Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2008
Publication Date: 1/1/2009
Citation: Pratt, R.G., Tewolde, H. 2009. Soil fungal population levels in cotton fields fertilized with poultry litter and their relationships to soil nutrient concentrations and plant growth parameters. Applied Soil Ecology. 41:41-49. Interpretive Summary: It has long been known that applying large quantities of poultry litter and other animal wastes to soils for their disposal causes major imbalances in levels of soil nutrients, and that these may ultimately lead to degradation of water quality in adjacent lakes and streams. Much less is known of whether or how applications of animal wastes affect populations of micro-organisms in the soil. Soil microbial communities are important because they maintain the health and quality of soils by breaking down plant residues and storing, translocating, releasing, and making available chemical nutrients essential for plant growth. Therefore, high populations of bacteria, fungi, and other microorganisms usually are associated with high soil quality. In this study, population levels of soil fungi were evaluated in cotton fields where poultry litter was applied as a fertilizer. Fungal population levels were measured by adding soil to agar in petri dishes and counting numbers of colonies that developed. During two years, fungal population levels were usually highest in soils that received poultry litter or conventional fertilizer and lowest in unfertilized soil. High levels were most often associated with high concentrations of nitrogen in soil, and less often with other nutrients. In several instances, fungal population levels also were positively correlated with growth and yield of cotton. Overall results indicate that applying poultry litter to cotton fields as a fertilizer does not negatively affect populations of soil fungi, but rather, that both poultry litter and mineral fertilizer cause populations of soil fungi to increase. Results also show that soil fertility factors that promote the growth and yield of cotton usually are related to increased populations of soil fungi as well.
Technical Abstract: Fungal population levels in soil and their relationships to nutrient concentrations and plant growth were evaluated in plots on two cotton farms in Mississippi where poultry litter (PL) was applied as a fertilizer to promote its safe disposal. Fungal population levels were estimated by dilution plating in soils obtained early and late in the 2005 and 2006 growing seasons from four treatments at each farm: low and high rates of poultry litter (PL), conventional fertilizer (CF), and no fertilizer. Years or seasons and fertilization treatments were significant (P=0.05) sources of variation in fungal population levels on both farms. Fungal population levels in soils of PL and CF treatments did not differ significantly, but both were often higher than in unfertilized controls. Concentrations of P and K usually were significantly higher in soils that received PL than in CF and 0-fertilization treatments, whereas concentrations of N and 7 other elements often did not differ significantly between treatments. Fungal population levels were most frequently correlated with N levels in soil and less frequently with 9 other elements. Fungal population levels also were significantly correlated with leaf area index, leaf chlorophyll content, and yield of cotton in some instances. Among genera and species of Fusarium, Penicillium, and Trichoderma, whenever population levels differed between treatments, highest levels usually were observed in soils of one or both PL treatments. Results indicate that fungal population levels in soils of cotton fields in Mississippi are not affected by addition of PL per se, but rather, that these usually increase in response to greater soil fertility and plant growth that is induced by both PL and CF treatments.