The harvest period for ‘Star’ began the first week of May and ended after the third harvest. Most other cultivars required five or more harvests, 1 week apart. Based on the berry size , the cultivars studied would be separated into large berry and medium berry . The cultivars studied have an erect plant stature, except for ‘Misty’, which has a spreading stature that makes hand-harvest difficult. Fruit quality. Quality attributes such as soluble solids concentration, titratable acidity, soluble-solids-totitratable-acidity ratio and firmness were significantly different among cultivars and seasons . There was wide variability in soluble solids concentration among cultivars. ‘Reveille’ had the highest average value of the 2005 to 2007 seasons, followed by ‘Misty’ , ‘Emerald’ and ‘Star’ . ‘Jewel’ and ‘O’Neal’ had the lowest soluble solids concentration within this group. Titratable acidity within cultivars was less variable, and only ‘O’Neal’ had a significantly lower average value than the rest of the tested cultivars. Titratable acidity varied from 0.70% to 0.80% within this group with the exception of ‘O’Neal’. Cultivars segregated into three groups based on their soluble-solids-to-titratable-acidityratio. Because of its low titratable acidity, ‘O’Neal’ had the highest ratio, while ‘Jewel’ had the lowest ratio due to its high titratable acidity. The rest of the cultivars formed an intermediate group in which the soluble-solids-to-titratableacidity ratio ranged from 17 to 20.3. ‘Jewel’ and ‘O’Neal’ also had the lowest firmness , while ‘Reveille’ and ‘Misty’ had the highest . ‘Emerald’ and ‘Star’ were significantly different than these two groups, forming an intermediate group . Quality attributes were also significantly affected by the season. Soluble solids concentration across all cultivars was highest in 2007 and lowest in 2006, procona valencia buckets while titratable acidity was highest in 2006. Soluble-solids-to-titratableacidity ratio and firmness were significantly higher in 2007 than the other years. There was a significant interaction between cultivar and season for all these quality attributes .
The lowest soluble solids concentration was 10.8% in 2006 for ‘O’Neal’ and the highest was 15.8% for ‘Reveille’ in 2007. During this 3-year period, all of the cultivars yielded soluble solids concentrations higher than 10%, which has been proposed as a minimum quality index for blueberries . Titratable acidity was similar among cultivars in these three seasons except for ‘O’Neal’ in 2007, which reached 0.3%, and ‘Jewel’ and ‘Emerald’ in 2006 with about 1.0%. ‘O’Neal’ and ‘Reveille’ had the highest soluble-solids-to-titratableacidity ratio, followed by the rest of the cultivars with ratios from 11.4 to 20.6. During this 3-year period, ‘Jewel’ and ‘O’Neal’ were the softest cultivars, and ‘Misty’ and ‘Reveille’ the firmest. Antioxidant capacity was significantly different among the cultivars but not between seasons . There was a wide variability of TEAC within cultivars. ‘Misty’ had the highest average TEAC followed by ‘Reveille’ and ‘Emerald’ . ‘Star’ , ‘O’Neal’ and ‘Jewel’ had the lowest TEAC within this group. Like the rest of the quality attributes, there was a significant interaction between cultivars and seasons for antioxidant capacity . Storage of the six blueberry cultivars at 32°F for 15 days did not affect either antioxidant capacity or firmness, except for ‘O’Neal’ and ‘Misty’, whose firmness was reduced slightly but not significantly . Consumer acceptance. During the 2006 season, our in-store test results indicated that consumers liked the three tested cultivars slightly to moderately, with an acceptance range of 73.3% to 80%. There were no significant differences in degree of liking between ’Jewel’, ‘O’Neal’ and ‘Star’. In these three cultivars the percentage of consumers disliking these fruit reached about 17% . During the 2007 season, there were significant differences in degree of liking between the six cultivars tested . In this test, degree of liking varied from liking slightly to moderately. ‘Reveille’ had the highest and ‘O’Neal’ the lowest degree of liking with an acceptance of 92.1% and 67.3%, respectively. Degree of liking of ‘Misty’ and ‘Jewel’ was significantly lower than ‘Reveille’, but higher than ‘Star’ and ‘Emerald’. Acceptance was near 80% for ‘Jewel’, ‘Misty’ and ‘Star’, while only 67% for ‘O’Neal’ and 72% for ‘Emerald’. The percentage of consumers that disliked these cultivars varied from 5.9% to 19.8%; ‘Reveille’ and ‘Misty’ had the lowest dislike percentage and ‘O’Neal’ the highest. Degree of liking for ‘Jewel’ and ‘Star’ were similar during the two seasons. For ‘O’Neal’, the degree of liking decreased from like slightly-moderately to like slightly.
This reduction in consumer acceptance can be explained by the change of titratable acidity from 0.6% to 0.8% in previous years down to 0.3% in 2007 that only occurred in ‘O’Neal’. This reduction of titratable acidity for ‘O’Neil’ was independent of soluble solids concentration, which remained between 10.8% and 11.8% for the 2005 to 2007 seasons. These results indicated that blueberries with very low titratable acidity , despite soluble solids concentrations between 10% and 12%, are not acceptable to consumers. A similar situation has been observed in white and yellow flesh peaches and nectarines with very low acidity . This reduction in consumer acceptance also points out that the ratio of soluble solids to titratable acidity is not a good indicator for blueberry taste when titratable acidity is low. We are not sure of the reasons for the low titratable acidity in 2007 of ‘O’Neal’ fruit, which appears to be independent of other cultivars. The 2007 season was characterized by high chilling accumulation and a hotter than normal spring, which could have affected ‘O’Neal’ ripening. Choosing a variety The six southern highbush blueberry cultivars studied growing in the San Joaquin Valley had soluble solids concentration levels above the 10% proposed for a minimum quality standard. Blueberries with very low titratable acidity, despite acceptable soluble solids concentration, had lower consumer acceptance and degree of liking, indicating that the solublesolids-to-titratable-acidity ratio is not a good indicator of consumer acceptance for blueberries. For San Joaquin Valley conditions, these cultivars are all good options for our fast-growing, early fresh blueberry market.Agricultural managed aquifer recharge is a recharge technique for groundwater replenishment, in which farmland is flooded during the winter using excess surface water in order to recharge the underlying aquifer . In California, for example, Ag-MAR is currently being implemented as part of the efforts to mitigate California’s chronic groundwater overdraft . Ag-MAR poses several risks for agricultural fields and groundwater that may influence its future adoption. This includes crop tolerance to flooding, soil aeration, biogeochemical transformations, long-term impact on soil texture, leaching of pesticides and fertilizers to groundwater, and potential greenhouse gas emissions. Some of these issues have been addressed in recent studies of Ag-MAR, including soil suitability guidelines , nitrate leaching to groundwater , crop suitability and soil aeration . In the current study, we focused solely on the question of “how long can water be applied for Ag-MAR with minimal crop damage?”, while ignoring some of the above-mentioned challenges involving Ag-MAR implementation. Preferably, Ag-MAR flooding is done during fallow or dormant periods, when crop damage is potentially minimal, so agricultural lands can serve as spreading basins for groundwater recharge.
Root zone residence time is defined as the duration that the root-zone can remain saturated during Ag-MAR without crop damage . RZRT is a crucial factor in Ag-MAR, as long periods of saturated conditions in the root-zone can damage crops due to oxygen deficiency or complete depletion of oxygen, which ultimately may result in yield loss . However, flood tolerance among crops varies considerably due to biotic and abiotic conditions , therefore only appropriate crops under specific conditions may be suitable for Ag-MAR application. For example, Dokoozlian et al. have found that grapevine during dormancy can be flooded for 32 days each year without yield loss. Dahlke et al. recently investigated the effect of different Ag-MAR flooding schemes on established alfalfa fields. Results suggest a minimal effect on yield when dormant alfalfa fields on highly permeable soils are subject to winter flooding. On the other hand, some crops are sensitive even to short-period flooding. Kiwi vines for example, are highly sensitive to root anoxia with reported yield lost and vines death due to extreme rainfalls and/or shallow groundwater levels . In a study on peach trees, flood cycles of 12 h per day with 5 cm ponding, applied for two months, resulted in branches with lower diameter and length growth, as well as smaller, low-quality, fruits, compared to the control trees . The above examples demonstrate the need for an RZRT planning tool that can estimate Ag-MAR flood duration with minimal crop damage. Usually, when Ag-MAR water application starts, aeration of the rootzone will be quickly suppressed by a water-layer covering the soil surface, as it prevents oxygen transport to the root-zone in the gas phase. When water application ceases, re-aeration of the root-zone will depend on the soil’s drainage rate that controls the formation of connected air pores between the root-zone and atmosphere . Hence, proper estimation of the planned flood duration during Ag-MAR requires prior knowledge of both crop characteristics and soil texture. Only a few attempts for estimating RZRT during Ag-MAR were made, as Ag-MAR is a relatively new MAR technique. O’Geen et al. used a fuzzy logic approach to rate the RZRT during Ag-MAR, procona buckets based on the harmonic mean of the saturated hydraulic conductivity of all soil horizons, soil drainage class, and shrink-swell properties. Their RZRT rating was combined with other factors generating a Soil Agricultural Groundwater Banking Index . Flores-Lopez et al. proposed a root-zone model that includes crop type, soil properties, and recharge suitability to estimate water application, flooding duration, and the interval between water applications. Their model was integrated with a Groundwater Recharge Assessment Tool to optimize Ag-MAR water application. Here, we propose a simple model to estimate the planned water application during Ag-MAR based on the following parameters: soil texture; crop saturation tolerance; effective root-zone depth; and critical water content. The concept of critical water content was proposed by several authors as it indicates a percolation threshold where the gas transport path is blocked by pore-water, which results in gas diffusivity and permeability of practically zero. Hence, when the water content is either below or above this threshold, gaseous oxygen transport into the soil is blocked or opened, respectively . As opposed to the previous Ag-MAR models mentioned above, our proposed model is physically based and includes explicitly the soil water content, that is used to infer the soil aeration status. Yet, thanks to its simplicity, this model can be integrated easily into various existing Ag-MAR assessment tools such as SAGBI or GRAT . In the following, we first describe the theory of the model and the methods used to test the model performance. Next, we present the model predictions and compare them with observations and numerical simulations. Last, we present an example of how to calculate Ag-MAR water application duration and we discuss the applicability of the model and its limitations.The potential for warmer temperatures to expand pathogen ranges and alter epidemiology is an important consequence of global climate change for human populations and the environment . Plant pathogens influence large-scale forest mortality events, so understanding their future range and impacts will assist conservation planning . Plant pathogens also impact agricultural production, meaning their response to climate change threatens global and regional food security . Pathogens are sensitive to multiple climatic and environmental factors, as reflected in the ‘disease triangle’ , a conceptual model that states that disease is the outcome of the presence of a virulent pathogen, a susceptible host, and suitable environmental conditions. Theoretical and empirical studies addressing climate change impacts on plant disease tend to focus on individual environmental factors such as temperature , elevated atmospheric carbon dioxide concentrations and water availability , despite the likelihood that climate change will alter temperature, precipitation, potential evaporation, and ecological regimes simultaneously. Retrospective analyses show that multiple environmental drivers and their interactions influence expansion of disease ranges . Understanding these interactions remains an area of outstanding research need . Climatic and edaphic factors could limit Phytophthora cinnamomi range in several ways. First, Pc is sensitive to cold temperatures . Temperatures warm enough to permit survival of Pc may still be cold enough to suppress its ability togrow, reproduce, and cause disease to hosts . Previous modeling studies considering temperature effects on Pc range in Europe suggest the potential for considerable expansion in warming climates . However, Pc growth rates also display a threshold-like response to soil moisture in laboratory conditions.