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Excessive rainfall in the soybean preharvest period can make mechanized crop harvesting technically and economically unfeasible, causing 100% losses in soybean grain yield. An alternative to reduce the economic losses of farmers would be using unharvested soybean crop residues as a source of nitrogen (N) for the subsequent corn crop. However, a question that still needs to be understood is whether the amount of N released from unharvested soybean residues (straw and grains) is sufficient to meet all the nutritional demand for this nutrient in the off-season corn. Therefore, this study investigated the impact of unharvested soybean crop residue persistence on the yield response of off-season corn crop (Zea mays L.) to the application of N fertilizer rates when grown in tropical Cerrado soils of medium and high fertility. Four simple corn hybrids (SYN7G17 TL, 30F53VYHR, B2433PWU, and AG 8700 PRO3) were grown in soils of medium fertility and medium acidity level (UFMS 1) and high fertility and low acidity level (UFMS 2) and fertilized with five of N fertilizer rates (0, 40, 80, 120, and 160 kg ha-1 of N) applied at 30 days after emergence (DAE). Canonical correlation analysis (CCA) was used to investigate the interrelationships between the groups of independent (agricultural production areas, corn cultivars, and N application rates) and dependent (corn agronomic traits) variables. Crop residues remaining on the soil surface from soybeans not harvested and inoculated with Bradyrhizobium spp. can supply most of the nitrogen requirement of off-season corn grown in succession, especially in tropical soils of medium fertility. However, in high-fertility tropical soils, the maximum grain yield potential of off-season corn cultivars can be obtained with the application of mineral N fertilizer in supplement the amount of nitrogen released from unharvested soybean residues. Therefore, the N requirement depends on the corn cultivar and the agricultural production area. However, our results show that when off-season corn is grown on unharvested soybean residues, nitrogen fertilization in topdressing can be dispensed. The agricultural area with high fertility soil (UFMS 2) enhances the grain yield of the off-season corn crop. The corn cultivar AG 8700 PRO3 has a higher thousand-grain mass and high grain yield potential under Brazilian Cerrado conditions., Competing Interests: The authors have declared that no competing interests exist.

Harnessing the beneficial potential of plant growth-promoting rhizobacteria may be an alternative strategy to improve plant tolerance to drought stress. The effect of inoculation with Bradyrhizobium japonicum and Azospirillum brasilense either alone or in combination on the plant growth and drought tolerance of soybean [Glycine max (L.) Merrill.] was investigated in this study in greenhouse conditions. Treatments were arranged in a randomized block design in a 3 × 4 factorial: three irrigation regimes [100% of pot capacity-PC (well-watered control), 50% of PC (moderate stress) and 25% of PC (severe stress)] and four inoculation treatments [control (non-inoculated), inoculation with B. japonicum, inoculation with A. brasilense, and co-inoculation with B. japonicum and A. brasilense]. Leaf relative water content, cell membrane stability, root nodulation, plant growth, and morphophysiological indexes were recorded. The inoculation of soybean plants with B. japonicum and A.brasilense either alone or in combination improved leaf membrane stability under drought stress conditions when compared to non-inoculated plants; however, this lower damage to cell membranes was not sufficient to maintain the leaf water content of the plant under drought stress. Plants co-inoculated with B. japonicum and A.brasilense improved the root nodulation under severe drought conditions. Inoculation of B. japonicum and A. brasilense either alone or in combination reduced the pod abortion rate under moderate drought stress, but had no effect under severe drought stress. In summary, the co-inoculation of A. brasilense and B. japonicum alleviate adverse effects limited by drought stress to the growth of soybeans.Author: Please check and confirm that the authors [Elijanara Raissa Silva, Carlos Eduardo Silva Oliveira, Alan Mario Zuffo, Eduardo Pradi Vendruscolo] and their initials have been correctly identified and amend if necessary.The authors were correctly identified.