Search

Soybean [Glycine max (L.) Merr.] is highly efficient in the biological N2 fixation (BNF) process through the association of bacteria of the genus Bradyrhizobium in the root nodules of the plants. However, there are still doubts about the need to complement soybean N demand through N fertilization in high‐yield environments. In addition, the real impact of co‐inoculation of soybean with Azospirillum brasilense and Bradyrhizobium spp. is not yet clear in such environments. A field experiment was conducted from 2012 to 2021 with six soybean cropping seasons in a crop rotation scheme with black oat (Avena strigosa Schreb), maize (Zea mays L.), and wheat (Triticum aestivum L.) under no‐till (NT) in Southern Brazil. Soybean seeds were co‐inoculated with A. brasilense (strains Ab‐V5 and Ab‐V6) shortly after inoculation with Bradyrhizobium japonicum, and different levels of N fertilization were used in top dressing at the start of pod formation (R3). Soybean nutritional status and grain yield were not benefited by co‐inoculation with A. brasilense. Since the increased inoculum rate of A. brasilense co‐inoculated with rhizobia in soybean compromised both N nutrition and grain yield, this practice should not be encouraged. There was no need to complement soybean N demand through N fertilization during the reproductive stage. Soybean achieved grain yields of 5.0–5.7 Mg ha−1 and, even so, there was no need to complement N demand through N fertilization. The results suggest that soybean N demand in a high‐yielding environment under NT could be satisfied exclusively through the optimization of BNF. Core Ideas: Benefits of co‐inoculation of soybean with Azospirillum brasilense are unclear.Late N fertilization in soybean is an unnecessary practice.Co‐inoculation and N fertilization did not improve soybean nutrition and yield.N fertilization for no‐till soybean production should not be encouraged.Increased inoculum rate of A. brasilense in soybean should not be encouraged. [ABSTRACT FROM AUTHOR]

Cereal crops have a high N requirement in a high‐yield environment. However, N use efficiency is still low in agricultural production systems and little is known about the effects of inoculation with Azospirillum brasilense in a high‐yield environment. A field experiment was conducted from 2012 to 2018 with a maize (Zea mays L.)–wheat (Triticum aestivum L.) rotation under a continuous no‐till in southern Brazil. Seeds were inoculated with A. brasilense (strains Ab‐V5 and Ab‐V6) and different levels of N fertilization were used in top dressing. Seed inoculation provided slight changes in N, P, and K concentrations in leaves and grains of maize and wheat. Increasing N input increased the leaf and grain N concentration and the maize and wheat grain yields. Seed inoculation caused varied responses on cereals in different cropping seasons. Wheat was more affected by inoculation in response to N application than maize. Rainfall distribution during the growing seasons possibly interfered on crop responses with inoculation between years and N fertilization levels. Under a similar N input, inoculation resulted in an average increase of 454 kg ha−1 yr−1 of maize and 242 kg ha−1 yr−1 of wheat by applying a higher N rate to the maize and a lower N rate to the wheat. An additional gain of US$409.72 ha−1 (2012–2018) was also achieved using this strategy. Although the possibility of inoculation causing economy with N fertilization in wheat was evident, for maize in rotation with wheat, A. brasilense inoculation was apparently more viable under higher N fertilizer input. [ABSTRACT FROM AUTHOR]

In a no-till system (NTS) on naturally acidic soils, surface liming is essential to neutralize soil acidity and increases crop productivity. As a result, the soil organic matter (SOM) pools of the soil surface layers may change, reflecting increased C inputs by crop residues. The objective of this study was to quantify changes in SOM pools and the rate of C sequestration that occur in response to surface liming in a long-term NTS experiment. The experiment was conducted in an Oxisol in southern Brazil. The treatments consisted of the application of 0 or 6 Mg ha-1 of dolomitic lime on the soil surface in 1993 and a reapplication of 0 or 3 Mg ha-1 of dolomitic lime in 2000 to plots with or without the previous lime application. Liming caused total organic C (TOC) accumulation, especially in the 0- to 2.5-cm layer. The amount of TOC stored in the 20-cm layer was 49.9, 52.9, 52.7, and 57.5 Mg ha-1 in the control, 6 + 0, 0 + 3, and 6 + 3 Mg ha-1 treatments, respectively. The levels of particulate organic C (POC) and mineral-associated organic C (MAOC) in the SOM were also enhanced by liming. The increase in POC was directly related (R² = 0.99, P = 0.002) to the accumulation of C from crop residues, which was greater in the plots receiving lime treatment. There were positive correlations between TOC and C extractable with hot water, total polysaccharides, and labile polysaccharides. The correlation analysis also demonstrated that TOC was more tightly correlated with POC than with MAOC, indicating a greater influence of the labile fraction on the increase in TOC with surface liming. [ABSTRACT FROM AUTHOR]