Crop Uptake Research Articles

Impact of zinc on yield, nutrient uptake and soil nutrient status in rainfed pea-maize sequence under high phosphorus regime soils of Northwestern Himalaya

Field trials were conducted at the experimental farm of Hill Agricultural Research and Extension Center, Bajaura, Kullu, during kharif (summer crop) and rabi (winter crop) seasons from 2014–2015 to 2015–2016 to investigate the impact of zinc (Zn) on yield, nutrient uptake and soil nutrient status in rainfed pea-maize sequence under high phosphorus regime soils of Northwestern Himalaya. The various priming levels of Zn (water soaking- without zinc, 1%, 2% and 3% of ZnSO4) with three priming durations (4, 8 and 12 hours) were compared with basal dose of recommended NPK + ZnSO4 @ 25 kg ha−1 and farmers’ practice (absolute control). The yield of pea crop was maximum with 1% ZnSO4 priming duration of 12 hours, whereas maize crop yield was highest with 2% ZnSO4 priming duration of 12 hours. The nitrogen (N), phosphorus (P) and potassium (K) uptake of pea pods and stover was highest with 1% ZnSO4 priming for 12 hours duration, whereas the N, P and K uptake of maize grains and stover was registered highest with 2% ZnSO4 priming for a period of 12 hours. The results showed a positive impact on the crop yield and uptake, while no significant improvement was noticed in soil nutrients status after harvest.

Effect of Enterobacter sp. EG16 on Selenium biofortification and speciation in pak choi (Brassica rapa ssp. chinensis)

Using plant growth promoting rhizobacteria (PGPR) to boost Se uptake and accumulation in crops is a promising recent approach to biofortification. Most studies, however, have focused on a certain dose of PGPR or Se, while the synergistic effects of simultaneously changing the concentration of both exogenous Se and PGPR on plant growth and Se bioaccumulation are rarely explored. In this study, the combined treatments of 0-2 mg L−1 Se and (3.83-11.3) ×107 CFU mL−1 PGPR strain Enterobacter sp. EG16 were used for the hydroponic experiments of pak choi (Brassica rapa) to investigate the mutual effects on plant growth and Se absorption. The growth of pak choi, in terms of plant height, number of leaves and root tips, was promoted by combining 7.65×107 CFU mL−1 EG16 and no more than 1 mg L−1 of Se. Growth was significantly inhibited when the concentration of EG16 was raised to 11.3×107 CFU mL−1. Chlorophyll content, superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities were also boosted under the same combination of Se and EG16 concentrations. In addition, the Se content of aboveground part and intact plants significantly increased with rising concentrations of EG16 and Se. Selenomethionine (SeMet), methylselenocysteine (SeMeCys) and selenocystine (SeCys2) were the main organo-Se compounds detected in pak choi, accounting for almost 90% when supplied with selenite. Among these compounds, SeMet accounted for a high proportion and SeCys2 for a relatively low percentage in most treatments. The two forms were inversely related, probably because the transformation was driven by EG16. On the other hand, the proportion of SeMeCys was significantly affected by different concentrations of exogenous Se and EG16. Selenate was also detected, indicative of selenite oxidation. In terms of both plant biomass and nutritional quality, the combined formulation of 1 mg L−1 Se and 7.65×107 CFU mL−1 of EG16 is a promising means of producing Se-enriched vegetables.

Integration of Transcriptome and Metabolome Analyses Reveals the Mechanistic Basis for Cadmium Accumulation in Maize.

Cadmium (Cd) pollution in soil has become a major environmental issue worldwide. However, the underlying molecular mechanism of low grain-Cd accumulation (GCA) in maize is still largely unknown. Herein, we report the mechanistic basis for low GCA in maize by a multiomics approach. The low GCA genotype L63 showed normal vacuolar formation and a lower capacity of xylem loading of Cd than the high-accumulator L42 under Cd stress. Transcriptomic sequencing identified 84 low-GCA-associated genes which are mainly involved in the S-adenosylmethionine (SAM) cycle, metal transport, and vacuolar sequestration. A metabolome analysis revealed that L63 plants had a more active SAM cycle and a greater capacity for terpenoid synthesis and phenylalanine metabolism than L42. Combining the analysis of transcriptome and metabolome characterized several genes as key genes involved in the determination of Cd accumulation. Our study identifies a mechanistic basis for low Cd accumulation in maize grains and provides candidate genes for genetic improvement of crops.

Nitrogen Fertilization Effects on Soil Nitrate, Water Use, Growth Attributes and Yield of Winter Wheat under Shallow Groundwater Table Condition

Shallow groundwater plays a vital role in water use and the yield of winter wheat. Nitrogen (N) application significantly affects crop uptake and utilization of water from irrigation, but little is known about groundwater use. More importantly, excessive N application will also bring a series of environmental problems. An experiment was carried out in micro-lysimeters at 0, 150, 240, and 300 kg/ha N fertilization rates based on 0.6 m groundwater depth with relatively strong alkaline soil in the winter wheat growing season. The results showed that increasing the N application rate significantly increased the sensitivity of the daily groundwater evaporation velocity of winter wheat to environmental meteorological factors (soil surface moisture, humidity, atmospheric pressure and atmospheric temperature), and promoted crop water use, crop growth and yield under the 0.6 m groundwater depth. From 150 kg/ha to 300 kg/ha N fertilization, LAI and yield increased by 26.95–82.02%, and evapotranspiration (ET) and groundwater use efficiency (GUE) increased by 11.17–14.38%. However, a high N application rate would sharply induce surface soil drought, leading to a rapid increase in nitrate accumulation in the vadose zone and a significant decrease in partial factor productivity of applied N (PFPN). With the N application of 150–300 kg/ha, the accumulation of nitrate in the vadose zone increased by 8.12 times, and soil moisture in 0–20 cm and PFPN significantly decreased by 19.16–57.53%. N fertilization had a significant effect on water transfer and could promote the consumption and utilization of groundwater at 0.6 m depth. Considering yield, water use, the accumulation of nitrate, and PFPN, the optimal N application was 219.42–289.53 kg/ha at 0.6 m depth.

Modelling the impact of the Nordic Bioeconomy Pathways and climate change on water quantity and quality in a Danish River Basin

A societal transformation towards bio-economy will have extensive implications for land use in Nordic countries. These expected changes in land use combined with a changing climate, will have unknown consequences for water quality and quantity. To address this issue, we used the Nordic Bio-economic Pathways (NBPs), which describe five possible future scenarios (NBP1-5) for the Nordic bio-economy in 2050. The NBPs were quantified by experts using local knowledge and translated into modelling scenarios. The SWAT model was applied to simulate the effect of NBP scenarios for changes in farming intensity (varying chemical fertilizer and manure application rates), land cover change (agriculture vs forest) and nutrient loss mitigation (buffer strips and wetlands) in the River Odense catchment. Subsequently, the NBPs were combined with medium (RCP4.5) and strong (RCP8.5) climate change scenarios for the period 2041–2070 utilising the median of an ensemble of 20 and 57 climate models, respectively. Our study clearly showed that only one of the pathways, namely NBP1 (sustainability first), would enable catchment managers to fulfil the Water Framework Directive reduction target set for the total nitrogen loads in the River Odense catchment by reducing total nitrogen loads by 66%. One of the pathways (NBP5; growth first) caused an increase in the average annual total nitrogen loads by 12%, while the NBP3 scenario (self-sufficiency) reduced the total nitrogen loads with 18% compared to 2% in the case of NBP2 (business as usual) and 29 % for NBP4 (cities first). Surprisingly, climate change had only limited added impacts on the total nitrogen loads due to increased nitrogen uptake of crops. Our study provides policy makers with information on the influence of the different choices and directions taken towards transforming societies into bio-economies in the future.

Effect of acidifying amendments on P availability in calcareous soils

Phosphorus (P) reactions in calcareous soils limit the concentration of P in the soil solution for plant uptake. Calcareous soils with high calcium carbonate content (CaCO3) and high pH have low P fertiliser efficiency, leading to crop deficiency and limited crop productivity. The aim of this work was to test if soil acidifying amendments could reduce soil pH and improve the solubility of fertiliser P to improve crop P nutrition and biomass. Three calcareous soils with varying CaCO3 content (14–29% w/w) were used to test acidifying amendments both with and without mono-ammonium phosphate (MAP). Soil was amended with oxalic acid, sulfuric acid, glucose, ammonium sulfate and elemental sulfur (S0). Initial titrations demonstrated the ability of oxalic and sulfuric acids to reduce pH and improve P solubility in all three soils. Incubation of the acidifying amendments in the soil with the lowest carbonate content over 14 days (52 days for S0) showed increased P solubility and diffusion from MAP granules in soil amended with glucose, sulfuric acid and oxalic acid. There was, however, no improvement in P fertiliser uptake in wheat crops grown in these highly calcareous soils.

Nutrient Concentration and Its Uptake in Various Stages of Wheat (Triticum aestivum L.) as Influenced by Nitrogen, Phosphorus, and Potassium Fertilization

ABSTRACT Effective management of nitrogen (N), phosphorus (P), and potassium (K) are crucial for increasing crop production and productivity as they are associated with a number of enzymatic and physiological activities in wheat (Triticum aestivum L.). Field experiments were carried out during the winters of 2019˗˗20 and 2020˗˗21 to study the influence of varying levels of N, P, and K on crop performance, nutrient concentration, and uptake at various growth stages of wheat in mid-hill of Nepal. The study was conducted with factorial combinations of three N levels (100, 125, and 150 kg N ha−1), three P levels (25, 50, and 75 kg P2O5 ha−1) and three K levels (25, 50, and 75 kg K2O ha−1) in a randomized complete block design with three replications. Increasing N and K rates significantly (p < .05) increased total dry matter, grain yield, nutrient concentrations and uptakes in wheat. Pooled means showed significantly higher grain yields of 6.3 t ha−1 were obtained with N @ 125 kg ha−1, and K2O @ 50 kg ha−1 than lower rates. At maturity, average concentrations of N, P, and K in grain were 15.5, 3.6, and 5.8 g kg−1, respectively, and 5.4, 0.9, and 10.9 g kg−1 in straw, respectively, depending on the rate of NPK applied. N and P were mostly accumulated in wheat grain, whereas K was found higher in wheat straw than in grain. The nutrient concentration values of grain and straw can be used as a reference for determining nutrient removal from soil using a yield-based technique in wheat.

Laboratory Extractions of Soil Phosphorus Do Not Reflect the Fact That Liming Increases Rye Phosphorus Content and Yield in an Acidic Soil.

In addition to aluminum and other heavy metal toxicities, acidic soils also feature nutrient deficits that are not easily overcome by merely adding the required amounts of mineral fertilizers. One of the most critically scarce nutrients in acidic soils is phosphorus, which reacts with aluminum and iron to form phosphates that keep soil phosphorus availability significantly low. Liming ameliorates acidic soils by increasing pH and decreasing aluminum contents; however, it also increases the amount of calcium, which can react with phosphorus to form low-solubility phosphates. In the present work, three liming materials, namely, dolomitic limestone, limestone and sugar foam, were applied on a Typic Palexerult cropped with rye. The effects of these materials on soil properties, including soil available phosphorus extracted with the Olsen and Bray-1 methods, rye phosphorus content in stems and stem and spike harvested biomasses were monitored for nine years. According to the Olsen extraction, the amount of soil available phosphorus generally decreased following liming, with limestone presenting the lowest values; however, the amount of soil available phosphorus increased according to the Bray-1 extraction, though only to a significant extent with the sugar foam from the third year onward. Regardless, the phosphorus content in rye and the relative biomass yield in both stems and spikes generally increased as a consequence of liming. Since crop uptake and growth are the ultimate tests of soil nutrient availability, the inconsistent stem phosphorus content results following the Olsen and Bray-1 extraction methods suggest a lowered efficiency of both extractants regarding crops in soils rich in both aluminum and calcium ions. This decrease can lead to important interpretation errors in the specific conditions of these limed acidic soils, so other methods should be applied and/or researched to better mimic the crop roots' phosphorus extraction ability. Consequently, the effects of the liming of acidic soils on phosphorus availability and crop performance in the short and long term will be better understood.

Reclaimed water in agriculture: A plot-scale study assessing crop uptake of emerging contaminants and pathogens

Nowadays, water is a scarce resource, hence, water management is crucial as demand for agricultural, urban, and industrial purposes increases. The use of reclaimed water in agriculture can be a suitable solution. However, pathogens and chemical contaminants of emerging concern (CECs) present in reclaimed water can accumulate in the soil and ultimately, in the crop. To evaluate the potential transfer of biological and chemical pollutants from water to crop, two plots were designed for the cultivation of lettuce under field conditions. In this study, the influence of water quality, soil composition, and irrigation system on plant uptake of CECs and pathogens was assessed. The applied reclamation process reduced total suspended solids, E. coli (3–5 ulog), sulfite-reducing clostridia spores (1 ulog), Helminth eggs, and Legionella spp levels (complete removal) in water. Sodium adsorption ratio (SAR) and electric conductivity (EC) in the soils irrigated with reclaimed water were lower, and E. Coli was not detected. In lettuces, E. coli was only present in the crops irrigated with wastewater. Pharmaceuticals were the most frequently detected CECs in soils and waters, whereas UV filters achieved the highest concentrations. Diclofenac and salicylic acid were the most accumulated in soils, and diclofenac, ofloxacin, and benzophenone-4 were the most prevalent in the WWTP effluent. The irrigation water quality was the factor driving the transfer of CECs to the crops. Results show that the best combination to reduce pathogens and CECs was the use of reclaimed water, soils with high content of clay, and a sprinkling irrigation system.

Quantifying groundwater phosphorus flux to rivers in a typical agricultural watershed in eastern China.

Increasing evidence indicates that groundwater can contain high dissolved phosphorus (P) concentrations, thereby contributing as a potential pollution source for surface waters. However, limited quantitative knowledge is available concerning groundwater P fluxes to rivers. Based on monthly hydrochemical monitoring data for rivers and groundwater in 2017-2020, this study combined baseflow separation methods and a load apportionment model (LAM) to quantify contributions from point sources, surface runoff, and groundwater/subsurface runoff to riverine P pollution in a typical agricultural watershed of eastern China. In the studied Shuanggang River, most total P (TP) and dissolved P (DP) concentrations exceeded targeted water quality standards (i.e., TP ≤ 0.2mg P L-1, DP ≤ 0.05mg P L-1), with DP (76 ± 20%) being the major riverine P form. Observed DP concentrations in groundwater were generally higher than those of river waters. There was a strong correlation between river and groundwater P concentrations, implying that groundwater might be a considerable P pollution source to rivers. The nonlinear reservoir algorithm estimated that baseflow/groundwater contributed 66-68% of monthly riverine water discharge on average, which was consistent with results estimated by an isotope-based sine-wave fitting method. The LAM incorporating point sources, surface runoff, and groundwater effectively predicted daily riverine TP [calibration: coefficient of determination (R2) = 0.76-0.82, Nash-Sutcliffe Efficiency (NSE) = 0.61-0.77; validation: R2 = 0.88-0.98, NSE = 0.54-0.64] and DP loads (calibration: R2 = 0.73-0.84, NSE = 0.67-0.72; validation: R2 = 0.88-0.97, NSE = 0.56-0.83). The LAM estimated point source, surface runoff, and groundwater contributions to riverine loads were 15-18%, 14-35%, and 46-70% for TP loads and 7-9%, 10-32%, and 59-82% for DP loads, respectively. Groundwater was the dominant riverine P source due to long-term accumulation of P from excess fertilizer and farmyard manure applications. The developed methodology provides an alternative method for quantifying P pollution loads from point sources, surface runoff, and groundwater to rivers. This study highlights the importance of controlling groundwater P pollution from agricultural lands to address riverine water quality objectives and further implies that decreasing fertilizer P application rates and utilizing legacy soil P for crop uptake are required to reduce groundwater P loads to rivers.

Silicon-nanoparticles doped biochar is more effective than biochar for mitigation of arsenic and salinity stress in Quinoa: Insight to human health risk assessment.

The increasing contamination of soil with arsenic (As), and salinity has become a menace to food security and human health. The current study investigates the comparative efficacy of plain biochar (BC), and silicon-nanoparticles doped biochar (SBC) for ameliorating the As and salinity-induced phytotoxicity in quinoa (Chenopodium quinoa Willd.) and associated human health risks. Quinoa was grown on normal and saline soils (ECe 12.4 dS m−1) contaminated with As (0, 20 mg kg−1) and supplemented with 1% of BC or SBC. The results demonstrated that plant growth, grain yield, chlorophyll contents, and stomatal conductance of quinoa were decreased by 62, 44, 48, and 66%, respectively under the blended stress of As and salinity as compared to control. Contrary to this, the addition of BC to As-contaminated saline soil caused a 31 and 25% increase in plant biomass and grain yield. However, these attributes were increased by 45 and 38% with the addition of SBC. The H2O2 and TBARS contents were enhanced by 5 and 10-fold, respectively under the combined stress of As and salinity. The SBC proved to be more efficient than BC in decreasing oxidative stress through overexpressing of antioxidant enzymes. The activities of superoxide dismutase, peroxidase, and catalase were enhanced by 5.4, 4.6, and 11-fold with the addition of SBC in As-contaminated saline soil. Contamination of grains by As revealed both the non-carcinogenic and carcinogenic risks to human health, however, these effects were minimized with the addition of SBC. As accumulation in grains was decreased by 65-fold and 25-fold, respectively for BC and SBC in addition to As-contaminated saline soil. The addition of SBC to saline soils contaminated with As for quinoa cultivation is an effective approach for decreasing the food chain contamination and improving food security. However, more research is warranted for the field evaluation of the effectiveness of SBC in abating As uptake in other food crops cultivated on As polluted normal and salt-affected soils.

Yield Productivity and Nitrogen Uptake of Wheat Crop Are Highly Dependent on Irrigation Water Availability and Quality under Water-Limited Conditions

ABSTRACT The water scarcity can limit yield productivity of wheat, and this issue can be controlled using various management practices. The main objectives of this study were: 1) to investigate how N application rates and water quality affect the yield productivity, and plant growth characterization and nitrogen uptake of wheat crop under water-limited conditions; 2) to describe the relationships between nitrogen application rates and yields of wheat plants at low-quality water application times; 3) to predict the efficiencies of applied N fertilizers at different rates and water use efficiency. Field experiments on wheat crop were conducted for two consecutive growing seasons (2016–2017) at a private farm at Abis-Alexandria. The experimental design was split-plot design with three replicates. The main plot was nitrogen application rates (0, 75, 150, and 225 kg N ha−1) in the form of urea fertilizer (46% N). The sub-main plot was low-quality water application (LQW) (0%, 25%, 50%, and 75% from applied water requirements of wheat crop) co-applied with high-quality water (HQW). The obtained results indicated that the application of nitrogen fertilization with different rates significantly increased the economical and biological yields, grain/biological-nitrogen use efficiency, agronomic efficiency, nitrogen uptake, and water use efficiency for both grain and biological yields in the two seasons of cultivations. Moreover, the yield attributes such as spike length, number of plants and tillers were also significantly affected by N fertilization. Application of LQW at 25% and 50% co-applied with 75% and 50% HQW did not significantly decrease the yield and yield attributes of wheat in both seasons of cultivations. In contrast, the application of LQW at 75% co-applied with 25% HQW was significantly decreased the studied parameters. In conclusion, the best application ratio of LQW and HQW was 1:1 at 50% of LQW co-applied with 50% HQW at which the yield and its attributes of wheat did not significantly reduced.

Potential benefits of climate change for potatoes in the United States

Potatoes are a mainstay of human diets and 4 million metric tons are produced annually in the United States. Simulations of future crop production show that climate change is likely to reduce the yields of the major grain crops around the world, but the impacts on potato production have yet to be determined. A model ensemble consisting of five process-based and one statistical model was used to estimate the impact of climate change on fully irrigated, well-fertilized potato crop across the USA under the RCP 8.5 scenario of high emissions. Results indicate that increasing temperature will reduce potato yields, but this will be mostly compensated by elevated atmospheric CO2. Yields are predicted to decline with climate change in the current highest-yielding areas, which might experience the highest rises in growing season temperature during short hot summers. Simulated yields increase slightly elsewhere in the southern regions of the USA. Planting potatoes earlier as adaptation to avoid hot summers might improve yields in most regions. Water use by the potato crop is predicted to decline despite higher temperatures, due to a shorter growing season and increased water use efficiency under elevated atmospheric CO2. With higher yields in many regions, crop uptake for (nitrogen + phosphorus + potassium) NPK fertilizer will increase, despite the reduced concentration of nutrients in potatoes due to a growth stimulus from elevated atmospheric CO2. With earlier planting, by 2050 water use will decline by 11.7%, NPK fertilizer uptake will increase by 10.4%, and yields of slightly less nutritious potatoes will increase by 14.9% nationally.

Modeling of nitrate and ammonium leaching and crop uptake under wastewater application considering nitrogen cycle in the soil

Modeling of nitrate and ammonium leaching and crop uptake under wastewater application considering nitrogen cycle in the soil

Insight into the uptake and metabolism of a new insecticide cyetpyrafen in plants

As new agrochemicals are continuously introduced into agricultural systems, it is essential to investigate their uptake and metabolism by plants to better evaluate their fate and accumulation in crops and the subsequent risks to human exposure. In this study, the uptake and elimination kinetics and transformation of a novel insecticide, cyetpyrafen, in two model crops (lettuce and rice) were first evaluated by hydroponic experiments. Cyetpyrafen was rapidly taken up by plant roots and reached a steady state within 24 h, and it was preferentially accumulated in root parts with root concentration factors up to 2670 mL/g. An uptake mechanism study suggested that root uptake of cyetpyrafen was likely to be dominated by passive diffusion and was difficult to transport via xylem and phloem. Ten phase I and three phase II metabolites of cyetpyrafen were tentatively identified in the hydroponic-plant system through a nontarget screening strategy. The structures of two main metabolites (M-309 and M-391) were confirmed by synthesized standards. The metabolic pathways were proposed including hydroxylation, hydrolysis, dehydrogenation, dehydration and conjugation, which were assumed to be regulated by cytochrome P450, carboxylesterase, glycosyltransferase, glutathione S-transferases and peroxidase. Cyetpyrafen and its main metabolites (M-409, M-309 and M-391) were estimated to be harmful/toxic toward nontarget organisms by theoretical calculation. The high bioaccumulation and extensive transformation of cyetpyrafen highlighted the necessity for systematically assessing the crop uptake and metabolism of new agrochemicals.

The role of nitrogen fixation and crop N dynamics on performance and legacy effects of maize-grain legumes intercrops on smallholder farms in Tanzania

Maize-grain legume intercrops form an important component of the cropping systems of smallholder farmers in many parts of sub-Saharan Africa. However, the effects of cropping system and fertilizer use on nitrogen fixation and nitrogen uptake of component crops in maize-legume intercrops are not well understood. Our study addressed the questions: (i) What is the capacity of pigeonpea and lablab to fix atmospheric nitrogen (N2) in sole crop and when intercropped with maize on smallholder farms across different agro-ecological conditions?; (ii) How does productivity and N-uptake by sole and intercropped maize and legumes respond to N and P fertilizer?; and (iii) What are the residual effects of the sole crops, intercrops and fertilizer treatments on the productivity of a succeeding maize crop? We studied additive intercropping systems on eight farms in Babati, Tanzania: maize-long duration pigeonpea, maize-medium duration pigeonpea and maize-lablab, with separate sole crops, at three fertilizer rates: no fertilizer; 40 kg P ha−1; and 90 kg N ha−1 + 40 kg P ha−1. Whereas P fertilizer was applied on maize and the legumes, the N fertilizer was only applied on maize. Maize and pigeonpea were sown simultaneously, while lablab was relay-planted one month later. N2-fixation was quantified using the 15N natural abundance method. N2-fixation differed among the legume species. Sole long-duration pigeonpea fixed significantly more N2 (20–63 kg ha−1 more) than all other cropping systems, corresponding to the greater shoot dry matter and N yield of this system. The combined N uptake of maize and legume in intercrops was consistently larger than that of sole maize or the legume. Application of fertilizer resulted in enhanced N uptake both in the current season (up to 40 kg N ha−1 more) and in a succeeding maize crop (up to 71 kg N ha−1 more). We observed positive associations between grain yield, dry matter production and total N uptake of a succeeding maize crop, and the N-fixed by legume species in the preceding season. Each kg of legume shoot N yield was associated with up to 14 kg ha−1 extra grain yield, 29 kg ha−1 extra dry matter and 0.5 kg ha−1 extra total N uptake of the succeeding maize crop. Our results show that maize-legume intercrops enhance N-uptake. Furthermore, N2-fixation by sole or intercropped legumes confers strong residual benefits on productivity of a succeeding maize crop.

Estimation of Biomass and N Uptake in Different Winter Cover Crops from UAV-Based Multispectral Canopy Reflectance Data

Cover crops are known to provide beneficial effects to agricultural systems such as a reduction in nitrate leaching, erosion control, and an increase in soil organic matter. The monitoring of cover crops’ growth (e.g., green area index (GAI), nitrogen (N) uptake, or dry matter (DM)) using remote sensing techniques allows us to identify the physiological processes involved and to optimise management decisions. Based on the data of a two-year trial (2018, 2019) in Kiel, Northern Germany, the multispectral sensor Sequoia (Parrot) was calibrated to the selected parameters of the winter cover crops oilseed radish, saia oat, spring vetch, and winter rye as sole cover crops and combined in mixtures. Two simple ratios (SRred, SRred edge) and two normalised difference indices (NDred, NDred edge) were calculated and tested for their predicting power. Furthermore, the advantage of the species/mixture–individual compared to the universal models was analysed. SRred best predicted GAI, DM, and N uptake (R2: 0.60, 0.53, 0.45, respectively) in a universal model approach. The canopy parameters of saia oat and spring vetch were estimated by species–individual models, achieving a higher R2 than with the universal model. Comparing mixture–individual models to the universal model revealed low relative error differences below 3%. The findings of the current study serve as a tool for the rapid and inexpensive estimation of cover crops’ canopy parameters that determine environmental services.

Plant Growth Promotion and Selenium Accumulation in Zea mays by Rhizobacteria Isolated from Natural Seleniferous Soils

AbstractSelenium (Se) is essential for life's basic functions but its sources are limited. Plant growth promoting bacteria is a potential source to increase Se accumulation and plant growth. Bacteria are isolated from native seleniferous soils,. and based on 16S rRNA (ribosomal RNA) sequenceanalysis, two plant growth promoting and selenium tolerant bacteria are selected. They are identified as Leclercia adecarboxylata (B49) and Cedecea neteri (B71). L. adecarboxylata and C. neteri produce indole acetic acid of 93 ± 3.2 and 68 ± 2.9 mg L−1 and a phosphate solubilization index of 1.26 ± 0.3 and 3.29 ± 0.2, respectively. L. adecarboxylata and C. neteri tolerate up to 350 mm of selenite with an inhibitory concentration 50 value of 225.6 ± 14 and 236.6 ± 14 mm, respectively. Inoculation of bacteria significantly increases the growth of Zea mays plants in seleniferous soil. Plant growth promotion is 36.6% more in C. neteri inoculated plants compared to L. adecarboxylata. Se accumulation significantly increases in plant tissues inoculated with C. neteri (20.2 µg g−1) than L. adecarboxylata (12.1 µg g−1). This study has provided evidence that microbial Se biotransformation through bacterial inoculation is an alternative way to improve the Se uptake in crops and maintain human health.

X-ray absorption near edge structure spectroscopy reveals phosphate minerals at surface and agronomic sampling depths in agricultural Ultisols saturated with legacy phosphorus

Legacy phosphorus (P) soils have received excessive P inputs from historic manure and fertilizer applications and present unique management challenges for protecting water quality as soil P saturation leads to increased soluble P to waterways. We used P K-edge X-ray absorption near edge structure (XANES) spectroscopy to identify and quantify the dominant P minerals in four representative legacy P soils under conventional till and no-till management in Maryland, USA. Various measures of extractable soil P, including water-extractable P (20.6–54.1 mg kg−1 at 1:10 soil-to-water ratio; 52.7–132.2 mg kg−1 at 1:100 soil-to-water ratio), plant available P extracted with Mehlich 3 (692–1139 mg kg−1), and Mehlich 3P saturation ratio (0.54–1.37), were above the environmental threshold values, suggesting the accumulation of legacy P in soils. The quantification of dominant P minerals may provide insights into the potential of legacy P soils to contribute to P release for crop use and soluble P losses. Linear combination fits of XANES spectra identified the presence of four phosphate mineral groups, consisting of (i) calcium-phosphate minerals (11–59%) in the form of fluorapatite, β-tricalcium phosphate, and brushite, followed by (ii) iron-phosphate minerals (12–49%) in the form of ludlamite, heterosite, P sorbed to ferrihydrite, and amorphous iron phosphates, (iii) aluminum-phosphate minerals (15–33%) in the form of wavellite and P sorbed to aluminum hydroxide, and (iv) other phosphate minerals (5–35%) in the form of copper-phosphate (cornetite, 5–18%) and manganese-phosphate (hureaulite, 25–35%). Organic P consisting of phytic acid was found in most soils (13–24%) and was more pronounced in the surface layer of no-till (21–24%) than in tilled (16%) fields. Of the P forms identified with XANES, we conclude that P sorbed to Fe and Al, and Ca–P in the form of brushite and β-tricalcium phosphate will likely readily contribute to the soil WEP pool as the soil solution P is depleted by crop uptake and lost via runoff and leaching.

Can As concentration in crop be controlled by Se fertilization? A meta-analysis and outline of As sequestration mechanisms.

Arsenic (As) is a pollutant with a strong toxic effect on animals, plants and human beings. Exogenous selenium (Se) has been suggested to reduce the accumulation of As in crops, but contradictory results were found in the published literature. In order to clarify the possible processes, we collected the literature that reports on the effects of Se application on As uptake and accumulation in crops, analyzed the data by meta-analysis, and tested the effects of different factors on As accumulation by meta-regression model and subgroup analysis. The results highlighted a significant dose-dependent reduction of As content in crops after Se addition. Exogenous Se can significantly reduce As concentrations in grains by 18.76%. The reduction was dose-dependent for rice grains under aerobic soil conditions but not for rice grains under anoxic soil conditions. Se-enriched soils (greater than 0.5 mg kg-1) significantly reduced As concentrations in grains. Selenium significantly decreased the transfer factor of As from root to shoot. Moreover, selenite had a stronger inhibiting effect on the transport of As from root to shoot than selenate. The inhibition of selenium fertilization on As concentrations seems to take place in root and soil, while physiological processes in rice may be involved in restricting uptake and transport from root to shoot. These findings provide new ideas for effectively alleviating the transfer of As to the human body through the food chain.