Challenges in Using Precision Agriculture to Optimize Symbiotic Nitrogen Fixation in Legumes: Progress, Limitations, and Future Improvements Needed in Diagnostic Testing

Abstract

Precision agriculture (PA) has been used for ≥25 years to optimize inputs, maximize profit, and minimize negative environmental impacts. Legumes play an important role in cropping systems, by associating with rhizobia microbes that convert plant-unavailable atmospheric nitrogen into usable nitrogen through symbiotic nitrogen fixation (SNF). However, there can be field-level spatial variability for SNF activity, as well as underlying soil factors that influence SNF (e.g., macro/micronutrients, pH, and rhizobia). There is a need for PA tools that can diagnose spatial variability in SNF activity, as well as the relevant environmental factors that influence SNF. Little information is available in the literature concerning the potential of PA to diagnose/optimize SNF. Here, we critically analyze SNF/soil diagnostic methods that hold promise as PA tools in the short-medium term. We also review the challenges facing additional diagnostics currently used for research, and describe the innovations needed to move them forward as PA tools. Our analysis suggests that the nitrogen difference method, isotope methods, and proximal and remote sensing techniques hold promise for diagnosing field-level variability in SNF. With respect to soil diagnostics, soil sensors and remote sensing techniques for nitrogen, phosphorus, pH, and salinity have short-medium term potential to optimize legume SNF under field conditions.

Evaluating the Effectiveness of Rhizobium Inoculants and Micronutrients as Technologies for Nepalese Common Bean Smallholder Farmers in the Real-World Context of Highly Variable Hillside Environments and Indigenous Farming Practices

“…When there is inadequate mineral N in the soil, legume crops need rhizobium inoculation under suboptimal conditions, specifically when compatible rhizobia in the soil are low/absent or ineffective for a particular legume host variety [13,15]. Furthermore, the micronutrients B and Mo are often deficient in South Asia, but are essential for optimal SNF [40,45]. This study attempted to measure the impact of rhizobia and associated micronutrients on Nepalese hillside smallholder farms in a real-world context, specifically across farm sites that were highly variable (e.g., variable soil physical and chemical properties, waterlogging, shading, Supplementary Table S1), and without disturbing variable household-specific cultivation practices (e.g., weeding, manure application, Supplementary Table S1), including diverse crop rotation histories.…”

Prospects of Bioenergy Cropping Systems for A More Social-Ecologically Sound Bioeconomy

“…Whereas, its practicability requires further validation. It is even possible to optimize legume-based N fixation through precision farming applications, for example, through mapping the field-level spatial variability for air-N fixation activity [173]. This could help to optimize the efficiency of other site-specific fertilization techniques, such as the application of solid manure or digestate.…”

Identifying the Relationship between Soil Properties and Rice Growth for Improving Consolidated Land in the Yangtze River Delta, China

“…Spatial clustering analysis was based on NDVI values [60]. We calculated the Local Moran's I index associated with the NDVI values of each pixel [62][63][64][65][66] using the following formula:…”