Visual Assessment of Soil Structure as an Early Indicator of Soil Quality in Response to Intensive Rotational Grazing

Grasslands can play a crucial role in mitigation of global warming by serving as carbon sink. Nevertheless, to achieve the grasslands’ potential, sustainable management is of the utmost importance as it determines system’s productivity and ecosystem services. Due to the increasing demand for animal products in developing countries, grazed areas increase exponentially in the tropics, mainly due to unsustainable management leading to low productivity and soil degradation. We evaluated the impact of intensive rotational grazing management (IRG) on early indicators of soil quality following land-use change based on on-farm observations of visual soil characteristics using two different widely used assessment methods: visual soil assessment-VSA and visual evaluation of soil structure-VESS. Correlation of visual methods were combined with measurements of soil macrofauna abundance and physical properties (e.g. bulk density, soil porosity). The IRG established in two study sites in Colombia was compared with traditional long-term continuous grazing with low stocking rate (1 LU ha-1). The IRG was based on rapid (1 day) cattle grazing in paddocks with high stocking rate (180 LU ha-1) followed by 60 days of recovery. In both study sites, IRG increased considerably total stocking rate to 4 LU ha-1 while improving grassland composition by enabling more valuable species, which contributed to soil quality and increased grassland productivity. Both VSA and VESS discriminated IRG-managed sites in less than one year after IRG adoption. Our results demonstrate that visual soil assessment is a useful mean for evaluation of soil quality and grassland productivity. Furthermore, VSA and VESS seemed to be more suitable in discriminating among management in early stages, when compared to commonly used soil physical properties, and were strongly correlated mainly to the abundance of earthworms. Furthermore, our study confirms the importance of grazing management in soil quality and ecosystem productivity/sustainability

Gross nitrogen transformation rates do not support previously described BNI capacities of selected Brachiaria genotypes

Nitrification is one of the key processes leading to water contamination and greenhouse gas emissions (N2O) in pasture systems. As vast areas of tropical pastures are nitrogen (N) limited, grasses from the Brachiaria genus have adapted to reduce N losses and increase N use efficiency by releasing substances capable of biological nitrification inhibition (BNI) in the rhizosphere. Although the release of BNI compounds and its impact on N2O emissions and net nitrification rates in soil have been studied, the impact of BNI on gross nitrogen transformation rates has not been addressed, despite its relevance to mechanistic understanding of this phenomena

Soil macrofauna as indicators of soil quality in improved (silvo) pastoral systems in the tropics

Silvopastoral systems are environmentally and economically beneficial alternative to cattle pastures formed by single grass species. The incorporation of trees, especially legumes, in pastures has several positive effects on soil properties and nutrient cycling while creating more favorable microclimate for the animals and increasing productivity. Soil macrofauna, the key element in soil food web regulating ecosystem services, has a direct effect on soil aeration and water movement due to the system of burrows and galleries, and on soil organic matter fragmentation. The legumes or legume-trees inclusion in the pastures will lead to improved nutrient cycling and increased biological activity resulting in increased accumulation of organic matter and improved soil physical properties within the silvopastoral system

Integral assessment of productive and environmental parameters of a forage-based silvopastoral system

Diversification of pastures and the incorporation of key plant functional groups (legumes) generally improve nutrient cycling and often lead to increased carbon sequestration in the soil. Furthermore, the inclusion of trees in the pastures improve soil properties while creating a microclimate more suitable for cattle, as well as for soil biological activity. Improved pastures with environmental benefits alongside with good management have vast potential to support region and country-level strategies to address relevant challenges related to the livestock sector in Latin America and the Caribbean (LAC) (Rao et al, 2015). The LivestockPlus project seeks to apply the concept of sustainable intensification of livestock systems in two countries of the LAC region such as Costa Rica and Colombia, to provide technical support, generate critical information and guidelines necessary for identifying options while contributing to planning and policies for scaling up of NAMAs

Tapping into the environmental co-benefits of improved tropical forages for an agroecological transformation of livestock production systems

Livestock are critical for incomes, livelihoods, nutrition and ecosystems management throughout the global South. Livestock production and the consumption of livestock-based foods such as meat, cheese, and milk is, however, under global scrutiny for its contribution to global warming, deforestation, biodiversity loss, water use, pollution, and land/soil degradation. This paper argues that, although the environmental footprint of livestock production presents a real threat to planetary sustainability, also in the global south, this is highly contextual. Under certain context-specific management regimes livestock can deliver multiple benefits for people and planet. We provide evidence that a move toward sustainable intensification of livestock production is possible and could mitigate negative environmental impacts and even provide critical ecosystem services, such as improved soil health, carbon sequestration, and enhanced biodiversity on farms. The use of cultivated forages, many improved through selection or breeding and including grasses, legumes and trees, in integrated crop-tree-livestock systems is proposed as a stepping stone toward agroecological transformation. We introduce cultivated forages, explain their multi-functionality and provide an overview of where and to what extent the forages have been applied and how this has benefited people and the planet alike. We then examine their potential to contribute to the 13 principles of agroecology and find that integrating cultivated forages in mixed crop-tree-livestock systems follows a wide range of agroecological principles and increases the sustainability of livestock production across the globe. More research is, however, needed at the food system scale to fully understand the role of forages in the sociological and process aspects of agroecology. We make the case for further genetic improvement of cultivated forages and strong multi-disciplinary systems research to strengthen our understanding of the multidimensional impacts of forages and for managing agro-environmental trade-offs. We finish with a call for action, for the agroecological and livestock research and development communities to improve communication and join hands for a sustainable agri-food system transformation

Biochar Reduces the Stability of Soil Aggregates during Intensive Leaching Experiment

The interplay of different mechanisms shaping the biochar impact on soil structure remains relatively unexplored. We investigated the impact of biochar application to two contrasting soils on the stability of soil aggregates under an intensive intermittent leaching regime. A greenhouse experiment was established using PVC columns filled with 500 g soil from an Acrisol or Calcisol amended with three biochar applications (0, 1 and 2% w/w). The columns were watered weekly (100 mL) during two leaching cycles (each lasting 10 weeks). The amount of leached base cations, the stability of 1–2 mm aggregates fraction and soil chemical properties were determined. Biochar enhanced the leaching of the studied cations, but the content of base cations and effective cation exchange capacity remained higher in the biochar-amended Acrisol when compared to control soil. In both soils, biochar reduced the amount of water-stable aggregates, which seemed to be attributed to the increase of K in the exchange complex in the Acrisol while no significant correlation was detected between aggregation in Calcisol and other variables. The negative impact of biochar on soil aggregation is likely linked to higher sensitivity of biochar-amended soils to aggregate disruption under changing moisture conditions caused by frequent and intensive leaching events. These results highlight the gaps in our understanding of biochar impact on soil aggregation, which have implications for soil erodibility or restoration of degraded lands under changing climate

Pasture diversification affects soil macrofauna and soil biophysical properties in tropical (silvo)pastoral systems

This is a post-print, peer-reviewed version of an article published in Agriculture, Ecosystems & Environment. The final authenticated version is available online at: https://doi.org/10.1016/j.agee.2020.10708