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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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Richard Smith, Bob Mullen and Tim Hartz

Pepper stip is a physiological disorder manifested as gray-brown to greenish spots occurring on fruit of bell, pimento, Anaheim, and other types of peppers, most noticeably on red fruit produced under fall conditions. The spots, ≈0.5 cm in diameter, occur singly or in groups; marketability for either fresh market or processing use is severely affected. The factors controlling the occurrence or severity of the disorder are not well understood; to date, control has been achieved primarily by the use of resistant cultivars. In 1995 replicated plots of susceptible (`Yolo Wonder L' and `Grande Rio') and resistant (`Galaxy' and `King Arthur') cultivars were grown in seven commercial fields in central California. `Galaxy' and `King Arthur' were essentially free of symptoms, while `Yolo Wonder L' and `Grande Rio' showed significant damage at all sites, with 23% to 88% of fruits affected at the mature-red stage. Petiole tissue analysis showed that resistant cultivars consistently had lower N and K, and higher Ca concentrations than susceptible cultivars; the same trend was apparent in fruit tissue. Stip was most severe at sites with low soil Ca and/or very high N and K fertilization rates. It is hypothesized that Ca nutrition significantly influences stip expression.

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Richard Smith, Robert Mullen and Tim Hartz

Pepper stip is a physiological disorder manifested as gray-brown to greenish spots occurring on the fruit of bell, pimento, Anaheim, and other types of peppers, most noticeably on red fruit that mature under fall conditions. Most hybrid bell cultivars are resistant to the malady; the problem is most severe for pepper growers reliant on less-expensive, open-pollinated cultivars. In 1995, we initiated studies to evaluate the possible link between mineral nutrition and this disorder. Two susceptible open-pollinated cultivars and two resistant hybrid cultivars were grown in randomized plots at seven sites. Significant correlations were seen between the levels of potassium (r = 0.59) and calcium (r = -0.37) in whole leaves and the incidence of stip (P = 0.05). The stip-resistant cultivars also maintained less total nitrogen in the whole leaves than susceptible cultivars (P = 0.05). In 1996 and 1997, we undertook field studies to evaluate the effects of varying calcium and nitrogen application rates. Inconsistent results were observed with calcium applications. Moderate reductions in stip incidence was observed at some sites and no reduction at others following foliar calcium applications. Nitrogen nutrition had no effect on stip severity. In 1998, evaluation of a large number of open-pollinated cultivars was undertaken; `Gusto' showed excellent tolerance to pepper stip, followed by `Taurus' and `Cal Wonder 300'. We conclude that growers that are reliant on open-pollinated cultivars can utilize these cultivars to minimize the incidence of pepper stip.

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Dean Martens, Tim Hartz and William Frankenberger Jr.

Exogenous application of auxins to plants has been reported to increase flowering, fruit set and decrease fruit abcission. This laboratory and field study determined that two auxins, identified by HPLC analysis with a long soil residence time and a high conversion to indole-3-acetic acid, synchronized and increased harvest of melons. The two watermelon varieties, `Tiffany' (seedless) and `Picnic' (seed) were treated with auxin and tryptophan (TRP) concentrations ranging from 10-4 to 10-10 M applied to the root ball one week before transplanting to a Buren soil. Optimum application levels (10-6 to 10-9 M) resulted in 86, 92 and 86% of the total harvested Tiffany melons mature at one date for the auxins and TRP, respectively, compared to <70% for the control plants. Optimum application rates significantly increased harvested weight 4.0 and 5.3 kg (Tiffany) and 10.0 to 10.5 kg (Picnic) plant-1. Soil-application of auxins and TRP significantly increased the number of harvested Tiffany melons, increased both weight and harvested number of Picnic melons and increased the uniformity of the harvested melons in both varieties when compared with control plants. Measurements of early growth, branching and early fruit set were not significantly correlated with harvest weight or number of harvested melons but auxin and TRP application stimulated flowering in both melons by 7-10 days.