Prosopis juliflora was introduced to the Brazilian semi-arid region as a forage and firewood plant and spontaneously dispersed to valley areas and now forms almost pure stands in more than 500,000 ha of the region. Since eradication is not being considered, studies on the advantages and disadvantages are necessary. One of the potential advantages is the capability of symbiotically fixing atmospheric N ₂ . We determined P. juliflora N fixation in six valley areas of Pernambuco state, Brazil. In each area, leaf and wood biomasses were estimated, N concentrations and amounts determined and N fixation in leaves estimated by the ¹⁵ N technique. Aboveground and leaf biomasses averaged 44.1 Mg ha ⁻¹ , and 2.1 Mg ha ⁻¹ , respectively. The nitrogen derived from the atmosphere (%Ndfa) in the leaves averaged 38.8%, corresponding to 24.2 kg ha ⁻¹ yr ⁻¹ of N fixation. An indirect rough estimation of the average N stock derived from fixation in the woody parts was based on the assumption that the ¹⁵ N values in the leaves and wood in the same plant was equal, and amounted to 74.1 kg ha ⁻¹ Considering the fixed N in the leaves as a stock, adding the estimated N stock in the wood, and extrapolating for the 113 thousand hectares covered by P. juliflora in Pernambuco, Paraíba and Rio Grande do Norte states would be equivalent to a stock of 11.1 Gg of N. Despite being a crude estimate, it indicates that P. juliflora can potentially contribute to a significant amount of fixed N in the plant-soil system in the Brazilian Northeast region.

Sustainable crop production in nutrient-poor sandy soils requires fertilization strategies that improve nutrient uptake while reducing environmental impact. This study evaluated anaerobic cattle manure digestate and carbon dot biostimulants as alternatives to conventional mineral NPK (nitrogen–phosphorus–potassium) fertilizer for corn (Zea mays L., cv. AG 1051) during vegetative development. A randomized greenhouse experiment compared nine treatments over three successive 45-day cycles, assessing shoot-tissue macronutrient content (N, P, K) and morphological parameters (shoot dry weight, stem diameter, and plant height). Digestate delivered approximately 1.4× more phosphorus and 8.4× more potassium per pot than mineral NPK, although nitrogen inputs were matched (~77 mg pot⁻¹). Digestate-based treatments achieved shoot dry weight 132% above control and 63% above mineral fertilizer (p < 0.001), with biomass advantages sustained across all three cycles while mineral fertilizer effects dissipated entirely by Cycle 3. Phosphorus content was the strongest biomass predictor (r = 0.86, p < 0.001), and a significant nitrogen–phosphorus antagonism (r = −0.59, p < 0.001) revealed relevant nutrient interaction dynamics. The higher biomass observed under digestate-based treatments reflects both the higher total P and K inputs from digestate and the beneficial effects of organic matter on nutrient bioavailability in this phosphorus-limited system. Carbon dot biostimulants did not improve biomass when applied alone (values at or below control), but they contributed to intermediate biomass gains when combined with nutrient sources, functioning as nutrient uptake enhancers rather than standalone fertilizers. Principal component analysis (74.3% variance explained) classified the nine treatments into three distinct treatment clusters. These findings support digestate valorization as a circular-economy alternative to conventional mineral fertilization, offering higher biomass under N-equivalent application and sustained residual effects in nutrient-poor sandy soils.