Jian Liu

Forsker

(+47) 464 22 528
jian.liu@nibio.no

Sted
Ås - Bygg O43

Besøksadresse
Oluf Thesens vei 43, 1433 Ås (Varelevering: Elizabeth Stephansens vei 23)

Biografi

I am a soil and water researcher working on agricultural effects on the environment. By combining research approaches of experimentation, modeling and data synthesis, I study drivers and processes controlling nutrient losses from land to water (and air) at soil core to catchment scales and explore mitigation measures to reduce the losses both at source and during transport. I have research experience in Norway, Sweden, Canada, USA and China. While my current research activities can be found on this webpage, my past research experience included: (1) water and nutrient transport from both surface and subsurface pathways, (2) climate and management effects on nutrient losses, (3) management of soil nutrient, fertilizer, manure and biochar, including place-based phosphorus management (variable rate applications), for crop production and environmental protection, (4) effects of crop management, including cover crops and crop residues in combination with tillage, on water and nutrient cycling, (5) drainage and irrigation in paddy and horticulture systems, and (6) field and catchment phosphorus modeling. Through collaborations with other researchers, students and stakeholders in many countries, my research has also involved soil health, crop production, greenhouse gas emissions, and generally sustainable agriculture.

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Sammendrag

Quantifying the similarities and differences in atmospheric nitrogen (N) deposition between different ecosystems is important to develop effective measures to reduce air pollution and maintain biodiversity. Here we show that the constitution of N deposition differed significantly between a grassland and a desert ecosystem in Northwestern China. Flux of bulk (wet plus part of dry deposition) and dry (gaseous NH3 and NO2) deposition were continuously monitored from 2018 to 2020. The grassland and desert sites had similar amount of total N deposition, being 7.29 and 6.33 kg N ha−1 yr−1, respectively. However, N deposition at the grassland was dominated by the bulk deposition (4.44 kg N ha−1 yr−1, 61% of the total N deposition), whereas that at the desert was dominated by dry deposition (4.20 kg N ha−1 yr−1, 66% of total deposition). The desert had greater ambient concentrations of NH3 (3.66 μg N m−3) and NO2 (1.52 μg N m−3) than the grassland (2.73 μg NH3–N m−3 and 0.72 μg NO2–N m−3). The amount of reduced N deposition (NH4+ and NH3) was around 3 times of that of oxidized N deposition (NO3− and NO2) in both ecosystems. The N deposition rates in both ecosystems have exceeded the critical load for the fragile ecosystems (5–10 kg N ha−1 yr−1), highlighting the importance of reducing N emission sources that are related with anthropogenic disturbance.

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Sammendrag

Soil salinization is a critical environmental issue restricting agricultural production. Deep return of straw to the soil as an interlayer (at 40 cm depth) has been a popular practice to alleviate salt stress. However, the legacy effects of straw added as an interlayer at different rates on soil organic carbon (SOC) and total nitrogen (TN) in saline soils still remain inconclusive. Therefore, a four-year (2015–2018) field experiment was conducted with four levels (i.e., 0, 6, 12 and 18 Mg ha–1) of straw returned as an interlayer. Compared with no straw interlayer (CK), straw addition increased SOC concentration by 14–32 and 11–57% in the 20–40 and 40–60 cm soil layers, respectively. The increases in soil TN concentration (8–22 and 6–34% in the 20–40 and 40–60 cm soil layers, respectively) were lower than that for SOC concentration, which led to increased soil C:N ratio in the 20–60 cm soil depth. Increases in SOC and TN concentrations in the 20–60 cm soil layer with straw addition led to a decrease in stratification ratios (0–20 cm:20–60 cm), which promoted uniform distributions of SOC and TN in the soil profile. Increases in SOC and TN concentrations were associated with soil salinity and moisture regulation and improved sunflower yield. Generally, compared with other treatments, the application of 12 Mg ha–1 straw had higher SOC, TN and C:N ratio, and lower soil stratification ratio in the 2015–2017 period. The results highlighted that legacy effects of straw application as an interlayer were maintained for at least four years, and demonstrated that deep soil straw application had a great potential for improving subsoil fertility in salt-affected soils.

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Sammendrag

Soil nutrient contents and stoichiometric ratios are determinants for soil biogeochemical cycling and functions. Variable rock fragment contents (RFC) may shape the soil nutrient status and availability in mountain ecosystems. We need to better understand how and why soil nutrients and stoichiometry shift across the RFC gradients. To investigate patterns of soil nutrient stoichiometry and underlying mechanisms in rocky soils, we conducted a field experiment involving four RFCs gradients (0%, 25%, 50% and 75%, V/V) and five vegetation treatments (four indigenous species, Artemisia vestita, Bauhinia brachycarpa, Cotinus szechuanensis and Sophora davidii, plus a non-planted treatment). Soil total carbon (C), total nitrogen (N), total phosphorus (P) and their molar ratios were measured. The contents of soil C, N and P, and C:N, C:P and N:P decreased with increasing RFC in all treatments, despite their trends were inconsistent in certain soil layers. The averages of soil N content significantly increased by 13.8% and 14.8% in C. szechuanensis and S. davidii, respectively. A. vestita and B. brachycarpa had higher soil C:N than C. szechuanensis and S. davidii. Soil nutrients and stoichiometry were positively related to soil water content (SWC) and soil capillary porosity, and negatively to bulk density and soil non-capillary porosity in all vegetation treatments, but varying relationships with biomass of plant components. These results demonstrated negative effect of RFC and discrepant effects of the plants on soil nutrients and stoichiometry. Soil structure, SWC and vegetation were the main drivers of variations in soil nutrient stoichiometry. We further concluded that soil nutrient stoichiometry in rocky soils is shaped by two influencing paths; effects of RFC on soil physical properties (SWC and soil structure) and effects of different vegetations. Our findings advance knowledge and mechanisms of soil nutrient stoichiometry in rocky soils and provide theoretical support for improving and restoring nutrient status in stony regions.

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Whether and how to synchronously regulate stream water nitrogen (N) and phosphorus (P) concentrations and ratios is a major challenge for sustainable aquatic functions. Soil carbon (C):N:P ratios influence soil N and P stocks and biogeochemical processes that elicit subsequent substantial impacts on stream water N and P concentrations and ratios. Therefore, bridging soil and stream water with ecological stoichiometry is one of the most promising technologies for improving stream water quality. Here, we quantified the ecological stoichiometry of soil and stream water relationships across nine catchments. Soil C:P ratio was the main driver of water quality, showing negative correlations with stream water N and P concentrations, and positive correlations with the N:P ratio in P-limited catchments. We revealed that soil C:P ratios higher than 97.8 mol mol−1 are required to achieve the simultaneous regulation of stream water N and P concentrations below the eutrophication threshold and make algal growth P-limited. Furthermore, we found that the relationships between catchment landscape and soil ecological stoichiometry likely provided practical options for regulating soil ecological stoichiometry. Our work highlights that soil ecological stoichiometry can effectively indicate the amount and proportion of soil N and P losses, and can be intervened through rational landscape planning to achieve sustainable aquatic ecosystems in catchments.

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Sammendrag

The introduction of cover crops in monoculture system to improve soil health has been broadly adopted worldwide. However, the environmental risk and application prospect of different cover crops in spring maize (Zea mays L.) monoculture proposed in the North China Plain are little known. A pot experiment was conducted to evaluate the effects of different winter cover crops on subsequent maize yield, soil fertility and environmental risks of N losses, and a survey was developed to examine the factors that influenced farmers’ willingness to adopt cover crops in the North China Plain. Based on the same fertilization regime during the maize growing period, four soil cover crop treatments were designed for winter use, including bare fallow, hairy vetch (Vicia villosa Roth), February orchid (Orychophragmus violaceus) and winter oilseed rape (Brassica campestris L.). The results indicated that winter cover crops significantly increased the subsequent maize yields, soil organic carbon, total N, soil microbial biomass carbon and nitrogen compared with bare fallow treatment. Incorporation of cover crops led to a negligible increase in N2O emissions and had a very limited effect on NH3 emissions. February orchid and winter oilseed rape treatment incorporation decreased NO3--N leaching compared with hairy vetch treatment in the maize growing season. The N loss by N2O, NH3 emissions and N leaching accounted for 71%–84% of the surplus N. However, yield increasing and environmental benefits were not main factors limiting farmers to accept cover crops. The amount and availability of financial incentives was strongest factor, accounting for 83.9%, followed by investment for cover crops. These results indicated that environmental benefits depend on different cover crops while maintaining maize yield and improving soil fertility, and the subsidies and unified cultivation of cover crops were the critical measures encouraging farmers to plant cover crops in the North China Plain.

Sammendrag

Livestock husbandry has raised enormous environmental concerns around the world, including water quality issues. Yet there is a need to document long-term water quality trends in livestock-intensive regions and reveal the drivers for the trends based on detailed catchment monitoring. Here, we assessed the concentration and load trends of dissolved reactive phosphorus (DRP) in streamwater of a livestock-intensive catchment in southwestern Norway, based on continuous flow measurements and flow-proportional composite water sampling. Precipitation and catchment-level soil P balance were monitored to examine the drivers. At the field level, moreover, the relationship between soil P balance and soil test P (measured using the ammonium lactate extraction method, P-AL) was assessed. Results showed that on average of 20 years 95 % of the P was applied to the catchment during March–August, when 40 % of annual precipitation and 25 % of annual discharge occurred. The low runoff helped reduce P loss following P applications. However, flow-weighted annual mean DRP concentration significantly increased with increasingly cumulative soil P surplus (R2 = 0.55, p = 0.0002). With a mean annual P surplus of 8.8 kg ha−1, the annual mean DRP concentration (range: 49–140 μg L−1; mean: 80 μg L−1) and annual DRP load (range: 0.35–1.46 kg ha−1; mean: 0.65 kg ha−1) significantly increased over the 20-year monitoring period (p = 0.001 and 0.0003, respectively). At the field level, P-AL concentrations were positively correlated with soil P balances (R2 = 0.48, p < 0.0001), confirming the long-term impact of P balances on the risks of P loss. The study highlights the predominant role of long-term P balances in affecting DRP loss in livestock-intensive regions through the effect on soil test P.

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Aims Root traits associated with resource foraging, including fine-root branching intensity, root hair, and mycorrhiza, may change in soils that vary in rock fragment content (RFC), while how these traits covary at the level of individual root branching order is largely unknown. Methods We subjected two xerophytic species, Artemisia vestita (subshrub) and Bauhinia brachycarpa (shrub), to increasing RFC gradients (0%, 25%, 50%, and 75%, v v− 1) in an arid environment and measured fine-root traits related to resource foraging. Results Root hair density and mycorrhizal colonization of both species decreased with increasing root order, but increased in third- or fourth-order roots at high RFCs (50% or 75%) compared to low RFCs. The two species tend to produce more root hairs than mycorrhizas under the high RFCs. For both species, root hair density and mycorrhizal colonization intensity were negatively correlated with root length and root diameter across root order and RFCs. Rockiness reduced root branching intensity in both species comparing with rock-free soil. At the same level of RFC, A. vestita had thicker roots and lower branching intensity than B. brachycarpa and tended to produce more root hairs. Conclusion Our results suggest the high RFC soil conditions stimulated greater foraging functions in higher root orders. We found evidence for a greater investment in root hairs and mycorrhizal symbioses as opposed to building an extensive root system in rocky soils. The two species studied, A. vestita and B. brachycarpa, took different approaches to foraging in the rocky soil through distinctive trait syndromes of fine-root components.

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Divisjon for miljø og naturressurser

Klima- og miljøvennlig bruk av husdyrgjødsel


Det er behov for å oppdatere kunnskapen om utnytting og tap av nitrogen og fosfor fra husdyrgjødsel for å bistå myndigheter og jordbruksnæringa i oppfylling av klima- og miljømål. Det er stort fokus på bruken av fosfor, fosforinnhold i jord og avrenning til vassdrag i forbindelse med revidering av gjødselforskriften. Spredetidspunkt og spredemetode for husdyrgjødsel, samt total mengde brukt gjødsel er viktige forhold som spiller inn på tapet. Redusert fordamping av ammoniakk og avrenning av nitrogen reduserer indirekte lystgasstap fra husdyrgjødsel, men også direkte- og indirekte lystgassutslipp gjennom redusert bruk av mineralgjødsel.Prosjektet omfatter en litteratursammenstilling og feltmålinger for å måle utnytting av næringsstoffer ved ulike spredetidspunkter for husdyrgjødsel i ulike landsdeler. I prosjektet vil det bli gjort feltmålinger på effekten av ulike spredetidspunkt på utnyttelse av nitrogen og fosfor til plantevekst. Feltmålingene vil bli utført i Rogaland, Vestland og Trøndelag fylke.

Aktiv Sist oppdatert: 08.02.2024
Slutt: des 2024
Start: jan 2022