Soil mineral-N Research Articles

Cereal-maize vs. legume-maize double-cropping: Impact on crop productivity and nitrogen dynamics under flood-irrigated Mediterranean conditions

Double-cropping is an interesting diversification strategy to increase profitability and sustainability. Besides, by including legumes, it may reduce the N inputs dependency. However, its management with flood irrigation can be challenging. The was the evaluation of the impact of two double-cropping and different nitrogen (N) rates on productivity and N dynamics under flood irrigation. Two double-cropping (barley-maize; pea-maize) and three N rates (unfertilized, 0N; medium: MN; high rate, HN) were evaluated in a field experiment located in NE Spain during two years. In barley-maize, N rates were 0, 125 and 250 kg N ha−1, and 0, 200 and 400 kg N ha−1 for barley and maize phases, respectively. In pea-maize, pea did not receive N, and the MN and HN rates in the maize were reduced (150 and 350 kg N ha−1, respectively).Crop productivity and N uptake were evaluated. The economic return and N use efficiency (NUE) were calculated. Soil inorganic N (Nmin) was measured after harvest.The pea-maize double-cropping allowed the saving of N fertilizer without yield penalties. Besides, a pre-crop effect of pea in the maize yield was observed. Regarding the cropping system, pea-maize obtained a higher economic return the first year. Besides, the economic return was higher the first year, due to crop penalties. In general, NUE was greater in 0N, and no differences were observed between fertilized treatments. Soil Nmin after pea/barley was higher the first year, coincident with a higher productivity. After maize harvest, the barley-maize led to larger residual Nmin.Therefore, in this study, pea-maize allowed a reduction in the N rate, showed greater potential to increase the economic return and reduced the N leaching risk. However, crop yield penalties associated with flood-irrigation, indicate that farmers should be aware of facing a more challenging management or consider other irrigation method to ensure profitability.

NITIRSOIL: A model that balances complexity with prediction uncertainty for improving nitrogen fertilization in agriculture

Mismanagement of the nitrogen (N) fertilization in agriculture leads to low N use efficiency (NUE) and therefore pollution of waters and atmosphere due to NO3− leaching, and N2O and NH3 emissions. The use of N simulation models of the soil-plant system can help improve the N fertilizer management increasing NUE and decreasing N pollution issues. However, many N simulation models lack balance between complexity and uncertainty with the result that they are not applied in actual practice. The NITIRSOIL is a one-dimensional transient-state model with a monthly time step that aims at addressing this lack in the estimation of, mainly, dry matter yield (DMY), crop N uptake (Nupt), soil mineral N (Nmin), and NO3− leaching in agricultural fields. According to its global sensitivity analysis for horticulture, the NITIRSOIL simulations of the aforementioned outputs mostly depend on the critical N dilution curve, harvest index, dry matter fraction, potential fresh yield and nitrification coefficients. According to its validation for 35 nitrogen fertilization trials with 11 vegetables under semi-arid Mediterranean climate in Eastern Spain, the NITIRSOIL presents indices of agreement between 0.87 and 0.97 for the prediction of total dry matter, DMY, Nupt, NO3− leaching and soil Nmin at crop season end. Therefore, the NITIRSOIL model can be used in actual practice to improve the sustainability of the N management in, particularly horticulture, due to the balance it features between complexity and prediction uncertainty. For this aim, the NITRISOIL can be used either on its own, or in combination with “Nmin” on-site N fertilization recommendation methods, or even could be implemented as the calculation core of decision support systems.

Effect of nitrogen addition on soil net nitrogen mineralization in topsoil and subsoil regulated by soil microbial properties and mineral protection: Evidence from a long-term grassland experiment

Soil net nitrogen mineralization (Nmin), a microbial-mediated conversion of organic to inorganic N, is critical for grassland productivity and biogeochemical cycling. Enhanced atmospheric N deposition has been shown to substantially increase both plant and soil N content, leading to a major change in Nmin. However, the mechanisms underlying microbial properties, particularly microbial functional genes, which drive the response of Nmin to elevated N deposition are still being discussed. Besides, it is still uncertain whether the relative importance of plant carbon (C) input, microbial properties, and mineral protection in regulating Nmin under continuous N addition would vary with the soil depth. Here, based on a 13-year multi-level field N addition experiment conducted in a typical grassland on the Loess Plateau, we elucidated how N-induced changes in plant C input, soil physicochemical properties, mineral properties, soil microbial community, and the soil Nmin rate (Rmin)-related functional genes drove the responses of Rmin to N addition in the topsoil and subsoil. The results showed that Rmin increased significantly in both topsoil and subsoil with increasing rates of N addition. Such a response was mainly dominated by the rate of soil nitrification. Structural equation modeling (SEM) revealed that a combination of microbial properties (functional genes and diversity) and mineral properties regulated the response of Rmin to N addition at both soil depths, thus leading to changes in the soil N availability. More importantly, the regulatory impacts of microbial and mineral properties on Rmin were depth-dependent: the influences of microbial properties weakened with soil depth, whereas the effects of mineral protection enhanced with soil depth. Collectively, these results highlight the need to incorporate the effects of differential microbial and mineral properties on Rmin at different soil depths into the Earth system models to better predict soil N cycling under further scenarios of N deposition.

Winter cover crops decreased soil mineral N contents and increased soil organic C stocks and N2O emission

Cover crops (CC) can contribute to climate protection as a result of their effects on soil nitrogen (N) cycling and nitrous oxide (N2O) emission and by increasing soil organic carbon (SOC) stocks. This study explored the influence of different winter CC (saia oat, winter rye and spring vetch) compared with bare fallow, followed by silage maize on N2O emissions and soil mineral N (SMN) dynamics, as well as on SOC stocks in year-round replicated field plot experiments in four fields located at two sites in northern Germany (Kiel, Uelzen) over two consecutive years (2018/19 and 2019/20). Non-legume CC decreased SMN contents in 0–30 cm during the CC period, but this did not result in decreased cumulative N2O emissions over that time. Decreased emissions during CC growth were offset by increased emissions during CC mineralisation after frost and incorporation. Higher cumulative N2O emissions during the maize period in all CC treatments compared with bare fallow (significant for non-legume CC) indicated that the incorporated CC biomass still boosted N2O emissions under the following crop. Overall, including CC in the cropping system increased annual and yield-related N2O emissions compared with bare fallow (significant only for non-legumes). The increase in annual N2O emissions of 0.84 ± 1.06 kg N2O-N ha−1 yr−1 was only partly offset by the estimated mitigation potential for indirect N2O emissions of 0.52 ± 0.14 kg N2O-N ha−1 yr−1. The mean annual increase in SOC induced by growing CC every fourth year over a 50-year period was 40–60 kg C ha−1 yr−1. In summary, CC had both positive and negative effects on greenhouse gas exchange. Site and crop rotation optimised CC systems, and a more precise and site-specific consideration of fertilising effects might help improve the net greenhouse gas budget of CC.

Drone Multispectral Imaging Captures the Effects of Soil Nmin on Canopy Structure and Nitrogen Use Efficiency in wheat

Drone Multispectral Imaging Captures the Effects of Soil Nmin on Canopy Structure and Nitrogen Use Efficiency in wheat

Validation of a sensor-system for real-time measurement of mineralized nitrogen in soils

When reducing the negative impact of agriculture on the environment, one major approach is to substantially decrease the nitrate contamination of the groundwater originating from mineral and organic fertilization. However, efficient plant production relies on sufficient nutrient supply. Finding the balance between appropriate plant nutrition and ground water conservation is a challenge. Appropriate nitrogen fertilization relies on the measurement of mineralized nitrogen (Nmin) - the total amount of nitrate and ammonium - in the soil. Taking soil samples with an auger and subsequent chemical analyses in a laboratory is state of the art. However, this process is time-consuming and often time-delayed. The Stenon FarmLab, a sensor spade, is a new device which claims to measure soil Nmin and other soil parameters in real-time with spectral methods. The aim of this study was to validate the Nmin measurements of the Stenon FarmLab with the common laboratory method. The authors conducted a series of 20 measurements consisting of a varying number of individual values per measurement. In total, 211 individual values on 15 different field sites in three regions in Bavaria, Germany were analyzed. Reference samples for laboratory analysis were taken simultaneously with a sampling auger. Only 181 of the 211 individual values were considered in the evaluation as Nmin contents of less than 42 kg N ha−1 and greater than 189 kg N ha−1 exceeded FarmLab's measurement range. The results showed that the Stenon FarmLab overestimated Nmin in 75 % of the cases in comparison to the laboratory analysis. On average, the mean values of the sampled sites differed by 38 kg N ha−1 showing a 69 % mean deviation from the laboratory. The overall coefficient of determination (R2) was 0.3 for individual measurements and 0.66 for the mean values of a site. In conclusion, the Stenon FarmLab is a good approach for a more time-saving method regarding relative differences within or between fields. However, absolute values measured with the Stenon FarmLab, which are required for demand-driven fertilization, are not accurate enough: the system needs to be further improved to match reference methods.

Will the endophytic fungus Phomopsis liquidambari increase N-mineralization in maize soil?

Endophytes can be developed into biocontrol agents and can be fungi, bacteria, or archaea that live inside plant tissues without causing symptoms of disease. Phomopsis liquidambari is an endophytic fungus that plays an important ecosystem role as a biofertilizer by helping its host obtain soil nitrogen. How this fungus impacts N mineralization and microbial communities is little known. Our understanding of soil nutrient transformations and soil-plant-microbe interactions in Phomopsis liquidambari-crop versus conventional crop systems is incomplete. This study provided a better understanding of the effect of Phomopsis liquidambari on nitrogen mineralization and investigated the interaction between P. liquidambari and nitrogen, which in turn will be helpful to the farmer in reducing the required amount of soil N fertilizer. This change in N availability in maize soil will have significant implications for soil productivity and plant N utilization, especially in N-limited soils, and significantly reduce the required amount of soil N fertilizer. The effect of P. liquidambari on N mineralization in maize soil was investigated by treating it with four levels of N (urea) at rates of 0, 1.25, 2.5, and 3.75 g of nitrogen. N-mineralization was determined by the anaerobic incubation method. Were stored for 7 days in an incubator at a constant 37 C. A colorimetric microplate procedure was used for NH4+-N analysis. A significant increase in the available NH4+-N contents was reported in soil maize (Zea mays L.) inoculated with P. liquidambari, which increased by 80%. A significant increase in N-mineralization was observed under all N conditions. This work highlighted the importance of the fungal endophyte for soil N-mineralization with lower N input. Using this fungal agent will almost certainly help reduce fertilizer input.

Effects of legumes and fertiliser on nitrogen balance and nitrate leaching from intact leys and after tilling for subsequent crop

Grass-legume leys combine multiple agronomic benefits, several of which are associated with symbiotic nitrogen (N) fixation. However, the best combinations of legume abundance and N fertilisation to achieve high productivity at low nitrate leaching are not yet established. Nitrate leaching risk of pure grass swards (Grs), grass-legume mixtures (Mix) and pure legume swards (Leg) at a fertiliser level of either 50, 150 or 450 kg N ha−1 yr−1 (N50, N150 and N450) was studied during two key periods: the intact ley for forage production and after tilling for subsequent winter wheat in crop rotation. The risk of nitrate leaching was determined from (i) monitoring of the nitrate concentration in the soil solution (NCSS) and (ii) the soil mineral N (SMN) content. Furthermore, the soil surface N balance was assessed by measuring N input from fertiliser and symbiosis, and N output with harvested biomass. During the period of intact plant cover, soil surface N balance of Grs swards was strongly negative at N50 and N150 with negligible NCSS and SMN. At N450, the positive N balance of Grs swards resulted in a high leaching risk after three years of cultivation (NCSS ≤ 13 mg NO3-N L−1 and SMN ≤ 20 kg N ha−1). For Mix swards, the N balance was close to zero at N50 and N150, which led to similarly low NCSS and SMN. At N450, the N balance of Mix swards was beyond zero, resulting in significantly increased NCSS and SMN (≤ 30 mg NO3-N L−1 and ≤ 35 kg N ha−1). For Leg swards, the N balance was far beyond zero at all fertilisation levels, resulting in a leaching risk even at N50 (≤ 8 mg NO3-N L−1 and ≤ 23 kg N ha−1). During the period following tilling the leys, SMN was similar or lower for Mix compared to Grs swards (≤ 43 vs. ≤ 62 kg N ha−1 at N50 and N150, 72 vs. 68 kg N ha−1 at N450), while it was significantly higher for Leg swards (SMN ≤ 95 kg N ha−1). We conclude that grass-legume mixtures combine high yields, low fertiliser requirements, and low nitrate leaching better than either pure grass or pure legume swards. This holds true both during the period with intact plant cover and after tillage for the subsequent crop.

Dissolved organic compounds in shale gas extraction flowback water as principal disturbance factors of soil nitrogen dynamics

Flowback water, a by-product of shale gas extraction, represents an extremely complex industrial wastewater characterized by high organic compounds content and high salinity. The prospect of flowback water entering the soil through various approaches concerns regarding its ecological risk. Nitrogen mineralization (Nmin), a key rate-limiting step in the soil N cycle, might be adversely affected by flowback water. Nonetheless, no previous studies have examined the effects of flowback water on soil Nmin rates, let alone quantified the relative contributions of the major components of flowback water to changes in Nmin rates. Therefore, this study investigated the effects of flowback water and sterile flowback water at two different concentrations on the Nmin rates of three distinct soil types. This study aimed to elucidate the predominant influence of the key constituents within flowback water on the changes in soil Nmin rates. The results showed that soil soluble salt content, dissolved organic carbon (DOC) and dissolved nitrogen (DN) content significantly increased by 8.37 times, 9.5 % and 26.4 %, respectively, in soils contaminated by flowback water. In comparison with the control group, the introduction of flowback water resulted in a significant 25.9 % reduction in Nmin rate in sandy soils. Conversely, in clay and loam soils, there was a significant increase in Nmin rates by 44.9 % and 131.8 % respectively. Throughout the incubation period, leucine-aminopeptidase activity exhibited irregular fluctuations. Analysis of microbial communities demonstrated that flowback water only significant impacted soil rare microbial taxa, inducing a significant increase in alpha diversity for sandy, clay, and loamy soils by −16.9 %, 10.12 %, and 1.63 %, respectively. Linear regression and random forest analyses indicated that alterations in soil DOC:DN ratio and salt content were responsible for changes in soil Nmin rates within flowback water-contaminated soils. In contrast, only salt content significantly contributed to shifts in alpha diversity among soil rare microbial taxa. Structural equation modeling highlighted that the total effect of dissolved organic compounds (DOC and DN, λ = 0.64) from flowback water was greater than the total effect of salinity (λ = 0.24) on soil Nmin rates. In conclusion, our findings imply that dissolved organic compounds within flowback water play pivotal roles in determining soil Nmin rates. To the best of our knowledge, this is the first study to reveal the effects of major components in the flowback water on soil N mineralization rates.

Maize yield and N dynamics after cover crops introduction

The use of cover crops (CCs) is widely suggested as a sustainable agricultural practice. Nevertheless, conflicting results have been reported about the short-term effect of CCs on cash crop yields and the soil nitrogen (N) dynamics. Within this framework, the present study aims to examine the short-term impact of CC introduction into a conventional agricultural system on silage maize yield and the N dynamics (maize N uptake, N use efficiency (NUE), soil nitrate content (Nmin), and apparent soil N mineralization and immobilization processes) in northern Italy. The CC systems (∼5.5 ha) included a fixed treatment (FI) with a gramineous species (triticale), a 2-year gramineous-legume species succession (SU) (rye, clover), and a weed-covered control treatment (NoCC). In the first year, triticale and rye had the same total (aboveground + root) final biomass (2.5 Mg ha−1 on average), C:N ratio (29), and N uptake (36.4 kg ha−1). However, triticale developed faster in the first winter months. Both grass species equally reduced the soil Nmin content over the winter season (as valid catch crops), but they caused apparent N immobilization during the following maize growing season. In the second year, clover produced the same total biomass as triticale did (1.8 Mg ha−1), but with a higher total N content (72.5 kg ha−1) and lower C:N ratio (27) which determined a lower apparent N immobilization. The introduction of CCs did not affect the yield of maize. During the maize growing season, lower N uptake and NUE were recorded after CCs grasses species cultivation compared to clover and NoCC. These observations suggest that a key aspect to be considered when dealing with CCs is understanding the N mineralization-immobilization processes related to CC residue decomposition, which might determine N availability for the subsequent crop and in turn its production quality (N uptake), even when the yield is not affected.

Excessive N applications reduces yield and biological N fixation of summer-peanut in the North China Plain

ContextThe North China Plain (NCP) is China’s largest peanut producing area, where winter-wheat summer-peanut is an important double cropping system. Excessive nitrogen (N) applications are widely used leading to declined N use efficiency (NUE) and biological N fixation (BNF). However, the influence of excessive fertilizer N inputs on yield and BNF of summer-peanut remains uncertain. ObjectiveThe study aims to evaluate the impacts of different fertilizer N inputs on yield and BNF of summer-peanut in the NCP, and explore the optimal N rates for achieving high NUE and low N losses without sacrificing yield. MethodsA three-year field experiment and pot experiment involving five N treatments (N rates with 0, 50, 100, 150, and 200 kg N ha−1, defined as N0, N50, N100, N150 and N200 in the study, respectively) were conducted in the NCP. The jointing use of field experiment and pot experiment were adopted to measure BNF of summer-peanut, and the partial least squares path model and a nightingale rose diagram were both included in the study. ResultsSummer-peanut yield increased quadratically with increasing N application, but N rates larger than 150 kg N ha−1 caused inadequate seed filling and thus led to slightly reduced yield. Generally, increased N applications significantly increased soil mineral N (SMN) between 0 and 60 cm depth, and dramatically reduced BNF as high SMN strongly inhibits biological nitrogenase activity. ConclusionsThe N application required to obtain an optimum yield of 3915 kg ha−1 with relatively high NUEoi (the ratio of N output and N input, 73.0%) and low N losses in the summer-peanut production was 150 kg N ha−1 in the NCP. ImplicationsThe sustainable development of summer-peanut systems will involve reduced N application rates, and N optimization in the winter-wheat summer-peanut rotation should receive further attention considering the N legacy effects.

Optimized Nitrogen Fertilizer Rate Can Increase Yield and Nitrogen Use Efficiency for Open-Field Chinese Cabbage in Southwest China

Intensive vegetable production has been characterized by high nitrogen (N) fertilizer input in southwest China. Optimizing the N fertilizer rate is the basis for the optimal management of regional N fertilizer. A two-year field experiment with five N fertilizer rates was conducted during 2019–2021 in southwest China, and the aim of this study was to identify the effects of different N application rates on yield, dry matter biomass (DMB), N uptake, N use efficiency (NUE) and soil mineral N (Nmin) residues for Chinese cabbage (Brassica chinensis L.) and further determine the critical plant N concentration and root-zone soil Nmin residues required to reach the maximum DMB of Chinese cabbage. Five N treatments were established: control without N input (CK); optimal N fertilizer rate decreased by 30% (70% OPT, 175 kg N ha−1), optimized N fertilizer rate (OPT, 250 kg N ha−1), optimal N fertilizer rate increased by 30% (130% OPT, 325 kg N ha−1) and farmers’ N fertilizer practice (FP, 450 kg N ha−1). The N source in all treatments was conventional urea (N ≥ 46.2%). The results showed that the total yield of Chinese cabbage followed a “linear-plateau” trend with an increasing N fertilizer rate. There was no significant difference in yield between the OPT, 130% OPT and FP treatments. The aboveground plant DMB and N uptake showed a ‘slow-fast-slow’ pattern with the growth period. There was no significant difference in aboveground plant DMB and N uptake between the OPT, 130% OPT and FP treatments. Moreover, the OPT treatment significantly increased the aboveground plant DMB and N accumulation by 29.6% and 40.5%, respectively, compared with the 70% OPT treatment. The OPT treatment significantly increased the NUE by 23.8%, 31.2% and 43.1% compared with that in the 70% OPT, 130% OPT and FP treatments, respectively. The linear-plateau model provided the best fit for the relationship among aboveground DMB of Chinese cabbage, plant N concentration and root-zone soil Nmin content. The critical root-zone soil Nmin and plant N concentrations were 94.1, 63.4 and 68.3 kg ha−1 and 34.4, 33.5 and 32.9 g kg−1 during the rosette, heading and harvest periods, respectively. In summary, compared to the FP treatment, the optimized N fertilizer rate (250 kg N ha−1) could significantly reduce the N application rate, maintain yield, increase aboveground plant DMB and N uptake, and improve NUE. Moreover, the study has great significance for guiding the green utilization of vegetable N fertilizer in southwest China.

Dynamics of soil net nitrogen mineralization and controlled effect of microbial functional genes in the restoration of cold temperate forests

Soil nitrogen mineralization (Nmin) generally controls the availability and circulation of soil nitrogen (N). To better understand the mechanisms of soil Nmin and environmental protection, this study explored the dynamics of net Nmin in soils from restored forests and the effect of soil physicochemical properties (SPPs) and soil microbial mineralization genes (SMGs) on Nmin. Field studies were conducted from July 2019 to April 2020 in five representative restored forests in the mountainous region of northwestern Hebei, China (i.e., Larix principis-rupprechtii forest (LF), Betula platyphylla forest (BF), mixed forest of Larix principis-rupprechtii and Betula platyphylla (MF), Picea asperata forest (SF) and Pinus sylvestris var. mongolica forest (MPF)), and soil net nitrogen mineralization rate (Rmin), SPPs and SMGs were determined after collecting soil samples in five plots. The influence of restored forests and seasonality on Rmin was investigated to determine the characteristics of the dynamics of soil net Nmin. Principal component analysis (PCA) and variation partitioning analysis (VPA) revealed that soil properties and functional genes could explain approximately 80 % of the variation in Nmin. SMGs significantly contributed to the variation in the soil net ammonification rate (Ramm) and nitrification rate (Rnit) compared to soil properties. SMGs were strongly correlated with Ramm\\Rnit (except in LF), implying that the shifts in functional genes may control Rmin. Given the debate on the role of soil properties and N cycling genes in driving soil N transformation, this study provides new insights into the controlled effect of microbial functional genes during the early stage of forest restoration in the cold temperate zone.

Effect of Two Seeding Rates on Nitrogen Yield and Nitrogen Fixation of Winter and Spring Faba Bean.

Faba bean (Vicia faba L. minor) is an important grain legume and is widely used as food and feed. It is traditionally used as a spring crop in Central European cropping systems. There is increasing interest in winter faba bean due to a higher yield potential, but limited knowledge of nitrogen (N) yields and nitrogen fixation (NFIX) exists. Therefore, the purpose of this study was to compare N concentrations, N yield of plant fractions, soil mineral N (SMN) and SMN sparing in the soil after harvest, NFIX and N balance of two winter faba bean varieties (Diva and Hiverna) to those of a spring faba bean (Alexia) using two seeding rates (25 versus 50 germinable seeds m-2) in a two-year field experiment under Pannonian climate conditions in eastern Austria. The winter faba bean varieties had higher N yields and NFIX, not only due to higher biomass yields, but also due to higher N concentrations and a higher percentage of N derived from atmosphere in the biomass. Conversely, the soil mineral N after harvest was lower compared to the spring faba bean. All treatments had a negative N balance due to higher grain N yield than NFIX. Winter faba beans left higher amounts of biologically-fixed N in residues for the subsequent crop, whereas spring faba bean left more SMN. Winter faba bean varieties obtained good results with both seeding rates, whereas the grain yield and the grain N yield of Alexia tended to higher with the higher seeding rate.

Potential of Bioassays to Assess Consequences of Cultivation of Acacia mangium Trees on Nitrogen Bioavailability to Eucalyptus Trees: Two Case-Studies in Contrasting Tropical Soils.

We hypothesized that the nitrogen-fixing tree Acacia mangium could improve the growth and nitrogen nutrition of non-fixing tree species such as Eucalyptus. We measured the N-mineralization and respiration rates of soils sampled from plots covered with Acacia, Eucalyptus or native vegetation at two tropical sites (Itatinga in Brazil and Kissoko in the Congo) in the laboratory. We used a bioassay to assess N bioavailability to eucalypt seedlings grown with and without chemical fertilization for at least 6 months. At each site, Eucalyptus seedling growth and N bioavailability followed the same trends as the N-mineralization rates in soil samples. However, despite lower soil N-mineralization rates under Acacia in the Congo than in Brazil, Eucalyptus seedling growth and N bioavailability were much greater in the Congo, indicating that bioassays in pots are more accurate than N-mineralization rates when predicting the growth of eucalypt seedlings. Hence, in the Congo, planting Acacia mangium could be an attractive option to maintain the growth and N bioavailability of the non-fixing species Eucalyptus while decreasing chemical fertilization. Plant bioassays could help determine if the introduction of N2-fixing trees will improve the growth and mineral nutrition of non-fixing tree species in tropical planted forests.

Strategies for high nitrogen production and fertilizer value of plant‐based fertilizers

AbstractBackgroundOrganic vegetable production has a demand for alternative fertilizers to replace fertilizers from sources that are not organic, that is, typically animal‐based ones from conventional farming.AimsThe aim of this study was to develop production strategies of plant‐based fertilizers to maximize cumulative nitrogen (N) production (equal to N yield by green manure crops), while maintaining a low carbon‐to‐nitrogen (C:N) ratio, and to test the fertilizer value in organic vegetable production.MethodsThe plant‐based fertilizers consisted of the perennial green manure crops—alfalfa, white clover, red clover, and a mixture of red clover and ryegrass—and the annual green‐manure crops—broad bean, lupine, and pea. The crops were cut several times at different developmental stages. The harvested crops were used fresh or pelleted as fertilizers for field‐grown white cabbage and leek. The fertilizer value was tested with respect to biomass, N offtake, N recovery, and soil mineral N (Nmin). Poultry manure and an unfertilized treatment were used as controls.ResultsThe cumulative N production of the perennial green manure crops ranged from 300 to 640 kg N ha–1 year–1 when cut two to five times. The highest productions occurred at early and intermediate developmental stages, when cut three to four times. Annual green manure crops produced 110–320 kg N ha–1 year–1, since repeated cutting was restricted. The C:N ratio of the green manure crops was 8.5–20.5, and increased with developmental stage. The fertilizer value of green manure, as measured in white cabbage and leek, was comparable to animal‐based manure on the condition that the C:N ratio was low (<18). N recovery was 20%–49% for green manure and 29%–42% for poultry manure. A positive correlation was detected between soil Nmin and vegetable N offtake shortly after incorporating the green manure crops, indicating synchrony between N release and crop demand.ConclusionsPlant‐based fertilizers represent highly productive and efficient fertilizers that can substitute conventional animal‐based fertilizers in organic vegetable production.

Optimizing nitrogen rates for synergistically achieving high yield and high nitrogen use efficiency with low environmental risks in wheat production – Evidences from a long-term experiment in the North China Plain

The optimization of nitrogen (N) fertilization has become an ever more important global challenge with the aim of achieving high crop yields and high N use efficiency (NUE) with low environmental risks. The North China Plain (NCP) is China’s most important wheat (Triticum aestivum Linn.) production region, and a global hotspot for N fertilizer use. How much nitrogen can be saved compared to the farmers’ level that would not influence wheat yield, and lead to high NUE with low N surplus? It is still challenging as there are not enough evidences from the long-term experiments. Thus, continuous detailed observations from an ongoing long-term experiment in the NCP since 2010 with five N rates, namely 0 (N0), 60 (N60), 120 (N120), 180 (N180) and 240 (N240) kg N ha−1, were included in the study. Our results indicated that stable high wheat yield cannot be achieved without enough N inputs from the long-term, because of severely depleted N pool in the N0 and N60 treatments seriously influenced root growth and wheat development thus damaged wheat yield. Though highest wheat yield was obtained in the N240 treatment, the high N rate caused lowest NUE and largest N surplus with high soil mineral N (SMN) with the mean value of 143 kg N ha−1 at the 0–60 cm layer at harvest. Besides, both root weight density (RWD) and root length density (RLD) were much lower in the N240 treatment compared to that in the N180 treatment. Our integrative analyses clearly indicate that the optimal N application for achieving high yield, high NUE and low environmental risks in wheat production was 180 kg N ha−1 based on long-term observations. Our results should be beneficial for promoting sustainable wheat production in the NCP and similar regions with wheat-based double cropping over the world.

Responses of soil carbon and nitrogen mineralization to nitrogen addition in a semiarid grassland: The role of season

Elevated atmospheric N deposition can profoundly alter soil carbon (C) mineralization (Cmin) and nitrogen (N) mineralization (Nmin), which could severely impact long-term productivity of grassland ecosystem. However, little is known about how N addition, season, and their interaction affect soil Cmin and Nmin rates and their relationships by regulating soil abiotic and biotic factors. Here we investigated the seasonal variations in soil Cmin and Nmin rates and their relationship in response to multi-level N additions in a semiarid grassland in 2014–2015, and further identified direct and indirect pathways by which soil abiotic and biotic factors regulated these variations using structural equation modeling. We documented the statistically significant impacts of N addition and its interaction with season on soil Cmin rates. In contrast, only a significant seasonal effect on the soil Nmin rate was observed. Random forest analysis revealed that across all seasons, dissolved organic carbon (DOC), soil water content (SWC), catalase, urease, sucrase, microbial biomass carbon (MBC), soil organic carbon (SOC) to total nitrogen (TN) ratio, and TN were the most pivotal predictors of the soil Cmin rate. Comparatively, catalase, MBC, DOC, NO3–-N, urease, TN, NH4+-N, SWC, and the MBC to microbial biomass nitrogen (MBN) ratio were the most dominant drivers of the soil Nmin rate. SEM results indicated that the identified potential drivers that regulated the soil Cmin and Nmin rates in response to N addition varied seasonally. Additionally, N addition decoupled the soil Cmin and Nmin rates, which was a consistent relationship among most seasons. In summary, our results show that, in this semiarid grassland, current N additions can enhance soil N immobilization across all seasons; however, its impacts on soil C sequestration were seasonally variable. These findings provide evidence that season and its interactions with elevated atmospheric N deposition have important implications for the grassland biogeochemical cycling.

Soil net N mineralization and hydraulic properties of carbonate-derived laterite under different vegetation types in Karst forests of China

Soil net nitrogen (N) mineralization (Nmin) is a key process in the forest N cycle regulating the N availability of plant growth. However, it is unclear how N transformation responds to soil hydraulic properties changes. The soil inorganic N pools and N transformation in the early growing season in karst forestlands were investigated by using an intact soil core in situ incubation method. Three different typical vegetation types were selected. The results showed that the mean values of NH4+-N, NO3−-N, and inorganic N were 1.05–1.36, 1.55–3.85, and 1.05–2.34 times greater for ferns than for shrubs. NO3−-N and NH4+-N mainly occur at soil depths of 0–5 cm and 5–15 cm, respectively. The soil Nmin was 2.21–232.03 times higher at 0–5 cm than at the 10–15 cm. Net N immobilization was found for the juvenile ferns and shrubs at 5–15 cm. The Nmin of juvenile and mature ferns was 1.90–11.78 times and 1.17–16.20 times higher than shrubs, respectively, and shrubs had the highest Ks (69.91 mm h−1) but the lowest water-holding capacity. Both ferns and shrubs were able to hold more water and available water was richest in mature fern soil, which provided an extra water source for fern growth. Principal component analysis (PCA) was used to test whether the measured variables affected Nmin, and the results showed that soil organic matter (SOM), pH, and saturated volumetric water content (θs) were the main soil factors affecting Nmin. In addition, the NH4+-N, NO3−-N, and inorganic N stocks were reduced by 3.98 %–59.04 %, 48.07 %–63.30 % and 8.18 %–57.37 % after rainwater input, respectively. Our findings suggest that soil inorganic N and Nmin in the karst forest were regulated by soil hydraulic properties. Changes in the soil hydraulic properties might therefore influence the functioning of soil N transformation.

Modified crop rotations for a sustainable intensification? A case study in a high-yielding environment with recurrent nitrogen surplus

Agriculture is a major contributor to nitrate groundwater contamination. Hence, farmers are demanded to reduce the environmental impact but simultaneously must provide sufficient food products. One important building block for this “sustainable intensification” are appropriate cropping strategies. The potential of modified crop rotations was evaluated in a high-yielding environment in Northern Germany. Therefore, in five consecutive growing seasons (2016/2017 – 2020/2021) three crop rotations were grown in a field trial and compared with respect to agronomic (cereal unit), economic (gross margin) and environmental (N surplus) parameters. A standard crop rotation, typical for the region of the study, was compared with rearranged and augmented crop rotations. Therefore, crops with a high autumnal N uptake (winter oilseed rape and catch crops) were grown after crops with typically high soil mineral N (SMN) amounts after harvest (faba bean and winter oilseed rape). Due to the change of preceding and subsequent crops, an increased N transfer was supposed to prevent N from leaching and a lower N fertilizer demand of the subsequent crop was expected. On average, the modified crop rotations achieved significantly higher cereal units (9.3 and 10.8 t · ha−1) compared to the local crop rotation (8.5 t · ha−1). The gross margin of the local crop rotation was 1474 € · ha−1 and the other crop rotations maintained (1443 € · ha−1) or significantly increased (1572 € · ha−1) this value, respectively. The local crop rotation had a N surplus of 47 kg N · ha−1. In contrast, the N surplus of the modified crop rotations was significantly lower (10 and 28 kg N · ha−1). In summary, the results showed that a thoughtful rearrangement of crop rotations is an appropriate measure to simultaneously improve yields and gross margins with less unfavorable environmental impacts.