Biochar addition and reduced irrigation modulates leaf morpho-physiology and biological nitrogen fixation in faba bean-ryegrass intercropping.

Intercropping legume with grass has potential to increase biomass and protein yield via biological N2-fixation (BNF) benefits, whereas the joint effects of biochar (BC) coupled with deficit irrigation on intercropping systems remain elusive. A 15N isotope-labelled experiment was implemented to investigate morpho-physiological responses of faba bean-ryegrass intercrops on low- (550 °C, LTBC) or high-temperature BC (800 °C, HTBC) amended sandy-loam soil under full (FI), deficit (DI) and partial root-zone drying irrigation (PRD). LTBC and HTBC significantly reduced intrinsic water-use efficiency (WUE) by 12 and 14 %, and instantaneous WUE by 8 and 16 %, respectively, in faba bean leaves, despite improved photosynthetic (An) and transpiration rate (Tr), and stomatal conductance (gs). Compared to FI, DI and PRD lowered faba bean An, gs and Tr, but enhanced leaf-scale and time-integrated WUE as proxied by the diminished shoots Δ13C. PRD enhanced WUE as lower gs, Tr and guard cell length than DI-plants. Despite higher carbon ([C]) and N concentration ([N]) in faba bean shoots amended by BC, the aboveground C- and N-pool of faba bean were reduced, while these pools increased for ryegrass. The N-use efficiency (NUE) in faba bean shoots was reduced by 9 and 14 % for LTBC and HTBC, respectively, but not for ryegrass. Interestingly, ryegrass shoots had 52 % higher NUE than faba bean shoots. The N derived from atmosphere (% Ndfa) was increased by 2 and 9 % under LTBC and HTBC, respectively, while it decreased slightly by reduced irrigation. Quantity of BNF in faba bean aboveground biomass decreased with HTBC coupled with reduced irrigation, mainly towards decreased biomass and soil N uptake by faba bean. Therefore, HTBC might not be a feasible option to improve WUE and BNF in faba bean-ryegrass intercropping, but PRD is permissible as the clear trade-off between BC and PRD.

Spatiotemporal Winter Wheat Water Status Assessment Improvement Using a Water Deficit Index Derived from an Unmanned Aerial System in the North China Plain.

Agricultural droughts cause a great reduction in winter wheat productivity; therefore, timely and precise irrigation recommendations are needed to alleviate the impact. This study aims to assess drought stress in winter wheat with the use of an unmanned aerial system (UAS) with multispectral and thermal sensors. High-resolution Water Deficit Index (WDI) maps were derived to assess crop drought stress and evaluate winter wheat actual evapotranspiration rate (ETa). However, the estimation of WDI needs to be improved by using more appropriate vegetation indices as a proximate of the fraction of vegetation cover. The experiments involved six irrigation levels of winter wheat in the harvest years 2019 and 2020 at Luancheng, North China Plain on seasonal and diurnal timescales. Additionally, WDI derived from several vegetation indices (VIs) were compared: near-infrared-, red edge-, and RGB-based. The WDIs derived from different VIs were highly correlated with each other and had similar performances. The WDI had a consistently high correlation to stomatal conductance during the whole season (R2 between 0.63-0.99) and the correlation was the highest in the middle of the growing season. On the contrary, the correlation between WDI and leaf water potential increased as the season progressed with R2 up to 0.99. Additionally, WDI and ETa had a strong connection to soil water status with R2 up to 0.93 to the fraction of transpirable soil water and 0.94 to the soil water change at 2 m depth at the hourly rate. The results indicated that WDI derived from multispectral and thermal sensors was a reliable factor in assessing the water status of the crop for irrigation scheduling.

Physiological and Growth Responses of Potato (Solanum Tuberosum L.) to Air Temperature and Relative Humidity under Soil Water Deficits.

Drought stress often occurs concurrently with heat stress, yet the interacting effect of high vapor pressure deficit (VPD) and soil drying on the physiology of potato plants remains poorly understood. This study aimed to investigate the physiological and growth responses of potatoes to progressive soil drying under varied VPDs. Potato plants were grown either in four separate climate-controlled greenhouse cells with different VPD levels (viz., 0.70, 1.06, 1.40, and 2.12 kPa, respectively) or under a rainout shelter in the field. The VPD of each greenhouse cell was caused by two air temperature levels (23 and 30 °C) combined with two relative humidity levels (50 and 70%), and the VPD of the field was natural conditions. Irrigation treatments were commenced three or four weeks after planting in greenhouse cells or fields, respectively. The results indicated that soil water deficits limited leaf gas exchange and shoot dry matter (DMshoot) of plants while increasing the concentration of abscisic acid (ABA) in the leaf and xylem, as well as water use efficiency (WUE) across all VPD levels. High VPD decreased stomatal conductance (gs) but increased transpiration rate (Tr). High VPD increased the threshold of soil water for Tr began to decrease, while the soil water threshold for gs depended on temperature due to the varied ABA response to temperature. High VPD decreased leaf water potential, leaf area, and DMshoot, which exacerbated the inhibition of soil drying to plant growth. Across the well-watered plants in both experiments, negative linear relationships of gs and WUE to VPD and positive linear relations between Tr and VPD were found. The results provide some novel information for developing mechanistic models simulating crop WUE and improving irrigation scheduling in future arid climates.

Biochar and alternate wetting-drying cycles improving rhizosphere soil nutrients availability and tobacco growth by altering root growth strategy in Ferralsol and Anthrosol.

Biochar has been advocated as a sustainable and eco-friendly practice to improve soil fertility and crop productivity which could aid in the mitigation of climate change. Nonetheless, the combined effects of biochar and irrigation on tobacco growth and soil nutrients in diverse soil types have been incompletely explored. We applied a split-root experiment to investigate the impacts of amendment with 2% softwood- (WBC) and wheat-straw biochar (SBC) on growth responses and rhizosphere soil nutrients availability of tobacco plants grown in a Ferralsol and an Anthrosol. All plants within same soil type received same amount of water daily by either conventional deficit irrigation (CDI) or alternate wetting-drying cycles irrigation (AWD). Compared to the un-amended controls, SBC addition enhanced biomass, carbon (C)-, phosphorus (P)- and potassium (K)-pool in the aboveground organs especially in Anthrosol, despite a negative effect on aboveground nitrogen (N)-pool. Regardless of soil type, biochar combined with AWD lowered root diameter while increased root tissue mass density to engage the plant in an acquisitive strategy for resources, therefore altered leaves stoichiometry as exemplified by lowered N/K, C/P and N/P and increased C/N. The addition of SBC induced a liming effect by increasing Anthrosol soil pH which was further amplified by AWD, but was unaffected on Ferralsol. Moreover, compared to the controls, SBC and AWD increased available P and K, and total C, total N and C/N ratio in the rhizosphere soil which coincided with the lowered soil C and N isotope composition (δ13C and δ15N), though a slight reduction in C and N stocks under AWD. However, such effects were not evident with WBC might be associated with its natures. Thus, combined SBC/AWD application might be an effective strategy to synergistically overcome nutrients restriction and improve tobacco productivity by intensifying nutrients cycling and optimizing plant growth strategies.

Long-term warming and nitrogen fertilization affect C-, N- and P-acquiring hydrolase and oxidase activities in winter wheat monocropping soil.

The enzymatic activities and ratios are critical indicators for organic matter decomposition and provide potentially positive feedback to carbon (C) loss under global warming. For agricultural soils under climate change, the effect of long-term warming on the activities of oxidases and hydrolases targeting C, nitrogen (N) and phosphorus (P) and their ratios is unclear, as well as whether and to what extend the response is modulated by long-term fertilization. A 9-year field experiment in the North China Plain, including an untreated control, warming, N fertilization, and combined (WN) treatment plots, compared the factorial effect of warming and fertilization. Long-term warming interacted with fertilization to stimulate the highest activities of C, N, and P hydrolases. Activities of C and P hydrolase increased from 8 to 69% by N fertilization, 9 to 53% by warming, and 28 to 130% by WN treatment compared to control, whereas the activities of oxidase increased from 4 to 16% in the WN soils. Both the warming and the WN treatments significantly increased the enzymatic C:N ratio from 0.06 to 0.16 and the vector length from 0.04 to 0.12 compared to the control soil, indicating higher energy and resource limitation for the soil microorganisms. Compared to WN, the warming induced similar ratio of oxidase to C hydrolase, showing a comparable ability of different microbial communities to utilize lignin substrates. The relationship analyses showed mineralization of organic N to mediate the decomposition of lignin and enzyme ratio in the long-term warming soil, while N and P hydrolases cooperatively benefited to induce more oxidase productions in the soil subject to both warming and N fertilization. We conclude that coupled resource limitations induced microbial acclimation to long-term warming in the agricultural soils experiencing high N fertilizer inputs.

An improved microelectrode method reveals significant emission of nitrous oxide from the rhizosphere of a long-term fertilized soil in the North China Plain.

Microsensors are able to accurately quantify nitrous oxide (N2O) emissions in microenvironments at high spatio-temporal resolution; yet, limited studies have been conducted on agricultural soils due to the inability to obtain electrical signal under conditions of low soil moisture. This study improved the calibration of a microelectrode for measuring N2O emissions from agricultural soil. The microelectrode was applied to evaluate the effect of long-term fertilization with mineral fertilizer (NPK), complemented with pig manure (MNPK), straw (SNPK), or without fertilizer (CK), all with and without urea addition, on N2O emissions from the soil, with explicit separation of the rhizosphere and the bulk soil compartments. The use of soil solution instead of pure water for calibration of the microelectrode doubled the signal and significantly improved the sensor sensitivity. The optimal electrolytic concentration of the soil solution, expressed as water: soil ratio, was found at the maximum vertex of the quadratic equation fitted on the slope values of the calibration equations for different soil solutions. The application of the calibrated microelectrode revealed significantly higher N2O emission from the rhizosphere compared to the bulk soil, accounting for 60% of the total emission. For the bulk soil, MNPK significantly increased N2O emissions compared to SNPK and NPK, whereas the differences between these treatments for the rhizosphere soil were insignificant. The statistical modeling revealed significant relation of the N2O emission with soil inorganic nitrogen contents and an additive effect of treatment (MNPK and SNPK), urea addition and rhizosphere soil. This study provides novel insights into the use of microelectrodes for measuring N2O emissions from the soil microenvironment and also points on the rhizosphere compartment and the management practices of agroecosystems able to reduce the N2O emission from agriculture.

Heavy Metal Soil Contamination Detection Using Combined Geochemistry and Field Spectroradiometry in the United Kingdom.

Technological advances in hyperspectral remote sensing have been widely applied in heavy metal soil contamination studies, as they are able to provide assessments in a rapid and cost-effective way. The present work investigates the potential role of combining field and laboratory spectroradiometry with geochemical data of lead (Pb), zinc (Zn), copper (Cu) and cadmium (Cd) in quantifying and modelling heavy metal soil contamination (HMSC) for a floodplain site located in Wales, United Kingdom. The study objectives were to: (i) collect field- and lab-based spectra from contaminated soils by using ASD FieldSpec® 3, where the spectrum varies between 350 and 2500 nm; (ii) build field- and lab-based spectral libraries; (iii) conduct geochemical analyses of Pb, Zn, Cu and Cd using atomic absorption spectrometer; (iv) identify the specific spectral regions associated to the modelling of HMSC; and (v) develop and validate heavy metal prediction models (HMPM) for the aforementioned contaminants, by considering their spectral features and concentrations in the soil. Herein, the field- and lab-based spectral features derived from 85 soil samples were used successfully to develop two spectral libraries, which along with the concentrations of Pb, Zn, Cu and Cd were combined to build eight HMPMs using stepwise multiple linear regression. The results showed, for the first time, the feasibility to predict HMSC in a highly contaminated floodplain site by combining soil geochemistry analyses and field spectroradiometry. The generated models help for mapping heavy metal concentrations over a huge area by using space-borne hyperspectral sensors. The results further demonstrated the feasibility of combining geochemistry analyses with filed spectroradiometric data to generate models that can predict heavy metal concentrations.

Effect of poplar trees on nitrogen and water balance in outdoor pig production - A case study in Denmark.

Nitrate leaching from outdoor pig production is a long-standing environmental problem for surface and groundwater pollution. In this study, the effects of inclusion of poplar trees in paddocks for lactating sows on nitrogen (N) balances were studied for an organic pig farm in Denmark. Vegetation conditions, soil water and nitrate dynamics were measured in poplar and grass zones of paddocks belonging to main treatments: access to trees (AT), no access to trees (NAT) and a control without trees (NT), during the hydrological year April 2015 to April 2016. Soil water drainage for each zone, simulated by two simulation models (CoupModel and Daisy), was used to estimate nitrate leaching from the zones in each paddock. N balances (input minus output) for the treatments were computed and compared. The results showed that, in terms of annual water balance and regardless of treatment, simulated evapotranspiration of poplar was 560-569 and 489-498 mm for CoupModel and Daisy, respectively, and corresponding evapotranspiration of grass-clover was 250 and 400 mm, against precipitation of 1076 mm. Simulated drainage below the root zone varied as 620-723 mm for Daisy and 568-958 mm for CoupModel, the higher end of the latter being probably overestimated. Annual nitrate leaching ranged from 32 kg N ha-1 in the poplar zone of NAT up to 289 kg N ha-1 in the control grass zone of NT. The poplar zone showed significantly lower nitrate leaching, by 75-80%, compared to the grass zone. For the control NT treatment, nitrate leaching was approximately 50% higher in the grass zone closest to the hut compared to the grass zone further away. NT treatment also had the largest surface N balance of 468 kg N ha-1 compared to 436 and 397 kg N ha-1 for AT and NAT, respectively. When N losses by leaching and volatilisation were included, soil N balances were 118, 157 and 113 kg N ha-1 for AT, NAT and NT, respectively. Overall, the two simulation models were found useful tools for analyses of water balance for complex agroforestry systems. The findings collectively suggest that it is possible to decrease nitrate leaching from outdoor pig production on sandy soils by inclusion of poplar trees. Additional measures are nevertheless needed to reduce N losses on a mean area basis in paddocks with 20% tree cover.

Estimation of land-surface evaporation at four forest sites across Japan with the new nonlinear complementary method.

Evaporation from land surfaces is a critical component of the Earth water cycle and of water management strategies. The complementary method originally proposed by Bouchet, which describes a linear relation between actual evaporation (E), potential evaporation (Epo) and apparent potential evaporation (Epa) based on routinely measured weather data, is one of the various methods for evaporation calculation. This study evaluated the reformulated version of the original method, as proposed by Brutsaert, for forest land cover in Japan. The new complementary method is nonlinear and based on boundary conditions with strictly physical considerations. The only unknown parameter (α e) was for the first time determined for various forest covers located from north to south across Japan. The values of α e ranged from 0.94 to 1.10, with a mean value of 1.01. Furthermore, the calculated evaporation with the new method showed a good fit with the eddy-covariance measured values, with a determination coefficient of 0.78 and a mean bias of 4%. Evaluation results revealed that the new nonlinear complementary relation performs better than the original linear relation in describing the relationship between E/Epa and Epo/Epa, and also in depicting the asymmetry variation between Epa/Epo and E/Epo.

Integrated modelling of crop production and nitrate leaching with the Daisy model.

An integrated modelling strategy was designed and applied to the Soil-Vegetation-Atmosphere Transfer model Daisy for simulation of crop production and nitrate leaching under pedo-climatic and agronomic environment different than that of model original parameterisation. The points of significance and caution in the strategy are: •Model preparation should include field data in detail due to the high complexity of the soil and the crop processes simulated with process-based model, and should reflect the study objectives. Inclusion of interactions between parameters in a sensitivity analysis results in better account for impacts on outputs of measured variables.•Model evaluation on several independent data sets increases robustness, at least on coarser time scales such as month or year. It produces a valuable platform for adaptation of the model to new crops or for the improvement of the existing parameters set. On daily time scale, validation for highly dynamic variables such as soil water transport remains challenging. •Model application is demonstrated with relevance for scientists and regional managers. The integrated modelling strategy is applicable for other process-based models similar to Daisy. It is envisaged that the strategy establishes model capability as a useful research/decision-making, and it increases knowledge transferability, reproducibility and traceability.