Mineral content of three olive cultivars irrigated with treated industrial wastewater

The reuse of saline treated industrial wastewater generated by textile firms mixed with municipal domestic effluent for irrigation was used to asses its effect on the mineral content of three olive (Olea europaea L.) cultivars under greenhouse and field conditions during two complete vegetative cycles. Chemical analysis of the treated wastewater indicated that the element concentrations fall within the permissible range of irrigation water used for plants. However, little impermissible accumulation of Na and Mg higher than the recommended maximum concentration was observed. Irrigation water with six electrical conductivities (EC = 0.78, 1.0, 2.0, 3.0, 4.0 and 5.0 dS m⁻¹ in treatments T₀, T₁, T₂, T₃, T₄, T₅, respectively) were compared in the greenhouse experiment. The olive trees in the field experiment were trickle irrigated with potable water and treated wastewater (average EC = 4.2 dS m⁻¹). The results of the greenhouse experiment showed that leaf N, Cu, Mn, Fe, Pb, and Na contents increased with increasing salinity of the treated wastewater. This increase was accompanied with a decrease in K and Mg contents. Leaf Ca and Cl concentrations were not considerably affected. Ion analysis in roots indicated that the contents of P, Na, Cl, Mn, and Pb increased while K decreased as treated wastewater salinity increased. Consequently, in most cases T₄ and T₅ gave a highly significant increase or decrease in accumulation of the previously mentioned minerals. A considerable variation in the studied cultivars was noticed. ‘Nabali’ was considered the most tolerant cultivar for the high salinity levels of the treated wastewater; its transporting selectivity of Na from root to leaf was higher and more Na was retained in the roots. Tissue analysis of leaves indicated that the element concentrations were within the adequate levels except those of Fe in ‘Nabali’ and ‘Manzanillo’, Na in ‘Improved Nabali’ and Cu in ‘Nabali’ and ‘Manzanillo’. In view of these findings, the negligible accumulation of minerals in leaves and roots indicated that this kind of textile effluent can be used as a valid alternative for irrigation of olive orchards with continuous monitoring of mineral levels.     

Yield and olive oil characteristics of a low-density orchard (cv. Cordovil) subjected to different irrigation regimes

The impact of different irrigation scheduling regimes on the quantity and quality of olive oil from a low-density olive grove in southern Portugal was assessed during the irrigation seasons of 2006 and 2007. Olive trees were subjected to one of the following treatments: A—full irrigation; B—sustained deficit irrigation (SDI) with 60% of ETc water applied with irrigation; C—regulated deficit irrigation (RDI) with irrigation water applied at three critical phases: before flowering, at the beginning of pit hardening and before crop harvesting and D—rain-fed treatment. Olive oil yield was significantly higher than rain-fed conditions in 2006, an “on year” of significant rainfall during summer. No significant yield differences were observed in the following “off year”. Among the irrigated treatments, olive oil production of treatment B was 32.5% and 40.1% higher in 2006 and 2007, respectively than the fully irrigated treatment A, despite receiving 49% less irrigation water. Such strategy could allow for an efficient use of water in the region, of very limited available resources, and for modest but important oil yield increase. Nonetheless, on the “on year” of 2006 treatment C used 13.9% of the water applied to treatment B and produced only 23.9% less olive fruits which could also make it illegible as the next possible strategy to use for irrigating olive trees in the region, provided that water is secured latter in the summer, a period of vital importance for oil accumulation and very sensitive to water stress as the poor results of 2007 revealed. The different treatment water regimes did not impact on the chemical characteristics of olive oils that were within the set threshold limits. Similarly, the sensory characteristics of the olive oils as well as bitterness and pungency were negligible for all treatments allowing them to be assessed as of “superior quality”.Overall, irrigation treatments had no influence on the commercial value of produced oils, being all classified as “extra virgin”. Such funding may be of vital importance to farmers willing to further their irrigation area, save water and still retain the protected designation of origin (PDO) seal of quality for their oil.     

Seasonal variations in sap flow and soil evaporation in an olive (Olea europaea L.) grove under two irrigation regimes in an arid region of Argentina

The emergence of intensively managed olive plantations in arid, northwestern Argentina requires the efficient use of irrigation water. We evaluated whole tree daily transpiration and soil evaporation throughout the year to better understand the relative importance of these water use components and to calculate actual crop coefficient (Kc) values. Plots in a 7-year-old ‘Manzanilla fina’ olive grove with 23% canopy cover were either moderately (MI) or highly irrigated (HI) using the FAO method where potential evapotranspiration over grass is multiplied by a given Kc and a coefficient of reduction (Kr). The Kc values employed for the MI and HI treatments were 0.5 and 1.1, respectively, and the Kr was 0.46. Transpiration was estimated by measuring main trunk sap flow using the heat balance method for three trees per treatment. Soil evaporation was measured using six microlysimeters in one plot per treatment. Both parameters were evaluated for 7-10 consecutive days in the fall, winter, mid-spring, summer, and early fall of 2006-2007. Maximum soil evaporation was observed in the summer when maximum demand was combined with maximum surface wetted by the drips and evaporation from the inter-row occurred due to rainfall. Similarly, maximum daily transpiration was observed in mid-spring and summer. Transpiration of MI trees was 30% lower than in HI trees during the summer period. However, this difference in transpiration disappeared when values were adjusted for total leaf area per tree because leaf area was 28% less in the MI trees. Transpiration represented about 70-80% of total crop evapotranspiration (ETc) except when soil evaporation increased due to rainfall events or over-irrigation occurred. We found that daily transpiration per unit leaf area had a positive linear relationship with daily potential evapotranspiration (r² = 0.84) when considering both treatments together. But, a strong relationship was also observed between transpiration per unit leaf area and mean air temperature (r² = 0.93). Thus, it is possible to predict optimum irrigation requirements for olive groves if tree leaf area and temperature are known. Calculated crop coefficients during the growing season based on the transpiration and soil evaporation values were about 0.65-0.70 and 0.85-0.90 for the MI and HI treatments, respectively.     

Effect of irrigation amounts applied with subsurface drip irrigation on corn evapotranspiration, yield, water use efficiency, and dry matter production in a semiarid climate

Quantifying the local crop response to irrigation is important for establishing adequate irrigation management strategies. This study evaluated the effect of irrigation applied with subsurface drip irrigation on field corn (Zea mays L.) evapotranspiration (ETc), yield, water use efficiencies (WUE = yield/ETc, and IWUE = yield/irrigation), and dry matter production in the semiarid climate of west central Nebraska. Eight treatments were imposed with irrigation amounts ranging from 53 to 356 mm in 2005 and from 22 to 226 mm in 2006. A soil water balance approach (based on FAO-56) was used to estimate daily soil water and ETc. Treatments resulted in seasonal ETc of 580–663 mm and 466–656 mm in 2005 and 2006, respectively. Yields among treatments differed by as much as 22% in 2005 and 52% in 2006. In both seasons, irrigation significantly affected yields, which increased with irrigation up to a point where irrigation became excessive. Distinct relationships were obtained each season. Yields increased linearly with seasonal ETc (R² = 0.89) and ETc/ETp (R² = 0.87) (ETp = ETc with no water stress). The yield response factor (ky), which indicates the relative reduction in yield to relative reduction in ETc, averaged 1.58 over the two seasons. WUE increased non-linearly with seasonal ETc and with yield. WUE was more sensitive to irrigation during the drier 2006 season, compared with 2005. Both seasons, IWUE decreased sharply with irrigation. Irrigation significantly affected dry matter production and partitioning into the different plant components (grain, cob, and stover). On average, the grain accounted for the majority of the above-ground plant dry mass (≈59%), followed by the stover (≈33%) and the cob (≈8%). The dry mass of the plant and that of each plant component tended to increase with seasonal ETc. The good relationships obtained in the study between crop performance indicators and seasonal ETc demonstrate that accurate estimates of ETc on a daily and seasonal basis can be valuable for making tactical in-season irrigation management decisions and for strategic irrigation planning and management.     

Using EPIC model to manage irrigated cotton and maize

Simulation models are becoming of interest as a decision support system for management and assessment of crop water use and of crop production. The Environmental Policy Integrated Climate (EPIC) model was used to evaluate its application as a decision support tool for irrigation management of cotton and maize under South Texas conditions. Simulation of the model was performed to determine crop yield, crop water use, and the relationships between the yield and crop water use parameters such as crop evapotranspiration (ETc) and water use efficiency (WUE). We measured actual ETc using a weighing lysimeter and crop yields by field sampling, and then calibrated the model. The measured variables were compared with simulated variables using EPIC. Simulated ETc agreed with the lysimeter, in general, but some simulated ETc were biased compared with measured ETc. EPIC also simulated the variability in crop yields at different irrigation regimes. Furthermore, EPIC was used to simulate yield responses at various irrigation regimes with farm fields’ data. Maize required ∼700 mm of water input and ∼650 mm of ETc to achieve a maximum yield of 8.5 Mg ha⁻¹ while cotton required between 700 and 900 mm of water input and between 650 and 750 mm of ETc to achieve a maximum yield of 2.0-2.5 Mg ha⁻¹. The simulation results demonstrate that the EPIC model can be used as a decision support tool for the crops under full and deficit irrigation conditions in South Texas. EPIC appears to be effective in making long-term and pre-season decisions for irrigation management of crops, while reference ET and phenologically based crop coefficients can be used for in-season irrigation management.     

Yield components and grape composition responses to seasonal water deficits in Tempranillo grapevines

A field experiment was carried out over three seasons on Vitis vinifera cv. Tempranillo in order to compare pre-veraison and post-veraison water restrictions on vine performance and fruit composition. Rain-fed vines were compared with a treatment named MAX that was constantly irrigated at 75?% of the estimated crop evapotranspiration (ETc). In addition, an early (pre-veraison) water deficit strategy (ED) was applied by withholding irrigation until plant water stress experienced by vines surpassed a threshold value of midday stem water potential of ?1.0?MPa. After that, 75?% of ETc was applied. A late season deficit (LD) treatment was irrigated as per the MAX up to veraison, and thereafter, water application was reduced to approximately 37?% of ETc. All irrigation regimes increased vine yield up to 58?% with respect to the rain-fed treatment, and no differences in yield among the irrigated treatments occurred. However, there were differences in berry composition among the different irrigation strategies. The ED strategy was more effective than the LD one in reducing berry growth leading to more concentrated berries in terms of sugars and anthocyanins. The LD water shortage impaired berry sugar accumulation due to the detrimental effect of water stress on leaf photosynthesis.     

Cost–benefit analysis of a regulated deficit-irrigated almond orchard under subsurface drip irrigation conditions in Southeastern Spain

A cost–benefit analysis was performed for a mature, commercial almond plantation [Prunus dulcis (Mill.) D.A. Webb] cv. Cartagenera in Southeastern Spain to determine the profitability of several regulated-deficit irrigation (RDI) strategies under subsurface drip irrigation conditions (SDI), compared to an irrigation regime covering 100% crop evapotranspiration (ETc). The plantation was subjected to three drip irrigation treatments for 4 years: T1 (control, surface drip irrigation)—irrigated at 100% ETc throughout the growth cycle, T2 (RDI treatment under SDI)—an irrigation strategy that provided 100% ETc except during the kernel-filling period, when only 20% ETc was provided and T3 (RDI treatment under SDI)—an irrigation strategy that provided 100% ETc except during the kernel-filling period (20% ETc) and post-harvest (50% ETc). A 45% water saving was achieved with strategy SDI T3, while almond production was reduced by only 17%, increasing water use efficiency compared to the control irrigation regime. SDI T3 had fixed overhead costs 9% higher than T1, however, the operating costs were 21% lower for SDI T3 compared to T1. This reduction in costs was basically due to the 45% saving in the cost of water and the corresponding saving in electricity. The break-even point was lower in SDI T3; each kilogram of almonds cost 0.03€ less to produce than in the control conditions. Related to this, the maximum price of water for obtaining profit 0 was 0.21€ m⁻³ for SDI T3 compared to 0.18€ m⁻³ for T1, indicating that higher water costs can be borne in SDI T3 (up to 0.03€ m⁻³ more expensive). Finally the profit/total costs ratio (used as an expression of the overall profitability of the orchard) indicated a greater profitability for the treatment SDI T3 compared to T1 (10.46 and 9.27%, respectively). The RDI strategy SDI T2 did not show economic indices or water use efficiency as much as those of SDI T3. From these results we conclude that RDI applied during kernel-filling and post-harvest under SDI conditions, and specifically the irrigation strategy SDI T3, may be considered economically appropriate in semiarid conditions in order to save water and improve water use efficiency.     

Financial analysis of wine grape production using regulated deficit irrigation and partial-root zone drying strategies

Cost-benefit analysis was performed to determine the profitability of producing wine grapes under different irrigation regimes. Vines irrigated by regulated deficit irrigation (RDI) and partial root-zone drying (PRD) were compared with vines grown under full irrigation in a typical vineyard in a semiarid environment with scarce water resources (south-eastern Spain) during three consecutive years. Five irrigation treatments were applied. The Control treatment irrigated at 60% of the ETc (Crop evapotranspiration) throughout the orchard cycle. PRD-1 and RDI-1 provided deficit irrigation from fruit set to harvest (irrigated 30% ETc) and post-harvest (45% ETc). PRD-2 and RDI-2 provided deficit irrigation from fruit set to harvest (irrigated 15% ETc) and post-harvest (45% ETc). From an economic point of view, only the Control, PRD-1 and RDI-1 treatments were economically viable since their profitability indicators were positive, although low, especially PRD-1. The more severe deficit irrigated treatments (PRD-2 and RDI-2) were unviable. The most profitable treatment was the Control which had a Net Margin/total cost ratio (NM/C) (representing the overall profitability of the vineyard) of 25.37% compared with the 1.90% of RDI-1 and 0.57% of PRD-1. The threshold price of water indicates that only the Control remains profitable with higher water prices of up to 0.46 € m⁻³. When the cost-benefit analysis took into account the extra quality achieved in PRD-2 and RDI-2, it indicated that these treatments, which were otherwise economically unviable, achieved high returns (17 and 16%, respectively) and were close to the Control treatment. Thus, a low or moderate bonus that encourages extra berry quality for premium wine production would make deficit irrigation practices profitable. Moreover, the financial indices estimated suggest that in the present situation, and with our soil and climatic conditions, PRD is less economically profitable (higher installation cost, lower NM/C, and threshold price of water) than RDI under the same conditions.     

Response of apricot trees to deficit irrigation strategies

During four growing seasons, 10-year-old apricot trees (Prunus armeniaca L., cv. ‘Búlida’) were submitted to three different drip irrigation regimes: (1) a control treatment, irrigated at 100% of seasonal crop evapotranspiration (ETc), (2) a continuous deficit irrigation (DI) treatment, irrigated at 50% of the control treatment, and (3) a regulated deficit irrigation (RDI) treatment, irrigated at 100% of ETc during the critical periods, which correspond to stage III of fruit growth and 2 months after harvest (early postharvest), and at 25% of ETc during the rest of the non-critical periods in the first two growing seasons and at 40% of ETc in the third and fourth. Soil–plant–water relation parameters were sensitive to the water deficits applied, which caused reductions in leaf and soil water potentials. The longer and severer deficits of the RDI treatment decreased fruit yield in the first two seasons. The RDI treatment pointed to two threshold values that defined the level at which both plant growth and yield were negatively affected with respect to the control treatment: (1) a predawn leaf water potential of around −0.5 MPa during the critical periods, and (2) a 22% drop in irrigation water. The total yield obtained in the DI treatment was significantly reduced in all the years studied due to the lower number of fruits per tree. No changes in the physical characteristics of fruits were observed at harvest. RDI can be considered a useful strategy in semiarid areas with limited water resources.     

Yield and quality of melon grown under different irrigation and nitrogen rates

During 2 years, a melon crop (Cucumis melo L. cv. Sancho) was grown under field conditions to investigate the effects of different nitrogen (N) and irrigation (I) levels on fruit yield, fruit quality, irrigation water use efficiency (IWUE) and nitrogen applied efficiency (NAE). The statistical design was a split-plot with four replications, where irrigation was the main factor of variation and N was the secondary factor. In 2005, irrigation treatments consisted of applying daily a moderate water stress equivalent to 75% of ETc (crop evapotranspiration), a 100% ETc control and an excess irrigation of 125% ETc (designated as I₇₅, I₁₀₀ and I₁₂₅), while the N treatments were 30, 85, 112 and 139 kg N ha⁻¹ (designated as N₃₀, N₈₅, N₁₁₂ and N₁₃₉). In 2006, both the irrigation and N treatments applied were: 60, 100 and 140% ETc (I₆₀, I₁₀₀ and I₁₄₀) and 93, 243 and 393 kg N ha⁻¹ (N₉₃, N₂₄₃ and N₃₉₃). Moderate water stress did not reduce melon yield and high IWUE was obtained. Under severe deficit irrigation, the yield was reduced by 22% mainly due to decrease fruit weight. The relative yield (yield/maximum yield) was higher than 95% when the irrigation depth applied was in the range of 87-136% ETc. In 2006, the interaction between irrigation and N was significant for yield, fruit weight and IWUE. The best yield, 41.3 Mg ha⁻¹, was obtained with 100% ETc at N₉₃. The flesh firmness and the placenta and seeds weight increased when the irrigation level was reduced by 60% ETc. The highest NAE was obtained with quantities of water close to 100% ETc and increased as the N level was reduced. The highest IWUE was obtained with applications close to 90 kg N ha⁻¹. The I₂₄₃ and I₃₉₃ treatments produced inferior fruits due to higher skin ratios and lower flesh ratios. These results suggest that it is possible to apply moderate deficit irrigation, around 90% ETc, and reduce nitrogen input to 90 kg ha⁻¹ without lessening quality and yields.     

Macromanagement of deficit-irrigated peanut with sprinkler irrigation

Precision irrigation management and scheduling, as well as developing site- and cultivar-specific crop coefficient (K_c), and yield response factor to water deficit (ky) are very important parameters for efficient use of limited water resources. This study investigated the effect of deficit irrigation, applied at different growth stages of peanut with sprinkler irrigation in sandy soil, on field peanut evapotranspiration (ETc), yield and yield components, and water use efficiencies (IWUE and WUE). Also, yield response factor to water deficit (ky), and site- and cultivar-specific K_c were developed. Four treatments were imposed to deficit irrigation during late vegetative and early flowering, late flowering and early pegging, pegging, and pod formation growth stages of peanut, and compared with full irrigation in the course of the season (control). A soil water balance equation was used to estimate crop evapotranspiration (ETc). The results revealed that maximum seasonal ETc was 488 mm recorded with full irrigation treatment. The maximum value of K_c (0.96) occurred at the fifth week after sowing, this value was less than the generic values listed in FAO-33 and -56 (1.03 and 1.15), respectively. Dry kernels yield among treatments differed by 41.4%. Deficit irrigation significantly affected yields, where kernels yield decreased by 28, 39, 36, and 41% in deficit-irrigated late vegetative and early flowering, late flowering and early pegging, pegging, and pod formation growth stages, respectively, compared with full irrigation treatment. Peanut yields increased linearly with seasonal ETc (R² = 0.94) and ETc/ETp (R² = 0.92) (ETp = ETc with no water stress). The yield response factor (ky), which indicates the relative reduction in yield to relative reduction in ETc, averaged 2.9, was higher than the 0.7 value reported by Doorenbos and Kassam [Doorenbos, J., Kassam, A.H., 1979. Yield response to water. FAO Irrigation and Drainage Paper 33, Rome, Italy, 193 pp.], the high ky value reflects the great sensitivity of peanut (cv. Giza 5) to water deficit. WUE values varied considerably with deficit irrigation treatments, averaging 6.1 and 4.5 kg ha⁻¹ mm⁻¹ (dry-mass basis) for pods and kernels, respectively. Differences in WUE between the driest and wettest treatment were 31.3 and 31.3% for pods and kernels, respectively. Deficit irrigation treatments, however, impacted IWUE much more than WUE. Differences in IWUE between the driest and wettest treatment were 33.9 and 33.9% for pods and kernels, respectively. The results revealed that better management of available soil water in the root zone in the course of the season, as well as daily and seasonal accurate estimation of ETc can be an effective way for best irrigation scheduling and water allocation, maximizing yield, and optimizing economic return.     

Financial feasibility of implementing regulated and sustained deficit irrigation in almond orchards

This study aims to assess the long-term economic viability of deficit irrigation (DI) strategies in almond trees (cv. Marta) grown in a semiarid area (southeast Spain). A discounted cash flow analysis (DCFA) was performed to determine the profitability of the different irrigation regimes. Four irrigation treatments were evaluated over the first 6 years of an almond plantation: (1) full irrigation (FI); (2) regulated deficit irrigation (RDI) receiving 40 % ETc during kernel-filling and 100 % ETc during the remainder of the growing season; (3) mild-to-moderate sustained deficit irrigation (SDI_mm), irrigated at 75 % ETc (first half of the experiment) and 60 % ETc (second half of the experiment) over the entire growing season; and (4) moderate-to-severe SDI (SDI_ms), irrigated at 60 % ETc (first half of the experiment) and 30 % ETc (second half of the experiment) over the whole growing season. Irrigation water profit was mainly determined by the annual volume of irrigation water applied (water costs are around 50 % of variable costs). DCFA indicates that RDI and SDI_mm are the most economically feasible treatments, whereas FI and SDI_ms presented a similar degree of profitability over the 6-year period. Simulation outputs derived for the whole useful life of the investment indicate that SDI_mm would be the most suitable irrigation treatment to be adopted by almond farmers in the study area. We conclude that in a context of water scarcity, DI is a financially feasible alternative to FI.     

Response of Leucadendron ‘Safari Sunset’ to regulated deficit irrigation: Effects of stress timing on growth and yield quality

Leucadendron ‘Safari Sunset’ is the most important cultivar in the worldwide Protea industry. The commercial product consists of long branches that terminate in a female inflorescence (“head”), surrounded by large, deep-wine-red leaves. The dimensions of the colourful head have a predominant effect on the attractiveness and price of ‘Safari Sunset’ in the floricultural markets. The objective of the present study was to assess the effect of regulated deficit irrigation at different growth phases, on plant growth and crop quality. The experiment included two control treatments applied throughout the growth season: non-stress irrigation and deficit irrigation (40% of non-stress irrigation). The intermittent deficit irrigation treatments included periodic water stress during the fast vegetative growth (phase I) or during the head development (phase II). In addition, short events of water stress in the middle of the growth season, followed by a water non-stress irrigation regime were tested. Water stress throughout the growth season induced significantly low vegetative growth and small heads. Intermittent water stress (both periods) impaired crop quality, mainly because of reduction of head dimensions. Short or moderate periodic water stress barely affected head dimensions or the number of marketable branches, but impaired the product by diminishing the leaf dimensions. Continuous measurements of soil-water tension or plant indicators such as stem diameter or length were found to be very useful for on-line control of plant-water status.     

Influence of plant traits on production costs and profitability of strawberry in southeast Queensland

In Queensland the subtropical strawberry (Fragaria × ananassa) breeding program aims to combine traits into novel genotypes that increase production efficiency. The contribution of individual plant traits to cost and income under subtropical Queensland conditions was investigated, with the overall goal of improving the profitability of the industry through the release of new strawberry cultivars. The study involved specifying the production and marketing system using three cultivars of strawberry that are currently widely grown annually in southeast Queensland, developing methods to assess the economic impact of changes to the system, and identifying plant traits that influence outcomes from the system.From May through September P (price; $ punnet⁻¹), V (monthly mass; tonne of fruit on the market) and M (calendar month; i.e. May = 5) were found to be related (r² = 0.92) by the function (±SE) P = 4.741(±0.469) − 0.001630(±0.0005)V − 0.226(±0.102)M using data from 2006 to 2010 for the Brisbane central market. Both income and cost elements in the gross margin were subject to sensitivity analysis.‘Harvesting’ and ‘Handling/Packing’ ‘Groups’ of ‘Activities’ were the major contributors to variable costs (each >20%) in the gross margin analysis. Within the ‘Harvesting Group’, the ‘Picking Activity’ contributed most (>80%) with the trait ‘display of fruit’ having the greatest (33%) influence on the cost of the ‘Picking Activity’. Within the ‘Handling/Packing Group’, the ‘Packing Activity’ contributed 50% of costs with the traits ‘fruit shape’, ‘fruit size variation’ and ‘resistance to bruising’ having the greatest (12-62%) influence on the cost of the ‘Packing Activity’. Non-plant items (e.g. carton purchases) made up the other 50% of the costs within the ‘Handling/Packing Group’. When any of the individual traits in the ‘Harvesting’ and ‘Handling/Packing’ groups were changed by one unit (on a 1-9 scale) the gross margin changed by up to 1%. Increasing yield increased the gross margin to a maximum (15% above present) at 1320 g plant⁻¹ (94% above present). A 10% redistribution of total yield from September to May increased the gross margin by 23%. Increasing fruit size increased gross margin: a 75% increase in fruit size (to ≈30 g) produced a 22% increase in the gross margin.The modified gross margin analysis developed in this study allowed simultaneous estimation of the gross margin for the producer and gross value of the industry. These parameters sometimes move in opposite directions.     

Use of maximum trunk diameter measurements to detect water stress in mature ‘Arbequina’ olive trees under deficit irrigation

Olive is one of the fruit tree species for which measurements of the trunk diameter variation (TDV) has shown a lower potential both for monitoring water stress and for scheduling irrigation. This is particularly true in the case of old, big olive trees with heavy fruit load. Fernández et al. (2011, J. Environ. Exp. Bot. 72, 330-338) observed that the daily difference for maximum trunk diameter between deficit irrigated ‘Manzanilla’ olive trees and control trees growing under non-limiting soil water conditions, termed D_MXTD, is more sensitive and reliable for detecting the water stress of the trees than other widely used TDV-derived indices. However, they considered their results as preliminary because of the lack of replications. The aim of this work was to evaluate the usefulness of the D_MXTD index for detecting plant water stress in an orchard with 12-year-old ‘Arbequina’ olive trees with heavy fruit load. The performance of D_MXTD for detecting water stress of the trees was compared to that of the signal intensity for the maximum daily shrinkage (S_I-MDS) derived from the same TDV records. Results showed that S_I-MDS was not useful for indicating the water stress of the trees. On the other hand, the dynamics of D_MXTD mimicked those of the soil and plant water status. Four instrumented trees per treatment (replicates) were enough to reduce the uncertainty of the TDV measurements to a reasonable level. Our results show that D_MXTD is a useful index to detect the onset, and severity, of water stress in mature ‘Arbequina’ olive trees with heavy fruit load. They also suggest a potential of D_MXTD for scheduling low frequency deficit irrigation strategies.     

Effect of timing of a deficit-irrigation allocation on corn evapotranspiration, yield, water use efficiency and dry mass

Water regulations have decreased irrigation water supplies in Nebraska and some other areas of the USA Great Plains. When available water is not enough to meet crop water requirements during the entire growing cycle, it becomes critical to know the proper irrigation timing that would maximize yields and profits. This study evaluated the effect of timing of a deficit-irrigation allocation (150 mm) on crop evapotranspiration (ETc), yield, water use efficiency (WUE = yield/ETc), irrigation water use efficiency (IWUE = yield/irrigation), and dry mass (DM) of corn (Zea mays L.) irrigated with subsurface drip irrigation in the semiarid climate of North Platte, NE. During 2005 and 2006, a total of sixteen irrigation treatments (eight each year) were evaluated, which received different percentages of the water allocation during July, August, and September. During both years, all treatments resulted in no crop stress during the vegetative period and stress during the reproductive stages, which affected ETc, DM, yield, WUE and IWUE. Among treatments, ETc varied by 7.2 and 18.8%; yield by 17 and 33%; WUE by 12 and 22%, and IWUE by 18 and 33% in 2005 and 2006, respectively. Yield and WUE both increased linearly with ETc and with ETc/ETp (ETp = seasonal ETc with no water stress), and WUE increased linearly with yield. The yield response factor (ky) averaged 1.50 over the two seasons. Irrigation timing affected the DM of the plant, grain, and cob, but not that of the stover. It also affected the percent of DM partitioned to the grain (harvest index), which increased linearly with ETc and averaged 56.2% over the two seasons, but did not affect the percent allocated to the cob or stover. Irrigation applied in July had the highest positive coefficient of determination (R²) with yield. This high positive correlation decreased considerably for irrigation applied in August, and became negative for irrigation applied in September. The best positive correlation between the soil water deficit factor (Ks) and yield occurred during weeks 12-14 from crop emergence, during the “milk” and “dough” growth stages. Yield was poorly correlated to stress during weeks 15 and 16, and the correlation became negative after week 17. Dividing the 150 mm allocation about evenly among July, August and September was a good strategy resulting in the highest yields in 2005, but not in 2006. Applying a larger proportion of the allocation in July was a good strategy during both years, and the opposite resulted when applying a large proportion of the allocation in September. The different results obtained between years indicate that flexible irrigation scheduling techniques should be adopted, rather than relying on fixed timing strategies.     

Subsurface drip irrigation of onions: Effects of drip tape emitter spacing on yield and quality

Improved irrigation water use efficiency is an important component of sustainable agricultural production. Efficient water delivery systems such as subsurface drip irrigation (SDI) can contribute immensely towards improving crop water use efficiency and conserving water. However, critical management considerations such as choice of SDI tube, emitter spacing and installation depth are necessary to attain improved irrigation efficiencies and production benefits. In this study, we evaluated the effects of subsurface drip tape emitter spacing (15, 20 and 30 cm) on yield and quality of sweet onions grown at two locations in South Texas—Weslaco and Los Ebanos. Season-long cumulative crop evapotranspiration (ETc) was 513 mm in Weslaco and 407 mm at Los Ebanos. Total crop water input (rain + irrigation) at Weslaco was roughly equal to ETc (92% ETc) whereas at Los Ebanos, water inputs exceeded ETc by about 35%. Onion yields ranged from 58.5 to 70.3 t ha⁻¹ but were not affected by drip tube emitter spacing. Onion pungency (pyruvic acid development) and soluble solids concentration were also not significantly influenced by treatments. Crop water use efficiency was slightly higher at Weslaco (13.7 kg/m³) than at Los Ebanos (11.7 kg/m³) partly because of differences in total water inputs resulting from differences in irrigation management. The absence of any significant effects of drip tape emitter spacing on onion yield may be due to the fact that irrigation was managed to provide roughly similar irrigation amounts and optimum soil moisture conditions in all treatments.     

Water relations,growth and yield of Fino lemon trees under regulated deficit irrigation

Fino lemon trees (Citrus limon L. Burm. fil.) on sour orange (Citrus aurantium L.), growing on a low water retention capacity soil, were submitted to three different irrigation treatments over four years: 100% ETc all year (T-0), 25% ETc all year except during the rapid fruit growth period when 100% ETc was applied (T-1) and 100% ETc all year, except during the rapid fruit growth period when 70% ETc was applied (T-2). A water saving of 30 and 20% was achieved in the T-1 and T-2 treatments, respectively. The plant responses to irrigation treatments were similar in all the years studied. Leaf water potential decreased during deficit irrigation periods in T-1 and T-2 treatments. Larger differences were found in values taken at predawn ( _pd) than at midday ( _md), indicating that _pd is a more useful indicator of plant water status. There was neither osmotic nor elastic adjustment in response to deficit irrigation treatment. A clear separation between the main periods of shoot and fruit growth was found, which can be considered an advantageous characteristic in applying regulated deficit irrigation strategies. Onset of the critical period of rapid fruit growth could be determined precisely by considering the decrease in relative fruit growth rate values. T-2 treatment did not induce a significant reduction in total yield, but it caused a delay in reaching marketable lemon fruit size. T-1 treatment did not affect total yield, with a reduction in yield on the first pick occurring in only one year. Chemical characteristics of lemon fruit were not significantly modified by irrigation treatment.     

Root dynamics of peach trees submitted to partial rootzone drying and continuous deficit irrigation

The root dynamics of young early-season peach trees (Prunus persica L. Batsch, cv. Flordastar) were studied during one growing season. The trees were submitted to three drip irrigation treatments: T1 (control) irrigated at 100% of the estimated crop evapotranspiration (ETc) requirements, T2 (continuous deficit) irrigated at 50% ETc and T3 (partial rootzone drying, PRD, treatment), alternating irrigation from one half to the other every 2–3 weeks. Root length was measured frequently using minirhizotrons and a circular-vision scanner. Overall, root length density was reduced by ≈73% in the continuous deficit irrigated treatment and by ≈42% in the T3 treatment with respect to the well irrigated treatment. A roughly similar amount of water was applied in both deficit irrigated treatments (44 and 56% of T1, for T2 and T3, respectively), but the continuous deficit irrigation applied to both sides of the root system in T2 resulted in a greater reduction in root growth than in T3. The dynamics of the root growth were similar in the three treatments. In general, root growth declined during the fruit growth period and increased after harvest, reaching its peak in mid July. By late July, root growth had declined again, and an alternating pattern of growth between the aerial and root parts of the tree was observed. Roots were mostly located in the upper 0.55 m of soil and were particularly concentrated at 0.40–0.55 m. More than 88% of these roots were very thin, with diameters of <0.5 mm. The study looks at the impact of deficit irrigation on the phenological processes related with root growth, and will help in making decisions concerning fertigation in areas with scarce water resources where deficit irrigation strategies are considered desirable.     

Irrigation requirements and transpiration coupling to the atmosphere of a citrus orchard in Southern Brazil

Crop evapotranspiration (ETc) was measured as evaporative heat flux from an irrigated acid lime orchard (Citrus latifolia Tanaka) using the aerodynamic method. Crop transpiration (T) was determined by a stem heat balance method. The irrigation requirements were determined by comparing the orchard evapotranspiration (ETc) and T with the reference evapotranspiration (ETo) derived from the Penman-Monteith equation, and the irrigation requirements were expressed as ETc/ETo (Kc) and T/ETo (Kcb) ratios. The influence of inter-row vegetation on the ETc was analyzed because the measurements were taken during the summer and winter, which are periods with different regional soil water content. In this study, the average Kc values obtained were 0.65 and 0.24 for the summer and winter, respectively. The strong coupling of citrus trees to the atmosphere and the sensitivity of citrus plants to large vapor pressure deficits and air/leaf temperatures caused variations in the Kcb in relation to the ETo ranges. During the summer, the Kcb value ranged from 0.34 when the ETo exceeded 5 mm d⁻¹ to 0.46 when the ETo was less than 3 mm d⁻¹.