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Jin-Sheng Huang and Paul V. Nelson

Salinity guidelines for seed germination substrates are extremely low and difficult to attain given the salinity contributions of components such as peatmoss, vermiculite, limestone, wetting agent, and nutrients. This study was conducted to determine the value of N, P, K, and S as pre-plant nutrients with the anticipation that some could be eliminated. Seed were sown in two similar experiments on 23 Mar. and 6 June 1995 in 288-cell plug trays containing a substrate of 3 sphagnum peat: 1 perlite (v/v) amended with 6 g dolomitic limestone and 1.5 g Esmigran micronutrient mix per liter. Test plants included impatiens `Accent Rose' (Impatiens wallerana L.) and gomphrena `Buddy' (Gomphrena globosa. L.) Six preplant treatments including none, all, or all minus one of the nutrients N, P, K, and S were applied, each at a rate of 100 mg·L–1, substrate, in a randomized complete-block design with three blocks. Post-plant fertilization with 13–0.9–10.8 at 50 mg N/L began 1 week after sowing and was increased to 100 mg N/L when the fourth true leaf appeared. Omission of pre-plant K and S did not result in any reduction in final plant size in impatiens and only a minor reduction in one of the two gomphrena crops. Omission of N and P consistently reduced final size of plants by a commercially significant amount. While K and S are not necessary, N and P should be considered in a pre-plant fertilizer for these crops. In each situation where shoot size was smaller the root/shoot ratio was unchanged.

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Jin-Sheng Huang and S.S. Snapp

The appearance of a fruit quality defect, shoulder check in fresh-market tomatoes (Lycopersicon esculentum Mill.), has devastated the Michigan industry, and caused sporadic concern elsewhere. The defect appears as a surface roughness that occurs primarily on the shoulder area of the fruit. The fruit appearance is damaged and storability is severely compromised. Microscopic inspection reveals that the surface roughness consists of many microscopic cracks that occur in parallel lines. Our objectives were to describe this defect and evaluate the role of weather conditions and fruit surface moisture in inducing it. Field experiments were conducted in 2001 and 2002 in Southwest Michigan, using the industry standard cultivar Mountain Spring and recommended practices for irrigated, staked fresh market production. The effects of fruit surface wetness and nutrition on quality were evaluated by comparing responses to a plastic rain shelter; Surround WP kaolin spray (to enhance surface wetness); a foliar spray of calcium (Ca at 2 g·L-1), boron (B at 300 mg·L-1), Ca plus B, water alone; and no treatment. A complementary greenhouse experiment investigated the effects of low and high rates of foliar sprays. A very consistent association was found between defect incidence and precipitation events that followed periods of hot, dry weather during rapid fruit expansion. Fruit quality was highest and incidence of defects least in fruit produced under plastic rain covers, with an average marketable yield of 62,270 vs. 44,340 kg·ha-1 for the control. A 28% reduction in defects was consistently associated with Ca + B sprays across harvests and years. In contrast, 18% more fruit had shoulder check defect with kaolin spray, a consistent increase in defect across years compared to control fruit. Greenhouse and field studies gave markedly similar results, except for a water spray control. Incidence of defect was consistently low with the highest rate of B foliar spray.

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Cheon-Young Song, Jin-Sheng Huang and Paul V. Nelson

The greenhouse industry successfully uses high NO3 fertilizers to produce plants with short, compact shoots. It is commonly assumed that NO3 results in compactness while NH4 or urea stimulate large shoot growth. However, high NO3 fertilizers contain little or no phosphate. Four sets of treatments were applied to five species of bedding plant plug seedlings in two experiments to differentiate the effects of N source vs. phosphate supply on growth. Seedlings were established on 20-4.4--16.6 fertilizer until 10 days into stage 3, when the following treatments began. Set 1: phosphate-P was held at 22 mg/L and total N at 100 mg/L with NH4 comprising 40%, 13%, 7%, or 0% of total N, the remaining being NO3. Differences in shoot size did not occur as a consequence of the shift in NH4:NO3 ratio. Set 2: N was supplied at a concentration of 100 mg/L from 40% NH4 plus 60% NO3 while PO4-P was varied over the series of concentrations of 21.9, 6.6, 3.3, and 0 mg/L. Set 3: the same as Set 2 except that N was supplied entirely as NO3. Height and weight of shoots in Sets 2 and 3 were positively related to PO4 supply. Set 4: three commercial fertilizers containing 0 PO4-P and 8, 13, or 20% of N in the NH4 form. Compact shoots developed in these treatments. When 22 mg phosphate-P/L was added to one of these fertilizers, compactness was reversed. Shoot suppression by high NO3 fertilizers was concluded to be a function of low phosphate and not N form.

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Lantian Du, Baojian Huang, Nanshan Du, Shirong Guo, Sheng Shu and Jin Sun

Soil sickness from the continuous cropping of cucumbers has become a major limiting factor for protected cucumber cultivation. The use of reasonable cropping systems and the employment of allelopathy between different crops are considered to be the major safe and effective measures for alleviating soil sickness. The objective of this study assessed the effects of garlic (Allium sativum L. cv. Yusuan No. 1)/cucumber (Cucumis sativus L. cv. Jinchun No. 4) relay intercropping on soil enzyme activities and the microbial environment in a continuous cropping regime. Cucumbers and garlic were selected and planted in plastic barrels. The following four treatments were included in the experiment: continuous cropping without crops (Cont), monoculture cucumbers (C), monoculture garlic (G), and the relay intercropping of garlic with cucumbers (CG). The results showed that relay intercropping with garlic promoted cucumber plant growth and attenuated damage caused by soil sickness. In comparison with the Cont treatment, the C treatment decreased soil urease, catalase, invertase, and phosphatase activities; by contrast, the CG treatment enhanced all soil enzyme activities. The C treatment resulted in lower numbers of soil bacteria and actinomycetes and a lower bacteria/fungi ratio, but there were a higher number of soil fungi than there were in the Cont treatment. However, the CG treatment increased the numbers of soil bacteria and actinomycetes as well as the bacteria/fungi ratio, and it decreased the number of soil fungi. In comparison with the Cont treatment, the C treatment reduced the microbial biomass carbon (MBC) and soil basal respiration (BSR) without affecting the metabolic quotient (qCO2), whereas the CG treatment increased all three variables. A polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analysis revealed decreased bacterial community diversity and increased fungal community diversity in soil with the C treatment; the opposite trend was observed in the CG treatment. The results indicated that the relay intercropping of garlic with cucumbers improved soil enzyme activities and promoted the conversion of continuous cropping soil from a “fungal” type to a “bacterial” type. Additionally, relay intercropping altered the soil bacterial community structure, increased the bacterial diversity indices, and enriched the dominant bacterial populations in the soil. These mechanisms improved the soil microbial environment and effectively alleviated damage caused by soil sickness, thus promoting cucumber plant growth.

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Jin-Sheng Huang, Paul V. Nelson, Douglas A. Bailey, William C. Fonteno and Nancy C. Mingis

Salinity guidelines for seed germination substrates call for low, difficult to attain levels. This study was conducted to determine the value of N, P, K, and S as preplant nutrients, with the anticipation that some could be eliminated to alleviate the high salinity problem in many substrates. Impatiens wallerana L. `Accent Rose' and Gomphrena globosa L. `Buddy' were tested in 288-cell plug trays containing a substrate of 3 sphagnum peat moss: 1 perlite (v/v) in two experiments. Seven preplant N, P, K, and S treatments, including none, all (each at 100 mg·L-1 of substrate), all minus one of each of the nutrients, and N at one additional rate of 50 mg·L-1, were tested. Postplant fertilization was applied to all treatments as 13 N-0.9P-10.8K at 50 mg·L-1 N beginning 1 week after sowing and was increased to 100 mg·L-1 N when the fourth true leaf appeared. The resultant seedlings were transplanted into 48-cell flats and grown into marketable stage for further evaluation. For maximum potential growth, N, P, K, and S were needed as preplant fertilizer. However, compact shoots, not maximum growth, are generally desired in commercial production. Thus, K and S can be omitted since their contribution to growth was only occasional and small. To further ensure a consistently desirable level of compactness, it was necessary to omit N or P or both in addition to K and S. Omission of N alone yielded the most desirable compact plant qualities, including suitable reduction in final seedling size. Omission of P alone yielded larger reductions in height and shoot dry weight of seedlings compared to N omission, and a delay of 2 to 4 days in flowering of bedding plants. Omission of the four nutrients, compared to -P, resulted in similar seedling growth reduction and bedding plant flower delay. Since N omission lowered the salt (electrical conductivity) level of substrate more than P omission and had no negative impact on subsequent bedding plant flowering compared to the other two treatments, N omission would be the more desirable of the three. However, N omission resulted in chlorotic seedlings, but these quickly turned green upon restoration of N. Omission of P or all four nutrients resulted in desirably deep green seedlings. Growth of gomphrena seedlings, a high-fertilizer requirement category of taxa, was suppressed when the preplant rate of N was 50 mg·L-1 compared to 100 mg·L-1, while growth of impatiens, a low-fertilizer requirement category of taxa, was essentially equivalent at these rates. Preplant additions of nutrients applied at 100 mg of nutrient element per liter of substrate lasted for the following numbers of days; NO3-N, 18-25 days; NH4-N, 12-20 days; K2O, 27 days; PO4-P, >35 days; and SO4-S, >35 days.