Non-irrigated Treatment Research Articles

Resource regulation of an invasive tree by a classical biological control agent

The invasive tree Melaleuca quinquenervia experienced substantial declines in growth and reproduction in response to chronic herbivory by the defoliating weevil Oxyops vitiosa. Plants subjected to unrestricted defoliation replaced leaves that were more suitable for feeding by the next generation, a process envisioned by the Resource Regulation Hypothesis which posits that attack by one generation increases the amount of the preferred host resources for the next, resulting in a positive feedback loop for the herbivore. The production of juvenile replacement leaves stimulated additional bouts of oviposition and feeding by O. vitiosa, which ultimately produced positive effects for the herbivore with negative consequences for the plant. The addition of water resources to the plant prolonged the positive feedback loop such that more than twice as many insects were produced on irrigated versus non-irrigated trees. In a more simple, reassembled food web on M. quinquenervia, the lack of biotic constraints like parasitoids may have prevented the earlier termination of the feedback loop and thus increased the impact of the biological control agent on the target. The overall effectiveness of this classical biological control program can be attributed, in part, to the phenomenon of the target plant’s induced susceptible response to a herbivore.

Long-term irrigation effects on Spanish holm oak growth and its black truffle symbiont

The Périgord black truffle is an exclusive culinary delicacy, but its Mediterranean harvests have declined, despite cultivation efforts since the 1970s. The role of long-term irrigation, symbiotic fungus-host interaction, and microbial belowground progression remain poorly understood, because generally too short experimental settings miss the necessary degree of real world complexity and reliable information from truffle orchards is limited. Here, we conduct the first dendrochronological and wood anatomical assessment of 295 holm oaks, which have been growing under different irrigation intensities in the world’s largest truffle orchard in Spain. The relationships between different climatic variables (monthly temperature means and precipitation totals) and dendro-parameters (ring width, vessel count and vessel size) of the oak hosts are utilized to disentangle direct and indirect drivers of truffle fruit body production. Irrigation at medium – instead of high – intensity is most beneficial for oak growth. Non-irrigated trees reveal overall lower stem increments. Warmer temperatures from February to April and wetter conditions from May to July enhance host vitality and possibly also its interplay with fungi symbionts via increased fine root production and mycorrhizal colonization. Adequately irrigated Mediterranean orchards may counteract some of the drought-induced natural truffle decline, and help stabilizing rural tourism, regional agriculture and global markets.

Variable-rate irrigation management using an expert system in the eastern coastal plain

Variable-rate irrigation (VRI) systems have the potential to conserve water by spatially allocating limited water resources. However, when compared to traditional irrigation systems, VRI systems require a higher level of management. In this 3-year study, we evaluated spatial irrigation management of a peanut crop grown under a VRI system using an expert system (Irrigator Pro). The irrigation management treatments evaluated were: (1) using Irrigator Pro (IP) to manage irrigation uniformly in plots with varying soils; (2) using Irrigator Pro to manage irrigation in plots based on the individual soils (IPS); (3) a treatment based on maintaining soil water potential (SWP) above −30 kPa (approximately 50 % depletion of available water) in the surface 30 cm of each soil within a plot; and (4) a non-irrigated treatment. Over the 3-year study, all irrigated treatments had significantly higher yields (4,230, 4,130, and 4,394 kg ha−1 for the IP, IPS, and SWP treatments, respectively) than the non-irrigated treatment (3,285 kg ha−1), yet the yields of the three irrigation treatments were not significantly different. Averaged over the 3-year experiment, the three treatments did not differ significantly in water usage. In the 2007 and 2009 growing seasons with below normal rainfall, the IP and IPS treatments required significantly greater total water than the SWP treatment. Overall, water use efficiency was significantly higher for the non-irrigated and SWP treatments (9.4 and 8.9 kg ha−1 per mm, respectively). The lower water use efficiency for the IP and IPS irrigation treatments (7.8 kg ha−1 per mm) was attributed to greater water applications mainly due to earlier growing season initiation of irrigation applications. However, the IP and IPS treatments maintained soil water potentials at the 30- and 60-cm depths at higher levels throughout most of the season. The two Irrigator Pro expert system treatments functioned as well as the SWP-based treatment. The Irrigator Pro expert system can be effectively used for site-specific management where management zone soils do not greatly differ. Further refinement of the expert system may be needed to improve its application in spatial irrigation applications.

Effects of different bud loads and irrigations applied at different leaf water potential levels on Kalecik Karası grape variety

Abstract: The effects of two irrigation practices (RDI-I and RDI-II) and two bud load treatments on the yield and quality of the Kalecik Karasi red wine grape variety were studied. The midday leaf water potential thresholds were used for irrigation timing, and those values were set as -10 bars until flowering, -13 bars between the berry set-veraison and the veraison-ripening periods, and -12 bars after harvest for both irrigation treatments. Water volumes applied in the irrigations of the RDI-I plots were 50% and 75% of the cumulative evaporation from a class A pan between the berry set-veraison and veraison-ripening growth stages, respectively, while those portions for the RDI-II treatment were vice versa. The effects of control (K) and two-fold increased bud loads (2K) based on mean pruning weight on the grape yield and quality were also investigated. Irrigation and higher bud load treatments considerably increased grape yield in both years of the study. The highest and lowest grape yields were obtained in the RDI-II and the nonirrigated treatments, respectively. The increase in grape yield of irrigated vines in relation to nonirrigated ones was 53.3% in the first year and 54.3% in the second year. With doubling the bud load, the achieved increases in grape yield were 37.8% and 45.1% compared to the traditional bud loads in the first and the second year, respectively. The bud load effect was more apparent for the irrigated vines compared to the rain-fed cultivation. Cluster weight was also higher for the irrigated vines. These increases can most probably be related to improved canopy development under irrigation application. The leaf stomatal conductance was higher as a consequence of the higher soil water contents in both irrigated treatments. The improved gas exchange due to the stomatal openings led to a higher leaf area index as well as an increase in grape yield of the irrigated plants. Our findings reveal that the grape yield of the Kalecik Karasi grape variety can be increased with irrigation and higher bud load applications. It is also worth noting that a limited irrigation application may help to maintain a better berry quality compared to the traditional rain-fed grape cultivation.

Effects of deficit irrigation on grain yield and ear characteristics of maize

In the Vojvodina region, drought is an important factor limiting grain yield in maize. The aims of this research were to compare irrigation scheduling in maize (cv. ZP SC 684), and to evaluate grain yield and ear characteristics. A 3-year field experiment was carried out in the Vojvodina region, a northern part of the Republic of Serbia (384 mm of rainfall in the maize-growing period). Maize was subjected to four irrigation levels (rainfed - I0 and supply at 80-85% - I1, 70-75% - I2 and 60-65% - I3 of field capacity). The results indicated a large yearly variability, mainly due to a rainfall event at the flowering, fertilization and grain filling stages. A significant irrigation effect was observed for all the variables under study, with significant differences between the three irrigation treatments. The grain yield ranged between 8.73 and 16.33 t ha-1. The highest grain yield of maize (average of 15.08 t ha-1) was in the I1 treatment, while the non-irrigated (I0) treatment had the lowest yield (average of 10.20 t ha-1), a 35% grain yield reduction. With the decrease of irrigation water, the grain yield of maize decreased. The most distinctive impact the irrigation had on maize yield was during the warm and very dry growth period of the year of 2008. Maize in the Vojvodina region can be cultivated with acceptable yields while saving irrigation water and maximizing resource-use efficiency.

The effects of bud load and regulated deficit irrigation on sugar, organic acid, phenolic compounds and antioxidant activity of Razakı table grape berries

This study aims at assessing the effects of increased bud load and irrigation applications on berry quality of the Razaki table grape. Two Regulated Deficit Irrigation (RDI) having different irrigation levels (RDI-I and RDI-II) based on the growth stages, in addition to a non-irrigated control treatment together with two different bud load practices (K-normal and 2K-two-fold buds of the normal) were examined for their effects on quality attributes such as sugar and organic acids contents, phenolic compounds as well as antioxidant capacity of the berries. The non-irrigated vines had highest sugar level (198.86 g/kg) in the first year (2013) of the experiment whilst the sugar content of the berries was increased with irrigation (RDI-II) in 2014. However the highest organic acid (7.10 g/kg) was recorded from the RDI-II treatment in 2013 whereas those of from non-irrigated vines were highest (7.81 g/kg) in 2014. Considering the sugar and organic acid content of the berries, bud load effects were not significant. The total phenolic acids were higher under non-irrigated and 2K bud load conditions. Antioxidant activity of berries was increased with RDI-I irrigation and 2K practices in the first year (2013) although no significant effect was recorded in the second year of the experiment. In all applications, glucose among the sugars, tartaric acid among the organic acids, catechin and epicatechin among the phenolic compounds were detected to be higher compared to other components in berries.

Respostas ecofisiológicas de cafeeiros submetidos ao deficit hídrico para concentração da florada no Cerrado de Minas Gerais

O objetivo deste trabalho foi avaliar o efeito de diferentes períodos de imposição do deficit hídrico sobre a concentração da florada do cafeeiro (Coffea arabica), bem como sobre as trocas gasosas, a produtividade, a maturação e a qualidade dos grãos. As cultivares Catuaí Vermelho IAC 144 e Bourbon Amarelo J9 foram avaliadas conforme os seguintes tratamentos: não irrigado (NI), irrigado continuamente (IC), e suspensão da irrigação em 1/7/2010 (D1) e em 1/8/2010 (D2), com retorno desta em 24/9/2010. Cerca de três dias após a retomada da irrigação, registrou-se a ocorrência de uma "chuva de florada", com precipitação de 69 mm. O potencial hídrico foliar de antemanhã (Ψam) nas cultivares Catuaí Vermelho IAC 144 e Bourbon Amarelo J9, em 22/9, foi de -0,59 e -0,82 MPa, -0,53 e -0,79 MPa, e -0,34 e -0,49 MPa, para os tratamentos NI, D1 e D2, respectivamente. O percentual máximo de botões florais no estádio E4, imediatamente antes da ocorrência da chuva, não foi afetado pelos níveis de deficit impostos durante o inverno, independentemente das cultivares. Os níveis moderados de deficit hídrico impostos pelos tratamentos (Ψam ~ -0,80 MPa) produziram pouco ou nenhum efeito sobre as trocas gasosas, a taxa de florescimento ou a uniformidade de maturação - percentagem de cerejas de 66% -, e a produtividade e a classificação dos grãos, de ambas as cultivares. O efeito dos diferentes tratamentos sobre o status hídrico dos botões florais não se sobrepõe ao efeito da chuva de florada, que foi determinante para sua abertura.

Effect of different irrigation strategies on vine physiology, yield, grape composition and sensory profiles of <em>Vitis vinifera</em> L. Cabernet-Sauvignon in a cool climate area

<p style="text-align: justify;"><strong>Aim</strong>: The efficacy of partial root zone drying (PRD) and regulated deficit irrigation (RDI) on vine physiology, yield components, fruit composition and wine sensory profiles of ‘Cabernet-Sauvignon’ was investigated in a cool climate region in Ontario, Canada.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Field experiments were conducted in a Cabernet-Sauvignon block in Niagara-on-the-Lake, ON Canada between 2006 and 2008. There were five treatments : non-irrigated control, PRD, full irrigation [100 % of crop evapotranspiration (ET<sub>c</sub>)] and two levels of RDI (50 and 25 % ET<sub>c</sub>). Treatments started immediately after fruit set and continued until post-veraison. Soil and vine water status were apparently controlled not only by the amount of water but also by the irrigation strategy used. In the PRD treatments, soil moisture, leaf water potential, and transpiration rate were generally lower than in 100 % ET<sub>c</sub> but higher than non-irrigated and RDI treatments. Almost all treatments were different than in non-irrigated vines in fruit composition and wine sensory attributes. Wine sensory attributes differed considerably due to the amount of irrigation water applied in 2007. RDI strategies were more consistent than the PRD treatments in their effect on vine water status, grape composition and wine sensory profiles. Inconsistent patterns across seasons for some variables indicated that besides soil and vine water status, there were other factors that impacted vine physiology, yield components and berry composition.</p><p style="text-align: justify;"><strong>Conclusions</strong>: RDI treatments improved wine quality when compared with full or either non-irrigated treatments. Overall, use of RDI irrigation or PRD during dry and warm years can improve grape composition in cool climates.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: To the best of our knowledge, this is the first evaluation of PRD and RDI on Cabernet-Sauvignon in a cool humid climate. It suggests that although RDI strategies are more effective, PRD also has value, particularly in dry seasons.</p>

Automated quantification of intra-annual density fluctuations using microdensity profiles of mature Pinus taeda in a replicated irrigation experiment

Key message We developed a new automated method to use wood microdensity profiles to detect and quantify intra-annual wood density fluctuations in earlywood of pine trees. Abstract We developed a new, automated method to use X-ray wood microdensity profiles to detect and quantify intra-annual density fluctuations within the earlywood region (IADFe) of each annual growth ring. The method quantifies the number and area of IADFe by detecting variations in wood density beyond the limits of ''normal'' values observed during periods without environmental stress. As a case study, we examined the effect of water availability and water stress associated with the formation of IADFe in irrigated and non-irrigated 11-year-old lob- lolly pine trees. As expected, non-irrigated trees formed significantly more IADFe than irrigated trees. Strong relationships were observed between IADFe formation (as a proportion of total earlywood area or as the number of IADFe formed each year) and the minimum monthly Pal- mer Drought Severity Index for the earlywood growing season (February to July). When compared against visual detection, the number of IADFe detected optically was significantly fewer than the number detected with densitometry. This difference likely comes from the higher resolution and more objective criteria that confidently detected and counted more very small IADFe than was possible optically at 109 magnification. The method to detect and quantify IADFe described in this study can allow climate analysis in long-lived species prone to pro- ducing intra-annual growth zones and false rings.

The Temporal Variation of Leaf Water Potential in Pistachio under Irrigated and Non-Irrigated Conditions

The present study was carried out in the experimental field of Pistachio Research Institute on pistachio trees which has uzun variety that was 30 years old. The aim of this research was to determine the Leaf Water Potential (LWP) of Pistacia vera L. under irrigated and non-irrigated conditions. In the study, the leaf water potential of pistachio was investigated under fully irrigated and non irrigated conditions. The leaf water potential values were measured one day before and after irrigation by using pressure chamber technique at the beginning, mid and end of irrigation season. According to the results obtained from measurements, the LWP value at the beginning of the irrigation season was -3.7 MPa at noon time due to relatively high temperature for both treatments. At the time of pre-dawn and sunset, this value increased and reached to -1.6 MPa due to relatively low temperature. In general, the LWP values during the mid of irrigation season, in the irrigated treatments, reached to almost -2.5 MPa in the non-irrigated treatment and the value was measured as -3.68 MPa.

Coffee productivity and root systems in cultivation schemes with different population arrangements and with and without drip irrigation

This study addressed the vegetative development, yield, and root development of coffee during cultivation in the absence and presence of drip irrigation and in different population arrangements over five years. A 6×2 factorial experimental scheme was used with a randomized block design and four replications. The six plantation densities were 1.60×0.50m; 1.60×0.75m; 1.60×1.00m; 3.20×0.50m; 3.20×0.75m; and 3.20×1.00m. These plantation densities were divided into irrigated and non-irrigated treatments. The analysis of variance of the interaction between planting density and irrigation revealed absence of synergism in changing the biometric parameters. However, the isolated analysis of the factors showed significant effects of plantation densities, with the arrangement of 1.60×0.50m getting the highest values of plant height and the smallest crown diameter, over the cycles. The adoption of irrigation caused significant effects on biometric parameters, with the irrigation of coffee causing increase in plant height, crown diameter and stalk diameter. The irrigated coffee in the four cycles resulted in a higher processed coffee production, especially when coffee was grown with small row spacing. The irrigated coffee obtained the average yield of 2623kgha−1, while the coffee without irrigation had an average yield of 1026kgha−1. The irrigated treatments had greater root concentrations as compared to the non-irrigated treatments. In addition, the root concentration was greater in the 0–0.5-m layer when smaller row spacing was used.

Yield and Fruit Quality Response of Drip-Irrigated Melon to the Duration of Irrigation Season

A field study was conducted in Ankara, a semi-arid region of Central Anatolia, Turkey. Yuva and Cantaloupe Sally F1 melon cultivars (Cucumis melo L.) were irrigated by drip method from transplanting to the beginning of the flowering (If), fruit set (Ifs), ripening (Ir), and harvest (Ih), and included a non-irrigated treatment (I0). Growth, yield, and fruit quality parameters in response to the duration of irrigation season were determined. The number of shoots and female flowers per plant, shoot length, and titratable acidity in Cantaloupe were lower than in Yuva, while similar total soluble solids content of fruit flesh was obtained in both cultivars. Irrigation application provided for an increase in the fruit number per plant, fruit size, fruit weight, and yield, and resulted in a decrease in total soluble solids and the ratings of sensory characteristics compared with non irrigated treatments in both cultivars, but these increases and decreases in the above parameters could not be correlated with the increase in the duration of the irrigation season, hence the amount of seasonal irrigation water. The highest yields were obtained in Ir treatment in Yuva and in Ir and Ih treatments in Cantaloupe. Continuing irrigation during fruit ripening furthered shoot growth in both cultivars, did not affect yield in Cantaloupe, and remarkably reduced yield in Yuva. Irrigation from the stage of transplanting until the beginning of fruit ripening was suggested as well for both cultivars with regard to considerably high yield and high fruit quality. In this irrigation program, irrigation water amounts of 388.3-441.4 mm were applied, seasonal evapotranspiration of 499.0-587.1 mm was found, and a yield per plant of 6105-6206 g in Yuva and 7533-7878 g in Cantaloupe was obtained.

Impact of fertilisation and the fluctuation of precipitation on the ecophysical and production characteristics of maize

The aim of this study was to analyse the problems caused by the unfavourable (dry and wet) weather and its consequences in the R1 growth stage of maize (Zeamays L.), as well as their management and the alternatives of preventing yield reduction by using agrotechnical measures fertilisation, irrigation), also, we wanted to examine whether the Chl content measured in the R1 growth phase provides reliable prediction of yield per hectare.
 The examinations were carried out in a moderately warm and dry production area at the Látókép Experiment Site of the University of Debrecen, Centre for Agricultural Sciences on calcareous chernozem soil in 2007 and 2008. Six different N doses (0,30,60,90,120,150 kg ha-1) were used in the irrigated and non-irrigated treatments of the field experiment.
 The results showed that there is a significant strong positive correlation between Chl content and yield both in the non-irrigated (P<0.001, R=0.777) and the irrigated (P<0.001, R=0.801) treatment. The results of the correlation analyses performed yearly showed that weather factors significantly influence the strength of correlations, but these correlations are always positive.
 The Chl content of maize leaves provided a reliable prediction of yield per hectare in the R1 growth stage. In the irrigated treatment, the correlation is always closer than in the non-irrigated treatment.

Proanthocyanidin accumulation and biosynthesis are modulated by the irrigation regime in tempranillo seeds.

The main effects of three different irrigation regimes, i.e., sustained deficit irrigation (SDI), regulated deficit irrigation (RDI) and non-irrigated (NI), on seed traits namely proanthocyanidins (PAs) were evaluated in the wine grape cultivar Aragonez (syn. Tempranillo) grown in Alentejo (Portugal) over two growing seasons. Results showed that while the number of seeds per berry was not affected by water availability, seed fresh weight differed among treatments, the NI treatment exhibiting the lowest values. The biosynthetic pathway of flavanols appeared to be modified by the irrigation treatment, and several genes responsible for PA synthesis were up-regulated in the most stressed seeds (RDI and NI). However, this effect had no impact on PA content, suggesting the influence of other factors such as oxidation and/or degradation of PAs at late stages of maturation in grape seeds. The seeds’ non-enzymatic antioxidant capacities (oxygen radical absorbance capacity (ORAC) and hydroxyl radical adverting capacity (HORAC)) were modulated by water deficit and correlated well with PA content. The impact of irrigation strategy on PA biosynthesis, content, and anti-radical activity during seed ripening is discussed in the context of increasing interest in the role of PAs in the color and taste of wine, and the potential health benefits relating to their antioxidant capacity.

Effect of Center-Pivot Irrigation in the Rust and Brown Eye Spot of Coffee

Incidence of rust (caused by Hemileia vastatrix) and brown eye spot (caused by Cercospora coffeicola) of coffee was evaluated for 2 years in southern Minas Gerais, Brazil, in a center-pivot-irrigated coffee crop with different water application levels. Treatments consisted of six water levels of 0 (nonirrigated), 60, 80, 100, 120, and 140% applied according to class A evaporation pan (CAE). Progress of disease was influenced significantly by different water levels; the highest incidence of rust occurred with lower water levels-0 (nonirrigated), 60, and 80% CAE-whereas the lowest incidence was detected with larger water levels: 120 and 140% CAE. There was one peak of rust incidence in August. The highest incidence of brown eye spot occurred with water levels of 100 and 140% CAE and the lowest incidence was found in the nonirrigated treatment. Two incidence peaks occurred in March and June. This study identified that irrigation methods and water levels can decisively affect the epidemiological behavior of diseases and, therefore, their management.

The effects of subsurface irrigation at different soil water potential thresholds on the growth and transpiration of Populus tomentosa in the North China Plain

SummaryIn order to find the optimal subsurface drip irrigation (SDI) scheduling for mature triploid Populus tomentosa plantations in the North China Plain, a field experiment was conducted in 2010 and 2011 to investigate the effects of SDI at different soil water potential (SWP) thresholds on the growth and transpiration of a P. tomentosa plantation when it was six and seven years old. The experiment included three SWP treatments, which initiated irrigation when the SWP at 20 cm depth and 10 cm distance from a drip emitter reached −25 (T25), −50 (T50) and −75 (T75) kPa, respectively. A control non-irrigation treatment (CK) was also included. Long-term SWP, soil water content (SWC), transpiration, tree growth, meteorological factors and groundwater level were monitored. Results showed that SDI influenced the SWC only in 0–80 cm of soil. From April to July, on average, the cumulative stand-level transpiration on a ground area basis (E) and growth of basal area at breast height accounted for 81% and 93% of their corresponding whole-season values, while the cumulative reference crop potential evapotranspiration (ET0) was 43% higher than the rainfall. In contrast, from August to October, the growth rate of P. tomentosa was very slow, while the cumulative rainfall was 36% higher than ET0 and the average groundwater level was relatively high (125 cm). Relative to CK, the E under the SWP treatments was significantly (P < 0.05) increased by 20–73%. Decreasing the SWP irrigation threshold from −25 to −50 kPa significantly reduced E by 31% (P < 0.05), but decreasing the threshold from −50 to −75 kPa did not further reduce P. tomentosa E. Relative to CK, T25, T50 and T75 increased the annual above-ground dry biomass (ADB) increment by 54% (P < 0.05), 34% (P < 0.05) and 24% (P > 0.05) in 2010, and by 28% (P > 0.05), 29% (P > 0.05) and 32% (P < 0.05) in 2011, respectively. However, no significant difference in ADB increment was detected among the SWP treatments. Based on these results, it can be concluded that when planting P. tomentosa at sites with similar characteristics to ours in the North China Plain: (1) SDI could be promoted in the cultivation of P. tomentosa to improve tree growth; (2) a range of −50 to −75 kPa at a depth of 20 cm and 10 cm distant from a drip emitter is recommended as the irrigation threshold for scheduling SDI in P. tomentosa plantations and (3) irrigation should be applied between April and July, while drainage should be implemented between August and October.

Usefulness of stem dendrometers as continuous indicator of loquat trees water status

Postharvest regulated deficit irrigation (RDI) is an effective strategy to hasten flowering and harvest in loquat (Eriobotrya japonica Lindl.) trees, which in the Mediterranean countries has been related to an increase in the economic return. The success of an RDI strategy, however, depends on the duration and severity of the water stress reached by the trees. When RDI is applied, then, it is important to regularly monitor the plant water status. The measurement of the trunk diameter variations by means of stem dendrometers, which can be automated to remotely determine the plant water status, is a proven method for many fruit trees. In loquat, however, its use has not been yet assessed. In this experiment performed in a loquat orchard planted with the cv. ‘Cardona’ during the summer of 2009, the suitability of using stem dendrometers to detect plant water stress was assessed by taking measurements in fully irrigated and trees subjected to a drought cycle of 47 days. Results showed that at the beginning of the drought cycle period there was an increase in the maximum daily trunk shrinkage (MDS) in non-irrigated trees even before that clear differences in stem water potential (Ψs) could be detected between treatments. However, when plant water stress became more severe (Ψs lower than −1.4MPa), MDS did not increase further. The maximum trunk diameter (MXTD) evolution in control trees showed a steadily increase in trunk growth during the whole experimental period. In non-irrigated trees, however, MXTD remained stable until the end of the treatment when irrigation was resumed. The Ψs was the most sensitive indicator to water stress due to its very low tree-to-tree variability in comparison with the other indicators. Overall results show that trunk diameter variations have some limitations to monitor plant water status in loquat RDI orchards and therefore new alternatives should be explored.

Effect of root pruning and irrigation regimes on pear tree: growth, yield and yield components

The effect of root pruning (RP) as compared with non-root pruning (NP) and the potential of supplemental irrigation in alleviating the negative effect of root pruning on fruit growth, yield and yield components were investigated in a pear orchard from 2010 to 2011. Results showed that the total shoot length and the number of shoots per tree decreased by 72% and 43%, respectively, in the RP compared to the NP trees; however lateral root growth was stimulated by the RP treatment in the upper soil layers (30&amp;ndash;40 cm). Full irrigation and deficit irrigation treatments stabilized the return bloom and improved fruit yield and size compared with the non-irrigated treatment without stimulating vegetative growth. Conclusively, the results indicate that root pruning is an effective practice controlling excessive shoot growth, and supplemental irrigation can improve fruit yield and quality in the root pruned trees. Therefore, a combination of root pruning and irrigation could be a promising alternative to control tree size and secure a stable fruit yield in pear orchards. &amp;nbsp;

Photosynthetic response of European beech to atmospheric and soil drought

Abstract Physiological response of European beech under soil and atmospheric drought conditions was investigated in this study. A group of six beech trees was irrigated during the growing season 2012, while the second group of non-irrigated (control) beech trees was treated under natural soil drought. During the experiment, we observed more than 45-day long period when no precipitation fell on the soil surface. The relationship of PN (CO2 assimilation rate) to gS (stomatal conductance) was very tight in both groups, which indicates that stomatal opening was the main factor limiting PN. The statistically significant differences in gS between the groups of trees were revealed only on the last measuring day. The significant differences in PN were confirmed on the days when the differences in soil water potential (ΨS) appeared. On these measurement days, the PN values of irrigated individuals were approximately 1.9 or 3.3 times greater than the values of non-irrigated individuals. At the level of primary photosynthetic processes (chlorophyll fluorescence parameters) we did not observe lower values of the control individuals in comparison with the irrigated trees in any of the evaluated parameters. Long-term soil water deficit caused strong decrease of leaf water potential (ΨL) in the control trees, but ΨL values of the irrigated trees were also rather low due to diurnal dynamics in higher parts of crown. Close relationship between ΨL and gS was confirmed for the control (non-irrigated) trees, but could not be confirmed for the irrigated trees. We revealed significant influence of VPD (vapour pressure deficit of the air) on gS only in the control group. On the days when ΨS decreased, the stomata of the non-irrigated trees were closed in spite of the low VPD values. Almost complete stomatal closure in both groups of trees was caused by the increase of VPD to 1.2 kPa.

How does soil water potential limit the seasonal dynamics of sap flow and circumference changes in European beech?

Abstract We focus on the analysis of sap flow and stem circumference changes in European beech (Fagus sylvatica, L.) in relation to available soil water and weather conditions during the growing seasons 2012 and 2013. The objective was to examine how soil water potential affects growth and transpiration of a mature beech stand situated at the lower distributional limit of beech in Slovakia. To be able to evaluate beech response to soil water shortage, we irrigated a group of 6 trees during the period of pronounced drought, while the control group of other 6 trees remained exposed to actual weather conditions. Mean air temperatures of both seasons were considerably above the long-term average and the temporal pattern of precipitation differed between the years. During the whole growing season 2012, beech samples transpired an average volume of 6.9 m3 of water in the control and 7.7 m3 in the irrigated group. A slightly higher average volume was found in the growing season 2013 under both treatments (7.7 m3 in control and 10.5 m3 in irrigated trees). In the drought period 2012, when the irrigation experiment was commenced, the sap flow in the control group was reduced by 30% as compared with the irrigated group. In 2013, a 38.1% difference in sap flow was observed between the groups. Sap flow in the non-irrigated trees decreased with reducing soil moisture, and ceased at soil water potential -0.6 MPa. In both treatments and years, we found significant correlations between hourly sap flow and investigated weather variables. A reduction in stem circumferences of the control trees, which was observed during stem shrinkage phase, was up to 19% in 2012 and 10% in 2013. We conclude that stem circumference shrinkage during the peak of soil drought was induced by the cessation in the sap flow process.