Search

In the low fertility acid soils of the Orinoquian savannas of Colombia, Urochloa humidicola cv. Tully or Humidicola is one of the most widely planted tropical forage grasses for improving livestock productivity. Low nutritional quality of this grass limits sustainable livestock production in this region. In this study, we conducted a phenotypic evaluation under field and greenhouse conditions of one of the first hybrid populations of U. humidicola generated from the forage breeding program of CIAT. Our objective was to identify a set of new hybrids of U. humidicola that combine improved productivity and nutritional quality plus the biological nitrification inhibition (BNI) trait/ability to reduce nitrogen (N) losses via leaching and nitrous oxide (N2O) emissions. To this end, we tested 118 hybrids (planted in pots) in the greenhouse for over 6 months and measured potential nitrification rates (NR) using soil microcosm incubation. NR values observed ranged from 0.27 to 5.75 mg N‐NO3− kg soil−1 day−1. Later, 12 hybrids with different levels of NR were selected and field‐tested in the Orinoquia region over a 4 years period (2013–2017) for dry matter production, nutrition quality (crude protein, in vitro digestibility and fibres content) and NR in each year. In the rainy season of 2018, two hybrids with superior agronomic performance and contrasting field level NR (Uh08/1149 and 0450) were subjected to analysis of soil‐borne N2O emissions after fertilization during 13 days. The NR values recorded were not directly correlated with the forage quality parameters evaluated, however, the two grasses with the lowest NR values were among those with the highest biomass production, crude protein content, and N uptake. The grass hybrid Uh08/1149 and the germplasm accession CIAT 16888 were found as materials with superior forage value, with production of 14.1 and 14.6 tons dry matter ha−1 year−1 (up to 8% higher than the cv. Tully), crude protein of 11.5 and 9.1% per cut (up to 20% higher than the cv. Tully), and N uptake of 31.6 and 25.7 kg N ha−1 cut−1 (up to 30% higher than the cv. Tully). Additionally, these two grasses are likely to exhibit high‐BNI ability, with potential to improve N use efficiency in managed pastures. [ABSTRACT FROM AUTHOR]

Synthetic nitrification inhibitors (SNI) and biological nitrification inhibitors (BNI) are promising tools to limit nitrogen (N) pollution derived from agriculture. Modern wheat cultivars lack sufficient capacity to exude BNIs, but, fortunately, the chromosome region (Lr#n-SA) controlling BNI production in Leymus racemosus, a wild relative of wheat, was introduced into two elite wheat cultivars, ROELFS and MUNAL. Using BNI-isogenic-lines could become a cost-effective, farmer-friendly, and globally scalable technology that incentivizes more sustainable and environmentally friendly agronomic practices. We studied how BNI-trait improves N-uptake, and N-use, both with ammonium and nitrate fertilization, analysing representative indicators of soil nitrification inhibition, and plant metabolism. Synthesizing BNI molecules did not mean a metabolic cost since Control and BNI-isogeniclines from ROELFS and MUNAL presented similar agronomic performance and plant development. In the soil, ROELFS-BNI and MUNAL-BNI plants decreased ammonia-oxidizing bacteria (AOB) abundance by 60% and 45% respectively, delaying ammonium oxidation without reducing the total abundance of bacteria or archaea. Interestingly, BNI-trait presented a synergistic effect with SNIs since made it also possible to decrease the AOA abundance. ROELFS-BNI and MUNAL-BNI plants showed a reduced leaf nitrate reductase (NR) activity as a consequence of lower soil NO-3 formation and a higher amino acid content compared to BNI-trait lacking lines, indicating that the transfer of Lr#-SA was able to induce a higher capacity to assimilate ammonium. Moreover, the impact of the BNI-trait in wheat cultivars was also noticeable for nitrate fertilization, with improved N absorption, and therefore, reducing soil nitrate content. [ABSTRACT FROM AUTHOR]

Critical micronutrient concentrations in soils and plants have not been clearly determined for marginal soils where deficiencies are likely to occur. The objective of this study was to develop a reliable method for assessing micronutrient deficiency in soils and plants. Soybean plants [Glycine max (L.) Merr.] were grown in the A and B horizons of two Brazilian Ustoxes and watered with a complete nutrient solution (i.e., control) or solutions lacking one of the following micronutrients: Mn, Zn, B, or Cu. Soybean plants were repeatedly grown in the same soils until maturity. The cumulative frequency of deficient plants where the relative seed dry weight was significantly decreased was recorded. The percent relative cumulative frequency (PRCF) is calculated as: cumulative frequency + total number of tested plants x 100. A linear-plateau regression line was fitted to the PRCF as a function of the micronutrient concentrations in the soil, the uppermost mature leaf, or seed. Critical concentrations (mg [kg.sup.-1]) for deficiency indicated as transition points of regression lines are: 6.4 for Mn (reference), 1.0 for Zn, 0.2 for B, and 0.2 for Cu in the soil (Mehlich-I extraction for Mn, Zn, and Cu; hot 0.005 mol [L.sup.-1] Ba[Cl.sub.2] extraction for B); 63 for Mn, 34 for Zn, 25 for B, and 4 for Cu in the uppermost mature leaf; 55 for Mn, 42 for Zn, 14 for B, and 5 for Cu in seeds. Thus, this determination method can clearly identify the critical values for micronutrient deficiency in soils and in plant tissues. Abbreviations: PRCF; percent relative cumulative frequency. doi: 10.2136/sssaj2010.0158

The tropical pasture grass Brachiaria humidiola (Rendle) Schweick releases nitrification inhibitory compounds from its roots, a phenomenon termed ‘biological nitrification inhibition’ (BNI). We investigated the influence of root exudates of B. humidicola on nitrification, major soil microorganisms and plant growth promoting microorganisms using two contrasting soil types, Andosol and Cambisol. The addition of root exudates (containing BNI activity that is expressed in Allylthiourea unit (ATU) was standardized in a bioassay against a synthetic inhibitor of nitrification, allylthiourea, and their function in soil was compared to inhibition caused by the synthetic nitrification inhibitor dicyandiamide. At 30 and 40 ATU g−1soil, root exudates inhibited nitrification by 95% in fresh Cambisol after 60 days. Nitrification was also similarly inhibited in rhizosphere soils of Cambisol where B. humidicola was grown for 6 months. Root exudates did not inhibit other soil microorganisms, including gram-negative bacteria, total cultivable bacteria and fluorescent pseudomonads. Root exudates, when added to pure cultures of Nitrosomonas europaea, inhibited their growth, but did not inhibit the growth of several plant growth promoting microorganisms, Azospirillum lipoferum, Rhizobium leguminosarum and Azotobacter chroococcum. Our results indicate that the nitrification inhibitors released by B. humidicola roots inhibited nitrifying bacteria, but did not negatively affect other major soil microorganisms and the effectiveness of the inhibitory effect varied with soil type. [ABSTRACT FROM AUTHOR]

Sorghum (Sorghum bicolor) roots are well-known for the release of Biological Nitrification Inhibitors (BNIs), such as sorgoleone (SGLN) and methyl 3–4-hydroxyphenyl propionate (MHPP). However, the deployment of sorghums with BNIs in agriculture practices has not been widely investigated and evaluated. In this study, sorghum and maize were intercropped in field and pot cultivation to investigate the Biological Nitrification Inhibition (BNI) effect of sorghum on the productivity of both crops and soil nitrification. Inorganic N content (NO 3 – and NH 4 +), N 2 O emission, and the abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in soil were analyzed. The results showed intercropping with sorghum have the potential to improve crop productivity, as indicated by the Land Equivalent Ratio greater than 1.0. Intercropping with sorghum reduced the transformation rate of NH 4 + to NO 3 – in soils and the emission of N 2 O, as compared to monoculture of maize. Additionally, the abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) under intercropping mode were reduced by 41% and 28% in field trials, and reduced by 59% and 23% in pot experiments, respectively. Incubation of the same soils with SGLN and/or MHPP showed that the combined treatment of both BNIs strongly inhibited nitrification and N 2 O emission, along with lower AOB and AOA abundances, as compared with those under the sole treatment of SGLN or MHPP. Our results indicated that the root exudates of sorghum play a significant role in inhibiting soil nitrification due to the overlapping or amplified effect of various BNIs, which contribute to the nitrogen nutrition of the neighbouring crops under intercropping mode. Therefore, intercropping with BNI crops provides an eco-friendly strategy to improve crop production with reduced N 2 O emission. • Intercropping mode of sorghum and maize reduced soil nitrification and N 2 O emission. • Intercropping mode decreased the abundance of AOA and AOB. • Effect of combined addition of SGLN and MHPP in soil was superior to sole addition. • Root exudates of sorghum were of significance in inhibiting soil nitrification. [ABSTRACT FROM AUTHOR]

Nitrification inhibitory activity was found in root tissue extracts of Brachiaria humidicola, a tropical pasture grass. Two active inhibitory compounds were isolated by activity-guided fractionation, using recombinant Nitrosomonas europaea containing luxAB genes derived from the bioluminescent marine gram-negative bacterium Vibrio harveyi. The compounds were identified as methyl-p-coumarate and methyl ferulate, respectively. Their nitrification inhibitory properties were confirmed in chemically synthesized preparations of each. The IC50 values of chemically synthesized preparations were 19.5 and 4.4 microM, respectively. The ethyl, propyl, and butyl esters of p-coumaric and ferulic acids inhibited nitrification, whereas the free acid forms did not show inhibitory activity.