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

Differences in arbuscular mycorrhizal colonization and P acquisition between genotypes of the tropical Brachiaria grasses : is there a relation with BNI activity?

In a field experiment in Palmira, Colombia, we studied mycorrhizal root colonization, phosphomonoesterase activities and P and N foliar content before and after N fertilization among different Brachiaria genotypes with demonstrated biological nitrification inhibition (BNI) capacity. Furthermore, we tested the potential nitrification rate (PNR) in soil in order to confirm the inhibition of nitrification of the selected genotypes and relate the BNI performance with P acquisition. We hypothesized that (i) genotypes will differ in key variables related to P acquisition, and that there will be a positive correlation between (ii) arbuscular mycorrhizal fungi (AMF) root colonization, P uptake, and BNI activity, and (iii) between the activity of acid and alkaline phosphomonoesterase and BNI performance. Higher N immobilization 1 week after application of synthetic fertilizer (ammonium sulfate) and low PNR of Brachiaria humidicola CIAT 679 and CIAT 16888 confirmed that these genotypes have high-BNI activity. Despite the relatively high soil P status, high affinity of Brachiaria grasses for AMF was observed at the study site: more than 60% of root length was colonized by AMF in high-BNI genotypes, versus 45% in low-BNI Brachiaria cv. Mulato. The N content of high-BNI genotypes was positively correlated with mycorrhizal root colonization suggesting the uptake of NH 4 + by AMF and its transfer to high-BNI genotypes and/or regulation of AMF colonization by P demand. Furthermore, increased activity of acid phosphomonoesterase (6.98 and 7.68 μmol g −1 h −1 in high-BNI versus 5.20 μmol g −1 h −1 in low-BNI genotypes) and the depletion of the most labile available P fractions in the rhizosphere of high-BNI genotypes (by 21–32%) suggest enhanced P uptake and P-use efficiency. To the best of our knowledge, this is the first study that explored relations between BNI and biotic factors affecting P acquisition. Our results highlight the importance of AMF in Brachiaria grasses even under high P availability and warrant further studies including a larger number of different BNI genotypes that can elucidate biotic plant-soil interactions affecting nutrient-use efficiencies in improved pastures under low and high P status. </p