Response of sweet orange cv ‘Lane late’ to deficit irrigation in two rootstocks. I: water relations,leaf gas exchange and vegetative growth

The influence of a deficit-irrigation (DI) strategy on soil–plant water relations and gas exchange activity was analysed during a 3-year period in mature ‘Lane late’ (Citrus sinensis (L.) Osb.) citrus trees grafted on two different rootstocks, ‘Cleopatra’ mandarin (Citrus reshni Hort. ex Tanaka ) and ‘Carrizo’ citrange (C. sinensis L., Osbeck × Poncirus trifoliata L.). Two treatments were applied for each rootstock: a control treatment, irrigated at 100% ETc (crop evapotranspiration) during the entire season, and a DI treatment, irrigated at 100% ETc, except during Phase I (cell division) and Phase III (ripening and harvest) of fruit growth, when complete irrigation cut-off was applied. Under soil water deficit, the seasonal variations of soil water content suggested that ‘Cleopatra’ mandarin had a better root efficiency for soil water extraction than ‘Carrizo’ citrange. Moreover, in all years, trees on ‘Cleopatra’ reached a lower water-stress level (midday xylem water potential values (Ψ_md) > −2 MPa), maintaining a better plant water status during the water-stress periods than trees on ‘Carrizo’ (Ψ_md < −2 MPa). Similarly, net CO₂ assimilation rate (A) was higher in trees on ‘Cleopatra’ during the water-stress periods. In addition, the better plant water status in trees on ‘Cleopatra’ under DI conditions stimulated a greater vegetative growth compared to trees on ‘Carrizo’. From a physiological point of view, ‘Cleopatra’ mandarin was more tolerant of severe water stress (applied in Phases I and III of fruit growth) than ‘Carrizo’ citrange.     

Responses of “Chardonnay” to deficit irrigation applied at different phenological stages: vine growth, must composition, and wine quality

Adoption of water-saving irrigation strategies is necessary especially for grapevine that has the highest acreage of any fruit crop in the world. We applied deficit irrigation to Chardonnay wine grape at the following phenological stages: anthesis to fruit set, fruit set to veraison, and veraison to harvest. Four irrigation levels (0, 25, 50, and 100?% of crop evapotranspiration, ET _c ) were applied in 2009. Vines grown in large containers were used to enable imposition of water stress early in the growing season. The following parameters were measured: midday leaf water potential, vine growth, yield, and quality of must and wine. The same parameters were measured in 2010 although all vines were fully irrigated. The 0 and 25?% treatments caused defoliation and had negative impacts on yield and wine quality in both 2009 and 2010. Chardonnay was most sensitive to water stress in post-veraison in terms of productivity and wine quality.     

Response of sweet orange cv ‘Lane late’ to deficit-irrigation strategy in two rootstocks. II: Flowering, fruit growth, yield and fruit quality

We evaluated the effects of a deficit-irrigation (DI) strategy in mature ‘Lane late’ sweet orange (Citrus sinensis (L.) Osb.) trees grafted on two different drought-tolerant rootstocks, ‘Cleopatra’ mandarin (Citrus reshni Hort. ex Tanaka) and ‘Carrizo’ citrange (Citrus sinensis (L.) Osbeck x Poncirus trifoliata L.). Two treatments were applied: a control treatment, irrigated at 100% of crop evapotranspiration (ETc) during the entire season, and a DI treatment, irrigated at 100% ETc, except during phases I (initial fruit-growth period,) and phase III (final fruit-growth period, ripening, harvest), when no irrigation was applied. Flowering, fruit abscission and fruit growth of trees on ‘Carrizo’ were more affected by DI than on ‘Cleopatra’. Deficit irrigation reduced yield in both rootstocks due mainly to a decrease in the number of fruits. The phase most sensitive to drought stress was phase I. Moreover, DI altered fruit quality depending on the period when drought stress was applied. Fruit quality was modified by DI: total soluble sugars and titratable acidity increased when a severe drought stress occurred only in phase III but only increased the peel/pulp ratio if it occurred only in phase I. The quality of fruits from trees on ‘Carrizo’ under DI was affected more than that of fruits from trees on ‘Cleopatra’. Under DI in semi-arid regions ‘Cleopatra’ mandarin can mitigate more the negative effects of drought stress on yield and fruit quality than ‘Carrizo’ citrange.     

The effects of crop load and irrigation rate in the oil accumulation stage on oil yield and water relations of ‘Koroneiki’ olives

The interactions between irrigation rates applied during the oil accumulation stage and crop load were studied in a six-year-old very-high-density Koroneiki (Olea europaea L.) orchard. Five irrigation rates, determined as thresholds of midday stem water potential, were applied from July 1st until harvest in 2008 and 2009 and from July 1st to the end of September in 2010. Oil yield increased with increasing crop load in all the irrigation treatments. Oil yield did not respond to increasing irrigation at very low crop load and the higher the crop load the higher the response to irrigation. There was no response to irrigation at the lowest crop loads, but the higher the irrigation rate the higher the oil yield at high crop loads. The predicted commercial oil yield at common fruit counts increased from 1.99 t/ha at the lowest irrigation rate to 3.06 t/ha at the highest irrigation rate. Stomatal conductance decreased with decreasing stem water potential but leveled off at 30–60 mmol m^?2 s^?1 at stem water potential values lower than ?4.0 MPa. High crop load increased stomatal conductance and decreased stem water potential relative to low crop load at low and medium irrigation rates. The effect of crop load on water relations became evident by the end of August and was well pronounced at the beginning of October. Physiological and irrigation water management implications related to the interactions between tree water status and crop load are discussed.     

Soil–plant water status and yield of sweet corn (Zea mays L. cv. Saccharata) as influenced by drip irrigation and planting methods

A field experiment was conducted during summer season of 1998 at the Main Research Station, University of Agricultural Sciences, Hebbal, Bangalore. Experiment consisted of four irrigation levels and two methods of planting. Drip irrigation at 0.8 Epan with normal planting recorded significantly higher green cob (20.07 t ha⁻¹) and fodder yield (24.87 t ha⁻¹) compared to either drip at 0.6 Epan or weekly surface irrigation at 0.8 Epan, while drip at 0.4 Epan under paired planting (10.53 and 15.23 t ha⁻¹, respectively registered the lowest. Drip at 0.4 Epan with normal planting recorded higher WUE of green cob and fodder (48.21 and 61.22 kg ha mm⁻¹) with total water requirement of 330.46 mm. With increase in water use (drip at 0.6 Epan, drip/surface irrigation at 0.8 Epan) the water use efficiency decreased. Drip irrigation at 0.8 Epan resulted in higher leaf water potential (−4, −7, −8 bars) at 20, 40 and 60 DAS before irrigation. Consequently, the RWC in the leaf was 81.10% and the available soil moisture ranged from 55.62 to 61.91%.     

Identifying irrigation zones across a 7.5-ha ‘Pinot noir’ vineyard based on the variability of vine water status and multispectral images

Vine water status, yield and berry composition are variables within a vineyard. There is current interest in defining zones of similar yield and berry composition. The aim of this study was to compare two methods for identifying zones of similar yield within a 7.5-ha ‘Pinot noir’ vineyard. The two methods were based on: spatial distribution of average midday leaf water potential (Ψ_L) and plant cell density (PCD?=?near-infrared/red) which is a vegetation index. A proposal for splitting the vineyard into eight new irrigation zones was assessed. A ‘blind’ zonation based on regular polygons of equal sizes was also established as a standard for comparison. Coefficients of variation (C _v) in yield for both methods were compared with that of the blind zonation. In 2006 and 2007, a k-means cluster analysis indicated that variability in Ψ_L was mainly effected by soil properties. In both years, the vineyard was fully irrigated (100?% ET_c). The two methods did not improve yield C _v for full irrigation in 2006 and 2007 compared to blind zonation. In 2009, regulated deficit irrigation (RDI) was applied resulting in higher variability in Ψ_L and yield. The Ψ_L method of zonation significantly reduced coefficient of variation under RDI but PCD method did not despite the reduction in C _v by 16.7?%. We recommend irrigation zonation based on Ψ_L when RDI is applied.     

Summer deficit-irrigation strategies in a hedgerow olive orchard cv. ‘Arbequina’: effect on fruit characteristics and yield

Maximum production in hedgerow olive orchards is likely not achieved with maximum evapotranspiration over the long term. Thus, regulated deficit irrigation (RDI) should be considered as a management option. Four irrigation treatments were evaluated during the summer, when olive is most drought resistant. Control (CON) was irrigated to maintain the root zone close to field capacity. Severe water deficit was applied by irrigating 30% CON from the end of fruit drop to end July (DI-J) and from end July until beginning of oil synthesis (DI-A). Less severe water deficit was applied during July and August (DI-JA) by irrigating 50% CON. Flowering, fruiting, abscission, fruit development, fresh and dry weight of fruits, and oil production were evaluated. There were not significant differences in number of buds initiated, number of fruits per inflorescence and fruit drop. Oil production was significantly different between irrigation treatments in all experimental years. CON produced more oil and fruit with higher oil % than DI-A and DI-JA. Oil production of DI-J was not significantly reduced compared with CON and oil% was greater. DI-J was the most effective RDI strategy; with 16% less applied water relative to CON. Average loss in oil production of 8% was not significantly different to CON. While DI-JA saved most water (27%), oil production was reduced by 15%. Greatest loss in oil production (21%) was observed in DI-A with water saving of 22%.     

Effects of different irrigation regimes on a super-high-density olive grove cv. “Arbequina”: vegetative growth,productivity and polyphenol content of the oil

The effects of multiple irrigation regimes on the relationships among tree water status, vegetative growth and productivity within a super-high-density (SHD) “Arbequina” olive grove (1950 tree/ha) were studied for three seasons (2008–2010). Five different irrigation levels calculated as percentage of crop irrigation requirement using FAO procedures (Allen et al. in Crop evapotranspiration. Guidelines for computing crop water requirements. Irrigation and drainage paper 56. FAO, Rome, 1998) were imposed during the growing season. Periodically during the growing season, daytime stem water potential (Ψ _STEM), inflorescences per branch, fruits per inflorescence and shoot absolute growth rate were measured. Crop yield, fruit average fresh weight and oil polyphenol content were measured after harvest. The midday Ψ _STEM ranged from ?7 to ?1.5 MPa and correlated well enough with yield efficiency, crop density and fruit fresh weight to demonstrate its utility as a precise method for determining water status in SHD olive orchards. The relationships between midday Ψ _STEM and the horticultural parameters suggest maintaining Ψ _STEM values between ?3.5 and ?2.5 MPa is optimal for moderate annual yields of good quality oil. Values below ?3.5 MPa reduced current season productivity, while values over ?2.5 MPa were less effective in increasing productivity, reduced oil quality and produced excessive crop set that strongly affected vegetative growth and fruit production the following season. On the basis of the result given here, irrigation scheduling in the new SHD orchards should be planned on a 2-year basis and corrected annually based on crop load. Collectively, these results suggest that deficit irrigation management is a viable strategy for SHD olive orchards.     

Postharvest regulated deficit irrigation in ‘Summit’ sweet cherry: fruit yield and quality in the following season

We examined, over the postharvest seasons of 2005–2007, regulated deficit irrigation (RDI) for its potential of saving water and maintaining fruit yield and quality in ‘Summit’ sweet cherry. The postharvest irrigation treatments were: full irrigation (Control), receiving 80% of water in Control (RDI-80%), and receiving 50% of water in Control (RDI-50%). Midday stem water potential (Ψ_stem) was used for assessing plant water status. In 2006, trees produced a large crop and commercial fruit thinning had to be applied, whereas 2007 was a low crop year. The RDI treatment, first applied in 2005, reduced fruit set in 2006 and also reduced root winter starch concentration. In 2006, fruit set was lower in RDI-50% than in Control. But fruit thinning had still to be done with the final yield being the same among treatments. In 2007, RDI-50% produced more fruit and higher yields than Control. Relationship between postharvest Ψ_stem and crop load in the following season varied according to the year. They were negatively correlated in 2006 and positively correlated in 2007. Fruit firmness did not vary with irrigation treatments in any of the years. Fruit soluble solid concentration (SSC) and fruit relative dry matter (RDM) for RDI-50% was the highest in 2006 when RDI-50% trees had the lowest fruit set. In 2007, SSC and RDM for RDI-50% were the lowest with the trees having the highest fruit set and crop load at harvest. This study indicates that RDI-50% firstly applied in an “off” year, after crop has been harvested, can maintain fruit yield at similar levels to fully irrigated trees while saving water by 45%. Correction of biennial bearing and partial saving of thinning costs are additional advantages of this treatment.     

The role of ‘virtual water’ in efforts to achieve food security and other national goals,with an example from Egypt

The term ‘virtual water’ has been used previously to describe the volume of water embodied in food crops that are traded internationally. This paper describes the economic dimension of the ‘virtual water’ concept as an application of comparative advantage, with particular emphasis on water as the key factor of production. The paper also extends the discussion of ‘virtual water’ by describing a nation’s goals regarding food security within a broader framework that includes other objectives such as providing national security, promoting economic growth, and improving the quality of life for citizens. The analysis suggests that land, labor, and capital must also be considered when evaluating a nation’s production and trade opportunities. In countries where one or more of those resources is limiting, focus on ‘virtual water’ alone will not be sufficient to determine optimal policies for maximizing the social net benefits from limited water resources. In countries where labor is relatively abundant, public policies that promote labor-intensive crop production and processing activities may be desirable. The role of ‘virtual water’ within a broader policy framework is demonstrated using crop production and international trade data from Egypt, where substantial amounts of ‘virtual water’ and ‘virtual land’ are embodied in wheat and maize imports. Policies that promote increased exports of labor-intensive crops will improve rural incomes and enhance food security.