Hurricanes Substantially Reduce the Nutrients in Tropical Forested Watersheds in Puerto Rico

Because nutrients including nitrogen and phosphorus are generally limited in tropical forest ecosystems in Puerto Rico, a quantitative understanding of the nutrient budget at a watershed scale is required to assess vegetation growth and predict forest carbon dynamics. Hurricanes are the most frequent disturbance in Puerto Rico and play an important role in regulating lateral nitrogen and phosphorus exports from the forested watershed. In this study, we selected seven watersheds in Puerto Rico to examine the immediate and lagged effects of hurricanes on nitrogen and phosphorous exports. Our results suggest that immediate surges of heavy precipitation associated with hurricanes accelerate nitrogen and phosphorus exports as much as 297 ± 113 and 306 ± 70 times than the long-term average, respectively. In addition, we estimated that it requires approximately one year for post-hurricane riverine nitrogen and phosphorus concentrations to recover to pre-hurricane levels. During the recovery period, the riverine nitrogen and phosphorus concentrations are 30 ± 6% and 28 ± 5% higher than the pre-hurricane concentrations on average.

Nutrient Use Efficiency Indices in Maize Hybrid as A Function of Various Rates of NPK in Mid Hills of Nepal

Field experiments were conducted to evaluate yield and nutrient use efficiency in maize in response to various rates of nitrogen (N), phosphorus (P) and potassium (K) in silty clay loam soil of Khumaltar, Nepal during 2019 and 2020. Three factorial randomized complete block designs with 27 treatment combinations were used in experiments, which were repeated three times. Three factors were N levels (150, 180, 210 N kg ha-1), P levels (40, 60, 80 P2O5 kg ha-1), and K levels (40, 60, 80 K2O kg ha-1). The results recommend to revise fertilizer dose since N210 kg ha-1 and K2O 80 kg/ha were optimum for increased maize production with grain yields of 10.95 t ha-1 and 10.54 t ha-1, respectively. Partial factor productivity, partial nutrient budget, internal efficiency, physiological efficiency, recovery efficiency, and agronomic efficiency of NPK for hybrid maize were mostly influenced by nutrient levels. Application of higher rate of P and K fertilizer improved maize N efficiencies, and case was valid for P and K efficiencies. Maize was more responsive to N and K fertilizer and lower rate of P application limited efficient use of applied N and K. To increase overall NUE, we recommend to revise dose of fertilizer for hybrid maize under mid hill condition of Nepal.

Long-Term Ecosystem Nutrient Pool Status for Aspen Forest Harvest Simulations on Glacial Till and Sandy Outwash Soils

Sandy outwash and glacial till soils compose large amounts of public forestland due to historically poor agricultural yields. The outwash soils have low fertility, poor nutrient retention and are restricted from whole-tree harvesting (WTH) in some states, whereas the glacial till has medium nutrient retention and fertility, and is unrestricted from WTH. To assess the long-term sustainability of harvesting, a nutrient budget was constructed from field measurements, the National Cooperative Soil Survey (NCSS) database, and literature values for stem-only harvesting (SOH) and WTH at a 45-year rotation length and 11 rotations were simulated. The budgets showed that SOH and WTH recovery years, or the time necessary for the inputs to match outputs through leaching and one harvest, exceeded common rotation lengths for both soil types under all weathering scenarios, and the average WTH reduced the total available rotations by one harvest. The large variation in soil nutrient pools and harvest removals complicated the ability to identify the difference between SOH and WTH early in the model, but differences became apparent with sequential harvests. The recovery years were 2–20 times the 45-year rotation length under all weathering rates. Taken together, models in this study bridge the gap between short- and long-term studies and bring into question the sustainability of WTH and SOH practices on nutrient-poor soils.

Spatiotemporal Heterogeneity of Mangrove Root Sphere under a Tropical Monsoon Climate in Eastern Thailand

Mangrove ecosystems under tropical monsoon climates experience changes in environmental factors, especially seasonal variations in salinity. These changes might have direct influences on the mangrove root sphere, which plays an important role in carbon dynamics and supports mangrove growth. We aimed to elucidate how the soil properties including salinity and nutrient budget affect the mangrove roots in the wet and dry seasons across the mangrove zonation (Avicennia, Rhizophora, and Xylocarpus zones). This area is in a secondary forest at the Trat River estuary, eastern Thailand. Root mass was observed at 0–10 and 10–20 cm depths across all zones and the living roots were separated into diameter classes. The soil water salinity was measured at a 10 cm depth. We analyzed the nitrogen, phosphorus, and carbon contents in the roots and soil. Spatiotemporal changes occurred due to the vegetation zonation and the variations in salinity and the content of soil available phosphorus that caused different root sphere conditions along the distance from the river. The highest root biomass was found in the riverward Avicennia zone, which was 4.8 times higher than that of the inland Xylocarpus zone in the wet season. The root necromass distribution along the zonation showed an opposite trend to that of biomass. Among seasons, the root size-class proportion differed, with high fine roots observed during the wet season. We confirmed that the root sphere showed both spatial and temporal heterogeneity. Mangrove roots, especially fine roots, interacted with changing salinity, inundation regime, and biological processes evoked by microtopographic gradients as a consequence of mangrove zonation and seasonal rainfall. Our findings indicate how the root sphere differed by specific vegetation structure in this mangrove forest. Therefore, these might provide an ecological perspective for the mangrove rehabilitation plans to facilitate below-ground carbon stock.

Subsoil-potassium depletion accounts for the nutrient budget in high-potassium agricultural soils

Continuous potassium (K) removal without replenishment is progressively mining Argentinean soils. Our goals were to evaluate the sensitivity of soil-K to K budgets, quantify soil-K changes over time along the soil profile, and identify soil variables that regulate soil-K depletion. Four on-farm trials under two crop rotations including maize, wheat and soybean were evaluated. Three treatments were compared: (1) control (no fertilizer applied); (2) application of nitrogen, phosphorus, and sulfur fertilizers -NPS-; and (3) pristine condition. After nine years, crops removed from 258 to 556 kg K ha−1. Only two sites showed a decline in the exchangeable-K levels at 0–20 cm but unrelated to K budget. Topsoil exchangeable-K levels under agriculture resulted 48% lower than their pristine conditions, although still above response levels. Both soil exchangeable-K and slowly-exchangeable K vertical distribution patterns (0–100 cm) displayed substantial depletion relative to pristine conditions, mainly concentrated at subsoil (20–100 cm), with 55–83% for exchangeable-K, and 74–95% for slowly-exchangeable-K. Higher pristine levels of exchangeable-K and slowly-exchangeable-K and lower clay and silt contents resulted in higher soil-K depletion. Soil K management guidelines should consider both topsoil and subsoil nutrient status and variables related to soil K buffer capacity.

Effects of Organic and Inorganic Fertilizers on the Growth of Senecio biafrae (WOROWO) OLIVE & HIERN

Soils have shown a negative balance in nutrient budget which poses a great threat to sustainable soil management for increase in growth and crop yield. This study thus investigated the effects of organic and inorganic fertilizers on the growth of Senecio biafrae (Oliv. &Hiern). Topsoil, organic (poultry manure) and inorganic fertilizers (NPK 15:15:15) were used. The fertilizers were weighed and applied to the soil at 5g, 10g, 15g each; control topsoil without application of fertilizers and were replicated five times. Growth parameters including height, number of leaves and stem diameter were taken weekly for the period of the experiment. Application ofpoultry manure and NPK fertilizer had significant effects on all the growth parameters considered. The application of poultry manure resulted into significant increase in the growth parameters towards the latter part of the study. This study has shown that organic manure has great potential for improving soil productivity and plant growth. Keywords: Senecio biafrae, investigate, organic, inorganic, plant yield

Overview of nutrient cycling in the sub-Arctic Atlantic regions: insights from nitrate & silicon isotopes

<p>The environmental consequences of rapid climate change are already becoming apparent in the Arctic. Polar amplification has led to major loss of sea ice, increasing freshwater run-off and a poleward intrusion of Atlantic waters, thereby affecting biogeochemical cycles. Additionally, while primary production in the Arctic has increased by >50% over the last two decades (Lewis et al., 2020), it is still unclear whether Arctic nutrient budgets can sustain this increase on the long-term. Increased primary production in the central Arctic has the potential to reduce nutrient concentrations of Arctic outflow waters and modify their nutrient ratios, having consequences for the Atlantic nutrient budget.</p><p>Primary production in the Arctic is principally nitrogen-limited as a result of benthic denitrification on Arctic shelves. This is contrasted by silicon limitation in water masses originating from the Atlantic basin. To untangle the complexities of dual nutrient limitation and to gain insights into the role of Arctic outflows in controlling nutrient export to the North Atlantic, we examine the cycling of both major nutrients, nitrate and silicic acid, in key Arctic seas and straits. Using stable isotopes of dissolved nitrate and silicic acid, we provide new insights into the  mechanisms and factors that control nutrient cycling in the Arctic Ocean: nutrient origins, transformation during transport, as well as the relative contribution of primary production, remineralisation and regeneration to water column inventories.</p><p>In this study, measurements of nutrient stoichiometry and stable isotopes of dissolved nitrate and silicic acid profiles are presented across the Fram Strait, Labrador Sea (AR7W transect), and the Iceland Basin and Irminger Sea (the Extended Ellett line and the OSNAP-East program). The measured variability in nutrient isotope signatures across the Arctic gateways brings to light the contribution of Arctic-sourced freshwater to the North Atlantic and its potential impact to the North Atlantic nutrient budget with future changes to primary production in these key regions.</p>