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Kevin Charles*, Mathieu Ngouajio and Darryl Warncke

Cover crops are commonly used to improve soil fertility and enhance crop performance. Field experiments were conducted to determine the effects of different cover crops and fertilizer rates on celery growth and development. The experiment was a two-way factorial with a split plot arrangement. The main plot factor was cover crop and included cereal rye (Secale cereale), hairy vetch (Vicia villosa), oilseed radish [Raphanus sativus (L.) var. oleiferus Metzg (Stokes)], and no cover crop. The sub-plot factor was fertilizer rate with three levels: full (160, 80, 400), half (80, 40, 200), and low (80, 0, 0) kg/ha of N, P2 O5, K2 O, respectively. The cover crops were grown during Fall 2002 and incorporated prior to celery transplanting in May 2003. During celery growing season, stalk length, above and below ground biomass were assessed at 23, 43, 64, and 84 days after planting (DAP). The biomass produced by oilseed radish (719 g/m2) exceeded that of cereal rye (284 g/m2) and hairy vetch (181 g/m2). At 23 and 43 DAP, celery fresh root (4.8 and 11.4 g/root) and shoot (6.1 and 53.6 g/shoot) biomass of oilseed radish exceeded the values of all other cover crops. At 84 DAP however, celery shoot fresh weight was similar in all cover crop treatments. Celery plants were tallest in the cereal oilseed radish and rye treatments early in the season; however final plant height at harvest was not affected by type of cover crop. The amount of fertilizer applied had a significant effect on celery growth starting at 64 DAP and continued until harvest. These results suggest that the large biomass produced by oilseed radish played an important role in early season celery growth.

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Gladis M. Zinati

Conventional agricultural systems increase per-area food production, but deplete natural resources and degrade both crop and environmental quality. Many of these concerns are addressed by sustainable agricultural systems, integrated pest management, biocontrol, and other alternative systems. Environmental and social concerns have escalated the need for alternative agricultural systems in the last decade. One alternative, the organic farming system, substitutes cultural and biological inputs for synthetically made fertilizers and chemicals for crop nutrition and pest management. Practices used for crop and pest management are similar during transition from conventional to organic farming systems, but produce is not certified to be organic during the transition period. During the transition from conventional to organic farming, growers may face pest control difficulties and lower yields when conventional practices are abandoned. The objectives of this paper are to 1) give an overview of the reasons for converting to organic farming and the challenges that growers face during the transition period, 2) outline some potential strategies for crop, soil, and pest management, and 3) list guidelines and recommendations for pest management during the transition to organic farming. Implementation of crop and pest management practices depends on geographical location, climate, available onsite resources, and history of the land. During transition, growers rely on cultural mechanisms and on organic and mineral sources to improve soil fertility, to build a population of natural enemies to suppress pest populations. Pest management practices during the transition period that reduce pest populations to economically manageable levels include crop rotation, cultivation, cover crops, mulches, crop diversification, resistant varieties, and insect traps. These practices also enrich the soil biota and increase crop yields before produce is certified organically grown.

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Massimo Tagliavini and Bruno Marangoni

Most deciduous fruit crops in Italy are grown in the north and especially in the eastern part of the Po River Valley (mainly in the Emilia Romagna and Veneto regions) and in the Adige River Valley (South Tyrol and Trento provinces). Soils in the wide Po River Valley, where pear (Pyrus communis), peach and nectarine (Prunus persica), kiwifruit (Actinidia deliciosa), plum (Prunus domestica and P. insititia), apricot (Prunus armeniaca), cherry (Prunus avium), and apple (Malus domestica) are grown, are alluvial, generally fertile, fine textured, alkaline, often calcareous and well enriched with Ca. Apple plantings are concentrated in the Adige Valley and located on a variety of soil types, including sandy loam, loamy sand soils or sandy clay, sometimes calcareous. Integrated fruit production is gaining importance and represents more than 80% of apple production in South Tyrol and about 60% of peach and nectarine production in Emilia Romagna. Under these conditions, the main objectives of mineral nutrition are to reconcile production and environmental concerns (minimize nutrient leaching, soil pollution, volatile emissions). In particular, fertilization aims to improve external and internal fruit quality and storage ability, reduce production costs, maintain soil fertility, avoid nutrient deficiency and excess and control tree vigor. Nitrogen applications have strongly decreased in recent years and there is a need to improve the efficiency of N fertilizers while avoiding deficiencies. Research is focussing on application technology, timing of N uptake, internal cycling of N and methods for assessing the need for N application (e.g., using estimates of native soil N availability). Early diagnosis of bitter pit is recommended for guiding applications of Ca sprays. Iron deficiency and chlorosis is a major problem in pear, peach and kiwifruit grown in alkaline and calcareous soils and Fe chelates are usually applied annually to the soil or to the canopy. Current research is focused on agronomic means for controlling the problem and on developing rootstocks tolerant to Fe deficiency.

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Kathleen Delate and Vincent Lawson

Organic farming has increased to a $6 billion industry in the U.S. and continues to expand 20% annually. In Iowa, organic acreage for all crops has increased from 13,000 in 1995 to 130,000 in 1999. Most organic farmers rely on crop rotations, compost, or manure applications, and cover crops to maintain soil fertility. In our trials at the Iowa State Univ. Muscatine Island Research Farm, a cover crop of hairy vetch (Vicia villosa) and rye was seeded in the fall and incorporated 2 weeks prior to transplanting `Lantern' pepper plants. Other organic and conventional soil treatments were applied at transplanting and at 3 weeks post-planting. Four replications of 40 peppers transplanted at 31 × 61-cm spacing under seven fertilization treatments were observed for plant growth and yields. The fertilization goal was to obtain equivalent nitrogen and calcium rates in the organic and conventional systems. Plants fertilized with the compost at 88 kg/ha N plus BioCal® (a liming industry by-product) were not significantly greater in leaf biomass than plants conventionally fertilized with equal amounts of N. All organic and conventional treatments had greater biomass and yield than the organic and conventional controls (no fertilizer), respectively (P = 0.05). Pepper fresh weight was greater in the vetch-strips treatment than in the vetch-incorporated, and the 44 kg/ha N compost treatment, but significantly less than the conventionally fertilized plants. Second year results demonstrated similar results to the 1998 trial where the greatest yields in the organic system occurred in the compost at 88 kg/ha N plus BioCal® treatment, demonstrating to organic farmers that comparable yields can be obtained in systems employing alternatives to synthetic nitrogen fertilizer.

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Manuel C. Palada, Stafford M.A. Crossman and Allison M. Davis

Chive (Allium schoenoprasum) is one of the most popular culinary herbs in the Virgin Islands, and local demand is always high throughout the year. However, local production is not sufficient to meet increasing demands. Chive production is constrained by insect pests, weeds, and high cost of irrigation water. A study was conducted to compare the influence of organic and synthetic mulches on yield and economic returns from chive production. The study also evaluated the effect of mulch on weeds and water use. Chives were planted in plots consisting of three rows 3.6 m long. Plants were spaced 20 cm within rows 41 cm apart. The plots were mulched with grass straw, wood chips, shredded paper, and white plastic. A control plot (no mulch) was also planted for comparison. Plots were arranged in randomized complete-block design with four replications. All plots were drip-irrigated and soil moisture tension maintaned at 30 kPa. Chives grown with grass straw mulch produced taller plants and higher number of tillers (slips) than all other mulch treatments. Total fresh yield of plots with grass straw mulch was superior to all other mulch treatments including the control. On the average, plots with grass straw mulch produced 1203 g/m2 of fresh chives. All mulches resulted in reduced weed population compared to the control (no mulch). Due to high rainfall during the growing season, differences in irrigation water use were not significant. Economic comparison indicated that the net return above mulch costs was 50% higher with grass straw than with other mulch treatments. To improve production and income, herb growers should consider using grass straw and realize other benefits, including weed control and improved soil fertility.

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Gene E. Lester, John L. Jifon and Gordon Rogers

Muskmelonfruit[Cucumis melo L. (Retiulatus Goup)] sugar content is related to potassium (K)-mediated phloem loading and unloading of sucrose into the fruit. During fruit growth and maturation, soil fertility is often inadequate (due to poor root uptake) to satisfy the demand for K. Potassium uptake also competes with the uptake of Ca and Mg, two essential minerals needed for melon fruit membrane structure, function and postharvest shelf-life. Supplemental foliar-applied K could alleviate this problem especially during the critical fruit growth/maturation period. We conducted experiments to determine the effects of timing of supplemental foliar K applications on fruit quality and health attributes of orange-flesh muskmelon `Cruiser'. Plants were grown in a greenhouse and fertilized with a regular soil-applied N–P–K fertilizer throughout the study. Entire plants, including the fruit were sprayed with a solution of a novel glycine amino acid-complexed potassium (Potassium Metalosate, 24% K), diluted to 4.0 mL·L-1, 3 to 5 d after anthesis (fruit set) and up to 3 to 5 d prior to abscission (full-slip). Three sets of plants were either sprayed weekly, or bi-weekly or not sprayed (control). Fruit from plants receiving supplemental foliar K matured on average 2 days earlier, and had significantly higher fruit K concentrations, soluble solids, total sugars, ascorbic acid (vitamin C), beta-carotene, and were firmer than fruit from control plants. In general, there were few differences in fruit quality aspects between bi-weekly or weekly treatments. The data demonstrate that fruit quality and marketability as well as some of the developmentally induced K deficiency effects can be alleviated through foliar nutrition.

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Victor A. Wegrzyn

Sustainable production systems are characterized as systems that can be physically and biologically maintained in perpetuity, can avoid adverse environmental and health problems, and can be economically profitable. Organic vegetable production systems are one example of sustainable farming enterprises. In California, organic production and postharvest handling techniques are closely defined by legislation. Of the several grower groups representing organic farmers in the state, the California Certified Organic Farmers is the largest, representing 382 growers that farmed a total area of 10,375 ha in 1988. Of these, 200 growers are vegetable producers. Another organization active among organic growers in California, as well as Mexico, Central American countries, and the Caribbean, is the Organic Crop Improvement Association. Marketing organizations such as the Nutri-Clean Program, which tests produce for pesticide residues and certifies specific residue standards, and the Organic Market News and Information Service facilitate the sale of organic produce in California. Cultural practice information for organic vegetable production is difficult to find, particularly techniques that would allow a grower to switch from conventional to organic production. University researchers and extension workers have so far been of little help, although the Univ. of California Sustainability Program at Davis is beginning research and education activities. Funding for these activities is inadequate, and the program is understaffed. There is need for long-term, interdisciplinary, on-farm studies to study organic production techniques in a realistic setting. At present, the reward system in place in land-grant institutions offers little encouragement to researchers to engage in this kind of work. There are formidable obstacles to increasing the use of organic materials for crop fertilization. The nutrient content of the state's manure and organic waste supplies is probably insufficient to meet the fertility needs of California's crops. In addition, since the majority of land currently producing vegetable crops in California is leased, long-term soil fertility investments are a risky undertaking.

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T.J. Radovich, H.R. Valenzuela, B. Kratky and N.V. Hue

To help develop fertilizer recommendations for organic vegetable production in Hawaii, the effects of organic amendments on basil yield were studied in two experiments. The treatments were synthetic nitrogen applied at 100 kg·ha–1 per crop, organic amendments applied at a rate of 8–160 MT·ha–1, and an unammended control. Each treatment was replicated four times in a RCB design. In the first experiment, chicken manure was the organic amendment at 8 MT·ha–1 with a single basil variety grown. In the second experiment, conducted at the same location immediately following the first experiment, the organic amendment was locally produced compost (0.3% N) applied at 40 and 160 MT·ha–1 with three basil varieties grown. Data taken included soil fertility levels before and after experimental completion, marketable yields recorded weekly over 5–10 weeks, and tissue N and nitrate sap analysis measured at two to three different plant growth stages. In the first experiment, treatments receiving chicken manure or synthetic N showed similar yields (256–289 g/plant), which were significantly greater than the control (197 g/plant). Tissue N levels were greatest in the synthetic fertilizer treatment (4.9%) and lowest in the control (4.5%). In the second experiment, there was a differential response by varieties to treatments with respect to yields. Yields from the compost treatments (292–700 g/plant) were equal to or greater than those receiving synthetic fertilizer (320–651 g/plant) and were generally greater than the control (324–532 g/plant). Tissue N levels were greatest in plants receiving synthetic fertilizer (4.6% to 4.7%) and lowest in the control (4.3% to 4.4%). A positive correlation was found between lab tissue N levels and nitrate sap analysis determination.

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T. Daw, T.J. Tworkoski and D.M. Glenn

Shoot growth of peach trees can be managed by manipulating edaphic conditions such as root volume and soil fertility. In this experiment, 2-year-old peach trees (Prunus persica L. cv. Sentry on `Lovell' rootstock) were planted in pots with a split root design, so that half the roots were not treated and the other half received one of four treatments: root volume restricted with polypropylene nonwoven fabric (FAB), fertilizer alone (FER), FAB + FER, and untreated control (UTC). Total shoot growth and root growth were measured, and root growth in the split halves was compared. FER increased leaf number and weight by 48% and 60%, respectively, but not stem growth. Leaf nitrogen concentration and photosynthesis were greatest in FER treatment. FAB did not affect shoot weight or reduce total root weight or length, although roots did not grow past the fabric barrier. FER increased root weight and length (116% and 57%, respectively, compared to UTC) on the treated half but did not affect root growth on the untreated half. Greatest root growth occurred in the root half that received FAB + FER, particularly in the 5-cm soil segment proximal to the fabric (4.6 cm•cm-3 compared to 0.8 in UTC). Shoot length was greater in FAB + FER than FAB. Thus, fertilizer applied near fabric increased root growth and the combination of fertilizer and fabric may be used to regulate shoot growth. Specific root length (root length per gram dry weight) was highest in trees with no treatment, suggesting root acclimation to low nutrient soil conditions. Lower specific root length resulted in soils that were fertilized. The results indicate that nonwoven fabric restricts root growth in peach trees and reduces shoot elongation. The combined effect of fabric plus selected application of fertilizer may be used to regulate growth of peach trees.

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Hector Valenzuela, Ted Goo, Dave Wall, Roger Corrales, Susan Migita and Milton Yamasaki

Regulatory agencies are concerned about the high levels of P fertilizers used in some agricultural areas because of potential runoff to aquatic habitats. Farmers in Hawaii traditionally make blanket P applications even in soils high in P. Many farmers, especially those growing leafy crops, claim to observe responses to P, especially during the cooler winter months. A series of 15 field experiments were conducted over a 2-year period to evaluate the response of three mustard cabbage varieties to five P fertilizer rates across three locations in the state, and across several planting seasons. All experiments were conducted in soils with P levels that the University of Hawaii determined to be high in P. The experimental design for each experiment consisted of three commercial mustard cabbage varieties, and five P application rates (from 0 to 400 kg·ha-1 of TSP). Each plot consisted of a 3-m double-row, with plants spaced 15 cm within the row, and 30 cm between rows, with four replications per treatment. Each experiment thus consisted of 60 plots (three varietie × five P rate × four replications). After the initial P applications were made on each site, three consecutive crops were planted on the same site without making any additional P applications. Data collected included soil fertility prior to initiation and after experiment completion, tissue nutrient levels, plant height during crop establishment, and individual head weight of 20 plants per treatment. Our data show that even in soils with initial high levels of P, mustard cabbage responded to P applications, especially at high elevations and during the cooler months of the year. From this data we recommend that the University recalibrate its P fertilizer recommendations for leafy vegetable production in Hawaii.