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Title: Foliar application of plant growth-promoting bacteria and humic acid increase maize yields

item CANELLAS, LUCIANO - Universidade Estadual Do Norte Fluminense
item DA SILVA, SILEZIO - Universidade Estadual Do Norte Fluminense
item Olk, Daniel - Dan
item OLIVARES, FABIO - Universidade Estadual Do Norte Fluminense

Submitted to: Journal of Food Agriculture and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2014
Publication Date: 1/1/2015
Citation: Canellas, L.P., Da Silva, S.F., Olk, D.C., Olivares, F.L. 2015. Foliar application of plant growth-promoting bacteria and humic acid increase maize yields. Journal of Food, Agriculture and Environment. 13:131-138.

Interpretive Summary: An ability to increase crop growth without needing more fertilizer would allow farmers to reduce their fertilizer applications, saving them money and helping to protect the environment. We found that application of a mixture of bacteria and carbon compounds increased corn grain yield in several different field studies, especially when rainfall was limited. This mixture increased the amounts of corn roots more than the grain. These results identify a tool for farmers to maintain or increase their yields while reducing fertilizer costs, improving soil quality, and protecting the environment. The results will benefit farmers, agronomists who seek strategies for more sustainable crop management, and plant scientists who study crop growth.

Technical Abstract: Plant growth promoter bacteria (PGPB) can be used to reduce fertilizer inputs to crops. Seed inoculation is the main method of PGPB application, but competition with rhizosphere microorganisms reduces their effectiveness. Here we propose a new biotechnological tool for plant stimulation using endophytic diazotrophic bacteria in combination with humic substances as a foliar spray application. Six field experiments were conducted using Herbaspirillum seropedicae (109 cells mL- 1) and humic acids (50 mg L-1) extracted from vermicompost. Two addressed different urea-N concentrations: 0, 45, 90 and 180 kg N ha-1 (year 1) and 0, 19, 37.5, 75, 112.7, and 150 kg N ha-1 (year 2). The inoculation was performed at the V6 physiological stage at the equivalent of 450 L-1 ha-1. A third experiment evaluated the timing of PGPB and humic inoculation on a maize crop, with spray applications 7 d after germination and at the V4, V6, and V8 growth stages. Two trials were conducted for silage production. The foliar application was at the V6 stage to two maize varieties. Finally, we evaluated the use of the inoculant on maize grown in soil with high fertility. In both years, the PGPB and humic acids promoted significant increases in grain yield at all urea-N rates less than 75 kg N ha-1, and in the drier of the two seasons it also promoted grain yield at the higher N rates. In the third experiment, grain production increased with increasingly later timing of foliar application. The use of inoculants increased shoot biomass in maize for silage production, but dry root weight showed a yet larger promotion. No benefit of the inoculant was observed in maize production on high soil fertility. We observed that PGPB used together with humic acids can provide environmental services besides grain or biomass production that include food security, efficient use of non-renewal fertilizers and water, and enhanced below ground root mass that can contribute to soil C sequestration and reduction of greenhouse gas emissions.