ABSTRACT Late sowings anticipate flowering and decrease the soybean vegetative plasticity. These changes may limit the ability of plants to tolerate leaf area losses. The objective of this research was to evaluate the sowing date effect on soybean tolerance to defoliation at the beginning of pod formation. The experiment was set in Lages (Santa Catarina State, Brazil) during the 2016/2017 growing season. Two sowing dates were tested: November 2, 2016 (preferential) and December 15, 2016 (late). Five levels of defoliation (0%, 17%, 33%, 50% and 67%) of cultivar NA 5909 RG were imposed at the R3 growth stage. Grain yield showed a quadratic response to defoliation, ranging from 4,313 to 6,478 kg ha-1 in the preferential sowing date and from 3,374 to 4,443 kg ha-1 in the late sowing date. The plants tolerated up to 45.6% of defoliation in early sowing and 55.8% in late sowing, without yield losses, in comparison to the control. The highest level of defoliation reduced grain yield by 26.9% and 13.4% in early and late sowings, respectively, compared to the control. The delay of sowing date did not increase the sensitivity of cultivar NA 5909 RG to defoliation at the beginning of pod formation.

ABSTRACT Soybean tolerance to defoliation may be affected by population density, as the plant population interferes with the crop leaf area index . This study aimed to evaluate the effect of defoliation at the beginning of pod formation on the agronomic performance of soybean at different plant densities. The experiment was conducted under field conditions in Campos Novos, SC, Brazil, during 2016/2017 and 2017/2018 growing season. The experimental design was a randomized block in a split-plot arrangement. The main plot consisted of three densities (100,000, 300,000, and 500,000 plants ha−1), whereas the subplots consisted of the cultivar NA 5909 RG submitted to five defoliation levels (0, 16.6, 33.3, 50, and 66.6%). Grain yield ranged from 4,219 to 5,356 kg ha−1 in the 2016/2017 growing season and 3,732 to 5,186 kg ha−1 in the 2017/2018 growing season. Plant density did not interfere with the grain yield response to defoliation performed at the beginning of pod formation. The 16.6% defoliation increase grain yield by 7.5 and 5.6% relative to the control in 2016/2017 and 2017/2018 growing seasons, respectively. The soybean tolerate defoliation of up to 33.3% at R3 with no significant decrease in grain yield, regardless of the plant density.

RESUMO A tolerância da soja à desfolha pode ser afetada pelo grupo de maturação relativa (GMR) da cultivar. Este trabalho foi conduzido objetivando avaliar os efeitos da desfolha artificial nas fases vegetativa e reprodutiva sobre o desempenho agronômico de cultivares de soja com diferentes grupos de maturação. Foram conduzidos dois experimentos em casa de vegetação, no município de Lages, SC. No primeiro a desfolha foi realizada em V6 e no segundo em R3. Avaliaram-se três cultivares com grupos de maturação relativa (GMR) contrastantes: BMX Veloz (GM 5.0, hábito de crescimento indeterminado), NA 5909 (GM 5.9, hábito de crescimento indeterminado) e TMG 7262 (GM 6.2, hábito de crescimento semideterminado). Cada cultivar foi submetida a cinco níveis de desolha: 0%, 16,6%, 33,3%, 50% e 66,6%. Avaliou-se a expansão foliar após a desfolha, o rendimento de grãos e seus componentes. A cultivar BMX Veloz apresentou menor capacidade de expansão foliar e menor rendimento de grãos do que as demais cultivares quando desfolhada em V6. O rendimento de grãos das três cultivares somente sofreu decréscimos significativos com desfolhas superiores a 16,6% em R3. Portanto, a cultivar BMX Veloz é menos tolerante à desfolha na fase vegetativa do que as cultivares NA 5909 e TMG 7262. O grupo de maturação da cultivar não interfere na tolerância da soja à desfolha na fase reprodutiva sob condições de casa de vegetação.

ABSTRACT Soybean tolerance to defoliation may be affected by relative maturity group (RMG) of the cultivar. For this reason, this study was carried out to evaluate the effects of artificial defoliation at vegetative and reproductive stages on the agronomic performance of soybean cultivars with different RMG. Two experiments were carried out in greenhouse conditions in Lages, Santa Catarina State, Brazil. Defoliation was carried out at V6 in the first experiment and at R3 in the second experiment. Three cultivars with contrasting RMG were used: BMX Veloz (RMG of 5.0, indeterminate growth habit), NA 5909 (RMG of 5.9, indeterminate growth habit), and TMG 7262 (RMG of 6.2, semi-determinate growth habit). Each cultivar was submitted to five defoliation levels: 0.0, 16.6, 33.3, 50.0, and 66.6%. Leaf expansion after defoliation, grain yield and its components were determined. The BMX Veloz showed lower leaf expansion capacity and lower grain yield when compared to the other cultivars when defoliated at V6. Grain yield of the three cultivars only showed significant decreases with defoliation levels higher than 16.6% at R3. The cultivar BMX Veloz is less tolerant to defoliation during the vegetative stage when compared to the cultivars NA 5909 and TMG 7262. Cultivar maturity group does not interfere with soybean tolerance to defoliation at the reproductive stage in greenhouse conditions.

ABSTRACT Currently, most nitrogen fertilizer is side-dressed when corn is in the four (V4) to eight (V8) expanded leaf stage. However, recent studies have shown that modern hybrids take up high amounts of nitrogen during grain filling. This indicates that a late nitrogen fertilization, at the time of crop flowering, may be important to optimize corn agronomic performance. This study aimed to evaluate the effect of the timing and splitting of nitrogen side-dress application on the agronomic performance of early corn hybrids in order to achieve high grain yield. The experiment was set in Lages, Santa Catarina, in the South of Brazil, during the 2014/2015 and 2015/2016 growing seasons. A randomized block design arranged in split plots was used. Two hybrids were tested in the main plots: P1680YH (very early) and P30F53YH (early). Six nitrogen side-dress systems were assessed in the split plots: control (without N), full N rate applied at V5, full N rate applied at V10, 1/2 N rate applied at V5 and 1/2 at V10, 1/3 N rate applied at V5, 1/3 at V10 and 1/3 at VT; and the whole N rate applied at VT. The nitrogen rate was 300 kg ha-1 N. Urea was used as the nitrogen source. Total grain yield and yield components, agronomic nitrogen use efficiency, and leaf area were determined. Grain yield ranged from 6,422 to 15,426 kg ha-1 in 2014/2015 and from 9,283 to 14,986 in 2015/2016. Nitrogen side-dress application performed one time at V5 or V10 or split into two or three applications at different growth stages had similar grain yield, number of ears per plant, kernels per ear, and 1,000 grain dry weight. Nitrogen side-dressed entirely at VT led to higher grain yield than the control. However, grain yield and agronomic nitrogen use efficiency were lower in this treatment than in the treatments involving the other growth stages of side-dress nitrogen. The early hybrid was higher yielding than the very early hybrid, regardless of the timing of nitrogen fertilization. Splitting of nitrogen fertilization up to tasseling was not an effective strategy to increase grain yield and agronomic nitrogen use efficiency of the corn hybrids P30F53YH and P1680YH.

Resumo: O objetivo deste trabalho foi avaliar o efeito da aplicação do regulador de crescimento Trinexapac-etil na resposta produtiva de milho ao incremento na densidade de plantas, em duas épocas de semeadura. O experimento foi conduzido no Município de Lages, SC, nas safras agrícolas 2014/2015 e 2015/2016. Foram testadas duas épocas de semeadura (15/10 - preferencial e 5/12 - tardia), quatro densidades de plantas (5, 7, 9, 11 plantas m-2), com e sem aplicação do regulador de crescimento Trinexapac-etil. O regulador de crescimento foi aplicado a dose de 150 g i.a. ha-1, nos estádios V5 e V10 do híbrido P30F53YH. A aplicação do regulador de crescimento diminuiu o comprimento do colmo acima da inserção da espiga, nas duas safras. O rendimento de grãos variou de 11.422 a 14.805 kg ha-1, aumentou de forma quadrática com a elevação da densidade e foi maior para a semeadura em outubro. A aplicação de Trinexapac-etil não afetou o rendimento, mas diminuiu a massa de 1.000 grãos nas duas épocas de semeadura. A utilização do regulador de crescimento Trinexapac-etil não aumenta o rendimento de grãos do híbrido P30F53YH em resposta ao adensamento, independentemente da época de semeadura.

Abstract: The objective of this work was to evaluate the effect of application of the growth regulator Trinexapac-ethyl on maize response to the increase in plant density at two sowing dates. A field experiment was carried out in the municipality of Lages, state of Santa Catarina, Brazil, during the 2014/2015 and 2015/2016 growing seasons. Two sowing dates (10/15 - preferential, and 12/5 - late), four plant densities (5, 7, 9, and 11 plants m-2), with and without Trinexapac-ethyl application, were tested. The growth regulator was sprayed at a rate of 150 g a.i. ha-1, when hybrid P30F53YH was at the V5 and V10 growth stages. The spraying of Trinexapac-ethyl decreased the stem length above the ear insertion node at both growing seasons. Grain yield ranged from 11,422 to 14,805 kg ha-1, and increased in a quadratic way with the increment in plant density. The highest yields were reached when maize was sown in October. The spraying of Trinexapac-ethyl did not affect grain yield, but decreased the 1,000 kernels mass at both sowing dates. The use of Trinexapac-ethyl does not enhance grain yield of maize hybrid P30F53YH at crowded stands in response to the densification, regardless of sowing time.

RESUMO O atraso na colheita do milho pode ocasionar perdas quantitativas e qualitativas aos grãos. Este trabalho avaliou os efeitos da época de colheita sobre o desempenho agronômico de híbridos de milho com ciclos contrastantes. O experimento foi implantado em Lages, Planalto sul de Santa Catarina, Brasil, nas safras 2012/13 e 2013/2014. O delineamento experimental utilizado foi blocos casualizados dispostos em parcelas subdivididas. Na parcela principal foram testados cinco híbridos simples: P32R22H e P1630H (hiper-precoces), P2530 (super-precoce), P30F53YH e P30R50YH (precoces). Nas subparcelas foram testadas cinco épocas de colheita: 0 (maturação fisiológica dos grãos), 10, 20, 30 e 40 dias após a maturação fisiológica. A semeadura foi realizada em 5/12/2012 e 5/10/2013. Avaliaram-se a percentagem de plantas acamadas e quebradas, a massa de 1.000 grãos, produtividade potencial e real de grãos. O atraso na colheita aumentou o acamamento e quebra de plantas. A época de colheita não interferiu sobre massa de 1.000 grãos. A realização da colheita após a maturação fisiológica reduziu a produtividade real de grãos, principalmente dos híbridos de ciclo hiper-precoce P1630H e P32R22H. Em regiões de alta latitude e altitude, as perdas de produtividade ocasionadas por colheitas tardias se devem ao incremento na quantidade de colmos acamados e quebrados.

ABSTRACT The delay of the maize harvest may cause qualitative and quantitative grain losses. This work evaluated the effects of the harvest time on the agronomic performance of maize hybrids with contrasting growth cycles. The experiment was set in Lages, Santa Catarina State, South Brazil, during the 2012/2013 and 2013/2014 growing seasons. A randomized block design, arranged in split plots was used. Five single-cross hybrids were tested in the main plots: P1630H and P32R22H (hyper-early), P2530 (super early) and P30F53YH and P30R50YH (early). Five harvest times were assessed in the split plots: 0 (grain physiological maturity), 10, 20, 30 and 40 days after physiological maturity. The sowing was performed on 12/5/2012 and 10/5/2013. The percentage of lodged and broken stems, grain mass, potential and real productivity were determined. The delay of the maize harvest increased the percentage of lodged and broken stems. The harvest time did not affect the weight of 1,000 grains. The harvests performed after physiological maturity decreased the real grain productivity, especially for the hyper-early hybrids P1630H and P32R22H. In the regions with high altitude and latitude, the productivity losses derived from late harvests are mainly due to the increase in the amount of broken and lodged stems.