Abstract
ABSTRACT Portable chlorophyll meters can be used to improve the prediction of nitrogen (N) doses for common bean. This study aimed to evaluate two chlorophyll meters (Minolta SPAD-502 and ClorofiLOG CFL 1030) to predict topdressing N doses for the Pérola, TAA Gol and BRSMG Uai cultivars and for the VR 20 line. Eight field experiments (four genotypes and two devices) were carried out in a randomized blocks design, with four replicates, being the treatments topdressing N applications corresponding to four nitrogen sufficiency indices. There were discrepancies between the indices obtained by the different devices for the same genotype, as well as among those obtained with the same device for the different genotypes studied. Thus, when the index is used to define the N doses, the genotype and the chlorophyll meter used must be considered. In addition, the recommended index of 95 % should not be generalized to all the cultivars and should be reduced.
Highlights
Common bean has an extreme socioeconomic importance in Brazil, where it is grown in an area of 2,946,000 ha, with an estimated production of 2,973,000 t for 2021, resulting in a national average yield of 1,009 kg ha-1 (Conab 2021).Among the factors that negatively affect the common bean yield in Brazil is the lack of adequate information for the management of nitrogen (N) fertilization for the main cultivars planted by farmers (Santi et al 2006)
The discrepancies between the N sufficiency index (NSI) observed at the time of the readings did not allow a joint analysis of the eight experiments, since they made the treatments personalized, as a function of the varied response of the sum of the cultivar and chlorophyll factors
The experiments were analyzed separately according to the genotype and device used. In both the experiments carried out with the TAA Gol cultivar, the grain yield responded linearly and positively to increases in the N dose applied as topdressing (Figures 1A and 1B), according to the experiments carried out with the SPAD-502 and CFL 1030 devices; the increase of 210 kg in the N dose, with the use of the SPAD 502, resulted in a variation of 380 %, while the variation for the CFL 1030 was 363 %, despite the increase in the dose being less than 150 kg, proving again the distinct behavior of the devices
Summary
Common bean has an extreme socioeconomic importance in Brazil, where it is grown in an area of 2,946,000 ha, with an estimated production of 2,973,000 t for 2021, resulting in a national average yield of 1,009 kg ha-1 (Conab 2021). Among the factors that negatively affect the common bean yield in Brazil is the lack of adequate information for the management of nitrogen (N) fertilization for the main cultivars planted by farmers (Santi et al 2006). N is the most required nutrient and, the crop has a high capacity to establish symbiotic associations with bacteria of the Rhizobium genus, when targeting grain yields higher than 2,500 kg ha-1 the biological N fixation alone does not supply the entire N demand of the crop (Pelegrin et al 2009); it is necessary to supply the nutrient using nitrogen fertilizers.
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