; Wadsworth, 1970 ). For these reasons, there is considerable interest among pecan producers in the potential of soil-applied Zn. Soil application of Zn has been successful in the acidic soils of the southeastern United States ( Sparks, 1976 ; Wood, 2007
James L. Walworth, Scott A. White, Mary J. Comeau, and Richard J. Heerema
Justin M. Vitullo and Clifford S. Sadof
control ( Table 1 ). These treatments compared the effectiveness of soil-applied imidacloprid [1.43 g/plant a.i. (Merit 2.5G; Bayer, Trafalgar, Ind.)], soil and foliar-applied azadirachtin [0.144 g/plant a.i. (soil) and 0.072 g·L −1 a.i. (foliar) (Azatrol
Rizwan Maqbool, David Percival, Qamar Zaman, Tess Astatkie, Sina Adl, and Deborah Buszard
Ismail 1981 ), or no effect ( Benoit et al., 1984 ; Blatt, 1993 ). Variable responses in soil-applied P and K have also been reported. P can either significantly increase berry yield ( Smagula and Dunham, 1995 ) or have no effect on yield potential as
M. Lenny Wells and Eric P. Prostko
application. Trees from the 2009 study were scheduled to be removed in the winter of 2009–10, thus, subsequent data could not be obtained. Table 2. Influence of soil-applied imazapic on pecan kernel development in 2008 and 2009. One explanation as to the
J. Pablo Morales-Payan and William M. Stall
Experiments were conducted to assess the effects of rate combinations of nitrogen (N) and a soil-applied biostimulant based on seaweed (Ascophyllum nodosum) extract (SSE) on the growth of papaya seedlings for transplant production. Seedlings were grown in 180-mL Styrofoam containers filled with a sphagnum/vermiculite/perlite growing medium. N (0 to 2 g per plant) and SSE (drench, 0 to 1 mL per plant) were applied at sowing and 15 days after emergence. N and SSE rates affected overall growth as well as time to attain adequate size for transplanting. In general, increasing N rates resulted in increased growth, and adding SSE enhanced N effects. In terms of increasing overall transplant growth and decreasing the time required from emergence to adequate transplanting size, the best results were found at the highest N and SSE rates.
David Percival, Gloria Thyssen, Kevin Sanderson, and David Burton
Environmental losses of soil-applied nitrogen fertilizers were examined during 2004 in commercial wild blueberry fields in the vegetative phase of production in Nova Scotia (NS) and Prince Edward Island (PE). A randomized complete-block experimental design with five treatments, five replications, a plot size of 8 × 6 m, and 2-m buffers between plots was used. Treatments consisted of a control (no fertilizer application) and nitrogen applications (N at 35 kg·ha-1) of ammonium sulphate (AS), urea (U), diammonium phosphate (DAP), and sulfur-coated urea (SCU). Nitrogen applications occurred on 19 May and 9 June at the Kemptown (NS) and Mount Vernon (PE) sites, respectively. Cumulative ammonia volatilization was determined through the use of open top chambers with volatilization samples collected on 1, 2, 5, 8, and 12 days after treatment application. In addition, leaf tissue and yield component data were collected. A significant volatilization treatment effect was present at the Kemptown site with the U and SCU treatments having volatilization rates that were 321% and 207% greater than the control, respectively. Therefore, results from this study indicate that volatilization losses are significant and site specific and can negatively influence blueberry growth.
Carol J. Lovatt
To protect groundwater from potential nitrate pollution, `Hass' avocado (Persea americana Mill.) growers in California divide the total annual soil-applied nitrogen (N) fertilizer (N at 56 to 168 kg·ha-1) into small applications made during the period from late January to early November. However, no research had been conducted to test the efficacy of this fertilization practice, and there was concern that the amount of N in the individual applications may be too little to meet the demand of the tree at some stages of its phenology. The research presented herein addressed the question of whether yield of `Hass' avocado could be increased by doubling the amount of N currently applied during specific stages of tree phenology. The control in this experiment was the practice of annually applying N as NH4NO3 at 168 kg·ha-1 (168 trees/ha) in six small doses of N at 28 kg·ha-1 in January, February, April, June, July, and November. From these six application times, five were selected on the basis of tree phenology and additional N as NH4NO3 at 28 kg·ha-1 was applied at each time for total annual N of 196 kg·ha-1. Two phenological stages were identified for which N application at 56 kg·ha-1 in a single application (double dose of N) significantly increased the 4-year cumulative yield (kilograms fruit per tree) 30% and 39%, respectively, compared to control trees (P ≤ 0.01). In each case, more than 70% of the net increase in yield was commercially valuable large size fruit (178 to 325 g/fruit). The two phenological stages were when shoot apical buds have four or more secondary axis inflorescence meristems present (mid-November); and during anthesis to early fruit set and initiation of the vegetative shoot flush at the apex of indeterminate floral shoots (about mid-April). When the double dose of N was applied at either of these two stages, the kilograms and number of large size fruit averaged across the 4 years of the study was significantly greater than the control trees (P ≤ 0.01). Averaged across the 4 years of the study, only the November treatment increased yield compared to the control trees (P ≤ 0.05). Application of the double dose of N at flower initiation (January), during early-stage gynoecium development (February), or during June drop had no significant effect on average or cumulative yield or fruit size compared to control trees. Application of the double dose of N in April significantly reduced the severity of alternate bearing (P ≤ 0.05). Yield was not significantly correlated with leaf N concentration. Time and rate of N application are factors that can be optimized to increase yield, fruit size, and annual cropping of `Hass' avocado. When the amounts of N applied were equal (196 kg·ha-1), time of application was the more important factor.
Osamu Kawabata and Joseph DeFrank
Sulfate, as K2SO4, was applied to silt loam (Leadvale) soils of pH of 5.0 and 7.1 at rates of 0, 6, 18 and 36 kg S/ha. Nitrogen, as NH4NO3, was split applied at 0 and 120 kg/ha. All treatments received 55 and 45 kg/ha of P and K, respectively. Twenty day-old plants of accession RRC 241 were transplanted on 12 July 1990 and harvested 47 days later. Supplemental SO. had no effect on plant ht or yield but increased soil solution SO4 levels at the end of the season. Leaf blade N and S levels were increased at the highest SO4 rate. Higher SO4 rates increased leaf blade chlorophyll (chloro) `a', total chloro and total carotenoid levels. Response of leaf blade total sulfur, sulfate and organic sulfur to supplemental SO4 was linear. Organic to inorganic S ratios were unchanged. Plants grown at pH 5 had lower yields but higher leaf blade K, Al, Fe, Mn, Zn and Cu levels. Plants grown at pH 7 had higher leaf blade P, Ca, Na, and chloro levels. Soil pH did not effect soil solution SO4 levels. N reduced soil pH, and leaf blade P, Ca, Mg, Zn but increased soil electrolytes, leaf blade N, Na, Mn, chloro `a' and `b', and total carotenoids. Leaf blade N was the only leaf consituent from plants grown at both pHs correlated with leaf blade pigments.
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.