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  • Author or Editor: Alberto Pardossi x
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Intensive vegetable cropping systems use large amounts of water and nutrients. Excess application of water and nutrients results in economic losses (higher fertilizers and pumping costs) and contributes to nutrient leaching and environmental degradation. Increasing nutrient use efficiency (NUE) and water use efficiency (WUE) should be a priority for sustainable horticulture. This increased NUE, WUE, or both depend on the utilization of efficient irrigation technology, including appropriate methods for irrigation scheduling (IS).Various methods are available for IS based on determination of crop water balance (weather-based method), soil/substrate moisture level, or plant water relations. Rather than discussing the physical and biological basis of irrigation management, this article focuses on currently available irrigation control devices for open-field and greenhouse production systems, with particular emphasis on soil moisture sensors (SMSs). SMS regulates the frequency of irrigation and, possibly, the water dose by continuously monitoring volumetric water content (θ) or matrix potential (ψ m) of the growing media. A new generation of dielectric SMS has been developed to measure both θ and the electrical conductivity (EC) of pore water in soil and artificial media. This provides the possibility of controlled fertigation based on measured EC. Despite the development in IS, in most regions worldwide, especially in less developed countries, many growers still rely on personal experience for determining crop water requirements and the timing of irrigation. Therefore, the main constraints to the improvement of irrigation efficiency are related to the overall cost of these technologies and to the policies adopted for their dissemination and transfer to professional growers.

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Primed, pregerminated, or nontreated seeds of bell pepper (Capsicum annum L.) `Early California Wonder' were grown in controlled conditions for 14 days in glass tubes containing a gel medium. The number of basal roots (one per plant), lateral roots (one per plant), and taproot length (64 mm) did not differ between seed treatments 14 days after seeding. Roots of seedlings from nontreated seeds weighed more than seedlings from primed seeds, and the seedlings had smaller shoot: root ratios than those from pregerminated or primed seeds. Seedlings from pregerminated seeds had heavier and taller shoots than seedlings from nontreated or primed seeds. Taproot length from 1 to 6 days after radicle protrusion increased linearly for all seed treatments. Seedlings from pregerminated seeds initially had longer taproots but had slower linear taproot growth up to 6 days after seeding than seedlings from nontreated or primed seeds.

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Bell peppers (Capsicum annuum L. `Early California Wonder') were seeded in glass tubes on agar-based media adjusted to pH 4.1, 5.9, or 7.3 to evaluate germination, emergence, shoot growth, and root morphology for 16-day-old seedlings. Taproot lengths were measured daily from 1 to 10 days following radicle protrusion. Time from seeding to germination (radicle protrusion) differed by only one-half day among pH treatments. Peppers in a pH 5.9 medium emerged (fully expanded cotyledons) 1 day earlier than plants grown in media at pH 4.1 or 7.3. Plants grown in a pH 5.9 medium had higher shoot and root weights and longer stems than plants grown at pH 4.1 or 7.3. Shoot: root ratios were similar regardless of medium pH. However, taproot growth rate from 1 to 10 days after radicle protrusion was faster for plants grown in a pH 5.9 than in a pH 4.1 or 7.3 medium. On average, there was one basal and one lateral root per plant and they were minimally influenced by pH. The data suggest that acidic or alkaline media adversely affect early shoot and taproot development of bell peppers, but with minimal influence on time to germination or emergence, and on subsequent lateral and basal root initiation.

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Bell peppers (Capsicum annuum L. ‘Early California Wonder’ and ‘Yolo Wonder’) were grown for 14 and 22 days in glass tubes with agar supplemented with 87.6 mm (30 g·liter–1) sucrose or without sucrose, respectively, under controlled conditions. Taproot length increased rapidly for 6 days after radicle protrusion, but its growth rate was reduced during the next 4 days for both cultivars in each medium. Basal and lateral roots emerged 5 and 6 days after germination, respectively, or just after cotyledons were expanded fully for both cultivars in either medium. However, ‘Early California Wonder’ produced basal and lateral roots 9 days after germination in agar medium without sucrose. The number of lateral roots did not increase between 6 and 10 days after radicle protrusion in agar medium without sucrose. However, emergence of lateral roots was pronounced during this period in agar amended with sucrose. Root morphological characteristics, shoot weight, shoot:root ratio, and stem height differed minimally between ‘Early California Wonder’ and ‘Yolo Wonder’. The sequence of root development in bell pepper seedlings was characterized by a) rapid taproot elongation from radicle protrusion to fully expanded cotyledons, b) emergence of basal roots followed by lateral roots when cotyledons were fully expanded, and c) increase in the number of basal and lateral roots numbers particularly in the presence of sucrose and reduction in the rate of taproot elongation. Exogenous sucrose reduced the variability for most measured shoot and root characteristics.

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