Repository logo

Theses and Dissertations

Permanent URI for this collection

https://hdl.handle.net/10217/100514

Browse

Browsing Theses and Dissertations by Subject "agriculture"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Analysis of land use change and greenhouse gas emissions in Kalasin Province, Thailand
    (Colorado State University. Libraries, 2018) Chailangka, Preeyarat, author; Paustian, Keith, advisor; Fonte, Steven, committee member; Leisz, Stephen, committee member
    Growing global population causes many stresses on the environment, perhaps the most serious is global warming due to Greenhouse Gas (GHG) emissions. Major contributors to GHG emissions include agricultural production and land use change. Southeast Asia is one of the world's fastest growing regions and provides many crops for export, so the land use changes are rapid and not always made in an environmentally conscious manner. The province chosen for this study, Kalasin, is located in a major economic development region with the multi-country East-West Economic Corridor (EWEC) running through it. The EWEC has brought many changes to this province such as expansion of the manufacturing sector, more urban growth to support new factories, and new roads to reach areas which were previously not developed. The largest single land use in Thailand and the Kalasin province is cropland. There have been many changes in farming practices in the province as well, from the types of crops grown to the increasing numbers of commercial farms. These shifts in land use are leading to changes in the amount of GHG emissions and are also leading to land degradation in parts of the province as well. The largest GHGs emissions in agricultural sector come from rice cultivation (45%), followed by biomass carbon stock losses (40%). Some government policies have led to crops being grown on unsuitable lands, which is often associated with greater use of fertilizers and intensive tillage practices applied. Other practices involve draining wetlands, creating rice paddies on unsuitable soils, or clearing forests to farm the area. In this study we look at land use and land use changes throughout the province and use that data to estimate a GHG emissions inventory in the agricultural sector in order to better understand the effects that growth, land use and land use changes in the Kalasin province have on the environment.
  • Thumbnail Image
    ItemOpen Access
    Modifications to temperature-based estimates of consumptive water use by mountain meadows
    (Colorado State University. Libraries, 2008) Temple, Darcy G., author; Smith, Dan H., advisor
    Legal and engineering water communities in Colorado utilize the original Blaney-Criddle method to manage competing demands for water in mountain meadows, yet Blaney-Criddle underestimates in semi-arid, high-elevation environments. Blaney-Criddle consists of a consumptive use (CU) term, f, that is the product of mean monthly temperature, t, and percentage of daylight hours; and a crop coefficient, k, which accounts for crop variation and additional meteorologic effects. Low night temperatures at high elevations incorrectly weight f, and year-to-year variability among k values often results in significant variation between computed consumptive use and lysimeter measurements. Three modifications of the Blaney-Criddle temperature expression were tested against two existing temperature methods (Blaney-Criddle with conventional mean t, and Hargreaves) using lysimeter measurements from nine irrigated grass meadow sites in the upper Gunnison River basin (1999-2003). Use of two modified temperature expressions resulted in improved correlation of estimated Blaney-Criddle f with lysimeter CU. These improvements were similar to those observed when estimating with Hargreaves, which incorporates an additional term, Tdiff, the difference between maximum and minimum daily temperature. Climatological sources of variability in the crop coefficient, k, were also examined. The May-September crop coefficients k were better correlated with Tdiff (r = 0.28 to 0.54) than with mean t (r = 0.01 to 0.43). Specific regression equations based on Tdiff were used to develop crop coefficients from a dataset comprising the current study and three previous calibration studies in Colorado mountain meadows. Based on the standard error of estimate (SEE), estimates using the modeled coefficients more closely predicted CU than did estimates based on averages of locally calibrated k's (SEE difference of up to 5 mm mo-1). Correlations of solar radiation (Rs, the primary energy input to evapotranspiration) with alternative temperature expressions and Tdiff were improved over correlations of Rs with mean t, supporting the improved prediction performance of alternative temperature expressions and of the modeled k based on Tdiff. Those modifications can be applied successfully throughout Colorado mountain basins, and it is hoped that the same technique can be applied to other areas of the western U.S.
  • Thumbnail Image
    ItemOpen Access
    The effects of soil structure on soil organic matter: a mechanistic approach
    (Colorado State University. Libraries, 2022) Even, Rebecca, author; Cotrufo, M. Francesca, advisor; Conant, Richard, committee member; Paustian, Keith, committee member
    Two key factors theorized to affect soil organic carbon (SOC) dynamics are type of plant carbon (C) inputs and soil structure (i.e., soil aggregation), both are influenced by management practices and are considerably intertwined. Research surrounding these factors has increased in the last several decades as the threat of climate change has forced policy makers to find natural based solutions to rising CO2 levels in Earth's atmosphere. Given that soil acts as the largest terrestrial C pool but has lost substantial amounts of C due to land use change and unsustainable agriculture, focus has shifted towards identifying better ways to manage arable lands that improve SOC storage. Among the conventional management practices tillage is likely the most studied, because of its damage to soil structure, leading to soil C losses. However, while research centered on tillage effects on soil aggregation and SOC cycling is vast, few studies explore how plant C input type (i.e., soluble versus structural) and disturbance (i.e., tilling) together affects SOC in soils with different degrees of aggregation. We examined the effects of soil texture, disturbance, and plant input type on soil aggregation, C mineralization, and formation and persistence of plant input-derived SOC to better understand the mechanisms by which soil aggregates help form and protect SOC, specifically as particulate and mineral associated organic carbon (POC and MAOC). POC and MAOC are expected to be formed by distinct pathways, respectively from structural and soluble inputs. Because of their different mechanisms of protection, POC and MAOC are also expected to respond differently to plant inputs and management practices, like tilling, that disturb soil aggregates. We aimed to parse the formation and persistence of POC and MAOC by adding 13C labeled plant residue separated into soluble and structural plant constituents to determine how these physically distinct plant compounds contribute to either pool when soil is intact or disturbed. In an in-lab incubation using 13C enrichment, we traced SOC over the course of one year in a factorial design with four factors: soil type*disturbance*plant input*harvest. Our results showed, as expected, that hot-water extractable (HWE) plant inputs contributed substantially to MAOC while structural plant components (SPC) inputs preferentially formed POC. Interestingly, we found that disturbance resulted in less HWE mineralized to CO2 and more MAOC formation in the highly aggregated (HA) soil suggesting that increased mineral surface area caused more efficient dissolved OM sorption. Moreover, HWE-derived MAOC persisted in both the undisturbed (U) and disturbed (D) HA soils but not in low aggregation (LA) soils, indicating that persistence of MAOC is dependent on soil type and aggregation (i.e., soil physical structure). Although we did not observe significant differences in aggregate-occluded POC (oPOC) formation between HAD and LAD soils, we did see higher oPOC persistence in HAD soil compared to LAD soil. Greater accumulation oPOC in HAD from day 22 to the end of the incubation suggests, again, that soil type influences the persistence of POC through occlusion in aggregates. To corroborate this, we also found that LAD soil had the highest CO2 mineralization of SPC plant inputs as SPC was left more unprotected in the soil with a low capacity to aggregate. Disturbance did not affect microbial biomass in either HA or LA soils. We saw more plant-derived microbial biomass C from HWE inputs compared to SPC inputs in the bulk soil, indicating that HWE inputs are assimilated into microbial biomass, thus incorporated into SOC with higher efficiency. Lastly, there was a significant drop in % plant-derived microbial biomass C in the bulk soil overtime, as expected. However, because the % HWE-derived MAOC persisted in HA soils regardless of disturbance, we illustrated the importance of microbial necromass in addition to direct DOC sorption for SOC stabilization as MAOC. Overall, my study provides mechanistic understanding for the role of soil structure and aggregation on POC and MAOC formation and persistence which can help improve the representation of these processes in models, to provide better predictions of SOC changes with changes in management practices affecting disturbance.