eskia seedlings under drought and frequent cutting stress. Festuca eskia seedlings were collected from the western part of the plant repartition area in a non-symbiotic population located in a mesic and heavily grazed site (W-NS) and from the eastern part in a symbiotic population from a xeric and lightly grazed site (E-S). The E-S population was experimentally freed from its endophyte (E-F). Two greenhouse experiments were conducted to compare growth and survival between the three seedling types under drought stress and frequent cutting. In the first experiment, 126 seedlings per seedling type (n = 378) were grown for 6 weeks under non-limiting conditions before the cessation of watering. After 3 weeks without irrigation, full irrigation was restored for 10 days to measure the survival rate. Leaf length, leaf elongation rate and survival rate were assessed per population. In the second experiment, 156 seedlings per seedling type (n = 468) were grown under non-limiting conditions. All seedlings were cut to 3 cm high, twice a week, during the first month of growth. Leaf elongation and tillering were monitored on 52 seedlings per seedling type. For each type, seedling survival rate was determined by the number of plants alive after 10 days of regrowth, without cutting. The drought experiment revealed a phenotypic differentiation to drought in 30 F. eskia populations, suggesting adaptive differentiation: the eastern seedlings showed the highest survival rate. A trade-off between growth and survival was highlighted: the highest drought survival rate was associated with the lowest leaf elongation rate under non-limiting water conditions. Endophyte presence in the eastern population increased seedling drought survival. In contrast, cutting survival rate was similar between W-NS and E-S because the presence of the endophyte increased seedling survival to frequent cutting. However, this positive effect came with a cost: the endophyte reduced seedling tillering rate.

Exotic C4Grasses Have Increased Tolerance to Glyphosate under Elevated Carbon Dioxide

The increase in atmospheric CO2levels can influence the growth of many invasive exotic plant species. However, it is not well-documented, especially for C4plants, how these growth responses will alter the effectiveness of the world's most widely used herbicide for weed control, glyphosate. We aimed to address this question by carrying out a series of glasshouse experiments to determine if tolerance to glyphosate is increased in four C4invasive exotic grasses grown under elevated CO2in nonlimiting water conditions. In addition, traits including specific leaf area, leaf weight ratio, leaf area ratio, root : shoot ratio, total leaf area, and total biomass were measured in order to assess their contribution to glyphosate response under ambient and elevated CO2levels. Three of the four mature grass species that were treated with the recommended concentration of glyphosate displayed increased tolerance to glyphosate under elevated CO2. This was due to increased biomass production resulting in a dilution effect on the glyphosate within the plant. From this study, we can conclude that as atmospheric CO2levels increase, application rates of glyphosate might need to be increased to counteract the growth stimulation of invasive exotic plants.

Morpho-structural and physiological performance of Sangiovese and Montepulciano cvv. (Vitis vinifera) under non-limiting water supply conditions.

Morpho-structural and physiological traits of Sangiovese and Montepulciano varieties (Vitis vinifera L. - two red grapes widely cultivated in Italy), grown outside under non-limiting water supply conditions were evaluated in 2007 and 2008 and results were correlated with yield components and grape composition. The 2-year analysis showed intraspecific differences in canopy characteristics, leaf and shoot properties, photosynthetic ability, water use efficiency, vine yield and grape composition. Compared with Sangiovese, Montepulciano was able to assure a higher whole-canopy seasonal net CO2 exchange rate during the season (+38% in mid morning and +49% in mid afternoon). It also had higher water use efficiency (especially early in the morning and in late afternoon) and a higher vine yield (+16%). Furthermore, total soluble solids (+1.7 °Brix), anthocyanins (+0.44mgcm-2 berry skin) and phenolic compounds (+0.88mgcm-2 berry skin) were higher in the grapes. To ensure this performance, Montepulciano vines have to support higher costs of growth and maintenance processes, made possible because of the increased respiration activity of the canopy during the night. We confirmed that vine yield and grape composition is strictly dependent on the seasonal photosynthetic capacity of the canopy. Therefore, Montepulciano should be put in a position to fully realise this substantial photosynthetic potential, by avoiding or reducing environmental stress. Sangiovese is structurally and morpho-physiologically better able to withstand any stress during the summer than Montepulciano. Sangiovese xylem tissue had larger mean vessel density and smaller mean vessel diameter and hydraulic conductance than Montepulciano, holding the hypothesis of less susceptibility to conduit damage.

Chickpea genotypes contrasting for seed yield under terminal drought stress in the field differ for traits related to the control of water use.

Chickpea (Cicer arietinum L.) is often exposed to terminal drought, and deep, profuse rooting has been proposed as the main breeding target to improve terminal drought tolerance. This work tested whether plant water use at the vegetative stage and under non-limited water conditions could relate to the degree of sensitivity of chickpea to terminal drought. Transpiration response to a range of vapour pressure deficits under controlled and outdoor conditions was measured with canopy conductance using gravimetric measurements and thermal imagery in eight chickpea genotypes with comparable phenology and contrasting seed yield under terminal drought in the field. Additionally, the response of plant growth and transpiration to progressive soil moisture depletion was assayed in the same genotypes. Drought-tolerant genotypes had a lower canopy conductance under fully irrigated conditions at the vegetative stage; this trend was reversed at the early pod filling stage. While two sensitive genotypes had high early growth vigour and leaf development, there was a trend of lower growth in tolerant genotypes under progressive soil drying than in sensitive ones. Tolerant genotypes also exhibited a decline of transpiration in wetter soil compared to sensitive genotypes. Canopy conductance could be proxied by measuring leaf temperature with an infrared camera, although the relationship lost sensitivity at the pod filling stage. This work suggests that some traits contribute to water saving when water does not limit plant growth and development in drought-tolerant chickpea. It is hypothesised that this water would be available for the reproduction and grain filling stages.

Relationships of grain carbon isotope discrimination (Δ) and ash content with yield and quality in dry bean

SUMMARYDry bean (Phaseolus vulgarisL.) is a traditional crop of north-western Macedonia, Greece, where two landraces (plaki PrespasandChrisoupoli) in particular are grown. The aim of this study was to test whether the grain carbon isotope discrimination (Δ) and ash content (ASH) are related to grain yield (GY), protein content (PC) and mean grain weight (MGW) in dry bean. As a part of a honeycomb selection programme, 21 genotypes (19 lines derived via intra-landrace honeycomb selection for single plant yield at low density plus the two original populations) were grown at two densities, 1·2 and 4·8 plants/m2under non-limiting water conditions in a glasshouse and in the field. Genotypes differed significantly for Δ, ASH and PC under the low density. In the dense stand, genotypes differed significantly only for ASH and PC. The environment (glasshouse or field conditions) affected all the traits significantly. Neither Δ nor ASH showed strong or consistent relationships with GY and thus, they cannot serve as reliable, indirect selection criteria for GY. Strong, negative relationships between Δ and PC were found especially in the dense stand, confirming analogous results in C3cereals. Inconsistent genotypic ranking for grain physiological traits under the different densities and environments was indicative of large genotype×environment interaction. Genotypes performed consistently for GY and MGW under both densities, showing the strong stability of these traits.

Effects of irrigation strategies and soils on field grown potatoes: Yield and water productivity

Yield and water productivity of potatoes grown in 4.32 m2 lysimeters were measured in coarse sand, loamy sand, and sandy loam and imposed to full (FI), deficit (DI), and partial root-zone drying (PRD) irrigation strategies. PRD and DI as water-saving irrigation treatments received 65% of FI after tuber bulking and lasted for 6 weeks until final harvest. Analysis across the soil textures showed that fresh yields were not significant between the irrigation treatments. However, the same analysis across the irrigation treatments revealed that the effect of soil texture was significant on the fresh yield and loamy sand produced significantly higher fresh yield than the other two soils, probably because of higher leaf area index, higher photosynthesis rates, and “stay-green” effect late in the growing season. More analysis showed that there was a significant interaction between the irrigation treatments and soil textures that the highest fresh yield was obtained under FI in loamy sand. Furthermore, analysis across the soil textures showed that water productivities, WP (kg ha−1 fresh tuber yield mm−1 ET) were not significantly different between the irrigation treatments. However, across the irrigation treatments, the soil textures were significantly different. This showed that the interaction between irrigation treatments and soil textures was significant that the highest significant WP was obtained under DI in sandy loam. While PRD and DI treatments increased WP by, respectively, 11 and 5% in coarse sand and 28 and 36% in sandy loam relative to FI, they decreased WP in loamy sand by 15 and 13%. The reduced WP in loamy sand was due to nearly 28% fresh tuber yield loss in PRD and DI relative to FI even though ET was reduced by 9 and 11% in these irrigation treatments. This study showed that different soils will affect water-saving irrigation strategies that are worth knowing for suitable agricultural water management. So, under non-limited water resources conditions, loamy sand produces the highest yield under full irrigation but water-saving irrigations (PRD and DI) are not recommended due to considerable loss (28%) in yield. However, under restricted water resources, it is recommended to apply water-saving irrigations in sandy loam and coarse sand to achieve the highest water productivity.

Effects of rootstocks and irrigation levels on grape quality of Vitis vinifera L. cv. Shiraz.

The influence of two rootstocks (SO4 and 1103P) on grape quality and berry chemical composition was studied in a factorial experiment, in field grown grapevines of cv. Shiraz (Vitis vinifera L.), subjected to five irrigation levels [0% (T1), 25% (T2), 50% (T3), 75% (T4) and 100% (T5) of irrigation depth (IW, mm): Class A pan evaporimeter (CPE)]. Spectrophotometric analyses of total anthocyanins (TA), total phenolics (TP) and total antioxidant activity (AA) in grape extracts were performed. Also, total soluble solids (TSS), total acidity, pH, total sugar content, ash, juice yield and color index of red grapes (CIRG) of berry samples were determined. TA, TP, AA, TSS, total sugar content, ash, and CIRG values decreased together with increasing irrigation levels. On the contrary, T4 and T5 irrigation treatments increased total acidity, pH and juice yield of samples compared to the effects of T1, T2 and T3 irrigation treatments for both rootstocks. Moreover, T1 or T2 treatments caused an increase in TA, TP, AA, TSS, total sugar content, ash, and CIRG index values of grape samples in comparison to that of vines irrigated with T3, T4 and T5 levels. Grape quality response to irrigation levels was altered by rootstocks and quality of grapes harvested from vines grafted on SO4 was higher compared to those from 1103P under all irrigation treatments. Based on the findings, it was suggested that T2 irrigation level might be sufficient to guarantee Shiraz yield potential without significant loss in grape quality under the study conditions. Also, the results make it possible to recommend use of SO4 rootstock under non-limiting water conditions because of its positive on grape quality parameters, while 1103P might be better choice under water-limiting conditions.

Sap flow measurements reveal influence of temperature and stand structure on water use of Eucalyptus regnans forests

We examined water use by maturing Eucalyptus regnans, growing with or without an mid-storey stratum of Acacia spp. ( Acacia dealbata or A. melanoxylon), for >180 consecutive days. Study sites were located in the Upper Yarra catchment area in south-eastern Australia. Depending on their contribution to stand basal area, mid-storey Acacia spp. increased total stand water use by up to 30%. Monthly water use in such stands reached more than 640,000 L ha −1 (compared to 545,000 L ha −1 in stands where acacias were absent) in early spring. Water use was curvilinearly related to sapwood area of Acacia spp. and logistically related to sapwood area of E. regnans. Water use of all three species showed a strong relation to daily maximum air temperatures. Distinct and simple relationships provide clear guides to the likely impacts of climate change and forest management on water yield. We compared a traditional up-scaling approach, from individual tree water use to stand water use, to a new approach that incorporates variation in temperature. Development of this approach can lead to greater precision of stand water use estimates – and in turn catchment water yield – under current climate change scenarios, which predict a rise in air temperatures of 0.6–2.5 °C by 2050 for the study area. Our temperature-dependent approach suggests that under conditions of non-limiting water availability, stand water use will rise by 2% for every 0.25 °C increase in maximum air temperatures during winter, and possibly more than that during summer.

Constitutive water-conserving mechanisms are correlated with the terminal drought tolerance of pearl millet [Pennisetum glaucum (L.) R. Br.

Pearl millet, a key staple crop of the semi-arid tropics, is mostly grown in water-limited conditions, and improving its performance depends on how genotypes manage limited water resources. This study investigates whether the control of water loss under non-limiting water conditions is involved in the terminal drought tolerance of pearl millet. Two pairs of tolerant×sensitive pearl millet genotypes, PRLT 2/89-33–H77/833-2 and 863B-P2–ICMB 841-P3, and near-isogenic lines (NILs), introgressed with a terminal drought tolerance quantitative trait locus (QTL) from the donor parent PRLT 2/89-33 into H77/833-2 (NILs-QTL), were tested. Upon exposure to water deficit, transpiration began to decline at lower fractions of transpirable soil water (FTSW) in tolerant than in sensitive genotypes, and NILs-QTL followed the pattern of the tolerant parents. The transpiration rate (Tr, in g water loss cm−2 d−1) under well-watered conditions was lower in tolerant than in sensitive parental genotypes, and the Tr of NILs-QTL followed the pattern of the tolerant parents. In addition, Tr measured in detached leaves (g water loss cm−2 h−1) from field-grown plants of the parental lines showed lower Tr values in tolerant parents. Defoliation led to an increase in Tr that was higher in sensitive than in tolerant genotypes. The differences in Tr between genotypes was not related to the stomatal density. These results demonstrate that constitutive traits controlling leaf water loss under well-watered conditions correlate with the terminal drought tolerance of pearl millet. Such traits may lead to more water being available for grain filling under terminal drought.

Adaptation of the STICS intercrop model to simulate crop growth and N accumulation in pea–barley intercrops

Cereal–legume intercrops are gaining increasing interest in Europe. Modelling, by taking into account the complexity of species interactions, can be a very useful tool to study such systems and to test new strategies in various soil and climatic conditions. The present work describes the adaptation of an intercrop model for pea–barley intercrops through the extrapolation of the STICS sole crop model and its parameterisation from experimental data recorded on sole crops. Several improvements have been added to the existing crop model to allow an inversion of dominance in height between species during the crop cycle and a trophic link between crop growth rate and the potential for N 2 fixation. A 2-year dataset on pea and barley sole crops grown under non-limiting water conditions and with full crop protection was first used for calibration. The intercrop model was subsequently tested on experimental datasets of pea–barley intercrops grown under the same conditions as the sole crops. The intercrop experiments used to test the intercrop model differed in soil type, soil N supply and plant densities of each species. The development of the intercrop model through the extrapolation of the sole crop model and its parameterisation from experimental data recorded in sole crops allowed an accurate simulation of the interactions for nitrogen between intercropped species. The simulated crop growth, N accumulation and N 2 fixation in intercrops were in agreement with the observations from the experimental dataset. Moreover the behaviour of the model was consistent with the general knowledge about those intercropping systems. However the simulation of competition for light needs to be improved, especially the simulation of height growth. A thorough validation on many data sets, independent of those used for parameterisation, is still required. This model needs to be tested under a wider range of situations and for other limiting factors than nitrogen occurring in low-input farming systems.

Dry matter and area partitioning, radiation interception and radiation-use efficiency in open-field bell pepper

The objective of this study was to determine some key components of a model for bell pepper growth and yield under non-limiting water and nutrient conditions using data from field trials conducted in Southern Portugal. DM partitioning, at least before fruiting, and specific area indices for leaves, stems and fruits were conservative in relation to normalized thermal time. The interception model had a good performance. It was based on the exponential extinction of radiation on the area covered by the plants, the ellipsoidal leaf-angle distribution model ( X-parameter 2.48 and 2.89), and absorptivities of the leaves for PAR and NIR, 0.8 and 0.2, respectively. Radiation-use efficiency (RUE) was determined and presented in four different forms. RUE did not change substantially throughout the growing season. RUE of irrigated pepper crops grown in our experiments was around 1.6 g MJ −1 of intercepted PAR. The models and parameter values presented in this study may be useful to simulate the development and growth of field-grown pepper crop.

MODELLING THE EFFECTS OF FLOWERING, DROUGHT AND FRUIT LOAD ON MANGO LEAF PHOTOSYNTHESIS

Our general objective is to design carbon-based models of flowering and fruit quality. The first step of our procedure consisted in modelling carbon gains in mango, cv. Cogshall, using the biochemical model of C3 leaf photosynthesis of Farquhar et al. (1980). Data are presented about the temperature-response of the key parameters of photosynthetic capacity which was assessed in 17-month old mango plants. The temperature-corrected photosynthesis model was then coupled to the model of leaf diffusive conductance (gs) of Ball et al. (1987). Simulation results obtained over one year on recently matured leaves from 13 to 13-year old trees show that our model is apparently robust for leaves from vegetative shoots, in orchard conditions characterized by mild seasonal changes in temperature and non-limiting water supply. However, our model failed to simulate Anet accurately during the flowering period and periods of drought, as well as when the source-sink balance is modified as, for instance, in girdled branches at different fruit loads. Using results obtained over the 5 last years about the effects of flowering, fruiting and waterstress on photosynthesis in mango, we tested three modifications of our model: 1) the fixed parameters of the model of gs were replaced by adapted values for leaves from water-stressed trees and leaves close to inflorescences; 2) the total light-driven photosynthetic electron flux (JT) was corrected to account for the existence of electron fluxes towards alternative sinks in leaves close to inflorescences; and 3) JT was corrected to account for the inhibiting effect of starch accumulation in leaves from girdled branches. Simulation results are presented and discussed in the perspective of our modelling approach. (Resume d'auteur)

Interactive effects of elevated [CO2] and temperature on growth and development of a short- and long-season peanut cultivar

Temperature and CO2 are two of the main environmental factors associated with climate change. It is generally expected that elevated [CO2] will increase crop production. However, other environmental factors such as temperature along with management practices could further modify a crop’s response to CO2. The goal of this study was to determine the interactive effects of elevated [CO2] and above-optimum temperature on growth, development and yield of two peanut (Arachis hypogaea L.) cultivars, e.g., Pronto and Georgia Green. One of the objectives was to determine if there was any variation in response between these two cultivars with respect to possible adaptation to climate change. Peanut plants were grown in controlled environment chambers in the University of Georgia Envirotron under conditions of non-limiting water and nutrient supply. Plants were exposed to day/night air temperatures of 33/21°C (TA), 35.5/23.5°C (TA + 2.5°C), and 38/26°C (TA + 5°C) along with CO2 treatments of 400 and 700 μmol CO2 mol − 1 air. The selected range of temperatures was based on the temperatures that are common for southwest Georgia during the summer months. The results showed that LAI of both cultivars responded positively, e.g., 28.3% for Pronto and 49.3% for Georgia Green to elevated [CO2]. Overall, elevated [CO2] alone resulted in a significant increase in total biomass at final harvest across all temperatures (P < 0.0001), but decreased final seed yield (P < 0.0005), except for Georgia Green at (TA + 5°C). The higher temperatures compared to TA reduced the relative response of total biomass to CO2 for both cultivars. It can be concluded that final seed yield response to CO2 depends on the sensitivity of individual cultivars to temperature, especially during the reproductive development stage.

Rootstock effects on the adaptive strategies of grapevine ( Vitis vinifera L. cv. Cabernet–Sauvignon) under contrasting water status: Leaf physiological and structural responses

The effects of two rootstocks (1103P and SO4) on water status, gas exchange, leaf structural characteristics and vine growth were studied in a factorial experiment over 2 years (2005–2006), in field-grown grapevines of cv. Cabernet–Sauvignon ( Vitis vinifera L.), subjected to three irrigation levels (FI: 100% of evapotranspiration, DI: 50% of evapotranspiration and NI: not irrigated). The experiment was conducted on 10-year-old vines, grown under the semi-arid conditions of central Greece. There was a significant depressive effect in water status (estimated by midday stem water potential, Ψ s) and net assimilation rate ( A) of Cabernet–Sauvignon with decreasing water supply, on both rootstocks. The down regulation of A was mainly due to decreases in stomatal conductance ( g s). NI treatment showed significantly higher intrinsic water use efficiency ( A/ g s) and lower leaf carbon isotope discrimination ( Δ) compared to irrigated treatments. Leaf area index (LAI) and pruning weight (PW) were found to be higher under FI treatment but this effect was more pronounced on the 1103P-grafted vines. Canopy growth was strongly controlled by rootstock, being significantly higher on 1103P, presumably due to its higher capacity to access soil water. Rootstock genotype affected scion water status via its effect on whole-vine transpiration. Cabernet–Sauvignon photosynthesis response to water status was not altered by rootstock. The only apparent difference between rootstocks was the higher A of SO4-grafted vines under NI treatment, associated with higher Ψ s. A/ g s and Δ were only altered under FI treatment, with 1103P showing more efficient use of available soil water than SO4. Vines on SO4 had a lower specific leaf area (SLA) as a result of lower growth rate than 1103P, which possibly provided a supplemental mechanism to maintain leaf water status and gas exchange. Concluding, SO4 could be better adapted on fertile soils under non-limiting water supply due to its capacity to achieve a balanced vegetative and reproductive growth while 1103P, a more water efficient rootstock, would be better to grow in semi-arid regions where water limitation occurs.

Plant traits and functional types to characterise drought survival of pluri-specific perennial herbaceous swards in Mediterranean areas

Perennial grasslands provide numerous environmental benefits but their response to severe drought and therefore their sustainability in arid and Mediterranean areas have been little studied. Due to climate change, models of pasture production should be able to predict sward evolutions under increasing aridity. Our general goal was to identify plant traits and functional types that could be included in models aiming to analyse the dynamics of contrasting types of herbaceous plants grown in mixtures under drought. The two steps were: (1) to investigate the morpho-physiological traits associated with drought survival within a mixture of perennial herbaceous populations and to test whether the physiological traits measured under optimum conditions of growth in Spring may predict plant responses under subsequent summer drought and (2) to identify functional groups of populations exhibiting similar responses to the disturbance regime caused by severe drought. Seven different populations from five species were grown in monocultures (pots, long columns) and mixtures (containers, field). Standard leaf functional traits, aerial and root biomass were assessed under non-limiting water supply in Spring. In Summer, under continuous severe drought, leaf water status and plant survival were measured. Senescence of aerial tissues at the end of Spring, associated with endogenous summer dormancy, water status maintenance in basal tissues during the intense drought, and root biomass in the field were the variables best correlated with drought survival. The standard leaf functional traits specific leaf area (SLA) and leaf dry matter content (LDMC) measured in Spring under full irrigation, were uncorrelated with drought survival. These results suggested no general trade-off between growth potential and drought survival. Under conditions of optimal production in Spring, correlations were established between functional traits and variables associated with aerial biomass productivity which discriminated the group of forage cultivars from the other genotypes. Under summer drought, four main functional types of genotypes were defined according to their strategy of water use and therefore contrasting survival and persistence. This typology will be used to base further modelling study aiming to assess the effects of increasing aridity on the stability and productivity of herbaceous swards on the long term.

Measurement of summer dormancy in temperate perennial pasture grasses

The search to improve drought survival in temperate perennial grasses has led to a renewed interest in summer dormancy and how to quantify it. This endogenously controlled trait, found in some temperate perennial grasses, is associated with drought that normally occurs in summer. While cessation of leaf growth and senescence of herbage occurs in all grasses in response to drought, it is under summer irrigation that these same responses are observed only in summer-dormant germplasm and hence the trait can be identified in germplasm. Across the spectrum from completely summer-dormant to non-dormant, there is a range of expression. Our objective here is to highlight differences in characteristics of indices which measure summer dormancy and to identify aspects for incorporation into a superior index for use in measuring this trait. The experimental program comprised three field trials that compared 6 cultivars and a fourth that assessed a larger group of 12 cultivars of the same three species, cocksfoot (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb.), and phalaris (Phalaris aquatica L.). Seasonal herbage yield and foliage senescence were measured under three summer watering regimes: complete drought, mid-summer storm, and full irrigation at Mauguio, France. Different indices were calculated to compare against the approach which evaluates senescence under drought. The key outcomes are as follows. (1) The assessment of summer dormancy needs to be viewed as the plant response to a period of non-limiting water supply over summer. It makes little difference whether this is produced by full summer irrigation or a mid-summer simulated storm after a drought. Assessment of this trait under conditions of unbroken drought is discouraged because it can result in false scores. (2) The determination of summer dormancy intensity under full summer irrigation is most appropriate for the intensive study of the dynamics of dormancy expression over the entire summer. A simulated mid-summer storm within a drought gives an instantaneous view of dormancy intensity at a specific observation date and may be well adapted to the requirements of plant breeding. These methods are complementary. (3) Summer dormancy intensity can be assessed either by measuring herbage production or by a visual assessment of the level of herbage senescence. (4) An index of summer dormancy based on comparing irrigated summer herbage yield of any cultivar with that of a high, summer-yielding, non-dormant control cultivar was able to provide a reliable score of dormancy intensity. This index functions across a range of cultivars and species of perennial grasses. Further refinement of the index is needed to identify ‘standard’ high and low summer-dormant populations.

Long-term effects of organics, fertilizers and cropping systems on soil physical productivity evaluated using a single value index (NLWR)

Effect of different cropping systems, viz. maize–wheat (M–W), rice–wheat (R–W), soybean–wheat (S–W), and perennial grasses (guinea grass and setaria grass), in vogue since 6–32 years, and long-term use of chemical fertilizers (N, NP, NPK and NPK + lime) and organic materials (FYM, wheat straw, lantana biomass) on physical productivity of medium-textured (silt loam and silty clay loams) soils was investigated using non-limiting water range (NLWR) as the soil physical index. Higher the NLWR better is the soil physical condition for crop growth. The sources of N, P and K were urea, single superphosphate and muriate of potash, respectively. The NLWR was highest in S–W (16.8%), followed by grasses (14.4–15.6%) and M–W (13.1–15.4%), and lowest in R–W (7.5–11.0%). Under M–W system (32 years), NLWR was highest in NPK (13.1%), followed by NP (12.2%), NPK + lime (9.4%) and control (9.0%), and lowest in N (7.7%). Application of organics increased the NLWR in both M–W and R–W (6–18 years) systems; the NLWR values with and without organics were 18.0 and 17.1% in M–W, and 14.1–15.9 and 15.7–17.2% in R–W system. The NLWR was linearly, significantly and positively correlated with wheat grain yield ( r = 0.646**, −0.706**). The NLWR:PAWC (plant available water capacity) ratio (higher the ratio, better is the soil physical condition), which was 0.58 in control, decreased with N (0.49) but increased with NP (0.72) and NPK application (0.77); use of organics further improved the ratio. The NLWR:PAWC ratio was highest in S–W (0.97), followed by grasses (0.88–0.91), M–W (0.77–0.86) and R–W (0.54–0.68) system. Thus, long-term use of urea alone deteriorated, while NPK at recommended rates improved soil physical productivity over the control of no fertilizer application; the effect further improved when NPK were combined with organic sources. Among different cropping systems, the soil physical productivity followed the order: S–W > grasses > M–W > R–W system.

Scots pine root distribution derived from radial sap flow patterns in stems of large leaning trees

This study characterizes whole tree root system distribution in a non-destructive way based on its functional parameters, particularly the sap flow patterns in stems. This approach particularly considers sap flow variation across stems, both radial and circumferential patterns of flow that are usually used for a better integration of sap flow density at the whole tree level. We focused at: (1) Showing examples of sap flow variation across stems at a defined situation (high midday values at the period of non-limiting water supply; (2) Analyzing radial flow patterns in terms of root distribution; (3) Validating these results at the stand level (mean data of series of individual trees) using results of classical biometric methods used at the same site; and (4) Applying the results for evaluation of root distribution around leaning trees. Sap flow rate was measured by the heat deformation method on a set of 14 trees at an experimental pine forest stand in Brasschaat (Belgium) during the growing season of 2000. Sap flow variation across stems was measured at a total of 700 points. Amounts of water supplied by superficial (horizontally oriented) and sinker (vertically oriented) roots were estimated from sap flow patterns. The vertical distribution of absorbing roots as derived from the analysis of sap flow patterns in stem sapwood was very similar to the distribution determined by the classical biometric analysis of fine roots. Trees leaning to the East had stem radii at the stump level and crown radii enhanced in the leaning direction. Sinker roots showed higher absorption activities in the leaning direction, but superficial roots were more absorbing in the opposite direction. The application of the above-described method allows for a better evaluation of the whole-tree behavior and facilitates the evaluation of tree and stand properties in traditional forest stands, which are not equipped for detailed scientific research. This may also facilitate practical applications in landscape-level studies.

Effect of root depth penetration on soil nitrogen competitive interactions and dry matter production in pea–barley intercrops given different soil nitrogen supplies

Competition for soil resources plays a key role in the outcome of intercropping systems. In cereal–legume intercrops, competition for soil nitrogen during the vegetative phase greatly influences the final performance of the intercropped species. However, there is a lack of knowledge on the main factors involved in interspecific soil N competitive interactions between species. The dominance of cereals over legumes is often attributed to their faster growing rooting system. Nevertheless, using only field experimental approaches makes it difficult to isolate the effect of one factor because of the strong interactions between processes and the environment. Given the complexity of intercropping systems, dynamic simulation models can be especially helpful for testing hypotheses about the key factors driving competition between species. The present work was designed to investigate, under non-limiting water conditions, through an experimental and modelling approach, whether differences in root depth penetration among pea and barley grown together determined competition for soil N and dry matter accumulation (DM) by each species during the vegetative phase. This hypothesis was tested through several simulated scenarios generated using the STICS crop model. The model was first used to compare competition for soil N according to differences in root depth penetration rates between species. This rooting depth penetration effect was then studied at three levels of soil N supply leading to different degrees of N demand and N stress. A field experiment carried out in 2003 including pea–barley intercrops grown either with 130 kg N ha −1 or without any fertilizer was used to test the model. Experimental results of aboveground biomass, nitrogen accumulation, N 2 fixation and rooting depth monitored regularly during the crop cycle were compared to simulated results. The simulated responses of the intercrops were in agreement with the observations from the experimental dataset. Using the model, it is clear that faster root growth in barley gives it access to more soil nitrogen than pea during the vegetative phase. However, this advantage, which is limited to the vegetative phase, only affects the outcome of the intercrop when soil N supply is low. With higher soil N supplies, soil N sharing is not affected by the differences in rooting depth penetration between species. It appears that with higher N supplies, the differences in N demand between species have more influence on species dominance than differences in rooting depth.