To evaluate effects of canopy and micro-irrigation under trees on accumulation and leaching of phosphorus (P) and heavy metals in agricultural sand soils, the horizontal and vertical variations of soil P and metals in a 408-m2 plot within a grove under grapefruit (Citrus paradisi Macf.) production near Fort Pierce, Fla., was examined. A high horizontal variation of labile soil P and metal concentrations was observed. Across the row, the highest values of pH, EC, water-soluble P, and all metals occurred in the soils under the canopies, and the lowest values occurred in the soils near the water furrow or the midway of the inter-row. Along the grapefruit row, the highest values of many measured variables occurred along the northern side of the citrus tree and close to the emitter. The downward movement of P, Cu, and Zn in the soils was more significant in the soils in open areas (near the water furrow and midway of inter-neighboring trees) than those under the canopies. The differences in labile P and metal spatial distributions in the soils were related to the location of emitter fertigation and differences in rainfall-induced leaching in the field. The results suggest that applying fertilizers to sites under the canopy rather than the spaces between the trees can minimize leaching losses of nutrients.
Zhenli He, David. V. Calvert, Peter. J. Stoffella, and Mingkui Zhang
Mark A. Ritenour*, Peter J. Stoffella, Zhenli He, and Michael S. Burton
Previous research suggests that treatment of sliced or vacuum-infiltrated tomato fruit with calcium chloride (CaCl2) solutions may reduce decay, but no work on dipping whole tomatoes has been reported. In the present experiments, `FL 47' tomato fruit were collected at the mature green or pink stage from a local packinghouse, held at 12.5 or 25.0 °C overnight, and then dipped in solutions with 0.5% to 5% CaCl2 with or without 150 ppm sodium hypochlorite. Fruit were dipped for 1 to 4 minutes at temperatures ranging from 0 to 35 °C. Mature green fruit dipped in solutions with 0.5% and 1.0% CaCl2 at 35 °C had significantly lower rates of decay following storage at 12.5 °C (90% RH) than the control (27% vs. 36% decay, respectively). These fruit were also significantly softer after 2 weeks of storage than control fruit (0.85 mm vs. 0.74 mm deformation, respectively) and appeared to be slightly more ripe. Decay in fruit dipped in 2% CaCl2 was not significantly different from the control, while fruit dipped in 3% to 5% CaCl2 developed significantly more decay than control fruit. The CaCl2 treatments had no significant effect on decay of fruit treated at the pink stage and none of the treatments at 0 °C significantly affected postharvest decay. Dips in 2% to 5% CaCl2 significantly increased tomato peel calcium content after storage. Dipping time had no significant effect on peel calcium content.
Mark A. Ritenour, Peter J. Stoffella, Zhenli He, Jan A. Narciso, and James J. Salvatore
Previous research showed that mature green tomato fruit dipped 1 to 4 min in a 1% CaCl2 solutions before storage had significantly increased peel calcium content and reduced postharvest decay. The present experiments, conducted over 3-day periods (reps), evaluate treatment effectiveness under commercial packinghouse conditions. Three cartons of 5 × 6 sized mature green `FL 47' tomatoes were collected from the line (control). CaCl2 was then added to the packinghouse 15,142-L dump tank to a concentration of 1% before more fruit were run through the line and three additional cartons collected. The cycle was repeated after bringing the concentration in the dump tank up to 2% CaCl2. After storage for ≤24 days at 20 °C, postharvest decay was significantly reduced in fruit receiving the 2% CaCl2 treatment. Calcium content in the tomato peel tended to increase with each successively higher CaCl2 treatment, but differences were nonsignificant. Laboratory tests showed Rhizopus more affected by 3% CaCl2, while Alternaria was affected by 2% and 3% CaCl2 solutions. Results were recorded as colony diameter, but colony morphology and sporulation were also affected. Inoculation studies of tomatoes dipped in 1% CaCl2 after wounding with Rhizopus or Alternaria showed better decay control when compared to treating before wounding.
Kristin R. Campbell, Sandra B. Wilson, P. Christopher Wilson, and Zhenli He
Interactive review exercises were developed as an online learning component of an existing native plant landscaping course. The instruments were designed with specific goals for students to 1) test their plant identification knowledge, 2) practice leaf terminology with specific plant examples, and 3) associate landscape performance with native ecosystem characteristics. The plant identification tool was developed within a spreadsheet application using formulas consisting of logic statements. This tool tests the students’ ability to identify plants and spell scientific and common names associated with high-resolution plant images. The leaf terminology tool was developed using a multimedia platform. It uses a drag-and-drop interface where students are asked to associate a specific leaf term (i.e., margin, apex, base, texture, arrangement) with a scanned image that best matches the taxonomic term. The ecosystem tool, also developed using a multimedia platform, uses digital images captured for each of Florida's major ecosystems in conjunction with sets of plant combinations and site characteristics. Students select the appropriate choices and submit their answers online, after which they receive immediate feedback. Students reported an improvement in plant recognition after they had access to these identification tools. These interactive learning tools not only benefit students enrolled in this specific course but can be adapted to a variety of online courses nationwide.