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.
Dean Martens, Tim Hartz, and William Frankenberger Jr.
James M. Spiers and John H. Braswell
Two-year studies were conducted on 4- to 6-year-old rabbiteye blueberry (Vacciniun ashei Reade) plants grown on a high (6.6) pH soil and irrigated regularly with water containing moderate amounts of Na and Ca (32 and 15 ppm, respectively). In one study, various levels (0, 280, 560, and 1120 kg·ha-1) of elemental S were applied in a single annual application. In another study, a single level (1120 kg·ha-1) of S was applied annually in either one, two, or four applications. Applications of S at up to 1120 kg·ha-1 were not detrimental to plant vigor of rabbiteye blueberries. Soil pH decreased with successively higher levels of applied S. Leaf P, K, and Mn contents were higher and soil pH was lower with single compared with multiple applications of S. Soil K, Ca, Mg, and S levels were negatively correlated with plant growth. Amounts up to 1120 kg·ha-1 of applied elemental S were not sufficient to lower soil pH to a level desirable for rabbiteye blueberry production when the soil was irrigated 7 months·year-1 with water containing moderate amounts of Na.
David M. Hunter and John T.A. Proctor
Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced photosynthetic CO2 uptake rate of leaves formed before paclobutrazol treatment within 3 to 5 days of treatment and the reductions were maintained for 15 days after treatment. The percentage of recently assimilated 14C exported from the source leaf was reduced only at the highest paclobutrazol dose, and there was little effect of treatment on the partitioning of exported 14C between the various sinks. In response to increasing doses of paclobutrazol, particularly at the higher doses, an increasing proportion of recent photoassimilates was maintained in a soluble form in all plant components. Reduced demand for photoassimilates as a result of the inhibition of vegetative growth may have contributed to a reduction in photosynthetic CO2 uptake rate, but this reduction in photosynthesis rate could not be attributed to a feedback inhibition caused by a buildup of starch in the leaves. Paclobutrazol had only a minor effect, if any, on photosynthetic electron transport. Chemical name used: β-[(4-chlorophenyl) methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).
David M. Hunter and John T.A. Proctor
Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced vegetative growth of `Seyval blanc' grapevines (Vitis spp.). At all rates, there was a reduction in internode length, while at rates higher than 10 μg a.i/g soil, there was also a reduction in node count. Leaf area produced following treatment declined in response to increasing rates, but specific leaf weight increased. Treatment with paclobutrazol delayed senescence and increased the retention of basal leaves that were nearly fully expanded at the time of treatment. Paclobutrazol application had no effect on fruit set or berry size, but the reduction in vegetative growth following treatment decreased the ability of the vine to supply sufficient photoassimilates for fruit maturation. Chemical name used: ß[(4-chlorophenyl)-methyl]-a-(1,1-dimethylethyl)1H-1,2,4-triazole-1-ethanol (paclobutrazol).
Jaime E. Salvo and Carol J. Lovatt
yield and protect the environment is to properly time the application and amount of soil-applied fertilizer to meet the nutrient demand of the crop. This practice increases nutrient-uptake efficiency and reduces the potential for nutrient runoff and
Richard J. Heerema, Dawn VanLeeuwen, Marisa Y. Thompson, Joshua D. Sherman, Mary J. Comeau, and James L. Walworth
through soil fertilizer application and a number of published studies have shown promising options ( Fenn et al., 1990 ; Núñez-Moreno et al., 2009a , 2009b ). We began a long-term experiment in 2011 to evaluate the use of soil-applied EDTA-chelated Zn
Joe E. Toler, Jason K. Higingbottom, and Lambert B. McCarty
effects of both soil-applied N and Fe on established centipedegrass quality and density when applied alone or in combination using single or split applications and to assess whether mowing height affects centipedegrass response to the fertility treatments
Carol J. Lovatt
precipitation under rainfed conditions, salinity, pH) during the growing season render soil nutrients and hence soil-applied fertilizers less available to the plant. Foliar fertilization provides the nutrients required for photosynthesis and other important
Cyrus A. Smith, James L. Walworth, Mary J. Comeau, Richard J. Heerema, and Joshua D. Sherman
relationship with P n in fundamentally different ways than when it is soil applied. In this study, we explore whether foliar Zn applications (in the form of Zn-EDTA, ZnSO 4 ·H 2 O alone or in combination with UAN) will increase leaf P n of ‘Wichita’ pecan
C.R Roberts, Dean E. Knavel, John Snyder, Terry Jones, and Dave Spalding
Internal brown spot (IBS) was found consistently in the `Atlantic' cultivar at Lexington in 1967, 1968 and 1989, and at Owensboro and Quicksand, KY in 1987, Treatments of foliar and soil applied CaSO4 in 1987, soil-applied CaSO4 in 1988, and straw mulching in 1989 did not reduce IBS. Irrigation increased IBS because of larger tubers and increased Ca content of plants as compared with non-irrigated plants. Tubers showing IBS had higher Ca content in affected tissue than in non-affected tissue. Both IBS and Ca content of leaves increased as the plants aged.