Using Relative Chlorophyll Meter Values to Determine Nitrogen Application Rates for Corn

Abstract

Determining specific N fertilization rates to achieve optimal return is difficult. Crop N stress sensing uses the plant as an indicator of N fertilization need and has potential to improve N management. However, for making N rate decisions, a calibrated relationship between measured N stress and optimum N rate is required. Corn (Zea mays L.) plant N stress was determined with a chlorophyll meter (CM) at 102 site-years of N rate trials conducted from 1999-2005 with corn following soybean [Glycine max (L.) Merr.] (SC) and continuous corn (CC). Normalizing CM readings to relative chlorophyll meter (RCM) values reduced variation and improved the calibration of N stress with the nitrogen rate difference (ND) from the economic optimum nitrogen rate (EONR). With SC the adjusted R 2 (adjR 2 ) was 0.53 for CM readings and 0.73 for RCM values, and with CC the adjR 2 was 0.57 for CM readings and 0.76 for RCM values. The same statistically significant (P , 0.001) relationship between RCM values and ND was found for both SC and CC, indicating RCM critical values of 0.97 and 0.98, respectively. This indicates the same calibration for N rate determination based on RCM values can be used for both rotations. Evaluation of RCM values at multiple corn growth stages indicated the same relationship to ND at the fifteenth leaf and silking growth stages, suggesting a period of time during mid-to-late vegetative growth to collect CM readings, and make in-season N rate decisions and applications. The calibration of RCM values to the rate differential from optimum N can be used by producers to determine inseason N applications for corn across varying production conditions.

<b>Relative chlorophyll contents in the evaluation of the nutritional status of nitrogen from xaraes palisade grass and determination of critical nitrogen sufficiency index

“…However, the crops where such rates were detected are high Nrequiring crops, such as corn (Hawkins et al, 2007) and rice (Hussain et al, 2000). These rates are the first to be reported in the literature for tropical grasses.…”

“…When NSI reaches the plateau, denominated critical nitrogen sufficiency index (cNSI), no additional response to production is expected (Samborski et al, 2009). According to Samborski et al (2009), cNSI ranges between 0.71 and 0.99 and has to be established for different crops (Esfahani et al, 2008;Hawkins et al, 2007;Maia et al, 2012), requiring its establishment for each crop and even for its varieties (Hussain et al, 2000). However, such information is not available for tropical grasses and the calculation of cNSI for forage grasses will be performed by chlorophyll meter so that nitrogen use in the fertilization of pastures could become more efficient.…”

Strengths and Limitations of Nitrogen Rate Recommendations for Corn and Opportunities for Improvement

“…The latter application is of use mainly when manure N is part of the N supply, creating a significant proportion of fields where the correct decision is "no additional N needed". Systems for making N rate decisions based on chlorophyll meter readings were later developed by Scharf et al (2006a), Hawkins et al (2007), and Varvel et al (2007). The relationships between relative chlorophyll meter reading and optimal N rate (or suggested N rate) are similar for these three references, suggesting that these sets of available interpretations are robust.…”

Avaliação do estado nutricional do nitrogênio em batateira por meio de polifenóis e clorofila na folha

“…Um desses medidores portáteis é o Spad-502, que vem sendo largamente pesquisado e utilizado com sucesso em várias culturas (Samborski et al, 2009). No entanto, em razão de limitações em seu uso (Hawkins et al, 2009), também têm sido propostas alternativas para melhorar a acurácia do aparelho em estimar as concentrações de clorofila, como o uso do peso específico da folha (Peng et al, 1993). Neste caso, a determinação desta variável é feita de maneira destrutiva e pouco aplicável na agricultura de precisão.…”