Date of Award

2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Dr. Ali El - Keblawy

Second Advisor

Dr . Osman Khalifa

Third Advisor

James E. Fletcher

Abstract

The efficacy of solarization in weed control under field conditions of the united Arabs Emirates (UAE} was evaluated by conducting field experiments in a farm near Al-Ain. The soil of the farm was artificially infested with seeds of the following weeds: Amaranthus viridus, A. hybridus, Cenchrus ciliaris, Chenopodium murale, Launea mucronata, Malva parviflora, Capsella bursa-pastoris, Echinochloa colona, Portulaca oleracea, and Melilotus indica. The soil was plowed, rotovated to provide a smooth surface and divided into 12 raised plots, 10 x 1 m each: seven were solarized and five non-solarized. Soils were solarized with 75 mum transparent polyethylene sheets for a period of two months (June 10 to August 10, 2003). Soil samples were collected after soil solarization and analyzed for major macro- and micro-nutrients. After solarization, cabbage seedlings were transplanted in the experimental plots on October 5, 2003-; with minimum soil disturbance, according to the standard methods of cabbage cultivation. The effect of solarization on weed disinfestation was determined by collecting the available weeds in both the solarized and non-solarized plots after 60 days of cabbage transplantation (15 days before the final harvesting of cabbage). Different weedy species were separated, counted and their dry weights were estimated. The effect of soil solarization on cabbage yield was evaluated by estimating the average head weight and total fresh weight of cabbage per acre.

The results indicated that population density and dry weight of most of the recorded weedy species were significantly affected by soil solarization. L. mucronata, C. bursa-pastoris and E. colona were completely absent in the solarized plots, indicating that these species are most sensitive to the solarization process. Out of the total 10-recorded species, the densities of seven species and dry weights of five species were significantly lower in the solarized plots as compared to the control. Solarization did not significantly affect frequency of occurrence, population density and the dry weight of P. oleracea and dry weight and frequency of occurrence of M. indica, indicating that these species are more resistant to solarization than the other species.

Solarization for a period of two months did not affect the concentrations of potassium, sodium and phosphorus, but significantly increased the concentrations of calcium, magnesium, nitrate and sulfate. In addition, solarization significantly increased the levels of some micro-nutrients, such as cupper, iron and zinc. Solarization increased the average yield of cabbage from 7443 kg/acre in non-solarized plots to 8857 kg/acre in solarized plots (about 19% increase). Similarly, the average head weight of cabbage increased by about 32% than that of the control.

Five experiments were performed in order to evaluate the effect of (1) differential response of different weeds to solarization (2) plastic types and thicknesses, (3) soil amendments, (4) seed age and (5) seed source on the efficiency of soil solarization. The last four experiments were conducted using seeds of P. oleracea. The experiments were conducted during the hottest period of the year from June 10 to July 25, 2003 in a private farm near AI-Ain, UAE. Seeds were cleaned and placed into 4cm x 6cm mesh bags.

The differential response in seed germination of different species to solarization process was assessed for seeds of three winter weedy species buried at three depths for different durations. These are Echinochloa cruss galli, Capsella bursa-pastor and Echinochloa colona. The results indicated that soil solarization resulted in a complete deterioration in the seed germination of E. cruss galli and C. bursa-pastor after 15 days of solarization at all depths (2.5 cm - 15 cm). This indicates that seeds of the two species are very sensitive to the solarization process even after short period and at a deeper depths of soils. For E. colona, 15 days of solarization resulted in complete inhibition for germination for seeds buried at soil surface, but seeds buried at 7.5 cm and 15 cm germinated to 37% and 56.4%, respectively. After 30 days of solarization, all the seeds were killed at the different depths of the soil. The overall results of this experiment indicates that the seeds of the three studied species are relatively more sensitive to solarization process than seeds of the summer annual P. oleracea.

The efficacy of using different polyethylene colors and thicknesses of polyethylene sheets on seed viability of P. oleracea was evaluated through the estimation of final germination percentage and germination rate. This species is often used as an indicator species, such that its control with solarization usually often result in control of most weed species. Fresh seeds of P. oleracea were buried in the soil at 2.5 cm and 15cm depths for a period of 15, 30 and 45 days. The used polyethylene colors and thicknesses were: 120µm opaque black, 50 mum transparent (thin), 75 mum transparent (medium) and 150 mum transparent (thick). The results showed that the most effective sheets in suppressing seed germination were the thin and medium thicknesses of the transparent sheets. The deterioration in seed viability increased with the increase in solarization duration and this was more pronounced in thin transparent plastic than in thick transparent and black sheets. Based on the results, it is strongly recommend using the thin or medium thicknesses of transparent sheets instead of black sheets, which are regularly used in UAE.

The effect of soil amendments prior to solarization on increasing the efficiency of this technique in controlling P. oleracea weed was evaluated by burying fresh seeds at 2.5 cm and 15 cm depths in soil amended with organic manure and plant residuals. Seed viability was assessed by calculating final germination percentage and germination rate after 15, 30 and 45 days of solarization. Results indicated that soil amendments, especially organic manure, were efficient enough to inhibit germination of P. oleracea seeds at 2.5 cm after 45 days of solarization. However, the amendments did not improve the efficiency of solarization to reduce viability of seeds buried at the lower depth (15 cm). In fact, plant residues protected the seeds at 15 cm from deterioration, as compared to organic manure and non-amended solarized plots. The germination rate was significantly slower for plots amended with manure (30), as compared with those amended with plant residues (36) and non-amended plots (39).

The differential response of seeds with different ages to solarization process was evaluated by comparing its efficiency on fresh and stored seeds of P. oleracea buried at two depths for different durations. The results showed that the efficiency of soil solarization on deteriorating stored seeds was significantly greater than that of fresh seeds. Final germination percentage and germination rates were lower for stored seeds as compared to fresh seeds.

The effect of solarization process on seed source, where seeds developed and matured, was evaluated by comparing the efficiency of this technique on viability of stored seeds of P. oleracea collected from UAE, Egypt and Canada. Seeds from UAE population were more resistant to solarization than seeds from both Egyptian and Canadian populations. The overall germination of seeds from Canadian, Egyptian and Emirates populations decreased from 30%, 22.3% and 37.5%, respectively, after 15 days of solarization to 10.4%, 10.6 and 19.7% after 45 days.

The positive effects of soil solarization, confirmed in the present study, on the yield and quality of cabbage, on most of the essential macro- and micro-nutrients in the soil and its efficiency in controlling weeds reveal the advantages of the technique as an alternative to soil fumigants, which are commonly in use to control most soilborne pests and weeds. Being an environmentally free technique, solarization will assume a predominant role in the future as a soil disinfestation method, particularly in the Arab Gulf region as it receives higher intensity of solar radiation for longer periods, compared to other regions of the world. In UAB, farmers leave their farms during summer uncultivated because of the extremely high temperature at that time. During summer, mulching the soil with transparent polyethylene sheets would be an effective, economical and acceptable method by farmers. This environmentally friendly method is simple, safe, involves no phytotoxicity or pesticide residues and does not require sophisticated mechanisms to app

Download
COinS