Browsing by Author "Fonte, Steven, advisor"

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Open Access
Amendment effects on soil physical properties and restoration of decommissioned forest roads
(Colorado State University. Libraries, 2017) Berlejung, John Michael, author; Fonte, Steven, advisor; Rhoades, Charles, committee member; Paschke, Mark, committee member
Unsealed forest roads, including logging roads and unauthorized roads created by hunters, miners, and recreational users, generate significant harmful effects to local ecosystems and waterways. Rapid restoration of these roads is necessary to prevent erosion, downstream implications for water quality, and a variety of other deleterious ecosystem impacts. Soil amendments, including mulches, composts, and other materials, offer promise to improve soil health, restore soil structure, and support revegetation of these sites. I tested the viability of three locally-sourced soil amendments wood straw mulch, Biosol fertilizer, and biochar alone and in paired combinations to restore soil physical properties important for improved hydrologic function and plant growth. I found that amendment combinations of biochar + mulch and biochar + Biosol significantly reduced soil bulk density when compared to unamended controls. Other factors (aggregate stability, infiltration, sediment production) suggested potential for improvement relative to unamended control plots, but no significant differences between treatments were observed due to high variability within and between sites. Regression analyses revealed that soil physical properties, particularly wet aggregate stability, was significantly correlated with key soil erosion parameters such as infiltration and runoff, suggesting aggregate stability could provide a useful measure of soil restoration success.
Open Access
Identifying grass-legume bicultures to increase above and belowground biomass production and improve traditional fallows in crop rotations of the Andean Highlands
(Colorado State University. Libraries, 2021) Meza Retamozo, Katherin Paola, author; Fonte, Steven, advisor; Schipanski, Meagan, committee member; Davis, Jessica, committee member
In the high Andes of Peru, intensification of crop rotation and agricultural land-use is reducing the practice and duration of traditional fallow (based on natural establishment of native vegetation). These fallows represent one of the main traditional soil management practices to sustain long-term productivity, while also providing key forage resources in these mixed crop-livestock systems. Improved forage-based fallows, with the intentional seeding of more productive annual and perennial forages, offer great potential for producing forage and contributing to soil restoration under intensified contexts; however, there remains a gap in knowledge about which plant species can best optimize tradeoffs between forage production and belowground inputs to support long-term soil fertility and contribute to the multifunctionality of Andean agroecosystems. To address this issue, a pot study was conducted with two contrasting soils to evaluate the above and belowground productivity of all possible grass-legume pairs involving five grasses (oat (Avena sativa), ryegrass (Lolium multiflorum), festulolium (Lolium x Festuca genera), brome grass (Bromus catharticus), and orchardgrass (Dactylis glomerata), and four legumes (vetch (Vicia dasycarpa ), red clover (Trifolium pratense), black medic (Medicago lupulina), and alfalfa (Medicago sativa)) in comparison to the performance of each species in monoculture. Grass-legume bicultures resulted in significant overyielding, producing 65% and 28% more total dry biomass and total N uptake on average than species in monoculture, respectively. Grass-legume shoot biomass production yielded 67% more compared to monocultures, while root biomass was on average 58% higher in bicultures than in monocultures. For aboveground biomass, production differences between grass-legume bicultures were significantly influenced by the species of legume present, while belowground biomass was more affected by the grass species present in the bicultures. Roughly 80% of the mixtures achieved a mean land equivalent ratio (LER) > 1.0. When examining total biomass production, the most successful bicultures were oat-vetch (LER=1.87), vetch-festulolium (LER=2.31), vetch-orchardgrass (LER=1.87), oat-red clover (LER=1.62), and red clover-ryegrass (LER=1.46). When examining partial LERs (the component of the LER attributed to each species), we found that overyielding in bicultures was mainly driven by increases in the biomass of the component grass species. Our findings suggest that mixtures of key functional species (e.g. grass and legume, annual and perennial species) offer greater promise in improved fallows compared to monocultures of the respective species. Additionally, I suggest that strategically designed improved fallow mixtures, with emphasis on perennial species that support long-term root inputs, can best support soil health and the multifunctionality of Andean agroecosystems.
Open Access
Soil health indicators for water-limited regions: sensitivity to compost and cropping intensification
(Colorado State University. Libraries, 2024) Noble Strohm, Tess, author; Schipanski, Meagan, advisor; Fonte, Steven, advisor; Ross, Matthew, committee member
In the water-limited agroecosystems of the Great Plains, USA, management strategies such as compost application and cropping system intensification have been promoted to increase soil health and help adapt to climatic variability. However, accurately assessing soil health to support production systems in such regions hinges upon a selection of indicators sensitive to management and linked to essential soil functions, especially those related to soil water dynamics. Using a suite of soil physical and biological parameters, this study assessed the effects of management on soil health metrics and evaluated the extent to which these metrics were related to soil water dynamics utilizing long-term studies in Akron, CO, and Clovis, NM. Soil physical indicators included aggregate stability (mean weight diameter; MWD), bulk density and saturated hydraulic conductivity, while biological indicators included measures of soil macrofauna and microbial communities. Compost application was the primary driver of increased aggregate stability and abundance of soil biota at both sites, though effects of cropping system intensification were observed for some indicators. Measures of soil microbial abundance were correlated with MWD, but saturated hydraulic conductivity was generally not correlated with other measured variables. Our findings indicate that MWD and microbial abundance are linked and sensitive to management, and further research to connect measures of soil biological and physical health to soil water dynamics in semi-arid systems is necessary to develop regionally relevant frameworks for soil health assessments.
Open Access
Soil nitrogen cycling in agroecosystems as modified by biochar amendment and plant processes
(Colorado State University. Libraries, 2019) Rocci, Katherine, author; Cotrufo, M. Francesca, advisor; Fonte, Steven, advisor; von Fischer, Joseph, committee member
Ecosystem productivity is dependent upon cycling of nutrients, such as nitrogen (N). In agricultural systems, humans have greatly altered N cycling through the application of synthetic fertilizers such that soil N in agroecosystems is lost at higher rates than N in unmanaged systems. A variety of strategies have been assessed to reduce losses of soil N through nitrous oxide (N2O) emissions and leaching, which can negatively impact climate and water quality, respectively. The application of biochar, a carbon-rich soil amendment, has shown promise for increasing N retention in agricultural systems, but field and greenhouse studies often present less dramatic and often conflicting effects, suggesting the need for greater study in these environments. Further, the effects of biochar do not occur in isolation, but rather depend on plant processes that may affect soil N dynamics. This thesis explores these ideas through: (1) a greenhouse study considering the effects of different biochar types on N cycling with and without plants and (2) a field study looking at seasonal patterns of N cycling and fixation in alfalfa as altered by strategically-placed, low rates of biochar application. Study 1 sought to determine differential effects of biochar and plants, and raw and engineered biochar, on both fertilizer and innate soil N cycling using isotopically labelled fertilizer. While biochar effects on soil-derived N were minimal, we found that engineered biochar led to significantly higher leaching losses of fertilizer N. Plants, in contrast, were found to reduce N loss and increase overall recovery of fertilizer N. Study 2 focused on the effects of low and economically feasible application rates of two different biochars on N fixation, N loss, and mineral N availability over a growing season. We found no biochar effects on any N cycling parameter and, rather, found significant temporal effects in all N pools. Seasonal dynamics suggest connections between SIN availability and N fixation and loss. Indications of increased N loss with engineered biochar in Study 1 urge the need for greater study of biochars in combination with a variety of fertilizer types in order to provide the best recommendations to farmers. Lack of effects with biochar in Study 2 indicate that low application rates of biochar may not be useful for increasing N retention, suggesting the need to find a balance between economic and effective biochar application rates. Since both studies suggest that plant processes have more substantial impacts on N cycling than biochar amendment, via reduced N loss (Study 1) or increased symbiotic N input (Study 2), it is important that plants are included in more biochar studies such that the strength of biochar effects can be more realistically evaluated.
Open Access
The impacts of deficit irrigation on crop production and sustainable soil management
(Colorado State University. Libraries, 2022) Flynn, Nora E., author; Fonte, Steven, advisor; Comas, Louise, committee member; Stewart, Catherine, committee member; von Fischer, Joseph, committee member
Growing issues of water scarcity around the planet highlight a need for more efficient use of agricultural water. Deficit irrigation (DI) offers a promising option to reduce water use with relatively small impacts on crop yield, when properly managed. However, the impacts of DI management on above and belowground crop growth and the interactions between plants and soil are complex and need further study. There are concerns that DI, because it often reduces crop biomass, could reduce soil carbon (C) stocks, and negatively impact soil processes related to soil health. Additionally, DI alters soil moisture conditions with significant implications for soil C turnover and for the movement, transformation, and fate of soil nitrogen (N). At the same time soil N could buffer crops from water stress. Therefore, the goal of this research was to examine the potential impacts of DI on crop production and water stress and implications for soil C and N dynamics. Chapter 2 explores the effect of DI on maize above and belowground growth, soil microbial community composition, soil aggregation as well as soil C concentrations in surface soils (0-20 cm) and at depth (40-60 cm). Deficit irrigation increased root length density in deep soils (40-60 cm), with a trend towards higher soil C in treatments with the most root growth. Deficit irrigation also reduced total microbial biomass in the surface layer and led to shifts in microbial community composition. While aggregation and soil C were not strongly impacted by DI here, increased root growth under DI could eventually increase soil C and benefit a range of soil health related parameters, which are advantageous for crop production in water-limited systems. Chapter 3 quantifies greenhouse gas emissions from DI compared to full irrigation and suggests that DI can reduce both N2O and CO2. While this is a promising result, we also found that yields were reduced under DI, such that yield-scaled emissions were higher under DI compared to FI. The tradeoff between reducing emissions at the cost of reducing yield is important to recognize in the development of more sustainable agricultural practices. An additional important observation in this study was that emissions from this drip-irrigated maize system appeared to be much lower than from sprinkler or furrow irrigated maize systems reported elsewhere in the Great Plains. Chapter 4 sought to elucidate the impact of DI on the fate of N and the interactions between water and N in a drip-irrigated maize system. Yield and the amount of N at the end of the growing season in the harvested material vs. N lost via N2O emissions or remaining in the soil. Deficit irrigation reduced grain yield compared to full irrigation was quantified. Less N was taken up by maize under DI, leaving more residual nitrate in the soil at the end of the growing season, which is vulnerable to subsequent loss via leaching or emissions. While DI reduced consumptive water use in this experiment, yields were also reduced, thereby reducing water use efficiency. Overall, the findings of this study suggest that farmers should apply less fertilizer when utilizing DI. Chapter 5 examines the impact of DI and N level on above and belowground growth of five different sorghum genotypes in a greenhouse experiment. We found that DI led to an increase in root biomass allocation for all the sorghum genotypes, and that a low N treatment further increased root biomass allocation and specific root length (SRL) compared to a high N treatment under DI. Importantly, increasing root biomass allocation did not decrease aboveground biomass which is a common tradeoff in drought-stressed agriculture. In summary, this research indicates that DI alters crop growth in important ways beyond just grain yield. Deficit irrigation can increase maize and sorghum root growth, which has important implications for water and nutrient acquisition and for building soil C. This finding is especially significant in semi-arid systems, where maintaining and building soil C presents a significant challenge for long term soil health. We also showed that DI can be used to reduce greenhouse gas emissions, but it is important to note that such management can also reduce yield. Overall, this research will help inform farmers and policymakers in making decisions around the adoption of DI practices. Most importantly, this work suggests that proper implementation of DI offers promise to maintain crop growth with less water and that doing so could maintain or increase soil C stocks and would require less N fertilizer application compared to full irrigation.
Open Access
Understanding the dynamics and management of organic nutrient sources in smallholder farming systems: an interdisciplinary approach
(Colorado State University. Libraries, 2021) Magonziwa, Blessing, author; Fonte, Steven, advisor; Davis, Jessica, committee member; Carolan, Michael, committee member; Paustian, Keith, committee member
Smallholder farmers often face challenges in managing soil fertility due to limited inputs and high spatial variability on their farms. In many places, soil fertility, and overall soil health, is on the decline, and management of organic nutrient sources (ONS) can play a vital role in sustaining the productivity of soils. However, in mixed smallholder crop-livestock systems there is often competition for crop residues between retaining residues within fields versus feeding them to livestock. Understanding how ONS produced on-farm are managed, and the flows and drivers of this essential resource is critical for the restoration and sustainable management of soil fertility and health in smallholder agroecosystems. The objectives of this study were to: i) validate a soil health tool kit developed to facilitate smallholder research and management involving the use of ONS and other soil management strategies; ii) evaluate how different maize-based ONS (shoot, roots, manure) influence soil organic carbon (SOC) dynamics; iii) understand socio-cultural, economic, and environmental drivers of ONS allocation and use; and iv) understand management and environmental drivers SOC and nutrient (N, P and K) balances across various management scenarios. To address these objectives, a soil health tool kit to provide in-field quantitative data that are comparable to formal laboratory methods was assembled. I then validated methods used in this tool kit against standard analyses conducted at national laboratories on soils collected from 36 smallholder farms in Kenya and 115 farms in Peru. My results showed that permanganate oxidizable C and pH measured with the tool kit from Kenyan and Peruvian soils were highly correlated to the same variables measured by a standard laboratory. The tool kit and standard laboratory measures of available P were less well correlated, but also showed a significant positive relationship. Both tool kit and standard lab analyses displayed similar abilities to predict maize grain yield in Kenya. My findings suggest that the tool kit methods proposed in this study have broad applicability to smallholder farms for explaining variability in crop yields, assessing soil properties of different plots and quantifying management-induced changes in soil health. In the next study, I used a mesocosm experiment and a 13C natural abundance approach, where organic residues (maize shoots, ex-situ maize roots, in-situ maize roots and cattle manure) were incubated for 11 months to trace maize-derived C into different SOC pools. My findings indicated that there was greater stabilization of shoot-derived C (2 X more than manure and 1.6 X more than ex-situ root C) in the mineral-associated organic matter fraction. At the same time, mineral additions of N, P and S (aimed at adjusting the stochiometry of the added residue inputs) led to a 60% decrease in C stabilization in the mineral-associated fraction, compared to a control with no nutrient additions. My study highlights the potential importance of residue retention as a strategy to maintain SOC and therefore soil health and did not support the idea that strategic N, P, and S additions can facilitate C stabilization in soil over the long-term. I then used focus group discussions and conducted a survey of 184 farming households to understand socio-economic, socio-cultural, and environmental drivers of ONS allocation and use at farm scale in three contrasting agroecological zones of western Kenya. I found that the more resource endowed a farmer is, the more ONS are allocated to the main production plot within a farm. However, beyond resource endowment I observed that agroecological location, and tenure, perceived soil fertility, gender and social connections also had important influences on ONS allocation. Lastly, I examined case studies from three representative farm types within three agroecological zones in western Kenya and used a modelling approach to estimate nutrient and C flows in and out of fields. Based on the estimated flows, I then examined different scenarios representing alternative possibilities for ONS management in the region. I noted differences in inputs and allocation between the three zones, but these did not affect the overall balances, which were largely influenced by fertilizer inputs, as well as nutrient export in harvest and soil erosion. Overall nutrient balances were variable, but largely negative across the zones, farm types and field types. When exploring the different management scenarios, reducing erosion led to significantly less negative N balances in all locations. A full residue retention scenario indicated the greatest impact on K balances, while for SOC scenarios with full residue retention and lablab (a high biomass legume) incorporation resulted in at least 50 % more SOC compared to current practices. Scenarios indicate that retaining residues as well as implementing erosion control measures have the potential to effectively reduce nutrient losses as well as improve SOC stocks and that these practices should be encouraged. As research and development organizations continue to engage with smallholder farmers to reduce the burden of global food insecurity, the insights gained by this research will allow for better anticipation of drivers and obstacles to improved nutrient management in these farming landscapes and communities.