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In recent years, vegetable growers on the central coast of California have come under increasing regulatory pressure to improve nutrient management and reduce nitrate losses to ground and surface waters. To achieve this goal, growers must understand the nutrient uptake and water use characteristics of their crops. For fresh market spinach (Spinacia oleracea), production methods and cultivars have greatly changed in the last 10–15 years, and as a result, few publications are available on nutrient uptake by modern spinach production methods. This study evaluated nutrient uptake and water use by spinach to provide strategies to better manage nitrogen (N) fertilizer and irrigation applications. In 2011, four fertilizer trials and a survey of 11 commercial fields of spinach grown on high-density plantings on 80-inch beds were conducted on the central coast of California. During the first 2 weeks of the crop cycle, N, phosphorus (P), and potassium (K) uptake was 7.0, 0.6, and 7.2 lb/acre, respectively. In the subsequent 2–3 weeks before harvest the N, P, and K uptake rate was linear and was 4.3, 0.6, and 7.8 lb/acre per day, respectively. N uptake at harvest for the three commercial size categories baby, teenage, and bunch was 74, 91, and 120 lb/acre N, respectively. Of the N in aboveground biomass at harvest, 41% was left in the field following mechanical or hand harvest. Growers at 14 of 15 study sites applied on average 111% more N than was taken up in aboveground biomass at harvest. Results from four fertility trials showed that first crops of the season had low initial soil nitrate concentrations (≤10 ppm), and an at-planting fertilizer application was necessary for maximum yields. For fields following a previous crop (second- or third-cropped) with initial soil nitrate concentrations >20 ppm, at-planting and midseason fertilizer applications could be greatly reduced or eliminated without jeopardizing yield. Rooting depth and density evaluations at four sites showed that 95% of roots were located in the top 16 inches of soil at harvest. To mitigate environmentally negative N losses, the N use efficiency (NUE) can be increased by the use of soil testing done at two critical time points: at-planting and before the first midseason fertilizer application.

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Strawberry (Fragaria ×ananassa Duch.) production in California uses plastic mulch–covered beds that provide many benefits such as moisture conservation and weed control. Unfortunately, the mulch can also cause environmental problems by increasing runoff and soil erosion and reducing groundwater recharge. Planting cover crops in bare furrows between the plastic cover beds can help minimize these problems. Furrow cover cropping was evaluated during two growing seasons in organic strawberries in Salinas, CA, using a mustard (Sinapis alba L.) cover crop planted at two seeding rates (1× and 3×). Mustard was planted in November or December after strawberry transplanting and it resulted in average densities per meter of furrow of 54 and 162 mustard plants for the 1× and 3× rates, respectively. The mustard was mowed in February before it shaded the strawberry plants. Increasing the seeding rate increased mustard shoot biomass and height, and reduced the concentration of P in the mustard shoots. Compared with furrows with no cover crop, cover-cropped furrows reduced weed biomass by 29% and 40% in the 1× and 3× seeding rates, respectively, although weeds still accounted for at least 28% of the furrow biomass in the cover-cropped furrows. These results show that growing mustard cover crops in furrows without irrigating the furrows worked well even during years with relatively minimal precipitation. We conclude that 1) mustard densities of ≈150 plants/m furrow will likely provide the most benefits due to greater biomass production, N scavenging, and weed suppression; 2) mowing was an effective way to kill the mustard; and 3) high seeding rates of mustard alone are insufficient to provide adequate weed suppression in strawberry furrows.

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High levels of residual soil nitrate are typically present in cool-season vegetable fields in coastal regions of California in the fall, after the production of multiple crops over the course of the growing season. This nitrate is subject to leaching with winter rains when fields are left fallow. Although the benefits of growing nitrate scavenging cover crops on soil and water quality are well documented, the portion of vegetable production fields planted to winter cover crops in this region is low. Most growers leave their fields unplanted in bare-fallow beds because the risk of having too much cover crop residue to incorporate may delay late winter and early spring planting schedules. A possible strategy to derive benefits of a cover crop yet minimize the amount of residue is to kill the cover crop with an herbicide when biomass of the cover crop is still relatively low. To evaluate whether this strategy would be effective at reducing nitrate leaching, we conducted field studies in Winter 2010–11 (Year 1) and Winter 2011–12 (Year 2) with cereal rye (Secale cereale). Each trial consisted of three treatments: 1) Fallow (bare fallow), 2) Full-season (cover crop allowed to grow to full term), and 3) Partial-season (cover crop killed with herbicide 8 to 9 weeks after emergence). In Year 1, which received 35% more rainfall than the historical average during the trial, the Full-season cover crop reduced nitrate leaching by 64% relative to Fallow, but the Partial-season had no effect relative to Fallow. In Year 2, which received 47% less rainfall than the historical average during the trial, the Full- and Partial-season cover crops reduced nitrate leaching by 75% and 52%, respectively, relative to Fallow. The Full-season cover crop was able to reduce nitrate leaching regardless of yearly variations in the timing and amount of precipitation. Although the Partial-season cover crop was able to reduce leaching in Year 2, the value of this winter-kill strategy to reduce nitrate leaching is limited by the need to kill the crop when relatively young, resulting in the release of nitrogen (N) from decaying residues back into the soil where it is subject to leaching.

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Abstract

Total weight loss of < 10% over a 10-week period was achieved by storing celery in atmospheres containing 1% O2 combined with 2% or 4% CO2 at 0°C. Significant increases in marketable celery resulted when C2H4 was scrubbed from some atmospheres. A combination of 1% or 2% O2 and 2% or 4% CO2 prevented black stem development during the storage period. Improved visual color, appearance, flavor, and increased marketable celery justifies the use of 4% CO2 in celery storages.

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Rapid posttransplant root growth is often a determining component of successful establishment. This study tested the effect of transplant timing on first-season root growth dynamics of bare-root Turkish hazelnut trees. Trees were either harvested and planted in the fall (F-F), harvested in the fall and planted in the spring after holding in refrigerated storage (F-S), or harvested and planted in the spring (S-S). All trees were transplanted into 51-L containers, adapted with root observation windows. Root growth began in F-F and F-S trees 1-2 weeks before spring budbreak, but was delayed in S-S trees until ≈3 weeks after budbreak. Budbreak was 6 days earlier for fall-harvested than for spring-harvested trees. No new roots were observed before spring. Root length accumulation against observation windows (RL) was delayed for S-S trees, but rate of increase was similar to F-F and F-S trees soon after growth began. Seasonal height, trunk diameter growth, and RL were similar among treatments. Surface area of two-dimensional pictures of entire rootballs was not correlated with seasonal RL.

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Abstract

A mathematical analysis of optimum locations for frozen green pea processing was conducted. Inputs to the model included: raw product costs, procurement costs, economies of scale in freezing and freezer storage, labor costs, fuel and electrical costs, state, local and federal taxes, length of the pea processing season, length of the total processing season, weighted regional consumption by state, and transportation costs to market centers (states). Analytical procedures used Stollsteimer’s method for number and sizes of plants combined with a transhipment model to compare regions.

The results suggest that the numbers of processing plants within an area are significantly less important than cost differentials between areas. The models developed were sensitive to changes in many costs – raw product costs, wage rates, length of season, allocation of overhead, freight costs, and in some states, state and local taxes.

The optimum solution called for a few large plants in each of the Eastern, Midwestern and Western regions. The Washington-Oregon-Idaho complex would predominate with approximately 59 percent of total production, followed by Maryland-Delaware with 14 percent and Wisconsin with 10 percent.

Open Access

Growers in the Salinas Valley are not able to rotate away from lettuce to other crops such as broccoli, as often as would be desirable due to economic pressures such as high land rents and lower economic returns for rotational crops. This aggravates problems with key soilborne diseases such as Sclerotinia minor, Lettuce Drop. Mustard cover crops (Brassica juncea and Sinapis alba) are short-season alternative rotational crops that are being examined in the Salinas Valley for the potential that they have to reduce soilborne disease and weeds. Mustard cover crops have been have been shown to suppress various soilborne diseases and there are also indications that they can provide limited control of some weed species. However, no studies have shown the impact of mustard cover crops under field conditions on S. minor. In 2003 we conducted preliminary studies on the incidence of S. minor and weeds following mustard cover crops in comparison with a bare control or an area cover cropped to Merced Rye (Secale cereale). There was a slight, but significant reduction of S. minor infection in one of three trials following mustard cover crops. Mustard cover crops also reduced emergence of Shepherd's Purse (Capsella bursa-pastoris) and Common Purslane (Portulaca oleracea) these studies. Mustard cover crops have distinct nitrogen cycling characteristics. They were shown to reach a peak of release of nitrogen in 30 to 50 days following incorporation into the soil. The levels of nitrogen that are released by mustard cover crops were substantial and could be useful in nitrogen fertilizer programs for subsequent vegetable crops.

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Lettuce growers in the Salinas Valley are often not able to rotate to other crops due to economic pressure, such as high land rent. Winter-grown cover crops (October to March) provide a short-term rotation from lettuce and have been shown to reduce nitrate leaching by 75%. However, the use of winter-grown cover crops is low due to the extended time these cover crops tie up the ground. As a result, growers are interested in the potential of fall-grown cover crops (September to October) to reduce nitrate leaching through the winter. Fall-grown cover crops are incorporated into the soil prior to the onset of winter rains and leave the soil bare over the winter; however, during fall growth, the cover crop has the potential to capture excess nitrate that may leach during the fallow period, but how much has not been previously measured. A long-term trial was established in Fall 2003 using treatments of Indian mustard (B. juncea) `ISCI 61', White mustard (S. alba) `Ida Gold', Cereal rye (Secale cereale) `Merced', and a no cover crop control. All cover crops contained ≈224 kg·ha-1 N upon incorporation. Anion resin bags were installed 90 cm deep in the soil following incorporation to trap leaching nitrate; they were left in place until planting of the lettuce the following spring. First-year results indicated that the mustard cover crops and `Merced' rye all reduced nitrate leaching to the 90-cm depth by 67% to 82% over the bare fallow treatment. These results indicate that fall-grown cover crops have the potential to reduce nitrate leaching in lettuce production systems in the Salinas Valley.

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Hops (Humulus lupulus) is a perennial, herbaceous crop cultivated for its strobiles, or cones, which contain a resinous compound used for flavoring and aroma in food, tea, and beer. The United States is the second largest global producer of hops with greater than 15,000 ha in production. Increased demand for hop products has recently resulted in production of hops in nontraditional production areas (non-Pacific northwest U.S. region). To examine cultivation potential of hops within the southeastern United States, 60 hop rhizomes consisting of four varieties were transplanted into native, deep sand soil (Candler and Tavares-Millhopper soil series) within a protected, open-sided greenhouse and evaluated for growth, strobile yield, and brewing values for a period of 2 years. Plant bine length was recorded weekly for 20 weeks throughout year 1 with mean bine lengths of 609, 498, 229, and 221 cm at harvest for ‘Chinook’, ‘Columbus’, ‘Amalia’ and ‘Neo1’, respectively. Mean harvested strobile dry weight recorded for year 1 was 21.2, 17.9, 9.0, and 8.2 g/plant for ‘Columbus’, ‘Chinook’, ‘Neo1’ and ‘Amalia’, respectively. With the exception of ‘Neo1’, mean strobile mass was lower for all cultivars during year 2 with 16.6, 10.3, 25.8, and 2.6 g/plant for ‘Columbus’, ‘Chinook’, ‘Neo1’ and ‘Amalia’, respectively. Alpha acid concentrations by percentage strobile mass for year 1 were 6.8%, 9.7%, 3.8%, and 4.3% for ‘Columbus’, ‘Chinook’, ‘Amalia’, and ‘Neo1’, respectively. Alpha acids varied year 2 with concentrations of 4.8%, 10.4%, and 5.6% for ‘Columbus’, ‘Chinook’, and ‘Neo1’, respectively. Findings support viability of hop production in the southeastern United States and establish the benchmark for future varietal trialing investigations.

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Intensive production of cool-season vegetables has contributed to nitrate pollution of groundwater along the central coast of California. Broccoli (Brassica oleracea L. var. italica), cabbage (Brassica oleracea L. var. capitata), and cauliflower (Brassica oleracea L. var. botrytis) are important crops in this region, but few data are available regarding the nitrogen dynamics of these cole crops under current production practices, and whether those practices are protective of groundwater. Monitoring was conducted in 14 commercial broccoli, 8 cabbage, and 8 cauliflower fields evaluating crop growth, rooting depth, N uptake and partitioning, patterns of soil N availability, and current N fertilization and irrigation practices. Aboveground biomass N at harvest averaged 367, 367, and 319 kg·ha−1 for broccoli, cabbage, and cauliflower, respectively, with mean N fertilization rates of 209, 280, and 256 kg·ha−1. The relatively small fraction of biomass N removed at harvest with cauliflower (23%) and broccoli (31%) resulted in a low partial N balance (PNB) of 30% and 57%, respectively, compared with cabbage (PNB of 70%). Rooting depth increased throughout the growing season, reaching ≈1 m by harvest, with about 70% of roots located in the top 40 cm in all crops. Soil mineral N (SMN; 0- to 30-cm depth) varied among fields, with the early-season median value of 18 mg·kg−1 declining to 5 mg·kg−1 by harvest. Seasonal N application was not correlated with early-season SMN. Irrigation applied, predominately through sprinklers, averaged >200% of estimated crop evapotranspiration. Substantial N mineralization from broccoli residue was observed within 2–3 months following fall incorporation, with potential NO3-N leaching losses exceeding 100 kg·ha−1 in both monitored fields. We conclude that improved irrigation management, adjusting N rates based on residual SMN, and employing a remediation practice such as cover cropping to limit winter NO3-N leaching losses could substantially improve N efficiency in cole crop production.

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