Residual effect of BNI by Brachiaria humidicola pasture on nitrogen recovery and grain yield of subsequent maize

Abstract

Background and Aims The forage grass Brachiaria humidicola (Bh) has been shown to reduce soil microbial nitrification. However, it is not known if biological nitrification inhibition (BNI) also has an effect on nitrogen (N) cycling during cultivation of subsequent crops. Therefore, the objective of this study was to investigate the residual BNI effect of a converted long-term Bh pasture on subsequent maize (Zea mays L.) cropping, where a long-term maize monocrop field (M) served as control. Methods Four levels of N fertilizer rates (0, 60, 120 and 240 kg N ha −1 ) and synthetic nitrification inhibitor (dicyandiamide) treatments allowed for comparison of BNI effects, while 15 N labelled micro-plots were used to trace the fate of applied fertilizer N. Soil was incubated to investigate N dynamics. Results A significant maize yield increase after Bh was evident in the first year compared to the M treatment. The second cropping season showed an eased residual effect of the Bh pasture. Soil incubation studies suggested that nitrification was significantly lower in Bh soil but this BNI declined one year after pasture conversion. Plant N uptake was markedly greater under previous Bh compared with M. The N balance of the 15 N micro-plots revealed that N was derived mainly (68-86%) from the mineralized soil organic N pool in Bh while plant fertilizer N recovery (18-24%) was not enhanced. Conclusions Applied N was strongly immobilized due to long-term root turnover effects, while a significant residual BNI effect from Bh prevented re-mineralized N from nitrification resulting in improved maize performance. However, a significant residual Bh BNI effect was evident for less than one year only.

Biological nitrification inhibition activity in a soil-grown biparental population of the forage grass, Brachiaria humidicola

“…In this regard, Moreta et al (2014) and Karwat et al (2017) found that the BNI effect of Bh on soil nitrifier activity could persist for at last one year after replacement of the pasture with maize. Gopalakrishnan et al (2007) reported several compounds with BNI activity in the root tissue of Bh, and our data suggest that there could be important allelic interactions within the biparental population related with the synthesis/accumulation of BNI compounds that could be exploited further through breeding to combine the high BNI potential with improved forage productivity and nutritional quality (Mackay et al 2009).…”

“…High BNI genotypes of Bh are capable of suppressing N2O emission from N inputs, e.g. animal excreta (Byrnes et al 2017) and it has been shown that they improve the NUE of a subsequent maize crop (Moreta et al 2014;Karwat et al 2017). Commercial cultivars of Brachiaria species are important for Latin American livestock production, the main economic activity in this region (Miles et al 2004;Rivas and Holmann 2004).…”

Differences in arbuscular mycorrhizal colonization and P acquisition between genotypes of the tropical Brachiaria grasses: is there a relation with BNI activity?

“…Potential nitrification rate (PNR) was estimated by aerobic soil incubation with the 174 methods described by Byrnes et al (2017) and Karwat et al (2017). The PNR assay has been 175 demonstrated to be a useful method to test the BNI activity in soils under different Brachiaria 176 genotypes (Nuñez et al 2018).…”

Low 15N Natural Abundance in Shoot Tissue of Brachiaria humidicola Is an Indicator of Reduced N Losses Due to Biological Nitrification Inhibition (BNI)

“…By preventing the microbial transformation of less soil mobile to more soil mobile nitrate ( ), BNI is expected to reduce leaching of nitrogen (N) from ecosystems ( Subbarao et al, 2009 , 2013 ; Coskun et al, 2017b ). Recent research has been undertaken to investigate the BNI effect by Bh on N dynamics, for example on the reduction of nitrous oxide (N 2 O) emissions from soils ( Byrnes et al, 2017 ), or on the influence of residual BNI effect on N uptake of subsequent crops ( Karwat et al, 2017 ). However, indicators for reduced leaching losses by effective BNI do not exist yet.…”