Preliminary studies on the factors affecting weed species composition in cement dust- polluted rice fields in Sitio Tagbac, Antipolo, Rizal.

Date

6-1995

Degree

Bachelor of Science in Biology

College

College of Arts and Sciences (CAS)

Adviser/Committee Chair

Virginia C. Cuevas

Abstract

Factors affecting the weed species composition in rice fields surrounding a cement factory in Sitio Tagbac, Antipolo, Rizal were studied using correspondence analyses. The study covered the rainy season from September, 1994 to January, 1995. Three rice fields that were most similar in cultural management but differed in their distances relative to the cement factory were chosen as sampling sites. Sites 1 and 2 were terraced, while site 3 was not The effects of soil physical and chemical proper-ties and cultural management on the weed vegetation were also studied. Weed sampling by the harvest method started two weeks after rice transplanting and ended one month after harvesting. The mean importance values of the species across the time they appeared in each site were calculated. The results showed that for all sites, only a few species had relatively large importance values across time. They were: Cynodon dactylon, Cyperus rotundus, Paspalum scrobiculatum, Echinochloa crudgalli, and Ammania baccifera. Most of the species had negligible contributions, although a few tend to be found exclusively in particular sites. The rate of cement dust deposition on each lot/site were determined by exposing pre-weighed, oven-dried filter papers on each lot/site under measured periods of time. Statistical tests showed that the interaction effect between terracing and site distance, and site differences in the rates of cement dust deposition were not significant. The estimated annual rates were 2.83 t/ha for site 1, 2.21 t/ha for site 2, and 4.3 t/ha for site 3. Composite soil surface samples were taken from each site after the harvest period and tested for total N, organic matter content (OM), available P, exchangeable Ca and K, pH, and waterholding capacity (WHC). Results showed considerable site differences in N, P, and (WHC). The soils were found to be alkaline, with the pH highest in site 2 at 8.1, followed by site 1 at 7.7, and site 3 at 7.6.Th relationship of cement dust deposition with the measured soil properties was not established because of the absence of data on the soil in the study site before the establishment of the cement factory which could have allowed a comparative analysis. Within-site correspondence analyses revealed considerable variation in the weed species composition in the terraced lots of sites 1 and 2. Different lots were associated with different weed groups (grasses, sedges, and broadleaf weeds). This indicates the possible effect of terracing. Analysis of site 3,on the other hand, also showed variation in the weed species composition in non-terraced lots. This suggests the possible presence of an environmental gradient within site 3 which could have caused the variation. Among-site correspondence analysis using the weed vegetation and environmental variables showed that the weed species composition in the three sites varied. The tendency of grasses and sedges to predominate in site 1 was explained by the continued use of the same herbicide for several years, which led to the build up of herbicide-tolerant species. The factors that most likely affect the weed population in site 2 are the sites' high soil WHC and available P. The high available P was attributed to high soil pH, while WHC probably is an inherent characteristic. The broadleaf weeds found in site 2 were also found in sites 1 and 3. Their tendency to predominate in this site indicates that the high soil pH and WHC are more favor-able for their growth, compared with that of the two other sites. For site 3, where, the weed composition is intermediate to that of sites 1 and 2, the 10-14.3 cm depth of water could have limited the growth of weeds. The large amount of fertilizer applied (135 kg N/ha). on the other hand, could have stimulated the growth of N-responsive weeds such as Fimbristylis littoralis and Echinochloa crus-galli. The effect of cement dust on weed species composition in rice fields was not established because the sites received similar amounts of cement dust under the period of observation, the observation period for the weed population was limited, and data on the plant population in the study before the establishment of the cement factory were also absent.

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

Thesis

Document Type

Thesis

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