N2 fixation, grain mineral accumulation, and water-use efficiency in 30 field-grown groundnut (Arachis hypogaea L.) genotypes in South Africa, measured using 15 N and 13 C natural abundance

Titus Ngmenzuma^1*Richard Oteng-Frimpong²Felix Dapare Dakora³

• ¹Tshwane University of Technology, Pretoria, South Africa
• ²CSIR-Savanna Agricultural Research Institute, Nyankpala, Ghana
• ³Department of Chemistry, Tshwane University of Technology, Pretoria, South Africa

African soils are inherently low in mineral nutrients. Incorporating N2-fixing legumes into cropping systems can improve soil fertility and increase crop yields. This study assessed N2 fixation, carbon assimilation, grain mineral accumulation and water-use efficiency of 30 groundnut genotypes grown in the field at the Mpumalanga Province, South Africa. The results revealed marked differences i n symbiotic performance between and among the groundnut genotypes, with IS-07273 and ICGV13910 exhibiting greater symbiotic dependency on N2 fixation for their N nutrition and higher amounts of N-fixed. The two high N2-fixing symbioses (IS-07273 and ICGV13910) also accumulated significantly high levels of K, Na, Zn, Cu, Mn and B in their grain. As a result, there were strong correlations between amounts of N-fixed and K, Na, B, Cu, Zn and Mn for genotype ICGV13910.Genotype IS-07273 also showed significant correlations between N-fixed and S, N concentration (%N) and P, %N and K, as well as nodule number and Ca. As to be expected, genotypes with the highest shoot %N accumulated the most protein in their grain. Out of the 30 groundnut genotypes tested in the field, YENYAWOSO, ICGV13848, ICGV13851, ICGV15033 and ICGV131065 showed greater shoot δ 13 C values, and hence higher water-use efficiency. The high N2 fixation in genotypes ICGV13910 and IS-07273 correlated positively with macro-and micronutrient concentrations in their grain, indicating their potential for use in breeding programmes to enhance nutritional secu rity in groundnut..