Browsing by Subject "fertilization"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Intensive culture of loblolly pine (Pinus taeda L.) seedlings on poorly drained sites in the Western Gulf region of the United States(Texas A&M University, 2004-09-30) Rahman, Mohd ShafiqurA significant acreage of poorly drained sites occurs in the Western Gulf region of the United States. These sites experience standing water through much of the winter and spring, resulting in poor seedling survival. In addition, the sites occasionally experience a summer drought that affects tree growth. This study was designed to determine the effects of intensive forest management on seedling growth and physiology, and to enhance seedling performance under these harsh conditions. Fertilization, chemical vegetation control and mechanical site preparation were used in different combinations to test the effects of these intensive forest management tools on seedling above- and below-ground growth, survival, water status, gas exchange attributes, and nutrient concentrations in the foliage and soil solution. Ten sites were established in southern Arkansas in 1998 and 1999 to monitor loblolly pine (Pinus taeda L.) seedling performance in three consecutive growing seasons between 1998 and 2000. Fertilization, chemical vegetation control and mechanical site preparation increased above-ground growth. Growth increment from mechanical site preparation was comparable to that from fertilization. Survival was not affected by any treatment. Fertilization enhanced root growth, more so in the shallow soil layers. Subsoil bulk density greatly restricted root growth, resulting in decreased above-ground growth. Chemical vegetation control made more soil water available to the seedlings during drought, resulting in increased seedling water potential. The effect of chemical vegetation control on seedling water potential was absent in the early growing season when soil moisture was abundant. Seedlings on plots treated with bedding-plus-fertilizer or bedding alone experienced stomatal closure at times of severe water stress while those treated with chemical vegetation control were able to continue net carbon dioxide assimilation. Fertilization did not increase needle nutrient concentrations, but increased needle weight, thereby increasing total nutrient content. Fertilization increased base cation concentrations in the soil solution, but had no effect on nitrogen and phosphorus concentrations. Intensive forest management was found to be a viable tool for optimum loblolly pine seedling growth and survival on poorly drained sites in the Western Gulf region of the United States.Item The effects of nutrient availability on the host plant resistance of gerbera to western flower thrips(2009-05-15) Spiers, James DavisNutrition of host plants has been shown to have a direct effect on the productivity of numerous insect pests, including western flower thrips [(WFT) Frankliniella occidentalis (Pergande)] ? a major pest on both horticulture and agronomic crops. Plants use constitutive and induced chemical defenses to aid in protection against phytophagous insects. Reductions in WFT abundance in response to decreased nutrient availability has been attributed to the reduced availability of nutrients required for WFT productivity. The goals of this research were to determine the effects of fertilization on chemical defenses, and subsequent effects on WFT feeding and abundance. More importantly, the effects of fertilization and WFT feeding on plant growth, development, physiology, and quality were determined to assess the viability of optimizing fertilization in order to increase host plant resistance in gerbera. Constitutive (i.e. phenolics) and induced (i.e. jasmonic acid) chemical defenses were enhanced when fertilization was reduced. Reducing fertilization increased the total phenolics and wound- and WFT-induced jasmonic acid (JA) accumulation in gerbera. The enhanced chemical defenses in lower fertility plants resulted in reduced WFT abundance and feeding damage. These results indicate that the strategy for some plant species under nutrient stress is to increase constitutive defenses, while maintaining, or possibly increasing inducible defenses instead of growth. Similar to 0X fertility plants (only supplied with initial fertilizer charge in commercial media), 0.3X (received 30% of recommended rate) gerberas had reduced biomass and greater chemical defenses compared to 1X plants, but these plants did not appear to be nutritionally stressed?and 0.3X plants without WFT were rated as marketable. Reducing fertilization by 70% (0.3X) did not affect flower dry mass (DM) or the rate of flowering, but the flower stalks (peduncles) were taller in response to the fertilizer reduction. Hence, reducing fertilization to a moderate level in gerbera production may reduce susceptibility to WFT, while producing marketable crops.