Abstract
Inhibition of N2 fixation in N-fertilized common bean (Phaseolus vulgaris L.) plants growing on the fields of farmers in the Eastern Cape of South Africa was measured using 15N natural abundance and tissue ureide analysis. The N-fertilized bean plants revealed greater soil N uptake, higher concentrations of nitrate in organs, low tissue ureide levels, and much lower percent relative ureide-N abundance when compared with unfertilized plants. In contrast, the unfertilized plants showed greater nodule fresh weight, higher N derived from fixation (e.g., 84.6, 90.4, and 97.1% at Lujecweni fields 2, 3, and 4, respectively), increased amount of N-fixed (e.g., 163.3, 161.3, and 140.3 kg ha−1 at Lujecweni fields 2, 3, and 4, respectively), greater ureide concentration in stems and petioles, higher % relative ureide-N abundance, and low soil N uptake. We also found that the percent N derived from fixation (%Ndfa) was very high for some bean plants receiving a double dose of N fertilizer [e.g., Lujecweni field 1 (51.8%) and Tikitiki field 1 (53.3%], and quite high for others receiving a single dose of N fertilizer [e.g., Tikitiki field 2 (50.1%), Mfabantu fields 1 and 2 (45.5 and 79.9%, respectively), and St. Luthberts field 1 (58.9%)]. Though not assessed in this study, it is likely that the rhizobia that effectively nodulated the N-fertilized bean plants and fixed considerable amounts of symbiotic N had constitutive and/or inducible nitrate reductase genes for reducing nitrate in nodules and bacteroids, hence their ability to form root nodules and derived high %Ndfa in bean with added N. While single- and double-dose N fertilizer applications increased plant growth and grain yield compared to unfertilized bean plants, the single-dose N fertilizer application produced much greater grain yield than the double dose. This indicates that farmers should stop using a double dose of N fertilizers on bean production, as it decreases yields and can potentially pollute the environment. This study has however shown that government supply of free N fertilizers to resource-poor farmers in South Africa increased bean yields for food/nutritional security.
Highlights
Legume N2 fixation is important for sustainable cropping systems in both tropical and subtropical environments, where the soils are naturally deficient in N (Graham and Vance, 2003)
This study aimed to assess the effect of N fertilization on plant growth, N2 fixation, and grain yield of common bean planted without rhizobial inoculation on the fields of farmers in the Eastern Cape Province of South Africa, using the 15N natural abundance technique and ureide assay
Single- and double-dose N fertilizer application increased plant growth and grain yield compared to unfertilized bean plants, single-dose N fertilizer application produced a much greater grain yield than double dose
Summary
Legume N2 fixation is important for sustainable cropping systems in both tropical and subtropical environments, where the soils are naturally deficient in N (Graham and Vance, 2003). Applying Rhizobium strain HB-429 to common bean crop increased plant growth, percent N derived from fixation (%Ndfa), the amount of N-fixed, and grain yield by 19, 17, 54, and 48%, respectively, over the uninoculated control in Ethiopia (Samago et al, 2018). These findings show that supplying rhizobial inoculants can replace chemical N fertilizer use and increase bean yields in Ethiopia. An additional benefit following grain harvest in legumes is the release of fixed-N by the legume residues into the soil, which is generally regarded as slow and can match plant uptake from the soil with symbiotic N supply by residues (Chikanai et al, 2018), reducing leaching, runoff, and environmental pollution, which are common with added N fertilizer
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
