Nitrogen Availability and Physiological Response of Corn After 12 Years with Organic and Mineral Fertilization

The study aimed to evaluate the effects of long-term organic and mineral fertilization on soil solution dynamics of nitrogen (N), as well as to understand its relationship with corn plant growth, plant N uptake, and grain yield. The study was conducted in Santa Maria, State of Rio Grande do Sul, Brazil, for 12 years. The treatments consisted of pig slurry (PS); cattle slurry (CS); pig deep-litter (PL); mineral fertilizer (NPK); and no fertilization (control). We determined concentrations of dissolved inorganic N (DIN) and dissolved organic N (DON) in soil solution in situ, prior to sowing and during the growing cycle of corn. In plants, we determined the gaseous exchange, shoot N content, grain yield, and indices of recovery and efficiency of N. DIN in soil solution was the predominant N form in all treatments, ranging from 53 to 80% of total dissolved nitrogen (TDN). NPK was the only treatment that maintained high NO3-concentration in the soil solution up to 35 days after plant emergence (DAE) and this resulted in higher grain yield. The plants fertilized with CS obtained a recovery of 80% of the N, and promoted improvements in crop growth. The results of this study showed the importance of combining the application of organic fertilizers (before sowing) with mineral sources of N (topdressing), allowing the maintenance of N availability in the soil solution during periods of demand of organic fertilizer.