Liangliang Jia

Use of Digital Camera to Assess Nitrogen Status of Winter Wheat in the Northern China Plain

Abstract The most widely used methods to assess the nitrogen (N) status of winter wheat (Triticum aestivum L.) are the determination of plant total N by combustion, the testing of nitrate in the leaf tissue and the use of SPAD readings. However, due to their labor requirements or high costs these methods can hardly be applied to the huge wheat growing areas of the Northern China Plain. This study therefore examined an alternative method to measure the N status of wheat by using a digital camera to record the visible green light reflected from the plant canopy. The experiment was conducted near Beijing in a multi-factorial field trial with three levels of N. The intensity of green light reflected from the wheat canopy was compared to the total N concentration, to the nitrate concentration of the basal stem, and to the SPAD readings of leaves. The results show significant inverse relationships between greenness intensity, canopy total N, and SPAD readings at booting and flowering. At booting, sap nitrate <2000 mg L−1 was inversely related to greenness intensity and to sap nitrate concentration in the basal stem. At sap nitrate ˜2000 mg L−1, the greenness intensity reached a plateau. At booting and flowering, significant inverse relationships between greenness intensity and shoot biomass were found. The results show the potential of the new method to assess the N status of winter wheat.

Pursuing sustainable productivity with millions of smallholder farmers

Sustainably feeding a growing population is a grand challenge, and one that is particularly difficult in regions that are dominated by smallholder farming. Despite local successes, mobilizing vast smallholder communities with science- and evidence-based management practices to simultaneously address production and pollution problems has been infeasible. Here we report the outcome of concerted efforts in engaging millions of Chinese smallholder farmers to adopt enhanced management practices for greater yield and environmental performance. First, we conducted field trials across China’s major agroecological zones to develop locally applicable recommendations using a comprehensive decision-support program. Engaging farmers to adopt those recommendations involved the collaboration of a core network of 1,152 researchers with numerous extension agents and agribusiness personnel. From 2005 to 2015, about 20.9 million farmers in 452 counties adopted enhanced management practices in fields with a total of 37.7 million cumulative hectares over the years. Average yields (maize, rice and wheat) increased by 10.8–11.5%, generating a net grain output of 33 million tonnes (Mt). At the same time, application of nitrogen decreased by 14.7–18.1%, saving 1.2 Mt of nitrogen fertilizers. The increased grain output and decreased nitrogen fertilizer use were equivalent to US

Optimum Nitrogen Fertilization of Winter Wheat Based on Color Digital Camera Images

12.2 billion. Estimated reactive nitrogen losses averaged 4.5–4.7 kg nitrogen per Megagram (Mg) with the intervention compared to 6.0–6.4 kg nitrogen per Mg without. Greenhouse gas emissions were 328 kg, 812 kg and 434 kg CO2 equivalent per Mg of maize, rice and wheat produced, respectively, compared to 422 kg, 941 kg and 549 kg CO2 equivalent per Mg without the intervention. On the basis of a large-scale survey (8.6 million farmer participants) and scenario analyses, we further demonstrate the potential impacts of implementing the enhanced management practices on China’s food security and sustainability outlook.

Harvesting more grain zinc of wheat for human health

Abstract Site‐specific nitrogen (N) fertilizer management based on soil Nmin (soil mineral N) and the plant N status (sap nitrate analysis and chlorophyll meter (SPAD) reading test) has been shown to be effective in decreasing excessive N inputs for winter wheat in the North China Plain, but the multiple sampling of soil and plants in individual fields is too time‐consuming and costly for producers and farmers. In this study, a color digital camera was used to capture wheat canopy images at a specific growth stage to assess N needs. Treatments included a farmers N treatment (typical farmer practice), an optimum N treatment (N application based on soil–plant testing), and four treatments without N (one to four cropping seasons without any N fertilizer input). Digital images were analyzed to get red, green, and blue color‐band intensities for each treatment. Normalized intensities of the red, green, and blue color bands were well correlated with soil Nmin, SPAD readings, sap nitrate concentration, and total N concentration of winter wheat. This research indicated the potential of using a digital camera as a tool combined with an improved Nmin method to make N fertilizer recommendations for larger fields.

Using High-Resolution Satellite Imaging to Evaluate Nitrogen Status of Winter Wheat

Increasing grain zinc (Zn) concentration of cereals for minimizing Zn malnutrition in two billion people represents an important global humanitarian challenge. Grain Zn in field-grown wheat at the global scale ranges from 20.4 to 30.5 mg kg−1, showing a solid gap to the biofortification target for human health (40 mg kg−1). Through a group of field experiments, we found that the low grain Zn was not closely linked to historical replacements of varieties during the Green Revolution, but greatly aggravated by phosphorus (P) overuse or insufficient nitrogen (N) application. We also conducted a total of 320-pair plots field experiments and found an average increase of 10.5 mg kg−1 by foliar Zn application. We conclude that an integrated strategy, including not only Zn-responsive genotypes, but of a similar importance, Zn application and field N and P management, are required to harvest more grain Zn and meanwhile ensure better yield in wheat-dominant areas.

Nitrogen Status Estimation of Winter Wheat by Using an IKONOS Satellite Image in the North China Plain

ABSTRACT Nitrogen (N) applications often increase crop yields significantly, but N needs vary spatially across fields and landscapes. The color of the wheat plant is sensitive to N status and may provide a means to accurately predict N fertilizer rates matching spatial variability. Previous researches have reported that remote sensing may contribute to N management decisions by collecting spatially dense information. The objective of this study was to determine the feasibility of using high-resolution satellite imaging for evaluating N status of winter wheat in the North China Plain. High-resolution images from a QuickBird satellite were taken on April 1, 2002 at booting stage of wheat with multi-spectral wavelengths (blue, green, red, and near-infrared). Correlation analyses indicated that all the broadband indices derived from the satellite images correlated well with sap nitrate concentration, SPAD readings, total N concentration, and aboveground biomass. The individual band reflectance values R, G, B correlated well with sap nitrate concentration, SPAD readings, total N concentration, and aboveground biomass. These results demonstrated the potential of using new generation high-resolution satellite imaging for large area wheat N status diagnosis.

Hyperspactral data analysis of nitrogen fertilization effects on winter wheat using spectrometer in North China Plain

The objective of this study was to determine relationship between high resolution satellite image and wheat N status, and develop a methodology to predict wheat N status in the farmers’ fields. Field experiment with 5 different N rates was conducted in Huimin County in the North China Plain, and farmers’ fields in 3 separated sites were selected as validation plots. The IKONOS image covering all research sites was obtained at shooting stage in 2006. The results showed that single band reflectance of NIR, Red and Green and vegetation indices of NDVI, GNDVI, RVI and OSAVI all well correlated with wheat N status parameters. Field validation results indicated that the prediction models using OSAVI performed well in predicting N uptake in the farmers’ fields (R2 = 0.735). We conclude that high resolution satellite images like IKONOS are useful tools in N fertilization management in the North China Plain.

COMPARSION OF MULTISPECTRAL REFLECTANCE WITH DIGITAL COLOR IMAGE IN ASSESSING THE WINTER WHEAT NITROGEN STATUS

This article presents results from hyperspectral analysis for winter wheat (Tricitum Aestivum L.) in the North China Plain during a research study in 2006. In the first part the focus was set on canopy spectral reflectance during the vegetation period under different N supplies. Four different experiments with variable N-inputs and winter wheat cultivars were set up in the study area of Huimin County, Shandong Province. Spectral reflectance data and agronomic data like biomass, plant height, N-uptake and LAI were collected at different phenological stages. In the second part of the study a spectral and agronomic library was set up. For this purpose, spectral reflectance was related to agronomic parameters. The results indicated significant difference in spectra characteristics, cultivars and N-inputs. Vegetation indices like NDVI, HNDVI, RVI, HVI, OSAVI and MCARI2 had the best performance in estimating agronomic parameters among the vegetation indices evaluated.

Deriving winter wheat characteristics from combined radar and hyperspectral data analysis

Previous researches have shown that the digital image color intensity could reflect the crops N status, but there is little information about the comparision of spectrum reflectance in the visible bands with the digital imagery color intensities. A field experiment was conducted to compare the wheat canopy reflectance at visible bands (400-700 nm) at shooting stage with near ground digital image to detect N deficiencies. Single color bands of R, G, B and ratio indices of G/R, G/B, R/B, R/(R+G+B), G/(R+G+B) and B/(R+G+B), which derived from digital image and spectral measurments, were regressed with wheat N status. The R, G, G/B, R/B, R/(R+G+B) and G/(R+G+B) all had negative correlations, while the G/R and B/(R+G+B) indices had positive correlations, with plant N status. For the B band, the digital image analysis data got positive correlations while the spectral measurements got negative correlations. With higher correlation coefficient than other indices, the R/(R+G+B) was the best index in this research. Considering the easiness of getting digital images and the accurate prediction of crops N status, the digital image analysis method seems to be a better way for in field plant N status evaluation.

Evaluating hyperspectral vegetation indices for estimating nitrogen concentration of winter wheat at different growth stages

The main objective of this study is to derive plant nitrogen (N) status and aboveground biomass via satellite remote sensing. To understand canopy spectral reflectance, the focus of the first part was set on the analysis of spectral signatures of winter wheat during its vegetation period under different N treatments. Spectral reflectance at different phenological stages, measured by a spectroradiometer (ASD HandHeld), is related to agronomy parameters like plant N, aboveground biomass and leaf area index (LAI). For this purpose, an extensive field survey was carried out in Huimin County in the North China Plain. For detection of plant N status of winter wheat and biomass on regional scale, hyperspectral (EO-1 Hyperion) and radar (Envisat ASAR) remote sensing data were obtained. First results of preprocessing of remote sensing data are presented in this contribution.