Management intensity affects density fractions of soil organic matter from grazed bahiagrass swards

Raiesi

2012

Nutr Cycl Agroecosyst

Sheep grazing is known to influence soil organic carbon (SOC) storage and dynamics in rangelands. However, very little is known of grazing impacts on measurable SOC pools associated with primary particles, particulate organic matter (POM) and carbohydrates in the heavily grazed rangelands of Zagros Mountains, Iran. Bulk SOC, total nitrogen (N), POM and hot-water extractable carbohydrates (HWC) as well as different SOC and N fractions in particle-size separates were studied in natural mountainous rangelands of arid (Boroujen with 255 mm annual rainfall) and semi-arid (Sabzkouh with 860 mm annual rainfall) sites, Central Zagros. Two sheep grazing regimes including grazed and ungrazed (for 20-25 years) rangelands with four replicates were identified as the grazing treatments at each site. Soil samples (0-15 cm) were taken and analyzed for bulk SOC, total N, POM, HWC, and SOC and N associated with physical fractions. Bulk SOC contents were similar for both ungrazed and grazed regimes, while total N contents significantly decreased under grazed conditions. Bulk soil POM and HWC contents decreased considerably and clearly by sheep grazing, indicating that these fractions of total soil organic matter (SOM) pool may be suitable indicators for detecting the grazing effects on bulk SOC changes and storage in these arid and semi-arid ecosystems. Semi-arid rangeland sites contained more bulk SOC, total N and POM contents than arid rangeland sites. These differences were primarily due to the large differences in vegetation composition, annual rainfall and soil conditions between the two rangelands. After 20-25 years of grazing over 10-33 % of SOC and total N losses occurred in the sand-and clay-size fractions with 10 % increases in the silt fraction. This means sheep grazing increases the contribution of the silt fraction to bulk soil N. We found evidence that sheep grazing decreases soil POM and HWC pools, and the sand fraction C, suggesting a lower recent annual input of decomposable organic C in heavily grazed rangelands. Sheep grazing had no influence on the potential C mineralization of the bulk soil at the semi-arid site (Sabzkouh), but reduced C mineralization at the arid-site (Boroujen), indicating that sheep grazing may affect SOC dynamics by changes in substrate quality at the former, but by substrate quantity at the later. In brief, long-term sheep grazing can potentially lead to losses of both labile and no-labile SOM in these arid and semi-arid rangelands.

Section: Introductionmentioning

confidence: 99%

Bulk soil and particle size-associated C and N under grazed and ungrazed regimes in Mountainous arid and semi-arid rangelands

Raiesi

2012

Nutr Cycl Agroecosyst

“…The difference in C stock between the two systems can be related to some practices adopted in VRG management that increases C in the soil, as observed in previous studies, including: the diversity of species (Steinbeiss et al, 2008), the deposition of cow manure on the pasture (Matsuura et al, 2014), high stocking rates (Dubeux et al, 2006a), herd effect (Savory and Butterfield, 1999), length of recovery period of plants (Abberton et al, 2010), and the use of perennial species (Bell et al, 2012). The richness of species in VRG pastures varied according to property, but it was never a monoculture.…”

Section: Discussionmentioning

confidence: 68%

“…In fact, Dubeux et al (2006b) observed a greater return and quality of residue at higher stocking rates, as well as greater C sequestration (Conant et al, 2001;Dubeux et al, 2006a), particularly in rotational systems. In VRG, the division of pasture plays an important role in guaranteeing a period of recovery from herbivory for the plants, preventing overgrazing and the consequent degradation of C stock (Tanentzap and Coomes, 2012).…”

Section: Discussionmentioning

confidence: 96%

Rationally Managed Pastures Stock More Carbon than No-Tillage Fields

Seó

Filho

Brugnara

2017

Front. Environ. Sci.

A significant share of Greenhouse Gases (GHG) produced from agriculture comes from cattle farming. The reduction in GHG emissions from ruminants fed with grains has led some researchers to recommend such a diet as a means of mitigating emissions in the sector. A more accurate balance of emissions, however, must include the carbon (C) stocked by feed crops. Within the grain production system, no-tillage (NT) cultivation systems have a greater capacity to increase and store soil organic carbon (SOC). Within grazing management systems, the rotation used in Voisin's Rational Grazing (VRG) allows the accumulation of SOC through root growth. The objective of this study was to assess the C stock of pasture under VRG and compare soil C stock between VRG pasture and fields under no-tillage management, in two seasons over a period of 1 year. The study included five dairy farms in Santa Catarina State, Brazil. In each property, we collected soil to quantify SOC from VRG pasture and NT fields, in summer and winter. In the pasture, to determine the total stock, we also collected samples from the aerial parts of plants and the roots. Further, we estimated how efficient would be producing milk from those pastures or from those crops. The VRG pasture showed a greater capacity to stock C in the soil than the no-tillage fields (VRG = 115.0 Mg C ha −1 ; NT = 92.5 Mg C ha −1 ; p < 0.00009), with the greatest difference at a depth of 0-10 cm (VRG = 41 Mg C ha −1 ; NT = 32 Mg C ha −1 ; p < 0.00008). In VRG, 95% of C was in the soil, 1% in the aerial part of plants, and 4% in the roots. On pasture was produced 0.15 kg of milk.kg −1 of C stored, and on NT system 0.13 kg of milk.kg −1 of C stored. In this study, we conclude that independent of season, the soil in well managed pastures had a greater stock of C, produced more milk and produced more milk.kg −1 of stored C than fields under NT management. Therefore, when comparing GHG emissions of ruminants with different diets, we must also quantify the SOC resulting from distinct feed production systems.

“…In non-degraded grasslands, grazing management represents the most important factor that can affect soil C accumulation. In a 2-year study , Dubeux Jr et al (2006b) reported that greater stocking rate and N fertilization of bahiagrass pastures resulted in accumulation of C in the light density (1.85 g cm -3 ) SOM fraction. These results demonstrated that SOM in grasslands is subject to short-term changes in grazing management.…”

Section: Nitrogen and Carbon Dynamics In Grasslandsmentioning

confidence: 99%

Nutrient cycling in tropical pasture ecosystems

Vendramini

Dubeux

Silveira

2014

Agraria

In most forage production systems, essential nutrients required for plant growth are provided by different pools in the ecosystem. In general, warm-climate grasslands are characterized by extensive grazing systems with minimal inputs of commercial fertilizer and supplemental feed, primarily because of unfavorable economics of fertilization or limited availability of fertilizer material. Low soil N availability is a major limitation in tropical and subtropical pasture systems, and it represents one of the main causes of pasture degradation. The major pools of N in grazed grasslands are soil, vegetation, grazing animals, and atmosphere. Fluxes among the various pools are complex and are affected by biotic and abiotic factors such as climate, soil organisms, forage species, and herbivores. Therefore, nutrient cycling is a vital component in maintaining pasture sustainability because it represents an important source of nutrients to warm-season grass pastures. Excreta and litter are the two major pathways for herbage nutrients to return to the soil. Litter quantity and chemical composition are determinants in litter deposition and decomposition and are greatly affected by grazing management practices. The use of warm-season legumes in warm-season grass stands is a potential management practice that can improve litter decomposition and N inputs to warm-season grass pastures. Approximately 70 to 90% of the nutrients consumed by ruminants return to the pastures via excreta deposition; however, nutrient return through excreta is not uniform. Stocking method, portable shade and water systems, and strategic fencing are effective management practices to improve excreta distribution on pastures. The adoption of management practices that improve nutrient cycling is a determining factor to reduce warm-season grass pasture degradation and optimize productivity and persistence.Key words: excreta, litter, pasture, warm-season grass, warm-season legume Ciclagem de nutrientes em pastagens tropicais RESUMOEm sistemas de pastejo os nutrientes necessários para promover o crescimento das plantas forrageiras são supridos por diferentes compartimentos do ecossistema. Em geral, pastagens em regiões tropicais são caracterizadas por sistemas de pastejo extensivos com a aplicação de níveis reduzidos de fertilizantes nitrogenados e suplementação animal devido principalmente aos retornos econômicos desfavoráveis e à disponibilidade limitada de fertilizantes. Baixa disponibilidade de N no solo está entre as maiores limitações para a produção de forrageiras em áreas tropicais e subtropicais e uma das maiores causas de degradação de pastagens. Os maiores compartimentos de nitrogênio em pastagens são o solo, vegetação, herbívoros e atmosfera. Portanto, ciclagem de nutrientes é vital para fornecer nutrientes para pastagens em regiões tropicais. Excreta e serrapilheira são os dois maiores contribuintes de retorno de nutrientes para o solo. Quantidade e composição química da serrapilheira são determinantes no processo de deposição e decompos...