The legacy of Brachiaria as a covercrop on soil nitrification, nitrous oxide emission and nitrogen use efficiency of maize
Abstract
Brachiaria humidicola was reported to reduce soil nitrification. The intercropping of maize with grasses have been used in Brazil to improve soil cover, fertility and land use efficiency. Thus, this study aims at evaluating the legacy of brachiarias intercropped with maize on soil nitrification when compared with maize monocrop. A field trial was set up in late 2016 in Brazil, designed as randomized blocks with 5 replicates. The treatments (6) consisted on combination of N rates (0 or 150 kg N ha-1) in maize intercropped with two Brachiaria species (B. brizantha and B. humidicola) and monocrop maize. During the third season of maize (2018/2019) N2O and grain yield (GY) were measured. The soil was sampled before (i) brachiarias desiccation and (ii) before N fertilization for a microcosm experiment to measure soil net nitrification rate (NR), dicyandiamide (DCD) applied to soil without brachiarias was used as a reference for nitrification inhibition, for comparison with the effect of brachiarias as a nitrification suppressor. Intercropping did not result in nutrient and water competition between plants and did not affect maize GY, but maize failed to reach the full plant population when sowed in the B. brizantha mulch and thus maize did not achieve its potential GY. B. brizantha mulch increased N2O and CO2 emissions during maize season, irrespectively of N fertilization. Non-fertilized plots with both brachiaria mulch resulted in higher N2O emission (p ≤ 0.1). N fertilizer increased maize GY, but the N2O emission only increased due N fertilization monocrop maize plots (p ≤ 0.1). No effect of residual N fertilizer and interaction between plants were observed on soil NR. Before desiccation brachiarias resulted in higher NR (4.4 to 5.4 mg d-1 of N-NO3) than that of the sole maize plots (3.4 to 3.5 mg d-1 of N-NO3) but the opposite was observed 41 days after brachiarias desiccation (3.4 mg d-1 of N-NO3 for sole maize and 2.4 and 2.0 mg d-1 of N-NO3 for B. brizantha and B. humidicola, respectively). NR did not significantly differ among the brachiaria species. DCD was efficient to reduce NR in before and after desiccation. The lower NR caused by brachiarias during the maize growing season did not result in higher GY but the higher N2O emission due to mulch may overcome the short-term benefit of lower NR.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGC54D..09C
- Keywords:
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- 0402 Agricultural systems;
- BIOGEOSCIENCES;
- 0470 Nutrients and nutrient cycling;
- BIOGEOSCIENCES;
- 1615 Biogeochemical cycles;
- processes;
- and modeling;
- GLOBAL CHANGE;
- 1630 Impacts of global change;
- GLOBAL CHANGE