High Carbon Amendments Increase Nitrogen Retention in Soil After Slurry Application—an Incubation Study with Silty Loam Soil

Excess nitrogen (N) after animal slurry application is a persistent problem of intensive agriculture, with consequences such as environmental pollution by ammonia (NH3) and nitrous oxide (N2O) emissions and nitrate (NO3−) leaching. High-carbon organic soil amendments (HCAs) with a large C:N ratio have shown the potential of mitigating unintended N losses from soil. To reduce gaseous and leaching N losses after the application of slurry, a laboratory incubation study was conducted with silt loam soil. We tested the potential of three different types of HCA—wheat straw, sawdust, and leonardite (application rate 50 g C L−1 slurry for each of the three HCAs)—to mitigate N loss after amendment of soil with pig and cattle slurry using two common application modes (slurry and HCA mixed overnight with subsequent addition to soil vs. sequential addition) at an application rate equivalent to 80 kg N ha−1. Compared to the control with only soil and slurry, the addition of leonardite reduced the NH3 emissions of both slurries by 32–64%. Leonardite also reduced the total N2O emissions by 33–58%. Wheat straw reduced N2O emissions by 40–46%, but had no effect on NH3 emission. 15 N labeling showed that the application of leonardite was associated with the highest N retention in soil (24% average slurry N recovery), followed by wheat straw (20% average slurry N recovery). The mitigation of N loss was also observed for sawdust, although the effect was less consistent compared with leonardite and wheat straw. Mixing the slurry and HCA overnight tended to reduce N losses, although the effect was not consistent across all treatments. In conclusion, leonardite improved soil N retention more effectively than wheat straw and sawdust.

Coordinating Carbon Metabolism and Cell Cycle of Chlamydomonasreinhardtii with Light Strategies under Nitrogen Recovery

Nutrient supplementation is common in microalgae cultivation to enhance the accumulation of biomass and biofunctional products, while the recovery mechanism from nutrient starvation is less investigated. In this study, the influence of remodeled carbon metabolism on cell cycle progression was explored by using different light wavelengths under N-repletion and N-recovery. The results suggested that blue light enhanced cell enlargement and red light promoted cell division under N-repletion. On the contrary, blue light promoted cell division by stimulating cell cycle progression under N-recovery. This interesting phenomenon was ascribed to different carbon metabolisms under N-repletion and N-recovery. Blue light promoted the recovery of photosystem II and redirected carbon skeletons into proteins under N-recovery, which potentially accelerated cell recovery and cell cycle progression. Although red light also facilitated the recovery of photosystem II, it mitigated the degradation of polysaccharide and then arrested almost all the cells in the G1 phase. By converting light wavelengths at the 12 h of N-recovery with blue light, red and white lights were proved to increase biomass concentration better than continuous blue light. These results revealed different mechanisms of cell metabolism of Chlamydomonas reinhardtii during N-recovery and could be applied to enhance cell vitality of microalgae from nutrient starvation and boost biomass production.

Reduction of Ammonia Emissions from Laying Hen Manure in a Closed Composting Process Using Gas-Permeable Membrane Technology

Nitrogen losses during composting processes lead to emissions problems and reduce the compost fertilizer value. Gas-permeable membranes (GPM) are a promising approach to address the challenge of reducing nitrogen losses in composting processes. This study investigated the applicability of two GPM membrane systems to recover N released during the closed composting process of laying hen manure. The ammonia (NH3) capture process was performed using two different systems over a period of 44 days: the first system (S1) consisted of 120 m of an expanded polytetrafluoroethylene (ePTFE) membrane installed inside a 3.7 m3 portable, closed aerobic composter with forced ventilation; the second system (S2) consisted of 474 m of an ePTFE membrane placed inside as an external module designed for NH3 capture, connected to a closed aerobic composter through a pipe. In both cases, a 1 N H2SO4 acidic NH3 capture solution was circulated inside the membranes at a flow rate of 2.1 L·h−1. The amount of total ammonia nitrogen (TAN) recovered was similar in the two systems (0.61 kg in S1 and 0.65 kg in S2) due to the chosen membrane surface areas, but the TAN recovery rate was six times higher in system S1 (6.9 g TAN·m−2·day−1) than in system S2 (1.9 g TAN·m−2·day−1) due to the presence of a higher NH3 concentration in the air in contact with the membrane. Given that the NH3 concentration in the atmosphere of the membrane compartment directly influences the NH3 capture, better performance of the GPM recovery system may be attained by installing it directly inside the closed aerobic composters. Regardless of the chosen configuration, this technology allows N recovery as a stable and concentrated 1.4% N ammonium salt solution, which can be used for fertigation. The presented GPM systems may be used in community composting systems with low volumes of waste to be treated or in livestock facilities that have implemented best available techniques such as solid–liquid separation or anaerobic digestion, provided that the use of GPM technology in combination with these techniques also contributes to odor mitigation and improves biogas yields.

Annual Nitrogen Balance from Dairy Barns, Comparison between Cubicle and Compost-Bedded Pack Housing Systems in the Northeast of Spain

The aim of this study was to determine N recovery and irreversible losses (i.e., through NH3-N volatilization) from manure in two different housing systems throughout a year using an N mass balance approach. Dietary, milk, and manure N were monitored together with outside temperatures in six dairy barns during six months, comprising two different seasons. Three barns were designed as conventional free stalls (cubicle, CUB) and the other three barns as compost-bedded packs (CB). All the barns were located in the Ebro’s valley, in the northeast of Spain. Mass N balance was performed simultaneously in the six barns, during two three-month periods (Season I and II) and sampling at a 15-day interval. Results of ANOVA analysis showed that annual N retained in manure (kg/head per year) from cows housed in CUB barns was significantly higher than in manure from cows housed in CB (133.5 vs. 70.9, p < 0.001), while the opposite was observed for N losses (26.9 vs. 84.8, for CUB and CB barn, respectively; p < 0.005). The annual mean proportion of irreversible N loss from manure in relation to N intake was much lower in barns using conventional free-stall cubicles than the mean ratio registered in bedded pack systems barns.

Low N use Efficiency in A Long-Term N-Fertilized Cunninghamia Lanceolata Plantation Ecosystem in Subtropical China: A 14-Year Case Study

Background and aims Forests host among the most important N pools of all terrestrial ecosystems. Influences of N application on forest N cycle have received increasing concern, which is particularly problematic given the increasing atmospheric N deposition in recent decades. However, accurate assessments of N storage and recovery rates in forest ecosystems remain elusive. We selected Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantation ecosystem to explore how long-term N fertilization affected the N storage and recovery rate. Methods Plots in the field have been fertilized continuously for 14 years (2004–2017) with urea at rates of 0 (N0, control), 60 (N60, low-N), 120 (N120, medium-N) and 240 (N240, high-N) kg N hm− 2a− 1. Data collected in the field include N content and biomass on various plant organs (i.e., leaves, branches, stems, roots, and bark), understorey layer and litter in the ecosystem as well as soil N content and density at different depths (0–20, 20–40 and 40–60 cm). Key results The total N storage of ecosystem in the N-fertilized treatments was 1.1–1.4 times higher than that in the unfertilized treatment after 14 years of N fertilization. About 12.36% of the total ecosystem N was stored in vegetation (plant, litter, and understorey layer) and 87.64% was stored in soil (0–60 cm). N storage varied among ecosystem components and plant organs; and the plant organs, litter, and soil had higher N storage than that in understorey layer. Significantly higher Chinese fir N uptake was found in the medium-N (1.2 times) and high-N (1.4 times) treatments than that in the control. The N recovery rate of understorey layer in the N-fertilized treatments was negative, and less than that in the control. Conclusions Application of long-term N fertilizer to this stand led to a low N recovery rate (averagely 11.39%) while high loss of N (averagely 91.86%) which indicate low N use efficiency in the Chinese fir plantation ecosystem.

Response of Cotton to Conservation Tillage Plus Wheat Straw Management and Nitrogen in Wheat Based Cropping System

Zero tillage straw retained with optimum N is an important strategy to increase soil fertility and cotton (Gossypium hirsutum L.) yield in wheat (Triticum aestivum L.)-cotton system. A 3 years field experiment was conducted during 2014, 2015 and 2016 to study the impact of two tillage techniques [zero tillage plus wheat straw retained- ZTsr and conventional tillage-CT straw burnt (CTsb, with disc plow, tiller, rotavator, and leveling operations)] and four nitrogen rates namely 0, 100, 150 and 200 kg N ha-1 on cotton yield and soil fertility. Results indicated that bolls/plant–1, weight per boll, seed cotton yields, lint percentage and N recovery efficiency were highest with 150 kg N ha–1. Interaction tillage into N indicated that ZTsr had graeter bolls plant-1, bolls weight, seed cotton yields, lint percentage and N recovery efficiency compared to CTsb. ZTsr had more soil organic matter (SOM) and total soil nitrogen (TSN) compared to CTsb. ZTsr with 150 kg nitrogen per hectare enhanced cotton yield and soil fertility on sustainable basis in arid environment of Dera Ismail Khan.

Nitrogen Dynamics in Tropical Soils Treated with Liquid and Granular Urea Fertilizers

The mineralization of urea fertilizer mostly regulates the nitrogen dynamics in the soil. A laboratory-scale study was conducted to compare the nitrogen dynamics in two tropical soil series incubated with either liquid urea (LU) or granular urea (GU) at 0, 300, 400 or 500 mg/kg of soil. The soils samples used in the experiment were the Bungor and Selangor soil series which have a sandy clay loam and clay texture, respectively. The NH4+-N, NO3−-N concentration in the soils were measured for four weeks to determine the urea-N mineralization while ten pore volumes of water were used for the NH4+-N and NO3−-N leaching loss. At the same application rate, higher NH4+-N and NO3−-N concentrations were recorded in the LU applied soils throughout the incubation period in case of N mineralization. Urea-N recovery was higher in GU than LU treated soils in the first two weeks while no urea-N was present in both GU and LU treated soils after the third week of incubation. The leaching of N (NH4+-N and NO3−-N) was higher in GU treated soils than that of LU and leaching was increased with increased application rate in both LU and GU in both soils. The NH4+-N and NO3−-N concentrations were higher in the Selangor soil whereas the total N leaching loss was higher in Bungor soil. The results suggest that the LU was a better N fertilizer source than GU for rapid mineralization, quicker N availability and lower N leaching loss.

Maize yield and nitrogen-use characteristics were promoted as consistently improved soil fertility: 6-year straw incorporation in Northeast China

Long-term impacts of straw incorporation on soil fertility, and maize production and nitrogen (N) use status had not been thoroughly investigated in Northeast China, the most vital agricultural base across the nation. We conducted a consecutive 6-year field experiment, including straw amendment at 4 000, 8 000 and 12 000 kg/ha, and no straw incorporation was set as the control. Our experiment confirmed that the grain yield and crop N uptake in straw treatments were raised due to consistently improved soil fertility indices (associated with soil N cycling), and larger straw addition generally exerted more profound influences. Boosted nitrogen harvest index (NHI) indicated that nitrogen use efficiency (NUE) was gradually enhanced if applying more straw. More specifically, greater straw amendment caused higher N recovery efficiency from straw N, even though the N recovery efficiency of accumulated N addition declined accordingly (considering fertiliser N besides straw N). Thus, these trends suggested that more efficient utilisation of straw N by crop was the probable reason for elevated NUE over multi-year time series. Our research offered helpful insight to optimally employ straw incorporation and N fertilisation for coordinating agricultural sustainability and environmental protection.

Reducing N Application by Increasing Plant Density Based on Evaluation of Root, Photosynthesis, N Accumulation and Yield of Wheat

(Aims) To clarify the mechanisms though which dense planting could alleviate the negative effect of the reducing N rate on yield, (Methods) an experiment with four nitrogen levels—0 (N0), 120 (N1), 180 (N2) and 240 (N3) kg N ha−1—and three plant densities—180 (D1), 240 (D2) and 300 (D3) × 104 basic seedlings ha−1—was conducted. (Results) Increasing plant density decreased the root length, root volume, root surface area and root tips of individual plant while it enhanced the aforementioned root traits in population. The chlorophyll content, photosynthetic rate, stomatal conductance and transpiration rate of the individual plants were decreased with the increase in plant density and enhanced with the increase in N level. The increasing density and N application rate enhanced the leaf area index, photosynthetic high-efficiency leaf area and canopy photosynthetically active radiation of population. N accumulation per plant was decreased with increasing density and was enhanced with an increasing N application level. Within the same N level, the N accumulation in the population, N production efficiency and N recovery efficiency were consistently D3 > D2 > D1. A high N application rate with high density was not conducive to improving the NR (nitrate reductase), GS (glutamine synthetase) and GOGAT (glutamate synthase) activities. The yield could be maintained as stable or improved if decreasing by 60 kg N ha−1 with increasing 60 × 104 basic seedlings ha−1 within the range of N application in this experiment. (Conclusions) These results indicated that the yield of wheat could be improved with less N application by adjusting the compensatory effects from the plant density in populations.