The phase-out of methyl bromide has proven to be a daunting task for the California strawberry industry. Not only are strawberry producers faced with the likelihood that methyl bromide will no longer be available to them by 2015, but they also must deal with increasing regulatory stringency on the use of all soil fumigants. While fumigants face an uncertain future in California, barrier films can help trap fumigants in the soil and reduce the likelihood of environmental or health impacts associated with fumigants in the atmosphere. It appears very likely in the near future that barrier films will be the only type of film approved for use with fumigants in California.Potential methods of strawberry production that do not use fumigants include growing plants in substrates and using steam treatments or anaerobic soil disinfestation. All of these systems are being evaluated on a much larger scale, from 1 to 10 acres, with different soil types, to determine commercial feasibility and cost effectiveness. It is not likely, nor is it desirable from a pest management perspective, that one nonfumigant system will dominate on a large percentage of the strawberry acreage. Multiple production systems, using fumigants and nonfumigants, would allow producers to rotate treatments to suppress soil pests.Increasing global temperatures coupled States . Long with unpredictable changes in climate term drought in California and other regions threaten food security globally . California has experienced United States has caused growers to abandon extreme drought conditions for several years,macetas de plástico fruit crops and seek alternatives with less causing fruit growers to face water limita- water demand in the short term. Options fortions affecting production and leading to mitigating long term drought in California hundreds of millions of dollars in crop rev- have included crop abandonment, stress irenue losses in 2016 alone .
To lessen the impacts of climate new plantings change and increasing temperatures on food and utilization of lower quality secondary security, it is important to utilize diversified water sources. cropping systems to reduce vulnerability to It has been proposed that physiologists and extreme climatic events as experienced in breeders focus on increasing the efficiency California and other regions of the United of water use in agriculture . Improving production efficiency and drought tolerance through cultivar or variety selection has been proposed in tree crops, such as citrus Prunus species , dates , and coffee . Because tree crops can have a considerable amount of variability in terms of physiological traits, it is useful to study diversity in crop species to determine if there are cultivars that use water more efficiently or are able to be productive in stressful conditions. Because pomegranate is a drought tolerant crop, especially once established , it is a candidate crop for growers wishing to switch from more water intensive species, such as avocado, citrus or almond. Pomegranate is a drought tolerant crop that has been grown in California since the Spanish missionaries arrived from Spain and planted mongrel seeds at missions up and down the coast . The pomegranate variety collection located at the United States Department of Agriculture – Agricultural Research Service National Clonal Germplasm Repository, Davis, CA conserves about 200 genotypes of pomegranate sourced from all over the world, many of which have unique phenotypic traits . Experiments have demonstrated differences in morphology and vegetative growth traits, including differences in relative chlorophyll content, plant vigor, and branching habit, which can be observed during propagation and in the field . Although available literature on pomegranate physiology is scarce, research has shown that there can be differences among cultivars for many physiological traits of pomegranate in other collections, including transpiration rate, stomatal conductance, water use efficiency, photosynthetic rate and chlorophyll content . The objectives of this study were 1) to evaluate four unique pomegranate cultivars for physiological field performance in a semi-arid agroecosystem during morning and afternoon hours; and 2) to determine if there are differences among cultivars for physiological traits that would be conducive to commercial crop production in drought conditions.‘Wonderful’ is the industry standard in many countries and was chosen as a control in the experimental cultivar field trial.
The other cultivars were selected for their unique phenotypes. ‘Eversweet’ is a dwarf-like cultivar bred for coastal climates, with pink fruit peel and aril color, and soft seeds. ‘Haku Botan’ is an ornamental Japanese cultivar that has an upright growth habit with double white flowers and darker green foliage than most other pomegranate cultivars and lacks visible anthocyanin pigments in stem, leaves and fruit. The fruit is very acidic and very light yellow in color. ‘Parfianka’ is an internationally-renowned cultivar that has a bright red peel and arils with soft seeds and a balanced sweet-tart flavor. The tree is extremely thorny and has a bushy, highly branched growth habit with smaller leaves than other pomegranate cultivars. ‘Wonderful’ is commercially widely-grown, and in the USA it accounts for approximately 90- 95% of production. It is a highly vigorous, thorny tree that has high yield with red fruit and red seeds with moderate seed hardness and a sweet-tart flavor. The growth habit is willowy, with a tendency to sucker at the base of the tree. Photosynthesis measurements. During fruit development , an infrared gas analyzer was used to measure maximum rates of net CO2 assimilation , stomatal conductance , and transpiration during the morning and afternoon . Morning photosynthetically active radiation ranged from 1500-1600 µmol m-2·s-1 photosynthetic photon flux density , while afternoon PAR was 1990 µmol m-2·s-1 PFD. Morning measurements were pooled for the four cultivars, which occurred on 22, 23 Aug. 2015 and 26 June 2016. Afternoon measurements were taken on 30 June 2016, which was representative of a typical summer afternoon in Riverside . Gas exchange characteristics were measured on two leaves per tree and a minimum of three trees per cultivar. All leaves were collected for leaf area, which was quantified on a leaf area meter to normalize photosynthesis data . Only the most recently fully-formed, sunexposed leaves were selected for this study. Cuvette temperatures were allowed to vary with field conditions. Leaves were measured in a chamber that provided 1500 µmol m-2·s-1 . Instantaneous water-use efficiency was calculated as A·E-1 and intrinsic water use efficiency was calculated as A·gs -1. Stem water potential measurements. Predawn and midday stem water potential measurements were recorded for each data tree. For predawn water potential, non-actively growing shoots were covered with a plastic bag for 10 min before being pruned, placed in a sealed plastic bag and kept in a cooler bag until transferred to an indoor environment for plant moisture stress measurements with a pressure chamber .
For afternoon stem water potential measurements, canopy-shaded nonactively growing shoots were covered with a plastic bag for 10 min before being pruned, placed in a sealed plastic bag and kept in a cooler until immediately transferred to a cool lit, indoor environment. Stem water potential was immediately measured after being removed from the cooler bag. One stem was measured from three individual trees per cultivar, for a total of three trees, for predawn and midday stem water potential. Statistical analysis. All variables were analyzed with Analysis of Variance . When ANOVA indicated significant differences, post-hoc comparisons were performed utilizing Tukey’s honestly significant difference with an experiment-wise type 1 error rate of α = 0.05. Relationships between all variables were analyzed using linear regression , with relationships among parameters determined using general regression with Minitab Software, version 16 . Block was coded as a random effect and interaction terms were included in the models. For the purposes of this work, the R2 value is the proportion of variation in one variable that is explained by the variation in the regressor variable. Regression models were fit to determine differences in slope coefficients and constants among variables. The focus of this review is on water use and water recycling in container-grown production of greenhouse and nursery specialty crops. The majority of information and insights in this review also have applicability to containerized edible crops grown in open air or under protected culture. In container-grown crop production, water application frequency varies from multiple times per day to once every few days depending on the production system, crop producer, growing season, and environmental conditions, such as rainfall. Use of containers has grown in popularity with nursery growers over the past 50 years because crops can be produced more rapidly and economically and the root zone is easier to modify when compared with field production . Ruter showed that total biomass increased by 27% by growing Betula nigra under pot-in-pot conditions compared with above ground container production,cultivo del frambueso which was likely due to more favorable root zone conditions. Container-grown plants also weigh less and therefore are easier to move and ship, allowing more flexibility at an operation and improving shipping efficiency. Containerization allows growers to sell plants throughout the year regardless of soil conditions or plant growth stage, which increases productivity per unit area. Field operations typically apply lower rates of fertilizer and water on a per meter or per hectare basis compared with container production because soil matrices are typically more chemically and water buffered . Field production also has wider plant spacing compared to both container production in nurseries and greenhouses . As inventories are sold, containerized plants can be consolidated to make room for additional plants, while field operations cannot be consolidated. This greater density of ornamental container-grown crop production results in both higher revenue and increased material and input costs compared with field production. Irrigation must be applied more frequently in containerized production systems compared to field soils, because plant available water is lower within containers filled with soilless substrates, which have high porosity and restricted root volumes . Any water, or agrichemicals applied in excess of the capacity of the container, are unable to be utilized by the plant, or fall outside of the container will likely leach and run off and may eventually impact surface water and groundwater .
Concerns persist that as runoff leaves an operation, sediment and agrichemical contaminants will also be exported . Some growers capture and reuse all or a portion of production runoff, whereas other growers allow runoff to drain from their operations to the surrounding ecosystem. Grower hesitation to capture and reuse runoff can usually be attributed to a reluctance to change practices because of concerns about the opportunity cost of lost production area, installation costs of containment and treatment systems, management costs for treatment technology, reintroduction of disease-causing organisms or plant growth regulators, phytotoxicity of reintroduced pesticides, or land characteristic restrictions . In this review, we will discuss these challenges, as well as potential solutions to these issues and limitations Greenhouses are typically characterized as covered or enclosed systems with the capacity to control environmental factors that impact plant growth, including temperature, humidity, irrigation, and light. Operation sizes typically range from a few hundred square meters to 5 ha but can exceed 10 ha. Greenhouse operations tend to be highly intensive production systems on a per unit area basis, but due to smaller container sizes are typically smaller than container-nursery operations. They typically use precise irrigation applications and can have a high degree of environmental monitoring and control. Thus, greenhouse operations typically require less water per unit area than open-air container or pot-in-pot nurseries . This higher degree of control capability can lead to higher distribution uniformity and water use efficiencies. However, efficiencies also depend on irrigation application method , application decisions , and system design and maintenance. The typical higher efficiency irrigation used in greenhouse operations requires higher-quality water and regular maintenance to avoid emitter clogging and subsequent plant loss or damage. Nursery container operations place containers at or below ground level . Plants are grown on various combinations of bare ground, gravel, landscape fabric, or other surfaces that are often graded to reduce standing water directly below containers. Nursery container operation sizes can vary from less than a hectare to thousands of hectares. Irrigation is typically applied overhead using impact sprinkler heads or similar-type heads. Larger containers are often irrigated using micro-irrigation via drip emitters or spray stakes. Although micro-irrigation is more labor intensive to maintain, the necessity of wider plant spacing due to canopy size makes overhead irrigation inefficient due to wind drift and decreased interception efficiency .