Maize-Brachiaria intercropping: A strategy to supply recycled N to maize and reduce soil N2O emissions?

Abstract

Nitrogen use in agriculture directly impacts food security, global warming, and environmental degradation. Forage grasses intercropped with maize produce feed for animals and or mulch for no-till systems. Forage grasses may exude nitrification inhibitors. It was hypothesized that brachiaria intercropping increases N recycling and maize grain yield and reduces nitrous oxide (N 2 O) emissions from soil under maize cropping. A field experiment was set up in December 2016 to test three cropping system (maize monocropped, maize intercropped with Brachiaria brizantha or with B. humidicola ) and two N rates (0 or 150 kg ha -1 ). The grasses were sown with maize, but B. humidicola did not germinate well in the first year. B. brizantha developed slowly during the maize cycle because of shading but expanded after maize was harvested. The experiment was repeated in 2017/2018 when B. humidicola was replanted. N 2 O and carbon dioxide (CO 2 ) emissions, maize grain yield and N content were measured during the two seasons. After the first maize harvest, the above- and below-ground biomass, C and N content of B. brizantha grown during fall-winter, and the biological nitrification inhibition potential of B. brizantha were evaluated. Maize yield responded to N fertilization (5.1 vs. 9.8 t ha -1 ) but not to brachiaria intercropping. B. brizantha recycled approximately 140 kg N ha -1 and left 12 t dry matter ha -1 for the second maize crop. However, the 2017/18 maize yields were not affected by the N recycled by B. brizantha , whereas N 2 O emissions were higher in the plots with brachiaria, suggesting that part of the recycled N was released too early after desiccation. Brachiarias showed no evidence of causing nitrification inhibition. The strategy of intercropping brachiarias did not increase maize yield, although it added C and recycled N in the system.

Legacy Effects of Intercropping and Nitrogen Fertilization on Soil N Cycling, Nitrous Oxide Emissions, and the Soil Microbial Community in Tropical Maize Production

“…The experiment was designed as a split plot randomized complete block design with five replicates. The main plots (4.5 × 30 m) consisted of three cropping systems: [1] maize hybrid 2B587 PW monocropped, [2] maize intercropped with Brachiaria brizantha, or [3] maize intercropped with Brachiaria humidicola cv. Tully.…”

“…In the two growing seasons (2016/2017 and 2018/2019) previous to the evaluations performed in this study, the only N removed with plant materials from the plots was that of the maize grains that ranged from 45 to 55.9 and from 116.6 to 168.6 kg N ha −1 for plots with 0 and 150 kg ha −1 of N as topdress maize fertilization (1). The B. brizantha accumulated 106 kg N ha −1 more than the plots under fallow during the fall-spring (maize monocrop) (1). The amounts of biomass produced in the first two cycles varied from 8 to 10 t stove ha −1 yr −1 for the fertilized maize, to 4-5 t stove ha −1 yr −1 for non-fertilized maize; the mulch of B. brizantha varied from 6 to 12 t DM ha −1 yr −1 and for B. humidicola was 2.5 t DM ha −1 in the second season as there was no production of this grass in the first year (1).…”

“…The B. brizantha accumulated 106 kg N ha −1 more than the plots under fallow during the fall-spring (maize monocrop) (1). The amounts of biomass produced in the first two cycles varied from 8 to 10 t stove ha −1 yr −1 for the fertilized maize, to 4-5 t stove ha −1 yr −1 for non-fertilized maize; the mulch of B. brizantha varied from 6 to 12 t DM ha −1 yr −1 and for B. humidicola was 2.5 t DM ha −1 in the second season as there was no production of this grass in the first year (1). In this study, we present the data from the final year of cultivation (2018/2019), in addition to data about the microbial processes resulting from the cumulative effect of the treatments applied in previous years.…”

“…Recently, Canisares et al (1) found that N 2 O emissions were higher during the maize growing season when brachiarias were included in the system than in the sole maize treatments. Despite the widespread adoption by farmers of the maizebrachiaria cropping systems, there is little information on the N cycle and microbial processes that drive N 2 O emission in such systems.…”

“…Moreover, lower N 2 O emission and AOB abundance, along with higher abundance of AMF, suggests possible competition for N mineralization products between mycorrizal fungi and ammonium oxidizing organisms (AOO) This tropical forage grass could also impact soil N cycling during its decomposition due to the release of BNI compounds from plant litter or the relative ratio of N immobilization to N mineralization depending on the residue C:N ratio (13). The C:N ratios of the shoot residue may vary with the brachiaria species and growing conditions (1,14). Thus, inclusion of this tropical forage grass in a cropping system with maize may lead to substantial relative differences in N immobilization vs. mineralization potential due to the residue C:N stoichiometry while chemically slowing soil nitrification through release of BNIs during decomposition (10,15,16), which highlights the importance of the whole microbial community to better understand the effect of plants with BNI potential on soil N dynamics (17).…”