Perennial C4 grasses increase root biomass and carbon in sown temperate pastures (2025)

Root Characteristics of Perennial Warm-Season Grasslands Managed for Grazing and Biomass Production

Agronomy, 2013

Minirhizotrons were used to study root growth characteristics in recently established fields dominated by perennial C4-grasses that were managed either for cattle grazing or biomass production for bioenergy in Virginia, USA. Measurements over a 13-month period showed that grazing resulted in smaller total root volumes and root diameters. Under biomass management, root volume was 40% higher (49 vs. 35 mm 3) and diameters were 20% larger (0.29 vs. 0.24 mm) compared to grazing. While total root length did not differ between grazed and biomass treatments, root distribution was shallower under grazed areas, with 50% of total root length in the top 7 cm of soil, compared to 41% in ungrazed exclosures. These changes (i.e., longer roots and greater root volume in the top 10 cm of soil under grazing but the reverse at 17-28 cm soil depths) were likely caused by a shift in plant species composition as grazing reduced C4 grass biomass and allowed invasion of annual unsown species. The data suggest that management of perennial C4 grasslands for either grazing or biomass production can affect root growth in different ways and this, in turn, may have implications for the subsequent carbon sequestration potential of these grasslands.

Root carbon inputs under moderately diverse sward and conventional ryegrass-clover pasture: implications for soil carbon sequestration

Plant and Soil, 2015

Background and aims A strategy to increase soil C under pasture-based systems is to increase the root mass inputs or increase rooting depth of plants. Our objective in this study was to measure the seasonal dynamics of root mass and C inputs under two different pasture types (ryegrass-clover vs moderately diverse) that differ in plant diversity and which are commonly used in New Zealand agriculture. Methods This study was carried out on an existing plant diversity field trial containing six replicate paddocks of both moderately-diverse and ryegrass-clover pastures. Soil cores (0-100-200-300 mm sections) were collected seasonally across 1 year and individual root traits assessed from all species. Results The moderately diverse pasture had greater root mass (5320-9350 kg ha −1 ) than the ryegrass-clover pasture (3810-5700 kg ha −1 ) for all seasons and had greater root mass lower in the soil profile. A secondary objective demostrated no significant difference in root mass between high and low sugar ryegrass cultivar. Increased root mass results in an estimated increase of C input to the soil of about 1203 kg C ha −1 (0-300 mm depth) under the moderately diverse pasture, excluding root exudates. Root trait measurements demonstrated a greater diversity of root traits in the moderately diverse sward compared to the ryegrass-clover pasture. Conclusions Moderately diverse pasture systems offer scope to increase soil C under grazed pastures through increased root mass inputs and rooting depth.

Quantifying shoot and root biomass production and soil carbon under perennial bioenergy grasses in a subtropical environment

Biomass & Bioenergy, 2019

Perennial bioenergy grasses can potentially replace fossil fuels and offset atmospheric CO 2 through soil C sequestration. However, limited information relevant to the impacts of bioenergy cropping on ecosystem services, especially above-and below-ground productivity and soil C sequestration is available for subtropical environments (e.g., southeastern USA). The objective of this study was to evaluate the impacts of perennial bioenergy cropping on C cycling and accumulation in the soil following four years of production in North Florida. Treatments consisted of six perennial grass species: giant reed, elephantgrass, energycane, sugarcane, sweetcane, and giant miscanthus. Elephantgrass, energycane, sweetcane, and sugarcane produced great shoot biomass (31-41 Mg ha −1) when harvested once per year. Giant reed's shoot biomass responded favorably to two harvests per year (27-43 Mg ha −1), whereas giant miscanthus did not perform well in any of the years (9-21 Mg ha −1). Additionally, giant reed, sweetcane, and giant miscanthus produced greater root biomass (9-11 Mg ha −1) compared with the other three species (2.5-3.2 Mg ha −1). Among the six grasses, sweetcane, energycane, and elephantgrass resulted in increases in soil C stocks (~15 Mg ha −1) relative to the initial level. Conversely, giant reed and giant miscanthus had no increase in soil C stock. Results suggested that interspecies differences observed in biomass yield among the six perennial bioenergy grasses could therefore affect soil C accumulation. High biomass yielding species such as sweetcane, energycane, and elephantgrass can effectively increase soil C within a few years following establishment in a subtropical environment.

Soil carbon stocks under grazed pasture and pasture-tree systems

Science of The Total Environment, 2020

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Opportunities to sequester carbon in soil: Management of perennial pastures

2012

Carbon sequestration in soil presents an opportunity for agricultural systems to be a net sink, rather than source of atmospheric carbon. It has been suggested that grazing and nutrient management of perennial pastures are the main drivers of carbon sequestration in agricultural soils. This paper outlines results from investigations into carbon concentration and carbon stock under perennial pastures in southeastern NSW. Forty eight sites were sampled at regular depth intervals to 0.70 m. Comparisons included: i) soil type (basaltvs granite-derived), ii) climate (summer dominant vs equiseasonal rainfall), iii) pasture type (native vs introduced perennial pasture), iv) grazing management (continuously vs rotationally grazed) and v) soil fertility. There was a significant difference in the mass of C in soil due to soil type (P <0.001) and climate (P = 0.008). Basalt derived soils had an average of 159 Mg C ha to 0.70 m, deep granite-derived soils had 76 Mg C ha and shallow granite-d...

Do Grazing Systems and Species Composition Affect Root Biomass and Soil Organic Matter Dynamics in Temperate Grassland Swards?

Sustainability

Elevating soil organic matter (SOM) levels through changes in grassland management may contribute to lower greenhouse gas concentrations in the atmosphere and mitigate climate change. SOM dynamics of grassland soils may be affected by grazing systems and plant species composition. We analyzed the effects of simulated grazing systems (continuous (CG), rotational (RG), and lenient strip grazing (LG)) and species composition (monocultures of perennial ryegrass fertilized (LP+) and unfertilized (LP−)), tall fescue (fertilized, FA+), and a mixture of these two species with white clover (fertilized, LFT+)) on root biomass and SOM dynamics in field experiments on loamy and sandy soils in the Netherlands. Dried cattle manure was added to all fertilized treatments. We hypothesized that SOM accumulation would be highest under CG and LG, and FA+ and LFT+ as a consequence of greater belowground biomass production. SOM was monitored after conversion from arable land for a period of two years (lo...

Sensitivity of soil carbon to management and environmental factors within Australian perennial pasture systems

Geoderma, 2014

Environmental factors such as parent material and climate can have a large effect on total carbon concentration and soil carbon stocks, yet unlike vegetation type, fertiliser use and grazing pressure, these cannot be changed by management. The relative effects of these environmental and land management factors were compared in the Monaro and Boorowa regions of New South Wales (NSW), Australia. Parent material, geographic region, soil depth and soil fertility had a significant influence on soil carbon stocks to 0.70 m while pasture type (introduced vs native pastures) did not. Parent material and soil depth significantly (P b 0.05) influenced the mean soil carbon stock (Mg C/ha) in the Monaro region; 159 (11 se) in basalt-derived soils, 77 (11 se) in deep granite-derived soils and 43 (3 se) in shallow granite-derived soils. Climate also significantly (P b 0.05) influenced the mean carbon stock, with deep granite-derived soils in the Monaro region having 76.5 (11 se) compared with 51.8 (3 se) Mg C/ha in the Boorowa region. A considerable proportion of the total carbon stock to 0.70 m for all sites was measured in the subsoil (0.30 to 0.70 m). In the Monaro region, basalt-derived soil contained 43% of the total carbon stock in the subsoil, compared with 28% in deep granite and shallow granite-derived soil. In the Boorowa region, deep granite-derived soil contained 33% of the total carbon stock in the subsoil. Restricting soil carbon measurements to the surface 0.30 m of soil may result in erroneous conclusions with respect to the influence of land management on the accumulation of carbon in soil. Total carbon concentration was positively correlated with labile carbon, total nitrogen, cation exchange capacity and extractable sulfur, suggesting that for a given parent material and climate, maintaining adequate pasture nutrition may substantially increase soil carbon stocks.

Carbon gain of C3 and C4 grasses in a dense canopy in the field

2010

Daily carbon gain of a C3 (Lolium perenne L.) and a C4 (Paspalum dilatatum Poir.) species growing in a mixed dense canopy was assessed at the end of summer, in Argentina. Chambers of transparent acrylic glass received 13 C-enriched CO 2 continuously from 12:00 to 19:00 on a given day. Immediately after labelling, samples were harvested and carbon gain was estimated as plant carbon mass times the proportion of newly assimilated carbon. P. dilatatum contributed more than L. perenne to both canopy standing biomass (164 vs. 22 g per m 2 ground) and canopy carbon gain (830 vs. 120 mg C per m 2 and per h). Both species showed a similar ability to capture carbon per unit canopy mass (P. dilatatum=5.1; L. perenne=5.5 mg C per g C and h), which suggested that the C3/C4-grasses composition of the canopy was not changing. Tiller-level analysis revealed that in both species big tillers captured more carbon per unit mass than small tillers (asymmetric competition), and that the C3 and C4 grass species achieved a similar relative photosynthesis rate (mg C per g C and h) in different ways: high gross assimilation rate (mg C per m 2 and h) in P. dilatatum, and high leaf area ratio (m 2 per g C) in L. perenne.

Estimating seasonal and annual carbon inputs, and root decomposition rates in a temperate pasture following field 14C pulse-labelling

Using a 14 C pulse-labelling technique, we studied the seasonal changes in assimilation and partitioning of photoassimilated C in the plant-root-soil components of a temperate pasture. Pasture and soil samples were taken after 4-h, and 35-day chase periods, to examine these seasonal 14 C fluxes. Total C and 14 C were determined in the shoot, root and soil system. The amounts of C translocated annually to roots and soil were also estimated from the seasonal 14 C distribution and pasture growth. The in situ field decomposition of newly formed roots during different seasons, also using 14 C-labelling, was studied for one year in undisturbed rhizosphere soil. The 14 C-labelled roots were sampled five times and decomposition rates were calculated assuming first-order decomposition. Annual pasture production at the site was 16 020 kg DM ha −1 , and pasture growth varied with season being highest (75-79 kg ha −1 d −1) in spring and lowest (18-20 kg ha −1 d −1) in winter. The above-and below-ground partitioning of 14 C also varied with the season. The respiratory 14 C-CO 2 losses, calculated as the difference between the total amounts of 14 C recovered in the soil-plant system at 4 h and 35 days, were high (66-70%) during the summer, autumn and winter season, and low (37-39%) during the spring and late-spring season. Pasture plants partitioned more C below-ground during spring compared with summer, autumn and winter seasons. Overall, at this high fertility dairy pasture site, 18 220 kg C/ha was respired, 6490 kg remained above-ground in the shoot, and 6820 kg was translocated to roots and 1320 kg to soil. Root decomposition rate constant (k) differed widely with the season and were the highest for the autumn roots. The half-life was highest (111 days) for autumn roots and lowest (64 days) for spring roots. About one-third of the root label measured in the spring season disappeared in the first 5 weeks after the initial 35 Day of allocation period. The late spring, summer, late summer and winter roots had intermediate half-lives (88-94 days). These results indicate that seasonal changes in root growth and decomposition should be accounted for to give a better quantification of root turnover.

Herbicide application during pasture renewal initially increases root turnover and carbon input to soil in perennial ryegrass and white clover pasture

Plant and Soil, 2016

Aims Increasing the input and turnover of root tissue is considered to be one method that may increase carbon (C) inputs and storage in soil. The use of herbicide during pasture renewal (periodic re-sowing of pasture) is expected to increase root inputs and turnover as plants die. The objective of this study was to quantify the shortterm impact of pasture renewal on root turnover and C input to soil of ryegrass-clover pastures. Methods Pastures were labelled in the field using a 13 C isotope pulse labelling method within 1 m 2 clear chambers. Five daily labelling events were carried out during one week in paired treatment plots within 3 replicate paddocks. One plot per paddock was sprayed with herbicide and then the pasture was renewed by direct drilling of seed. The 13 C of roots and soil (0-100 mm) was measured at regular intervals over an 89-day period. Results Herbicide application caused an initial rapid turnover time of 17 days followed by a slower turnover time of 524 days, compared to unsprayed pasture which had a root turnover of 585 days. Faster root turnover following herbicide application resulted in greater cumulative C input to soil over 89 days with approximately double the C input in the sprayed treatment (3238 ± 378 kg C ha −1) compared to the unsprayed treatment (1726 ± 540 kg C ha −1). Conclusions The use of glyphosate during pasture renewal increased root turnover and resulted in a greater short term cumulative C input to soil. This study provides the first values of root turnover and C input to soil during a pasture renewal event in New Zealand pasture systems and contributes to the understanding of how pasture roots may influence the soil C input following plant death in grassland systems.