Nitrogen is a key nutrient for soybean cropping and can be fully supplied by the biological nitrogen fixation (BNF) process. Inoculation with elite Bradyrhizobium strains greatly improves the supply of N to soybean; however, inoculation of large areas in short-sowing windows delays the sowing process, demanding the development of technologies for pre-inoculation. Here we report the evaluation of a liquid formulation containing cell protectors that proved, in four field experiments located in different edaphoclimatic conditions of Brazil, symbiotic performance comparable to the peat-based inoculant, traditionally considered as the best carrier. The liquid inoculant was also effective when applied to seeds not treated with pesticides 15 days before sowing, providing efficient BNF and timeflexibility to the farmers. Benefits of the liquid inoculant in improving grain yield were confirmed in two areas cropped for the first time and devoid of Bradyrhizobium, with an average increase of 89%, and also in two areas traditionally cropped with inoculated soybean, with an average increase of 6.8%, both in comparison to the non-inoculated control without N-fertilizers (NI). It is worth mentioning that, also in comparison to the NI control, the addition of 200 kg N ha −1 impacted grain yield in +54% and −1,8%, in new and traditional areas, respectively, indicating that BNF was more effective than the application of N-fertilizer. Large increases in total N content in grains were observed as well in response to the liquid inoculant, on average 47% and 27%, when compared to the NI and NI + N controls, respectively.
The objective of this work was to evaluate the incidence of corn stunt disease and its effects on the grain yield of off-season corn (Zea mays) hybrids in different sowing seasons. The experiment was conducted in three sites in the state of Tocantins, in different sowing seasons, in a randomized complete block design, with 30 hybrids (treatments) and three replicates. Corn stunt disease incidence was assessed at 80 days after emergence, varying between hybrids and sowing seasons, with a marked effect of sowing season. The most resistant hybrids were: MG652 PW, Penta VIP, MG600 PW, NS90 PRO2, LG3040 VIP3, MG580 PW, and Defender VIP. The Fórmula VIP2 hybrid was the most susceptible to corn stunt disease. The incidence of the disease increased in the later sowing seasons, causing significant declines in grain yield. The most productive hybrids were: MG580 PW, SYN 5T78 VIP, 2B810 PRO, MG600 PW, Supremo VIP, 2B512 PW, NS92 PRO2, P30S31 VYH, MG652 PW, Penta VIP, SX5371 VIP3, and LG6036 PRO. Corn hybrids vary greatly in their resistance to corn stunt disease, and, the later the sowing season, the higher the disease incidence and the lower the grain yield.
RESUMO -O estresse hídrico e a ocorrência de doenças foliares são os principais desafios para o cultivo do milho safrinha em Tocantins, que é realizado no final do período chuvoso. O presente trabalho teve como objetivo avaliar o efeito da época de semeadura e das doenças foliares no desempenho de cultivares de milho cultivado na safrinha em Tocantins. Foram avaliadas 11 cultivares nas safrinhas de 2014 e 2015. As semeaduras foram realizadas em 03/02/2014, 25/02/2014, 12/02/2015 e 12/03/2015. Foi utilizado o delineamento experimental de blocos ao acaso, em arranjo fatorial 11x2 (cultivares x épocas de semeadura). Foram observadas diferenças para os fatores cultivares e épocas de semeadura para todas as variáveis estudadas. O atraso na época de semeadura reduziu drasticamente a produtividade da cultura do milho safrinha, por causa da intensa restrição hídrica após a fase de florescimento. As maiores produtividades foram obtidas para os plantios realizados no início do mês de fevereiro. As cultivares AG7088 PRO, AS1596 PRO e DKB310 PRO apresentaram maior estabilidade e potencial produtivo. A severidade da ferrugempolissora foi maior nos plantios realizados no início de fevereiro, e reduziu com o atraso na semeadura. As cultivares mais suscetíveis foram 30F53 YF e CD355. Palavras-chave: milho safrinha, ferrugem-polissora, estresse hídrico. CORN CULTIVARS AFFECTED BY SOWING TIME AT OFF-SEASON IN TOCANTINS, BRAZILABSTRACT -Water stress and occurrence of foliar diseases are the main challenges for the cultivation of off-season corn in Tocantins, which is carried out at the end of the rainy season. The objective of this work was to evaluate the effect of sowing season and foliar diseases on the performance of corn cultivars in the State of Tocantins, Brazil, at off-season. Eleven cultivars were evaluated in the 2014 and 2015 off-season. Sowing was performed on 02/03/2014, 02/25/2014, 02/12/2015 and 03/12/2015. Randomized block experimental design was used in factorial arrangement 11x2 (cultivars x sowing times). Differences were observed for the cultivar and sowing times for all variables studied. The delay in the sowing season drastically reduced the off-season corn yield, due to the intense water restriction after the flowering phase. Highest yields were obtained for the planting carried out at the beginning of February. The cultivars AG7088 PRO, AS1596 PRO and DKB310 PRO presented greater stability and yield potential. Southern rust severity was higher in the planting carried out in early February, and reduced with the sowing delay. The most susceptible cultivars were 30F53 YF and CD355.
The objective of this work was to assess yield losses due to stalk rot in corn (Zea mays) hybrids, as well as to identify the main pathogenic fungi responsible for the disease during the off-season, in the state of Tocantins, Brazil. Two field experiments were carried out, one with five hybrids, in 2015, and another with four, in 2016. Ears of healthy and stalk rot-infected plants were collected from each plot, at harvest. Ear size, grain and ear weights, and grain moisture content were measured. From each diseased plant, a stalk piece with two to three nodes was removed for pathogen identification and quantification. The most common pathogens were: Fusarium graminearum, Stenocarpella maydis, and Macrophomina phaseolina. All yield parameters were significantly lower in stalk rot-infected plants, with average losses of 30.6%, in 2015, and of 34.3% in 2016. The highest yield losses are observed in hybrids with the highest grain/ear weight ratio.
This study aimed to verify the effect of co-inoculation, association between Azospirillum brasilense and Bradyrhizobium japonicum bacteria, on soybean plants subjected to water deficit at two sowing dates. Two field experiments were conducted at the Universidade Federal de Tocantins, campus of Palmas, Brazil, in 2016. The experimental design was randomized blocks in a split-split-plot arrangement with four repetitions, where the plots consisted of two irrigation depths (100 and 25% of crop evapotranspiration - ETc), the subplots was composed of two methods of inoculant application (inoculation with Bradyrhizobium japonicum and co-inoculation with Azospirillum brasilense + Bradyrhizobium japonicum) and the sub-subplots comprised two soybean cultivars (TMG 132 and ANTA 82). The cultivars responded differently to the sowing dates. Co-inoculation did not influence grain yield under full irrigation conditions (100% ETc), in neither cultivar evaluated. However, under the water deficit condition (25% ETc), the grain yield of the cultivar TMG 132 increased 77.20%, indicating that there are different responses of interaction between Azospirillum brasilense, plant genotype and sowing dates.
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.
Artificial drying, although costly, ensures a safe storage and preserves post-harvest grain quality. Alternatively, a more costeffective measure is to delay harvest to promote natural drying, but this management may increase the risk of mycotoxigenic ear rot fungi contamination. The objective was to evaluate the effect of increasing maize harvest delay on fungal disease and fumonisin levels. Three maize hybrids (BRS1035, Attack and DKB390 YG) were sown in the field to study the effect of five harvest delays (15, 30, 45, 60 and 75 days) after the optimum date (18% grain moisture). There was a significant trend of increasing the incidence of kernel rot and total fumonisins in the grains when delaying harvest, but fungal incidence and mycotoxin contamination varied with the hybrid. The main fungi detected in the grain samples were Fusarium verticillioides and Stenocarpella maydis. The hybrid DKB390 YG showed significantly lower incidence of F. verticillioides contamination and lower fumonisin accumulation in the grains than the other hybrids. The hybrid Attack was the least susceptible to kernel rot incidence. Our data shows that delaying harvest for minimizing drying costs may increase the risk of mycotoxin contamination in maize in the tropics of Brazil.
The soybean chemical composition is strongly influenced by genetic factors, as well as their interaction with the environment and management practices. Among the environmental factors, water deficit and temperature are those that most contribute to modify the chemical composition of beans, especially oil and protein contents. The present study aimed to assess the effects of co-inoculation with Azospirillum brasilense on soybean oil and protein contents. Two field experiments were carried out on different sowing dates. The design consisted of randomized blocks, in a split-split-plot arrangement, with four replications, including two irrigation depths (25 % and 100 % of the ETc), two inoculation methods [Bradyrhizobium japonicum (strains Semia 5079 and Semia 5080) and Azospirillum brasilense (strains AbV5 and AbV6 + Bradyrhizobium japonicum)] and two cultivars (ANTA 82 and TMG 132). The co-inoculation did not affect the oil and protein contents of beans for any of the assessed management conditions. The water deficit in the reproductive stage, combined with the sowing dates, altered the oil and protein contents in both the assessed cultivars, showing, respectively, a higher average protein and oil content in the beans for the cultivars TMG 132 and ANTA 82.
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