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Mark Gaskell

Organic vegetable production acreage is expanding in California, but little research-based information is available to guide growers. Several new organic fertilizer materials are available but little data exists on efficient use of these materials. During 1998, the following materials: compost (C), pelleted chicken manure (PCM), fish meal (FM), liquid fish (LF), liquid soybean meal (LSM), feather meal (FTM), and seabird guano (SG) were evaluated. Each material was applied at treatment rates of 0, 60, 120, and 180 kg nitrogen (N)/ha to transplanted, sprinkler irrigated bell peppers. The materials were applied as 30N pre-transplant (PRE) and 30N at 20 days post-transplant (POST) for the 60N treatment; 60N PRE and 30N at 20 days POST and 30N at 40 days POST for the 120N treatment; and 60N PRE, 30N at 20 days POST, 45N at 40 days POST, and 45N at 70 days POST for the 180N treatment. Weekly soil nitrate nitrogen (SSN) over 16 weeks POST and fresh pepper yield was determined for all treatments. Weekly SSN varied from lows of 4 mg·kg-1 in 0N-treated plots to over 80 mg·kg-1 in FTM 180N-treated plots. Highest SSN was observed in FTM-, SG-, LSM-, LF-, and FM-treated plots at 180N and peaks in SSN lagged fertilizer application 3 to 4 weeks. Total pepper yield was not as markedly affected as early yield and size. Highest early yield and largest sizes were observed in FTM 180N-treated plots. Compost treated plots at 180N produced highest economic return per fertilizer dollar.

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Mark Gaskell and Rachel Grande

Fertilization is the most expensive cultural practice for increasing numbers of organic vegetable growers in California. Nitrogen (N) is the most important and costly nutrient to manage and cost-effective N management practices are needed for efficient organic vegetable production. Compost and green manure cover crops are widely used, economical sources of N for organic vegetable production, but the pattern of release from these pre-plant incorporated N sources may not adequately match crop need for N. Additional application of an organic N fertilizer material is needed to provide adequate N to long-season vegetable crops. Seven types of organic fertilizers–feather meal (13% N), blood meal (14% N), liquid fish waste (6% N), a micronized liquid feather meal (4% N), a micronized feather/blood meal (13% N) for injection as a liquid suspension, and the two micronized materials with an added microbial inoculant—were each applied to fall cabbage at N rates of 0, 90, 180 lb/acre. Weekly residual soil nitrate N (SNN) was proportional to applied N rate much of the season and varied from 5 to over 70 ppm. Marketable yield ranged from 8000 to 33,300 lb/acre. The SNN was highest in plots receiving the liquid fish waste most weeks, and marketable cabbage yield was also highest following application of N as liquid fish waste at 180 lb/acre. A positive marketable yield response to increasing rates of applied N was also observed for the other organic N materials.

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Mark Gaskell and Tim Hartz

Nutrient management practices must be tailored to the crop, environment, and production system if nutrient efficiency and environmental water quality protection are to be achieved. This requires consideration of fertilizer choice, placement, application rate, and timing. These factors have been characterized as the “4Rs” of nutrient stewardship—right material, right placement, right rate, and right timing. The factors affecting the choice of fertilizer material have been described previously for agronomic crops, and include plant nutritional requirements, soil conditions, fertilizer delivery issues, environmental risks, product price, and economic constraints. Although those factors are applicable to all crops, the unique features of intensive horticultural production systems affect their interactions. This article discusses fertilizer choice as it affects productivity, profitability, sustainability, and environmental impact of intensive horticultural crop production. Diverse fertilizer materials are available for specialized application to provide nitrogen, phosphorus, potassium, and other plant nutrients for different horticultural needs. These fertilizer sources can be formulated as dry or liquid blends, but increasingly higher solubility materials are used to target plant growth needs even in field operations. Composts can have useful applications—particularly for certified organic production—but their high cost, bulk, and relatively low efficiency limit their use. Profitability can be affected by fertilizer cost—typically a relative small percentage of overall costs in intensive production systems—and the improved efficiency of these specialized materials often improves profitability. There are also sustainability issues with the manufacture, transport, and efficient use of different fertilizer sources. Such factors as soil chemical reaction changes, effects on soil salinity, and loss of organic matter also can adversely affect sustainability, but systems are available to maintain soil quality while using more efficient fertilizer sources.

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Mark Gaskell and Richard Smith

Fertilization is the most expensive cultural practice for the increasing numbers of organic vegetable growers in the United States. Nitrogen (N) is the most important and costly nutrient to manage, and cost-effective N management practices are needed for efficient organic vegetable production. There is a wide array of organic N sources available, but they vary in cost, N content, and N availability. Compost and cover crops are commonly used sources of N for vegetables because they are relatively inexpensive and offer additional nutrients or soil improvement qualities in addition to N. Studies have shown that compost quality factors that affect N mineralization vary by source and among different batches from the same source. Compost carbon to N ratio should be equal to or less than 20:1 to assure net short-term mineralization. Cover crops also vary in N content and mineralization rate after incorporation. Leguminous cover crops decompose and release N more rapidly than grass or cereal cover crops at the preheading stage typically incorporated. Even the most efficient N-supplying composts, cover crops, or other organic N sources do not release appreciable N to a subsequent crop beyond 6 to 8 weeks from incorporation, and this burst of early N may not synchronize with N requirements for many vegetable crops. Other potential organic fertilizer N sources have been evaluated for vegetables, and they vary in N cost and N mineralization rate. Materials evaluated include seabird guano, liquid fish, feather meal, corn meal (Zea mays), blood meal, and liquid soybean meal (Glycine max) among others. Of those evaluated, feather meal, seabird guano, and liquid fish stand out as more economical organic sources of available N. Organic sources generally lack uniformity and are bulky, unstable, and inconsistent as a group, and this contributes to additional hidden management costs for organic growers. Liquid organic N sources for use in microirrigation systems may have additional disadvantages caused by loss of valuable nutrient N that is removed by filters.

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Elizabeth Mitcham, William Biasi, Mark Gaskell, Ben Faber, and Ramiro Lobo

Blueberry fruit were harvested at commercial maturity from variety trials and shipped overnight to UC Davis. Fruit quality was evaluated upon receipt and after 6 and 20 days of cold storage at 0.5 °C in air shelf life. Firmness, external color, soluble solids, and titratable acidity were measured. Sensory evaluations were conducted by trained tasters to rate the blueberries for crispness, mealiness, sweetness, tartness, blueberry flavor, and off-flavors at harvest and again after 21 days of storage. Many of the blueberries increased in firmness during cold storage. Firmness at harvest tended to be softer in `Santa Fe' and `Jewel' and firmer in `Star'. Sensory data also found `Sharpblue' and `Southmoon' to be more firm; however the objective measurements did not agree. Overall, `Saphire' was low in sugars and acids, and `Jewell' and `Star' were high in acids. `Misty' and `Sharpblue' were consistently high in sugars and acids. Overall objective fruit quality ratings were highest for `Misty', `Sharpblue', and `Southmoon', and lowest for `Santa Fe'. Blueberry flavor was rated highest in `Jewell', `Star', and `Sharpblue', and lowest in `Santa Fe', `Saphire', `Misty', and `Emerald'. These data indicate that blueberry flavor may be closely tied to acid content, as most of the high-flavor varieties had high acid and many of the low-flavor varieties had low acid. Over 3 years, the varieties consistently rated highest for overall objective quality were `Misty' and `Southmoon'. `Star' was rated high for overall quality in 2 years and moderate in 1. `Jewell', `Star', and `Sharpblue' were rated highest in flavor. `Santa Fe' was ranked low in flavor quality in 2 out of 3 years. Selection of variety appears to have a strong influence on the sensory quality of the blueberries marketed.

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P. DeCarli, F. Rivera, W. Brown, and Mark Gaskell

Coastal California vegetable growers produce a wide range of specialty crops for diverse domestic and export markets. Vegetable-type soybean (Glycine max L.) cultivars are grown and consumed fresh in many parts of the world, but particularly in Japan and Asia, where they are known as edamame. Traditional soybean maturity group classification may not be applicable for fresh-market edamame, particularly in mild coastal California growing conditions. We evaluated a total of 55 vegetable soybean cultivars during the 1998 growing season from maturity groups ranging from group 00 to group VI. Replicated field plots were planted on 30-31 May 1998 in San Luis Obispo, Calif. (lat. 35.12°N.). Cultivars from maturity Groups 00 and I began producing on 4 Sept., followed in 7 to 10 days by maturity Group II and III, and by harvest of maturity Group III and IV cultivars on 19 Sept. Harvest of Group IV cultivars continued until 24 Oct. Percent marketable (two- and three-seeded) pods ranged from 86% to 17% among the cultivars. Marketable yields ranged more than 15-fold, with cultivars such as `Sapporo Midori', a group 00 cultivar popular in Japan, producing 348 g/plant, to cultivars such as `Early Hakucho' and `Envy' producing 20 and 5 g plant, respectively.

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Thomas G. Bottoms, Mark P. Bolda, Mark L. Gaskell, and Timothy K. Hartz

Diagnosis and recommendation integrated system (DRIS) leaf blade and petiole optimum nutrient ranges were developed through tissue sampling in 53 commercial strawberry (Fragaria ×ananassa) fields in the coastal valleys of central California in 2010 and 2011. All fields were in an annual production system using the day-neutral cultivar Albion. Leaf blades and petioles were sampled five times from early flowering through the fruit harvest period. Data on soil nutrient availability and grower fertilization practices were also collected. DRIS analysis was used to develop nutrient optimum ranges based on nutrient concentrations observed in nutritionally balanced, high-yield fields. Blade nitrogen (N), phosphorus (P), and potassium (K) concentrations declined from the vegetative stage until the main harvest period, and stabilized thereafter. Blade calcium (Ca), boron (B), and iron (Fe) increased over time while magnesium (Mg), sulfur (S), manganese (Mn), zinc (Zn), and copper (Cu) decreased. The blade N optimum range was lower than previously published sufficiency ranges during the fruit harvest period, and the Zn optimum range was lower throughout the season. Other nutrients were in general agreement with previously established sufficiency ranges with the exception of Ca, Mn, and Fe, which were higher. Petiole nitrate-nitrogen (NO3-N) was highly variable among high-yield fields, was not correlated with soil NO3-N at any growth stage, and was therefore of limited value as an indicator of crop N status. Comparison of soil nutrient availability with grower fertilization practices suggested that significant improvement in fertilizer management was possible.

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Mark Gaskell, Benny Fouche, Steve Koike, Tom Lanini, Jeff Mitchell, and Richard Smith

This article summarizes the current status of organic vegetable production practices in California. The production of vegetables organically is growing rapidly in California, led in large part by growth in the market demand for organically grown produce. Key aspects of organic vegetable production operations such as certification and farm production planning, soil management, weed management, insect management, and plant disease management involve special practices. Many practices have not been thoroughly researched and the scientific base for some practices is still being developed.

Open access

Oleg Daugovish, Mark Gaskell, Miguel Ahumada, and Anna D. Howell

Increased productivity of recently developed primocane raspberry (Rubus idaeus) and blackberry (Rubus sp.) cultivars have been accompanied by dramatic improvements in fruit firmness, shape, size, color, and flavor. These traits have contributed to the establishment of these crops throughout California. In this study, we evaluated publically available raspberry and blackberry cultivars for fruit yields, postharvest quality, and production in response to pruning management, at two locations in the central coast of California. Among raspberries, ‘Imara’ and ‘Kweli’ were the highest yielding cultivars at both trial locations while ‘Kwanza’ produced 30% to 50% larger fruit, by weight, with postharvest shelf life superior to that of ‘Vintage’. Among blackberries, ‘Prime-Ark® 45’ was the top-yielding cultivar and had the largest fruit at both locations during both years. ‘Prime-Ark® 45’ and ‘Prime-Ark® Traveler’ had comparable weights after 13 days in cold storage in 2018, while in 2019 ‘Prime-Ark® 45’ and ‘APF 268T’ had comparable fruit weight. Greater and earlier fruit yields of both blackberries and raspberries were obtained with combined production from floricanes and primocanes compared with primocane production alone. However, increase in cane density in combined production can complicate management of pests, fertigation, and fruit harvest efficiency. With increased interest in primocane cultivars, the information generated in this study has provided new resources to guide successful production by small, independent, and direct-sale growers.