Abstract
Abstract. Biological nitrogen fixation (BNF) from grain legumes is of significant importance in global agricultural ecosystems. Crops with BNF capability are expected to support the need to increase food production while reducing nitrogen (N) fertilizer input for agricultural sustainability, but quantification of N fixing rates and BNF crop yields remains inadequate on a global scale. Here we incorporate two legume crops (soybean and faba bean) with BNF into a dynamic vegetation model LPJ-GUESS (Lund–Potsdam–Jena General Ecosystem Simulator). The performance of this new implementation is evaluated against observations from a range of water and N management trials. LPJ-GUESS generally captures the observed response to these management practices for legume biomass production, soil N uptake, and N fixation, despite some deviations from observations in some cases. Globally, simulated BNF is dominated by soil moisture and temperature, as well as N fertilizer addition. Annual inputs through BNF are modeled to be 11.6±2.2 Tg N for soybean and 5.6±1.0 Tg N for all pulses, with a total fixation of 17.2±2.9 Tg N yr−1 for all grain legumes during the period 1981–2016 on a global scale. Our estimates show good agreement with some previous statistical estimates but are relatively high compared to some estimates for pulses. This study highlights the importance of accounting for legume N fixation process when modeling C–N interactions in agricultural ecosystems, particularly when it comes to accounting for the combined effects of climate and land-use change on the global terrestrial N cycle.
Highlights
The agricultural sector is the main contributor to anthropogenic nitrous oxide (N2O) emissions (Reay et al, 2012; Tian et al, 2020) and a key nitrate pollution source to freshwater systems (Moss, 2008), mostly due to the intensive use of synthetic nitrogen (N) fertilizer and animal manure (Lu and Tian, 2017)
The simulated biological N fixation (BNF) compared to observations was notably improved when using site-specific parameters, with the regression slope increasing to 0.41 and the absolute bias being reduced to 31 % (Fig. 4e)
In this study we implemented a mechanistic process of symbiotic biological N fixation in grain legumes into the crop module of LPJ-GUESS
Summary
The agricultural sector is the main contributor to anthropogenic nitrous oxide (N2O) emissions (Reay et al, 2012; Tian et al, 2020) and a key nitrate pollution source to freshwater systems (Moss, 2008), mostly due to the intensive use of synthetic nitrogen (N) fertilizer and animal manure (Lu and Tian, 2017). This trend has been amplified by the expansion of agricultural land to provide food for a growing population and changing dietary patterns (FAO, 2018).
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