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Long-term manure and inorganic fertilizer application in row crops may significantly influence soil pore characteristics, thereby impacting soil aggregation and structure. Understanding the influence of such soil amendments on soil pore characteristics is useful to develop proper conservation practices. However, there is limited information on the impact of cattle manure and inorganic fertilizer application on soil pore characteristics at a microscale level in the soil profile. Therefore, in this study, the X-ray computed tomography (XCT) technique was utilized to quantify the impact of manure and fertilizer amendments under a corn (Zea mays L.)-soybean (Glycine max L.)-spring wheat (Triticum aestivum) rotation system on soil pore characteristics to 40 cm soil depth. The study was conducted at Brookings (initiated in 2008) and Beresford (2003) in South Dakota. The study treatments included: low manure (LM), medium manure (MM), high manure (HM), medium fertilizer (MF), high fertilizer (HF), and control (CK). Four replicated intact cores were collected from all the treatments at 0–10, 10–20, 20–30, and 30–40 cm depths. Image visualization and processing were performed using ImageJ software at a pixel resolution of (0.26 × 0.26 × 0.28) mm3. Data showed that treatments by depth interactions were mainly significant for soil organic carbon (SOC) content at 0–20 cm. The HM treatment increased the SOC by 8 to 68% compared to the CK and MF at 0–20 cm for either site. However, treatments did not always impact these parameters beyond 20 cm depth. Considering treatment as the main effect, the MM, HM, and HF increased the total number of pores (TP) compared to the CK at Beresford site. Soil depth impacted the TP and total number of macropores (Tmacro), where more Tmacro was observed at 0–10 cm compared to the 30–40 cm depth at Beresford site. In general, manure application improved SOC and TN contents and soil pore characteristics at 0–20 cm for both sites. This study illustrates the importance of the XCT technique in quantifying soil pore characteristics and highlighted the improvement in the XCT-derived pore characteristic with the long-term application of manure to a greater depth in the soil.

Combined application of biochar and nitrogen (N) fertilizer has the potential to reduce N losses from soil. However, the effectiveness of biochar amendment on N management can vary with biochar types with different physical and chemical properties. This study aimed to assess the effect of two types of hardwood biochar with different ash contents and cation exchange capacity (CEC) on soil N mineralization and nitrous oxide (N2O) production when applied alone and in combination with N fertilizer. Soil samples collected from a temperate pasture system were amended with two types of biochar (B1 and B2), urea, and urea plus biochar, and incubated for 60 days along with soil control (without biochar or urea addition). Soil nitrate N, ammonium N, ammonia-oxidizing bacteria amoA gene transcripts, and N2O production were measured during the experiment. Compared to control, addition of B1 (higher CEC and lower ash content) alone decreased nitrate N concentration by 21% to 45% during the incubation period while the addition of B2 (lower CEC and higher ash content) alone increased the nitrate N concentration during the first 10 days. Biochar B1 also reduced the abundance of amoA transcripts by 71% after 60 days. Compared to B1 + urea, B2 + urea resulted in a significantly greater initial increase in soil ammonium and nitrate N concentrations. However, B2 + urea had a significantly lower 60-day cumulative N2O emission compared to B1 + urea. Overall, when applied with urea, the biochar with higher CEC reduced ammonification and nitrification rates, while biochar with higher ash content reduced N N2O production. Our study demonstrated that biochar has the potential to enhance N retention in soil and reduce N2O emission when it is applied with urea, but the specific effects of the added biochar depend on its physical and chemical properties.

Steppe soils are important biological sinks for atmospheric methane (CH4), but the strength of CH4 uptake remains uncertain due to large spatiotemporal variation and the lack of in situ measurements at regional scale. Here, we report the seasonal and spatial patterns of CH4 uptake across a 1200 km transect in arid and semi-arid steppe ecosystems in Inner Mongolia, ranging from meadow steppe in the east plain to typical and desert steppes on the west plateau. In general, seasonal patterns of CH4 uptake were site specific, with unimodal seasonal curves in meadow and typical steppes and a decreasing seasonal trend in desert steppe. Soil moisture was the dominant factor explaining the seasonal patterns of CH4 uptake, and CH4 uptake rate decreased with an increase in soil moisture. Across the transect, CH4 uptake showed a skewed unimodal spatial pattern, with the peak rate observed in the typical steppe sites and with generally higher uptake rates in the west plateau than in the east plain. Soil moisture, together with soil temperature, soil total carbon, and aboveground plant biomass, were the main drivers of the regional patterns of CH4 uptake rate. These findings are important for model development to more precisely estimate the soil CH4 sink capacity in arid and semi-arid regions.

Soil organic carbon (SOC) plays a critical role in the sustainability of grazingland ecosystems around the world. However, maintaining or increasing SOC levels remains a major challenge, particularly in subtropical regions where coarse-textured soils predominate. This study evaluated the long-term (>20 years) impacts of grazingland intensification (conversion of native rangelands into more intensively managed silvopasture and sown pasture) on SOC and nitrogen (N) responses in particle size/density fractions. Treatments consisted of field replicated (n = 2) experimental sites that represented a gradient of intensification ranging from native rangelands (low intensification), pine (Pinus spp.)-bahiagrass (Paspalum notatum) silvopasture (moderate intensification), and bahiagrass pastures (high intensification). Soil organic C and N increased in response to the conversion of native rangelands into more intensively managed grazinglands, but no difference was observed in total SOC and N between silvopasture and sown pasture. Despite the positive impact of intensification on SOC and N pools, accumulation occurred primarily in more labile fractions. For instance, at the 0 to 10 cm depth, light-free C (LF-C) increased from 12.9 g kg−1 soil in the native rangeland to 24.7 g kg−1 soil in the sown pasture. Largest differences between the ecosystems were observed at the 10 to 20 cm depth where LF-C increased by as much as 170% following the conversion from native rangelands to sown pasture. Similar responses were also observed for N. Grazingland intensification showed no effect on soil aggregation, but SOC and N associated with macroaggregates (2,000 to 250 μm) increased with intensification. Results indicate that grazingland intensification promoted SOC and N accumulation, primarily through an increase in the LF fraction.

Soil organic carbon (C) is a key component regulating grazing land ecosystem production and sustainability. In this study, we investigated the impacts of wet vs. dry physical separation of soil C fractions in representative sandy Coastal Plain Spodosols subjected to different levels of management intensification. X-ray diffraction and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy were used to characterize the structural composition of the fine (

Land use intensification often results in modification in plant cover and nutrient inputs with subsequent potential effects on composition and structure of soil microbial community and fractions. The objective of this study was to understand the long-term (> 22 yr) impacts of land use intensification (introduction of productive vegetation type, greater N fertilizer input and stocking rate) on soil microbial community composition and activity in Florida grazing lands. Experimental sites consisted of a gradient of management intensities ranging from native rangeland (lowest), silvopasture (intermediate), to sown pasture (highest). Increasing management intensity from native rangeland to sown promoted microbial biomass and activity. At the 0–10 cm, soil microbial biomass carbon (MBC) concentration was greater in sown pasture (334 mg kg− 1) compared to silvopasture and native rangeland (193 and 232 mg kg− 1, respectively). Similarly, potentially mineralizable C (PMC) increased in response to grazing land intensification (1.2 mg CO2-C kg− 1 d− 1 for sown pastures vs. 0.5 and 0.6 mg CO2-C kg− 1 d− 1 for native rangeland and silvopasture, respectively). Sown pastures exhibited the greatest levels of β-glucosidase activity (203 nmol g− 1 soil h.− 1) and phospholipid fatty acid (PLFA) biomass (222 μmol kg− 1 soil) compared to native rangeland and silvopasture. Results also demonstrated greater relative abundance of bacteria and less fungi as land use intensification increased from native rangeland to silvopasture or sown pasture. Our study indicated that long-term land use intensification affected the size, activity, and composition of soil microbial community in subtropical grazing lands.

Although the Great Lakes Region has abundant fresh water, the area can be dry, especially during the summer growing season. Beef producers are considering use of irrigation because of this combined with diminished access to grazing land. Our objective was to investigate the combination of irrigation, genotype, and stocking rate on northern Michigan cow-calf production systems. Treatments were a combination of 2 irrigation levels, 2 breeds of cattle of contrasting body size, and 3 stocking rates expressed in animal unit equivalents (AU/ha). Sixty-four Red cow-calf pairs in total were assigned to 1 of 4 treatments: (1) 3 small Angus cow-calf pairs without irrigation (3SWO; 2.1 AU/ha); (2) 3 small Angus cow-calf pairs with irrigation (3SW; 2.1 AU/ha); (3) 5 small Angus cow-calf pairs with irrigation (5SW; 3.5 AU/ha); and (4) 5 large Simmental cow-calf pairs with irrigation (5LW; 4.4 AU/ha). Both animal and forage performance were monitored from May to August 2011. Irrigation aided forage growth with 17.8 and 16.0% greater pregrazing forage biomass in August compared with May in the 5SW and 5LW treatments, respectively. The greater stocked treatments returned more performance per hectare; 5SW had twice the overall cow and calf BW gain/ha in July to August when compared with 3SW. Overall, irrigation may sustain greater stocking rates and herbage production later in the grazing season and may be a viable tool for Midwest beef producers. This study was limited to 1 yr, so more long-term studies are needed to address the effect of variable precipitation and climatic conditions in Midwest beef systems.

Genetic engineering has been used to decrease the lignin content and to change the lignin composition of switchgrass (Panicum virgatum L.) to decrease cell wall recalcitrance to enable more efficient cellulosic biofuel production. Previous greenhouse and field studies showed that downregulation of the gene encoding switchgrass caffeic acid O-methyltransferase (COMT) and overexpression of the switchgrass PvMYB4 (MYB4) gene effectively improved ethanol yield. To understand potential environmental impacts of cultivating these transgenic bioenergy crops in the field, we quantified the effects of field cultivation of transgenic switchgrass on soil organic carbon (SOC) dynamics. Total and active SOC as well as soil respiration were measured in soils grown with two COMT-downregulated transgenic lines (COMT2 and COMT3), three MYB4-overexpressed transgenic lines (L1, L6, and L8), and their corresponding non-transgenic controls. No differences in total SOC, dissolved organic carbon (DOC), and permanganate oxidizable carbon (POXC) were detected between transgenic and non-transgenic treatments for both COMT (10.4–11.1 g kg−1 for SOC, 60.0–64.8 mg kg−1 for DOC, and 299–384 mg kg−1 for POXC) and MYB4 lines (6.89–8.21 g kg−1 for SOC, 56.0–61.1 mg kg−1 for DOC, and 177–199 mg kg−1 for POXC). Soil CO2-carbon (CO2-C) production from the COMT2 transgenic line was not significantly different from its non-transgenic control. In contrast, the COMT3 transgenic line had greater soil CO2-C production than its non-transgenic control (210 vs. 165 µg g−1) after 72 days of laboratory incubation. Combining the improvement in ethanol yield and biomass production reported in previous studies with negligible change in SOC and soil respiration, COMT2 could be a better biofuel feedstock than COMT3 for environmental conservation and cost-effective biofuel production. On the other hand, MYB4 transgenic line L8 produced more biomass and total ethanol per hectare while it released more CO2-C than the control (253 vs. 207 µg g−1). Long-term in situ monitoring of transgenic switchgrass systems using a suite of soil and environmental variables is needed to determine the sustainability of growing genetically modified bioenergy crops.

Grazing lands should be monitored to ensure their productivity and the preservation of ecosystem services. The study objective was to investigate the effectiveness of an Ecological Health Index (EHI) for assessing ecosystem ecological health in grazing lands. The EHI was developed by synthesizing existing vegetation and soil cover indicators. We implemented long-term transects at 44 farms from two ecological regions in Patagonia, the Humid Magellan Steppe (HMS) (n = 24) and Subandean Grasslands (SG) (n = 20), to collect data on established quantifiable vegetative and soil measurements and the EHI. Using known quantifiable measures, the HMS had numerically greater species richness compared to SG. Similarly, the average percentage of total live vegetation was more favorable in HMS. Correlating the EHI with these known quantifiable measures demonstrated positive correlations with species richness, the percentage of total live vegetation and carrying capacity and was negatively correlations with bare ground. These results suggest that EHI could be a useful method to detect the ecological health and productivity in grazing lands. Overall, we conclude that EHI is an effective short-term monitoring approach that ranchers could implement annually to monitor grazing lands and determine the impacts of ranch decision-making on important ecosystem indicators.

Monitoring long-term grazing management practices influence on soil quality (SQ) is essential to ensuring pasture sustainability, which is the largest land use in world agroecosystems. The aim of this study was to quantify SQ based on long-term (15-years) conservation pasture management and landscape position using the Soil Management Assessment Framework (SMAF). Treatments were setup in 15 watersheds (0.14 ha each, 8% slope) in a completely randomized design with five pasture management practices: continuously grazed (CG), hayed (H), rotationally grazed (R), rotationally grazed with an unfertilized buffer strip (RB), and rotationally grazed with an un-grazed, unfertilized, and fenced riparian strip (RBR). Each watershed was divided in three zones (A, B, and C), with the riparian buffer strip (RBS) corresponding to the RBR D zone. Selected soil chemical, physical, and biological properties were determined on soil samples collected in 2017 (0−15 cm depth) per zone. Total P, organic C, and total suspended solids (TSS) were measured in 2017 runoff samples. The SMAF SQ scores were evaluated individually and as an overall SQ index (SQI). Exponential models were used to investigate the relationship between SQI and total P, organic C runoff, and TSS loads. Continuously grazed watersheds had improved soil fertility, with greater nutrient concentration at the shoulder landscape position (zone A). Degradation of soil physical properties were not observed for this practice. After 15 years of continuous management, CG and R watersheds had the greatest SQI (7.07 and7.05, respectively), not differing from RBR (6.93), likely owing to cattle manure deposition for these treatments. Increased SQI in RBS (7.33) improved SQI for RBR watersheds. Differences in SQI were mostly driven by changes in pH, electrical conductivity, soil P and K concentrations. The exponential models indicated that 34 and 28 % of the variation in P and TOC runoff loads, respectively, can be explained by the SMAF SQI (p

Grazing land ecosystem services including food provision and climate regulation are greatly influenced by soil health. This paper provides a condensed review of studies on the response of three important soil properties related to soil health to grazing land management: water infiltration, carbon (C) sequestration, and nitrogen use efficiency (NUE). Impacts of management strategies that are often used in grazing lands are discussed in this review including vegetation composition, grazing methods, and other factors such as fertilizer use and climatic conditions. In general, proper grazing management such as continuous moderate grazing and rotational/deferred-rotational grazing with low or moderate stocking rates tends to benefit all three soil properties. Water infiltration can usually be increased with full vegetation cover, increased soil C, and aggregate stability, or be decreased with greater soil bulk density. Adoption of highly productive plant species with faster turnover rates can promote soil C sequestration by increasing C input. However, excessive C removal from ecosystems due to overgrazing or improper soil fertilization management results in higher C loss, which can have detrimental effects on soil C sequestration. Proper stocking rate and a balanced manure/fertilizer management was found to be critical for enhancing NUE. Grazing land management sometimes simultaneously influence the three soil properties. Techniques that can increase soil C such as introduction of high productive plant species can often promote water infiltration and soil nitrogen (N). Some other practices such as adoption of N fertilizer may enhance C sequestration while being detrimental to NUE. An integrated management plan for a specific location or farm should be considered carefully to improve soil health as well as ecosystem production. This review provides farmers and policy makers the current state of general knowledge on how health-related soil processes are affected by grazing land management.

Grazing lands worldwide are increasingly subjected to intensification to meet global demand for food; however, management practices intended to increase production can also affect ecosystem carbon (C) stocks. This study evaluated long-term (>22 years) ecosystem C responses to conversion of native grazing lands into more intensively managed silvopasture and sown pastures. Above- and below-ground C pools in each land use type were evaluated. Silvopasture exhibited the greatest total ecosystem C stock (168 Mg ha−1) compared with sown pasture and native rangeland (121 and 94 Mg ha−1, respectively). This response was due to the greater aboveground biomass (59 Mg ha−1 in silvopasture vs. 2.1 and 3.8 Mg ha−1 in sown pasture and native rangeland, respectively), primarily from the tree component. Soil organic C (SOC) accounted for 81 and 90 % of total ecosystem C stocks in native rangeland and sown pasture, respectively, while in silvopasture SOC represented ~ 61 % of total ecosystem C. Soil organic C increased from 76 Mg ha−1 in native rangeland to 110 Mg ha−1 sown pasture. Data indicated that grazing land intensification through the adoption of proper management promoted ecosystem C primarily due to increases in SOC and the associated benefit of a greater above-ground woody biomass.

Sustainable management of grassland ecosystems for improved productivity can enhance their potential to sequester atmospheric CO2 in the soil. However, land-use management influences the quantity and quality of carbon (C) inputs which may, in turn, affect microbial activity and soil C decomposition rates. Understanding the potential changes in magnitude of soil C loss through respiration is critical for a comprehensive assessment of land-use conversion and grassland management impacts on terrestrial C dynamics. Thus, this study was designed to assess the effect of land-use management intensification on soil respiration in subtropical grasslands. Experimental sites consisted of a gradient of management intensities ranging from native rangeland (lowest), silvopasture (intermediate), to sown pasture (highest). Increasing management intensity from native rangeland to sown pasture elevated soil respiration. There was a significant effect of ‘season vs. management’ interaction on total soil respiration (RS), with greater increases in RS from summer to winter in sown pasture (∼200%) compared to native rangeland and silvopasture (∼91%). The temperature sensitivity of RS and heterotrophic soil respiration (RH) increased with management intensification, with a highest Q10 of 1.55 and 2.29, in sown pasture, compared to Q10 values of 1.09 and 1.48 in native rangelands. These results suggested that potential increases in soil C stock with intensification may be susceptible to faster turnover under warming climate scenarios. Improved resilience (and longer residence) of additionally sequestered soil C after intensification may be crucial for long-term ecological resilience, especially with changing climatic conditions. These findings are relevant for sustainable grassland management, especially within subtropical ecoregions, and add to the understanding of changes that may occur in rates of soil C losses as native grasslands are converted to more productive grassland ecosystems.

Proper management of grassland ecosystems for improved productivity can enhance their potential to sequester atmospheric CO₂ in the soil. However, the direction and extent of soil C changes in response to improved grassland management or land-use conversion varies depending on the ecoregion or management practice. The objectives of this study were to: (i) assess the long-term (>20-yr) impact of grassland management intensification on soil C fractions after conversion of native rangelands to silvopasture and sown pasture ecosystems; and (ii) determine the contribution of sown grass species to soil C sequestration in both the labile and more stable soil C fractions. Experimental sites consisted of a gradient of management intensities ranging from native rangeland (lowest), to silvopasture (intermediate), to sown pasture (highest). After 22 yr following land-use conversion from native rangeland to silvopasture or sown pasture, total soil C stocks (0–30-cm depth) were greater under silvopasture (69.2 Mg C ha⁻¹) and sown pasture (62.0 Mg C ha⁻¹) than native rangeland (40.9 Mg ha⁻¹). Conversion to sown pasture increased particulate organic C concentration (10.6 g C kg⁻¹) compared with native rangeland (6.3 g C kg⁻¹), while silvopasture increased the mineral-associated C fraction (5.7 vs. 10 g C kg⁻¹ for native rangeland and silvopasture, respectively). Isotopic analysis indicated that the C₄ grass component contributed significantly to soil C accumulation within these ecosystems. Data also showed that grassland management intensification has the potential to promote soil C sequestration, and the use of strategic management practices such as integration of trees can improve soil C stability under similar subtropical conditions.

Impacts of land intensification on soil organic carbon (SOC) responses are important components of sustainable management evaluation. Because of poor aggregation often associated with coarse-textured soils and the limited potential for chemical and physical protection of SOC, we hypothesized that the fine aggregate fraction (

Soil Sci. Soc. Am. J. 78:977–986 doi:10.2136/sssaj2013.12.0523 Received 10 Dec. 2013. *Corresponding author: (mlas@ufl.edu). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Management Intensification Impacts on Soil and Ecosystem Carbon Stocks in Subtropical Grasslands Soil & Water Management & Conservation

Soil organic carbon (SOC) content is strongly influenced by agricultural management practices. Leveraging three long-term field experiments in Tennessee, this study analyzed the effect of crop rotation, tillage, and cover crops on SOC and permanganate-oxidizable C (POXC) at various soil depth increments (0–2.5, 2.5–5, 5–7.5, 7.5–10, 10–15, 15–22.5, 22.5–30, 30–45, and 45–60 cm), as well as at the 0- to 15-cm profile. Corn ( L.) and cotton ( L.)–based systems showed increased SOC from 0 to 22.5 cm compared with soybean [ (L.), Merr.]–based systems. Additionally, no-till systems accumulated more SOC than tilled systems from 0 to 5 cm, but cover cropping showed no effects. Results also showed a significant positive relationship between SOC and POXC ( < 0.0001, = 0.93). This study revealed that SOC and POXC are strongly influenced by management practices in the surface shallower depth increments of southeastern US croplands.

The influences of winter climate on terrestrial ecosystem processes have been the subject of growing attention, which is necessary to make the predictions about ecological responses to global warming in the future. However, little information can be found about the impacts of a large range of soil temperature fluctuation (e.g. −10 to 5 °C) over winter on the soil nitrogen (N) dynamics in the field. In the present study, we employed an intact soil core in situ incubation technique, and measured soil N mineralization and nitrification rates under three plant communities, i.e. a grassland, a shrub and a plantation, during the non-growing season (October 2004–April 2005) in Inner Mongolia, China. Our results demonstrate the significant effects of different plant communities on soil net N mineralization and the great temporal variations of soil N dynamics during the incubation period. The mean soil net N mineralization rates were 0.93, 0.77 and −1.28 mg N m−2 d−1, respectively, in the grassland, shrub and plantation. The mean soil NH4+-N in the three plant communities declined by 40%, but the mean soil NO3−-N increased by 190% by the end of the incubation compared with their initial concentrations at the beginning of incubation. The differences in plant communities significantly affected their soil N mineralization rates, accumulations and turnover rates, which followed the order: grassland > shrub > plantation. During the winter time, the studied soils experienced the three phases consisting of mild freezing (−7 to −2 °C soil), deep freezing (approximately −10 °C soil) and freeze–thaw (−2 to 5 °C soil). The results suggest that temporal variations of soil N mineralization are positively affected by the soil temperature and the soil nitrification is dominant in the N transformation process during the non-growing season. Our study indicates that the soil N mineralization over winter can make a substantial contribution to the mineral N pool that plants are able to utilize in the upcoming spring, but may also pose a great risk of mineral N leaching loss if great rainfalls occur during spring and early summer.

The impacts of land intensification on carbon (C) responses are important components of soil organic carbon (SOC) management. Grazing land intensification typically involves the use of highly productive plant species that can support greater grazing pressure, removal of higher proportions of site biomass and nutrients during mechanical harvest or grazing, and increased use of fertilizers, particularly N. Current improved grazing land management strategies are aimed at increasing above-ground biomass yield, with less regard for below-ground C dynamics. Since intensive management affects aboveand belowground C inputs (Schuman et al. 1999; Liu et al. 2011a, 2011b), it can have important implications for the amount and characteristics of SOC stored in grazing lands (Franzluebbers and Stuedemann 2003; Dubeux et al. 2006; Silveira et al. 2013). The objective of this study was to investigate the long-term impacts on SOC dynamics in subtropical ecosystems of converting native rangeland ecosystems into intensively managed systems.