Greenhouse and field experiments were conducted in 1988 and 1989 to determine the effect of seed size and cultivar on seedling emergence through crusted soil for several hybrid broccoli cultivars (Brassica oleracea ssp. italica). Seed was separated into four sizes (2.0, 1.8, 1.6, and 1.4 mm in diameter) for the greenhouse investigations, and soil crusting was achieved using a crusting resin. In 1989, field experiments using three seed sizes (small = 1.4 to 1.6 mm, medium = 1.7 to 1.9 mm, and large = 2.0 to 2.2 mm in diameter) were planted at the Long Island Horticultural Research Laboratory in a Riverhead sandy loam that crusted readily following rainfall. Seedling emergence data from the greenhouse and field studies indicate that seed size and cultivar significantly affect emergence and stand establishment. Seedling stand, dry weight, and final yield significantly increased as seed size increased for both cultivars in the field experiments. The emergence of `Mariner' generally was significantly better than that of `Greenlady' for each seed size. Seed of `Greenlady' also weighed significantly less than that of `Mariner' within each seed size tested.
D.W. Heather and J.B. Sieczka
P.L. Minotti, D.E. Halseth, and J.B. Sieczka
We report three N rate experiments conducted on a gravelly loam soil to assess the N status of potato (Solanum tuberosum L.) using a Minolta SPAD-502 chlorophyll meter. Highly significant linear and quadratic trends were obtained for the regression of N rate on marketable tuber yields and SPAD readings. SPAD readings were taken at four times during the growing season and decreased as plants aged. Based on regression analysis, the early season SPAD readings, associated with N rates giving maximum marketable tuber yields, ranged from 49 to 56 units depending on year, variety, and location. Potato variety significantly affected SPAD values in eight of the 12 situations where readings were obtained. Precision in interpretation was improved when the highest N rates were considered “reference strips” to standardize the SPAD readings across varieties and growing seasons. Our results suggest that field SPAD readings can readily identify severe N deficiency in potatoes, have the potential to identify situations where supplementary sidedressed N would not be necessary, but would be of limited value for identifying situations of marginal N deficiency unless reference strips are used.
D.W. Heather, J.B. Sieczka, M.H. Dickson, and D.W. Wolfe
Forty hybrid broccoli [Brassica oleracea L. (Italica Group)] accessions were screened for heat tolerance and holding ability over three planting dates in 1988 at the Long Island Horticultural Research Laboratory in Riverhead, N.Y. Holding periods were quantified using the number of consecutive days between the time individual heads reached 10 cm diameter and cutting, which occurred when the sepals had fully expanded and had just begun to separate. In 1989 and 1991, heat stress was applied at various weeks during maturation to determine the most sensitive stage or stages of plant development in terms of reduction in holding period and head weight. Field studies and heat stress experiments indicate that heat stress may be most critical during the time the immature inflorescence measures 5 to 10 mm in diameter. This stage corresponds to ≈ 3 weeks before harvest for summer plantings in the northeastern United States.
Joseph R. Heckman, Thomas Morris, J. Thomas Sims, Joseph B. Sieczka, Uta Krogmann, Peter Nitzsche, and Richard Ashley
The pre-sidedress soil nitrate test (PSNT) was evaluated in 27 fields in New Jersey, 6 in Connecticut, 5 in Delaware, and 2 on Long Island in New York for its ability to predict whether sidedress N is needed to grow fall cabbage (Brassica oleracea var. capitata) as a double crop. Soil NO3-N concentrations measured on 20 field sites on the day of transplanting and 14 days after transplanting indicated that NO3-N concentrations over this time period increased, and that residues from the previous crop were not causing immobilization of soil mineral N. The relationship between soil NO3-N concentration measured 14 days after transplanting and relative yield of marketable cabbage heads was examined using Cate-Nelson analysis to define the PSNT critical level. Soil NO3-N concentrations ≥24 mg·kg-1 were associated with relative yields >92%. The success rate for the PSNT critical concentration was 84% for predicting whether sidedress N was needed. Soil NO3-N concentrations below the PSNT critical level are useful for inversely adjusting sidedress N fertilizer recommendations. The PSNT can reliably determine whether fall cabbage needs sidedress N fertilizer and the practice of soil NO3-N testing may be extendable to other cole crops with similar N requirements.