Biological Nitrogen Fixation by Local and Improved Genotypes of Cowpea in Burkina Faso (West Africa)‎: Total Nitrogen Accumulated can be used for Quick Estimation

Abstract EN

Biological nitrogen fixation (BNF) by legumes is an indicator of their potential contribution to recycling nitrogen in cropping systems.

Many techniques exist for the quantitative measurement of legume BNF.

The isotopic dilution (ID) methods are the most accurate but are too expensive, time-consuming and require technical expertise.

There is a gap between the simple but less accurate Total Nitrogen Difference (TND) method and the Isotopic Dilution (ID) methods.

By measuring the BNF of 11 cowpea (Vigna unguiculata) genotypes, this study aimed to develop a simple model as an improved tool for the quick estimation of BNF.

Total N accumulated by traditional genotypes from Burkina Faso varied from 23 to 41 kg ha−1.

Approximately 40 to 65% of this was nitrogen derived from the atmosphere (Ndfa) when the TND method was used (Ndfa-TND), while the ID method indicated that 29 to 37% of N accumulated was derived from the atmosphere (Ndfa-ID).

The TND method overestimated the BNF of high N-yielding genotypes but underestimated the BNF of low N-yielding genotypes (N-accumulated below 31 kg N ha−1).

The relationship between N-accumulated and Ndfa-ID was described by a polynomial regression: Yi = 0.0127 Xi2 - 0.5354 Xi + 17.44, where Yi and Xi represent Ndfa-ID and N-accumulated, respectively (P<0.05, R2 =0.92).

The model was validated and could be used for quick estimation of BNF directly from the N accumulated.