Evaluation of nutrients removed and recycled in a commercial peach orchard over a 14-years-production cycle

Understanding nutrient dynamics within a peach orchard is fundamental to the development of accurate nutrient management practices. The present study investigated the nutrient uptake and redistribution in a 14-years-old commercial orchard in the Po valley. At the end of the experiment, trees were harvested, biomass and organ nutrient concentration were determined. Skeleton and roots accounted for the highest plant biomass, followed by fruits at harvest, pruned wood and abscised leaves; thinned fruits were less than 1 kg tree-1. The difference between the amounts of nutrients in leaves sampled in summer and in autumn (at abscission) was used to estimate the fraction of nutrients remobilized during the vegetative season inside the tree. The decrease of N, P, S, Cu, Mn and Zn concentration in abscised, compared to summer-sampled leaves was the result of the translocation of nutrients into fruits and storage organs. Nutrient circulation in a commercial nectarine orchard was calculated by determination of the fractions of each nutrient recycled (sum of nutrients in abscised leaves, thinned fruits and pruned wood) and remobilized (sum of nutrients in fruits at harvest, roots and skeleton). In our experimental conditions, on average, nectarine Stark RedGold showed an annual request of (in kg ha-1) 100, 17, 73, 129, 16, and 6 of N, P, K, Ca, Mg and S, respectively. More than half of these quantities were recycled in the orchard and returned back to the soil; consequently, if the nutrient use efficiency is maximized, the fertilization of nectarine requires only small amount of external inputs.

Silvopastoral Systems Enhance Soil Health in the Amazon Region

Silvopastoral systems (SPS), an integrated farming system in which tropical grasses are combined with trees and shrubs, have been implemented in the last years in the Amazon region in order to mitigate the impacts generated by the traditional cattle ranching system. However, despite the multiple SPS’s benefits to soil and ecosystem, there is a paucity of comprehensive studies revealing the potential soil health (SH) restoration through SPS. Here, by developing an overall SH index using local native vegetation (Amazon rainforest) as a reference, we aimed to assess SH changes induced by the land transition from the traditional livestock production system to the SPS in the Colombian Amazon region. A chronosequence conformed by three areas: (i) native vegetation, (ii) traditional pasture and (iii) silvopastoral system was established in two study sites located in the Colombian Amazon, specifically in Caquetá State, the second hotspot of deforestation in the Amazon Basin. The results indicated high soil compaction and loss of macrofauna diversity and richness due to pasture management, causing a loss of 9% of soil capacity to function. In contrast, by integrating 31 soil indicators, our SH assessment revealed that SPS was an effective strategy for the recovery of SH, impacting positively multiple soil functions related to nutrient dynamics, water retention and supply, and biological activity.

Spatial and Temporal Patterns in Carbon and Nitrogen Inputs by Net Precipitation in Atlantic Forest, Brazil

Understanding both carbon and nitrogen temporal and spatial inputs by rainfall in tropical forests is critical for proper forest conservation and management and might ultimately elucidate how climate change might affect nutrient dynamics in forest ecosystems. This study aimed to quantify the net precipitation contribution to the Atlantic Forest’s total carbon (C) and total nitrogen (N), identifying potential differences between these inputs regarding temporal (seasonal and monthly) and spatial scales. Rainfall samples were collected before and after interacting with the forest canopy from May 2018 to April 2019. The rainfall was enriched after crossing the forest canopy. Significant differences were found for gross rainfall and net precipitation between annual carbon (104.13 kg ha−1 and 193.18 kg ha−1) and nitrogen (16.81 kg ha−1 and 36.95 kg ha−1) inputs, respectively. Moreover, there was seasonal variability in the C and N inputs with 75% occurring in the wet season. Overall, the spatial patterns revealed that the same locations had the highest inputs regardless of the analyzed period. The forest-rainfall interactions provide constant C and N inputs, especially in the wet season, and are fundamental for the maintenance of ecological processes. Study Implications The hydrological and nutrient cycles are tied together. There was significant nutrient enrichment after rainfall interacts with the forest canopy. Rainfall seasonality and canopy deciduousness and heterogeneity drive the temporal and spatial variabilities of carbon and nitrogen. The wet season represented an average of 75% of the total annual carbon and nitrogen contribution, via net precipitation. Such findings enhance our understanding of nutrient deposition, leaching, and absorption processes by canopies and the importance of the tropical forest in the hydrological and nutrient cycle. This knowledge might serve as a guide to improve management practices and justify conservation initiatives.

Nutrient pathways and their susceptibility to past and future change in the Eurasian Arctic Ocean

Climate change is altering nutrient cycling within the Arctic Ocean, having knock-on effects to Arctic ecosystems. Primary production in the Arctic is principally nitrogen-limited, particularly in the western Pacific-dominated regions where denitrification exacerbates nitrogen loss. The nutrient status of the eastern Eurasian Arctic remains under debate. In the Barents Sea, primary production has increased by 88% since 1998. To support this rapid increase in productivity, either the standing stock of nutrients has been depleted, or the external nutrient supply has increased. Atlantic water inflow, enhanced mixing, benthic nitrogen cycling, and land–ocean interaction have the potential to alter the nutrient supply through addition, dilution or removal. Here we use new datasets from the Changing Arctic Ocean program alongside historical datasets to assess how nitrate and phosphate concentrations may be changing in response to these processes. We highlight how nutrient dynamics may continue to change, why this is important for regional and international policy-making and suggest relevant research priorities for the future.

Does the Introduction of N2-Fixing Trees in Forest Plantations on Tropical Soils Ameliorate Low Fertility and Enhance Carbon Sequestration via Interactions Between Biota and Nutrient Availability? Case Studies From Central Africa and South America

Plant and/or crop growth rely on nutrient dynamics driven by specific soil biota in different environments. This mini-review aims to provide an overview of interactions between soil organisms, nutrient dynamics, and C sequestration. To this end, we investigated published results from three forest plantations (eucalyptus monocultures and mixed plantations with N2-fixing acacia) on tropical nutrient-poor soils. One case study is located in Central Africa (Congolese coastal plains) and two others in South America (Southeastern Brazil). Overall, the studies showed that soil biota activity exerted positive effects on (i) C accretion, as both soil carbon and belowground and aboveground biomass are driven and enhanced by soil biota; and (ii) on nutrient dynamics and biogeochemical cycles in nutrient-poor soil of tropical ecosystems, which are boosted following C accumulation. On the other hand, the pedoclimatic environment may potentially impact soil functioning of mixed-species plantations through its influence on the composition and activity of bacterial communities. Regardless of the potential risk of acacia invasiveness, benefits such as pulp, fuelwood, electric pole and non-timber products supply, have been reported in Central Africa. We, therefore, conclude that including N2 fixing trees in forestry plantations as reported in this mini-review helps strengthen the links between soil biota, nutrient and SOC dynamics in mixed-species plantations on tropical nutrient-poor soils.