Nitrogen Release in Soils Amended with Different Organic and Inorganic Fertilizers under Contrasting Moisture Regimes: A Laboratory Incubation Study

Understanding nitrogen (N) release patterns and kinetics is a key challenge for improving N use efficiency in any agroecosystem. An incubation experiment was done to study the N release pattern and kinetics of contrasting soils amended with compost (CO), poultry manure (PM), rice husk biochar (RHB), poultry manure biochar (PMB) and cowdung (CD) combined with chemical fertilizer (integrated plant nutrient system, IPNS approach) under two moisture regimes, viz. field capacity (FC) and continuous standing water (CSW) at 25 °C for 120 days. Our results revealed that NH4+-N was the dominant under CSW conditions, whereas NO3−-N was dominant under FC conditions. Net mineral N data fitted well to the first order kinetic model. Both N release potential (N0) and rate constant (k) were greater in acidic soil than those of charland soil. The maximum N release varied between 24.90–76.29% of input depending on soil type and moisture status. N mineralization was strongly correlated with urea N application. PM and PMB mineralized in all soil and moisture conditions whereas N immobilization was observed in the case of RHB. N mineralization was strongly correlated with urea N application. Gaseous N losses were different for the organic amendments exhibiting more gaseous N losses in PM, CD and CO based IPNS whereas the lowest gaseous N loss was observed in PMB based IPNS. Biochar based IPNS increased soil pH in all conditions. Thus, the present study suggests that N release depends on soil type, soil moisture and type of organic amendment. However, CO, PM and CD based IPNS can be recommended for both acidic and charland soils in terms of N release as short duration crops will suffer from N deficiency if biochar based IPNS is used in the field.

In-depth analysis of N2O fluxes in tropical forest soils of the Congo Basin combining isotope and functional gene analysis

Primary tropical forests generally exhibit large gaseous nitrogen (N) losses, occurring as nitric oxide (NO), nitrous oxide (N2O) or elemental nitrogen (N2). The release of N2O is of particular concern due to its high global warming potential and destruction of stratospheric ozone. Tropical forest soils are predicted to be among the largest natural sources of N2O; however, despite being the world’s second-largest rainforest, measurements of gaseous N-losses from forest soils of the Congo Basin are scarce. In addition, long-term studies investigating N2O fluxes from different forest ecosystem types (lowland and montane forests) are scarce. In this study we show that fluxes measured in the Congo Basin were lower than fluxes measured in the Neotropics, and in the tropical forests of Australia and South East Asia. In addition, we show that despite different climatic conditions, average annual N2O fluxes in the Congo Basin’s lowland forests (0.97 ± 0.53 kg N ha−1 year−1) were comparable to those in its montane forest (0.88 ± 0.97 kg N ha−1 year−1). Measurements of soil pore air N2O isotope data at multiple depths suggests that a microbial reduction of N2O to N2 within the soil may account for the observed low surface N2O fluxes and low soil pore N2O concentrations. The potential for microbial reduction is corroborated by a significant abundance and expression of the gene nosZ in soil samples from both study sites. Although isotopic and functional gene analyses indicate an enzymatic potential for complete denitrification, combined gaseous N-losses (N2O, N2) are unlikely to account for the missing N-sink in these forests. Other N-losses such as NO, N2 via Feammox or hydrological particulate organic nitrogen export could play an important role in soils of the Congo Basin and should be the focus of future research.

Well-Aerated Southern Appalachian Forest Soils Demonstrate Significant Potential for Gaseous Nitrogen Loss

Understanding the dominant soil nitrogen (N) cycling processes in southern Appalachian forests is crucial for predicting ecosystem responses to changing N deposition and climate. The role of anaerobic nitrogen cycling processes in well-aerated soils has long been questioned, and recent N cycling research suggests it needs to be re-evaluated. We assessed gross and potential rates of soil N cycling processes, including mineralization, nitrification, denitrification, nitrifier denitrification, and dissimilatory nitrate reduction to ammonium (DNRA) in sites representing a vegetation and elevation gradient in the U.S. Department of Agriculture (USDA) Forest Service Experimental Forest, Coweeta Hydrologic Laboratory in southwestern North Carolina, USA. N cycling processes varied among sites, with gross mineralization and nitrification being greatest in high-elevation northern hardwood forests. Gaseous N losses via nitrifier denitrification were common in all ecosystems but were greatest in northern hardwood. Ecosystem N retention via DNRA (nitrification-produced NO3 reduced to NH4) ranged from 2% to 20% of the total nitrification and was highest in the mixed-oak forest. Our results suggest the potential for gaseous N losses through anaerobic processes (nitrifier denitrification) are prevalent in well-aerated forest soils and may play a key role in ecosystem N cycling.

Emissions of nitrous acid (HONO), nitric oxide (NO), and nitrous oxide (N2O) from horse dung

Horse dung contains considerable amounts of nitrogen which is partly lost during the storage period. Leaching of nitrogen from the dung can be prevented with constructions but also gaseous N-emissions occur. However, the emission rates are not reported in the literature. We measured in laboratory conditions nitrous oxide (N2O), nitric oxide (NO) and nitrous acid (HONO) emissions from fresh, one month old and one year old horse dung samples. NO and HONO emissions increased with the storage time of the dung. The mean emission rates of HONO and NO were from 36 to 280 ng N kg dw-1h-1 and from 15 to 3500 ng N kg dw-1h-1, respectively. N2O emissions were more variable showing also highest emissions (20.3 µg N kg dw-1 h-1) from the oldest samples. Thus, the longer storage of horse dung increases gaseous N losses which should be taken into account when planning the environmental friendly way to handle horse dung.

Robotic urine-patch treatment and effluent application - technology to support intensification of New Zealand dairy farming while protecting the environment

The need to minimise nitrate leaching and gaseous N losses from dairy farming is increasing; simultaneously dairy farming is undergoing rapid intensification. Robotic targeted application of nitrification and/or urease inhibitors is proposed as a route to addressing the "urine-patch" issue without risking milk contamination. This paper demonstrates a new robotic product under development and scheduled for commercial release for the 2015/2016 dairy season. The paper then discusses two developments of the product that will enable (i) highly-efficient fluidised-N application, and (ii) effluent application. These new products have the potential to greatly reduce nitrate leaching and gaseous N losses from dairy farming. Keywords: robotic urine-patch treatment, nitrogen (N) losses, N inhibitors, effluent management, robotic effluent spreading, robotic fertiliser spreading

GASEOUS NITROGEN LOSSES FROM CONVENTIONAL AND CHEMICAL SUMMERFALLOW

The gaseous losses of N (N2O + N2) measured for 130 days (May-September 1983) from conventional fallow at Yorkton, Oxbow and Weyburn soil sites ranged from 9 to 11, 15 to 31 and 60 to 87 kgN∙ha−1 for upper, middle and lower slope positions, respectively. The corresponding values for chemical fallow were 18–28, 24–51, and 69–98 kgN∙ha−1. In both tillage systems, gaseous N losses increased in the order of upper < middle < lower slope positions and were associated with the variations in soil moisture. The results obtained from additional widely scattered field studies on chernozemic soils further confirmed that the more dense surface soil and relatively higher soil moisture (lower air-filled porosity) were the major factors affecting increased denitrification under chemical fallow. Volumetric soil moisture was the only factor which showed a very highly significant correlation with N2O emmisions. Key words: Acetylene inhibition-soil core technique, chemical fallow, denitrification, nitrification