Uptake Of Winter Wheat Research Articles

Enhancing nitrogen use efficiency and plant productivity in long-term precrop/crop rotation and fertilization management

ContextLong-term experiments are an important tool to investigate the effects of crop rotation and fertilization measures under climate change conditions. However, there are few studies on nitrogen use efficiency (NUE) of crops in long-term cropping systems in Europe, but no consolidate studies in Germany. ObjectiveWe analyzed a long-term experiment established in 1982 to observe the role of legumes on total nitrogen uptake, NUE, agronomic efficiency, nitrogen response index and N recovery efficiency compared to fallow land and cereals in a crop rotation over the long-term. MethodsThe experiment included five different precrops (fallow land, maize, oat, field bean and clover mulch) in combination with four levels of fertilization (control, PK, PK+N with reduced dosage, and PK+N with full dosage followed by three years of cereal cultivation (winter wheat, winter rye, summer barley) in all treatments. The field trial was conducted as a fully factorial split plot design, with spatially randomized field repetitions in four blocks. ResultsLong-term mineral NPK fertilization improved the N uptake of winter wheat (185.7 kg N ha−1), winter rye (152.2 kg N ha−1) and summer barley (92.2 kg N ha−1) when the higher level of fertilization (NPK 100%) was implemented. A year-round application of clover mulch as green manure in the rotational system resulted in higher NUE (up to 37%) compared to fallow land after 40 years. Crop rotation with oat and maize (100% cereals) led to lower NUE (up to 30%) compared to fallow land. Clover mulch (198%), field bean (155%), fallow land (148%) and maize (119%) significantly increased the N uptake of wheat compared to oat in 2015. Over time, the agronomic efficiency was increased. This increase was 4 or 5 times higher in the 9th and 10th crop rotation compared to the beginning of the experiment (in 1983). Nitrogen response index of clover mulch was approximately 33–37% lower than fallow land at the beginning of the experiment in 1983 and 45–50% lower over the 40 years. N recovery efficiency values of winter wheat (94%), winter rye (66%) and summer barley (46%) increased within the 10th crop rotation compared to the beginning of the long-term experiment. ConclusionsCombining clover mulch as a green manure with mineral fertilizer has greater potential to improve NUE and crop productivity by increasing soil N availability. ImplicationsOur study highlights the importance of evaluating agronomic management practices in long-term field experiments to understand their sustainable effects.

Seed treatment with plant-defense elicitors decreases the abundance of ammonia oxidizers associated with winter wheat roots

Priming with elicitors, including phytohormones, is known to induce physiological changes in plants that affect resource allocation and nutrient uptake strategies. However, effects of these changes on belowground microbial communities, particularly those involved in nitrogen (N) transformations, remain poorly characterized. Here, we tested the hypothesis that treating seeds with elicitors would affect N-transforming communities associated to roots and rhizosphere, influencing soil N availability and thus plant performance. We measured the effects of treating winter wheat seeds with cis-jasmone, methyl jasmonate or methyl salicylate on plant traits and on the genetic potential for ammonia oxidation by ammonia-oxidizing bacteria (AOB) and archaea (AOA), the initial inorganic N transformation process resulting in N loss. Elicitors reduced the genetic potential for ammonia oxidation by AOB in root-associated microbial communities and increased traits reflecting N uptake in winter wheat. Proposed mechanisms include increased exploitative competition for ammonium, limiting substrate availability for microorganisms, and induced biological nitrification inhibition capacity actively suppressing ammonia oxidizers. There were minor effects on the composition of the AOB and AOA communities, but an indicator species analysis showed that several AOB and a few AOA genotypes were indicative of elicitor treatments. Seed treatment with elicitors may represent an overlooked strategy to minimize nitrification to mitigate N losses from arable soils.

Optimizing Phosphorus Application for Winter Wheat Production in the Coastal Saline Area

Phosphorous (P) fixation in saline soils is a concern worldwide. To investigate optimization strategies for P fertilizer application that improve P use efficiency (PUE) and crop yield in saline soil, in terms of P sources and rates, we conducted a two year field experiment in the coastal saline area of China to investigate the effects of P rates and sources, including superphosphate (SSP), monoammonium phosphate (MAP) and ammonium polyphosphate (APP) on yield, aboveground P uptake, agronomy efficiency (AEP), and soil available P of winter wheat (Triticum aestivum L.). Wheat yield, under the three P sources, increased with P rates and reached a plateau under 20 kg P ha−1 SSP,18 kg P ha−1 MAP, and 17 kg P ha−1 MAP, respectively. The application of SSP increased the wheat yield by 9–11% compared to MAP and APP. The aboveground P uptake of winter wheat under SSP was 14% and 13% higher than MAP and APP, respectively, under the optimal P application rate. The AEP under SSP was higher than the other two P sources under the same P rate. SSP increased the soil Ca2+ concentration by 20–42%, but decreased the Na+ concentration by 14–18% at the P rate of 26 kg P ha−1 in all soil layers, including 0–20, 20–40, 40–60 cm, compared to CK (0 kg P ha−1). The soil Olsen-P concentration under APP was higher than the other P sources. This study suggests that optimizing P sources and rates can improve wheat yield, PUE, and soil quality in the coastal saline soil.

Analysis of Nitrogen Uptake in Winter Wheat Using Sensor and Satellite Data for Site-Specific Fertilization

Sensor- and satellite-based determination of nitrogen uptake provides critical data in site-specific fertilization algorithms. Therefore, two basic noncontact measurement methods (sensor and satellite) were investigated in winter wheat, and their precision was evaluated in this study. Nitrogen uptake at four characteristic growth stages (BBCH 31, BBCH 39, BBCH 55, and BBCH 65) was determined using algorithms based on sensor and satellite data. As a reference, nitrogen uptake was determined using biomass samples in the laboratory (ground truth data). The precision of the tested methods was evaluated using statistical indicators (mean, median, minimum, maximum, and standard deviation) and correlation analyses between the nitrogen uptake of the ground truth data and that of the respective method. The results showed moderate to strong correlations with the nitrogen uptake of the ground truth data for both methods (R2 = 0.57–0.83). Both sensor and satellite data best represented nitrogen uptake in BBCH 39 and 55 (R2 = 0.63–0.83). In sum, there were only slight deviations in the absolute amount of nitrogen uptake (≤±15%). Clear deviations can be explained by external influences during measurement. Overall, the investigations showed that the nitrogen uptake could be appropriately determined as a data basis for site-specific fertilization systems using sensor and satellite data.

Digital image analysis estimates of biomass, carbon, and nitrogen uptake of winter cereal cover crops

Over-wintering cereal cover crops contribute to greater cropping system sustainability by reducing risk of erosion, adding carbon (C), and sequestering inorganic nitrogen (N) between fall harvest and spring planting of annual crops. Carbon and N pools can be measured by manual sampling and laboratory analysis of roots and shoots. However, this is expensive and unscalable to field levels. This study aimed to (1) determine relationships between shoot biomass and total biomass, C and N uptake of winter wheat (Triticum aestivumL.), cereal rye (Secale cerealeL.), and triticale (XTriticosecaleWittm.); and (2) develop models to estimate shoot biomass using green cover (%) from digital images. Shoot and root biomass, C, and N uptake of cover cropped fields were determined by destructive sampling within rectangular quadrats (97.8 × 20.3 cm) in fall 2011 prior to snowfall (58 fields) and spring 2012 prior to termination (30 fields). In addition, shoot biomass and digital images (top view of crop canopy taken at shoulder height) were collected in fall 2013 and spring 2012–2014 (266 quadrats) using four different cameras (Canon, Nikon, Apple iPhone, Motorola Droid) for a total of 589 images. Four approaches were evaluated to estimate green cover: (i) estimation from “Canopeo” software; (ii) RGB color space with a set cutoff; (iii) the Lab color space with fixed adjustment of the “a” channel per camera; and (iv) the Otsu thresholding method applied to the “a” channel of the Lab color space. Shoot biomass ranged from 37 to 2657 kg DM ha−1 and was linearly correlated with total biomass (R2 = 0.99), total C (R2 = 0.99), and total N (R2 = 0.92), independent of species or season. The Otsu method best estimated shoot biomass from green cover (R2 = 0.66; green cover ranging from 10 to 70%). This method also reduced differences among cameras and the influence of lighting conditions on green cover estimations. Exponential models for shoot biomass estimation from green cover (%) determined with the Otsu method had the highestR2 for cereal rye (R2 = 0.79), followed by triticale (R2 = 0.54), and wheat (R2 = 0.52). We conclude these models, combined with linear equations to predict total biomass, C, and N uptake from shoot biomass can be used to estimate the same from imagery. Additional research is needed to validate models across more locations, different growth stages, and to expand across a larger range of green coverage.

Arbuscular mycorrhizal fungi increase the bioavailability and wheat (Triticum aestivum L.) uptake of selenium in soil

The interaction between arbuscular mycorrhizal (AM) fungi and selenium (Se) bioavailability in rhizosphere soils of host plants is still unclear. Pot trials were conducted to investigate the effects of inoculation of AM fungi on Se uptake in winter wheat growing on selenite (Se (IV)) or selenate (Se (VI)) spiked soils (2.5 mg kg−1) and on Se bioavailability in the rhizosphere soils. Inoculation of Funneliformis mosseae (F.m) and Glomus versiforme (G.v) significantly (P < 0.05) increased concentration of available Se (SOL–Se or EXC–Se) in the rhizosphere soils by 30.21 %–189.19 % and 12.03 %–76.35 % in Se (IV)- or Se (VI)- spiked soils, and the effect of inoculatingF.m was better than G.v. Se content in winter wheat was significantly (P < 0.05) enhanced by 24.11–56.06 % and 20.27-56.49 % in Se (IV)- or Se (VI)- spiked soils inoculated with F.m and G.v. The present results also showed that Se availability in rhizosphere soils of wheat was apparently influenced by speciation of exogenous Se. In addition, correlation analysis showed that soil organic matter (SOM), dissolved organic carbon (DOC), easily extractable glomalin-related soil protein (EE-GRSP), fungi and actinomyces abundance were significantly positively correlated with available Se in the rhizosphere soils, while were negatively correlated with pH. The present study indicated that inoculation of AM fungi could increase Se bioavailability in the rhizosphere soils via influencing partial soil chemical properties including pH, SOM, DOC, EE-GRSP and microbial quantities, consequently enhancing Se uptake in winter wheat. This study can provide a theoretical basis for the study of AM fungi on Se biofortification of winter wheat.

Zinc fractions in soils and uptake in winter wheat as affected by repeated applications of zinc fertilizer

This field study was conducted to determine the effect of repeated zinc (Zn) applications at different rates on the concentrations and availability of different forms of Zn in the calcareous soil, in relationship to their contributions to Zn uptake by wheat. Plot-based field experiment was established in 2009 in a winter wheat-summer maize rotation. In each growing season of wheat and maize, six levels of Zn (0, 2.3, 5.7, 11.4, 22.7 and 34.1 kg Zn ha−1) as ZnSO4·7H2O were applied at planting. Following the harvest of the winter wheat in 2010, 2012, 2014 and 2016, soil samples (0−30 cm) from 5 selected Zn levels except 2.3 kg Zn ha-1 were collected and subjected to a sequential extraction to examine the concentrations of Zn fractions including water soluble plus exchangeable Zn (Ex-Zn) and Zn as bounded to carbonate (Car-Zn), manganese oxide (MnO-Zn), iron oxide (FeO-Zn), or organic matter (OM-Zn), and residual (Res-Zn). Stepwise multiple regression was used to identify the contributions of each soil Zn fraction to variation in crop Zn uptake. The results showed that repeated Zn fertilization over the multiple years increased concentrations of all soil Zn fractions. However, the percentage of each Zn fraction to total Zn varied with Zn inputs. Increasing Zn input increased the percentages of Ex-, Carb-, MnO- and FeO-Zn to soil total Zn, whereas reduced that of OM- and Res-Zn. The FeO-, Ex-, and Res-Zn were selected by the stepwise regression procedure as the significant variables explaining the variation in wheat Zn uptake, with partial adjusted coefficient (R2) of 0.81, 0.03 and 0.04, respectively. Crop Zn uptake also increased linearly with soil DTPA-extractable Zn and reached a maximum at DTPA-extractable Zn concentration of 12 mg kg−1. In conclusion, repeated Zn fertilization increased the concentrations of Zn in exchangeable and adsorption forms, which in turn resulted in higher uptake of Zn by winter wheat. DTPA-extractable Zn is a good indicator of Zn availability for wheat. Fraction of FeO-Zn is an important Zn retention pool for determining crop uptake on the calcareous soil. These results emphasize the importance of Zn retention capacity in response to repeated application of Zn fertilizer.

Effects of sulfate on cadmium uptake in wheat grown in paddy soil - pot experiment

Rice-wheat rotation is common in China. Cadmium (Cd) and sulfur (S) are added to rice fields through various activities. The sulfur amendment has been recommended to control the uptake of Cd in rice. However, the effect of S on Cd uptake in winter wheat cultivated in paddy soil is rarely reported. A greenhouse pot experiment including two Cd levels (0, 10 mg Cd/kg, as CdCl&lt;sub&gt;2&lt;/sub&gt;) combined with three S rates (0, 30, 60 mg S/kg, as Na&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt;) was performed to investigate the effect of S application on uptake and allocation of Cd in wheat cultivated in paddy soil. Cadmium concentrations in wheat grain significantly (P &amp;lt; 0.05) increased by 37% at 30 mg S/kg, and the percentage of Cd allocation to grain significantly (P &amp;lt; 0.05) increased by 7% at 60 mg S/kg compared with non-S addition treatment when wheat was grown in Cd-added soil. For the low Cd soil, a similar trend was seen, but Cd increases were insignificant for grain while significant (P &amp;lt; 0.05) for root at 60 mg S/kg. In conclusion, S fertiliser may promote Cd accumulation in wheat grain and should be considered when it is used for wheat in paddy soils.

Yield, content and nutrient uptake by winter wheat and spring barley in response to applications of digestate, cattle slurry and NPK mineral fertilizers

ABSTRACT Digestate represents an alternative source of nutrients for crops in sustainable agriculture. We aimed to evaluate the effects of digestate fertilization on grain (GY) and straw yield (SY) and nutrient content and uptake in winter wheat (WW) and spring barley (SB). The study duration was from 2012 to 2016, with the following crop rotation: WW/WW/SB/WW. Every year, the same fertilizers were applied to each respective plot: control, digestate, digestate + straw, cattle slurry and mineral NPK fertilizer. Significantly higher GY and SY were noted after fertilizer application each year compared to the non-fertilized control. The average effect of the fertilizers on GY of WW was control < NPK ≤ digestate + straw ≤ cattle slurry ≤ digestate. Fertilizer application also increased N, S, Na, Zn and Fe content in the grains, especially when digestate was used as fertilizer. However, in non-fertilized plants (control), only the K content increased in the grains, although the uptake of K is positively correlated with GY. Our results show that digestate can be used not only as a replacement for cattle slurry but also as an alternative fertilizer, which, under certain soil conditions, is more effective than NPK fertilizer.

Positive effects of free air CO2 enrichment on N remobilization and post-anthesis N uptake in winter wheat

Elevated atmospheric CO2 concentration (e[CO2]) often increases cereal yield, but can also decrease vegetative and grain tissue nitrogen (N) concentration that might affect future food and feed quality. However, data about CO2 x N interactions on key processes determining grain N yield and concentration, which are remobilization of vegetative N taken up before anthesis (Nrem) and post-anthesis N uptake (Nabs), are scarce. Therefore, a two-year Free Air CO2 Enrichment (FACE) experiment was conducted with winter wheat grown under two CO2 (˜393 and 600 ppm) and three N levels (severe deficiency with N nutrition index (NNI) of 0.4, adequate with NNI of 0.8 and excess with NNI of 1.1).e[CO2] did not influence the allometric relation between aboveground N concentration and biomass up to anthesis. At anthesis, e[CO2] increased N acquisition of stem and ear, but not of leaf. Correspondingly, e[CO2] increased Nrem of stem and chaff. Moreover, e[CO2] enhanced the efficiency of Nrem of stem and aboveground plant in the first year, indicating increased N mobilization from vegetative tissue. Nabs tended to be increased by e[CO2], especially in the second year. Finally, e[CO2] increased grain N yield (8 to 12%), N use efficiency (13 to 18%) and N uptake efficiency (10 to 12%). Grain N concentration was slightly decreased by e[CO2] in both years (-1 to -6%), while grain N concentration was considerably larger (9 to 19%) in the second year compared to the first year. There was a strong linear relation between grain N yield and grain number (r2 = 0.98) that was not influenced by e[CO2], suggesting grain number as important factor determining the grain N yield increase under e[CO2]. Grain N concentration was more strongly affected by e[CO2] than mean N content per grain.

Remotely Estimating Aerial N Uptake in Winter Wheat Using Red-Edge Area Index From Multi-Angular Hyperspectral Data.

Remote sensing techniques can be efficient for non-destructive, rapid detection of wheat nitrogen (N) nutrient status. In the paper, we examined the relationships of canopy multi-angular data with aerial N uptake of winter wheat (Triticum aestivum L.) across different growing seasons, locations, years, wheat varieties, and N application rates. Seventeen vegetation indices (VIs) selected from the literature were measured for the stability in estimating aerial N uptake of wheat under 13 view zenith angles (VZAs) in the solar principal plane (SPP). In total, the back-scatter angles showed better VI behavior than the forward-scatter angles. The correlation coefficient of VIs with aerial N uptake increased with decreasing VZAs. The best linear relationship was integrated with the optimized common indices DIDA and DDn to examine dynamic changes in aerial N uptake; this led to coefficients of determination (R2) of 0.769 and 0.760 at the −10° viewing angle. Our novel area index, designed the modified right-side peak area index (mRPA), was developed in accordance with exploration of the spectral area calculation and red-edge feature using the equation: mRPA = (R760/R600)1/2 × (R760-R718). Investigating the predictive accuracy of mRPA for aerial N uptake across VZAs demonstrated that the best performance was at −10° [R2 = 0.804, p < 0.001, root mean square error (RMSE) = 3.615] and that the effect was relatively similar between −20° to +10° (R2 = 0.782, p < 0.001, RMSE = 3.805). This leads us to construct a simple model under wide-angle combinations so as to improve the field operation simplicity and applicability. Fitting independent datasets to the models resulted in relative error (RE, %) values of 12.6, 14.1, and 14.9% between estimated and measured aerial N uptake for mRPA, DIDA, and DDn across the range of −20° to +10°, respectively, further confirming the superior test performance of the mRPA index. These results illustrate that the novel index mRPA represents a more accurate assessment of plant N status, which is beneficial for guiding N management in winter wheat.

Effect of experimental warming on nitrogen uptake by winter wheat under conventional tillage versus no-till systems

Despite the perceived importance of nitrogen (N) to growth and production of wheat, few studies have attempted to examine the effect of warming on wheat N uptake or its preference for NO3−-N vs. NH4+-N, especially under different tillage systems. In the North China Plain, an experimental warming (2 °C increase in soil during the jointing stage) study was conducted using in situ 15N labeling under till and no-till systems. We aimed to investigate the uptake of NO3−-N, NH4+-N, and glycine-N by winter wheat. Warming strongly enhanced wheat biomass (14.7% and 13.2% for till and no-till, respectively) and N content in biomass (11.1 and 7.4 g N m−2 for till and no-till, respectively). Total N uptake rates increased by 47% and 40% under till and no-till treatments, respectively. Warming changed the uptake pattern for the three N forms by significantly increasing the contributions of NO3--N by 16% and glycine-derived N by 5%, while decreasing the contribution of NH4+-N by 20% under the two tillage systems, on average. Collectively, high soil temperatures accelerated N uptake in winter wheat and improved the preferential contribution of NO3−-N and glycine-N due to the increase in soil glycine and NO3− content. Our findings suggest that enhanced N uptake improved growth of wheat and could reduce N losses through increased uptake of NO3− under till and no-till systems in the North China Plain under the warmer conditions that are likely in future.

Root development and water uptake in winter wheat under different irrigation methods and scheduling for North China

A field experiment was conducted on winter wheat (Triticum aestivum L.) during 2013–2014 and 2014–2015 to study the root distribution profile and soil water dynamics under the main currently used irrigation methods in the North China Plain (NCP). The WinRHIZO system and the HYDRUS-1D model were used to identify a promising irrigation schedule. In this two-factor experiment, three irrigation methods, i.e., sprinkler irrigation (SI), surface drip irrigation (SDI) and surface flooding (SF), were scheduled to irrigate the crop as soon as the soil water content decreased to 70%, 60% and 50% of the field capacity. The results showed that both the irrigation method and irrigation schedule influenced root development, the profile root distribution pattern and the profile root water uptake (RWU). The soil surface temperature fluctuated very rapidly depending on the irrigation method and scheduling system used, whereas profile soil temperature fluctuations became more consistent with depth. The RWU was higher in the upper soil layer (0–60cm) for all irrigation methods for frequently irrigated treatments, and the maximum was observed in SDI compared to SI and SF due to the higher root length density (RLD) in the top soil under SDI. On the other hand, the RWU was higher in SF at a deep soil profile below 60cm, where it had a higher RLD compared to that of SI and SDI. SDI at 60% of FC not only improved water uptake but also resulted in better water productivity and produced the highest grain yield (9.53t/ha). The simulated RWU and soil water dynamics presented in this paper will be helpful to improve winter wheat production in the NCP and can be used as a reference for further research on water management practices.

Contrasting effects of biochar on N2O emission and N uptake at different N fertilizer levels on a temperate sandy loam

Biochar has been frequently suggested as an amendment to improve soil quality and mitigate climate change. To investigate the optimal management of nitrogen (N) fertilization, we examined the combined effect of biochar and N fertilizer on plant N uptake and N2O emissions in a cereal rotation system in a randomized two-factorial field experiment on a sandy loam soil in Brandenburg, Germany. The biochar treatment received 10Mgha−1 wood-derived biochar in September 2012. Four levels of N fertilizer, corresponding to 0, 50%, 100%, 130% of the recommended fertilizer level, were applied in winter wheat (Triticum aestivum L.)) and winter rye (Secale cereal L.) in 2013 and 2014 followed by the catch crop oil radish (Raphanus sativus L. var. oleiformis). Biomass and N uptake of winter wheat and winter rye were significantly affected by the level of N fertilizer but not by biochar. For N uptake of oil radish an interaction effect was observed for biochar and N fertilizer. Without applied fertilizer, 39% higher N uptake was found in the presence of biochar, accompanied by higher soil NH4+ content and elevated cumulative CO2 emissions. At 130% of the recommended fertilizer level, 16% lower N uptake and lower cumulative N2O emissions were found in the biochar-mediated treatment. No significant change in abundance of microbial groups and nosZ gene were observed. Our results highlight that biochar can have a greenhouse gas mitigation effect at high levels of N supply and may stimulate nutrient uptake when no N is supplied.

Remotely assessing leaf N uptake in winter wheat based on canopy hyperspectral red-edge absorption

Abstract Remote sensing is a rapid, non-destructive method for assessing crop nitrogen (N) status. In this research, we investigated the quantitative relationship between leaf N uptake and ground-based canopy hyperspectral reflectance in winter wheat (Triticum aestivum L.). We conducted field experiments over four years at different sites (Xinyang, Zhengzhou and Shangshui) in Henan, China using different N application rates, growth stages and wheat cultivars and developed a novel spectral index with improved predictive capacity for leaf N uptake estimation. Sixteen vegetation indices in the publications were examined for their reliability in monitoring leaf N uptake in winter wheat. Linear regression was integrated with optimized common indices DIDA and SDr/SDb to investigate the dynamic nature of leaf N uptake, which resulted in coefficients of determination (R2) of 0.816 and 0.807 and root mean square error (RMSE) of 1.707 and 1.767, respectively. Our novel area index, designated shifting red-edge absorption area (sREA), was constructed according to analysis of the red-edge characteristics and area-based algorithm with the formula: s R E A = 1 2 × ( R 680 + Δ λ − R 680 ) × Δ λ , Δ λ = 320 × D 725 + 140 × D 756 − 140 × D 680 7 × D 700 + 4 × D 725 . This index is highly correlated with leaf N uptake (highest R2 = 0.831; lowest RMSE = 1.556). On the whole, calculation of R2 and RMSE confirmed that sREA prediction models were better than optimized common indices for 16 out of 17 datasets across growing seasons, sites, N rates, cultivars and stages. Fitting independent data to the equations resulted in RE values of 19.6%, 18.8%, 17.6% and 16.2% between measured and estimated leaf N uptake values for RSI(D740, D522), SDr/SDb, DIDA and sREA, respectively, further confirming the superior test performance of sREA. These models can therefore be used to accurately predict leaf N uptake in winter wheat. The novel index sREA is superior for evaluating leaf N status on a regional scale in heterogeneous fields under variable climatic conditions.

Remote estimation of above ground nitrogen uptake during vegetative growth in winter wheat using hyperspectral red-edge ratio data

Hyperspectral sensing can provide an effective means for fast and non-destructive estimation of crop above ground nitrogen (N) status. In this study, quantitative correlations between above ground N uptake and ground-based canopy hyperspectral reflectance in winter wheat (Triticum aestivum L.) were investigated. Field experiments were conducted over four years at different sites (Xinyang, Zhengzhou and Shangshui) in Henan, China. Different N rates, planting densities, basal/topdressing N ratios and wheat cultivars were tested, and a novel spectral index was developed with improved predictive capacity for above ground N uptake estimation. Linear regression was integrated with previously reported CIred-edge3 and MTCI indices to investigate the dynamic nature of above ground N uptake, which resulted in coefficients (R2) of 0.761 and 0.760, and square error values (SE) of 4.527 and 4.534, respectively. The optimum combination of SR (759,742) and ND (759,742) were derived from two waveband-based algorithms that corresponded to red-edge ratio spectral indices. R2 for the novel SR and ND models was 0.794 and 0.788, respectively, confirming the superiority of the SR index. The modified red-edge ratio (mRER) was constructed based on the ratio vegetation index (RVI) that was derived from the third waveband (λ3) using the formula (R759−1.8×R419)/(R742−1.8×R419). This novel index was highly correlated with above ground N uptake and had the highest R2 (0.813) and lowest root mean square error (4.005) of all models tested. Fitting independent data to the equations resulted in RMSE values of 21.9, 20.4, 18.6 and 16.4% between measured and estimated above ground N uptake values for CIred-edge3, MTCI, SR(759,742) and mRER, respectively, further indicating a superior fit and better performance for mRER. These models can therefore accurately estimate above ground N uptake in winter wheat, and the novel mRER index is superior for estimating above ground N uptake on a regional scale in heterogeneous fields under variable climatic conditions.

Comparing hyperspectral index optimization algorithms to estimate aerial N uptake using multi-temporal winter wheat datasets from contrasting climatic and geographic zones in China and Germany

Timely and accurate quantification of aerial nitrogen (N) uptake in crops is important for the calculation of regional N balances and the study of the N budget in agro-ecosystems. Experiments in the present study were conducted from 2007 to 2011 to remotely estimate the aerial N uptake of diverse winter wheat cultivars grown in contrasting climatic and geographic zones in China and Germany. Potentials and limitations of hyperspectral indices obtained from (i) optimized algorithms and (ii) 15 representative indices reported in the literature were tested for stability in estimating the aerial N uptake of winter wheat across different growth stages, cultivars, sites and years. Growth stage, cultivar, N application rates, site and year greatly influenced the relationship between hyperspectral indices and aerial N uptake. The optimized hyperspectral indices generally had more robust aerial N uptake prediction abilities than the published indices. Compared with the algorithms of all possible two-band combinations and red-edge position-based algorithms, area-based algorithms for a three-band optimized combination were more stable in deriving the aerial N uptake of winter wheat. Optimized algorithms can potentially be implemented in future aerial N uptake monitoring by hyperspectral sensing.

A New Method to Determine Central Wavelength and Optimal Bandwidth for Predicting Plant Nitrogen Uptake in Winter Wheat

Plant nitrogen (N) uptake is a good indicator of crop N status. In this study, a new method was designed to determine the central wavelength, optimal bandwidth and vegetation indices for predicting plant N uptake (g N m−2) in winter wheat (Triticum aestivum L.). The data were collected from the ground-based hyperspectral reflectance measurements in eight field experiments on winter wheat of different years, eco-sites, varieties, N rates, sowing dates, and densities. The plant N uptake index (PNUI) based on NDVI of 807 nm combined with 736 nm was selected as the optimal vegetation index, and a linear model was developed with R2 of 0.870 and RMSE of 1.546 g N m−2 for calibration, and R2 of 0.834, RMSE of 1.316 g N m−2, slope of 0.934, and intercept of 0.001 for validation. Then, the effect of the bandwidth of central wavelengths on model performance was determined based on the interaction between central wavelength and bandwidth expansion. The results indicated that the optimal bandwidth varies with the changes of the central wavelength and with the interaction between the two bands in one vegetation index. These findings are important for prediction and diagnosis of plant N uptake more precise and accurate in crop management.

Comparison and Intercalibration of Vegetation Indices from Different Sensors for Monitoring Above-Ground Plant Nitrogen Uptake in Winter Wheat

Various sensors have been used to obtain the canopy spectral reflectance for monitoring above-ground plant nitrogen (N) uptake in winter wheat. Comparison and intercalibration of spectral reflectance and vegetation indices derived from different sensors are important for multi-sensor data fusion and utilization. In this study, the spectral reflectance and its derived vegetation indices from three ground-based sensors (ASD Field Spec Pro spectrometer, CropScan MSR 16 and GreenSeeker RT 100) in six winter wheat field experiments were compared. Then, the best sensor (ASD) and its normalized difference vegetation index (NDVI (807, 736)) for estimating above-ground plant N uptake were determined (R2 of 0.885 and RMSE of 1.440 g·N·m−2 for model calibration). In order to better utilize the spectral reflectance from the three sensors, intercalibration models for vegetation indices based on different sensors were developed. The results indicated that the vegetation indices from different sensors could be intercalibrated, which should promote application of data fusion and make monitoring of above-ground plant N uptake more precise and accurate.

NITROGEN FERTILIZER MANAGEMENT FOR IMPROVED GRAIN QUALITY AND YIELD IN WINTER WHEAT IN OKLAHOMA

From 2002 to date, a long-term field experiment has been conducted at Lake Carl Blackwell, Oklahoma, with different rates and times of nitrogen (N) fertilizer application to determine their effect on grain yield, protein and N uptake of winter wheat. Trend analysis for N rates (0, 50, 100, 150 and 200 kg N ha−1) and orthogonal contrasts for different application times (pre-plant, top-dressed in February and March) were performed. With increasing fertilizer N, wheat grain yield and protein content increased from 2110 kg ha−1 to 6783 kg ha−1 and from 8.96 to 17.19%, respectively. For grain yield, protein, and N use efficiency, split applications of N fertilizer were much more efficient than applying all N pre-plant. Large differences in grain yields were noted for different years at the same N rate (range exceeded 5.0 Mg ha−1) and that illustrated the need for making within-year-specific N rate recommendations.