Ecological and sociological aspects of the Phalaris minor epidemic in the rice-wheat system of Haryana, India

Franke, Angelinus Cornelius (2003) Ecological and sociological aspects of the Phalaris minor epidemic in the rice-wheat system of Haryana, India. PhD thesis, University of Glasgow.

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The fertile Indo-Gangetic plains of northern India are well suited for intensive crop production systems and provide food grains to millions of people living on the Indian subcontinent. The prevalent agro-ecological circumstances in the rice-wheat system of the Indo-Gangetic plains allowed Phalaris minor to become a ubiquitous weed infesting around 16m hectares of wheat, and causing yield losses up to 80%. The weed has hitherto been controlled by the phenyl-urea herbicide isoproturon, but the development of herbicide resistance among P. minor biotypes in the early 1990s drastically reduced control. Since then, newly introduced herbicides have relieved the weed pressure. However, the continuing risk that P. minor biotypes develop cross-resistance against other herbicides stresses the need for an integrated weed management strategy for the region. The present thesis addressed ecological and wider socio-economic aspects of the P. minor epidemic in the rice-wheat system of Haryana State in northwest India. Three types of complementary field studies have been conducted: (1) studies of the soil seedbank dynamics of P. minor, (2) research on the lifecycle of P. minor as affected by tillage regime and herbicides and (3) a farmer survey concerned with the wider agronomic and socio-economic impacts of the P. minor epidemic. A population dynamics model of P. minor in competition with wheat was developed to organise and integrate existing knowledge of biology and ecology of P .minor with new experimental observations made in the current study. The model was used to test alternative weed control strategies. A second modelling study, of the effect of aggregation among farmers on the adoption rate of technological innovations, aimed to provide novel techniques to incorporate heterogeneity in societies into quantitative models of adoption processes. Soil seedbank studies showed that P. minor seed half-life time is often limited to less than one year. Location and depth of burial were among the factors that affected seed longevity and longest seed longevity was observed when seeds were buried under anaerobic soil conditions at 30cm depth. Studies on the effect of soil cultivations on the vertical movement of seeds throughout the soil profile suggested that the practice of mouldboard ploughing before wheat sowing may assist in curbing P. minor populations by moving seeds to depths from which they cannot emerge. Straw burning was found to have a strong impact on the survival of seeds lying on the soil surface, while seeds covered with soil and slightly protected from strong heat usually survived straw burning. The results highlighted the importance of soil seedbank processes for P. minor's entire population dynamics. Lifecycle studies have revealed that application of zero tillage systems reduces P. minor pressure by diminishing the emergence rate of first and second flush seedlings. Herbicide applications suggested that isoproturon-resistant P. minor biotypes exhibit cross-resistance against the newly introduced herbicide fenoxaprop-P-ethyl. A strong linear relationship was found between P. minor vegetative weight and reproductive output. The data suggested that large seed losses occur between the stage of seeds on the mother plant and the soil seedbank at the beginning of the following growing season. The lifecycle model assigned an important role to zero tillage in curbing P. minor populations when herbicide inputs are low. The model also suggested that P. minor can be controlled effectively without the use of herbicides provided that 50% of land is used for winter crops other than wheat each season. It is concluded that crop diversification should have a central place in the development of an integrated weed control strategy to reduce reliance on herbicide for weed control. The socio-economic survey gave evidence for the existence of classes of farmers in Haryana with different socio-economic backgrounds, who had unequal access to information on farming and varied in their ability to adopt technical innovations aiming to improve P. minor control. This may lead to a widening gap in adoption levels of technology and socioeconomic strength between farmer classes in the future, which may ultimately result in expulsion of many small farmers out of farming. While the resulting consolidation of farming might be advantageous for the business at a macro-economic scale, the social consequences of disappearing rural livelihoods may be grave. This can be avoided by making innovative technologies available to small-scale farmers. As small farmers are likely to remain a significant feature of farming in Haryana in the near future, improving the accessibility of higher technologies to smaller farmers would enhance the general level of technology adoption in Haryana. This in turn, may provide opportunities to diversify the present cropping pattern, benefiting P. minor control as well as the entire sustainability of the farming system in Haryana.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Plant pathology.
Colleges/Schools: College of Science and Engineering
Supervisor's Name: McRoberts, Neil
Date of Award: 2003
Depositing User: Enlighten Team
Unique ID: glathesis:2003-72676
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 07 Jun 2021 07:05
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