Nitrogen fixation of Poaceae and Leguminoseae in a green manure experiment in the Brazilian semiarid region

Abstract

Mixtures of green manure species, including Leguminosae and Poaceae, planted prior to commercial crops may incorporate more biomass than Leguminosae alone and fix more nitrogen than Poaceae alone. Biomass and nitrogen incorporation of three plant treatmens were compared under irrigation condition. In two mixture treatments, the same seven green manure species were planted together but with different seeding proportions. Treatment (1) (low-legume) had 50% the recommended seeding rate of the legume species (jack beans, cowpea and sunn hemp) and 150% the recommended seeding rate of the non-legume species (maize, pearl millet, sorghum and sun flower). The other treatment (2) (high-legume) had opposite proportions. In the third treatment, no green manure plants were sown and weed plants were allowed to grow. The results showed that biomass (9.1 and 8.2 Mg ha -1 ) and nitrogen accumulation (160 and 161 kg ha -1 ) did not differ between the low-legume and high-legume treatments, respectively, which were 2.5 times higher than those of the weed treatment (3.3 Mg ha -1 and 58.1 kg ha -1 ). Despite the higher non-legume biomass proportion and lower nitrogen concentration, the low-legume treatment symbiotically fixed as much N (52 kg ha -1 ) as the high-legume treatment because sorghum derived more N from the atmosphere (79 %) and maize in the same range as the legume species (37 to 54%). Therefore, sorghum and maize can have high N endophytic fixation and green manure prior to commercial crops can be produced both with legume and Poaceae species mixed together, providing a high input of N and biomass in a short period.

The 15N natural abundance technique to assess the potential of biological nitrogen fixation (BNF) in some important C4 grasses

“…The proportions found are within ranges reported by Miranda et al (1990), for different guinea grass genotypes, and Montañez et al (2009), for maize genotypes. Sorghum performance was lower than that reported by Ferreira Neto et al (2017) and Santos et al (2017) in the field, the only latest report of BNF in sorghum. Nevertheless, sorghum cultivar IPA-1011 was able to benefit from a higher proportion of atmospheric N 2 than sugarcane variety RB863129.…”

“…Over the 180 days of experiment, no major differences in the soil exploitation by plant roots were observed, which was limited due to the pot volume. Furthermore, the high isotopic enrichment of the soil (Freitas et al, 2015) enables greater accuracy in BNF estimation (Boddey et al, 2000). Under the conditions of our experiment, the differences below 2 % among species should be carefully discussed for quantitative BNF estimates (Högberg, 1997).…”

“…This soil layer has a high isotopic enrichment (δ 15 N > 16 %) and low N (0.038%) and C (0.69%) contents (Freitas et al, 2015), which favors the determination of 15 N dilution due to BNF. Soil characteristics in the 0 to 20 cm superficial layer (analyzed following the procedures recommended by EMBRAPA, 1997) The planting of sugarcane and elephant grass was performed using stem pieces (sets), measuring about 10 cm, containing one gem.…”

“…For example, results have shown that some varieties cultivated in Brazil Baptista et al, 2014) and Uruguai (Taulé et al, 2012) may obtain significant amounts of atmospheric N, but no evidence of BNF was found in sugarcane grown in other places, such as Australia (Biggs et al, 2002) and South Africa (Hoefsloot et al, 2005). For other grasses such as sorghum (Santos et al, 2017;Ferreira Neto et al, 2017), Guinea grass (Miranda et al, 1990), maize (Montañez et al, 2009) and elephant grass , reports are scarce.…”

Carbon and nitrogen stocks of soils under different land uses in Pernambuco state, Brazil

“…Fertilizers, both inorganic and organic, may have been applied to a higher degree than reported in regional surveys. Symbiotic N fixation from the atmosphere could contribute tens of kg ha −1 to the agricultural systems, usually through cowpea intercropped with maize, both of which are capable of fixation (Ferreira Neto et al, 2017;Freitas et al, 2012b). Fixation by native legume species growing in the pasture areas could also add symbiotic N (Freitas et al, 2011).…”