published_or_final_version / Botany / Master / Master of Philosophy

No description available.

No description available.

A one-year field study was conducted at the Maricopa Agricultural Center in the winter and spring of 1991-92 with the purpose of comparing the response of leaf lettuce grown with subsurface drip irrigation to various broadcast and banded phosphorus (P) fertilizer applications and rates. Two rates of banded treble superphosphate, 250 lbs. (1X) and 125 lbs. (1/2X) of P2Osper acre, were applied immediately before planting in a concentrated strip 1 inch directly below the row to be seeded. One broadcast rate, 250 lbs. (1X) of P205 per acre of the same material, was applied and folded into the planting beds during listing. Control plots, in which zero P fertilizer was applied, were also maintained. Whole plant total P concentrations were higher in the first one-third of the growing season for the band treatments, though the differences in responses between band and broadcast applications were not statistically significant in the final third of the season. The 1X band treatment exhibited both greater plant heights and diameters than all other treatments during the first one-half of the growing season, and maintained greater height dimensions in the second half. The 1X broadcast and 1/2X band treatments exhibited similar growth throughout the season. By harvest there were not significant differences in head or plant size or in marketable yield among the three P treatments.

Studies are being conducted which aim to improve the efficiency of irrigation and N fertilization for lemons produced on sandy soils in the low desert. The first experiment evaluates the response of 'Lisbon' lemons to various flood irrigation intervals. Irrigation intervals are based on soil moisture depletion (SMD) as calculated from frequent neutron probe soil moisture measurements. Individual treatments were irrigated when total SMD was 25 %, 40 %, 55 %, and 70 %, respectively. The second experiment compares the performance of young lemons produced under flood, trickle, and micro -spray irrigation systems. The third experiment evaluates the response of young lemons to water and N combinations (3 by 3 factorial) under micro -spray irrigation. The three irrigation rates were targeted for 30 cnbar, 20 cnbar, and 10 cnbar tension. The three N rates were 0.1, 0.2, and 0.4 kg N /tree. One flood irrigation treatment was added for comparative purposes. Overall, results obtained in experiment 1 during 1994 and 1995 indicate optimal fruit growth ,and yield is obtained at approximately 40% SMD. The results of experiment 2 show that after 18 months micro -spray irrigation produced significantly more tree growth than flood and drip irrigation methods. Additionally, first year fruit yields were significantly greater for pressurized irrigation compared to flood irrigation. Results from experiment 3 show a linear response in tree growth up to 10 cnbar soil moisture tension. Furthermore, tree growth at 10 cnbar tension was significantly greater than trees irrigated by flood. Yields were also increased to irrigation regime. There were no significant differences in tree growth to N fertilization rates. However, there was a yield increase to N fertilizer rate at the highest soil moisture regime.

Deficiency of boron (B) in citrus has serious consequences for tree health and crop production. There is evidence that B deficiency may be a problem in Arizona citrus. Certainly, many symptoms of B deficiency are apparent, especially on the Yuma Mesa. A field trial was conducted at Yuma, Arizona to examine the effect of foliar boron application on fruit yield and quality of Citrus sinensis and C. limon. Boron was applied to 5 year old Citrus sinensis cv. Hamlin and C. limon cv. Rosenberger Lisbon trees at 5 different concentrations (0 ppm, 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm) either before flowering or after flowering. At harvest, fruit yield and quality, and boron concentrations were determined. Foliar application appeared to increase leaf boron concentration (r= 0.50, p= 0.004). Fruit set was increased in Hamlin trees receiving bloom and post bloom applications of boron at the 1000 ppm level. Boron applications had no significant effect on lemon yield in these studies. This fruit set increase in Hamlin accounted for a 35% increase in overall yield relative to control trees. However, there was no significant difference in fruit weight, fruit pH, titratable acidity, peel thickness, juice volume, or soluble solid content of the fruits among treatments. Previous studies indicate that boron influenced in vivo and in vitro pollen germination in many crops. A plausible explanation for increased fruit yield may be that the applied boron was transported to the flowers where it exerted its influence of increased fruit set through an effect on pollen viability and/or pollen tube growth. However, clearly boron supplementation must be performed judiciously to avoid fruit drop from over -application of the element.

Four arbuscular mycorrhizal (AM) fungal isolates (Glomus sp.) from disparate edaphic conditions were screened for effects on whole -plant transpiration of juvenile 'Volkamer' lemon (Citrus volkameriana Ten. and Pasq.) plants of similar shoot mass and canopy leaf area. Mycorrhizal and non -mycorrhizal plants were grown in 8 -liter containers for 2.5 months under well- watered conditions before subjection to three consecutive soil drying episodes of increased severity (soil moisture tensions of -0.02 [still moist], -0.06 [moderately dry], and -0.08[dry] MPa respectively). Whole plant transpiration measurements were made on the last day of each soil drying episode and measurements were repeated on the first and second days after re- watering, when soil profiles were moist. The percent root length colonized by AM fungi differed among isolates. Three AM fungal isolates, Glomus sp. 25A, Glomus mosseae (Nicol. & Gerde.) Gerde. & Trappe 114C, and Glomus intraradices Schenck & Smith FL 208-3 increased root length and subsequently increased lemon plant water use. Conversely, plants inoculated with Glomus mosseae 51C did not enhance lemon plant root length nor improve plant water use compared with nonmycorrhizal control plants. Inoculating citrus with AM fungi that promote root extension may reduce plant water deficit stress under field conditions.

A field experiment was conducted at the Maricopa Agricultural Center on a Casa Grande sandy loam soil to compare the nitrogen (N) utilization efficiency achieved using slowrelease and conventional nitrogen fertilizers under subsurface drip irrigated melon production conditions. 'Mirage' watermelon, 'Laguna' cantaloupe and 'Gallicum' honeyloupe were used as the test crops. Single, preplant applications of three slow - release products (methylene urea, coated ammonium sulfate and coated urea) were compared with the use of urea -ammonium nitrate added in either one or three split applications. The total amount of N applied to all treated plots was 100 lbs. per acre. Whole plant samples were taken four times during the season to determine N uptake patterns. Petioles from the youngest fully expanded leaves were sampled on four dates throughout the season to monitor the N status of all plots. At harvest, total and marketable melon yields were determined. In general, the methylene urea treatment was superior to the use of coated (NH₄)₂SO₄ which in turn was far superior to the coated urea product. The split UAN and preplant UAN treatments had the highest numerical values for total N uptake for all three melon types. However, these values were usually not statistically different from the N uptake in response to the three slow- release N treatments. The type of water delivery system may have reduced the potential advantages of using slow-versus fast-release N fertilizers.

No description available.

Of all the plant nutrients, nitrogen has been subjected to the most extensive study. The amount of inorganic nitrogen in the soil is small while the quantity needed annually by crops is comparatively large. Of the macronutrients usually applied in commercial fertilizers, nitrogen seems to have the quickest and most pronounced effect on plant growth. In applying the nitrogen fertilizer for crop use, one must be concerned with placement, form, and availability, and with keeping the fertilizer where it is placed throughout the critical part of the growing season. The nitrogen supply molded by non-leguminous plants is of extreme importance and its availability is complicated by the fact that nitrogen in soils is easily converted into forms which are more or less mobile and available. The time of application of nitrogen fertilizer can significantly affect its availability. It commonly is applied in either the spring or fall in row crop culture. Under our climatic conditions, nitrogen applied in the fall tends to be lost by denitrification and leaching over the winter period, and the practice is not economical. There are also disadvantages associated with spring application of nitrogen. Application is needed at a time when the farmer is extremely busy and where the soil may be too wet to support the application equipment. No-tillage farming, which is relatively new, apparently increases the rate of nitrogen movement through the soil profile. No-tillage results in a mulch of dead plant material on the surface. The mulch tends to keep more moisture in the soil. This extra moisture can be beneficial to the crop but it also permits the nitrogen to move more rapidly through the soil. The present student was initiated to study the effects of tillage practice and time of nitrogen application on the movement of nitrate through a Pembroke silt loam soil. This soil is typical of the well-drained limestone soils found in Southern Kentucky.