Desenvolvimento e senescência foliar de cultivares de feijoeiro sob diferentes suprimentos de nitrogênio e fósforo

Abstract

The study was divided into two stages. The first stage aimed to evaluate the use of digital image analysis for the diagnosis of N nutrition in the leaf tissue of common bean plants. Three cultivars were grown in pots at two doses of N and P applied to the soil. At the stage of pod setting, the chlorophyll content Falker in trifoliate leaves was measured, images of trifoliate leaves were scanned and leaf N concentration was determined. In the images, a note was given with AFSoft software, based on the area occupied by green standards previously established. Leaf N concentration was correlated to the chlorophyll index Falker and the note given by AFSoft. The note AFSoft is a viable tool for estimating leaf N status in plants. The second stage had the objective to evaluate the leaf development and senescence of bean cultivars in response to different levels of N and P in the soil. Two experiments were conducted. The first experiment had a 3x2x2x3 factorial design combining three cultivars (Iraí, ICA Pijao and Carioca), two P levels applied to the soil (20 and 100 mg P kg-1), two N levels (low N with 30 mg N kg-1 at planting, and high N with 60 mg N kg-1 at planting and two covering applications with 300 mg of N per pot) and three harvests (stages of pod setting, early pod filling, and 10 days after the second harvest) in pots with 11 kg of soil. Senescent leaves were collected and grouped into two phases of the experiment. At harvests, plants were separated into roots, stems, leaves, primary and trifoliate leaves, and the leaf area and N concentration in plant tissues were determined. In the second experiment a 5x2x2x2 factorial design was used, combining five cultivars (Iraí, ICA Pijao, Manteigão, Carioca and Ouro Negro), two N levels, two P levels (the same levels used in the first experiment) and two harvest (beginning of pod filling and grain maturity). The leaves were counted weekly and senescent leaves collected. At harvests, the plants were separated into roots, stems, leaves, pods and grains. In plant material concentrations of N and P were determined. In general, plants at lower P levels had lower dry mass of leaves, roots, stems, pods, shoots and greater deposition of senescent leaves, thus the limited P supply increased the bean leaf senescence. The maximum stage of number of leaves was oberved around 50 days after emergence and did not vary with the soil supplies of N and P. The specific leaf area remained relatively stable in different parts of the plant. The effects of P levels were more intense than the effects of N levels, throughout the growth cycle and leaf senescence, since there was a greater interference of P in the amount of N in plant tissues of bean. At low P levels, plants translocated more N and P from the leaves, stems and roots to the pods and grains. From the total of N and P that was translocated to pods and grains, the leaves were responsible for the translocation of 84% of N and 57% of P, stems by 10% of N and 24% of P, and roots by 6% of N and 19% of P, in the average of fertilizers levels. The apparent harvest index showed similar results to the real harvest index. Thus, the apparent harvest index may be used for expressing the ability of allocation of biomass, N and P in grains of a bean genotype. The Ouro Negro cultivar was more efficient in the translocation of N and P during the formation of the seeds.