Finger millet (Eleusine coracana (L.) Gaertn) is a staple food crop grown by subsistence farmers in the semi-arid tropics of South Asia and Africa. It remains highly valued by traditional farmers as it is nutritious, drought tolerant, short duration, and requires low inputs. Its continued propagation may help vulnerable farmers mitigate climate change. Unfortunately, the land area cultivated with this crop has decreased, displaced by maize and rice. Reversing this trend will involve achieving higher yields, including through improvements in crop nutrition. The objective of this paper is to comprehensively review the literature concerning yield responses of finger millet to inorganic fertilizers (macronutrients and micronutrients), farmyard manure (FYM), green manures, organic by-products, and biofertilizers. The review also describes the impact of these inputs on soils, as well as the impact of diverse cropping systems and finger millet varieties, on nutrient responses. The review critically evaluates the benefits and challenges associated with integrated nutrient management, appreciating that most finger millet farmers are economically poor and primarily use farmyard manure. We conclude by identifying research gaps related to nutrient management in finger millet, and provide recommendations to increase the yield and sustainability of this crop as a guide for subsistence farmers.

The experiment was conducted to determine whether cover crops reduce N losses of fall‐applied liquid hog manure and whether sequestered N by cover crops is “transferred” to subsequent corn (Zea mays L.). Two locations (Elora and St. Mary's) in southern Ontario from 2003–2004 were used consisting of six cover crop treatments (red clover [RC] [Trifolium pratense L.] fall‐killed, RC spring‐killed, oat [Avena sativus L.] fall‐killed, oilseed radish [Raphanus sativus L.] fall‐killed, perennial ryegrass [Lolium perenne L.] spring‐killed, and no‐cover crop), and three target manure rates (0, 100, and 200 kg N ha⁻¹). Non‐legume cover crops positively responded to fall manure application, where biomass increased by 50 to 130%. Red clover biomass increased 0 to 25% at higher manure rate application. A similar trend was found with plant N uptake. Generally applied manure N recovery was low (0–25%) in all the cover crops. Ammonia losses from manure applications to RC was higher than other cover crops due to inability to incorporate manure. During the period corresponding with corn N uptake, non‐legume cover crop impact on soil mineral N did not differ from the no cover control. When non‐legumes were used as cover crops following manure application, corn biomass, grain yield, and N uptake were equivalent to no cover crop treatment. However, when RC was used as a cover crop, above corn parameters were equivalent for all manure application rates and greater than the no‐cover crop treatment, so “transfer” of manure N could not be confirmed.

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.

Studies have shown the potential of rhizobia and associated micronutrients to enhance symbiotic nitrogen fixation in legumes. Tens of millions of smallholder farmers, however, farm on mountain hillsides in highly variable soil and microenvironments, with different crop rotations, inputs and cultural practices. Here, on the terraces of the Nepalese Himalayas, we evaluated rhizobium inoculants (local, exotic), micronutrients (molybdenum, boron) and their combinations as technologies for smallholder farmers under highly variable microenvironments and traditional practices. The study was conducted as a series of participatory on-farm trials with 39 terrace farmers in two mid-hill districts of Nepal (Dhading, Kaski) from 2015 to 2017. Plots were measured for relevant agronomic traits. As expected, when comparing treatment plots with adjacent control plots within each farm, the results demonstrated tremendous farm-to-farm variability for nodulation, vegetative biomass, shoot nitrogen content, grain yield, and grain N content. Despite the variation observed, the data showed that the number of farms that showed yield increases from the rhizobium interventions, compared to those that suffered yield losses, was generally 2:1. We discuss potential experimental and socio-agronomic reasons for the variable results, including rainfall, which appeared critical. The results demonstrate the promise of rhizobium interventions for hillside smallholder farmers, even in a highly variable context.

Forage legumes experience defoliation from grazing and injury in both natural and agricultural ecosystems. Defoliation induces rhizodeposition of nitrogen (N) compounds from root systems that can feed microbes and plants that depend on the rhizosphere. The literature suggests that N exudates are primarily released from root tips, and those from legume nodules are released via slow nodule decomposition. However, the early timing and precise locations of N release postdefoliation are poorly characterized. The objectives of this study were to directly image tissue-specific N exudation sites in forage legumes, specifically for glutamine, and to do so at early time points postdefoliation. Glutamine is the primary assimilate of symbiotic nitrogen fixation in nodules and a key transport form of fixed N in amide-exporting legumes. Three amide-exporting forages, alfalfa (Medicago sativa), red clover (Trifolium pretense), and white clover (Trifolium repens), were defoliated or not, and placed on agar embedded with whole cell biosensor cells (GlnLux) that detect glutamine. There were two unexpected findings. First, Gln release occurred rapidly, starting within 2 h postdefoliation, depleting rapidly. Second, the sources of early Gln release were primarily nodules in addition to the expected young lateral roots/root tips. Lux quantification statistically confirmed the key findings. These observations suggest that N exudate release should be added to the list of defoliation stress early responses in nodules, and may have implications for our understanding of how defoliation impacts the rhizosphere microbiome. Furthermore, GlnLux-agar imaging represents a new assay to explore the proposed but yet unknown mechanisms underlying organic N exudation in plants.