ABSTRACT: Integrating plant density and nitrogen (N) management is a strategy for improving corn yields, especially for off-season corn production in the tropics. This study tested the hypothesis that increasing plant densities and N rates promotes yield gains for off-season corn production in high-yielding environments. The aim of the study was to investigate the yield performances of two hybrid versions (DKB PRO and DKB PRO3) submitted to three plant densities (55,000; 65,000 and 75,000 plants ha−1) and four N rates (control, 60, 120 and 180 kg ha−1 N). Field trials were undertaken at Uberlândia-MG (site1 and 2) and Pedro Afonso-TO (site 3), Brazil from which data on corn yield parameters were collected and analyzed. Multivariate analysis separated the three trial areas into two groups, presenting high (sites 1 and 2) and low yields (site 3), which were related to weather conditions. There was no influence of a hybrid version or plant densities on crop yields at site 1 or 2. In contrast, there was a positive response to increasing plant densities and the use of DKB PRO3 at site 3. A significant response to N was observed at sites 2 and 3, following a plateau model. Our results suggest that N application rates and plant densities do have the potential to increase off-season corn yields in low yielding environments.

ABSTRACT: Determining nutrient uptake and accumulation rates by cotton crops is important to define management strategies, especially for transgenic varieties, which are cultivated using high-technology approaches that require substantial investment to maximize yield. Currently in Brazil, the states of Bahia and Mato Grosso are responsible for 84.4 % of the total cotton growing area. In the present study, two trials were conducted in 2013, one that involved planting FM 940 GLT, FM 980 GLT, and FM 913 GLT varieties in the state of Bahia and the other which involved FM 940 GLT and FM 980 GLT varieties in the state of Mato Grosso. The aim of the two trials was to represent the two regions that currently encompass the largest areas of cotton cultivation. Tissue samples, consisting of leaves, stems, and reproductive components, were collected eleven times during the crop cycle for determination of nutrient content and shoot dry matter. After weighing, plant tissue samples were dried and ground to determine nutrient contents. Because there were no overall differences in nutrient contents and biomass accumulation of the varieties during the crop cycle, we undertook joint analysis of the data from all varieties at each site. Favorable climatic conditions in Bahia promoted plant biomass production that was twice as much as plants grown in Mato Grosso, with cotton yields of 6.2 and 3.8 t ha−1 of lint and seed, respectively. The maximum nutrient accumulation occurred between 137-150 days after emergence (DAE) for N; 143-148 for P; 172-185 for K; 100 for Ca; 144-149 for Mg; and 153-158 for S. Maximum uptake ranged from 218-362 kg ha−1 N; 26-53 kg ha−1 P; 233-506 kg ha−1 K; 91-202 kg ha−1 Ca; 28-44 kg ha−1 Mg; and 19-61 kg ha−1 S. On average, the sites revealed nutrient export of 14, 2, 23, 3, 2, and 2 kg t−1 of lint and seed for N, P, K, Ca, Mg, and S, respectively, with little variation among sites. Extraction of nutrients per area by cotton vary among sites, but nutritional requirement of cotton per unit of lint and seeds is similar independently of yield potential.

Mikania glomerata Sprengel é uma importante espécie medicinal popularmente conhecida como guaco, coração-de-jesus, guaco-liso, guaco-cheiroso, cipó-caatinga e erva-de-cobra. Foram estudados os fotoperíodos de 8, 12, 16 e 20 horas. Após 90 dias de tratamento, determinaram-se o peso de matéria seca total, particionada (entre folhas, ramos e raízes), área foliar, razão de área foliar, razão de peso foliar e área foliar específica. O crescimento das plantas variou em função do fotoperíodo, havendo um acréscimo na matéria seca total e particionada até 16 horas de fotoperíodo, seguido de uma queda, quando o fotoperíodo foi aumentado de 16 para 20 horas. A área foliar e o número de folhas foram crescendo até o fotoperíodo de 20 horas. Houve redução da área foliar específica e na razão de área foliar com o aumento do fotoperíodo. Quanto à razão de peso foliar, houve também um decréscimo nesse caráter quando o fotoperíodo aumentou de 8 para 16 horas; em contrapartida, quando o fotoperíodo aumentou de 16 para 20 horas, houve uma tendência de aumento. Foi verificado efeito dos tratamentos no espessamento dos tecidos foliares. O fotoperíodo influenciou positivamente as características associadas ao crescimento, anatomia foliar e fotossintética, como produção de biomassa total, área foliar, número de folhas, particionamento de biomassa para os diversos órgãos da planta.

Mikania glomerata Sprengel, an important medicinal species, popularly known as "guaco", "coração de Jesus", "guaco liso", "guaco cheiroso", "cipó caatinga" and "erva de cobra" was investigated. The photoperiods of 8, 12, 16 and 20 hours were studied. After 90 days' treatment; total dry matter weight, partitioned (among leaves, branches and roots), leaf area, leaf area ratio, leaf weight ratio and specific leaf area were determined. The plants growth changed with photoperiod there was an increase in the total and partitioned dry matter up to 16 hours followed by a fall when photoperiod was increased from 16 to 20 hours. Leaf area and number of leaves have been growing till the 20-hours photoperiod. There was a reduction of the specific leaf area and leaf area ratio with the increase of photoperiod. Concerning leaf weight ratio, there was also a decrease when photoperiod was from 8 to 16 hours, however, when photoperiod was from 16 to 20 hours, there was a trend toward increase. The treatments effect on the thickening of leaf tissue was observed. The photoperiod had positive result in the characteristics associated with growth, foliar anatomy and photosynthetic as: total biomass production, leaf area, leaf number, partitioned biomass to several plant organs.