Theses and Dissertations

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Open Access
Parent material-topographic-management controls on organic and inorganic nutrients in semiarid soils
(Colorado State University. Libraries, 1984) Aguilar, Richard, author; Heil, Robert D., advisor; Barbarick, K. A., committee member; Schumm, S. A., committee member; Franklin, W. T., committee member
Paired native grassland and cultivated landscapes were characterized to evaluate parent material and topographic controls on organic matter and phosphorus along catenary sequences in southwestern North Dakota. Site selection was based on parent material (sandstone, siltstone, and shale residuum), similar cropping history (44-yr wheat-fallow rotation), and uniform range management. Parent material-soil process relationships were established by evaluating chemical and physical data for soil profiles at the native-summit landscape segments on the three contrasting parent materials. The effects of topography on the amounts and vertical distribution of organic matter and phosphorus were evaluated by studying soil profiles at various geomorphic landscape components along the catenas. The effects of 44 years of cultivation were evaluated by comparing cultivated and virgin soils at each landscape segment using the soils on native pasture as benchmarks. The finer textured soils weathered in shale were found to have much higher levels of organic C, N and Total P. Soils weathered in sandstone were found to have more uniform decreases in organic matter with profile depth and the highest quantities of organic P. On the native pastures, quantities of organic matter were much higher in the lower landscape segments because of higher moisture contents and/or the deposition of organic matter-enriched soil. Soils at lower landscape segments (lower backslopes, footslopes) have been enriched with Total P at the expense of soils at the upper portions of the catenas. Changes in organic and inorganic soil constituents resulting from cultivation were found to vary as a function of parent material and topography. Mineralization losses of organic constituents appear to have been higher in the sandstone soils. The fine-textured shale soils, which appear to have a large proportion of highly humified, clay associated organic matter, lost the lowest quantities of organic constituents relative to total soil loss. Losses of organic matter were generally lower at the lower landscape segments in all three sites, reflecting soil deposition. Redistribution of soil material by both mechanical (tillage practices) and natural processes (wind and water erosion) must be considered when evaluating cultivation-induced changes in soil properties along catenary sequences.
Open Access
Factors controlling soil spatial variability in a native range landscape
(Colorado State University. Libraries, 1984) Paroussis, E. (Elias), author; Heil, Robert D., advisor; Weitz, Joseph Leonard, 1922-, committee member; Cipra, Jan E., committee member
Soils were characterized along three transects of the same catenary sequence within the semi-arid shortgrass (Bouteloua gracilis) steppe of north central Colorado. The objectives of the study were to: 1. Evaluate which factor or combination of factors (i.e. parent material, topography, biota) is/are the most important controls on soil development, soil organic matter accumulation and soil textural attributes in this environment. 2. Evaluate the spatial variability of selected soil properties and relate this variability to geomorphic form and process. The results indicate a high degree of spatial variability in all soil properties studied. Parent material, erosional (both wind and water) processes, and topographic relationships appear to be the major controlling factors on the degree of soil development, accumulation of soil organic matter, and distribution of particle sizes within the surface horizon of the soils found on the catena. Evaluations of organic carbon, nitrogen and phosphorus, thickness of the surface horizon and solum, depth to lime and particle size data indicate that soil development on this landscape is highly atypical when compared to soil landscape relationships reported in the literature. Soil properties are highly variable within landscape segments as well as across the transects of the same landscape.
Open Access
Studies of the mechanisms of stabilization of organic matter in semiarid soils
(Colorado State University. Libraries, 1985) Payne, Bryce F., author
The effectiveness of three mechanisms of stabilization of soil organic matter (OM) were studied. These mechanisms are (1) chemical recalcitrance, (2) physical stabilization by adsorption onto soil particles, and (3) physical stabilization by occlusion within microaggregates. Mechanisms 1 and 2 were studied by incubation (mineralization) experiments using soil particle size fractions as sources of native soil OM of different chemical quality. These experiments examined microbial utilization and transformations of the C and P associated with the particle size fractions. The characteristics of particle size fractions and the effects of ultrasonic dispersion on them were examined during fractionations using different combinations of sedimentation and ultrasonic dispersion of aqueous soil suspensions. The chemical compositions (C, N, and P) were consistently different for the ultrasonically dispersible and readily water-dispersible fine soil particle-sizefractions. Carbon contents of the fine fractions ultrasonically dispersed from water-stable aggregates of >50 μm equivalent spherical diameter (ESD) were greater than those from smaller (<50 μm ESD) water-stable aggregates. Evidence was obtained that ultrasonic dispersion causes a redistribution of the organic matter associated with different particle size fractions. This has important implications for interpretations of information obtained using ultrasonic dispersion techniques. Several observations indicated the existence of anaerobic microsites inside the larger (>50 μm ESD) water-stable aggregates. Alight blue-gray clay sediment indicating reduced forms of Fe and/or Mn appeared whenever ultrasonic dispersion was used. The fine silt from water-stable aggregates had DTPA-extractable Mn levels 53 times higher than the water-dispersible fine silt. The consistently higher C contents and different qualitative chemical character of the fractions from water-stable aggregates indicated that the decomposition of organic matter in these aggregates is limited by oxygen stress. Occlusion of organic matter in microaggregates is an important mechanism of organic matter stabilization. The concepts of chemical recalcitrance and clay adsorption as mechanisms of organic matter stabilization were studied using incubations of three particle size fractions obtained from two semiarid grassland soils. Microbial transformations of C and P were assessed as indices of relative availability of native forms of these elements. Chemical recalcitrance was hypothesized to increase with increasing particle size. Stabilization by clay adsorption was hypothesized to increase with decreasing' particle size. Three levels of cellobiose-C amendment were used to establish different levels of microbial activity. No utilization of soil organic C occurred without the cellobiose amendment. Net mineralization of P to plant-available forms was found after 124 hours at the lowest C amendment level for all particle size fractions. Net utilization of unextractable P was apparent during the period of increasing biomass. Among the fractions equivalent microbial P was not held in equivalent extractable forms. Native soil C was extensively utilized for all fractions and at all C amendment levels. Although sorptive phenomena were active for all three fractions, there was no greater stabilization of soil organics by clay-sized than by fine-silt-sized particles. It was concluded that chemical recalcitrance was of relatively little importance in stabilizing native soil organic matter. The utilization of native organic nutrients was most closely related to the amount of readily available energy (cellobiose C) present. From the results of the fractionation and incubation studies it was concluded that occlusion within microaggregates is the dominant mechanism of stabilization of soil OM.
Open Access
Lead, cadmium and zinc: evaluation of contamination using the NH4HCO3-DTPA soil test
(Colorado State University. Libraries, 1985) Boon, David Y., author; Soltanpour, P. N. (Parviz Neil), 1937-, advisor; Ells, James E., committee member; Lindsay, Willard Lyman, 1926-, committee member; Redente, Edward F., committee member
The NH4HCO3-DTPA (AB-DTPA) soil test of Soltanpour and Schwab was developed for the simultaneous determination of P, K, Z, Fe, Cu and Mn in calcareous soils. However, its use for evaluating other elements has been demonstrated. The objective of the present research was to evaluate the AB-DTPA soil test for Pb, Cd, Zn and Ni on contaminated soils. Use of the AB-DTPA soil test for evaluating contaminated soils was examined using two laboratory studies. The first study compared the AB-DTPA with the DTPA soil test for Pd, Cd, Zn and Ni on 26 contaminated garden soils from Aspen, Colorado. The second study correlated the AB-DTPA soil test with total soil digests for Pb, Cd and Zn on 21 contaminated soils from Aspen, Colorado. The results indicate that the AB-DTPA soil test was highly correlated with the DTPA test for Pb, Cd, Zn and Ni. Correlation coefficients (r) were 0.96 for Pb, 0.99 for Cd, 0.99 for Zn and 0.90 for Ni. The results of the total soil digests demonstrate that the AB-DTPA soil test is highly correlated with total element concentrations for Pb, Cd and Zn. Correlation coefficients (r) were 0.92 for Pb, 0.93 for Cd and 0.89 for Zn. Additional laboratory studies were conducted to evaluate the nitric acid plant digest procedure of Havlin and Soltanpour for plant analysis of Pb, Cd, Zn, Ni and Mo. Results obtained from digestion of National Bureau of Standards (NBS) Reference materials (1571, 1573 and 1575) demonstrated that the nitric acid digestion procedure compared well with NBS certified values. Field sampling of Aspen soils and plants from Aspen resulted in high levels of Pb, Cd and Zn in both soils and plants. Soil Pb levels in excess of 100 ug/g AB-DTPA Pb may pose potential health hazards from the ingestion of contaminated soil. Plant concentrations of Pb, Cd and Zn were highest in leafy vegetables. Root crops were intermediate and took up less metals than leaves but more than vegetable fruits. The NH4HCO3-DTPA soil test was a good predictor of Pb and Cd concentrations in lettuce (Lactuca sativa) and spinach (Spinacia oleracea). Correlation coefficients (r) were (0.95) and (0.86) for Pb and Cd, respectively.
Open Access
Effect of tillage on soil physical properties and crop production
(Colorado State University. Libraries, 1989) Abdi, Abdullahi Abdurahman, author; Sutherland, Lorenz, advisor; Schmehl, W. R., advisor; Eckert, Jerry, committee member; Danielson, Robert E., committee member; Johnson, Duane L., committee member
The objective of this study was to determine the effect of two tillage systems -- conventional tillage (CT) and reduced tillage (RT) -- for a three-year corn-corn-watermelon rotation on: 1) biological production of corn and watermelon, 2) changes in soil physical properties, and 3) effect of tillage on irrigation at the Arkansas Valley Research Center, Rocky Ford, Colorado. Treatments were designed to evaluate tillage systems over the entire duration of the rotation rather than evaluating individual tillage operations or tillage implements. The results of this study showed neither a benefit nor loss in corn grain-yield under RT when compared to CT. The effect of tillage system on dry matter yield of corn varied with planting method. With flat planting for both CT and RT, yields of total dry matter were higher than CT. When corn was ridge-tilled, the RT system was higher yielding. Tillage system did influence marketable melon production. The yield of marketable melon over the three years averaged 26% higher for RT. Seed yield was not effected by tillage system in 1985, but a decrease in seed yield was observed in 1986 with RT where the disk was used as the primary tillage tool. Tillage system also had varied effects upon physical properties of the soil. The RT system resulted in greater aggregate stability, a higher residual soil moisture content, and increased infiltration. In 1986, these benefits may have been counteracted by lower early-season soil temperature and greater soil compaction at the 15-30 in depth. The increased moisture storage resulted in savings of irrigation water, labor and energy -- an economic advantage. Lower soil temperatures for the RT system may have contributed to reduced evaporation and reduced runoff -- also possible economic and societal benefits. Results of this study indicate that lower soil temperatures may have been the cause for retarded early-season corn growth. The RT system has several beneficial attributes that offer promise for becoming an attractive management system. In terms of immediate benefit to the farmer, greater savings in energy, labor and machinery would be possible under this system. Given proper management and the application of improved cultural practices, i.e. rotation, fertilization, weed control, etc., the farmer may, by using the RT system, produce crop yields equal to or even greater than CT with less dollars, the greatest potential being under rainfall situations.
Open Access
Energy, structure, soil and self-regulation in plant/soil systems: a conceptual model
(Colorado State University. Libraries, 1989) Payne, Bryce F., author
A new concept is presented which suggests that in stable plant/soil systems, plants control the soil environmental factors that affect plant growth and the interactions among those factors by controlling system structure. The concept is based on the plant-control hypothesis and rhizocentric model of soil structural development. The plant-control hypothesis declares that in plant/soil systems energy is the primary resource, and structure an essential regulator of energy flows. The rhizocentric model of soil structural development in grass-dominated plant/soil systems describes the process which results in plant-control of soil structure, and, consequently, of energy and nutrient flows for such systems. In conjunction, the plant-control hypothesis and rhizocentric model form a conceptual model of control in plant/soil systems. The conceptual model may help explain the self-regulatory capabilities of stable plant/soil systems, and the causes of instability in some agricultural plant/soil systems. Examination of published data from various sources has revealed no case in which application of the conceptual control model did not result in logically consistent, reliable prediction of experimental outcomes, plausible interpretation of previously uninterpretable results, and often, formulation of testable new hypotheses. It is concluded that the control model -- and the plant-control hypothesis and rhizocentric model which it implies -- has enough credibility to merit further critical examination as a potentially useful conceptual tool for soil and agricultural science, biology, and ecology.
Open Access
Soil textural control over decomposition and soil organic matter dynamics
(Colorado State University. Libraries, 1991) Scott, Neal A., author; Cole, C. Vernon, advisor; Sanford, R. L., Jr., committee member; Elliott, E. T., committee member; Peterson, G. A., committee member
Soil texture is an important factor that influences litter decomposition and soil organic matter (SOM) dynamics, but few experiments have addressed specific mechanisms. Even less work has been done to answer the question of how important abiotic driving variables interact with soil texture to affect decomposition. I used laboratory soil incubations coupled with a simulation model to describe the interaction of soil texture with soil water availability and nutrient availability. I also addressed the importance of litter placement (surface vs. incorporated) across a gradient of texture, moisture and nutrient availability. The laboratory experiment was a randomized complete block design. Treatments consisted of texture (73%, 55%, 40% sand), water availability (- 0.012 MPa, -0.033 MPa and -0.3 MPa), nutrient availability (plus nitrogen (100 mg kg-1) and phosphorus (40 mg kg-1), ambient soil levels), litter placement (surface and incorporated), and replicates (3). Soils were packed into cores at a bulk density of 1.45. Wheat litter (C/N = 19) labeled with 14C was added to the soil cores at a rate approximating 2200 kg ha-1 total C addition being 2170 mg C kg-1. The cores were incubated for 90 d. Respiration (14C/12C-CO2) was measured weekly except during the first 10 d, when it was measured every 5 d. The fine textured soil lost more 14CO2 and 12CO2 than either of the other soils when litter was incorporated. Soil water potential significantly affected litter decomposition, the -0.012 MPa treatment decomposing faster than either the -0.033 or -0.3 MPa treatment, both of which were similar. Nutrient addition had no effect on decomposition for either litter placement treatment. Litter placement had no effect on the rate of decomposition. When the respiration data were divided into 3 time periods (0-10, 11-51 and 52-90 d), there was greater loss of surface 14CO2 from the coarse soil during 0-10 d (surface litter only). The overall 90 d effect of texture was not significant. Respiration rates correlated significantly to percent water-filled pore space (%WFPS) regardless of litter placement, although incorporated litter showed much less variability than did surface litter. Addition of litter carbon stimulated the mineralization of soil organic C, contributing significantly to the overall respiration rates during the incubation. Nutrient interactions may play an important role in decomposition and organic matter d3mamics, though they appeared unimportant in this experiment. A simulation model was constructed to analyze possible interactions between carbon, nitrogen and phosphorus during decomposition. Percent water-filled pore space controlled the utilization rate of litter C and SOM. Microbial C/N ratio controlled uptake rates of all C pools. Simulated results using high C/N ratio substrates showed slower decomposition than laboratory data, leading me to suspect that the simulated division of plant C into structural and metabolic C was incorrect. The model provided the opportunity to test ideas about the effect of texture and soil water potential on decomposition and SOM dynamics across a range of abiotic conditions and litter types.
Open Access
Soil evolution on a terrace chronosequence in the Wind River Basin, Wyoming
(Colorado State University. Libraries, 1994) Peacock, Charles R., author; Kelly, Eugene F., advisor; Barbarick, K. A., committee member; Wohl, Ellen E., 1962-, committee member
A series of strath terraces overlain with alluvial deposits from glacial and inter-glacial periods were used to develop a chronosequence. The sequence of soils examined in this study illustrate the effects of time on soil formation. Clay and carbonate percentages showed significant increases over time. Other indicators of soil evolution were less useful in evaluating the relationship between time and soil properties. Mineralogy characterization shows a predominance of smectite throughout the clay size fractions at each site. Chlorite, vermiculite and palygorskite are also abundant as well as intergrades of chlorite-smectite and mica-smectite. Results of this study demonstrate the dominance of aeolian additions to soil vs. chemical weathering in these environments. This work provides a greater understanding of the relationship between soil properties and time and should prove useful to pedologists, geologists and other scientists interested in landscape evolution.
Open Access
Improvement of soil test P calibration and fertilizer P management in crop rotations in Moroccan dryland agriculture
(Colorado State University. Libraries, 1997) Amrani, Mohamed, author; Westfall, Dwayne G., advisor; Peterson, Gary A., committee member; Barbarick, Kenneth A., committee member; Moore, Frank Devitt, III, committee member
Although the main limitation of crop production in the arid and semiarid regions of Morocco is lack of sufficient rainfall, phosphorus (P) nutrient deficiencies also are major obstacle to maximum crop production. Fertilizer management is an important step in sustainability of crop production where both economic and environmental concerns are important. The objectives of this study were (i) to improve fertilizer P recommendations by the inclusion of P sorption capacities of individual soils in the P requirement model and (ii) to determine the effect of direct, cumulative, and residual P on wheat (Triticum aestivum) and chickpea (Cicer arietinum L.) yields under field conditions in two cropping systems: continuous wheat and chickpea-wheat. Phosphorus buffering indices were determined from sorption isotherms developed using 19 soils from the Abda, Chaouia, and Ben Sliman zones of Morocco. The greenhouse study consisted of growing wheat (cv. Merchouch) on 13 soils with four Prates (0, 3.4, 6.7, and 13.4 mg P kg-1). Maximum buffering capacity (MBC) of soils was incorporated into the Mitscherlich model to determine P fertilizer requirement. Soils showed a contrasting ability to adsorb P. Maximum P adsorption (Xm) varied from 146 to 808 mg P kg-1 soil. The tentative calculations of P requirement, assuming the soil test P levels in all 13 soils was 3 mg P kg-1, showed that the amount of fertilizer needed for 90% of maximum yields varied from 1 to 15 mg P kg-1 soil. However, the fertilizer P recommendation by the usual method was 12 mg P kg-1 for all soils with a soil test P of 3 mg kg-1. These results suggest that the inclusion of buffer indices in determining P requirement can increase the accuracy of P recommendations. In a greenhouse study, two other crops were grown after wheat. Com (Zea mays L., cv Kamla) was harvested after 60 days and wheat was grown to maturity. The treatments were four Prates applications (0, 3.4, 6.7, and 13.4 mg P kg-1) using 13 soils on the first and third crop (wheat). This greenhouse study showed that a significant response of com to residual P occurred in soils with initial NaHC03-P test levels less than 6 mg P kg-1. The response was inconsistent between 6 and 10 mg P kg-1, and no response occurred above a soil test P level of 10 mg P kg-1. In general, soils with more than 14 mg kg-1 NaHC03-P level provided adequate P for maximum yield for three succeeding crops under greenhouse conditions. Field experiments were conducted in 1994-96 at three locations: Khmis Zemamra, Sidi El Aydi, and Khmis Sidi Rhhal. Phosphorus was applied at 0, 8.9, 17.8, and 26.7 kg P/ha on both wheat and chickpea the first year. The second year, plots were split into with and without P fertilizer treatments. Phosphorus rates of 8.9, 17 .8, and 53.4 kg P ha-1 were required to increase and maintain soil test P level to a sufficiency level for three succeeding crops at Khmis Zemamra, Sidi El Aydi, and Khmis Sidi Rhhal, respectively. The effect of cropping system was not consistent. The residual P effect did not produce maximum wheat yield. Based on the range of P rates used in this study, a single application of P will not supply adequate nutrition for the following crop. If we assume that a chickpea grain yield of 2 Mg ha-1 is a satisfactory yield in a CP-W rotation where wheat is the principal crop, P requirement for chickpea can be met by residual P. Using current wheat and fertilizer prices, the combinations of 17.8-17.8, 26.7-0, and 8.9-17.8 kg P ha-1 would be the recommended P application rates for continuous wheat, W-CP, and CP-W rotations, respectively. Based upon my results I recommend that farmers consider both soil adsorption capacity and rotation (previous P applications and cropping system) to better manage P and optimize profit from fertilizer use.
Open Access
The influence of soil hydraulic property estimation on the predictive accuracy of solute transport modeling
(Colorado State University. Libraries, 1999) Prieksat, Mark Alan, author; Butters, Greg L., advisor; Ahuja, Laj, committee member; Cardon, Grant, committee member; McWhorter, David B., committee member
Because of the complexity of processes governing water and chemical movement in the unsaturated zone, numerical models will necessarily play a key role in predicting the fate and transport of chemicals. If models are to fulfill their role as a tool in managing agrichemicals, then clearly models need to be tested for sensitivity to the method used to measure the soil hydraulic properties used in the model. The objectives of this study were to compare hydraulic parameter estimates obtained using alternative methods and to evaluate the effect of the parameter estimation method on the predictive accuracy of the HYDRUS-20 model. Soil hydraulic parameters were determined at multiple depths within a 2 meter deep soil profile using a variety of methods; field methods included the instantaneous profile method (IPM) and tension infiltrometry at two scales (5.08 cm-diameter (4TI) and 20.32 cm-diameter (8TI)); lab methods included determination of saturated hydraulic conductivity using the falling head method and analysis of moisture retention using pressure plate analysis at two scales (5.08 cm-diameter x 5.08 cm-long soil cores (2C) and 10.16 cm-diameter x 5.08 cm-long soil cores (4C)); indirect methods (IND) included determining hydraulic parameters from three literature sources based on soil textural data. In addition, identical parameter estimates were made under two tillage treatments (non-tilled (NT) and tilled (T)). It was found that estimation of soil hydraulic properties was sensitive to the measurement method selected. Estimation of α and Ks parameters was more sensitive to method and scale than was estimation of the n and ɵs parameters. The IPM method showed the least variability in parameter estimates. Tillage introduced significant changes in the hydraulic properties and increased spatial variability in the parameter estimates. Data obtained using the alternative estimation methods was used as input to the HYDRUS-2D model to predict water and solute movement. Water content and solute concentration profiles estimated using the model were compared with observed water content and solute concentration profiles obtained during a field-scale solute transport study using bromide tracer. Most of the parameter estimation methods resulted in simulated water content that were within about 2 to 5 percent of the measured data. The IND method had the largest deviations (about 10 percent) from the measured data. Under T soil conditions, all the methods (except the IND) predicted bromide movement well and simulated bromide concentration data were well correlated to measured data at all times throughout the simulation. Under NT conditions, all methods, except the 8TI, under-predicted the center of mass movement of bromide. Analysis of the simulation data revealed that the hydraulic properties of the surface soil are extremely important in controlling water and solute movement. Results indicate that the IPM is probably the most reliable method, but other estimation methods may result in similar predictions of water and solute movement when made in repetition.
Open Access
The role of organic matter and other soil properties in Zn2+ activity and AB-DTPA-extractable Zn in soils
(Colorado State University. Libraries, 2000) Catlett, Kathryn M., author; Lindsay, Willard Lyman, 1926-, advisor; Heil, Dean, advisor; Sutton, Sally J., committee member; Barbarick, K. A., committee member; Ebinger, Michael, committee member; Soltanpour, P. N. (Parviz Neil), 1937-, committee member
Zinc is a plant micronutrient as well as a potential heavy metal contaminant in soils. In soil solution, the free Zn activity determines the availability of Zn as a micronutrient and its characteristics as a heavy metal contaminant. A better understanding of the mechanism that controls free Zn activity could improve soil treatments of Zn deficiency or toxicity. In this study, Zn2+ activity (measured by chelation) was related to soil properties for 18 alkaline soils from three farms in eastern Colorado. Organic carbon and pH were statistically significant parameters in a regression with log Zn2+ activity. Principal component analysis and path analysis were studied and applied to these soils. Results of principal component analysis showed that the first principal component, summing clay and total soil Zn and subtracting soil carbon, accounted for 52% of the variability in the soils. Soil pH and inorganic carbon dominated the second principal component, which accounted for 32% of the variability. Results of path analysis showed that direct effects of pH, total soil Zn, and organic carbon are important in predicting free Zn activity in these soils. Indirect effects of clay through organic carbon, of inorganic carbon through pH, and between pH and organic carbon were also important. Results from statistical analyses indicate that adsorption of Zn on organic matter may control Zn solubility in soils. To further explore this potential mechanism, Zn adsorption to organic matter was modeled using the chemical equilibrium model, MINTEQA2, and model results were compared to experimental data from the three Colorado farms. Experimental and model results were in close agreement. Adsorption onto organic matter may control Zn solubility in acidic to neutral soils, while precipitation may control Zn in alkaline soils. The AB-DTPA soil test can also be used as a measure of the availability of micronutrients to plants. AB-DTPA-extractable Zn was measured and correlated to soil chemical properties for soil samples described above. Soil organic carbon and total soil Zn were statistically significant parameters in a linear regression with AB-DTPA extractable Zn. Organic matter and clay contents were positively correlated with AB-DTPA-extractable Zn.
Open 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.
Open Access
Dairy farm phosphorus recovery and re-use to reduce water quality risk and improve phosphorus cycling in agriculture
(Colorado State University. Libraries, 2008) Massey, Michael Stanley, author; Archibeque, Shawn L., advisor; Ippolito, James A., committee member; Sheffield, Ron E., committee member; Davis, Jessica G., committee member; Peterson, Gary A., 1940-, committee member
Phosphorus (P) is a limited natural resource, and its efficient use and cycling are important for the long-term sustainability of agricultural and industrial production. The over-application of P in dairy wastewater to fields, in addition to being inefficient, can lead to the degradation of water quality through P-induced eutrophication from agricultural runoff. This is especially true in areas where dairies and other livestock operations are increasingly concentrated around sources of fresh water such as rivers. Phosphorus recovery and re-use has the potential to reduce the amount of P applied to fields near the dairy while providing a useful, marketable, and easily transportable P fertilizer. This study evaluated the efficiency of magnesium (Mg) phosphate recovery on dairy farms using actual wastewater under field conditions, the nature of various recovered products including magnesium ammonium phosphate hexahydrate (struvite) and magnesium ammonium phosphate hydrate (dittmarite), and the feasibility of using Mg phosphates as fertilizers in slightly acidic and alkaline soil conditions. Dairy wastewater was treated using a cone-shaped fluidized bed reactor and two treatment processes which differed in the chemicals used for pH manipulation. The "conventional" process made use of hydrochloric acid and anhydrous ammonia for pH adjustment, while the "new" process used acetic acid and potassium hydroxide. The "new" process has the potential to produce a certified organic soil amendment with minimal modification to current organic production standards. After wastewater treatment, the recovered P products, along with other samples of recovered Mg phosphates including crystalline struvite and dittmarite, were examined with powder x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy. Finally, struvite, dittmarite, and a heterogeneous recovered product were applied in greenhouse fertilizer trials alongside commercial triple superphosphate (TSP) and certified organic rock phosphate (RP). The fertilizers' performance was tested at two application rates (45 kg ha- 1 and 90 kg ha-1 ) and two soil pH levels (6.5 and 7.6). The "conventional" treatment method removed 14% of the total phosphorus (TP) in the dairy wastewater, while the "new" method removed 9% of TP, along with 12% and 9% of the Mg for the conventional and new methods, respectively. Detailed analysis and characterization of the products, as well as recovered struvite and dittmarite, showed great variation among the chemical, microscopic, and macroscopic characteristics of the different types of recovered Mg phosphates. Fertilizer trials found that TSP and recovered struvite and dittmarite crystals increased plant P concentration in spring wheat (Triticum aestivum L.) grown in slightly acidic soil. At high soil pH, the recovered Mg phosphates increased plant dry matter production over the control and also performed similarly to TSP. The results of the current study indicate that P recovery through Mg phosphate precipitation is possible on dairy farms, but improvements must be made in removal efficiency and consistency of product characteristics. Furthermore, the resulting recovered phosphates may be useful as fertilizers in both acidic and alkaline soils.
Open Access
Pedological and ecological controls on biogenic silica cycling in grass dominated ecosystems
(Colorado State University. Libraries, 2009) Melzer-Drinnen, Susan E., author; Kelly, Eugene F., advisor
The biogeochemical behavior of silica is closely linked to the carbon cycle as marine Si-based diatoms are a major control on the distribution of silica in oceans, and play a major role in controlling atmospheric pCO2 via the "biological pump." The importance of biological controls on silica cycling in the terrestrial environment has only recently been known and our studies point to grasslands and grass dominated ecosystems as important repositories. Although the structure and ecological functioning of these ecosystems are strongly influenced by fire and grazing, the role of these key ecological drivers in the production and storage of Si represents a significant knowledge gap. Additionally, the effect of biogenic silica dissolution on the weathering of rock with different mineral assemblages is also insufficiently understood. I evaluated the effects of fire, grazing and parent material on the range and variability of plant derived biogenic silica stored in plant biomass and soils by sampling plants and soils in the mesic grasslands of North America and savannas of South Africa. Using these and other intensive study sites, along with extant productivity and soil texture data I estimated the global Si storage based on two approaches: "measure and multiply" and "paint by numbers".
Open Access
Precision manure management across site-specific management zones
(Colorado State University. Libraries, 2009) Moshia, Matshwene Edwin, author; Khosla, Rajiv, advisor
In the western Great Plains of the USA, animal agriculture is an important contributor to the agricultural economy, and many livestock farms are close to water bodies where manure can potentially contaminate the environment. The objectives of the study were to (i) assess the influence of variable rate applications of animal manure on grain yield in continuous maize production fields across management zones (MZs) in dryland and limited irrigation cropping systems, (ii) to study the effects of variable rate application of animal manure on selected surface soil quality parameters across MZs, (iii) to evaluate the variable rate application of manure using environmental risk assessment tools of N leaching and P runoff indices and to understand its impact on environmental quality, and (iv) to evaluate and compare the nitrogen (N) mineralization of variable rates of dairy cattle manure applied on low, medium and high MZs in a controlled environment. To accomplish objectives (i) through (iii), the study was conducted under a continuous maize cropping system on dryland and limited furrow-irrigated fields in northeastern Colorado, USA. For objective (iv), a 120 day laboratory incubation study was conducted. The results of this project indicated that using animal manure alone for maize grain yield production was economically inefficient using enterprise budget analysis. The study suggests that manure can, therefore, be used in conjunction with synthetic N fertilizer to meet crop N requirements at early growth of maize, while animal manure improve soil quality of low productivity soils over time. This can potentially help to limit the amount of N and P lost into the environment. For N mineralization, the study showed a significant difference (P≤0.05) in mineralized N across zones when dairy animal manure treatments were compared. However, N from animal manure does not mineralize differently between low, medium and high management zones. The key in precision manure management was to find a balance between economically, agronomically and environmentally sound manure management strategies across spatially variable soils.
Open Access
A mechanistic approach to modeling saturation and protection mechanisms of soil organic matter
(Colorado State University. Libraries, 2009) Olchin, Gabriel Peter, author; Paustian, Keith, advisor
Simulation models have been used extensively as a research tool in the field of soil organic matter (SOM) dynamics and should embody our best understandings of the processes and mechanisms controlling these dynamics. Our objective was to develop and evaluate a SOM model based upon measureable soil organic carbon (SOC) fractions and optimize it against long-term tillage experiments in North America. This model will include (1) soil aggregate dynamics, with direct influence from tillage events; (2); and the mechanisms of SOM stabilization; and (3) explicitly address the concept of potential SOC saturation. The major proposed mechanisms for SOM stabilization-physical occlusion, organic recalcitrance, and organo-mineral interactions-have limited explicit inclusion in current SOM models.
Open Access
Ground based active remote sensors for precision nitrogen management in irrigated maize production
(Colorado State University. Libraries, 2009) Shaver, Timothy Michael, author; Westfall, Dwayne G., advisor; Khosla, Rajiv, advisor
Precision agriculture can increase farm input efficiency by accurately quantifying variability within a field. Remotely sensed normalized difference vegetation index (NDVI) has been shown to quantify maize (Zea mays) N variability. Ground-based active remote sensors that can determine NDVI are commercially available and have been shown to accurately distinguish N variability in maize. There are several active sensors available but no studies directly comparing active sensors have been reported. Therefore, a study was conducted to evaluate active sensor performance and develop an in-season maize N recommendation algorithm for use in Colorado using NDVI. Previous studies have demonstrated an association of active sensor NDVI with maize N content and height. However, the NDVI from a GreenSeeker™ green NDVI prototype active sensor had not yet been tested when our study began. Therefore, the green sensor was evaluated to determine if differences in plant growth across MZ could be determined by the active sensor. Results show that the prototype active sensor did not record NDVI values that were associated with MZ. The NDVI from two different sensors (Crop Circle™ amber NDVI and GreenSeeker™ red NDVI) were then examined under greenhouse and field conditions. Results show that NDVI from the amber and red sensors equally distinguished applied N differences in maize. Each active sensor's NDVI values had high R2 values with applied N rate and plant N concentration. Results also show that each sensor's NDVI readings had high R2 values with applied N rate and yield at the V12 and V14 maize growth stages. An N recommendation algorithm was then created for use at the V12 maize growth stage for both the amber and red sensors using NDVI. These algorithms yielded N recommendations that were not significantly different across sensor type suggesting that the amber and red NDVI sensors performed equally. Also, each N recommendation algorithm yielded unbiased N recommendations suggesting that each was a valid estimator of required N at maize growth stage V12. Overall results show that the amber and red sensors equally determine N variability in irrigated maize and could be very important tools for managing in-season application of N fertilizer.
Open Access
Grass and grass-legume mixes for irrigated pasture using organic production methods
(Colorado State University. Libraries, 2010) Booher, Matthew R., author; Brummer, Joe E., advisor; Davis, Jessica G., committee member; Meiman, Paul J., committee member
Species selection and fertility management are two of the greatest challenges facing producers of organic pasture. The objectives of this study were to: 1. Identify irrigated grass and grass-legume mixtures that possess the productivity, durability, and forage quality to meet the needs of organic dairies in the western US. 2. Evaluate the use of legumes and compost as nutrient sources for pastures being managed in accordance with organic protocols. Research was conducted for two years at the Agricultural Research, Development, and Education Center located about 4 km south of Wellington, CO. Four grass mixes: tall fescue (TF), hybrid wheatgrass-tall fescue-hybrid brome (HWG-TF-HB), orchardgrass-meadow brome-smooth brome (OG-MB-SB), and orchardgrass-meadow brome-Kentucky bluegrass (OG-MB-KB), were established in fall 2007. In 2008, plots received either a compost treatment of 22.4 Mg ha-1, or were part of a control set that received no compost. Plots were harvested six times in 2008 to simulate rotational grazing, and dry matter (DM) yield, crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) were determined at each cutting. Fertility (compost) had no effect in 2008. Total DM yield of TF (10,864 kg ha ha-1) was higher than OG-MB-SB (9,241 kg ha ha-1) and OG-MB-KB (8,079 kg ha ha-1). Dry matter yield of TF in late-September was 120% higher than the other grass mixes. In general, forage contained higher CP and lower NDF and ADF as the season progressed, resulting in increased forage quality over time. Averaged across cutting date, CP of TF (19.8 %) was 9% lower than the other grass mixes; however, CP remained adequate to meet most ruminant needs for all grass mixes at all cutting dates. In 2009, the 22.4 Mg ha ha-1 compost fertility treatment was divided to include an 11.2 Mg ha ha-1 treatment and a 0 Mg ha ha-1 control, in an effort to observe nitrogen mineralization from previous compost applications. Also in 2009, alfalfa, birdsfoot trefoil, sainfoin, and white clover were interseeded into the 2008 control plots to observe legume effects on yield and forage quality. Yield and quality data were taken for five cuttings in 2009. As a result of a low level of nitrogen in the compost, fertility had no effect on yield or quality in 2009. Total DM yield in 2009 averaged about 45% less than in 2008. Total DM yields of TF and HWG-TF-HB averaged 23% higher than the other grass mixes. Crude protein content averaged about 6 percentage points lower in 2009 than in 2008, most likely due to nitrogen deficiency. Similar to 2008, TF was lower in CP than the other grass mixes. In general, forage quality improved over the season. On average, TF (56.2 %) and HWG-TF-HB (56.9 %) had a 4% higher NDF content than the other grasses, while all grass mixes had a similar average ADF content of around 32%. Because legumes did not significantly contribute to harvested yield until cuttings 4 and 5 in 2009, cuttings 1-3 were not included in analyses of the legume treatments. The alfalfa treatment had 25% higher DM yield than the other legume treatments, due to the greater presence of alfalfa in the plots. Mix and cutting date affected CP content of the sward within the legume treatments. Similar to the results observed in the compost treatments, tall fescue had lower average CP content than the other grass mixes within the legume treatment, while OG-MB-SB averaged higher than the other grass mixes. Cutting effects for the legume treatment were similar (decreasing CP) to the compost treatment for the period analyzed (cuttings 4 and 5). NDF was affected by legume species, probably due to the greater abundance of alfalfa in the plots. The OG-MB based mixes in the legume treatments averaged 6% lower in NDF content than the other grass mixes. The management implications of this study vary based on the relative importance of pasture in an animal's diet. Tall fescue tended to yield higher than the other grass mixes in the study, but had lower CP content. While this difference may be statistically significant, levels of CP for all grasses (including TF) were adequate for most animal needs. In addition, digestible fiber content was highest in mixes containing TF, making this grass an excellent choice for producers desiring high yields, durability, and overall good quality. Conversely, the OG-MB-SB mix, while showing a moderate yield and CP content, had a higher proportion of indigestible fiber than all other mixes. This appears to be a product of the smooth brome component in the mix, and presents a case for avoiding this species if high digestibility is desired. In general, forage quality of all grass mixes improved over the growing season, peaking in late summer and fall. This study found that the addition of legumes to grass-based pasture is an excellent tool for increasing forage quality, especially crude protein content. Additionally, nitrogen management (i.e. compost testing) is vital to forage productivity and quality when using organic fertility sources.
Open Access
Risk of gene introgression from transgenic wheat to jointed goatgrass
(Colorado State University. Libraries, 2010) Econopouly, Bethany F., author; Byrne, Patrick F., 1948-, advisor; McKay, John K., advisor; Funk, W. Chris, committee member; Lapitan, Nora Lyssa V., committee member
To view the abstract, please see the full text of the document.
Open Access
The utility of near-infrared reflectance spectroscopy for wheat quality assessment
(Colorado State University. Libraries, 2010) Butler, Joshua Donald, author; Haley, Scott D., advisor; Brick, Mark A., committee member; Chapman, Phillip L., committee member; Seabourn, Bradford W., committee member
End-use quality improvement is an important objective in most wheat (Triticum aestivum L.) breeding programs. Limited sample size, destructive parameter testing, and the short duration between harvest and planting of winter wheat are challenges for testing early-generation breeding material for end-use quality parameters. Near-infrared reflectance (NIR) spectroscopy is a rapid and non-destructive technique that could facilitate early-generation selection for end-use quality. The precision and accuracy of an NIR equation for prediction purposes is dependent on the construction of a reliable calibration. The objectives of this study were to: 1) develop and validate NIR calibration models for grain volume weight, kernel characteristics, and Farinograph parameters, and 2) evaluate the performance of NIR calibration models in a breeding context for grain volume weight and single kernel characteristics. Calibration models for prediction of grain volume weight and single kernel characteristics were developed using NIR spectra and laboratory reference values from up to 10,000 samples collected from breeding nurseries under multiple environments over four crop years. Models encompassing all years of data revealed R2 (validation) of 0.73 for kernel diameter, 0.74 for kernel weight, 0.70 for kernel hardness, and 0.81 for grain volume weight. Of the Farinograph parameters, only absorption was effectively predicted using NIR calibration models for whole grain and flour with R2≥0.70. Realized heritability was estimated as a response to selection using NIR predicted values and laboratory reference values and was generally larger when using the reference values when compared to predicted values (0.17-0.77 vs. 0.05-0.77), but suggested that genetic gain was possible when using NIR models for selection. Classification errors when using the NIR models were highest in the mid-range reference values (56-66%), but could allow for divergent selection of high and low reference values. The results suggest that NIR models suitable for screening grain volume weight, SKCS kernel characteristics, and Farinograph absorption could be utilized in a breeding program and could aid in the elimination of early-generation samples with unacceptable values.