C. Bélec

A comparison of crop data measured by two commercial sensors for variable-rate nitrogen application

Nitrogen (N) fertilizer rates applied spatially according to crop requirements can improve the efficiency of N use. The study compares the performance of two commercial sensors, the Yara N-Sensor/FieldScan (Yara International ASA, Germany) and the GreenSeeker (NTech Industries Inc., Ukiah, California, USA), for assessing the status of N in spring wheat (Triticum aestivum L.) and corn (Zea mays L.). Four experiments were conducted at different locations in Quebec and Ontario, Canada. The normalized difference vegetation index (NDVI) was determined with the two sensors at specific growth stages. The NDVI values derived from Yara N-Sensor/FieldScan correlated with those from GreenSeeker, but only at the early growth stages, where the NDVI values varied from 0.2 to 0.6. Both sensors were capable of describing the N condition of the crop or variation in the stand, but each sensor had its own sensitivity characteristics. It follows that the algorithms developed with one sensor for variable-rate N application cannot be transferred directly to another sensor. The Yara N-Sensor/FieldScan views the crop at an oblique angle over the rows and detects more biomass per unit of soil surface compared to the GreenSeeker with its nadir (top-down) view of the crop. The Yara N-Sensor/FieldScan should be used before growth stage V5 for corn during the season if NDVI is used to derive crop N requirements. GreenSeeker performed well where NDVI values were >0.5. However, unlike GreenSeeker, the Yara N-Sensor/FieldScan can also record spectral information from wavebands other than red and near infrared, and more vegetation indices can be derived that might relate better to N status than NDVI.

Evaluation of the Dualex for the Assessment of Corn Nitrogen Status

ABSTRACT The Dualex is a new leaf-clip instrument that can be used to monitor corn nitrogen (N) status. It is based on the measurement of polyphenolics (Phen), which are secondary metabolites affected by stress factors. The purpose of this study was to compare Dualex to SPAD (chlorophyll meter), the latter having been used for several years in monitoring crop N status. As well, the interest of combining Dualex and SPAD information in Chl/DUAD (ratio of SPAD to Dualex reading on adaxial side), Chl/DUAB (ratio of SPAD to Dualex reading on abaxial side), and Chl/Phen (ratio of SPAD to the sum of DUAD and DUAB) ratios were considered. Significantly positive and negative correlations with corn leaf N concentration were found for SPAD and Dualex, respectively. Successful N status diagnosis could be achieved with either Dualex or SPAD for corn within 21 days after topdressing while the Dualex lost sensitivity at later stages. Dualex measurements could be limited to leaves abaxial side or adaxial side, instead of adaxial + abaxial sides, with no inconvenience. Among all parameters considered, the combined ratios with SPAD (Chl) and Dualex readings, Chl/DUAD, Chl/DUAB, and Chl/Phen were strongly related to applied N dose at all samplings dates, and found the most sensitive and robust through the season.

PERFORMANCE OF DUALEX IN SPRING WHEAT FOR CROP NITROGEN STATUS ASSESSMENT, YIELD PREDICTION AND ESTIMATION OF SOIL NITRATE CONTENT

Dualex and SPAD are devices developed for the purpose of testing crop nitrogen (N) status. These instruments were used in a wheat experiment in order to compare their respective performance in assessing leaf nitrogen (N) concentration, response to N topdressing application, soil nitrate (NO3)-N levels and in predicting grain yield. The experiment included different N rates in 2005 and 2006 in the Montérégie region of Quebec, Canada. Dualex readings correlated negatively with SPAD readings, leaf N concentration, soil NO3-N content and wheat grain yield. SPAD alone and the ratio of SPAD to Dualex measurements (Chl/Phen) were linearly related to N application rate but no effect of N application rate was found for individual Dualex parameters. However, both SPAD and Dualex readings were affected by year effects. The Dualex was also capable of indirect evaluation of in-season soil NO3-N accumulation and the prediction of wheat yield, but more so as Chl/Phen.

Influence of nitrogen fertilization on yield, hollow stem incidence and sap nitrate concentration in broccoli

This study, spanning 2 yr at two different sites, compared the effects of nitrogen fertilization on broccoli yield and quality in relation to the influence of site and production season. This research also evaluated the potential use of measuring nitrate in petiole extracts to determine broccoli nitrogen requirements when making a second fertilizer application 5 wk after transplant. Treatments consisted of factorial combinations of three nitrogen fertilization rates at transplant (Nmin, 50-Nmin and 100-Nmin kg N ha–1, where Nmin was the soil nitrate concentration) and four nitrogen fertilization rates 5 wk after transplant (0, 50, 100 and 150 kg N ha–1). The marketable yield of broccoli increased with the rate of nitrogen application. Hollow stem incidence showed the same trend as yield, and was greatest when high levels of nitrogen were applied 5 wk after transplant. Interactions between the 5-wk nitrogen application and production year, as well as growing site were significant. The nitrate content of th...

Fuzzy logic approach for spatially variable nitrogen fertilization of corn based on soil, crop and precipitation information

A fuzzy Inference System (FIS) was developed to generate recommendations for spatially variable applications of nitrogen (N) fertilizer using soil, plant and precipitation information. Experiments were conducted over three seasons (2005-2007) to assess the effects of soil electrical conductivity (ECa), nitrogen sufficiency index (NSI), and precipitations received in the vicinity of N fertilizers application, on response to N measured at mid-season growth. Another experiment was conducted in 2010 to understand the effect of water supply (WS) on response to N, using a spatially variable irrigation set-up. Better responses to N were observed in the case of high ECa, low NSI and high WS. In the opposite cases (low ECa, high NSI or low WS), nitrogen fertilizer rates can be reduced. Using fuzzy logic, expert knowledge was formalized as a set of rules involving ECa, NSI and cumulative precipitations to estimate economically optimal N rates (EONR).